Engineering Education for skilled engineers

DESIGN & DEVELOPMENT

skilltech1970@gmail.com (Dattatray) — Thu, 22 Jun 2017 16:17:00 +0530

DESIGN AND DEVELOPMENT

With the changing scenario of technology development in the world, it has become very essential to keep pace with the technological advancement to be in market. The design and development department of any company is mainly responsible for updating the existing product to match with the latest technology available and also to develop the new products anticipating the future need of the society. The basic function of the design and development department can be divided into following three categories.

INNOVATION

Innovation is the process of generating products that are unique in terms of performance, material or use.

RENOVATION

Renovation is the process of modifying the existing products to extend their life in the existing markets or to fulfill the needs of the future markets. This function is essential to be competitive in the market.

ELIMINATION

Elimination is the process of pruning the old or unprofitable products from the product range. Planned and purposeful elimination of old and unprofitable product is a key to innovation,

Because, it frees necessary resources and

It stimulates the search for new products to replace the old.

THE MAIN ACTIVITIES GENERALLY PERFORMED BY DESIGN AND DEVELOPMENT DEPARTMENT:

1. Design of new product using the latest know-how and computer aided facilities.

2. Redesign of the old products with a view of weight and cost reduction and/or performance improvement to meet the market requirement.

3. Development co-ordination of the new products

4. To provide technical support to the marketing department.

Anticipating the need of the customer, nation, the company has to develop a new generation of products with the sole objective of total energy conservation, free from environmental hazards and to reach at affordable price to the users. Such new generation products are today universally acclaimed as the best in the world.

All such activities from design and development department have been grouped into a logical pattern or frame work and assigned to specific positions and people in the organization. The company has a line and staff concept and structure in the organization where each member of the group knows as to what is expected of him to contribute in accomplishing the organizational objectives in measurable terms. The way by which the goals conceived in planning can be achieved is made known to each unit. This is accomplished through appropriate delegation of authority, power and accountability system as adopted in the organization. At each level, departments are accountable to someone at the next higher level in the organization. Due important has been given to safety and security of men, materials and machines in the factory. Thus, Design and Development Department has a remarkable focus towards the end users.

WHAT SKILLS FRESH GRADUATE ENGINEERS NEED TO BE A MECHANICAL ENGINEER?

skilltech1970@gmail.com (Dattatray) — Mon, 10 Apr 2017 13:14:00 +0530

It gives me an immense pleasure to bring out this blog intended for the benefit of mechanical engineering students and professionals. The important features of engineers’ portal are:

It is user friendly and provides information in a well structured manner.

It provides comprehensive and critical study of the aforesaid subject.

It contains questions solutions with examples.

This contains most useful topics to cater the basic requirements of mechanical engineering students and industrial professionals with a view to manage systematically in the plant on a particular subject.

The subject has been presented in a simple engineering script and easy to understand language. The relevant subject explanation arranged in the form of basic concept of engineering and its utilization. The treatment and presentation of the subject has been such as to be within easy grasp of mechanical engineers of varying degrees of intellectual attainment.

Mechanical engineering is one of the oldest and most comprehensive branches of engineering that involves the designing tools, production, planning and control and operations of mechanically functioning equipment. It also includes maintenance, repairs and overhauling. A well versed mechanical engineer should possess knowledge of core areas that includes material science, electricity, basic physical sciences, math, material engineering, hydraulics IC engines, thermodynamics and many more.

Except the above mechanical engineers are also expected to study and apply basic concepts of other areas such as Chemical Engineering, Electrical Engineering and Automobile Engineering etc. thus a mechanical engineer is bound to possess the basic knowledge and skills of the below given segments such as

Role of Mechanical Engineers in Tool Engineering

Industrial Engineering and its activities

Knowledge of Electrical Instruments and Measurements to Plant Engineers

Maintenance of Equipments

Sealing of Flanges, Pipe Joints, Hydraulic Joints and Pneumatic Joints

Method of Casting Process and Its Importance

Managing Quality Control and Assurance

What Is Production Planning and Control?

Importance of Health Safety in Industries

Thus the above given areas provide an insight to fresh graduate engineers and industrial personnel, who would like to enter into the same. Since mechanical engineering and electrical engineering go hand in hand and mechanical engineering is adapted in electrical studies, a mechanical engineer’s presence is worthwhile in electrical field.

ELECTRICAL INSTRUMENTS AND MEASUREMENTS

skilltech1970@gmail.com (Dattatray) — Mon, 20 Feb 2017 20:04:00 +0530

Basics on "Electrical Instruments and Measurements" for Electrical Engineers is an essential requirements of Mechanical Engineers as most of the times they will have to involve Engineers Meeting at management level about the progress and status of the plant. Generally, mechanical engineers may not be familiar with electrical field, but as a plant engineer he should have basic knowledge of the instruments which they are using including motors, generators and bus-bar systems. Many a times plant engineers fails to express their views about other tools or equipment and unable convenience the working progress of the equipment or tools to the management or seniors. Hence, as per my experience, one should know basics existing products of his related field so as to control the plant situation.

As already you may be aware that these are divided into (1) absolute instruments and (2) secondary instruments. Absolute instruments are those which give the value of the quantity to be measured in terms of the constants of the instrument and their deflection only. No previous calibration or comparison is necessary in their case. The example of such an instrument is tangent galvanometer which gives the value of current in terms of the tangent of deflection produced by the current, the radius and number of turns of wire used and the horizontal component of earth’s field.

Secondary Instruments are those in which the value of electrical quantity to be measured can be determined from the deflection of the instruments only when they have been pre calibrated by comparison with absolute instruments. Without calibration, the deflection of such instrument is meaningless.

It is the secondary instruments which are most generally used in everyday work, the use of the absolute instruments being merely confined within lab as standardizing instruments.

ELECTRICAL PRINCIPLES OF OPERATION

All electrical measuring instruments depend for their action on one of the many physical effects of an electric current or potential and generally classified according to which of these effects is utilized in their operation. The effects generally utilized are:-

Magnetic Effect- for ammeters and voltmeters usually.

Electrodynamic effect- for ammeters, voltmeters and wattmeter usually.

Electromagnetic effect- for ammeters, voltmeters, wattmeter’s and watt hour meters.

Thermal effect- for ammeters and voltmeters.

Chemical effect- for d.c. ampere hour meters.

Electrostatic effect- for voltmeters only.

Another way to classify the secondary instrument is to divide them into (1) indicating instruments, (2) recording instruments and (3) integrating instruments.

Indicating instruments are those which indicate the instantaneous value of the electrical quantity being measured at the time at which it is being measured. Their indications are given by pointers moving over calibrated dials. Ordinary ammeters, voltmeters and wattmeter belong to this class.

Recording instruments are those which instead of indicating by means of a pointer and a scale the instantaneous value of an electrical quantity, give a continuous record of the variations of such a quantity over a selected period of time. The moving system of the instrument carries an inked pen which rests lightly on a chart or graph that is moved at a uniform and low speed, in a direction perpendicular to that of the deflection of the pen. The path traces out by the pen presents a continuous record of the variations in the deflection of the instruments.

Integrating instruments are those which measure and register by a set of dials and pointers either the total quantity of the electricity (in amp-hours) or the total amount of electrical energy (in watt hours or Kwh.) supplied to a circuit in a given time. Their summation gives the product of time and the electrical quantity but gives no direct indication as to the rate t which the quantity or energy is being supplied because their registrations are independent of this rate provided the current flowing through the instruments is sufficient to operate it.

Ampere hour and watt hour meters are fall in this class.

ESSENTIALS OF INDICATING INSTRUMENTS

Indicating instruments are those which indicate the value of quantity that is being measured at the time at which it is measured. Such instruments consist essentially of a pointer which moves over a calibrated scale and which is attached to a moving system pivoted in jeweled bearings. The moving system is subjected to the following three torques:

1. A deflecting (or operating) torque.

2. A controlling (or restoring) torque.

3. A damping torque.

DEFLECTING TORQUE

The deflecting or operating torque (Td) is produced by utilizing one or other effects mentioned in figure 1. i.e. magnetic, electrostatic, electrodynamics’, thermal or inductive etc. The actual method of torque production depends on the type of instrument and as you can see in next page. The deflecting torques causes the moving system (and hence the pointer attached to it.) to move from its zero position i.e. its position when the instrument is disconnected from the supply.

CONTROLLING TORQUE

The deflection of the moving system would be indefinite if there were no controlling or restoring torque. This torque opposes the deflecting torque and increases with the deflection of the moving system. The pointer is brought to rest at a position where the two opposing torques are equal. The deflecting torques ensures that currents of different magnitudes shall produce deflections of the moving systems in proportion to their size. Without such a torque, the pointer would swing over to the maximum deflected position irrespective of the magnitude of the current to be measured. Moreover, in the absence of restoring torque, the pointer once deflected, would not returns to its zero position on removing the current. The controlling, restoring or balancing torque in indicating instruments is either obtained by a spring or by gravity as explained below.

SPRING CONTROL

A hair spring, usually of phosphor bronze, is attached to the moving system of the instruments as shown in figure. With the deflection of the pointer, the spring is twisted in the opposite direction. This twist in the spring producing restoring torque which is directly proportional to the angle of the deflection of the moving system. The pointer comes to a position of rest (or equilibrium) when the deflecting torque (Td) and controlling torque (TC) are equal. For example, in permanent magnet moving coil type of instruments, the deflecting torque is proportional to the current passing through them.

Therefore, TD is proportional to I,

And for spring control, TC is proportional to theta,

As TC = Td, Theta is proportional to Current I.

Since deflection theta is directly proportional to current I, the spring controlled instruments have a uniform or equally spaced scales over the whole of their range as shown in figure.

To ensure that controlling torque is proportional to the angle of deflection, the spring control should have a fairly large numbers of turns so that angular deformation per unit length, on full scale deflection, is small. Moreover, the stress in the spring should be restricted to such a value that it does not produce a permanent set in it.

Springs are made of such material which are non-magnetic, are not subject to much fatigue, have low specific resistance-especially in cases where they are used for leading current in or out of the instrument and have low temperature co efficient.

GRAVITY CONTROL

Gravity control is obtained by attaching a small adjustable weight to some part of the moving system, such that the two exert torques in the opposite directions. It can be seen in figure that the controlling torque or restoring torque is proportional to the sine of the angle of deflection,

I.e. TC is proportional to sine theta. The degree of control is adjusted by screwing the weight up or down the carrying system.

If Td is proportional to current I,

The position of rest,

Td=TC OR Current is proportional to sine theta. It will be seen from the figure that, as

Theta approaches 900, the distance AB increases by a relatively a small amount for a given change in the angle than when theta is just increasing from its zero value. Hence, gravity controlled instruments have scales which are not uniform but are cramped or crowded at their lower ends as shown in figure.

As compared to spring control, the disadvantage of gravity control is,

It gives cramped scale.

The instruments have to be kept vertical.

However, gravity control has the following advantages:

It is cheap.

It is unaffected by temperature.

It is not subject to fatigue or deterioration with time.

DAMPING TORQUE

A damping force is one which acts on the moving system of the instruments only when it is moving and always opposes its motion. Such stabilizing and damping force is necessary to bring the pointer to rest quickly; otherwise due to inertia of the moving system, the pointer will oscillate about its final deflected position quite for some time before coming to rest in the steady position. The degree of damping should be adjusted to a value which is sufficient to enable the pointer to rise quickly to its deflected position without overshooting. In that case the instrument is said to be dead-beat. Any increase in damping above this limit i.e. over damping will make the instrument slow and lethargic. Fig shows the effect of damping on the variation of position, with time of the moving system of instruments.

The damping force can be produced by (1) air friction, (2) eddy current and (3) fluid friction. (Very occasionally)

Two methods of air friction damping are shown below.

In the light aluminum piston attached to the moving system of the instruments is arranged to travel with a very small clearance in a fixed air chamber closed at one end. The cross section of the chamber is either circular or rectangular. Damping of the oscillation is affected by the compression and suction actions of the piston on the air enclosed in the chamber. Such a system of damping is not much favored these days and being preferred. In the latter method, one or two light aluminum vanes are mounted on the moving system which moves in a closed sector-shaped box.

Fluid friction is similar in action to the air friction. Due to greater viscosity of oil, the damping is more effective. However oil damping is not much used because of several disadvantages such as objectionable creeping of oil, the necessity of using the instrument is always in the vertical position and its obvious unsuitability for use in portable instruments.

The eddy current form of damping is the most efficient of the three. The two forms of such a damping are shown in fig. It is shown a thin disc of a conducting but non-magnetic material like copper or aluminum mounted on the spindle which carries the moving system and the pointer of the instruments. The disc is so positioned that, its edges when in rotation, cut the magnetic flux between the poles of a permanent magnet. Hence, eddy currents are produced in the disc which flow and so produce a damping force in such a direction as to oppose the very cause producing them. Since the cause producing them is the rotation of the disc, these eddy currents retard the motion of the disc and moving system as a whole.

The figure shows second type of eddy current damping generally employed in permanent magnet moving coil instruments. The coil is wound on a thin light aluminum former in which eddy currents are produced when the coil moves in the field of the permanent magnet. The direction of the induced currents and of the damping force produced by them is shown.

The various types of instruments and the order in which they would be discussed is briefly explained below.

AMMETERS AND VOLTMETERS

Moving Iron Type (both for D.C./A.C.)

The attraction type and,

Repulsion type

Moving Coil Type

Permanent magnet type (for D.C. only)

Electrodynamic or dynamometer (for D.C/A.C.)

Hot wire type (both for D.C./A.C.)

Induction Type (A.C.only)

Split phase type and shaded pole type

Electrostatic type- for voltmeters only (for D.C/A.C.)

WATTMETERS

Dynamometer type (both for D.C./A.C.),

Induction Type (for A.C. Only)

Electrostatic Type (both for D.C. /A.C.)

ENERGY METERS

Electrolytic Type (for D.C.only)

Motor Meters

Mercury Motor Meter: for D.C. work only. Can be used as amp hour or watt hour meter.

Commutator Motor Meter. Used on D.C./A.C. Can be used as Ah.or Wh. Meter.

Induction Type for A.C. only

Clock Meters (as Wh-meters)

MOVING –IRON AMMETERS AND VOLTMETERS

There are two basic forms of these instruments that is the attraction type and the repulsion type. The operation of the attraction type depends on the attraction of a single piece of soft iron into a magnetic field and that of repulsion type depends on the repulsion of two adjacent pieces or iron magnetized by the same magnetic field. For both types of these instruments, the necessary magnetic field is produced by the ampere- turns of a current- carrying coil. In case the instrument is to be used as an ammeter, the coil has comparatively few turns of thick wire so that the ammeter low resistance because it is connected in series with the circuit. In case it is to be used as a voltmeter, then the coil has high impedance so as to draw as small a current as possible since it is connected in parallel with the circuit. As the current through the coil is small, it has large number of turns in order to produce sufficient ampere –turns.

ATTRACTION TYPE

The basic working principle of an attraction- type moving- coil instrument is shown in figure. It is well known that if a piece of an unmagnified soft iron is brought up near either of the two ends of a current carrying coil, it would be attracted into the coil in the same way as it would be attracted by the whole of a bar magnet. Hence, if we pivot an oval shaped disk of soft iron on a spindle between bearings, near h coil the iron disk will swing into the coil when the latter has an electric current passing through it. As the field strength would be strongest at the center of the coil, the oval shaped iron disk is pivoted in such a way that the greatest bulk of an iron moves into the center of the coil. If a pointer is fixed to the spindle carrying the disk, then the passage of current through the coil will cause the pointer to deflect. The amount of deflection produced would be greater when the current producing the magnetic field is greater. Another point worth noting is that whatever the direction of current through the coil, the iron disk would always be magnetized in such a way that it is pulled inwards hence such instruments can be used both for direct as well as for alternating currents. When the current to be measured is passed through the coil or solenoid C, the magnetic field is produced which attracts the eccentrically-mounted disc inwards thereby deflecting the pointer which moves over a calibrated scale.

REPULSION TYPE

It consists of a fixed coil inside which are placed two soft iron rods or bars A and B parallel to one another and along the axis of the coil. One of them i.e. A is fixed and the other B, which is moveable carries a pointer that moves over a calibrated scale. When the current to be measured, is passed through the fixed coil, it sets up its own magnetic field which magnetizes the two rods similarly i.e., the adjacent points on the length of the rods will have the same magnetic polarity. Hence, they repel each other with the result that the pointer is deflected against the controlling torque of a spring or gravity. The force of repulsion is approximately proportional to the square of the current passing through the coil. Moreover, whatever may be the direction of the current through the coil; the two rods will be magnetized similarly and hence will repel each other. In order to achieve uniformity of scale, two tongue shaped strips of iron are used instead of two rods. The fixed iron consists of a tongue shaped sheet iron bent into a cylindrical form; the moving iron also consists of another sheet of iron and is so mounted as to move parallel to the fixed iron and towards its narrower end.

The deflecting torque is due to the repulsive force between the two similarly magnetized iron rods or sheets.

There are two types of possible errors in such instruments, firstly, those which occur both in a.c. and d.c. work and secondly, those which occur in a.c. work alone.

ERRORS WITH BOTH D.C. and A.C.WORK

Error due to hysteresis- because of hysteresis in the iron parts of the moving system, the readings are higher for descending values but lower for ascending values.

The hysteresis error is almost completely eliminated by using Mumetal or Parmalloy which have negligible hysteresis loss.

Error due to stray fields- unless shielded effectively from the effects of stray external fields, it will give wrong readings. Magnetic shielding of the working parts is obtained by using a covering case of cast-iron.

ERRORS WITH ALTERNATING CURRENT WORK ONLY

Changes of frequency produce (i) change in the impedance of the coil and (ii) change in the magnitude of the eddy currents. The increase in impedance of the coil with increase in the frequency of the alternating current is of importance in voltmeters. For frequencies higher than the one used for calibration, the instrument gives lower values. However, this error can be removed by connecting a capacitor of suitable value in parallel with the swamp resistance R of the instrument. It can be shown that the impedance of the whole circuit of the instrument becomes independent of frequency if C=L/R where C is the capacitance of the capacitor.

ADVANTAGES AND DISADVANTAGES

Such instruments are cheap and robust, give a reliable service and can be used both on a.c. and d.c. circuit. Although they cannot be calibrated with a high degree of precision with d.c. on account of the effect of hysteresis in the iron rods or vanes. Hence, they are usually calibrated by comparison with an alternating current standard.

MOVING COIL INSTRUMENTS

There are two types of such instruments i.e. (1) permanent magnet type which can be used for direct current work only and (2) the dynamometer type which can be used for both direct current and alternating current work.

The operation of moving coil permanent magnet type instruments is based upon the principle that when a current carrying conductor is placed in a magnetic field, it is acted upon by a force which tends to move it to one side and out of the field.

As its name indicates, the instruments consists of a permanent magnet and rectangular coil of many turns wound on light aluminum or copper former inside which is an iron core. The powerful U-shaped permanent magnet is made of Alnico and has soft iron pole pieces which are bored out cylindrically. Between the magnetic poles is fixed a soft iron cylinder whose function is,

(I)To make the field radial and uniform and (ii) to decrease the reluctance of the air path between the poles and hence increase the magnetic flux. Surrounding the core is a rectangular coil of many turns wound on a light aluminum frame which is supported by delicate bearings and to which is attached a light pointer. The aluminum frame not only provides support for the coil but also provides damping by eddy currents induced in it. The sides of the coil are free to move in the two air gaps between the poles and core. Control of the coil movement is affected by 2 phosphor-bronze hair springs, one above and one below, which additionally serve the purpose of leading the current in and out of the coil. The two springs are spiraled in opposite directions to neutralize the effects of temperature changes.

When current is passed through the coil, forces act upon it’s both sides which produce a deflecting torque.

Advantages and Disadvantages of moving coil instruments

ADVANTAGES: They have low power consumption and their scales are uniform and can be designed to extend over an arc of 2700 or so. They possess high (torque/weight) ratio. They can be modified with the help of shunts and resistances to cover a wide range of currents and voltages. Further they have no hysteresis loss and they have very effective and efficient eddy current damping. Since the operating fields of such instruments are very strong they are not much affected by stray magnetic fields.

DISADVANTAGES: Due to delicate construction and the necessary accurate machining and assembly of various parts, such instruments are somewhat costlier as compared to moving iron instruments. Some errors are set in due to the aging of control springs and the permanent magnets. Such instruments are mainly used for direct current work alone, but they have been sometimes used in conjunction with rectifiers or thermo-junctions for a.c. measurements over a wide range of frequencies.

Moving coil permanent magnet instruments can be used as ammeters (with the help of a low resistance shunt) or as voltmeters. (With the help of a high series resistance) The principle of moving coil permanent magnet type instruments has been utilized in the construction of the following:

For direct current galvanometers which can be used for detecting extremely small d.c. currents. A galvanometer may be used as an ammeter or as a voltmeter. By eliminating the control springs, the instruments can be used for measuring the quantity of electricity passing through the coil. This method is used for flux meters. If the control springs of such instruments are purposely made of large moment of inertia, then it can be used as ballistic galvanometer.

ELECTRODYNAMIC INSTRUMENTS:

An electrodynamics instrument is a moving coil instrument in which the operating field is produced, not by a permanent magnet but by another fixed coil. These instruments can be used either as an ammeter or as voltmeter but is generally used as a wattmeter. The fixed coils are usually arranged in two equal sections placed together and parallel to each other. The two fixed coils are air cored to avoid hysteresis effects when used on a.c. circuits. This has the effect of making the magnetic field in which moves the moving coil, more uniform. The moving coil is spring controlled and has a pointer attached to it.

The production of the deflecting torque can be understood from above. The current passing through the fixed coil is I1 and that through the moving coil is I2. Since there is no iron, the field strength and so the flux density is proportional to current I1. For more useful information and books on Electrical Engineering please visit for more details ELECTRICAL TECHNOLOGY

SKILLS IN PLANT & EQUIPMENT MAINTENANCE

skilltech1970@gmail.com (Dattatray) — Mon, 2 Jan 2017 23:30:00 +0530

Maintenance of equipment and maintenance of plant is a delicate and severe issue for maintenance engineers and managers in the plant. Sometimes no one knows that how sudden breakdown of machines may occur. Moreover, there is no definite and exact cause of the problem in the beginning, unless and until the problem is rectified. Thus such issues causes for shutdown of the particular machines or process line. It may be pipeline, pumps, motors, generators,Fluid carrying systems, hydraulic systems or pneumatic lines of the plant. During this course of time, obviously, concerned engineer may have to face pressure from his management or managers. Even one minute breakdown of equipment may result in

to decrease in production rate and huge loss on overall performance and production rate target of the companies. Most of the industries consider and treat such issues very seriously and they always recruit skilled and experienced manpower to reduce the overall maintenance cost of the production. Company also provides suitable training to the engineers and managers enable them to get acquainted with the machinery.

So, no need to worry about your manager’s comments, if you are well trained or having technical ideas about root cause of the problem. Better to sit for a while and plan for the next steps. First understand the problems and start working on that. That’s all.

For instance, when it comes to sealing, the first thought that comes to mind is leakage. Leakage exists in all field (gas, vapor or liquid) systems to one degree or another. The amount of leakage that cab tolerated is a matter of choice. Acceptable leak rates can range from a slight drip, to bubble-tight, to mass spectrometer measurements, to diffusion of molecules through the base materials. Equipment users want trouble-free operation but it is not always practical to specify “zero” leak rates. Over specification in this area usually leads to increased costs, and sometimes impractical or unwieldy designs. Toxicity product or environmental contamination, combustibility, economics, and personnel considerations are factors, influencing the establishment of acceptable leak rates.

An increased awareness of leakage has come about through conscientious efforts to conserve fuel and energy. It has been estimated that leakage from hydraulic systems alone costs industry over thousands of dolor per day to provide make up. This cost becomes substantially greater when we combine the leakage encountered in other fluid systems, such as water, air, steam, refrigeration, and so forth. Leakage can also be hazardous.

Discharged fluids leaking onto the floors or walkways present a safety hazard to personnel as well as a potential fire hazard. And, of course, from an aesthetic point of view leakage is messy, unsightly and produces housekeeping problems. These and other problem area can be eliminated or at least minimized through proper leakage control. In addition to the savings in material and labor costs, other benefits that accrue from proper leakage co prevention of product spoilage. In general, the safe, continuous and proper operation of all fluid systems relies on the integrity of the systems and excessive leakage defeats this. Read more on.....

Industrial Health and Safety

Further when it comes to threaded systems, technological advancements in manufacturing have enabled a great many fluid carrying systems to be build with fewer components, thus reducing, the number of areas that might otherwise leak. This is the designer’s objective, but in some cases it is not practical, especially, accessibility for maintenance and repair is required, also, fluid systems such as water or steam are usually assembled permanently in their place of use. They require some type of connection to attach the various elements. These connections may be permanent or replaceable. Examples of permanent fittings using welded or brazed connections are shown in figure 1. The removable fittings, which will be discussed in this, are used more often because of their cost and convenience, they come in a variety of sizes, shape, materials, and performance capabilities. Of course, to be acceptable, they must be leak tight under the maximum surge pressure, vibration, shock or other fluid system abuses. Removable fitting end in either male or female threads. The main function of the threaded portion is to mechanically bond or attach fittings to other fittings or equipment housings, but they may also provide the necessary seal as we will see shortly.
There are three types of threads currently used on fittings. Two are tapered from the outside to the inside end of the fitting, and the third type is parallel or straight from one end to the other. The taper, shown in figure 2, provides a gradually increasing interference fit as the joint is tightened. A verity of common types of fittings using this taper is shown in sketches.

TYPICAL TAPER FITTINGS

STRAIGHT THREAD AND TAPER THREAD ASSEMBLIES

The straight thread and American Standard Taper Pipe Thread (NPT) are assembled with a sealant to provide a satisfactory pressure tight joint. As indicated in figure 4, the straight thread assembly has open channels or leak paths that must be sealed. The NPT assemblies’ produces more metal to metal contact along the thread flanks but still leaves a spiral leak path at the thread crest and root. The dry seal standard taper pipe thread (NPTF), also shown in figure 4, was adopted to eliminate the use of a sealant. To accomplish this some modification of thread form, greater accuracy in manufacturing and more analytical gauging is required. The roots of the both external and internal threads are truncated slightly more than the crests, i.e. roots have wider flats than the crests, so that metal to metal contact occurs, at the crests and roots coincident with or prior to flank contact. Thus as the Dry seal thread is assembled, the roots of the threads crush the sharper crests of the mating threads. The result is a leak tight connection without spiral voids. Due to the crushing and wear that occur with disassembly and reassembly, tapered threads are less effective on re use than straight threads. The method of overcoming this disadvantage is to use a straight thread and a lock nut with an embedded seal or insert, The lock nut is threaded on to the male fitting and the fitting is then threaded in to the female component only far enough to ensure a mechanical connection. After positioning the fittings, the lock nut is tightened down on to the fitting until it makes a secure contact. In this way, the straight threads provide the mechanical attachment and insure re usability while the embedded insert seals against fluid leakage.

PIPE THREAD LOCKNUT

The O-Ring seal is another way of providing the leak tightness while the thread furnishes the mechanical attachment only. Two types of straight thread O Ring fittings are available. One type (non-adjustable) is used for adapters, plugs, connectors, etc., and utilizes an O-ring mounted in a groove about the threaded portion of the fitting, Figure6 The other type, which permits angular adjustments of these fittings, utilizes a backup washer and lock nut.

NON ADJUSTABLE & ADJUSTABLE STRAIGHT THREADS

Tube fittings are another form of connection. Figure 8 shows a typical 2-piece and 3-piece flared assembly. They derive their seal from the swaged portion of the tube. The female tubing nut, once engaged and tightened, compressed the flared tubing against the mating cone of the male fitting. The 3 piece fitting adds an extra element that provides better structural integrity and is less affected by vibration.
If all of the fittings discussed were 100% efficient, industry would not have the expense noted earlier in providing make up. The facts remain that fittings leak. Some fittings control leakage better than others but usually at higher cost. The most crucial factor involved with the selection, installation, and maintenance of fittings is the “human factor”. Designers will strive to cut costs by using less expensive fittings that are borderline for a particular condition. The assembler often fails to follow recommended installations practices and the maintenance worker will re use the old fittings rather than buy new ones.

TYPICAL FLARED FITTING

NPT fittings (ref. figure 4) were shown to have spiral leak paths at the thread crest and root after installation. Straight threads had similar gaps but much more pronounced and extended along the thread flanks. Sealants are required on fittings or port connections that utilize these thread forms. Although the Dry seal (NPTF) thread eliminated these spiral gaps, galling may occur during assembly. The galling is produced when the threads are crushed and deformed, creating small scratch- like leak paths. A lubricating sealant is recommended to reduce the associated friction and prevent galling of the threads. Also, extremely high stress points are developed at the threads crests and roots on the Dry seal fittings. Over tightening may create cracks in the mating fitting or housing because of these stress points. Initially, the crack might not be visible but could show up later as fatigue failures or fluid seepage, as the cracks begin to grow.

The fittings shown in fig 5, 6 and 7 all used plastic or rubber inserts to form their seal. For these fittings to properly seal, the insert or O- Ring must flow in to all surface imperfections. Under tightening of the fittings does not allow proper deformation of the insert to occur and conversely, over tightening could crack or extrude the seal from its mating surfaces. The compatibility of the insert with the environment is also important because some plastics and rubbers degrade when in contact with certain fluids. Temperature extremes will also cause some materials to become brittle and crack over a period of time.
The tube fittings shown in figure 8, are also subjected to the same human factors as the others. The proper flaring of the tube could be cited as the single most important factor. A flare that is too short reduces the clamping area and the wall thickness may be decreased when clamped. A flare that is too long may stick or jam on the fitting thread when assembling. Examples of incorrect flares are shown in figure 9. The correct length and diameter should provide a flare which extends beyond the maximum I.D. of fitting sleeve but not beyond the O.D. of the sleeve.

CORRECT & INCORRECT FLARE FITTINGS

In summary, fittings rely on intimate contact to form their seal. The threaded portion of a fitting has three functions:
1. To form the seal as was shown with the Dry seal thread.
2. Provide the Mechanical attachment to other fittings or equipment ports.
3. Provide the force needed to compress the sealing element, i.e. O- Ring, Plastic insert, flared tubing, etc,

Each function requires that the proper tightening torque be observed and that movements of the fittings in a loosening direction should not occur. Such movements cause either some or all of the contact pressure to be lost depending upon the nature of the seal. For example, Dry seal threads and flared tubing having very little compatibility and small movements in the loosening direction caused immediate loss of the original metal to metal contact. The O-Ring or plastic seal, on the other hand, can accommodate some movement which is proportional to the elasticity of the elastomeric material used. Vibration loosening of fittings has always been a major concern in controlling leakage. Even though fittings are considered to be static seals, they are subjected to a variety of dynamic forces that are discussed in the next section on gasket assemblies.

FLANGE SYSTEMS STATIC SEALS

All types’ fluid seals perform the same basic function and that is keeping the process fluid (gas, liquid and vapor) where it belongs. They accomplish this by forming an impervious barrier against fluid transfer between two mating surfaces. Traditionally seals have been categorized as either static or dynamic. The primary distinction between them involves the degree of movement with respect to the mating surfaces. For example, dynamics seals are used to retain fluids or throttle leakage between a sliding or a rotating part and a stationary one where as static seals prevent fluid loss between two stationary surfaces. This generic classification of seals is somewhat misleading and implies that static joints are completely rigid. Granted there are no gross movements between the mating parts, but movements are present because of several agents that act alone or in combination with one another. The four most important agents are temperature, fluid pressure, fluid velocity and system vibration. These agents produce adverse affects on the seal in ways that are not always fully understood. The following discussion will attempt to develop an understanding of these agents.

TYPICAL FLANGE SYSTEM

TEMPERATURE EFFECT

Fluctuations in temperature of a gasket-ed assembly create a variety of changes, all of which can affect sealing properties of that assembly. High thermal stresses can be developed within the gasket-ed joint because of the various sizes, shapes and materials of the elements involved, i.e. bolts, flanges and gaskets. Stresses from thermal load occur when the components are subjected to temperature gradients or to uniform temperatures where the components have different coefficients of thermal expansion. These thermal loads are high enough to be of engineering concern. The thermal stresses can produce abrading, crushing, extrusion or loss of bold load. A thermal change of 370 degree F. a change in bolt length by the same amount as an 80,000 psi prestress. This means that for each 10F difference in temperature between the bolt and the flange bolted to a steel flange expands radial, 0.013 inches more than the steel for every 10” of flange diameter and for in change temperature.

PRESSURE AND VELOCITY EFFECTS

Fluid pressure and velocity surges can also be present in the system. Surges of this type usually result in vibration. For example, if a valve is suddenly closed or an obstruction blocks the flow of fluid, a pressure wave is generated by the kinetic energy of the fluid. This pressure waves travels at the speed of the sound for the fluid through the downstream line until the wave is reflected back to the point of origin. If the system has separate branches, the wave is reflected separately through each branch. This phenomenon is repeated with shock waves over lapping each other until the original kinetic energy is absorbed by friction. In a water system the shock waves are referred to as water hammer because of noise and vibration that usually accompanies the waves.

EXTERNAL VIBRATION

External vibrations also stress a gasket joint in a manner similar to the internal vibrations caused by shock waves. An out of balance pump can vibrate the connected pipe rather severely, causing premature joint failure. Likewise, joints made on cars, airplanes and boats will be subjected to all of the vibration and twisting motions of that vehicle.

In summary, we can say that static seals are not truly static, but are a throbbing, squirming and shaking system composed of several elements. These elements are the flanges, bolts, and gaskets or seal and sometimes the attachment of the pipe to a shaking vehicle frame. The design, material section and maintenance of any gasket-ed joints must include consideration of all the agents acting on the system. We shall see that, very often the system is a compromise of choices. For instance, the material that will seal rough flanges may not be the material that will withstand hydraulic Hammering. Sometimes this compromise means changing some of the elements in order to get an effective joint seal. For ease of analysis, however, we will study each one of the important elements of a gasketed system individually and not attempt to pull them together until the end of this discussion.

REQUIREMENT OF PERFECT FLANGE SEALING

skilltech1970@gmail.com (Dattatray) — Mon, 2 Jan 2017 20:41:00 +0530

Fig.1.

FLANGES

Although the gasket material is considered the most important element in the system, it may fail to provide seal, because the other elements were not designed and constructed to make the best use of its properties. It is the contact pressure between the gasket material and the flanges that produce sealing. These pressure must be satisfactory for resisting the movements caused by those agents previously discussed (temperature, fluid pressure, fluid velocity and system vibration).

The flanges are important because they must transmit a compressive load to the gasket. This load must be maintained above a critical pressure called the minimum sealing stress. This stress is defined as the minimum stress a gasket must experience to close its internal structure to the passage of the sealed fluid and conform to the surface irregularities of the flange. The minimum sealing stress is highly dependent on the gasket material used, viscosity of sealed fluid, the width to thickness ratio of the gasket, the gasket shape factor, surface finish of the flange, and the stiffness of flange. For instance, a firm cork and rubber gasket requires a sealing stress of 600 psi to seal 800 psi internal pressure with stiff flanges (4).

FORCES ON A FLANGE ASSEMBLY

Fig.2.

If the working pressure is too high for the design of the flanges, adverse flange and bolt distortions will occur. The major problem encountered with flanges is distortion. Distortions most commonly found are:bowing, bolt hole distortions, non-parallelism and surface roughness.

FLANGE BOWING

Distribution of stress on a flexible flange.
The area where this joint is most likely to leak is right at the center of the flange ( c ) where the smallest stress is produced by the bolts and where the maximum bending occurs from internal pressure. One way to improve this situation is to stiffen the flange to get the result shown in fig. 14. As obvious as this seems, the economics of producing stiff flanges often precludes this approach. The bowing of flange is the most common reason for leakage.

EFFECT OF STIFFENING THE FLANGES & STRESS DISTRIBUTION

Fig.3

Fig.4.

BOLT HOLE DISTORTION
This occurs around the bolt holes in a flange. Figure 15 shows a stamped sheet metal flange before bolt loading (bottom) and deformation after loading (TOP). High stresses are transferred to the gasket material under the bolt head causing the gasket to crack, tear, rupture or extrude, as shown in fig 16. Bolt hole distortions do not necessarily lead to leakage but can cause bolt load losses that will result in fatigue failures if the system is subjected to dynamic forces.

NON - PARALLELISM

Flange cocking or non-parallelism. Cocking in itself does not create serious problems until the pressure in the area of low gasket compression falls below the minimum sealing stress. This type of distortion is usually caused by improper machining, improper heat treating, casting irregularities or improper tightening sequence of the bolts.

SURFACE ROUGHNESS

The various operations required to fabricate the surface of a flange face produce distortions or irregularities. A commercial finish is made by milling machines, grinders and abrades. The roughest surface normally found in flange joints is 250 micro inches. On the other hand, an exceptionally smooth or mirror finish is rarely found because expensive machining operation are required. There are some rough surface finishes that are planned and are defined as phonographic and concentric. They are not random irregularities but carefully dimension-ed in width, height and depth of cut. The serrated finish is almost always found in pipe flange assemblies and is used more or less as a stress riser. To eliminate leakage from surface irregularities, the minimum sealing stress must be achieved thereby ensuring that the gasket flows into all flange face imperfections.

BOLTS

The next element in the gasket joint is the bolts. The life of the gasket-ed joints can be greatly affected by the design of the bolting system. Almost all of the force for producing the minimum sealing stress is generated by the bolts (a small amount may come from gasket adhesion and gasket swelling from chemical and pressure effects). It is important that the bolts not only produce the design pressure initially on the gasket but maintain that pressure throughout the service life of the assembly.

Bolts lose their initial stress or clamp load in a variety of ways. Some of the more important reasons are listed as follows.

Gasket relaxation.
Bolt hole distortions of the flange.
Temperature effect.
Vibration loosening and,

System load changes.It is sometimes helpful to use a spring analogy in explaining the bolts specific function within a gasketed assembly. The bolts stretch or deform like a spring when a load is applied. The necessary clamp load cannot be exerted on the flange and gasket if this axial stretching did not occur. The amount of clamp load that can be applied depends on the bolts strengths, the rigidity of the flange and the compressive strength of the gasket material. After the assembly has been tightened, the bolts stretches in tension and the flanges and gaskets are in a state of compression. Assuming the flange is infinitely rigid and the gasket is thin so that its effects are negligible, the goal is to increase the amount of elongation that a bolt experiences helps to maintain the required clamp load.

There are two ways to increase bolt elongation:

By increasing the effective bolt length Decreasing the spring constant of the bolt
The rule of thumb is that, when the length of the bolt is five times greater than the diameter it can be elongated sufficiently to work as a spring between two flanges and will dampen vibration. The relationship between the effective bolt length and the clamp load might be understood more clearly with a hypothetical example. For instance, a bolt with an effective length of 1 inch elongates 0.004 inches under a given load. Now, what if the gasket material used relaxed in compression approximately 0.002 inches over some period? The original clamp load would be decreased by 50%. However, if the effective bolt length was increased to 2 inches under the same load, the bolt now would elongate 0.008 inches. The gasket relaxes about the same amount (the load has not changed) but this time only 25% of the original clamp load has been lost. Clearly a 25% load loss is more desirable if we are concerned with maintaining a clamping pressure above the minimum sealing pressure requirements.

Several things can be done to increase the effective bolt length:

Use a thicker washer under the bolt head
Design a boss on the flange
Use a thicker flange

Machine down the top portion of the engaged threads.The other method used to increase bolt elongation is to decrease the spring constant of the bolt. The spring constant (k) of the bolt is simply the ratio of the applied load (f) to the elongation (x) produced by that load:
K=F/X
EFFECTIVE BOLT LENGTH

Fig.5

Assemblies using bolts with low spring constants have a smaller clamp load loss than do high spring constant systems and provide longer gasket life in designs involving dissimilar metals with different coefficients of thermal expansion. Lowering the spring constant reduces the pounding of the flanges, causing the gasket to crush or fail. Low spring constant bolts elongate more than high spring constant bolts.

As mentioned earlier in the effective bolt length section, for a given clamp load, a gasket material will relax over a period of time. The low spring constant bolt loses less clamp load than the high spring constant bolt, thus adding more reliability to the sealing function.

The spring constant can be lowered by decreasing the number of bolts used, reducing the diameter of the bolts down to the root diameter, increasing effective bolt length, increasing the length of the threaded sections, or decreasing the size of the bolts. Decreasing the size of the bolts from 3/8 to 5/16 might involve going to a stronger grade of fastener to achieve the proper clamp load. Of course, any of these changes must be checked against the entire system to ensure proper performance and lasting service life.

GASKETS

The third and final element in the flange system is gasket. The main function of the gasket is to create a barrier against the transfer of fluids across two mating surfaces. There are, however, other reasons for a gasket’s existence, such as, cost and accessibility. Manufacturing and shipping costs are much lower when assemblies are composed of small elements that are joined later with a gasket to form a complete and leak tight unit. The assembled unit can at any time be disassembled for repair or maintenance. Without this accessibility, repair might be extremely difficult. If not impossible. Gaskets are also used to join dissimilar materials, dampen vibration, and insulate against the transfer of heat.
Materials used for gaskets fall into two categories: metallic and nonmetallic. The metallic gaskets can be steel, copper or metallic and organic composite. Materials such as asbestos, cork, cellulose, and rubber are non metallic gaskets. Other types of non metallic gaskets are sealants or formed in place of materials. These materials can be applied to any shape flange and generally considered to be pressure containing, but not load bearing, because of their fluid consistency upon application.

All gaskets, whether metallic or nonmetallic must perform four basic functions:

Must create a seal
Must maintain the seal
Must be impervious to fluid flow
Must be compatible with the environment

Each function has its own relative importance with respect to the integrity of the gasket assembly. A brief discussion of each one will point out their relative importance.
First, a gasket must create a seal between the flanges by conforming to all flange face irregularities.

On smooth and polishes flanges a relatively firm material may be used. When surfaces are rough or show excessive tool marks, either a thicker, softer gasket or heavier bolting pressures must be used. The effects of changing the gasket thickness on the other elements will be pointed out next.

Second, the gasket must maintain the seal throughout the life expectancy of the joint. Joints are sometimes subjected to considerable movements caused by vibration, mechanical strain, changes in temperature, pressure and velocity. Despite these movements, the gaskets and flange surfaces must remain in intimate contact. The major factor in maintaining contact is the elastic response of not only the gasket, but the bolts and the flanges.

Third, the gasket must be impervious to fluid flow, both internal and external. Material such as cork with rubber or straight rubber normally is impermeable even with small flange loads. Others such as fiber sheet packing’s and cork are impermeable only when compressed sufficiently to close their natural holes.

The fourth requirement is compatibility with the environment. A gasket material must be able to withstand the full range of temperature changes without deteriorating. Flange staining and corrosion, which is generally promoted by vulcanizing agents, accelerators and moisture present in the gasket material, should not be visible on the flange face. Gaskets must also be relatively inert to the effects of sealed fluids. Slight swelling is often beneficial, whereas deterioration of the material or contamination of the sealed fluid is not tolerable.

PHYSICAL PROPERTIES

Various physical characteristics have been defined to evaluate gaskets performance properties and to measure its ability to meet the four requirements previously discussed. The most important physical properties of a gasket material are:

COMPRESSIBILITY

This property indicates the degree to which the material is compressed and deformed, in thickness, by the application of a specific load. This property is expressed in terms on a percentage of the original thickness. Compressibility is used to determine whether a material can compress sufficiently to compensate for surface irregularities or non-parallel conditions in the flange.

COMPRESSIVE STRENGTH

Compressive strength can be described as the maximum compressive stress that a material is capable of withstanding without rupture or excessive extrusion. From a functional standpoint, this physical property is important because it is directly related to the ability of a gasket to resist flange loading without breaking down.

STRESS RELAXATION

This is a transient stress strain condition in which the stress decays as the strain remains
constant.

CREEP:

This is a transient stress strain condition in which the strain increases as the stress remains constant.

CREEP RELAXATION

This is a transient stress strain condition in which the strain increases concurrently with the decay of stress.

FLUID COMPATIBILITY

Immersion tests provide a simple means of measuring the effects of various liquids on a gasket material. The procedure consists essentially of immersing a prepared specimen in the desired fluid for a specified length of time at a specific temperature. The weight, thickness or volume increase is the properties most frequently measured after removal of the specimen from the fluid.

FLEXIBILITY

This property is usually determined by bending a specimen 1800 around a mandrel of a specified diameter. As applied to materials in their original condition, flexibility is of value in determining the handling qualities of the material. It does not directly correlate with other physical properties.

HEAT AGING

Heat aging properties consist of exposing the material at a specified material at a specified temperature in a circulating air oven for a specified length of time. Physical characteristics measured after removal of the test specimen may include flexibility, durometer hardness and elongation and are compared with those values for the same materials prior to testing.
There are many other considerations to be made before a suitable gasket can be selected, such as its ability to resist tearing, weather, fire, fungus and vermin. Most of the physical properties listed above pertain to pre-cut gaskets; however, formed-in-place materials must also meet many of these requirements, especially degradation from fluids, heat or other environmental constraints.

GASKET THICKNESS VERSUS STRESS DISTRIBUTION

Perhaps the most important requirements of any gasket material are to create and maintain the seal. In the section on flanges we defined minimum sealing stress as the minimum pressure the gasket must experience to close its internal structure to the passage of the sealed fluid and to conform to the surface irregularities of the flange. As we shall now see, the thickness of a gasket material has a profound effect on two of the major requirements of the gaskets, that is, creating and maintaining the seal. Figures 13 and 14 showed how stiff flanges improved the load distribution on a gasketed joint. To increase the minimum sealing stress between the bolts, figure 14 suggested stiffening the flange. The same effect can be obtained by making the flange bow more, through the use of a softer or thicker gasket.
Increasing the thickness of the gasket will enhance its capability to create the initial seal. Now it would be instructive to see exactly what effect increasing the gasket thickness has on maintain the seal. Relaxation is one of the major considerations for maintaining the seal, primarily because pre-cut gaskets creep or relax in service to some degree. The relaxation of the gasket as measured by torque loss in the bolt vs. thickness of the gasket. The solution to this effect is to use a harder or thinner material.

Formed in place material should also be considered with respect to creating and maintaining the seal. Flange loading was increased by using a thicker gasket. Now, if the stress distribution was redrawn for a non liquid formed-in-place material and non liquid material will not follow the movements of the flanges. What happens if the material is mildly liquid sealing agent? A mildly liquid sealant material will seal more flexible flanges, provided that liquid is also flexible enough to follow the flange bowing under internal pressure. Usually this liquid technique cannot be carried to the extreme because flange disassembly becomes very difficult. What can be done if the flanges are prestressed in such a manner that internal pressure does not exceed or add to the pre stress? This is accomplished by providing pre-bowed covers, or bosses on the mating surfaces. In other words, the gasket surface can be prestressed so that the stress distribution is more uniform as discussed.

We have seen that a sealed joint is not a static device. It moves under the influence of temperature, fluid pressure and velocity, and external vibration. If a joint leaks, it may not suffice to change only one element within the system. With any change, one must always keep in mind its effect on the minimum sealing stress.

SYSTEM RELIABILITY

The fatigue or dynamic loading characteristics of any assembly have not been fully discussed here. Their importance to the physical integrity of the joint cannot be overemphasized because the service life of an assembly is directly related to its ability to absorb and transfer these dynamic forces.

In most assemblies, the ratio of assembly rigidity to fastener rigidity is high enough to almost discount any addition to bolt tension produced by dynamic forces. In a flexible joint with a soft gasket between bolted flanges, the rigidities of the joint and the bolt are quite different; here, a much greater proportion of the externally applied tension is added to the bolt preload. The fatigue strength of a gasketed assembly must be evaluated in two ways: fatigue of the bolt, and fatigue of the bolted material. The properly tightened bolt will not fail in fatigue in rigid joint. Initial bolt tension will stay relatively constant until the external tension load on the joints exceeds the bolt load. If the service load is less than bolt preload, the bolt will experience no appreciable stress variations, and without stress variation, there can be no failure by fatigue. This is not the case where considerable flexibility is present. Variable stress in screw or bolt fastenings increases with the flexibility of the connected parts. If flexibly is too great, the variable stress present may be high enough to cause eventual fatigue failure of the fastener regardless of the initial bolt preload.

SUMMARY

Selecting rigid joint members and choosing flexible fasteners are important steps to successful design. Soft materials in joint members may spell trouble unless extra design precautions are taken. If gaskets are used, they should be as rigid and thin as practical. But this is not always possible because thick and soft gaskets are required to seal imperfections and produce the minimum sealing stress. Formed in place sealants (new liquid technology available worldwide) offer some advantages in this area. Here the load on the bolt was essentially the preload P1 (Since C is approximately 0) for stiff or hard gaskets. Liquid gaskets create metal to metal flange contact to form a rigid joint.
P= Pi +CFe Where P= final load on the bolt, lb.; Pi = initial preload or clamping load developed through tightening, lb.; Fe = external applied load, lb.; and the constant
C =EbAb /Lb /EbAb/Lb+EgAg/tg,
Where Eb = modules of elasticity of the bolt, psi;Eg =modules of elasticity of the gasket, psi; Ab = effective cross-sectional area of bolt, sq. in.; Ag = loaded area of gasket, sq. in.; Lb = effective length of bolt, in.; and tg = gasket thickness, in.

SYSTEM RELIABILITY - GASKET

Fig.6

The greatest single factor that can eliminate stress variations due to cyclic loading is proper preloading of the fastener. Test result indicates that rigid members bolted together by relatively elastic bolts after the best assurance for preventing fatigue failure.
Static seals are subjected to a variety of dynamic forces that cause movements and create stresses within the joint. Loss of fluid and catastrophic failure, such as, fatigue fracture of the bolts is the end result of poorly designed assemblies. The gasketed joint must be thought of as a system for affecting a seal. Each component of the joint plays an important role in creating a seal but more importantly, maintaining that seal throughout the expected life of the assembly.

IMPORTANCE OF TRAINING TO ENGINEERS

skilltech1970@gmail.com (Dattatray) — Sun, 1 Jan 2017 17:40:00 +0530

Training has become the most essential part of an organization and every Engineer must undergo training to become more efficient and reliable. Training is quite essential for a newly appointed Engineer as well as an old employee of an organization. It helps the new Engineer to get the full knowledge of the productions and Machines that he has to operate the working technique and managing skills to different machines and tools depends upon the industrial segment. It has helps the old engineer to acquaint
themselves with the new machines and tools of the company, to understand the new techniques of working operation and improve or increase their ability and efficiency. Therefore the company arranges for the training of new as well as old engineers.

The extent of training depends upon several factors such as the nature of the job, the educational qualifications of the engineer, their past experience, the nature of the tools or machines to be handled and the types of customers with whom the engineer have to deal. The aims and objects of giving training are various. The following are the common aims and objects of providing training or coaching to Engineers.

AIMS AND OBJECTS OF TRAINING

To acquaint the new engineer with the principles and techniques of handling machine and cost saving procedures.

To increase or improve the efficiency of an old employee.

To enable the engineers to get full knowledge of the production and operation and increasing the production rate skills of the organization where they are employed.

To enable the engineers to be familiar with the tools and machines practices of the plant and to render better services to the management.

To keep the engineers well informed about the laws regulating the warranty and guaranty, company policy, about the types of customers, about the position of the competing firms and about the ways of overall cost of the company.

To find in the course of training inefficient persons and weed them out.

Thus, training is very important in producing effective, efficient and strong team of engineers. It is often said that a good engineer can handle anything and therefore a trained engineers affects the growth of any production system and under any circumstances. This is so because a trained engineer has thorough understanding of the task entrusted to him.

WHY "INDUSTRIAL ENGINEERING"?

skilltech1970@gmail.com (Dattatray) — Mon, 5 Dec 2016 14:15:00 +0530

Today the importance of Industrial Engineering is known to all. Decades ago the importance of industrial engineering was limited to few. But today, we see vast changes in industrial engineering sector, and with more than years of combined research by experts it has been able to play a major role in industrialization.

A nation’s economy is dramatically improving with the introduction of industrial engineering. Not only large corporations have benefited from this, but the industrial engineers are using their skills and talents for economic problem saving in the country.

This development is possible through the systematic implementation of industrial engineering.

The main cause for the drastic development in Western and European countries is due to industrial engineering. Industrial Engineering believes in the concepts of low cost and high production. Industrial Engineering adopts and alters its techniques in accordance with the business structure of a particular sector.

Industrial Engineering is a broader concept, and we provide expertise tips to cautiously approach this technique to all the interested people out there.

Industrial Engineering is that branch of engineering knowledge and practices which,

Analyses, measures and improves the methods of performing the assigned tasks to individuals.

Designs and installs better systems of integrating the tasks assigned to a group.

Specifies, Predicts and evaluates the results obtained.

It does so by applying to materials, equipment, and works specialized knowledge and skill in the mathematical and physical sciences and the principles and methods of engineering analysis and design.

The contribution of industrial engineering lies in the management of decision making process. The problems existing in this area deal with the optimum utilization of men, materials, equipment and energy to achieve the purpose of organization.

The managers of the organization need factual information arranged to define alternatives and consequences to help them recognize and solve existing problems. Industrial engineering collects analysis and arranges this information in such a way as to fulfill the management need, as well as searches for better way to do the job. Industrial engineering operates in two major areas, the design of new systems and the maintenance and improvement of existing systems.

Present management expects industrial engineering to be capable of assisting in and performing the following services.

Assist management in never ending cost reduction.

Assist management in increasing the productivity of human and productive resources.

Develop management information flow systems.

Conduct organizational studies and design new organizational systems.

Develop data processing and computer control system.

Coordinate development of corporate maintenance policies and program.

Formulate and recommend corporate inventory management policies and procedures.

Initiate, develop and recommend corporate equipment replacement policies.

Assist management in developing long range planning strategies.

Develop production planning and scheduling procedures.

Establish engineered standards of performance for management control.

Determine and recommend the optimum usage of plant, equipment and office facilities.

Verify economic feasibility of capital expenditure requests.

Conduct manufacturing and office methods survey.

Provide assistance to all levels of management in solving problems requiring statistical and applied mathematical analysis.

Assist management in decision making through the use of computers or through the development of mathematical models simulating complex business problems.

Co-ordinate studies involving line and staff functions crossing divisional lines.

Assist management in formulating and developing corporate policies and procedures.

Develop and recommend production and quality control programmers.

PRODUCTIVITY

Productivity is defined as the ratio between output and input in enterprises, an industry or an economy as a whole.

Resources may be land, materials, plant machines, tools and services of men.

Productivity of land may be said to have increased if the output of goods or services within that area of land is increased by whatever means.

Productivity of materials may be due to greater skill on the part of worker, to improved design also.

Productivity of machines- It is said to have increased if produced components per shift are more than existing production by means of more improved of machining.

Productivity of men due to effective utilization of manpower.

WORK STUDY

Work study is a general term for those techniques particularly method study and work measurement, which are used in the examination of human work in all its contexts and which leads systematically to the investigation of all the factors which affect the efficiency and economy of the situation being renewed in order to effect improvement.

Work study is thus especially concerned with productivity since it is used to increase the amount of produced from a given quantity of resources without further capital investment except perhaps on a very small scale.

Method study is concerned with the reduction of the work content of a joint or an operation, while work measurement is mostly concerned with the investigation and reduction of any ineffective time associated with it and with the subsequent establishment of time standards for the operation when carried out in the improved fashion as determined by the method study.

Both of these do not take in to account the increase in productivity or reduction in cost, brought about by development of new basic process or installation of more modern or higher capacity plant of equipment. Work study is service to management and supervision.

How ‘Work Study’ is a valuable ‘tool’ of management?

It is a means of raising the productive efficiency (productivity) of a factory or a operating unit by the re organization of a work method which normally involves little or no capital expenditure on plant and equipment.

It is systematic. This ensures that no factor affecting the efficiency of an operation is overlooked whether in analyzing the original practices or in developing the new and that all the facts about that operation are available.

It is most accurate means – evolved of ‘Standards of Performance’, on which, the effective and control of production depends.

The saving resulting from properly applied work study, once started will continue as long as the operation continuous in the improved form.

It’s a ‘Tool’ which can be applied everywhere. It can be used with success wherever manual work is done or plant is operated, not only in manufacturing shop but in offices, stores, lab, and service industries such as whole sale and retailed distribution and restaurants.

It is a most penetrating tool of ‘Investigation’ available to management. This makes it an excellent weapon for starting an attack on the inefficiency of any organization, since in investigating one set of problems, the sickness of all the other functions affecting it, will gradually be laid bare.

Managers and foremen have generally failed to achieve the savings and improvements which can be affected by work study because they have been unable to apply themselves continuously to such timings even when, they have been trained. It is not enough for work study to be systematic. The full effect is felt in an organization when work study is applied everywhere, without relaxation and when everyone begins to be filled with the attitude or mind which is the basis of successful work study.

Intolerance of waste in any form, whether material, time effort or human – ability and the refusal to accept without question that things must be done in a certain way because ‘ that is the way they have always been done’.

METHOD STUDY

If you study the economic history of any advanced country, you will find that major factor which has brought this advancement is higher productivity of each and every factor of production. But one should clearly understand the meaning of higher production and productivity. Higher production means, production of more number of goods and services. But productivity means ratio of outputs in to inputs. When we say productivity is high, it means production is high with less input or with less use of resources.

When productivity is more, we use fewer resources. This means less per unit cost and hence we can have fewer prices of goods and services. When prices are less, there would be more demand for goods and services. When demand is more, we have to produce more to meet the demand. Naturally this results into increase in the national wealth. To increase productivity, the most important effective technique is method study.

Method study is defined as the systematic recording, analysis and critical examination of existing and proposed ways of doing work and the development and application of easier and more effective methods.

As a matter of fact techniques of method study is not very difficult to understand but one has to follow the technique rather religiously and should have faith in the saying that there is always a better way for doing the things.

This study is a systematic approach to investigate the operations; hence proper steps are required to be followed. These steps are…

Select- Work to be studied.

Record- All the facts about the present method.

Examine- Critically all the facts in ordered sequence.

Develop- The most practical and effective method.

Install- New method as a standard practice.

Maintain- New method by regular checks.

SELECT

While selecting job or operation for study, one has to undertake preliminary study and has to consider economical, technical and human aspects involved in it. In the preliminary study, we must get at least some rough idea for possible reduction in either effort required to be put in or in material cost or where a lot of manual work is involved. A small saving occurred per piece manufactured in large quantities results into saving of thousands of dollars.

Similarly when costly material is being used for the production, there is a tremendous scope for saving. Therefore, proper selection of job for a study is a first important step in the method study.

RECORD

Next step is of recording all the relevant facts about the operation of components under study. This recording in detail is necessary for critical examination of the facts in the present method. For this purpose, various charts are developed with the help of which, one can get quick understanding of the whole situation as well as one can get clues for the improvement, like operation process charts, flow process charts, man-machine charts, flow diagrams, operator movement diagrams etc.

These charts are prepared by using some specific symbols having specific meanings.

CRITICAL EXAMINATION

The next and most important step in the method study is critical examination of existing ways of doing the work. This is done with the help of charts already prepared for this purpose and questioning technique, every aspect of the work is challenged.

We have already seen that in manufacturing, there are some ‘do’ operations and some storage operations. Generally ‘do’ operations are productive operations and storage or transport activities are non productive activities. While doing this, there is a well established pattern of series of questions. These are what – why – where – when – who – and – how. By these questions we have to challenge the purpose, sequence, place, means and person. Many times, we do not get satisfactory answers. Here, we can start thinking of better alternatives.

One should keep it in mind that in method study, nothing should be taken for granted. Even in case of very simple things, we should minutely examine the facts and try to find out better alternatives. Some simple things also results into great loss or waste of efforts material and money.

DEVELOP

Steps Involved:

Record the method proposed through the critical examination.

Consult all level of managements and workers for their suggestions and objectives.

Test thus modified proposed method for its advantages claimed over the original method.

Prepare and put up the report on proposed method to the management for its final approval and subsequent implementation.

Comparison of the existing and proposed (new) method is essential, in order to show that improvements are factual and it is important, therefore, that all activities are portrayed in the same scale and at the same level.

The synthesis of possible improvements will be viewed from the fact that the proposed method is practical, feasible, safe, effective and economical.

INSTALL

The proposed method is installed in two stages.

PREPARATION.

IMPLEMENTATION.

PLANNING.

Actual installations involve the introduction of developed method as standard practice.

Arranging.

Rehearing.

Preparation.

Implementation.

Planning.

Arranging.

Rehearing.

Actual installations involve the introduction of developed method as standard practice.

MAINTAIN

Once the new installations has been installed, it should be maintained in its specified form and workers should not be allowed to slop back in to the old method and introduce elements not allowed, unless there is a very good reason for doing so.

The proper functioning of the installed method is ensured by periodic checks and verification.

WORK MEASUREMENT

Work measurement is the application of technique, designed to establish the time for a qualified worker to carry out a specific job, at a defined level of performance. In simple words you can say that it is a method to this time required for performing any job.

In the present industry work measurement is the primary necessity. Work measurement is required right from the foundation of an industry. The uses of work measurement can be listed as under.

Manpower and machinery requirement.
Machine utilization and operation productivity.
Balancing of work centers.
Compare alternative method.
Calculate cost of existing product.
Calculate cost of new product.
Filling in the quotations or tenders.
Make delivery promises.
Decide rates of sub contracting.
Control on costs.
Incentive schemes.

TECHNIQUE OF WORK MEASUREMENT
Time study.
Activity sampling, rated activity sampling.
Synthesis from standard data.
Analytical estimation.
Predetermined motion time systems.

TIME STUDY

Time study is a work measurement technique for recording the time and rate of working for the elements of a specified job carried out under specified conditions and for analyzing the data, so as to obtain the time, necessary for carrying the job, at a defined level of performance.

For carrying out time study, some equipment is required.

Stop Watch
Study Board
Time Study Forms

STEPS FOR MAKING TIME STUDY

Select the job to be studied.Obtain and record all the information.

Break down the operation into elements.

Measure the record elemental time.

Assess the speed of the worker.

Calculate the basic time.

Determine the allowances.

Complete the standard time.

Select the job to be studied

There is always some reason for making the time study. It may be:

Introduction of new job.

New Method.

New Tools/Tooling.

Change in material.

Bottle-necking operation.

In the case of new jobs, we have to see that the jobs are properly set, the sequence of operation is properly decided and best available methods and tooling are used.

Obtain and Record all the information.

Name of the job.

Drawing Number of the job.

Material used for the job.

Quality requirements.

Jigs and fixtures and tools used.

The machine used and the speed and feed available on the machine.

Material removal for the job.

Details of operation.

Small sketch of the job.

BREAKDOWN THE OPERATIONS INTO ELEMENTS

Once all the information is recorded, the time study engineer has to observe the complete operation and break down the operation in to small elements.

An element is a distinct part of the specific job selected for convenience of observation, measurement and analysis.

The detailed breakdown in to elements is essential to isolate the effective time, to facilitate checking of method, to decide the fatigue and fatigue allowance, to rate the working speed of the operator accurately etc.

Measure the record elemental time.

Once the elements are noted down, timing can start. Timing methods are of two ways:

Cumulative Timing

Fly Back TimingIn cumulative timing method, the stop watch is continuously running. The watch reading after completion of every element is recorded. The difference between two successive readings gives the observed time of the element.

In fly back method, after completion of each element, the watch reading is recorded and the reading is brought to zero by pressing the fly back knob. This method gives the elemental time directly.

Number of cycles to be timed.

The time study is a sampling technique and hence the accuracy is depends upon the sample size i.e., number of cycles timed. Number of cycles to be observed depend upon:

The accuracy required.

Variation in time from one place to another.

Assess the speed of the worker.

While making the time study, as far as possible, a competent and steady worker should be put on the work. His pace of work should be average. He should be physically fit and should have acquired sufficient job knowledge and experience. An average qualified worker can be defined as one who is accepted as having necessary physical attributes, possesses the required intelligence and education and has acquired necessary skills and knowledge to carry out the work to satisfactory standards.

PERFORMANCE RATING

Whenever you observe any operation being done, its performance may be slower, faster or normal speed. The time study engineer has to judge the working pace of the operator, whether it is normal slow or fast. This is called as performance rating.

The performance rating is the assessment of a worker’s rate of working relative to the observer’s concept of rate corresponding to standard pace.

While rating the workman, time study engineers has to be very careful because this is the area where he can go wrong or he can be cheated by the worker, because everybody knows that the work measurement is ultimately related to the earnings/productivity of the operator. Hence, the time study engineer has to be very cautious in rating; sometimes he is over-careful. When the worker is having smooth and rhythmical movements, he should not rate that worker very low.

CALCULATE THE BASIC/NORMAL TIME

Now we know that the observed time, need not be the normal time. Hence, all the elemental observed times are required to be converted into the normal time. When the observed time is multiplied by the performance rating, the product is known as the basic/normal time.

Observed time X Performance rating = normal time.

Normal time may be defined as the time required for carrying out an element of work at standard rating.

If the observed time for an element is 0.5 minutes, performance rating is 80%, and then normal time is,

0.5 X 80/100 = 0.4 minute.

Work cycle contains manual elements as well as machine elements. With the help of performance rating, the manual elements are normalized. Similarly, we have to see that the machining elements are also normal.

Depending upon the job material, tool used, and material removed, surface finish and dimensional accuracy required, the cutting speed and feed are decided.

While conducting the time study, the time study engineer has to see that the standard cutting speed and feeds must be used. By different tool travel, the time for machine elements can be calculated. This is a counter check on the observed machine time.

Hence, the total normal time of a job or a work cycle is the summation of the basic for all the manual and machine elements.

Determine the Allowance.

The type of allowances added to ‘Normal –Time’ is as follows:

FATIGUE ALLOWANCE OR RELAXATION ALLOWANCE (Afj, Ajm)

This is in addition to the normal time intended to provide the workers with the opportunity to recover from physiological and psychological effects of carrying out specific work under specified conditions. The amount of allowance will depend on the nature of the job.

Constant Allowance

VariableThis allowance depends upon standing, abnormal position, use of muscular energy, bad light, atmospheric conditions, close attention, noise level, mental strain, monotony etc.

Personal Allowance (Ap)This provides for the necessity to go away from the work place to attend the personal needs such as washing, going to fresh room, getting a drink. The allowance is made as constant percentage of normal time, common figure being 5% for men.

Miscellaneous Allowance (Am)This allows for time required to perform other jobs related to the tasks he is performing such as getting tools from tool-crib, tool regrinding, consultation with supervisor etc. The percentage of allowance depends on the nature of the job.

COMPLETE THE STANDARD TIME

Standard time may be defined as the total time in which the job should be completed at standard performance.

Standard Time =

(Tn ) = ( 1 + Afh/100 X Th + ( 1 + Afm/100 ) X Tm

Tn = Standard Time

Ap = Personal Allowance

Afh = Fatigue Allowance for handling

Afm = Fatigue Allowance for machining

Tm = Normal Time for machining

JOB EVALUATION

It is defined as the complete operation of determining the value of an individual job in relation to the other jobs in the organization. It begins with the job analysis and is designed to determine the relative value of the jobs or groups of jobs. It also involves the pricing of these values by establishing minimum and maximum salaries for each group of jobs, based on their relative value. The operation ends with the final checking of the resulting salary system.

Job evaluation deals with jobs only and in no way is concerned with the persons doing these jobs.

Decides the relative values of different jobs in an organization.

Helps to formulate an appropriate and uniform wage structure. The aim is to provide equal pay for all jobs of equal value. The salary should be proportional to the job difficulty and responsibility associated with it.

Clarifies the responsibility and authority concerned with each job.

Provides a basis for recruitment, selection, training, promotion and transfer of the employees.

Improves employer – employee relationship.

Adds job satisfaction.

Minimize labor turnover.

Describe and evaluates new job.

Ranking MethodThe different jobs depending upon their requirements, responsibilities involved and their importance to the organization are ranked, graded or placed from top to bottom.

ADVANTAGES

Simple and fast, less expensive.

Easily mastered and administered.

Suitable for small organizations involving lesser number of jobs to be evaluated.

DISADVANTAGES

There is no commonly accepted base for deciding the rank. Method is not very correct and not useful for large organizations.

CLASSIFICATION OR GRADING METHOD

Jobs are classified or graded in groups or levels of equal skill, difficulty, responsibility, importance and other requirements. It may be a production job, a sales job or an office job. Each job family can be broken into a number of grades. Each grade carries an appropriate monetary value.

ADVANTAGES

Simple, easily mastered and administered.

It is more accurate as compared to ranking method

DISADVANTAGES

It is not useful for long organizations.

Method does not involve detailed job analysis.

Sometimes, it is difficult to correlate the classified grade of the job with the present salary of the worker.

FACTOR COMPARISON METHOD

The method employs a five factor scale for analyzing, comparing and evaluating different jobs. The five factors are skill, mental effort, physical effort, responsibility and working conditions.

PROCEDURE

Identify a few key jobs in the organization and record their wages. Key jobs are those representative jobs which are assumed to be correctly or fairly paid.

Analyses the key jobs for each of the positive factors mentioned above.

Allocate the salary (paid for each key job) among the five factors in proportion to their requirement, necessity or importance of the job.

This formulates a money rating scale for each of the five factors.

EXAMPLE

For fixing wages for a new job, this method uses a ready-made job comparison (Monetary) scale and thus the wages can be calculated speedily. This method finds the wages for a job from existing wage rates.

DISADVANTAGES

Selection of unfairly paid jobs as key jobs, can introduce considerable error in the wages calculated by this method.

It is difficult to decide each factor into a large number of sub factors and unless done so, accurate results may not be achieved.

Complicated, not easily understood and hence less popular as compared to point method.

The method depends upon subjective judgment; different persons may attach different monetary value with each factor for the same importance.

POINT METHOD

The point method basis itself on dividing the jobs into infinite number of factors which in turn are further sub divided into grades or degrees. Each degree is awarded certain points and when such points for all the degrees are totaled, they indicate the importance of the job in the organization, consequently a suitable wage rate proportional to the total points is determined. The steps involved in point method are given below:

Select a few jobs which can be taken as representative of the job to be evaluated in the organization. Key jobs are those which can be clearly defined and fairly paid.

Establish and define job factors. Following are the factors:

Skill, education and training, experience judgment and initiative.

Effort- physical, mental.

Responsibility towards materials, equipment, machinery, tools and fellow workers.

Working condition- exposure to hazards, dust, smoke, fumes and noise, high temperature, glare and harmful radiations, etc.

For the range of jobs to be evaluated, establish the importance of each factor and decide its weight age points.

Select and define grades for each factor.

Allocate points to each grade.

Break the key jobs into factors and the factors into grades. Total up all the grade points for each key job.

Establish the factors and grades for the job to be evaluated.

Since this method involves points that is numerical numbers, it is considered to be more correct and reliable.

CAUSED ESTIMATION

The basic method of cost estimation used by Industrial Engineering Division or Cost Accounts Department is the same, the only difference being that whereas the actual cost is based on actual data, estimated cost is based on assumed data. All the assumptions regarding the product specifications, material of construction and inspection standards are listed down on the estimation sheet and should there be any change in these assumptions, the cost structure would also change. It has been our experience so far that many changes take place from the estimation stage to the execution stage resulting in variation in cost.

SCOPE OF INDUSTRIAL ENGINEERING DIVISION

Cost estimation of the following items is done by industrial engineering division.

Tailor-made products and spares (excluding BHR,BHF,NKS)

Newly developed products and spares(until the first lot)

Regular products with modifications in design, involving major estimation work.

Job work of outside parties excluding minor repair work.

As such, if request for cost estimation other than those mentioned above are sent to Industrial Engineering Division, by mistake the same are passed onto Cost Accounts Department.

PROCEDURE FOR GETTING ESTIMATIONS FROM INDUSTRIAL ENGINEERING DIVISION

The tender enquiries regarding products are referred by sales department to research and development division or product engineering division. They study the tender specifications, discuss with manufacturing and inspection divisions and furnish the designed details(such as name of the product, its drawing and overall dimensions, materials of construction, shaft diameter ,component thickness, and other related tools required to assemble etc) with comments on various clauses to industrial engineering division. Based on this data, the cost is estimated by industrial engineering division and informed to sales department. Even if, in some cases, the enquiry is directly sent to industrial engineering division, the same is forwarded to the concerned division (i.e. R and D/product engineering division), because unless the designed details are arrived, cost cannot be estimated.

Job work enquiries are referred by sales department to the concerned division. If the enquiry is regarding costing only, the cost is given by other concerned division. The division checks up the capacity and inform the process to be followed to industrial engineering division who estimates the cost and inform the sales department. Enquiries sent directly to IED for cost estimation are forwarded to the division because, unless the availability of capacity is ensured and process to be followed is finalized, cost cannot be estimated.

COST ESTIMATION METHOD

After receipt designed data (or process in case of job work), IED estimates the cost on the following lines:

MATERIAL COST

Weights of castings are estimated by comparing with the existing similar components. In case of castings, the weights are of rough castings after removing runners, risers, gates, etc. weights of purchased raw materials are calculated from charts, considering suitable machining allowance, available stock, sizes, etc. these weights are multiplied by the actual rates to arrive at the material cost.

MACHINING COST

It is a product of machining time and hourly rate. Machine- hour rate is the sum of labor cost, overhead cost and depreciation. Labor and overhead rates are informed by cost accounts. Depreciation computed by straight line method assuming current price of the machine and 32000 utilized hours as life. For machine- hour rate for job work, one more factor is introduced in addition to labor, overheads and depreciation. It’s interest on capital at current market rates.

For undeveloped standard product, timings will be high initially and will taper down gradually. For cost estimation purposes, the final achievable time is considered and not the initial time.

ASSEMBLING COST

It is the product of assembling time and hourly rate. Man hour rate is the sum of labor and overhead rates informed by cost accounts departments from time to time. Assembling time and cost are also worked out on the same considerations as machining time and cost.

PAINTING AND PACKING COST

It varies from 1% to 4% of the total direct product cost depending upon the product and whether it is completely packed crate packed or partly packed. Cost of export painting and packing will be higher and may go up to 10%.

SALES AND DISTRIBUTION COST

This is expressed as a percentage of manufacturing cost and is informed by cost accounts department from time to time at present it is 7%. For job work, it is taken at 5%.

This is also expressed percentage of manufacturing cost and is informed by cost accounts department from time to time. At present it is 9%. For job work it is taken at 5%.

DEVELOPMENT COST

All the costs mentioned above are included in the cost of the product. Development cost which consists chiefly of cost of pattern equipment and tooling is shown separately and is not included in the cost of the product. Development cost is given only once for one product. Afterwards, even if it is not given, same value may be taken. After a product has been developed, development cost is not given.

TOTAL COST

Following example will explain the calculation of total cost.

REASONS FOR VARIATION FOR COST

In spite of doing the cost estimation part meticulously there may be some variation in the original estimated cost and cost worked out after execution of the order. This variation can be due to one or more of the following reasons:

TERMS OF TENDER

Cost estimation is carried out as per the terms of the tender. R&D Division or Product Engineering Division go through the tender specifications and recommend the material of constructions, quality requirements etc. If the tender specifications are wrongly interpreted and costly materials are recommended, estimated cost will be high.

DESIGN DATA

Design data for cost estimation such as over all dimension of the products and components, diameter of shaft, driving units and specifications of each components and parts are given by R&D Division or PED. From estimation stage to executive stage, there are drastic changes in the design parameters. Sometimes, the product itself changes. It results in variation in cost.

ESTIMATION SYSTEM

The variation in cost due to estimation system may be because of the following reasons:

MATERIAL COSTCost

estimation is based upon general market rates ruling at the time of estimation. Demand and supply position, relationship with the vendor, bargaining power of the company in a particular situation and market rates ruling at the time of order execution will make considerable difference between estimated and actual cost. Similarly, casting rates are based on average rejection index. In a particular case, this rejection percentage may be higher or lower than average resulting in higher or lower casting rates respectively.

PROCESSING COST

Variation in processing cost may be due to change in machining and assembly techniques over a period of time. In a particular case, the material may be unduly hard and rejection and wastage may be excessive (or too less). For some products, the initial processing time may be more than the estimated time because it takes some time for the regular process to establish.

CONCLUSION

It is clear from the above that for a realistic cost estimate, three things are very essential:

Correct interpretation of tender specifications.

Realistic and sufficient design data, and,

Sufficient time for cost estimation.

Finally, the tender should be so routed that about three week’s clear time is available for cost estimation, some changes are suggested after receipt of data by Industrial Engineering Division. They need confirmation by R&D Division/PED before taking up for cost estimation. Moreover, the products being off tailor-made type, the weight and cost of each component is to be estimated and complied for every tender separately. Without sufficient time, it is difficult to critically examine the cost structure.

A NOTE ON THE PROJECT REPORT

This article is aimed at giving guidance to those who experience difficulty with report writing. It is not suggested that there is only one way to write a project report since people have their own individual’s preferences and style of writing but most reports would contain the following sections:

Title and Index.

To identify report.

Introduction.

To set the scene.

Analysis.

Essentially the ‘findings’.

Conclusions.

What we have reduced.

Recommendations.

What requires to be done.

Evaluation.

Qualifying the cost and benefits.

Implementations.

Installation procedures.

Appendices.

For the details,

In addition to above, a summary of the contents is essential for every report of reasonable length. Acknowledgment section should only be made where genuine assistance is given. Thus these two sections conclude the requirement of a project report.

Summary for the busy executive.

Acknowledgements Give credit where due.

The summary section favored by the author serves to provide the busy executive with the main points of the study.

The essential sections of a report described earlier are now discussed in more details followed by general comments.

TITLE & INDEXE

very project report must have relevant title (preferable short), together with the name of investigator/s, circulation list, date of investigation and/or report, and the name of the place where the study occurred. All this should be typed on a single front page followed by the table of report contents on a separate page.

It is necessary to inform the reader what the report sets out to do and this is accomplished in this section. Anew page should be commenced. The introduction should be brief to the point.

Reasons for the investigation.

A statement of objectives (purpose)

SUMMARY

Care is needed in compilation of the summary because it decides whether whole report will b read by higher authorities.

The summary must obviously be pertinent and short in length; a rough guide might suggest no more than 10% of the words contained in the main report excluding appendices.

Thus, the contents of the summary will indicate the main findings, conclusions, recommendations and method of implementations with the cost and benefits. In short, this section provides an overview of the detailed report.

ANALYSIS

A new page should be started commencing with a short description of present situation and historical back-ground if considered important. Note, that proper diagnosis and analysis of the problem requires adequate information, a point that cannot be over stressed. An analytical approach rather than simply describing an existing or proposed set of conditions is very essential. A common flaw in project work is that the person arrives at a solution long before he has completed his analysis. This must be avoided at all costs.

From an examination of the data, various findings will emerge. The selection of the reference period must be discussed and agreed with the appropriate departments i.e. accountancy and the section where the investigations takes place. Findings which will be particularly important and useful are those relating to cost and this, such costs as of labor, machine, material and capital must be treated with caution, work measurement data will be utilized but the appropriate technique must be used.

THE CONCLUSION

Persons frequently find difficulty in differentiating between findings, conclusions and recommendations. The author draws the distinction in the following manner.

FINDINGS

Findings are a statement of facts without drawing any deduction or stating any action to be followed, e.g. machine utilization is 20%.

CONCLUSION

This is the inference made from the findings e.g. the machine utilization of 20 percent is mainly due to the improper use of the machine by the operator. However, it does not include any statement of action to be taken.

RECOMMENDATION

The operator requires training in the use of the machine immediately i.e. it is a statement of action.

Thus, conclusions are an interpretation of the findings. Nevertheless, there will possibly arise different deductions of the facts, and this is a common feature of industrial disputes. But the report is essentially a vehicle for discussion irrespective of the conclusions reached.

Recommendations- This part is another main component of the report and stats the positive course of action suggested by the investigator.

Recommendations must be unambiguous and care should be taken to point out any implications likely to arise.

EVALUATION

A report is not complete without a proper quantitative assessment of gains and losses usually in monetary terms. However, in some instances, subjective gains such as improvements in staff morale may be extremely difficult to quantity and the technique of cost benefit analysis may be utilized. Any claims must be checked and verified and usually the net saving resulting from the recommendations will be stated.

IMPLEMENTATION

It is extremely helpful to management if the report gives an indication of how, the recommendations are to be implemented. This will include a time table of events plus personnel involved.

ACKNOWLEDGEMENTS

The inclusion of this section should help to create good relationships but a personal view is that thanks should only be given where assistance has been contributed outside the normal work role. The acknowledgement should be contained in or two sentences avoiding any flowery language.

APPENDICES

This section completes the report and will commence on a new page for each appendix (numbered alphabetically or sequentially from 1). The purpose of this section is to avoid excessive details in the main body of the report and reference is made to the appendix. If a particularly piece of a data is vitally important to the argument, it may be included at the appropriate part in the body of the report or as a footnote. If the report contains technical jargon, a ‘Glossary of Terms’ should be included, and a bibliography containing the appropriate reference is essential.

GENERAL POINTS

The number of words required meeting the project requirements, the institute do not appear to stipulate any figure but 3,000 should be adequate. In addition to the page numbering, most reports carry an additional indexing system which falls, into 2 main types:

DECIMAL NOTATION

In which each main section given a consecutive number e.g.

Introduction.

Summary and each sub heading given the decimal notation.

Any further breakdown of sub sections would continue the process.

PARAGRAPH NUMBERING

Each succeeding paragraph is given a consecutive number.

Style of writing is unique to each author but it should be as simple as possible, eliminating jargon, consideration being given to good sentence construction, without flowery language is avoiding the first and the second person, since the author’s relationship to the report should be an impersonal one. The report should thus low in a logical sequence and the writer must attempt to strike the correct balance between sections.

Finally the cardinal rules of project reports are accuracy, brevity and clarity.

BASICS OF CASTING PROCESS

skilltech1970@gmail.com (Dattatray) — Sat, 7 May 2016 16:40:00 +0530

Casting may be defined as a ‘Metal object obtained by allowing molten metal to solidify in a mould, “the shape of the object being determined by the shape of the mould cavity.” Founding or casting is the process of forming metal objects by melting metal and pouring it into moulds. A foundry is a commercial establishment for founding or producing castings.

Significant in these definitions is the use of liquid metal to cast the shape of the object directly, producing cast metal. Wrought metal products differ from cast metal products in that the metal has received mechanical working treatment such as forging, rolling, or extruding. Practically all metal is initially cast.Castings obtain their shape principally when molten metal solidifies in the desired form. Wrought objects, however, are cast as ingots and then plastic-ally worked to approximately the desired shape.

METAL CASTING, “A PROCESS OF SHAPING”

The strength of the foundry industries rests on the fundamental nature of casting as a process for causing metals to take shapes that will serve the needs of man. There are other methods of shaping, machining, forging, welding, stamping, hot working etc. Each has applications in which it is unexcelled and others for which it is unsuited. Rarely is an engineering product completed which does not use several or all of the fundamental metal processing methods. The foundry industry is thus built on one of the truly basic methods available for shaping metals to useful ends.

Certain advantages are inherent in the metal casting process. These may form the basis for choosing casting as a process to be preferred over other shaping process in a particular case. Some of the reasons for the success of the casting process follow:

REASONS FOR THE SUCCESS OF THE CASTING PROCESSES

1. The most intricate of shapes, both external and internal. May be cast. As a result, many other operations, such as machining, forging, and welding, may be minimized or eliminated.

2. Because of their metallurgical nature, some metals can only be cast to shape since they cannot be hot worked in to bars, rods, plates, or other shapes from ingot form as a preliminary to other processing. The highly useful and low cost cast irons, which exceed the total of all other metals in tonnage cast, illustrate this fact.

3. Construction may be simplified. Objects may be cast in a single piece which would otherwise require construction in several pieces and subsequent assembly if made by other methods.

4. Metal casting is a process highly adaptable to the requirements of mass production. Large numbers of a given casting may be produced very rapidly. The use of castings in the automotive industry provides ample illustration of this point.

5. Extremely large, heavy metal objects may be cast when they would be difficult or economically impossible to produce otherwise. Large pump housing, valves, and hydroelectric plant parts weighing up to 200 tons illustrate this application.

6. Some engineering properties are obtained more favorably in cast metals. Examples are:-

7. Mach inability and vibration damping capacity in cast irons.

8. More uniform properties from a directional stand point, i.e. properly cast metals can exhibit the same properties regardless of which direction is selected relative to the original casting for the test piece. This is not generally true for wrought metals.

9. Strength and lightness in certain light metal alloys which can be produced only as casting.

10. Good bearing qualities are obtained in cast bearing metals.

In general, a wide range of alloy composition and properties is produced in cast form.

A decided economic advantage may exist as a result of any one or a combination of points 1 to 6. The price and sales factor is a dominant one which continually weighs the advantages and limitations of any process used in a competitive system of enterprise.

The list of disadvantages accruing to the metal casting process may be expanded beyond that given above. It is also true that conditions may be stated where the casting process must give way to other methods of shaping. Such conditions are those in the area of the principal advantages to be gained by the other metal processing methods. For example, machining produces smooth surfaces and dimensional accuracy not obtainable in any other way; forging aids in developing the ultimate of fibered strength and toughness in steel; welding provides a convenient method of joining or fabricating wrought or cast products into more complex structures; and stamping produces light weight sheet metal parts. Thus the engineer may select from a number of metal processing methods that one or combination which is most suited to the needs of his work.

2.0 REQUIRED BASIC STEPS IN MAKING SAND CASTINGS

Practically all the detailed operations that enter into the making of sand castings may be categorized as belonging to one of five fundamental steps of the process:

1. Pattern making (including core boxes).

2. Core making.

3. Moulding.

4. Melting and pouring.

5. Cleaning.

The detailed and technical process involved in each of the above operations is the source of the foundry man’s principal problems, other than personnel and marketing. The integration of the various steps to produce casting is briefly summarized for the benefits of those unfamiliar with the foundry. The processes and the equipment as explained.

2.1 PATTERN MAKING

Fig.2.

Patterns are required to make molds. The mold is made by packing some readily formed plastic material, such as molding sand around the pattern. When the pattern is withdrawn, its imprint provides the mold cavity, which is ultimately filled with metal to become the casting. Thus, molding requires, first, that pattern be made. A pattern maybe simply visualized as an approximate replica of the exterior of a casting. If the casting is to be hollow, as in the case of a pipe fitting additional patterns, referred to as core boxes, are used to form the sand that is used to create these cavities.

2.2 CORE MAKING

Fig.3

Cores are forms, usually made of sand, which are placed into a mold cavity to for the interior surfaces of castings. Thus, the void space between the core and old cavity surface is what eventually becomes the casting. A core and core box for a mixing valve and cores are ordinarily made separately from molds in a designated area of the foundry referred to as core room. They are then transported to the molding department to be placed in the molds. Core boxes are required to produce cores, so that this operation is again dependent on the patterns department.

2.3 MOULDING

Fig.4.

Molding consists of all operations necessary to prepare a mold for receiving molten metal. Molding usually involves placing a molding aggregate around a pattern held within a supporting frame, withdrawing the pattern to leave the mold cavity, setting the cores in the mold cavity and finishing and closing the mold. The old is then ready for pouring. A finished mold is ready for closing. Fig 1.1

2.4 MELTING AND POURING
The preparation of molten metal for casting is referred to simply as melting. Melting is usually done in a specifically designated area of the foundry and the molten metal is transferred to the molding area where the molds are poured.

2.5 Cleaning refers to all operations necessary to the removal of sand, scale, and excess metal from the casting. The casting is separated from the molding sand and transported to the cleaning department. Burned – on sand and scale are removed to improve the surface appearance of the casting. Excess metal, in the form of fins, parting line fins, and gates, is cut off. Defecting castings may be salvaged by welding or other repair. Inspection of the casting for defects and general quality follows. The casting is then ready for shipment or further processing, for example, heat treatment, surface treatment, or machining. A rough mixing valve casting and a cleaned casting are shown in fig.

The preceding paragraphs have briefly summarized the basic steps in the foundry process. There are, of course, other steps, not discussed which are exceedingly important in some foundries. For example, with certain alloys, every casting must be given a heat-treatment.

THE ENGINEER AND THE FOUNDRY INDUSTRY

Because of the scope of the industry and the widespread of castings, engineers often find themselves in a position where knowledge of foundry processes and casting problems becomes a vital part of their work. Design of castings, specifications, intelligent use of the properties of cast metals, purchasing of castings, and processing of castings, all require the application of engineering principles unique to castings and the foundry process. The engineer who designs a casting must have accurate information about the properties of the cast metal he would use. Further, he may achieve considerable economies by selecting a design that facilitates molding, coring, and other foundry problems. When specifications are more limiting than necessary, foundry problems and costs rise. Designs which make it difficult to obtain sound castings result in low mechanical properties in the cast metal, so that hand book data are not reliable. Many engineers face these problems in their work even though they themselves are not directly engaged in foundry work. Engineers are also finding increasing opportunity for professional work in the foundry field itself. To provide a foundation for work in this field, indirectly or directly, course work in the principles of metal castings finds a place in the educational preparation of student engineers. In addition, certain principles of material science and engineering are best studied in the foundry process.

FUNCTIONAL ROLE OF FOUNDRY RAW - MATERIALS

*SL.NO.*	*MATERIAL*	*PLACE OF USE*	*FUNCTIONAL ROLE*
01	Sand	Core shop Moulding.	Provide porous structure for gases to go out.

02	Core Oil	Core Shop.	To provide hot strength after baking.

03	Dextrine	Core and Mould.	Provide green strength in the sand.

04	Bentonite	Moulding.	Green strength with less gases.

05	Coal Dust	Moulding.	Increase permeability and improve surface finish.

06	Wax Rope	Core.	Venting for gases to go out at critical areas.

07	G.I. Wire	Core.	Provide necessary strength.

08	Stick Hard	Core.	For sticking the cores.

09	Graphite powder	Core.	Improve the surface finish.

10	Chaplet	Moulding.	Support to the core in the mould.

11	Chills	Moulding.	To increase the cooling rate to avoid shrinkage Defect

12	Pig Iron	Cupola Charging.	To base metal.

13	Coke	Cupola Charging.	To melt pig iron and to achieve required temperature.

14	Lime Stone	Cupola Charging.	To make slag fluid.

15	Ferro Silicon	Cupola/Furnace.	To maintain the required % of silicon in the metal to achieve the required hardness.

16	Innoculine	Cupola/Furnace.	To improve mach inability.

17	MS Scrap	Cupola/Furnace.	To increase tensile strength.

WHAT IS PATTERN SHOP?

Patterns are the foundryman’s mold – forming tool. The mold cavity, and therefore ultimately the casting, is made from the patterns.

TYPE OF PATTERNS

Several types of patterns are used in foundries. Depending on the casting requirements, the pattern may conform to one of the following types:

1. Single or loose pattern

2. Gated pattern (loose)

3. Match plate patterns

4. Cope and drag patterns

5. Special patterns and devices

Each of the patterns types has characteristics uses.

PATTERN ALLOWANCES

Although the pattern is used to produce a casting of the desired dimensions, it is not dimensionally identical with the casting. For metallurgical and mechanical reason, a number of allowances must be made on the pattern if the casting is to be dimensionally correct.

WHAT IS SHRINKAGE ALLOWANCE ON PATTERNS

Shrinkage allowance on patterns is a correction for solidification shrinkage of the metal and its contractions during cooling to room temperature. The total contraction is volumetric, but the correction for it is usually expressed linearly. Pattern shrinkage allowance is the amount the pattern must be made large than the casting to provide for total contraction. It may vary from a negligible amount to 5/8 inch per feet, depending on the metal and the nature of the casting.

MACHINE FINISH ALLOWANCE

Machine finish allowance is the amount; the dimensions on a casting are made oversize to provide stock for machining. These allowances are influenced by the metal, the casting design, and the method of casting and cleaning. Other casting processes permit different finish allowances to be used, as is pointed out in a subsequent chapter. In general, machine finish allowances may be a minimum if the surfaces to be dimensional variation and other defects are usually least prevalent there.

PATTERN DRAFT

Draft is the taper allowed on vertical faces of a pattern to permit its removal from the sand or other moulding medium without tearing the mold cavity surfaces. A taper of 1/16 inch per feet is common for vertical walls on patterns drawn by hand. Machine – drawn patterns require about one degree taper. In some cases, even vertical is very smooth and clean and the drawing equipment is properly aligned. In the case of pockets or deep cavities in the pattern, considerably more draft is necessary to avoid tearing the mold during withdrawal of the pattern.

SIZE TOLERANCE

The variation which may be permitted on a given casting dimension is called its tolerance, and is equal to the difference between the minimum and the maximum limits for any specified dimension.

DISTORTION ALLOWANCE

Certain objects, such as large flat plates and dome are U shaped castings, sometimes distort when re produced from a straight or perfect pattern. In such cases, the pattern may be intentionally distorted, or ‘faked’. The distorted pattern then produces a casting of the proper shape and size.

FUNCTION OF PATTERNS

The main purpose of pattern is its use in molding. However, to produce a casting successfully and render it suitable for further processing, the pattern may be required to perform other functions besides producing a mold cavity. These are briefly considered as follows-

MOULDING THE GATING SYSTEM

Good gating practice for castings generally requires that the system of channels and feeding reservoirs (gates and risers) for introducing metal into the mold cavity be attached to the pattern. The gating system may then obtain the benefits of machine molding.

ESTABLISHING THE PARTING LINE

On a flat pattern plate, the parting surface is a simple plane. Many castings, however, require curved parting surface of their shape, and these are established by the pattern where match plates or cope and drag plates are used. Loose patterns follow board or match be constructed for establishing the parting surface in successive molds.

MAKING CORE PRINTS

When a casting requires cores, provision is made on the pattern for core prints. Core prints are portions of the patterns for core prints. Core prints are portions of the pattern and mold cavity which serve to anchor the core in proper position in the mold. The core print is added to the pattern, but does not appear on the castings because it is blocked off by the core.

ESTABLISHING LOCATING POINTS

The foundry, pattern shop, or machine shop employs locating points or surfaces on the casting to check the casting dimensions. Machining operations may also use the locating points in establishing the position of machined surfaces relative to the balance of the casting.

MINIMISING CASTING DEFECTS ATTRIBUTABLE TO THE PATTERN

Properly constructed, clean and smooth surfaced patterns are a necessity in making good castings. Patterns with rough, nicked surfaces and undercuts, loosely mounted, and in a generally poor condition contribute substantially to defective castings containing sand inclusions and other imperfections.

PROVIDING FOR RAM-UP CORES

Sometimes a part of a mold cavity is made with cores which are positioned by the pattern before the molding and is rammed. The ram-up core then is held by the sand which has been packed around it.

PROVIDING ECONOMY IN MOLDING

The pattern should be constructed to achieve all possible savings in cost of the casting. Here such items may be considered as the number of castings in the mold, the proper size of the pattern plate to fit available molding equipment, method of molding, and other factors

FUNCTIONAL ROLE OF PATTERN EQUIPMENTS

*SL.NO.*	*PATTERN EQUIPMENTS*	*FUNCTIONAL ROLE*
01	Core Box.	Achieve required shape of the core.

02	Pattern.	Provide required cavity in the sand for producing casting.

03	Gating System.	To feed the castings.

	Sprue.	To maintain a satisfactory level of the metal for feeding.

	Runners.	To entrap the sand and slag in the flowing metal.

	Ingots.	To feed metal.

	Risers.	To feed the metal into thick section of the casting.

	Flow Off.	To escape the gases.

04	Moulding Box.	To prepare a mould cavity of sand with adequate ramming and provide alignment between cope and drag.

REQUIREMENT OF A GOOD MOULD

1. Good Finish.

2. Sufficient Strength.

3. Sufficient Venting.

4. Proper Core Assembly.

5. Proper Gating System.

6. High Gas Permeability.

7. Proper Box Closing.

PRECAUTIONS IN MOULD MAKING AND POURING OF METAL

*SL. NO*	*ACTIVITY*	*PRECAUTIONS*	*CONSEQUENCES*
01	Pattern Fixing	Check pattern for damage.	Casting dimensions and poor finish.

		Avoid repairing of damage PTN.	Perfect repairs not. Feasible due to inadequate tools.

		Use thin film of releasing agent.	Rough surface and pattern stripping is difficult.

		Use correct size of under damaged box.	Mix-match, inadequate area for packing sand drop inadequate feeding head mould breakage.

		Place chill, Chaples, gaggess reinforcement as specified.	Defective castings.

		Loose pieces firmly at its position.	Defective castings.

02	Sand Filling and Ramming	Check moisture of sand by feel.	Blow hole, rough surface and swelling in case moisture more and sand fall erosion, inclusion in core moisture less.

		Don’t add any water to the sand.	Non uniform sand.

		Pack the facing sand reinforcly (2”-3”).	Desired effect of facing sand will not be achieved.

		Take care in ramming the sand in deeper cavity.	Sand fall and poor finish at the cavity.

		Ram the backing sand in layers to a hardness of 65 to 70 throughout the mould.	Swelling.

		Fill the sand to the box height.	Mould may sag.

		Start jolting after half filling the box with sand. Loose pieces should not change its position while jolting.	Shift in the loose piece cannot be noticed and sand may be loose at certain cases.



		Continue jolting for specified line.	Mould hardness will be less.

		Squeeze head should be less by ½” around compare to box size.	Force will be on the box and not on the sand.

		Release the moulding box evenly.	Damage the mould and pattern.

03	Venting Cope Assembly	Vent the box throughout.	Blow holes, pin holes.

		Check the position of cope pattern with reference to drag.	Miss-match.

		Fix the match plate in a position such that round bush of the box is on the same side of the pattern as in the drag.	Miss-match.

		Place sprue, riser, flow off ram up core and chills as per the method cards.	Cold shuts, Shrinkage, and blow holes.

04	Box Removal	Remove the box slowly and evenly.	Mould Breakage.

		Slag hammer round hammer should not use for wrapping the patterns.	Mould Breakage.

05	Venting	Vent the box throughout.	Blow holes or pin holes.

06	Mould Finishing	Repair minor damages. near corners etc.	Defective castings, dimensional in accuracy.

		Scrap the mould in case of major damage.	De-formed castings.

		Clean sand from chill surface sprue and riser seating.	Sand inclusion.

		Drive away the loose sand by air.	Sand inclusion.

		Provide venting ¼” to 3/8” wire the spigot surface and at the highest point of the mould.	Blow holes.

		Venting to align the core venting and the centre.	Blow holes.

		Agitate the coating mixture before using.	Poor coating finish.

		Take core in coating deeper position like leg cavity.	Poor finish at the spots.

		Avoids brush marks on the mould surface.	Poor casting finish.

		Ignite or Dry the mould fully using a burner as specified.	Blow holes.

07	Core Assembly	Use Cheplet as specified.	Uneven metal thickness.

		Place the core correctly without damaging either the core or mould.	De-shaped castings.

		Check Core Assembly.	Out., extra metal.

		Avoid repairing Cores.	Roughness, extra metal.

		Avoid using under-baked, over baked, under coated cores.	Core Breakage, Sand.

08	Box Closing	Closing pins should go Wright through the bush freely.	Shift, Sand fall.

		Check the box alignment.	Shift.

		Clamp the box correctly.	Metal leak.

		Keep the proper weight as specified.	Metal leak, swelling.

		Match the marking while assembly the box.	Shift.

DESIGN OF GATING SYSTEM

Fig.5.

The quality of casting is determined to a large extent by the way in which the molten metal is transferred from the ladle in to the mould cavity. Though it would appear that casting manufacturing is so simple, lot of factors must be controlled if good casting is to be produced. Due consideration to the gating and riser is very important to produce the castings of required quality. This paper makes an attempt to give some information in this regard.

A proper gating system has to fulfill the following basic requirements-

1. To eliminate or reduce turbulence to minimize dross formation.

2. To eliminate or reduce aspiration of air and mould gases.

3. To decrease velocity to minimize mould erosion.

4. To eliminate premature freezing of casting.

5. To assist in developing proper temperature gradient.

6. To get the maximum casting yield.

7. It must be of simple design so as to facilitate moulding, particularly with machine moulding.

8. It must incur the minimum fettling and grinding cost.

9. It should assist to have a fast flow rate to avoid excessive pouring temperature.

BASIC ELEMENTS AND FUNCTIONS OF GATING SYSTEM

Pouring Basin:

The enlarged offset portion of the mouth of the mould into which molten metal is first poured.

Sprue:

A vertical passage which conducts metal down in to the sprue base

Sprue Base:The area directly below the sprue into which molten metal falls. This helps to streamline the flow of metal in to runner.

Runner:

Fig.6.

A horizontal passage way through which molten metal flows into the gates.

Gate:The short passageway that connects the runner to the mould cavity or riser.

Runner Extension:The part of the runner which extends beyond the farthest ingrate as a blind end.

GUIDELINE FOR A BETTER PERFORMANCE OF A GATING SYSTEM

Use pouring basin with generous radius into sprue opening.

Pour away from the sprue opening. Never directly down the sprue.

Keep the pouring lip low and the system full during the full period of pouring.

Use tapered sprue (big end up) to avoid aspiration of air or mould gases into the system.

Use either a well or enlargement at the base of the sprue.

Use well rounded corners in runners and ingates, enabling to eliminate the low pressure zone and thus aspiration effect.

Stepping of runner by an amount equal to each gate passed may help in getting equal flow from different ingates.

After the last ingate, a runner extension of 100 to 150 mm may be provided, so that, the first rush of metal which might have picked up some dirt or loose sand on the way is collected in runner extension.

Use a wide ingate, but the thickness of the ingate should be small.

Metal should be delivered to the mould cavity by shortest route possible to have a good yield. This also enables to eliminate the loss of temperature.

Ingates should never be provided near protruding points of mould sand and should never be arranged at the chill or studs. Possibilities of metal hitting the core directly should be avoided.

Casting may be divided into different parts which may be provided with individual gates so as to avoid hot spot conditions at ingates.

Attempt should be made to achieve unidirectional movement of metal to get the favorable temperature conditions of proper working of riser.

WHAT IS GATING RATIO?

Metal should flow in a full gating system with uniform pressure and velocity in all parts of the runners and gates. This condition can be achieved by using proper gating ratio. Gating ratio is the ratio between the cross sectional areas of three parts of the gating system that governs the flow of metal from sprue to mould. These parts in order are the bottom of down sprue (choke) the runners and the gates. Depending upon the nature of the metal or alloy and size, geometry and thickness of casting various gating ratios are used.

TYPES OF GATES

Metal can be directed into mould cavity in many ways. Design of each gating system depends upon its primary objectives. Improper gating system may lead to casting defects, such as:

1. Inclusions.

2. Rough Surface.

3. Entrapped Gases.

4. Localized Shrinkage.

5. Dispersed porosity.

6. Miss run and Cold shut.

7. Metal Penetration, etc.

In general, following are the some of the gating systems followed in various foundries:

1. PARTING LINE GATE

Fig.7

Fig.8.
These are placed in the parting line separating the cope and drag portions of the mould.
2. BOTTOM GATE

Fig.9
Bottom gates are placed in the drag portion of the mould. A bottom gate is preferred in heavy castings to reduce erosion and gas entrapment and to prevent splashing which can result in cold shuts.
3. BRANCH GATEBranch gate is designed either to feed a single casting at several points or a number of slag from the flowing metal.

4. WHIRL GATE
Fig.10
This gate employs centrifugal force to aid in the separation of slag from the flowing metal.
5. LAP GATE

Fig.11
PROCESS FLOW CHART- MOULDINGIn this, the gate is overlapping the mould cavity of the drag portion for a calculated amount of area. This gate considerably reduces the fettling time to a maximum extent.

CORE MAKING
REQUIREMENT OF A GOOD QUALITY CORE

1. Good Finish.

2. Sufficient Strength.

3. Sufficient Venting.

4. Gas Permeability High.

5. Proper Baking.

6. Proper Assembly.

7. Dimensional Accuracies.

PROCESS FLOW CHART – CORE MAKING

PRECAUTIONS IN CORE MAKING

*SL. No.*	*ACTIVITY*	*PRECAUTIONS*	*CONSEQUENCES*
01	CORE BOX PREPARATION	Check pins and Bushes of Core Box.	Shift.

		Check for warpage of Core Box.	Oversized core, pins.

		Ensure proper clamping.	Pins and oversize cores.

		Ensure parting media application.	Core will get damage while removing from core box.

02	Sand Filling	Ensure proper filling of Core Box.	Proper shape of core will not achieve.

		Ensure the use of lamp free sand.	It will give a poor finish cracks.

03	Ramming	Ensure adequate ramming by using proper tools.	It will result core breakage and poor surface finish.

04	Venting Chills and Reinforcement	Ensure proper venting.	Blow hole in casting.

		Ensure coated chills in right position.	Shrinkage in castings.

		Ensure the position and size of reinforcement wire.	Core Breakage.

05	Core Removal	Ensure the leveling of the core.	De-shape or damage.

		Use warpage free core plate.	De-shape during baking.

06	Core Painting	Ensure the proper density of coating material.	Poor surface finish.

		Stir the paint before use for ensuring proper density of coating material. Check spray gun before use.	(1) Core Damage. (2) Core Finish.

07	Baking	Ensure the proper stacking of plates inside the oven.	Core damage, over loading.

		Ensure the proper temperature and time for baking.	Under Baked or Over Baked Core.

08	Finishing	Use gauges for critical dimensions.	Over size or Under size cores.

		Ensure the proper density of stick hard, in case of assembly of core.	Core will open out.

		Ensure proper core slick on parting line.	Cavities in the linings.

		Ensure proper stacking of finishing core.	Damage of core.

09	Inspection	Check critical dimension by gauges.	Problem is core assembly.

		Ensure visual inspection.	Defects in the castings.

MELTING OF CAST IRONS PROCESS

Fig.12.

Historically, the development of the blast furnace for the reduction of iron ore gave birth to iron founding. At first pig iron from the blast furnace was used directly for making iron castings. As time went on and the use of iron castings became more common, smaller shaft type furnaces were introduced for re melting pig iron specifically for making grey iron castings. Thus evolved the cupola. The first English patent on a cupola furnace was granted in 1794, and the first American cupola was erected in 1820. Since that time the cupola has gradually developed into a furnace especially adapted to the needs of cast iron melting. Although, other types of furnaces are used, by far the greatest tonnage of iron is produced by cupola melting.

THE CUPOLA

Fig.13.

Widespread use of the cupola for grey – iron melting rests upon its unique advantages, which includes:

1. Continuous melting. Foundry production is facilitated since a ladle of molten iron may be tapped from the furnace at regular intervals. The flow of molten metal’s and molds for pouring may be synchronized for quantity production as required by the automotive, agricultural equipment, and similar industries.

2. Low cost of melting. Raw materials and operating costs are lower than on any other type of melting furnace producing equivalent tonnage.

3. Chemical compositions control is possible by proper furnace operation with continuous melting.

4. Adequate temperature control for fluidity in pouring castings can be obtained. Certain limitations also are characteristics of the cupola furnace. Low carbon percentages in the iron below about 2.80% C are difficult to attain because of direct contact of molten iron and the carbonaceous fuel. Some alloying elements such as chromium and molybdenum are in part lost by oxidation in the cupola. Higher temperatures are obtained with air-furnace melting. The use of several furnaces by duplexing, i.e., transferring of the molten metal from one furnace to another, may be utilized to combine the advantages of each type of furnace. For example, white iron may be melted in the cupola and have its carbon percentage lowered from about 3.0 to 2.20 to 2.40 percent by decarburization in the air furnace.

MECHANICAL STRUCTURE OF A CONVENTIONAL CUPOLA

The structural features of a conventional cupola are illustrated in fig 20. It consists of a vertical shaft or shell built of ¼- 3/8- in. steel plate. The shell is lined with refractory bricks. A wind box and tuyeres for delivering air into the shaft are shown in fig 20. About 20 or more feet above the bottom an opening in the side is provided for charging the materials into stack. The cupola bottom is hinged so that the furnace may be emptied by dropping the bottom doors. The cupola bottom itself is generally of molding sand rammed in place on top of the bottom doors. At the bottom in front is a top-hole and spout for the molten iron. At the rear and above the tap-hole level is a slag hole. The stack is topped by a spark – arrestor hood or dust suppressor. Finally, some type of blower and blast control is required to supply air for combustion.

Some of the dimensions of standard cupolas are given in table 20. The figures in table 20, define the characteristics of the various sizes of the common cupola and are worthy of some discussion, as follows:

1. Cupola size. Cupola is rated by number from 0 to 12 and varies in capacity designated as melting rate in tons per hour from approximately 1 to 35 tons per hour.

2. Shell Diameter. The outer shell diameter is the dimension which ultimately limits the capacity of the cupola. Shell diameter of common cupolas varies from 27 to 108 in, although they have been operated with much smaller and larger diameters.

3. Thickness of lower lining – This is the lining thickness in zones A & B (fig. 19.1.) where the maximum amount of refractory erosion occurs.

4. Diameter inside lining. The inside diameter establishes the operating cross sectional area of the cupola.

5. Area, inside cross sectional area in the melting zone. This dimension determines the range of the melting rates of a particular cupola size. A cupola melts approximately 10 lb of iron per hour per square inches of inside cross sectional area in the melting zone when the weight of iron and coke charges is in the ratio of about 10:1. Thus, the melting rate figure in the column under iron to coke ratio of 10 in table 19.1 expressed in pounds divided by 10 and the inside cross sectional area are the same. A No. 0 cupola has 254 sq. in, inside area and at a 10:1 iron to coke ratio, will melt approximately 2540 lb per hour or 1¼ tons per hour. Of course, within limits it may melt faster or more slowly than this figure, depending on the way in which it is operated.

6.Total area of tuyeres, square inches. The tuyere openings serve to introduce air for combustion of the coke. The combined area of the tuyeres in standard cupolas is usually cross sectional area of the cupola at the tuyere level, although much smaller and larger ratios are sometimes used.

Other information in table 19.1 will be considered relative to actual cupola operating procedures.

STEPS IN OPERATION

A cupola heat includes not only the actual melting operation but all the operations which precede and follow the period during which iron is being melted. A certain cycle of events occurs each time a heat is made, including the following:

1.Preparation of the refractory lining, bottom and tap hole and slag hole.

2.Lighting and burning in the coke bed.

3.Charging.

4.Melting.

a) Starting the air blast.

b) Charging.

5.Tapping and Slagging.

6.Dropping the bottom.

Each step above is an important one and must be properly carried out for a successful heat.

MAIN FREQUENCY CORELESS INDUCTION FURNACE

Fig.14

If a primary coil of an inductor is placed as close as possible to metal contained in the crucible of an induction furnace, a magnetic field will be concentrated in the crucible. This magnetic field is induces eddy currents in the metal due to which heat in generated and melting is commenced. A higher current frequency is required for a smaller crucible and low frequency for bigger crucible.

The eddy current produced in the metal stir the metal in the crucible due to which temperature and composition homogeneity is obtained.

The charging of raw material is done from the top. The raw material consists of Cast iron scrap, borings, pig iron or steel depending upon the requirement, Ferro silicon, silicon carbide and carburizers are also added to maintain the carbon and silicon which generally decide the grade of grey iron made.

Coreless furnaces are preferred for intermittent melting and for production of several different compositions. They provide total melting flexibility for jobbing work.

ADVANTAGES OVER CUPOLA

1. One of the main advantages of induction furnace is the control over metal composition. Since this offers batch melting, the composition can easily be controlled. In the cupola the control is difficult as the process in continuous.

2. In induction furnace there is a great flexibility of raw material.

Practically everything can be charged if it has sufficient metal value.
Unlike cupola the shape and size do not affect much.

3. In jobbing foundries where the metal composition varies from casting to casting, induction furnace can be used without any problem regarding charging and composition control.

4. Easy charging and cleaner work atmosphere in a future of induction furnace. Now, when greater attention is being paid to pollution, the induction furnace scores over the cupola.

DISADVANTAGES

1. Cost of electricity is a major factor if the induction furnace is to be run economically. The availability of power and cost make the induction furnace suitable only at those places where the supply is uninterrupted and cheap.

2. The lining of the furnace has to be made carefully. The frequent wearing out of the lining makes the metal costly.

3. At those places where a continuous supply of metal is required the cupola
is preferred.

METAL PREPARATION AND POURING

*DESCRIPTION*	*PRECAUTIONS*	*CONSEQUENCES*
*Metal Preparation*	Ensure the charge composition by weighing the material.	Grade of castings affected.

	Conduct Chill test for every heat and adjust the process accordingly.	Grade of Castings affected.

*Pouring*	Check metal temperature.	Cold shut.

	Bring sufficient quantity of clean metal.	Short poured.

	Add innaculin if necessary.	Hardness.

	Poured the metal in a continuous stream.	Miss-run.

	Avoid intermittent pouring.	Cold Shut.

	Allow the metal to overflow little.	Shrinkage.

	Avoid use of dirty ladle.	Slag.

	Light the escaping gases during pouring.	Blow holes, metal leaking.

	Use strainer core for pouring.	Slag.

CONSEQUENCES OF USING INCONSISTENT QUANTITY OF MATERIAL

*SL.NO.*	*MATERIAL*	*PLACE OF USE*	*QUANTITY SPECIFIED*	*STATUS*	*CONSEQUENCES*
01	Sand	Core Section	100 kg	120 kg	Less strength.

			60, 40	80 kg	More strength.

				40, 60	Permeability gets affected.

02	Core Oil	Core Section	1.2 to 2.3	1.0(less)	Less strength.

				1.0(more)	More strength.

03	Dextrine	Core Section	.9 to 1.1	More	More strength.

				Less	Less strength.

04	Bentonite	Moulding	7 to 8%	More	Less permeability.

				Less	Low strength.

05	Lime Stone	Cupola Charging	4 to 5%	More	More oxidation.

				Less	Low fluidity of slag.

06	Ferro Silicon	Cupola Furnace	2kg/375kg of charge	More	Lower grade of the castings.

				Less	More Hardness.

07	Innoculine	Cupola Furnace	50gm/70kg	More and Less.	To improve the machinability by improving the structure/.

CONSEQUENCES OF USING SUBSTANDARD MATERIAL

*SL.NO.*	*MATERIAL*	*QUALITY PARAMETER*	*STATUS*	*CONSEQUENCES*	*REMEDIAL MEASURES*
1	Sand	Refractoriness	More	Low permeability.	Add medium/course sand in consultation with supervisor. Add fine/medium sand in consultation with supervisor. Wash the sand before use for core making.

			Less	Sand sticking on surface of the casting.	Sand should be rejected.

2	Core Oil	Bending strength of the oil	Less	Core breakage more gases by the use of higher % in the sand mix.	Increase the oil % (2) such oil should be rejected.

3	Bentonite	Liquid limit	More	More gas evolution.	Reduce the % in the mix.

			Less	Less strength breakage of mould, sand wash etc.	Material should not be used.

4	M.S.Scrap	C	More	Low tensile, low hardness and open grain structure.	Increase steel scrap up to 30% in the charge calculation.
		P	More	Shrinkage, poor machinability, and lower impact strength	Mix with low P scrap.
5	Lime Stone	CaO	Low	More viscous slag than fluid slag.	Increase % of lime stone addition.

		SiO2	More	Reduces the effectiveness of the flux.	Mix with low SiO2 % lime stone with a maximum of 10% inferior quality.

FELTING SHOP OPERATION

There are several operations of cleaning castings in the felting shop. Here, three shot blasting machines and three tumbling barrels are placed in line one after another. Some castings are directly shot blasted and some are to be barreled for thirty minutes and then shot blasted.

1. Black castings hauling operation is done by forklift, the pallets are filled with castings and then directly taken to the required place.

2. After the barreling the castings for 20 to 30 minutes, maximum quantity of sand is removed, but the castings are not damaged in any way and the shot blasting time is also reduced. Due to gravity, the castings slide down to the shot blasting station.

3. After cleaning the castings in shot blasting machine, the operator unloads the castings on a chute for next operation.

4. Chipping operation: In this operation, the operator removes the ingates and extra metal from the castings. After chipping, the operator keeps the castings on a chute. Due to gravity, the castings slide down for the next operation.

5. In pedestal grinder, parting line of the casting is removed by grinders and castings are kept on a chute. Due to gravity, the castings slide down for the next operation.

6. Finishing operation: The castings are finished by pneumatic hand grinder. Motor body castings are prepared by flexible shaft grinder.

7. After completing the finishing operation, the same operator loads the castings on the conveyor.

8. After that, the inspection of the casting is done on the conveyor itself.

9. Castings are painted as the conveyor passes through the painting booth.

10. After painting, the castings travel to the drying zone for natural drying for about 20 to 30 minutes.

11. Thereafter the castings reach the unloading station where pellets are already kept below the conveyor. The operator takes out the castings and places them in the pallet. As soon as the pellets are full, they are taken to the required place in the machine shop.

IMPORTANCE OF QUALITY CONTROL

skilltech1970@gmail.com (Dattatray) — Sat, 7 May 2016 12:21:00 +0530

Today, our daily lives and schedules totally depend upon the satisfactory performance and operation of products and services – whether of a city electrical distribution and power system net work, transportation system network, communication system, or even the pen with which we write. This no – alternative situation is new for our society where the customer has become more demanding than before. The customers demand for durability and reliability in products/services has increased tremendously in recent years.

Our markets, which were earlier based only on pricing, now are based on price as well as quality. The systems and procedures adopted to meet this new customer demand i.e., quality have improved and have been updated in recent years as never before.

This pursuit of quality is not new for any manufacturer. It has been a continuous process ever since the inspection of the manufacturing unit. Producer’s policy is to “deliver error – free competitive products and services on time to his customers. Their products take care of their needs of today as well as tomorrow”.

The following are a brief idea of the quality system generally adopted by manufacturers.

Manufacturer must have a well organized Quality Control Department. The department should have skilled supervisory system with necessary tools and work as per the company’s policy and procedures.

QUALITY CONTROL ACTIVITIES

Design and Developments. The drawing at the design stage is reviewed by the representatives from marketing, quality control and manufacturing. After approval from all the representatives, they are released for prototype testing. After finalization and necessary modifications if any, they are released for production.

Raw material and incoming components.

The manufacturer must have established standards for all units’ raw materials.

Tests should be conducted on all incoming materials consignment –wise before unloading it in stores/godown.

They must introduce quality certification by supplier in some of the major areas.

They must develop technically approved source for raw materials and in last two years there should not be any rejection report from the company side.

They may also inspect the incoming materials at the supplier’s end before loading it to delivery.

After receiving drawings from the design department, check lists are prepared for raw materials, and other components and necessary parts as well as for inspection. During this period of time the concerned authorities must follow the components and raw materials testing procedures strictly. And these should be inspected periodically for their accuracy. With the help of design of experiment technique, they must have evaluated and improved testing procedures, reduced testing errors, and time for testing significantly in determining loopholes and faults in raw materials and components/parts which is an original concept.

Improved quality of product by proper checking of each job after each operation is a must. This also saves the money and labor of further operation.

Manufacturers have to introduce inspection cum process cards giving details of process operation, inspection process and details of gauges and instruments to be used. This card should be displayed on each machine enable the concerned person to take immediate action on any faults. Further it is essential that daily conference to be held in each shop, to find out main causes of rejections. Corrective actions should be taken to sort out the problems on the same day. This is a group activity. Pneumatic wrenches, chemical solutions etc have to be used for tightening studs, nuts etc. These controls’ tightening torque and maintains the breakaway torque and prevailing torque and thus minimize the failure rates. Check lists have to be prepared to check sub – assembly and assembly. Ensure that all components or parts using Improved quality of paint, varnishes, grease, lubricants, oil at source and painting procedure for prolonged protection pleasing appearance.

PRINCIPLE OF MEASUREMENT

“When you can measure what you are speaking about and express it in numbers, you know something about it, when you cannot measure and express it in numbers, and your knowledge is of a meager and unsatisfactory kind. It may be the beginning of knowledge, but you have scarcely in your thought advances to the stage of science”

Measurement is the first step leading to scientific analysis. One of the recently developed sciences namely management science began with measurement of work.

In order to measure, we need a unit in terms of which the quantity can be expressed. A unit can be defined as the magnitude of a quality in terms of which magnitudes of other quantities of the same kind are expressed.

Again, in order to measure we need an embodiment of the unit against which the unknown is compared. This physical embodiment of the unit is the standard of measurement.

Any measurement, thus, involves the comparison of the unknown against the standard end finding out how much it varies from the standard.

Precision is the repeat ability of a measuring process or simply, how well identically performed measurements agree with each other.

Accuracy is the agreement of the result of a measurement with the true value of the measured quantity. The true value cannot be known. The best that can be done is to estimate the magnitude of the error.

Precision in measurement is dependent upon the consistency of the set – up employed and datum used, i.e. the process of measurement.

Achieving accuracy is more difficult and more expensive. The standard and the unknown must be as much alike a possible and the operations performed on the standard and on the unknown must be as identical as feasible.

Systematic errors are those due to the measuring procedure. Systematic errors must be identified and rooted out if possible. If not, an allowance must be made in the measurement for a systematic error.

Constant errors are those which affect all measurements in a measurement process by the same amount, or by an amount proportional to the magnitude of the quantity being measured.

It is, therefore, necessary for accuracy in measurement that any standard used be traceable to the defining standard for that quantity. This means that it must have been compared with the defining standard or with some standard in a chain of standards, which leads back to the defining standard. The longer this chain is, the less well known is the value of a standard at the far end of the chain.

LIMITS, FITS AND TOLERANCES

LIMITS

The actual size required of an object is called basic size. The allowable variation of a job above and below of basic size is called limit.

TOLERANCE

The difference of high and low limit of job is called tolerance.

ALLOWANCE

The permissible difference in sizes of two parts to be assembled is called allowance. It is intentionally kept to have the required fit during the assembly. In other way, we can say the difference of sizes of hole and shaft is called allowance. It may be positive or negative.

TYPE OF ALLOWANCES

Maximum Allowances: The difference of minimum size of shaft and maximum size of the hole is called maximum allowance.

Minimum Allowance.

The difference of maximum size of shaft and minimum size of hole is called minimum allowance.

DIFFERENCE BETWEEN TOLERANCE AND ALLOWANCE

TOLERANCE

ALLOWANCE

Depends upon basic size.

Depends upon type of fit to be required.

Can be different on different parts of the same job.

Given on two matching parts.

FIT:

The type of relation between the two matching parts is called fit.

TYPE OF FIT

Clearance Fit:

This type of fit occurs when the diameter of the hole is greater than the diameter of the shaft to be assembled. There is distinct clearance between the mating parts.

Example: Running and push fit.

INTERFERENCE FIT:

This type of fit occurs when the diameter of the hole is lesser than the diameter of the shaft to be assembled. There is a distinct interference between mating parts.

Example: Force fit, driving fit, and shrinkage fit.

TRANSITION FIT:

The fit between clearance and interference fit is called transition fit which means, assembly can be obtained by just a slight push.

Example: Sliding fit and push fit.

WHAT IS INSPECTION AND QUALITY CONTROL?

Inspection may be defined as an effort to ensure the production of parts or machine that will be satisfactory to both maker and the user, in other words, inspection as considered as the process of sorting good and bad. It includes the following:

Interpretation of specification.

Measurement of the product.

Comparison of specification with actual measurements.

Quality control may be defined as an effective system for co-coordinating the quality maintenance and quality improvement effort of the various groups in an organization so as to enable production at the most economical levels which satisfy the customer.

WHAT IS QUALITY?

Quality can mean different things to different functional components, within the same organization. Thus it can mean:

Technical specification, to design.

Conformance to specification, to inspection.

Demand for product, to sales.

Usability including visual appeal, to customer.

Rejection and complaints to production.

All the above at lower cost, to management.

Thus, it follows that the most appropriate meaning of quality is achieving ‘FITNESS FOR USE” at economic cost.

WHAT IS STATISTICAL QUALITY CONTROL?

It is a scientific method of analyzing data and using the analysis to solve practical problems.

The word “statistical” means “Having to do with numbers”.

The word “Quality” means much more than the goodness or badness of a product.

The word “Control” means to keep something within boundaries. Taken together, the word Statistical Quality Control means:

STATISTICAL

QUALITY

CONTROL With the help of numbers or data.

We study the characteristics of our process.

In order to make it behave the way we want it to behave.

OBJECTIVE OF S.Q.C.

The major objectives of statistical quality control are:-

To achieve the required quality at economic cost.

Improvement in product quality.

Reduction in operating cost and losses.

Improvement in employee morale and quality consciousness.

Organizing a quality improvement program to solve existing quality problems.

Improving means for maintaining control during production.

Providing for pre-planning of quality.

IMPORTANT TOOLS OF S.Q.C:

Graphical devices.

Frequency distribution.

Control charts.

Process capabilities analysis.

Acceptance sampling.

GRAPHICAL DEVICES

The main important features of graphical devices are:

Collection of data.

Summarization of data.

Scrutiny of data.

Tabulation of data.

Presentation of data.

CONTROL CHARTS

To achieve the objectives of avoiding defects, it is often necessary that the process be uniform. This means that the variability in the product should be due to numerous small chance cause of variation rather than to a few large assignable causes of variation.

In controlling a process, the objectives is to restrict the cause of variation to chance cause only, assignable causes must be eliminated. The key purpose of a control chart is to detect the presence of assignable causes of variation. This is done by taking a series of samples from the process and testing these samples for significant differences from the aggregate of all samples.

CLASSIFICATION OF SAMPLE CHARTS

Even though the objectives remain same, the technique of charting varies with the type of quality characteristics. Table shows the type of control chart and their characteristics.

CHARACTERISTICS AND CONTROL CHART CHARACTERISTICS

Attribute

P-Chart or fraction defective chart.

NP-Chart or number of defective chart.

C-Chart or number of defects per unit chart.

Variable

X-R Chart- Average and range chart.

DIFFERENCE BETWEEN ATTRIBUTE AND VARIABLEATTRIBUTE

VARIABLE

When a record shows the number of items conforming and number of item failing to conform to any specified requirement, it is said to be record by attributes. It provides an estimation that the products either conform or do not conform to the specifications. Attributes charts is usually associated with Go and No Go gauges.

When a record is made of actual measured quality characteristics, a quality is said to be variable.

P-Chart, NP-Chart, C-Chart, and X-R-Chart

Fraction Defective Chart (P-Chart)

It shows the variation in the fraction defectives of output. It is also known as chart for Go and No Go date. Fraction defective of output is defined as the value obtained by dividing the total number of units inspected over number of defectives obtained out of the submitted lot.

NP-Chart

P Chart can readily used where group size is variable and the NP Chart is used, where group size is constant.

No. of defect per unit chart (C-Chart)

In number of cases, it is more convenient to work with number of defects per unit rather than with the fraction defective. There can be number of such situations where C-Chart can be successfully applied.

Examples are: Inspection of Radio, Furniture etc.

Average and Range Chart (X-R Chart)

To secure information to be used in establishing or changing specification in determining whether a given process can meet specifications.

To secure information to be used in establishing or modifying production procedure.

To secure information to be used in establishing or changing inspection procedure or acceptance procedure or both.

PROCESS CAPABILITY ANALYSIS

Process capability refers to the minimum variation that has to be tolerated on any process under the existing situations. Thus process capability is quality – performance capability of the process with given factors under normal, in control conditions. Without an action of fundamental importance like reconditioning the machine or replacement of the machine or improving operator skill etc., the process capability cannot be improved. Two significant elements in this concept of process capability are –

Process factors

Process conditions

The first consideration necessary to the concept of process capability is that a process is made up of a number of distinct factors. These factors include raw material, machine or equipment, the operator skill, measuring devices and the inspector skill. A change in one or more of these factors may change the process capability. Hence a process capability to be meaningful must be stated with respect to a given set of specifically listed process factors.

The second elements implies that for process capability study to be meaningful, the process being analyzed should be one that has measurements normally distributed and in a state of control.

When X-R Chart shows that the process is in control, it means that variations in the dimension subjected to control is within the limits of the natural variation. But it is not possible to say beforehand whether dimensions turned out in a state of statistical control meet the design specifications, or not. The answer to this question depends on the nature of relationship that exists between the processes within control.

It is also necessary that the process average and the process capability should be such as to permit the production of items, almost all of which comply with the specification. Capabilities of the machines must be evaluation periodically or after every maintenance of the machine and compared with specifications of the jobs loaded on the machine. The process capability can be calculated by the expression;

= 6 X R/d2

The process capability is also called natural tolerance.

COMPARISON WITH DESIGN TOLERANCE

A comparison of the process capability ( Natural Tolerance ) with the specified tolerance will bring out the following three types of situations.;

Process capability smaller than the specified tolerance.

Process capability equal to specified tolerance.

Process capability larger than the specified tolerance.

The possible actions/decisions to be taken in the above situations are listed as under:

RELATIONSHIP

ACTIONS/DECISIONS

Case (a)

Process capability (Natural Tolerance) smaller than specified tolerance.

Job can be changed to a less costly machine.

Specified tolerance can be squeezed if it is economically worth – wise.

Inspection interval can be increased and 100% inspection of employed can be dispensed with. The product can be accepted on the basis of control chart as long as it shows the process on control.

Case (b) Process capability equal to specified tolerance.

Greater attention to the centering of the process maintains the process average at the specification should give.

Set the machine at the most economic level if it is advantageous to change the process average at the risk of allowing scrap or re work.

Investigate the possibility of reducing process variability.

Case ( C )Process capability more than the specified tolerance.

Scrap and re work are inevitable.

Report to minimum machine adjustment.

100% inspection must be resorted to.

Examine the possibility of widening the specified tolerance to suit the process capability or affect fundamental changes in the process to reduce its variability.

Maintain X-R Chart and set the machine level at the most economic level.

RESULTS OF S.Q.C

Successful application of S.Q.C. program is expected o yield the following results:

Improvement in quality and Reliability.

Reduction in scrap and rework.

Efficient use of men and machine.

Locating and removing productions bottlenecks.

Scientific evaluation of standards for quality and production.

Decreased inspection costs.

Quality consciousness at all levels.

Improved level of customer satisfaction and quality image in the market.

SAMPLING

In factories, many measures are taken on the basis of data. Since every produced item cannot be inspected individually, these data’s are derived through sampling. It is an over all system containing a range of sampling plan and procedures based on mathematical theory of probability and statistics whereby the result of inspecting one or more samples is used to determine the acceptance or rejection of a lot or to access its quality.

TYPES OF SAMPLING

RANDOM SAMPLING.

TWO STAGE SAMPLING.

STRATIFIED SAMPLING.

CLUSTER SAMPLING.

SELECTED SAMPLING.

PARETO ANALYSIS.

The pare to analysis of failures occurring ensures that when curative action is decided on, efforts are concentrated on those failures that have a major effect on the service under guarantee call rate. This avoids wasting effort on minor problems.

The actions are discussed in committee with quality assurance, laboratory, development, marketing, service and manufacturing.

A Pareto diagram indicates which problem should be solved first in eliminating defects and improving the operation.

The problem contributing to maximum number of defects is tackled first and so on. Such tools are extremely useful in factory quality control. A pareto diagram also reveals whether attempts at improvements produce results.

CAUSE AND EFFECT DIAGRAM

Making cause and effect diagrams (General Steps)

The factors involved in problems with quality are almost uncountable. A cause and effect diagram is useful in sorting out the causes of dispersion and organizing mutual relationships. The following steps are taken in making cause and effect diagram.

STEP-1 Determine the quality characteristics. This is something we would want to improve and control. In this case, most of the factory defectives were due to wobble during rotation and to eliminate the wobble, the causes must be determined.

STEP-2 Write the main factors which may be causing the wobble, directing a branch arrow to the main arrow. It is recommended to group the major possible casual factors of dispersion into such items as raw materials (materials), equipment (machines or tools), method of works (workers), measuring method (inspection), etc. Each individual group will form a branch.

STEP-3 Write in detail the factors which may be regarded as the causes, these will be like twigs. On to each of these factors, write even more details making smaller twigs. Defining and linking the relationships of the possible casual factors should lead to the source of the quality characteristics.

QUALITY ASSURANCE

Quality assurance can be defined as all activities and functions concerned with the attainment of quality. This term has a broader sense as compared to quality control. Quality assurance would broadly cover the following areas. –

Standardization/specifications.

Reliability engineering.

Documentation.

Design reviews.

Vendor appraisal.

Inspection.

Testing.

Market Surveys.

Complaints.

Product rating and audit.

Product rating and audits are gaining increasing importance today. Product ratings involves the following:

Identifying critical parameters of a system.

Selecting a product at random at the final stage.

Check to see if the parameters identified are within specified limits.

Assigning a demerit score if not,

Taking corrective action.

Whereas, a quality audit is a non-executive function, it relates to a quality of a product, process or system. It is carried out on a periodic basis and involves an independent and systematic examination of actions that influence quality. The object is to ascertain compliance with the implementation of the quality system, program, plan and specifications.

RELIABILITY

Reliability was somewhat a vague term, a few years ago and was not given much importance in the design, development, manufacture and use of a system. But today, with the increasing complexity of systems, reliability considerations have entered every aspect of a product cycle. This has resulted in a vast improvement in the form of cost reduction, superior workmanship, a higher probability of satisfactory operation and improved customer-vendor relationship.

Reliability may be defined as the ‘Ability of an item to perform a required function under stated conditions for a stated period of time’. This is linked to the concept of failure. A failure is the termination of the ability of an item to perform a required function. A study of failure would include the following:

Failure cause study.

Failure mode study.

Failure mechanism study.

Failure criteria study.

A reliability study would, there are, consist of the following:

Study of failure based on file surveys, customer complaints and life test.

Documentation of data and analysis.

Implementation in design and/or process of above.

Conduct life tests.

QUALITY COST

Traditionally, the quality control function has been responsible for reporting quality performance to management in terms of rejection and defective material reports. This vital information is often difficult to analyze and interpret in terms of costs. As a result, cost saving opportunities is often overlooked. Successful business requires financial planning and control, it is advisable that quality failures be represented in financial terms.

Quality related costs can be classified as follows-

Prevention cost: The costs of any action taken in to investigate prevent or reduce defects and failures.

Appraisal cost: The costs of assessing the quality achieved.

Internal failure cost: The costs arising within the manufacturing organization, of failure to achieve quality specified (before the transfer of ownership to the customer).

External failure costs: The costs arising outside the manufacturing organization of failure to achieve quality specified (after the transfer of ownership to the customer).

PRODUCTION SYSTEM, PLANNING AND CONTROL

skilltech1970@gmail.com (Dattatray) — Wed, 4 May 2016 17:56:00 +0530

A production system is concerned with the processing of physical materials or conversion of materials and parts of goods and products. In general terms, the services, marketing and distribution of finished goods are also included in overall production system. But, in everyday usage, the term production system is normally associated with the manufacturing of raw materials/parts, and assembly and provisioning of physical inputs rather than with the provision of services and support systems.Basically the production

system deals with process at three distinct levels: raw materials supply, manufacture of parts and lastly assembly of parts and sub assemblies. Many times upon the nature of industry or more explicitly upon the nature of the product being produced.

The efficiency of a production system depends upon seven basic components or resources – men, materials, machines, tools and jigs and other essential methods, space and time which are coordinated by plans with a specific objective of completing them within a time frame work and controls exercised by management.

The aim of any productive and or manufacturing system is to meet the customer demand on time. The operation managers face two uphill tasks of meeting the promised delivery date of supply to customer and arranging a well balanced a mix of resources to achieve high levels of operating efficiency within the productive system.

Once the delivery dates are promised to the customer, these form a driving force for triggering a chain of reactions in the productive system. Operation managers are increasingly coming under pressure to give delivery dates favorable to customers in the present day competitive field.

The quantity of products or services that can produce depends upon the capacity of the system and economics of production. The productive system capacity nab increased over a period by augmenting the machinery, recruitment and training of workers, and increasing support facilities.

When the productive system is over or under loaded, it is bound to create strain resulting in high labor and material cost per unit, decrease in labor efficiency and morale, and unfulfilled delivery promises. To maintain high internal operating efficiency, the productive capacity has to match with production or manufacturing plan.

Aggregate or capacity planning is the process of devising plan productive resources to support these intermediate or long term sales forecasts or product demand estimates.

WHAT IS EXHIBIT- CONTRACT PLANNING?

skilltech1970@gmail.com (Dattatray) — Tue, 3 May 2016 19:19:00 +0530

DIFFERENT CHARACTERISTICS OF PRODUCTION SYSTEM:

In a production planning and control system, the various subsystems dealing with planning for resources, identifying the requirements.

for production and ensuring their flow, feedback on actual conditions and performance, will have to be designed and fitted together in a time dimension.
In a manufacturing organization, the following subsystems are interdependent and regularly interact to form an integrated production planning and control systems.
Long term capacity planning (3 to 5 years and above)

Aggregate planning/Master scheduling (actual, half yearly, revision, rolling 2 year plans)
Operative planning/ short term scheduling (quarterly/monthly/weekly)
Shop for planning and control (monthly/weekly/daily/shift plans).
While in the continuous process plants and high volume repetitive production, the capacity planning and aggregate planning sub-systems more or less specify the system fully and the lower level planning is minimal and limited to shipment plans, changes in priorities, sequencing of product mix, deployment of over time or sub-contracting etc. in intermittent manufacturing i.e. job shops and large scale products, etc the lower level planning is crucial and involves considerable detail and documentation for each individual order.
For intermittent manufacturing, the system must be flexible so as to react to new information and significant deviations from the forecasts and higher level plans. Feedbacks on actual conditions must flow upward through the system to ensure that the higher level plans and strategies are based on a realistic assessment of the organization’s ability to produce.
The enclosed exhibits show the information flows in the various sub-systems and their linkages with each other in an engineering manufacturing organization.

Exhibit 1

Shows the information flows in the long term capacity planning sub-system, business trends and long term demand forecasts by marketing, combined with preliminary engineering data and historical need ratios specify the long term production plan and the capacity requirements to support the plan.

These requirements when adjusted with the information on current shop performance, planned productivity improvement measures, policies on subcontracting and ancillary development, etc and the constraints of capital budgets will provide the capacity plans. These plans will cover the manpower plans and skill mix, plant and equipment purchases, modifications and replacements as well as the investments in inventories. The inventory levels will take into consideration the policies on project / product deliveries and the operations cycle time of the project/ products and the stage at which the stocks are to be kept. Long term capacity plants commit the organization to a configuration of manpower, skills and equipment which provide boundaries to lower level planning and constrain the development of more complete, detailed plans closer to the actual dates. If this sub-system is not well designed with the needed information flows, no amount of perfection in the lower level sub-system will be of much use, as major capacity changes cannot be affected at short notice.

Exhibit 2
Shows the master scheduling or aggregate planning sub-system. This forms the basis for the annual budget and the profit plan. Customer order and anticipated orders (sales forecast) are combined with engineering information to generate aggregate lead on different resources at different times. Various techniques PERT, Time cycle charts, Graphical methods and Bar charts are used for this purpose. Combining the planned capacity with current information on shop leads, and aggregate loads, for the various products/ projects and their deliveries are arrived at. The aggregate planning or master scheduling process involves consideration of alternative plans and their costs implications for choosing the best course and adopting the same as the basis for the annual profit plan. The alternatives, within the capacity plan which is predetermined by the previous sub-system, will consider for different periods in the year, sub-contracting, over-time, Inventory build-up, number of shifts for different types of equipment, temporary manning, machinery re-layouts, product mix and what orders to forego and what orders to increase. The master schedule will specify the needed level of utilization of critical resources, the policy guidelines for short term capacity adjustments, and the overall time schedules for starting and completion of projects/ products and major assemblies in respect of the various pre production and manufacturing activities.

Exhibit 3
Shows the information flows in the short term scheduling or operative planning. Within the time frame provided by the master schedule for various products, customer orders are combined with engineering and manufacturing process information to determine the sub assembly and component stocks already available, the net requirements to be manufactured are planned. The possible rejections during manufacture and spares requirement, if any, and pending unfulfilled orders if any, are considered while arriving at net requirements relating to different periods. Start and completion time for each sub assembly and components are arrived at and the process times and lead times are superimposed on the existing available capacities, provision is made for pattern of breakdowns and unavoidable down time, worker efficiency, rejection rates and the planned improvements in these.

The process of watching the due dates for start and completion of sub assemblies and components, with the existing shop loads may lead to one or more of the following processes.

Alter Priorities.
Reduction or increase in batch sizes.
Adjust capacities by additional shifts, sub contracts, over time, temporary hiring of skills, regrouping men, etc within the aggregate plan.

Altering delivery dates in consultation with marketing.One important feature in the design of this sub-system is the extent of centralization vs. decentralized scheduling of components and sub assemblies and load of critical equipment.

A high degree of decentralized scheduling maybe fairly effective if the shops are relatively independent such as a product layout, etc where there is a high degree of inter dependence as in a process layout, the short term scheduling will have to be centralized and the scheduling period, i.e. the period of time over which, a schedule can be considered fixed with very few changes, will have to be short to retain the necessary flexibility. If the system permits long schedule periods and a high degree of de centralized scheduling in such cases, the inter dependent nature of operations will require constant chasing in between shops and it will degenerate into an expediting system needing continual intervention by higher management on routine scheduling decisions.

The fourth sub-system in an integrated production planning and control system is shop floor planning and ensuring upward flow of information on actual conditions and performance. This involves the following process.

Production Authorization.
Translate schedules in to sets of production order papers..
Issue orders to release materials, and tools against the production orders.
Arrange for proper sequencing through appropriate priority decision rules.
Arrange for material handling, coordinating work flow between operations and keep records of work in process (shop stores).
Use appropriate physical systems for workcentre leading, indicating availability of materials and tools, job priority, etc. such as loading boards, pigeon hole tracks against work centers etc.
Simple priority rules will have to evolved and used by shop planners for sequencing jobs on work centers, such as:
Earliest due date.
Minimum slack.Jobs in the order of shortest processing time out of all jobs for the period etc.
Acquire Performance Data and Feedback.
This relates to designing the flow of information in the upward direction and ensuring timely feedback to the higher levels of planning. The system should facilitate reporting in respect of planned events as well as unplanned events.

Relating Performance to Plans.

Data relayed from shop floor is used for comparing actual performance to planned performance. There is no justification for acquiring any data and the related paperwork if it is not used for this purpose. Such an evaluation will generate information such as the following:

Items behind schedule for completion, for starting and for any other events.

Completion of production orders against planned.
Progress of total production against planned, for the period and cumulative, in terms of standard hours/value added/physical units. Etc.
Actual utilization of critical facilities as against the planned utilization.
Shop efficiencies, actual Vs planned.
Utilization of high value materials as against planned.
Corrective Actions.
Identifying significant variations in respect of various performance parameters will lead to corrective actions to be taken at different levels of management.
Short term corrective actions may be confined to:
What course of action to follow for items behind schedule, any additional shift, over time, subcontract, delay other jobs, etc, within the policy frame work and aggregate plans?
Whether special measures are required for improving utilization of critical facilities like higher maintenance effort, relief operators to operate facilities during rest pauses etc to be considered.

What course of action to follow when product quality has dropped to unacceptable levels, withdrawing particular lot of raw material which is unsatisfactory, intensify supervision, change operator, correct machine etc.

Whether special task forces/expeditors are to be appointed.
Whether schedules are to be modified or priorities reviewed etc.
Long term corrective actions are aimed at preventing recurrence of such problems ensuring that organization s’ abilities match requirements, and increasing the effectiveness of the production planning and control system.

The various assumptions incorporated in the higher level plans in respects of capacities, facility utilization,, lead times, sub contract and ancillary skills, etc., will have to be continuously checked with the actual occurrence and appropriate corrective actions taken, wherever necessary, the planning process will have to be improved with the help of the information available on actual performance.

A very important concern in the long term is the design of the production planning and control system itself for its adequacy and flexibility, whether the feedback time lags, or the sensitivity of the systems and amount of control actions are appropriate.
While each sub-system described are to be are designed appropriately for the given manufacturing organization, these have to be fitted together and the linkages between them established for an integrated production planning and control systems.

PRODUCTION CONTROL

skilltech1970@gmail.com (Dattatray) — Mon, 2 May 2016 18:17:00 +0530

ASSEMBLY BASED ON:

Demand Forecasting.

Preparation of suitable plans for meeting the demand.

From forecasts of demand and plans for production, production schedules prepared.

From production schedules production load is derived which is translated into action.

Forecast of Demand.

Plans.

Schedulers.

Load.

Action. In PPC loading and scheduling are important steps and they go hand in hand.

Loading differs from scheduling only in terms of detail and time span.

A schedule will time table a dept. for a month or so.

A load will time table a machine or operator for a day or a week.

SCHEDULE

Representation of time taken to carry out a task.

Takes into account the time relationship between the various functions.

A route or list of work to be done would not show the overlapping of activities where as schedule would take this in to account.

LOADING

Load work assigned to a machine or an operator, evaluates, capacity volume of out put capable of being produced in a period of time.

Preparation of loading schedules for machine or operator is capable of providing substantial improvements in productivity.

GENERAL RULES FOR SCHEDULING

Schedule first those operations with the shortest first operation.

Schedule first those operations with the shortest last operations.

Schedule jobs according to their total work content.

Schedule jobs according to their dates of promises made.

Assign jobs according to the customer.

SIMPLIFYING THE SCHEDULING PROBLEM

Reduce product range.

Reduce component range.

Examine available resources.

Enlarge all jobs wherever possible.

Use sub contractors.

Separate big and small jobs.

Close liaison with marketing.

PROBLEMS AND ISSUES IN SCHEDULING

Centralized scheduling Vs Decentralized scheduling.

Availability of realistic time estimates for various jobs/operations.

What is the time span/period for which a rigid schedule is to be made?.

Feedback on the schedules and rescheduling of jobs/activities.

Change of priorities and extraneous causes that affect schedules.

Assessment of delivery schedules given by vendors/suppliers (outside source) and synchronization of internal and external schedules.

Optimization in scheduling – the role of quantitative techniques.

Compares in production scheduling and control.

Integrating production scheduling with maintenance schedules.

SCHEDULING TECHNIQUES

Run Out List for Selecting Items.

The time when inventory on hand plus production of the items already schedules will be used.

Objective is to assign available production capacity in such a way that runs out time for all items are the same.

Inventory of each item expected on hand at the end of the period being scheduled.

Inventory on hand or scheduled in production on the scheduling date scheduled production of the item.

Expected usage of the item during the period.

Inventory expected on hand (end of scheduled period).

RUN OUT TIME WITH ECONOMIC RUN LENGTHS

A run out list can be used for scheduling an operation which makes a number of stock items which are to made in economical, fixed or minimum batches or lots and where the operating length has been set.

Divide the inventory on hand (or in production) for such item by estimated usage rate. This gives the run out time if no extra production is scheduled.

Then standard lots are scheduled beginning with item with the shortest run out time until the total time scheduled equals the planned production time.

LOADING SCHEDULES WILL HELP IN…

To make maximum possible use of plant and personnel.

To establish and meet target dates.

To determine the necessities of new plant.

To improve operator’s morale.

LOAD GENERALLY EXPRESSED IN HOURS OF WORK/MONEY/WEIGHT/LENGTH/QUANTITY

Load Delivery date Schedule Load.

It is faulty to set a delivery date without due regard for the load yet this is done frequently that it can be the general practice.

IN PREPARE SCHEDULES ATTENTION MUST BE PAID TO:

Variations to schedule.

Capacities of various sections/departments.

Efficiencies of various sections/departments.

Maintenance schedules.

Holidays.

Anticipated sickness/Absenteeism.

Existing commitments.

Availability of materials.

Basic Objective of Scheduling to obtain a Smooth, Timely Flow of Product through Manufacturing Steps.

GANNT charts, network techniques, line of balance etc. Modern software technology, Help in scheduling.

LINE OF BALANCE

Just as critical path analysis cab used to schedule and controls a single project; LOB can be used to schedule and control a single batch.

LOB – PRE – REQUISITES

There must be identifiable stages in production at which managerial control can be exercised.

Manufacturing times between these stages must be known.

A delivery schedule must be available.

Resources can be varied as required.

In controlling a number of batches the computational difficulties become great.

STEPS IN LOB

Construct a CPA diagram to show the logic and timing of production.

Carry out a reverse forward pass from time ‘0’ at the final event.

Rank the activities in the descending order of ‘equivalent week Number’. (this is also reported as stages).

Prepare a calendar and accumulated delivery quantity.

From the tables schedule the quantity of each actively which should be completed by a particularly date.

Record the actual progress on LOB chart or life table.

MANUFACTURING PROCESS AND MACHINES

Metal cutting process forms the basis of the engineering industry and is involved either directly or indirectly in the manufacture of nearly every product.

Manufacturing requires tools and machines that can produce economically as well as accurately. Economy depends to large extent on the proper selection of the machine or process that will give satisfactory finished products.

In small lot or jobbing type manufacturing, general purpose machines such as the lathe, drill press and planer may prove to be the best type, since they are adaptable, have lower initial cost, require less maintenance and process the flexibility to meet changing conditions in shop.

A special purpose machine should be considered for large quantities of a standardized product. A machine built for one type of work or operation will do the job well, quickly and at low cost with the service of a semi skilled operator.

In manufacturing any product, there are usually a number of machining operations, which are as follows:

Turning

Grinding

Broaching

Drilling

Milling

Reaming

Shaping etc

The type of different tools and machines most commonly used in the manufacturing sector:

Turning. Machines: Turning machines are more commonly known as lathes.

Centre lathes or Engine lathes.

Gap bed lathes.

Tool room lathes.

Bench lathes.

Hollow spindle lathes.

Special purpose engine lathes.

Turret lathes & Drum turret lathes.

Capstan lathes.

Vertical turret lathes.

Automatic lathes.

Copying lathes.

Numerically controlled lathes.

Chucking lathes.

Grinding and abrasive machines.

Abrasive

Machines Abrasive machining is a primary stock removal process which competes favorably with other stock removal methods. It is not a finishing operation like conventional grinding or lapping. Not limited to bonded wheel operations, it includes coated and free abrasive processes as well.

Grinding Machines-

Classification of grinding and abrasive machines:

Cylindrical grinder.

Internal grinder.

Surface grinder.

Universal grinder.

Tool grinder.

Special grinding machines.

Surface preparing.

Abrasive grinding.

Broaching-Broaching is a machining process in which a cutting tool, having multiple transverse cutting edges, is pushed or pulled through a hole or a surface to remove metal by axial force.

Broaching Machine:

Drilling.

Drilling machines.

Drilling machine size.

TYPES

Hand feed drilling machine, Radial drilling machine,

Milling-

Milling is a machining process in which metal is removed by a rotating multiple tool cutter.

Milling machines-

Milling machines are employed for machining flat surfaces, contoured surfaces, surfaces of revolution, external and internal threads and helical surfaces of various cross sections.

TYPES

Column and knee-type machines, Horizontal milling machines, vertical milling machines.

TYPES of milling cutters- There are 3 general designs of cutters Arbor cutters.

Shank cutters.

Face cutters.

The cutters most generally used are classified principally according to their general shape or the type of work they do.

Plain milling cutter, Slide milling cutter, Metal slitting saw cutter, Angle milling cutter, Form milling cutter, End milling cutters, T-slot cutters and Inserted tooth cutter.

A number of different types of machines are available for different type of operations. (Now a day’s improved version of new software technology are being used to build additional strength for the above to have more accuracy and prompt fine finished work)

The above information is a brief idea about production planning and control. It may differ slightly from an industry to industry due to improved versions of technology.

This information is an instance about the sector I have been involved with. The reader is advised to use the information according to his needs on the basis of his/her manufacturing segment.

INDUSTRIAL HEALTH AND SAFETY

skilltech1970@gmail.com (Dattatray) — Mon, 2 May 2016 17:18:00 +0530

The management should attach higher attachments to training in safety and health, better maintenance of equipment, dangerous machines, safe working conditions and use of personal protective equipment. But unfortunately, the workers do not prefer to use the personal protective equipments and discard it on or the other pretext. The trade unions have also treated the safety and health issues as secondary before wages, monetary incentives and other benefits.

Both management and workers should lay equal stress on safety and health. The cooperation of management and employees will certainly reduce the industrial accidents and contribute to the company’s performance and profitability. Framing of rigid laws and providing harsh punishments may not be sufficient. Safety is a joint responsibility of workers and management.

ROLE OF SUPERVISORS/MANAGERS

Experience and research have established that accidents just do not happen, they are caused. It is found that 98% of accidents are preventable and 88% happen due to human failures, act and attitudes. Here supervisors especially have a great responsibility. The supervisors and managers are the key person in any safety programmed. To the workers, he is the management because he is in constant touch with the workers. The supervisor should have the responsibility to see that:

Each of his employees understands the properties and hazards of the materials, stores – handled, processed and used by them. He should make his workers safety conscious.

The necessary precautions are observed while using equipment including the use of proper safeguards and personal protective equipments.

They must understand and properly follow the established rules and procedures safety.

A supervisor should understand and concentrate on sources of accidents, maintain detailed statistics on accidents that happen in their department.

A supervisor can render great help in investigating employee suggestions regarding safety and their implementation.

He sets a good example and maintains good employee relations.

A STUDY ON TOOL ENGINEERING

skilltech1970@gmail.com (Dattatray) — Sun, 1 May 2016 12:52:00 +0530

Tool design is a specialized area of manufacturing engineering which comprises the analysis, planning, design, and construction and application of tools, methods and procedures necessary to increase manufacturing productivity.

RESPONSIBILITY OF A TOOL DESIGNER MUST BE FAMILIAR WITH THE FOLLOWING:

Cutting tools, tool holders, and cutting fluids.

Machine tools, particularly modified or special type

Jigs and fixtures

Gauges and measuring instruments

Dies for sheet metal cutting and forming Dies for forging, upsetting, cold finishing and extrusion

Fixtures and accessories for welding, riveting and other mechanical fastening.

OBJECTIVES OF TOOL DESIGNER

The tool designer must realize the following objectives or goals.

Reduce the overall cost of manufacturing a product by producing acceptable parts at the lowest cost.

Increase the production rate by designing tools that will produce parts as quickly as possible.

Maintain quality by designing tools which will consistently produce parts with the required precision.

Reduce the cost of special tooling by making every design as cost effective and efficient as possible.

Design tools which will be safe to operate.

THE DESIGN PROCESS

The design process consists of 5 basic steps:

Statement and analysis of the problem.

Analysis of the requirements.

Development of the initial ideas.

Development of design alternatives.

Finalization of design ideas.

a. PROCESS ENGINEERING

The process engineering takes place immediately after the product engineering has completed the design of a product. The output of product engineering namely part drawings, bill of material, engineering specifications, are the fundamental data on which process engineering function starts. In addition to above the data the information regarding the quantity of manufacture is of paramount importance in process engineering. An important decision has to be made at the outset as to what components are to be made in the plant, and what are to be bought from vendors. This goes by the name of “MAKE BY DECISION”

Make by decision must be based on various factors:

Quality, reliability and availability of supply.

Control of trade secrets and patents.

Research and development facility.

Flexibility and alternate source of supply.

Economic analysis.

b. PROCESS PLANNING

Process planning involves the determination of the method and the sequence of operations, tools and equipment required as well as the specification of the parameters of the process like speeds, feeds. The decision involved in this process has an important bearing on the cost of manufacturer and thus on the profitability of a manufacturing enterprises.

VARIOUS STEPS IN PROCESS PLANNING

Analysis of the part print.

Consultation with the product design, wherever clarification or modification regarding product design is required.

Preparation of rough method layout.

Detailed operation planning.

Final method of layout.

Fixing the in process dimensions and tolerances.

Writing out process shut and detailed operation plan.

2.0. ECONOMICS OF PROCESS AND MACHINE TOOL SELECTION

The managers and technicians are frequently encountered with the problem of process and machine tool selection. They are called upon to take decisions with regard to choice of our alternative from several proposals. There can be several alternative avenues for an investment to get more than a specified rate of return. In such situations break down concept play an important role in decision making.

BREAK EVEN ANALYSIS

In many situations encountered in engineering economy, the cost of 2 alternatives may be affected by a common variable. When such a condition occurs it may be desirable to find the value of the variable that will result in equal total cost for the alternatives considered. The value of the variable so designated is known as the break-even point. The total cost of any alternative is made up of fixed cost and variable cost.

FIXED COST

It is defined as that group of cost involved in a going activity who’s total will remain relatively constant throughout the range of operational activity.

VARIABLE COST

It is defined as that group of costs which vary in relationship to the level of optional activity. In general, all costs such as direct labor, direct material, direct power etc. which can readily be allocated to each unit of product, are considered to constitute the variable costs.

The above mentioned concept on breakeven point is also applicable for the evaluation of alternative machine tools for performing a particular operation on a particular component considering the costs of set up, tooling and operation time.

3.0. SEQUENCE OF OPERATION

While planning different operations to be performed on a part, it is important to decide which to follow which. There are several considerations to this effect. To analyze the relative importance of different considerations, operations can be classified in to:

Critical operations.

Secondary operations.

Qualifying operations.

Re qualifying operations.

CRITICAL OPERATION

The operation that must be given special consideration in order to accomplish some unique characteristics on or from some surface of the work places.

SECONDARY OPERATIONS

The operations which are not critical but have a function purpose on the work piece and are generally performed without much special effort. Drilling and tapping way serve as one example of two secondary operations performed sequentially.

QUALIFYING OPERATIONS

The operations performed on work pieces like cast or forged pieces to establish qualified locating surfaces prior to accomplishing process critical areas.

RE QUALIFYING OPERATIONS

The operations performed on the work pieces in order return it to its original machined geometry. Heat treatment operations are one of the major causes of re qualifying operations.

4.0. SELECTION OF PARAMETERS OF DIFFERENT PROCESSES

To select various parameters for different processes, it required to know how these affect the machinability of a given material. The term machinability is a complicated one to lead to any clear definition. In a simpler way, machinability means ‘the ease’ with which a given material may be machined with a specific cutting tool. Commonly used yardsticks to measure machinability are:

Cutting force and power.

Tool life.

Surface finish.

These three factors together represent the machinability. For a particular machine set up and for a particular process, the above factors are considerably influenced by various parameters of the process. These parameters of the processes can be divided broadly in to:

Machine variables.

Work material variables.

Cutting fluids, vibration and chatter.

The above variations can be listed as follows:

MACHINE VARIABLES/TOOL VARIABLES/WORK MATERIAL VARIABLES

Cutting speed.

Dimensions of cut (a) feed (b) depth of cut.

Rigidly and freedom from chatter of machine tool work and work holding devices.

Tool material.

Tool shape i.e., various angles of tool.

Tool temperature.

Hardness.

Tensile strength.

Chemical composition.

Microstructure.

Degree of cold work.

Strain harden ability.

Chemical, physical prosperities of cutting fluid.

There is no single theory available considering all these parameters of metal cutting. Only empirical relations are available, which were arrived at after conducting a series of experiments to study the relationship of above variables with cutting force and power, tool life and surface finish. Here the discussions would be about these relations taking turning process as example. The same principles can be applied to other process tool life, drilling, milling etc., with due modifications and considering special factors of the respective processes. Before starting this, it is required to know about cutting force and power, tool life and surface finish as applied to turning process.

CUTTING FORCE AND POWER

Below shows three components of forces in turning.

Fig.8.(a)

The tangential force, Ft does most of the work in turning and responsible for most of the power consumed. Hence, when cutting force in turning is mentioned, for practical purpose, tangential force Ft need be taken.
The feed force Ff does very little work and the radial force Ft does not work. The tendency of this component of force is to deflect the work piece. The approximate ratios of…

Fig.9(b)

Ft: Ff: Fr is 4: 2:1

The power consumed in turning operation is given by the formula:

Fe x v/4500 H.P.

Fc = Cutting force – (tangential force alone is considered here) in Kgf.

V = Cutting speed. In metre/mt.

Cutting force can be measured by the use of a dynamic meter. Cutting force can also be computed from the specific cutting pressure of the work material. Specific cutting pressure is the cutting force per unit area of under formed chip cross section. For any other chip thickness; the formula for specific cutting pressure corresponding to that thickness would be,

=Kc 1.1/(h)p

Where, kC 1.1 is the specific cutting pressure for unit area (1mm x 1mm)

H= undeformed chip

P= is an index

New cutting force = specific cutting pressure x feed per revolution x depth of cut.

TOOL LIFE

The life of the tool in between resharpening cab specified in several ways like:

Actual cutting time in between resharpening.

No. of pieces produced.

Volume of metal removed.

Equivalent Cutting speed. For example V 60, cutting speed at which 60 mts. Of actual cutting time of machine time is obtained, under a given set of cutting conditions.

Tool failures occur ordinarily, in any of the following ways:

By flank wear, wear on the flank below the cutting edge.

By crate wear; caused by the flow of chip on the rake face. This wear occurs slightly away from the cutting point and has cup shape, gradually spreads towards the cutting edge.

By chipping wear, breaking off of tool. This can occur due to built up edge formation or due to shock loads.

Due to temperature failure.

Some of the common criteria for judging the tool failure area;

Complete failure: Tool completely unable to cut.

Flank failure: By judging the width of wear land developed on the flank of the tool.

Finish failure: Loss of surface finish on the workpiece.

Size failure: Change in dimensions of the finished parts.

Cutting force or power failure: Increase in cutting force or increased in power consumed.

Thrust force failure: Difficulty in feeding indicative of tool failure.

SURFACE FINISH

A typical machined surface when enlarged would look as shown in below:

Fig.9(C)

It shows peak and valleys super imposed on a wave form. The peaks and valleys themselves are produced due to feed marks and the part of built up edge left on the machined surface. The waviness of the surface is due to vibrations inherent in machining process.

How the various parameters of the processes affect cutting force and power, tool life and surface finish can be seen now.

CUTTING SPEED

a. Cutting Force and Power

Based on the results of a many investigations it can be said that the cutting force is independent of the cutting speed beyond 100 ft/mt it can be seen that cutting force increase as the cutting peed is reduced. This is because of built up edge formations at very low cutting speeds (please refer graph).

b. TOOL LIFE

Cutting speed is the parameter having maximum influence on tool life. There is a well known equation formulated by Taylor and which is

Vtn= constant (c)

Where, V =Cutting speed in meters/mt.

T = Tool life in mts.

h= Exponent whose value is primarily dependent on tool material and varies, to some extent, with other machine and work material variables.

C= Constant whose value is depends primarily on the material being cut and other machine and work other variable. Numerically equal to the cutting speed that gives a total life of /mt.

The approximate values of ‘n’ in the above equation are for

H.S.S. tool = 0.1 to 0.15

Carbides = 0.2 to 0.25

Ceramics = 0.6 to 1.0

These values can also be found by conducting machining at two different cutting speeds and noting the tool life in each case.

From the above relation, it can see that when cutting speed is increased, tool life is decreased and vice versa. But in the case of machining steel and cast iron with carbide tools it is seen that the tool life goes down when the cutting speed is reduced below a certain value, this is because of built up edge formation at very low cutting speeds.

c. SURFACE FINISH

As cutting speed is increased, there are fewer tendencies for built up edge formation because of lesser duration of contact and lesser strain hardening. Because of this, surface finish is improved at higher cutting speeds.

DIMENSIONS OF CUT OUT (Feed and depth of cut)

a. Cutting Force and Power:

Increase in both feed and depth of cut will result in increase of force and power. It can also be seen that increase in depth has more effect than increasing feed on cutting force and thereby on power. This is because when speed is increased, chip thickness is also increased and hence specific cutting pressure decreases, but the thickness does not change. Because of this reason for the same increase in area of chip, cross section depth will have more effect.

The relation can be expressed,

Fc = kdufw

K = Constant, when value depends mainly on the material being cut and true rake angle of tool,

v & w are exponents.

In average machining where the nose radius is small in relation to depth u = 1 and w = 0.8

Hence, fc = k x d1x f 0.8

b. TOOL LIFE

Tool life obtained at a given cutting speed is affected by dimensions of cut. Tool life is reduced when dimensions of cut are increased.

As there will be more contact area with chip and tool when depth of cut is increased, heat dissipation is better than in the case of increasing the speed. When feed is increased, contact area remains same. Hence increase in feed will reduce tool life faster than increase in depth of cut. The general empirical relation between cutting speed for chosen tool life and feed and depth of cut is,

Vt = CA/dxfy

VT = Equivalent lant cutting speed for a chosen tool life.

CA = A constant whose value is depends on work and other variables.

f = Feed per revolution (or feed per tooth)

d = Depth of cut

x&y = Exponents. In practice common machining of steel,

x = 0.14 and y = 0.43

For cast iron;

X = 0.10 and y = 0.30.

This formula states that a combination of larger depth of cut and a high rate of feed with a low cutting speed will allow a large amount of metal to be removed during a given life of the tool.

c. SURFACE FINISH

Depth of cut has no influence on surface finish. But indirectly more depth of cut may induce vibration of tool and work piece system, and in turn surface finish may be affected. To see the effect of increasing feed, first of all, how the feed ridges are formed must be seen. Figure shows two consecutive positions of a tool after a revolution of the work.

Fig.1

The dimension ‘h’ in the figure is the height of the feed ridge. It can be directly seen from the figure that if feed per revolution is reduced, height of the feed ridge will also be reduced thereby increasing the surface finish.

By calculation, it can be found out that,

H = fr2/8R

This means the height of the feed ridge varies as square of the feed revolution.

TOOL MATERIAL

a. Cutting Force and Power:

With a few exceptions like diamond tools, cutting force and power consumption are practically independent of tool materials.

b. TOOL LIFE

Tool materials have no effect on tool life.

c. Surface Finish: Diamond has a minimum tendency to weld on to metals and thus very little built up edge is formed and a high quality of surface finish can be achieved. Other than diamond all rest of the tool materials have no effect by themselves on the finish. But if the tool material is capable of machining at high cutting speeds than a better surface finish can be achieved because of high cutting speeds.

TOOL SHAPE AND ANGLES

a. Cutting Force and Power: When rake angle is increased in the positive direction, cutting force also reduces. It is proved by experiments that cutting force reduced by 1% if 1o rake angle is increased in the positive direction.

The clearance angles have no effect on cutting force and power. If the side cutting edge angle is increased, feed force reduces and radial component of force increases.

If the nose radius is increased, radial force increases. This indicates that, if a slender job is to be machined, too high a side cutting angle and nose radius will increased radial forces and bend the job.

b. TOOL LIFE

Cutting temperature is only slightly effected by the rake angle and so also tool life.

The side and clearance angles if provided to avoid rubbing, then they have negligible effect of temperature and so also the – tool life. If side cutting edge angle is increased, the length of the cutting edge is increased and heat is generated and distributed over a longer length. This renders better tool life. End cutting edge angle ordinarily has minor influence on temperature and hence no tool life.

c. SURFACE FINISH

Tools angles and shape have remarkable effect on surface finish. An increase in tool rake angle, reduces cutting forces and consequently reduces built up edge formation. This leads to better finish.

Coming to clearance angles, if equal size variation is allowed on work piece (because of tool wearing off), tool with larger clearance angle will give better surface finish than with a tool with lesser clearance. This is because of lesser amount of rubbing than in the latter case.

Figure -4 -, show how cutting and end cutting edge angles on surface finish side.

Fig.11.

An increase in side cutting edge angle and a decrease in end cutting edge angle will improve surface finish because feed ridge height is reduced. By this reason, a broad nose tool should give a good surface finish.

An increase in nose radius invariably improves the surface finish, as it can be seen from figure 3, and from relation,

H = fr2/8R

HARDNESS AND TOUGHNESS OF THE WORK MATERIAL

a. Cutting Force and Power: As a general rule, cutting forces and power increases with increasing hardness and toughness.

b. TOOL LIFE

If the hardness of the work material is increased then the hard particles exist in the chip. As the chip impinging on tool force with high momentum, may pluck particles from tool surface, causing reduced tool life. But if work material is too soft like pure iron on low carbon steels, even then tool life will be less because of built up edge formation. In these cases, it is better to slightly increase the hardness of these materials and machine to get better tool life.

c. SURFACE FINISH

The softer materials produce poor surfaces because of the same reason, built up edge formation. Hardening these soft materials to certain degree will render better surface finish in subsequent machining. Thus a cold drawn bar of steel which is work hardened can be expected to produce surface finish than hot drawn bar.

MICRO STRUCTURE

Cutting Force and Power: Micro structure as such has little effect on force and power consumption excepts as it affects hardness or strength materials. As already mentioned, harder or stronger materials require more power to machine.

b. TOOL LIFE

Carbon steels consists of a materials with particles of hard iron carbide distributed out in geometrical patterns depending upon the conditions of heat treatment. While machining low carbons steel, whatever to be the micro structure, have poor machining characteristics because of built up edge formations. This affects the tool life. In medium and high carbon steel microstructure is very important. To avoid built up edge formation while machining: a harder structure is wished, that means a mean ferrite path large dispersion of carbide particles. But avoid hard particles impinging on tool face and increasing wear; it is require to have larger mean ferrite path with a relatively few, large, widely spaced carbide. This means an optimum structure is required for an optimum tool life. Empirically it can be said a particle structure in best suited for medium carbon steel and a spheroidised (larger mean ferrite path0 structure is most advantageous for high carbon steels. The dependence of optimum structure upon machining operation may be illustrated by comparison of turning and broaching. Broaching is a slow speed operation and hence is a tendency built up new formation. This calls for a harder structure in broaching than in turning. High carbon spheroidised steel is usually too soft and hence produces built up edge and less tool life in broaching.

c. SURFACE FINISH

For a good surface finish consideration also, an optimum structure in steels are required. In the case of cast iron, greater the size of graphite particles, rougher is the surface finish.

CUTTING FLUID

Cutting Force and Power:

Cutting fluid performs two functions in machining.

Lubrication.

Cooling.

Lubrication effect is more required in slow speed operations where chance of built up edge formation is high. Cooling effect is more required in high speed operations to cool the tool and work. In slow speed operations, especially cutting fluid reduce the cutting force because it reduces the effect of built up edge formation.

b. TOOL LIFE

Tool life is extended because of cutting fluids. Apart from reducing the effect of built up edge. It cools down tool and reduces the friction at tool chip interface, forming a thin film coating.

c. SURFACE FINISH

Surface finish is improved because of lesser built up edge formation. Nowadays the technology has been improved in tool design and tool process with a intention to achieve more productivity at lesser cost.

JIGS AND FIXTURES

Fig.12

Jigs and fixtures are special work holding devices used while machining a job in machine tool. Devices used to hold parts at a definite relation to each other during assembly, welding, brazing are also commonly called as “Fixtures.” Fixtures are also used for inspection. These help in increasing productivity and to maintain the dimension of the part within a specified tolerance limit.

The distinction between jigs and fixtures is of purely academic interest.

A jig is normally defined as a device for holding a component, for specific operation, in such a way that it will guide one or more cutting tools to the same position on any number of similar components that may be used upon it.

A fixture is a device to which a component is fastened for a specific operation, but the cutting tools are not guided. Some people distinguish between jigs and fixtures as follows:

A jig is a work holding device which is not fastened to the machine on which it is used.

A fixture is also a work holding device but one that is fastened to the machine.

ADVANTAGES OF JIGS AND FIXTURES

Eliminate laying out work piece before machining and consequently eliminates setting up the work piece on the machine tool to the layout lines.

Increases machining accuracy, because the work piece is automatically located without aligning on the machine tool. Tolerances are maintained and interchangeability is attained.

Increases productivity due to increasing the number of work piece simultaneously machined.

Due to higher clamping rigidity, higher speeds and feeds, depth of cut can be used and thereby increases in productivity.

Save operator’s labor.

Use of lower skilled operator made possible.

Decreases expenditure on quality control and reduces scrap.

Increases versatility of machine tool.

Either fully or partly automates the machine tool.

ELEMENTS OF JIGS AND FIXTURES

Locating elements properly positioning the work piece.

Clamping elements.

Power devices for operating the clamping element.

Tool guiding or cutter setting elements.

Indexing devices for accurately changing the position of the work piece in the jig and fixture.

Auxiliary elements (locating and holding assembly for machine tool)

Fastening parts which serve to hold the elements or components together.

Body, Base or Frame.

PRINCIPLES OF LOCATION

Locating elements help in positioning similar components, repeatedly in the same relative position with respect to the body of fixture. Two important principles relating to the design of locating elements are as follows:

Reduce all possible degrees of freedom of the component to zero.

Avoid redundancy of location. If unavoidable, the redundant location should be floating.

THE SIX DEGREES OF FREEDOM

A body in space is free to make in six definite ways. It consists of linear movement along the three axis OX, OY and OZ, and rotational movement about the three axis. Sum of these movements gives six degrees of freedom. In order to locate a component i.e. to define a component in space, it is necessary that all the six degrees of freedom are arrested.

CLAMPING DEVICES

For any machining operation, it is essential to make suitable clamping arrangements. The selection depends upon type of working. Different clamps are required depending upon whether the components are produced in batch quantities or in mass production.

The clamps are broadly classified in following varieties.

Simple hand operated clamps.

Quick acting hand operated clamps.

Power operated clamps – pneumatic or hydraulics.

The selection of suitable clamp is based on an effort to balance the cost of clamp against the cost of the operation, in order to obtain the lowest possible total cost of fixtures and operation.

Tool designer should use sound judgment for selection of specific clamping arrangements for the job in hand. In general, clamping arrangement should be as simple as possible. Complicated arrangements tend to lose their effectiveness as the parts become worn, necessitating excessive maintenance, which might readily off-set the saving of faster operation.

CLAMPING PRINCIPLES

The purpose of a clamp is to exert a force to press a work piece against the locating surfaces and hold it there in opposition to the action of cutting forces. Clamping forces should be directed within the locating area, preferable through heavy sections of the work piece directly upon locating spots or supports. Cutting forces should be taken by fixed locators in jig or fixtures as much as possible, but in case of some components, moments set up by the cutting forces must be counteracted by clamping forces. To be effective, a clamp should be designed to exert a force equal to the largest force imposed upon it in the operation.

TURNING FIXTURES

Main principle of turning is rotating the work against traversing tools. The work is ordinarily set upon a horizontal lathe, but heavy odd shaped jobs are mounted on a vertical lathe. In actual practice, the types of turning and boring fixtures are as many as the numbers of components exist. However an attempt is made to generalize the fixture design to some extent with regard to the type of components.

1) S.No.

Type of Fixture.

Type of Component.

Chucks: Standard and special.

L/D ratio up to 1.

2) Face drivers, centers and spring collects.

For components like shaft, L/D ratio up to 2.

3) Mandrels and Arbor type fixtures.

L/D about 1. Suitable for finish operation.

4) Face plate or angle plate type fixture.

Components for mostly unsymmetrical shapes e.g. bearing housing and components of hydraulic units.

5) Special boring fixture.

For semi finishing and finishing operation.

6) Special turning fixture. For components like engine cranks shaft.

BORING FIXTURE

Boring means internal work of enlarging a cored or drilled hole. The class of work allocated to boring machines consists mainly of boring and facing the bosses of components which are too large or difficult to be set on centre lathe.

Alignment of boring fixture is very important. Careful tool setting is required.

MILLING FIXTURES

Milling fixtures are to be designed for rigid work holding because of the very nature of operation for which they are used. Milling operations throws intermittent load of varying intensity during the course of operation, usually multipoint tools are used and the teeth which remove material intermittently unlike lathe tools.

Factors which dictate the use of fixtures is work piece accuracy, odd and complicated shapes, heavy metal removal, quick and fool proof loading.

FACTORS TO BE CONSIDERED WHILE DESIGNING A MILLING FIXTURE

Type of milling machine used horizontal, vertical or universal type.

Milling machine and accessories data like, dimensions of machine table, its travel and position in 3 directions with respect to column and spindle, centre – to- centre distance and dimensions of T slots etc.

Clamping elements and supporting body should be rigid and sufficient to withstand shock loads without deforming the job.

Work piece area to be milled, should always be located within the area termined by supporting points, or the supporting points should be under the area to be milled.

Supporting and locating elements should be rigid as the cutting forces are directed against them.

Centre setting block hardened and ground, should be provided in the fixture to set the cutter properly in relation to the locating surfaces of the job.

Provide lifting points for fixture handling and access for loading and locating the part on to the fixture.

The projecting parts of clamping studs and nuts should be kept to minimize height over the milled surface.

TOOL ROOM

It is well known to everybody that tool room is the heart of the factory as all development, inspection, tooling, maintenance, and production activities depend on it. Tool room functions just like a human heart, it gives fresh tooling, inspection aids and many other helps to productive body to function well.

HOW TOOL ROOM WORKS?

As soon as tool design completes design of any jig, fixture, tooling or inspection gauge, it is sent for manufacturing to tool room with tool room number. This number is then included a pre-planned program for the month.

After receiving the drawing, tool room people fill the requirement of the raw materials.

As soon as the raw materials come, it is inspected in stores and then it is sent to tool room for further operation.

Meanwhile for any tooling, jigs or fixtures, tool room decides the processing (or in simple words sequence of operations)

As soon as the processing is finalized, the job is sent on different machines for various operations.

Different companies have different working operations and various operating function depending upon the factory’s tooling system, but working principle is same to all organizations.