D8NDiodePosts

We're Moving in to a New Space

Joshua Stults — Sat, 31 May 2014 21:29:00 +0000

Much Larger New Space for Dayton Diode

Come help use move:

The new space is at the end of the same building we've always been in. About twice as much square footage as our old space.

Prusa Mendel RepRap Frame Vertex Topology Optimization Using ToPy

Joshua Stults — Sat, 07 Dec 2013 16:02:00 +0000

This post is about a free/open-source work-flow for topology optimization. At the last monthly meeting I showed a bunch of folks a neat real-time topology optimization app that is great for sketching out concepts quickly. That app has a good user interface for defining loads, boundary conditions, and solid/void regions. The thing that makes it good for getting a concept quickly fleshed out is that the optimization happens in real-time as you change the loads and constraints. One drawback with that app is that it is not really free software (no source available), so the opportunity for tinkering and learning is limited. ToPy, on the other hand, is free software, and it is well documented with a thesis and available source code. However, the user interface is a text file so it is a bit more work to set up a problem, and for this small 2-D problem it takes 90 iterations at about 15 seconds per iteration to converge to a final part (it may be possible to improve this by changing the solution method it uses for 2D problems).

Motivation

I found this interesting discussion about optimizing infill for 3D printing a few weeks ago. I think the drawback to the sort of method put forward in that post by Gary Hodgson is related to this point he makes at the end of the post:

The main obstacles are computational intensity and ensuring the resulting model has sufficient strength, regardless of its form.

There is no way for an "infill algorithm" to be smart enough to do this without additional information about the design intent. By taking a topology optimization approach, that design intent is captured in the definition of the loads and boundary conditions that are input (which is mentioned in the thread). People recognize that topology optimization is a killer enabling app for additive manufacturing, and the barriers to entry are coming down:

While there is still some cost associated with adopting topology optimization, not least of which is a software license starting around $6000, a process that used to be “by PhDs for PhDs” and almost prohibitive to manufacture can now be incorporated into designs after only four hours of training and access to additive manufacturing.

The good thing about ToPy is that there is no licensing cost, so it is very accessible from that perspective. However, I did spend considerably more than 4 hours reading William Hunter's thesis, and digging into the code enough to understand it, YMMV.

There is some interesting related development along the lines of making RepRap parts faster/easier to print by making them hollow and filling with epoxy (or not). A couple examples that I thought were interesting:

Mendel Frame Vertex - Aced based on "thin shell" design approach
Hollow Mini-Mendel
Prusa Mendel Frame Vertex which was the part for my point of departure (specifically the dxf and scad files) for the proof-of-concept in this post

Work Flow

Here's an outline of the work-flow I used:

Define optimization problem: ToPy input deck (*.tpd, ToPy Problem Definition file) containing the type of problem (2D, 3D, stiffness/heat conduction), domain size, boundary conditions and any solid/void regions. I used Gimp to help me do this because I can define multiple layers for solid and void areas and view these simultaneously or one at a time. I export these layers to separate pngs and then process with a simple python script to generate text suitable for inclusion in a tpd file.
Run the optimization problem: python optimise.py [name of your file].tpd
Import the output of the optimization (*.png in the 2-D case) into Inkscape, trace the bitmap to create a Path, and export as dxf. I followed the recipe given here.
Extrude the profile in the dxf file in OpenSCAD and perform additional operations to make the complete part. Here's the scad file.
Export the part as an stl from OpenSCAD.
Slice and Print! Lately I've been using Cura for this, and have been pretty happy with the speed and results.

Here is the resulting stl:

One of the main stumbling blocks in this work-flow is in step 1. Defining an input deck for ToPy is a very manual affair. I used Gimp and a simple Python script to define the solid void regions. This works OK for 2D problems, but becomes cumbersome in 3-D. Also, the number of nodes is one greater in each dimension than the number of elements. The solid and void regions are defined element-wise, and the boundary conditions and loads are defined node-wise. I haven't found a clean way to handle this difference in an integrated way yet. My current approach consists of manually counting pixels in Gimp and then calculating the appropriate offset to find the right node numbers according to the ToPy convention. Not ideal. It makes experimenting (fiddling with resolution especially) pretty painful.

The solidThinking folks have some interesting demo videos showing a CAD-like GUI for defining a topology optimization problem. A pure graphical approach isn't really required, it would be great to be able to use OpenSCAD to define the problem instead of counting pixels in Gimp. I haven't figured out how to do that yet.

Future Work

The proof-of-concept frame vertex shown in this post is not a formally designed and validated part. No actual analysis was used in deciding what volume fraction (amount of material, comparable to "infill density") to use, or what the relative magnitudes and locations of the loads and boundary conditions should be. I just took a look at a picture of an assembled Prusa Mendel to get an idea of where the loads would be acting. The part demonstrated here is the vertex with a foot for the lower portion of the frame. A different part (different loads/boundary conditions) is needed for the "no foot" vertex used at the top of the frame.

Moving away from this particular application to open source topology optimization more broadly: there is a good amount of room for improvement in the user interface. Being able to use a CAD-like tool to define the design domain, boundary conditions, and solid/void regions would be a huge improvement that would lower the amount of work it takes to set-up a problem. In addition, ToPy can currently handle a single "load case", but multiple load cases are probably needed to design a "robust" part for many applications. Extending the software to handle multiple load cases would be a useful improvement.

Optimizing material layout in a single part is an interesting marginal improvement, but it would be better to think bigger: what about optimizing the layout of an entire RepRap frame? Interfaces to motors and electronics could be defined by suitable solid/void regions and boundary conditions. Improving the stiffness of the machines seems to be the direction that development is taking (e.g. Prusa Mendel i2 --> i3), and this is a tool that would be suitable for helping that effort with some improvements to lower the amount of "touch labor" in problem definition.

Retail 3D Printing Comes to Dayton

Joshua Stults — Mon, 11 Nov 2013 17:46:00 +0000

Dayton now has a retail 3D printing location. Rapid Directions opened their second retail 3D printing location here on North Dixie drive. Needless to say I was pretty excited to stop by and check it out (and pick up a spool of ABS since we're running low in the space).

Makerbot 2X

They have a variety of printers on display actively cranking out parts. One of the most interesting things they have set up is a 3D scanning room. Step into the photo booth of the future... today! They are offering a variety of items that are customized by using your personal scan, or you can simply get your own little statuette of yourself or loved ones.

3D Scan Room

Customized 3D-Scan Items

They also have a "Creation Station" with modeling and slicing software available to try out. Since many of the printers they sell come with their own custom software you are able to try it out before you buy.

As you would expect from these commercial printers, the quality of parts is pretty impressive. I like our little printrbot, but the Afinia they had was making some awfully nice parts!

Afinia 3D Printer

Dayton Engineering Sciences Symposium 2013 Keynote

Joshua Stults — Tue, 29 Oct 2013 15:14:00 +0000

A batch of 3D-printed Ti parts

I went to the Dayton Engineering Sciences Symposium today. Greg Morris of GE Aviation gave the keynote address on additive manufacturing. It was a broad, high-level discussion of additive manufacturing in general, and gave an overview of the many different technologies available today from plastics, to ceramics to metals. Of course, given his background, he focused in on the additive metal manufacturing capabilities and applications.

He mentioned several times that the real key to getting value out of additive manufacturing was to design with the process in mind. It would be very rare that it would make economic sense to take a part that is traditionally fabricated and just print it. What makes much more sense is to redesign the part so that it is lighter weight, higher performing, or has reduced parts count but would be unproduceable with any other method, and print that. An example he gave was of the reduction in parts count from 20 to 1 for the LEAP Engine fuel nozzle.

Also, for prototype parts that support testing where fatigue life is not so critical 3D printed high pressure turbine blades can save 6 months of lead time and 15% in cost. These printed blades will not have the life of a single-crystal turbine blade, but they only really need to last long enough for the engineers to collect the performance data that feeds back in to the next design iteration.

Another topic he hit on was the "long and expensive path" to full characterization of the material (Cobalt-Chrome) they are using in their fuel nozzle application. This is an area that requires work in good design of experiments techniques to optimize how many tests are needed to reach a given level of confidence. One way to tackle this problem is by finding initial application areas that are more tolerant of risk such as prototype hardware, wind tunnel models, or ancillary hardware like brackets.
As far as future directions for additive manufacturing, he mentioned in passing that there was plenty of misinformation in the press that lead people to have unrealistic expectations about 3D printers in every home producing replacements for consumer goods. He did say that being able to produce repair parts in remote environments was a possible future application, which sounds a lot like the Army program to take mobile fab labs into the field.

Some other high-lights from the symposium from a 3D printing perspective were a presentation from two OSU students on an ultrasonic additive metal process, and some work from a WSU student on topology optimization for hot structures. One of the things I really liked about the work on the ultrasonic additive method was the design of experiments approach they took to characterizing and optimizing the manufacturing process parameters. Despite the popular media hype, he sees huge potential for more applications and more exciting business models built around additive manufacturing.

In line with the point Greg Morris made about designing for the process, many of the existing topology optimization methods are ideal design tools to really take full advantage of the capabilities that additive processes bring. Expanding these methods to include more physics beyond elastic compliance, such as heat transfer and thermal growth, is an important research area.

Dayton Engineering Sciences Symposium 2013

Joshua Stults — Sat, 12 Oct 2013 05:00:00 +0000

The 9th Annual Dayton Engineering Sciences Symposium (DESS 2013) is coming up on 29 Oct 2013. The theme this year is 3-D printing, and the keynote speaker is Greg Morris of GE (Morris Technologies).

Sponsored by the American Society of Mechanical Engineers (ASME) Dayton Section, the symposium is designed to facilitate communication between members of the regional technical community, as well as to provide a forum for students (both undergraduate & graduate), engineers, and researchers to present their work. The symposium program will include several parallel sessions in the morning and afternoon, addressing Applied Engineering; Biomechanics; Controls Science; Design & Optimization; Electronics & Sensors; Engineering Education; Fluid Mechanics; Industrial & Human Factors; Materials & Processing; Nanotechnology; Power, Propulsion, & Energy Systems; Structures & Solid Mechanics; Thermal Sciences; Engineering Innovation; and Undergraduate Design Projects. The symposium will also include a luncheon, keynote address, and poster session.

Here are some of the interesting titles on 3-D printing presentations (list of current abstracts) that caught my eye:

Internet Drone Based on Additive Manufacturing and the Raspberry Pi
Design of Thermal Structures using Topology Optimization
Statically Equivalent Serial Chain Modeling With Kinect and Wii Balance Board
A Conceptual Template for Product Technology Transfer Visualization Using 3D Printing
3D Printing of Smart Structures using Ultrasonic Additive Manufacturing
Control of Ceramic Microstructures Using ‘Drop on Demand’ Piezoelectric-Driven Inkjet Fabrication
Integrated Control of Beam-Based Additive Manufacturing Microstructure of IN 718 by Linking Design Parameters and Grain Growth
Development of Microstructure-Property Relationships via Electron Beam-Based Manufacturing

Looks like lots of neat 3-D printing research going on right here in Dayton!

The Future of Additive Manufacturing

Joshua Stults — Mon, 07 Oct 2013 20:57:00 +0000

GE put on this panel recently to discuss additive manufacturing. If you've got an hour to burn, the whole thing is worth a listen. I think Terry Wohler makes some of the most interesting points.

Early on (around the 10 min point IIRC), he makes a good point about the difference in quality you should reasonably expect for machines that vary in price by a factor of 1000. Our $500 Printrbot is not going to make parts as nice or as large as the half-million professional-grade machine. That is a simple fact. Despite this, I would still argue that our Printrbot is a pretty darn cool capability!

Here's a section I transcribed from later in the video (about the half hour mark) where Wohler is talking about early adopters of additive manufacturing (I took the liberty of adding my links and emphasis to his words).

.. low volume, high complexity, high value parts. [...] If you simply take a design that you have manufactured the old way, whether it's CNC milling or injection molding, die casting, blow modling, whatever process. Just take that design and try to manufacture it with additive manufacturing is possible, but it's difficult from an economic stand-point to make it worth it. The business case just isn't there. You have to in most cases re-design, just as GE Aviation has done, taken about 20 parts and consolidated them into 1 in the CAD software. So to through part consolidation, methods of [...] topology optimization where you can mathematically decide where to put material to optimize the strength to weight ratio. To use mesh and lattic structures, and this part consolidation concept collectively that's where we can see some very big gains. However we don't necessarily have the tools, the tools are very crude, and the work-force out there are still designing for different manufacturing processes. So there's a lot of work that needs to be done, both on the CAD tools and methods of topology optimization and 'light-weighting' as well as creating awareness and understanding the strengths and limitations of these processes...

There is a lot to digest in that passage, but I have to agree that there is a huge opportunity for improvement in the area of design software suited to additive manufacturing. There are open source options available for the classic minimum compliance problem, and these use basically the same procedure that more sophisticated and integrated options such as Altair Optistruct use (SIMP or variations thereof).

They talk about "the Maker movement" starting at about 45 minutes in. One of the panelists predicts that multi-material printers will be down at the $500 level (no date given on the prediction though). They expect that "innovation" will be coming from many sources, not just large companies, such as individuals, small start-ups and Universities. GE's GrabCAD contest seems to be an effort along this "crowd-sourced innovation" line that is often associated with 3-D printing. Wohlers mentions that along with the hobbyist ("very low end of the cost spectrum") opportunities for community collaboration there is also some good opportunity for collaborative standards development through bodies like ASTM. He estimates that there are 35k under-$5k machines sold last year (compared to roughly 7k of the industrial grade machines). He argues that these low-end machines are great for people to learn on through first-hand experience, but the average house-hold will probably not be using these machines to make stuff at home.

One of the neat things brought up at the end of the video was a 3-D printed brushless DC motor done by the Keck Center.

Open Source Plug Heard on NPR

Joshua Stults — Sat, 07 Sep 2013 09:06:00 +0000

I was surprised this past week to hear a plug for using open source software on the morning news program on NPR. The piece was about NSA code cracking and encryption circumvention, sorry I can't find a link now. Bruce Schneier also suggests using open source software in his recent essays:

The NSA deals with any encrypted data it encounters more by subverting the underlying cryptography than by leveraging any secret mathematical breakthroughs. [...] As was revealed today, the NSA also works with security product vendors to ensure that commercial encryption products are broken in secret ways that only it knows about. We know this has happened historically: CryptoAG and Lotus Notes are the most public examples, and there is evidence of a back door in Windows. [...] Closed-source software is easier for the NSA to backdoor than open-source software.

Here are Bruce Schneier's 5 security tips:

Hide in the network. Implement hidden services. Use Tor to anonymize yourself.
Encrypt your communications. Use TLS. Use IPsec.
Assume that while your computer can be compromised, it would take work and risk on the part of the NSA – so it probably isn't. If you have something really important, use an air gap.
Be suspicious of commercial encryption software, especially from large vendors. My guess is that most encryption products from large US companies have NSA-friendly back doors, and many foreign ones probably do as well.
Try to use public-domain encryption that has to be compatible with other implementations. For example, it's harder for the NSA to backdoor TLS than BitLocker, because any vendor's TLS has to be compatible with every other vendor's TLS, while BitLocker only has to be compatible with itself, giving the NSA a lot more freedom to make changes.

Here are some bits of software he uses:

Stay safe out there on those interwebs!

LIfe Imitates Art: Authentise vs Makers

Joshua Stults — Fri, 30 Aug 2013 11:06:00 +0000

Download Makers for Free (txt)

A recent Maker Pro Newsletter links to an article on MIT Technology Review about copy protection for 3-D printing. The whole thing smells a bit like a joke. The basic idea (which is broken) behind Authentise is to send gcode to a user's machine just-in-time, so that they never have a full model of the part they are printing. It sounds similar to the path the villian in Doctorow's Maker story does to monetize 3-D printing:

And there, in the pit of despair, at the bottom of his downward arc, Sammy was hit by a bolt of inspiration:
Put Disney into people's living rooms! Put printers into their homes that decorated a corner of their rooms with a replica of a different ride every day. You could put it on a coffee table, or scale it up to fill your basement rumpus-room. You could have a magic room that was a piece of the park, a souvenir that never let go of Disney, there in your home. The people who were willing to spend a fortune on printed skull finials would cream for this! It would be like actually living there, in the park. It would be Imagineering Eye for the Fan Guy.

He could think of a hundred ways to turn this into money. Give away the printers and sell subscriptions to the refresh. Sell the printers and give away the refreshes. Charge sponsors to modify the plans and target different product placements to different users. The possibilities were endless. Best of all, it would extend the reach of Disney Parks further than the stupid ride could ever go -- it would be there, on the coffee table, in the rumpus room, in your school gym or at your summer place.
He loved it. Loved it! He actually laughed aloud. What a *great* idea! Sure he was in trouble -- big trouble. But if he could get this thing going -- and it would go, *fast* -- then Hackelberg would get his back. The lawyer didn't give a shit if Sammy lived or died, but he would do anything to protect the company's interests.
Sure, no one from Imagineering had been willing to help him design new rides. They all had all the new ride design projects they could use. Audience research too. But this was new, *new new*, not old new, and new was always appealing to a certain kind of novelty junkie in Imagineering. He'd find help for this, and then he'd pull together a business-plan, and a timeline, and a critical path, and he'd start executing. He wanted a prototype out the door in a week. Christ, it couldn't be that hard -- those Wal-Mart ride assholes had published the full schematics for their toys already. He could just rip them off. Turnabout is fair play, after all.

This comparison to Netflix in that article is interesting,

Authentise’s approach is similar to the way Netflix sends viewers at home a stream of video frames only as their computer needs them to play a movie. Instructions that tell a 3-D printer about how to squirt out material are sent to it only as it needs them. Once the process is done, the instructions are instantly discarded, leaving a completed print but no full digital representation of its design.

But as a commenter points out, the analogy is not very good,

Quite right...to copy real-time digital video, you've got hundreds of megabytes of uncompressed, unencrypted data per second to deal with, and even that's not impossible to capture. Capturing the actions of a 3D printer...a few stepper motors operating at audio frequencies, and extruder temperature? A piece of cake in comparison. cjameshuff2 comment

3D Printing Price Comparison Services

Joshua Stults — Tue, 20 Aug 2013 06:00:00 +0000

Mini-Estes Rocket printed by Fabbr

One of the recent MakerPro Newsletters had some coverage of a couple 3D printing price comparison or service discovery sites. For members and friends of Dayton Diode, using our printrbot, sweet talking Rocket to use his Prusa, or buying a part from our local 3d print friends at Fabbr is still probably your best bet towards a plastic part on the quick and on the cheap.
For more emerging options...

MakeXYZ: get your designs printed by a maker or print shop in your neighborhood
3D Printing Price Check: Compare 3D printing prices across 140 materials from eight vendors (and counting)
SupplyBetter: Comparison shopping for 3D printing. Know your options. Get cheaper parts.

For larger orders there is RedEye on Demand, and while not 3D printing per se, sites like FirstCutCNC (3-axis machining) and MFG.com (many types of suppliers) are also options to get your parts fabricated.

I tried this part that I used as a test part on Shapeways. I was not able to load the part on the 3dprintingpricecheck site (using an up to date Firefox on Fedora). I did successfully load it to the SupplyBetter site (which also involves creating a user account). This site actually goes out and gets quotes from suppliers, so getting the price is not instantaneous like Shapeways or RedEye. I do recognize some local suppliers in the profiles on SupplyBetter: MorrisTech and Bastech. Any others?