Manufacturing guy-at-large.

Filtering by Tag: 3dprinting

Stem prints

Added on by Spencer Wright.

Almost a year ago, I posted a rendering of my printed bike stem on my blog here. Now:

These parts were printed by my friends at Playground Global on their 3D Systems DMP320 in titanium 6/4. Like the titanium parts I've had printed (and written about extensively) in the past, these are done via laser metal powder bed fusion - the generic name that often gets referred to as "DMLS". These parts were, of course, designed in nTopology Element Pro; you can see more of my design process here

As loyal readers will know, I've put a lot of time into using Abaqus to predict these parts' mechanical properties; more on that in the near future. For the time being, the goal with this print was to test the manufacturing process - and use any lessons here to guide future design iterations. As you'd imagine, there's a *lot* that goes into printing a part that has ~45,000 beams; establishing manufacturing parameters was a good way to filter out nonviable design strategies.

It'll take a bit more work to characterize the as-built design fully, but at first inspection it seems to have been a total success. I was careful to keep most of the beams' orientations at a high angles, thicknesses above .45 mm, and lengths below 3 mm; the result is a structure that's almost completely self supporting.

At this point, the part has been roughly cleaned up and bead blasted to remove any surface discoloration. The next step is to tap the holes, clean up the clamp surfaces, and mock the entire assembly up.

More soon :)

See also: DMLS lattice sample prints, where I describe the part's design a bit more.

Changing the world around us

Added on by Spencer Wright.

Every few weeks, someone asks me what I think the future of 3D printing is - whether it's going to really change the way things are made.  My response is to ask if the name "PCC" means anything to them - a question that almost always elicits a blank stare.

PCC is a manufacturer of castings and forgings, primarily for aerospace and power generation. They live mostly outside of the public eye; to most folks, casting pretty much begins and ends with old-school iron cookware, and few stop to consider how improvements in casting techniques might have changed the cost and availability of electricity and air travel over the past half century.

And yet they have had a big impact. PCC sells about $10B worth of products every year, supplying critical propulsion and airframe components to companies like Boeing and Airbus. Many of these parts allow airplanes to reduce weight and improve engine efficiency, helping along significant improvements in fuel economy per seat. And so, in 2016, Precision Castparts Corp was acquired by Berkshire Hathaway for $37.2B. It's the largest amount that Warren Buffett has ever spent on an acquisition. 

I bring this up to say: The tech press may maintain their interest in 3D printing, or they may not. It's possible that, in a few years, I'll walk into a retail shop and have made-to-fit parts printed for me on demand. It's possible that manufacturing will become distributed; that supply chains will spin up and down at a moment's notice; that computers will engineer products from start to finish.

But there are many other, less sexy ways to change the world around us. And we'd all be well off if some 3D printing method achieved one of those instead.

Standards Orgs

Added on by Spencer Wright.

This week, I participated in ASME's Technology Advisory Panel on Additive Manufacturing. This is the third standards body that I've gotten involved with in the past year or so (I also sit on ASTM F42, and represent nTopology at the 3MF Consortium), and I wanted to post a few thoughts about standards development for anyone who's curious about them or interested in being involved in similar work.

  • Most standards bodies were formed out of some deep-seeded industry need: A spate of high profile product failures, a growing sense of frustration amongst customers, etc. Standards are the industry's way of improving their overall product quality, or their public image, or their relationship with key customers (the US military especially).
  • Standards orgs make money partly by selling standards and partly by enforcing them and certifying products/companies that comply. As an independent product developer, that can be frustrating (I wrote about this years ago); spending a few hundred dollars to find out how your part will be tested can often seem like a shitty alternative to more... open approaches. On the other hand, most standards orgs are all-volunteer and nonprofit. 
  • The fun thing about standards development is that if you care, they'll (for the most part) take you seriously. It doesn't particularly matter if you're officially "in the industry," and you certainly don't need to work at a huge company or have any specific set of interests in the matter at hand. When I joined F42 (ASTM's subcommittee on additive manufacturing), I was working at a consultancy whose primary clients were in marketing and HR. I was working on AM in my free time, and like any intelligent person had developed thoughts on issues the industry was facing; ASTM took me in like any other.
  • As something of an outsider myself (in a strict sense, I am not an engineer per se), the experience of being on a more or less level playing field with folks who have spent their careers at global engineering & manufacturing companies is really something. I get a lot out of hearing their takes on the industry, and am glad that someone (me) is there to provide the perspective of a generalist working across disciplines. Standards orgs tend to be places with a high degree of empathy, and it's a pleasure to talk openly - from competitor to competitor, supplier to customer - about how to push an industry in a better direction.

DMLS lattice sample prints

Added on by Spencer Wright.

I'm *very* excited about these parts from C&A:

These parts were printed in titanium 6/4 by C&A Tool in Churubusco, Indiana; they were designed in nTopology Element. 

This is a pure lattice structure - the entire geometry is designed as beams and nodes, with no explicitly defined solid regions. The beam lengths are on the order of 2-3 mm; their thicknesses range between .45 mm and 1.1 mm. In some areas (for instance, the bolt holes) this results in a fully solid part, but the transition from lattice to solid is continuous rather than discrete. The result is a structure that's solid where it needs to be and sparse elsewhere, with no stress risers where solid and lattice meet.

The parts are, of course, sample regions of the bike stem that I've been working on for some time now. The intent of the samples was to prove the printability of the structure and identify any potential difficulties. The results were overwhelmingly positive: With the exception of a few small flaws, the parts printed very well, and I believe the problematic areas can be addressed in the design pretty easily.

Given the good quality of the sample prints, I'm planning on printing a full version of the part soon. I'm also experimenting with a few other design variations (intended for a variety of different metal AM machines), and am running them through a beam sizing optimization process with Abaqus and Tosca in order to reduce mass and decrease strain energy. More on these soon :)


Thanks to Rich Stephenson for his ongoing help on this project - and for continuing to educate me on the metal AM industry.

EBM and chemical surface finishing

Added on by Spencer Wright.

As I've written here before, the field of high performance surface finishes is fascinating - and complex. Surface finish plays a big role in the mechanical and aerodynamic properties of a part, and (in the case of consumer products) it can have a huge effect on marketability too. And so, as I've gone through the process of developing my titanium 3D printed bicycle seatpost, I've been conscious to evaluate many different surface finishing options to find a manufacturing process chain that's both effective and economical.

And so, this past spring, I reached out to Dr. Agustin Diaz to see how REM Surface Engineering could help my parts.

For a bit of context, allow me to quote myself (from EBM surface finishes and MMP):

The part's nomenclature

The part in question is the head of a seatpost assembly for high end road bikes. The part itself is small - about 70mm tall and with a 35mm square footprint. As built, it's just 32g of titanium 6/4. Add in a piece of carbon fiber tubing (88g for a 300mm length) and some rail clamp hardware (50g), and the entire seatpost assembly should be in the 175g range - on par with the lightest seatposts on the market today.

As a product manager who's ultimately optimizing for commercial viability, I had three questions going into this process:

  1. How do the costs of the different manufacturing process chains compare? 
  2. How do the resulting parts compare functionally, i.e. in destructive testing?
  3. Functionality being equal, how do the aesthetics (and hence desirability) of the parts compare?

Towards these ends, Dr. Diaz and REM finished three parts for me:

The parts were printed in titanium 6/4 on an Arcam A2X by Addaero Manufacturing. They were then HIP'd (hot isostatic pressing is a whole other area of interest - more on it soon, I hope) before being treated by REM's isotropic superfinishing process.

The results are very interesting, and contrast in many ways with MicroTek's MMP process. REM ISF is a chemical accelerated vibratory finishing process. In it, parts are placed in vibratory finishers with a nonabrasive media and a chemical activating agent. The chemical agents are selected by the part's composition: Different metal alloys will react to different chemicals. The media, on the other hand, is selected depending on the part's geometry: Parts with small features will require smaller media, etc.

As with any vibratory finishing process, then, REM tunes the frequency and amplitude of the machine to adjust the aggressiveness of material removal. The media chambers in these machines are shaped like toruses, and parts take a rotating helical path around them as they vibrate. Adjusting the frequency and amplitude of the vibration affects that helical path, and REM tunes the rolling angle to produce the result that's needed. "It's an art and a science," Dr. Dia zaddtold me.

REM finished three parts for me, in two slightly different design variations. The first part went through their Extreme ISF process - a quick treatment that removes excess powder and some higher-order roughness. The second two parts went through Extreme ISF *and* an additional ISF treatment, removing .020" (about .5 mm) and producing a much smoother surface. In order to compensate for the material removal, one of the Extreme ISF + ISF parts was printed with .020" of  extra stock on all of its surfaces (if you look closely, you can see the additional stock as a stair-stepping effect on the inside of the skirt edge). The results are below - click on the photos to enlarge.

Incidentally, I found REM's process nomenclature a bit confusing at first. As described above, all of these processes include some chemical agent and some media. The difference in the different processes has to do with the balance of those two factors: Extreme ISF uses aggressive chemistry but relatively little media interaction, whereas ISF is a longer process with less aggressive chemistry and more media interaction. REM also offers a Rapid ISF process, which is to ISF much as a lathe is to a milling machine. In it, the parts are fixtured and then moved through the chemical/media mixture. It's a much faster process, but one which requires more tooling and setup and hence is reserved for high volume parts.

The surface character of the REM parts differs significantly from the parts that I had MMP'd. ISF interacts with the full surface of the part, with the result being that both peaks and valleys are rounded out. Note that the color scale in the images below are not constant; click on the images to see the color scale key.

The roughness values for the two methods are also quite different. The key metrics are below; full roughness profiles & filter data are here for Untreated, Extreme ISF, and Extreme ISF + ISF parts (thanks to REM).

Ra - Roughness average

All values in µm. Evaluation length = .5"

Rq - Roughness, root mean square

All values in µm. Evaluation length = .5"

Rsk - Roughness skewness

All values in µm. Evaluation length = .5"

Rt - Roughness total

All values in µm. Evaluation length = .5"

As with most things, the numbers above both a) capture interesting differences between these five finishing methods, and b) are abstractions which ultimately fail to capture the entirety of the physical parts. Such is the nature of data; in and of itself, it's not particularly insightful.

As I've described previously (and above), my interests are functional, aesthetic, and economical. The latter two of these sit more or less in balance, but the former is bound by the composition & arrangement of matter. To that point, Agustin referred me to a paper by Kwai Chan called "Characterization and analysis of surface notches on Ti-alloy plates fabricated by additive manufacturing techniques," which shows a correlation between notch depth and a shortened fatigue life in EBM parts. To quote:

The presence of surface notches is likely to promote crack initiation and reduce the fatigue performance of LBM and EBM materials. Since the depths of the surface notches correspond to the maximum valley depths on the surface, fatigue life of the various Ti–6Al-4V materials is expected to decrease with increasing maximum Rvm values...
To improve fatigue performance, the surface notches on the EBM and LBM materials must be removed by machining.

Of course, those last two words - "by machining" kind of begs the core question that I'm asking here. To wit, see the Rvm numbers from REM:

Rvm - Maximum valley depth

All values in μm. Evaluation length = .5".

The goal, here, is to improve fatigue life - and avoid the fate that my last parts met during testing. My hope - and one that's balanced by my lingering concerns about my glue joint design - is that the much reduced Rvm numbers here will help significantly.

More soon.

New desk

Added on by Spencer Wright.

About a year ago, when I refurbished an old Wilton vise for my home office, I noted that I intended to build myself a new desk as well. Like many projects, I ended up moving a bit more slowly on that than I expected - which in this case was convenient, as it allowed me to settle into a new house and think about what my work will look like over the next few years. And so last weekend I opened up Inventor and started putzing with my desk design again:

Like so many of the things I've designed in the past few years, the idea here is to use modern materials & assembly methods, and make something that is highly functional and also aesthetically pleasing. The tabletop will be lab-grade phenolic resin - a material that is strong, seamless, and durable to impact, scratching, and liquids. The legs will be monofilament wound carbon fiber tubing, which I'll probably apply a clear sealer to. And the whole structure will be held together with - you guessed it - 3D printed node connectors.

The exact dimensions and assembly methods are still TBD; I'm also considering a few details for attaching/mounting things (my vise, my monitor stand, lighting, the power strip that I like). I'm also still considering integrating the desk with the 7-drawer tool cabinet that I have, although at this point it's more likely that they just sit side-by-side.

Timeline on this moving forward is... medium? But hoping to show some progress soon :)

Notes on Arcam and SLM

Added on by Spencer Wright.

Yesterday, GE announced that they had put in bids to acquire both Arcam and SLM for a combined total of $1.4B. This move poses some interesting questions about the next few years in industrial AM, and will no doubt have a big impact on both the companies involved and their customers and competitors. I don't have any privileged insight into any of these companies' decision making process, but I have a longstanding interest in the industry and what they're working on. Here are a few observations & questions that occurred to me about the deals and their impact.

Background

In 2012, GE Aviation made three large acquisitions in industrial AM. The first was the combined purchase of Morris Technologies and Rapid Quality Manufacturing, two sister companies based in Cincinnati who had already been a big supplier to GE Aviation (terms of the deal were not disclosed). Later that year, they bought Avio Aero, and Italian parts supplier, for $4.3B. These two purchases showed an interesting balance in technologies. While Morris and Avio had very similar business models (both were job shops that produced parts for GE Aviation and other business units; Avio also produces parts by traditional manufacturing methods), they focused on different additive technologies: Morris on laser, and Avio on EBM.

I've written about the difference between laser and EBM in the past, but a few points here:

  • The fuel nozzle that GE is so famous for printing is made by laser in Auburn, Alabama on EOS machines. I believe that their (lesser known) T25 temperature sensor is made on the same machines.
  • The laser (Note: I'm using "laser" here to refer to processes that are variously called DMLM, SLM, DMLS, lasercusing, and the generic "laser metal powder bed fusion." Note also that SLM can be used to refer both to the printing process AND to the machine manufacturer that GE just acquired.) machine market has a number of providers: Aside from EOS and SLM (the two machine manufacturers that GE is most known for using) there's Renishaw, Concept Laser, Additive Industries, 3D Systems, and a variety of Chinese entrants.
  • While GE Aviation has tended towards EOS machines (see the video above), GE Power & Water uses machines made by SLM in their Greenville, SC plant (Note: Here I'm drawing from an AMUG 2015 and other industry sources; sorry for the lack of a hyperlink reference).
  • Arcam sits apart from these: it's currently the only company making machines for EBM (electron beam melting, or "electron beam metal powder bed fusion" if you're picky).
  • Avio Aero has done some really interesting things with EBM since the GE acquisition. Perhaps most notably, last year they printed low pressure turbine blades out of titanium aluminide, an intermetallic alloy. TiAl has excellent mechanical properties at high temperatures (an important feature of any part that's in the hot stage of a jet engine), and is traditionally cast by companies like Precision Castparts Corp (PCC). Printing in TiAl brings advantages but is extremely difficult due to the material's tendency to fracture. Printing TiAl could be a big deal as GE ramps up production of TiAl blades for the GEnx engine, and it was very interesting to note that after the successful prints, Avio bought an additional ten Arcam systems - the largest purchase that Arcam had ever accepted.

So: GE already had a strong portfolio in additive. What are the implications of the Arcam and SLM acquisitions, and how will this impact the industry?

A full stack, in-house

The most interesting part of the acquisition to me is the fact that GE will now be able to in-house the entire industrial AM supply chain (minus software; more on that below). Previously, they were focused primarily on basic research and applications development (Morris, Avio, CATA, and the Niskayuna Global Research Center) and serial part production (Auburn, Greenville, and Avio). Now, they'll own not one but two machine manufacturers - allowing them to push upstream and make a more direct impact on the development of the additive industry.

But perhaps more importantly, GE gains both powder production (through AP&C, the Canadian powder supplier that Arcam acquired for CAD 35MM in 2014) and final parts manufacturing (through DiSanto, the medical implants manufacturer that Arcam acquired for $18.5M later the same year). When Morris was acquired, they shut down their sales organization and focused on printing parts for internal GE customers. DiSanto is a very different business, though, and I wonder whether it might make sense as part of GE's healthcare unit - with its traditional focus on medical imaging and healthcare IT.

AP&C is a bit of a different beast. They manufacture the raw materials for not only powder bed fusion but also MIM, HIP, and other powder metallurgy applications. Their website advertises commercially pure titanium and ti64, but Arcam also markets cobalt-chrome - which both the fuel nozzle and the T25 sensor housing are made of. I'll be very curious to see whether AP&C continues selling powders to the public, or if they focus on internal use.

Improving - and selling - manufacturing machines

Separate and apart from the implications to GE's internal operations, I'm particularly interested in the way that GE's involvement at these new levels of the tech stack will affect how the industry matures. Try though they may, it's difficult for a company whose bottom line depends on selling machines (as opposed to, say, selling machines AND printing parts, or selling machines AND developing manufacturing software) to truly impact the end-to-end engineering process much. And while GE has been at the forefront of additive research (and, no doubt, collaborates very closely with both their hardware and software providers), I'm hopeful that having them at the helm will push both EBM and laser powder bed fusion forward in a cohesive way. 

Some might suggest that keeping expertise in house would be the strategic choice here, but I disagree. Powder bed fusion today suffers from both a lack of talent (easiest to change by expanding the number of use cases for the process, many of which GE ultimately is not going to compete on) and a lack of process predictability and reliability. GE has more knowledge about improving AM part yield than just about anyone else in the world, but that doesn't mean that there aren't other approaches that they're not trying. Inasmuch as sharing whatever process improvements they come up with will encourage others to try their own approaches, I hope that GE does just that. And they have in the past: through their involvement with standards and industry organizations like America Makes, 3MF, and ASTM F42; through their participation in sessions at AMUG and RAPID, and through their open innovation work (some of which I worked on while at Undercurrent) with GrabCAD and NineSigma.

My hope would be that GE continues to market and improve both SLM and Arcam machines. The latter is particularly dear to me, as EBM equipment isn't currently made by anyone else (and because I've had many parts printed on Arcam machines). SLM is a bit different, as the market for laser powder bed fusion is already so rich. But by that same rationale, the potential impact that any updates to SLM's machines would have could be huge, as they would force other players to respond in kind.

Software

I take GE at their word: They want to be a contemporary engineering company, and they believe that contemporary engineering companies need formidable software capabilities. And if they're going to truly make their mark with a software solution, it would be wise to do so in a realm where they know the problems well.

Even before these acquisitions, GE knew the pain points in additive as well as anyone else. Adding a few machine manufacturers, plus a raw materials supplier and a finished parts manufacturer, will only help that along. So my question is this: Why wouldn't GE make a play in additive manufacturing software? This is, after all, the whole subtext behind the Brilliant Factories initiative: GE knows how hard it is to make things, and they can help you make them better.

As you'll know from my previous writing, I'm excited for advances in build processing (see netfabb and Magics), build simulation (see 3DSim and Pan Computing, and research by Wayne King at LLNL), and in-process monitoring & control (see Sigma Labs, plus the product spec sheets for a *lot* of the current class of laser printers). Each of these is extremely hard in itself, and recreating the entire stack would be extraordinarily complex; I don't expect any one company to solve (or even attempt) them all. But whether they build their own solutions or work with external providers to build them, GE will be a huge stakeholder in the next generation of additive manufacturing software. And if they're serious about being a formidable software company, then why wouldn't they take a shot at building it themselves?

Regardless of how these acquisitions shake out, the next year should be interesting. I'm looking forward to it :)

The first 14mm

Added on by Spencer Wright.

This week I got some good news: Researchers at The MTC had begun printing one of my latticed bike stems.

The first 14mm of my latticed bike stem, printed in titanium on an Arcam A2x. The part is upside down (relative to the build orientation) in this photo.

This part was printed in titanium 6/4 on an Arcam A2X. Unfortunately the build failed at 14mm high; on the upside, it appears that the failure was *not* caused by my part. It's a bit early to make any judgments about its feasibility, but I'm pleased to see that these beam diameters (which are between .8mm and 1.8mm) seem to print without support structures. As you can see below, many of them (almost all, in fact) had very low angles relative to the XY plane.

The build orientation of my latticed bike stem.

I'm hoping to have more progress on this soon. Thanks to my friends at The MTC for their help with printing - and with debugging the design!

Seatpost testing post-mortem

Added on by Spencer Wright.

This week I got my seatposts back from testing at EFBE. As you'll recall, these failed ISO 4210-09:2014, 4.5.2. 

The part's nomenclature

Both seatposts failed in essentially the same way: The shoulder straps rotated backwards, breaking the skirt in two locations and cracking both of the side legs as well. The front of the skirt separated completely from the carbon fiber post at the bottom, and the top/front of the seatpost cylinder appears to have slipped upwards (sheared) as well.

The "BLING" part (see this post for details on the difference between the two samples) failed slightly before the as-printed version, at 70,770 cycles. It's a bit hard to tell in the photos, but there are definitely some areas where I didn't have enough glue to form a complete bond. Part of this is operator error (i.e. my fault for not assembling the seatpost well), and part of it is engineer error (i.e. my fault for not designing the seatpost so that it could be assembled by any grease monkey). 

The as-printed part failed a bit later, at 80,904 cycles. Again, close inspection shows that the glueline had many defects.

I take a few lessons from this:

First, it's clear that my assembly design needs to be improved. It's possible that the part still would have failed with a better glue joint, but at this point in my process it's important that I'm able to isolate possible issues - and variations in bond quality makes that *really* hard. I suspect the best approach here is to make the glue cavity captive, such that during assembly the uncured adhesive is forced to fill the full volume between the seatpost head and the carbon fiber post.

This likely means eliminating the windows from the seatpost cylinder. It also means either creating a double lap shear joint (like Robot Bike uses) or making the joint blind on both sides (by capping the end of the carbon post, which I did on this assembly, *and* closing the top of the seatpost cylinder, which I didn't do). 

Second, I should probably be HIPing these parts - at least until I've isolated everything else and determined whether, and how, HIP affects performance.

Third, I'd like to dial in the inner diameters of both the seatpost cylinder and the saddle clamp cylinder. The latter can probably tolerate a bit of play, but the former directly affects the glueline and should probably be controlled more tightly.

On the upside: The failure mode on these parts wouldn't have hurt the rider, whereas failure in the shoulder straps could have been dangerous. In addition, I've got a chance to try this again - with the parts that REM treated for me recently. I won't be able to change the original design at all, but I can at least try to see whether a change in technique can improve the glue joint.

Regardless, it's good to get tested parts back. More soon!


Note: Thanks to Addaero Manufacturing for printing these parts, and to MicroTek Finishing for finishing them!

Seatposts, tested

Added on by Spencer Wright.

Today I got word from EFBE that two of my EBM seatpost had been tested - and failed.

These are the as-printed and the "bling" samples (see this blog post for details); they failed after 80,904 and 70,770 fatigue cycles (at 1230N), respectively. As a result of their failure, I decided to not test the third "fatigue resist" part.

I'll write up a longer description of the results soon, but two thoughts here:

  • These parts were *not* HIP treated - which might possibly have helped their fatigue resistance.
  • It appears that some delamination occurred between the printed parts and the carbon fiber post, which makes me question whether the glueline itself was faulty. If so, it's possible that by improving my glue joint I could have relieved some stress from the printed part. Regardless, I will note that the glueup process was kind of a pain in the ass - and I'd like to redesign that anyway.

As it happens, I have three more of these parts on my desk now. They *were* HIP treated, and I intend to glue one of them up and send it for testing. It won't be a perfect 1:1 test (these parts were treated by REM Surface Engineering, through a different process than MicroTek uses), but the results will be interesting at the least :)

Onwards!

(Another iteration of my) Bike stem

Added on by Spencer Wright.

This.

The lattices here were, obviously, designed in nTopology Element Free (which is free!). I happen to have done the mechanical design in Inventor, but the rendering was done in Fusion 360 (effectively free, and totally capable of doing the mechanical design as well). I separated face groups and remeshed surfaces in MeshMixer (free!), and very well could have done the booleans there too (I used netfabb).

^ I just think that's a bit remarkable.

Anyway, it's ready. Printed part (DMLS titanium) soon.

Seatposts assembled

Added on by Spencer Wright.

Before I send these three seatposts out for testing, a quick update:

The seatpost heads (which I wrote a detailed post on a few months ago) are now glued to carbon fiber posts. I also added a thin carbon fiber disc to the top of each of the posts, so that water can't get into the bike's seat tube. The whole thing was assembled using 3M DP420 epoxy.

These are headed back to EFBE this week, where they'll go through the same ISO test as my seatmast topper was subjected to. More details soon!

EBM surface finishes and MMP

Added on by Spencer Wright.

When I visited MicroTek Finishing, a Cincinnati based precision finishing company, in late 2014, I was intent on printing my seatmast topper with laser powder bed fusion. DMLS's install base is relatively large, making it easy to source vendors and compare pricing. And while their surface finish and dimensional accuracy can leave something to be desired, DMLS parts can be put into service with minimal post processing.

But as I was saying goodbye to Tim Bell (my host at MicroTek) that afternoon, he planted a seed. I should try building my parts in EBM, he said - and see if MicroTek's MMP process could bring the rough parts up to a useable state.

That same day, I asked Dustin and Dave (both of whom I worked with on my seatmast topper) what they thought of the idea. Dave had extensive experience on an Arcam A2, and thought it was definitely worth trying out. Relative to DMLS, EBM is a quick process (for more details on Arcam and EBM, see the Gongkai AM user guide), and a big portion of the cost structure of metal AM parts is the amount of time they take to print. Furthermore, parts can often be stacked many layers high on EBM machines, allowing the fixed costs of running a build to be distributed over a larger number of parts. And while EBM parts do tend to be rough (and have larger minimum feature sizes than DMLS), they also tend to warp and distort less - making the manufacturing plan a bit simpler in that respect.

Shortly after that trip, I reached out to Addaero Manufacturing. I visited them soon after, and then asked if they'd be interested in exploring an EBM->MMP process chain. They were, and provided three identical parts to experiment on.

The part in question is the head of a seatpost assembly for high end road bikes. The part itself is small - about 70mm tall and with a 35mm square footprint. As built, it's just 32g of titanium 6/4. Add in a piece of carbon fiber tubing (88g for a 300mm length) and some rail clamp hardware (50g), and the entire seatpost assembly should be in the 175g range - on par with the lightest seatposts on the market today.

As a product manager who's ultimately optimizing for commercial viability, I had three questions going into this process:

  1. How do the costs of the different manufacturing process chains compare? 
  2. How do the resulting parts compare functionally, i.e. in destructive testing?
  3. Functionality being equal, how do the aesthetics (and hence desirability) of the parts compare?

I'll write more about the second point later; in this post, my primary aim is to introduce MMP and compare the different process chains from a financial and operational standpoint.

Basics of surface texture

As confirmed by a 1990 NIST report titled Surface Finish Metrology Tutorial, "there is a bewildering variety of techniques for measuring surface finish." Moreover, most measurement methods focus only on the primary texture - the roughness itself - and incorporate some method of controlling for waviness and form. From the same report:

The measured profile is a combination of the primary and secondary texture. These distinctions are useful but they are arbitrary in nature and hence, vary with manufacturing process. It has been shown, but not conclusively proven that the functional effects of form error, waviness and roughness are different. Therefore, it has become an accepted practice to exclude waviness before roughness is numerically assessed.

Surface finish is usually measured using the stylus technique:

The most common technique for measuring surface profile makes use of a sharp diamond stylus. The stylus is drawn over an irregular surface at a constant speed to obtain the variation in surface height with horizontal displacement.

The most common surface texture metric is Ra. (For a good, quick, technical description of the varieties of surface texture metrics, see this PDF from Accretech.) Ra measures the average deviation of the profile from the mean line (the related Rq also measures deviation from the mean line, but using a root mean square method), and is used across a variety of industries and manufacturing methods. But it's incapable of describing a number of important aspects of a part. For instance, it's critical (for both aestetic and functional reasons) that my parts have Rsk (skewness) values close to zero - meaning that their surfaces are free from flaws like pits and warts. In other words, I'd take a consistent, brushed surface over one that's highly polished but has a few deep cuts/pits.

I should note, of course, that surface finish is a result of the total manufacturing process chain. If the near net shape part (straight out of the EBM machine) is rough and pitted, then it'll be difficult to ever make it acceptable - and the methods required to do so will vary widely. 

MicroTek and MMP

MicroTek is just one in an international network of companies that perform MMP, which grew out of a Swiss company called BESTinCLASS Industries. The MMP process is closely guarded; neither MicroTek nor BiC disclose enough about the process to really understand how it works. From MicroTek's website:

MMP Technology is a mechanical-physical-catalyst surface treatment applied to items placed inside a processing tank.  MMP technology is truly different from traditional polishing processes because of the way it interacts with the surface being treated.
MMP Technology uses a mechanical cutting process at a very small scale (not an acid attack or any other process that could alter the part's metallurgical properties), meaning it can distinguish between micro-roughness and small features. The process actually maps the surface as a collection of frequencies of roughness, removing first the highest frequencies, then removing progressively lower frequencies.
Unlike other polishing processes, MMP Technology can stop at any point along the way, so now for the first time it is possible to selectively remove only the ranges of roughness that you don't want on the surface, giving you the option of leaving behind lower frequencies of roughness that could be beneficial to the function of the part.

To hear Tim and JT Stone tell it, MicroTek essentially does a Fourier transform on the topography of the part. They analyze the surface finish as the combination of many low and high frequency functions, and begin the MMP process by characterizing those different functions and identifying which ones to remove. Then, by selecting "an appropriate regimen of MMP Technology from the several hundred treatments available," they selectively remove the undesirable aspects of the surface finish - while still preserving the underlying form of the part.

This is worth highlighting: traditionally, polishing is a process whereby a part is eaten away by abrasive media. With each successive step, progressively smaller scratches are made in the part's surface. You're constantly cutting down the peaks of the part, and as a result the form gets smaller and smaller over time. With MMP, you have the flexibility to remove fine frequencies while keeping longer ones - maintaining the original intended shape.

The parts

Addaero printed three identical parts for me. I sent two to MicroTek. They processed one for fatigue resistance, and the other they "made BLING."

(Note that you can click on the photos above to see a larger version.)

MicroTek sent detailed inspection reports with the parts, and the picture they paint is fascinating. MMP reduced both Ra and Rq drastically, and Rt dropped significantly as well. Rsk is a bit of a different story, however: in one of the measurement locations ("Side of leg"), it dropped well into the negative range. You'll recall that the absolute value of skewness is really the issue here; a negative number (indicating pitting) is just as bad as a positive (indicating warts/spikes) one.

I've put the raw data in a Google Sheet, here; the full inspection reports are here and here. The charts below show most of the relevant information, broken down by the area of the part being tested. A helpful description of the part's areas ("V-neck face," etc) is here.

Ra - Roughness average

All values in μm

Rq - Roughness, root mean square

All values in μm

Rsk - Roughness skewness

All values in μm

Rt - Roughness total

All values in μm

MicroTek also sent a series of photos taken with a Hirox digital microscope at a variety of magnifications:

If it's not clear from all of the photos and charts above, the improvement on the parts due to MMP is really remarkable. The as-printed part is really rough - on average, it's about as rough (Ra/Rq) as 120 grit sandpaper (see this for a good analysis of sandpaper surface texture). MicroTek was able to eliminate the vast majority of the total and arithmetic mean roughness; both parts they processed feel very much like finished products.

The pitting, however, is a problem. To be clear, it's not a result of the MMP process; all they did was expose flaws that were already in the part. Many of these could probably be eliminated on future batches. First, printing the parts on a newer Arcam system (like the Q20) might improve the as-printed texture significantly. And second, MicroTek can investigate more complex treatments that allow for the offending frequencies to be eliminated more thoroughly. I'll be exploring these (and other) options in the coming months.

Assembly

Before putting the seatposts together, a little bit of prep was necessary. The inner diameter of both the seatpost and saddle clamp cylinders were slightly undersized, and there were warts (remnants of support structures) left on the undersides of the shoulder straps. I had intentionally left these untouched when I sent the parts to MicroTek, as I wanted to see how little post processing I could get away with. The MMP process took them down slightly, but not nearly enough to put the parts into service.

Fixing that was pretty straightforward - just a few minutes each with a file. In future iterations, I'm hoping that by making some light design modifications - and by dialing in the EBM build parameters - will minimize this work. If not, then I'll probably add CNC machining into my process chain (after printing and before finishing).

With the inner diameters trued up, the parts could be dry fitted to the carbon fiber tubing I'm using as a seatpost:

I'll be gluing the assemblies together with 3M DP420 this week, and then I'll send them out for testing. These parts will be put to the same ISO standard that my seatmast topper passed last summer, and I'm particularly curious to know whether the different levels of post processing has any effect on their strength. In high fatigue cycle applications (this paper defines "high fatigue cycle" as N>100,000, which is exactly what my parts will be tested to), improvements in surface finish (lower Ra) have been shown to increase fatigue life. If some form of surface finishing (MMP or otherwise) means that I can print a lighter AND stronger part, that'll definitely help justify the expense.

Cost

With my current design and a batch size of 275 (a full batch in an Arcam Q20) my as printed cost will be under $100. MMP will cost an additional $40-75 (depending on finish level), though those numbers were based on smaller quantities. I'd hope that the rollup cost to me is under $150.

In addition to these parts, a full seatpost requires about $25 worth of carbon fiber, a few dollars worth of glue, and (I suspect) under ten minutes of assembly time. They'll also require saddle rail hardware, which I'm budgeting an additional $25 for, and some packaging - under $10. All told, my cost of goods sold would be about $215.

That's a fancy seatpost, but it's not completely unreasonable. My goal, at the moment, is to get that price down to $150.

More updates soon :)


Thanks to Addaero and MicroTek for their ongoing help with this project.

Coming soon

Added on by Spencer Wright.

Today I *finally* found time to photograph the parts that I got back from MicroTek a few weeks ago:

As you can probably see, the part on the left is unfinished. In the middle is an intermediate finish (~25µ" Ra), and on the right is a fine finish (~1.5µ" Ra). All three of these parts were printed on Addaero's Arcam A2X; their raw finish is about 600µ" Ra. 

Incidentally, I'll note that photographing the surface finishes on these parts has been remarkably challenging. I probably need a strobe or something, but hey - it's a labor of love.

I'll be writing up the results in the next few weeks. Stay tuned!

Computer aided design

Added on by Spencer Wright.

Over the past week, one particular tweet has showed up in my timeline over and over:

 
 

The photos in this tweet have been public for over a year now. I've been aware of the project since last June; it was created by Arup, the fascinating global design firm (whose ownership structure is similarly fascinating). They needed a more efficient way to design and manufacture a whole series of nodes for a tensile structure, and for a variety of reasons (including, if I recall correctly, the fact that each node was both unique and difficult to manufacture conventionally) they decided to try out additive manufacturing. As it happens, I was lucky enough to speak to the designer (Salomé Galjaard) by phone a few months ago, and enjoyed hearing about the way they're thinking of applying AM to large construction projects.

In short: I'm a fan of the project, and love to see it get more exposure. There's something about the particular wording of Jo Liss's tweet, though, that is strange to me. Specifically, I find myself asking whether a computer did, indeed, design the new nodes.

(Note: I don't know Jo Liss and don't mean to be overly critical of her choice of wording; it's simply a jumping off point for some things I've been mulling over. I also don't believe that I have any proprietary or particularly insightful information about how Arup went about designing or manufacturing the nodes in question.)

As far as I can tell, Arup's process worked like so: Engineers modeled a design space, defined boundary conditions at the attachment points (which were predefined), and applied a number of loading conditions to the part. Here the story gets less clear; some reports mention topology optimization, and others say that Arup worked with Within (which is *not* topology optimization). My suspicion is that they used something like solidThinking Inspire to create a design concept, and then modeled the final part manually in SolidWorks or similar. Regardless, we can be nearly sure that the model that was printed was indeed designed by a human; that is, the actual shapes and curves we see in the part on the right were explicitly defined by an actual engineer, NOT by a piece of software. This is because nearly every engineered component in AEC needs to be documented using traditional CAD techniques, and neither Within nor solidThinking (nor most of the design optimization industry) supports CAD export. As a result, most parts that could be said to be "designed by a computer" are really merely sketched by a computer, while the actual design & documentation is done by a human.

This may seem like a small quibble, but it's far from trivial. Optimization (whether shape, topology, or parametric) software is expensive, and as a result most of the applications where it's being adopted involve expensive end products: airplanes, bridges, hip implants, and the like. Not coincidentally, those products tend to have stringent performance requirements - which themselves are often highly regulated. Regulation means documentation, and regulating bodies tend not to be (for totally legitimate reasons which are a bit beyond the scope of this blog post) particularly impressed with some computer generated concept model in STL or OBJ format. They want real CAD data, annotated by the designer and signed off by a string of his or her colleagues. And we simply haven't even started to figure out how to get a computer to do any of that stuff.

I'm reminded here also of something that I've spent a bunch of time considering over the past six months. The name "CAD" (for Computer Aided Design) implies that SolidWorks and Inventor and Siemens NX are actively helping humans design stuff. To me, this means making actual design decisions, like where to put a particular feature or what size and shape an object should be. But the vast majority of the time that isn't the case at all. Instead, traditional CAD packages are concerned primarily with helping engineers to document the decisions that they've already made.

The implications of this are huge. Traditional CAD never had to find ways for the user to communicate design intent; they only needed to make it easy for me to, for instance, create a form that transitions seamlessly from one size and shape to another. For decades, that's been totally fine: the manufacturing methods that we had were primarily feature based, and the range of features that we've been good at making (by milling, turning, grinding, welding, etc) are very similar to the range of features that CAD packages were capable of documenting.

But additive manufacturing doesn't operate in terms of features. It deals with mass, and that mass is deposited layer by layer (with the exception of technologies like directed energy deposition, which is different in some ways but still not at all feature based). As a result, it becomes increasingly advantageous to work directly from design intent, and to optimize the design not feature by feature but instead holistically. 

One major philosophical underpinning of most optimization software (like both Within and solidThinking Inspire) is that the process of optimizing mass distribution to meet some set of design intentions (namely mechanical strength and mass, though longtime readers of this blog will know that I feel that manufacturability, aesthetics, and supply chain complexity must be considered in this calculation as well) is a task better suited to software than to humans. To that effect, they are squarely opposed to the history of Computer Aided Documentation. They want CAD software to be making actual design decisions, presumably with the input and guidance of the engineer.

If it's not clear, I agree with the movement towards true computer aided design. But CAD vendors will need to overcome a number of roadblocks before I'd be comfortable saying that my computer designs anything in particular:

First, we need user interfaces that allow engineers to effectively communicate design intent. Traditional CAD packages never needed this, and optimization software has only just begun the task of rethinking how engineers tell their computers what kind of decisions they need them to make. 

Second, we need to expand the number of variables we're optimizing for. Ultimately I believe this means iteratively focusing on one or two variables at a time, as the curse of dimensionality will make high dimensional optimization impractical for the foreseeable future. It's because of this that I'm bullish on parametric lattice optimization (and nTopology), which optimizes strength and weight on lattice structures that are (given input from the engineer) inherently manufacturable and structurally efficient.

Third, we need a new paradigm for documentation. This is for a few reasons. To start, the kinds of freeform & lattice structures that additive manufacturing can produce don't lend themselves to traditional three view 2D drawings. But in addition, there's a growing desire [citation needed] within engineering organizations to unify the design and documentation processes in some way - to make the model itself into a repository for its own design documentation.

These are big, difficult problems. But they're incredibly important to the advancement of functionally driven design, and to the integration of additive manufacturing's advantages (which are significant) into high value industries. And with some dedicated work by people across advanced design and manufacturing, I hope to see substantive progress soon :)


Thanks to Steve Taub and MH McQuiston for helping to crystalize some of the ideas in this post.

After publishing this post, I got into two interesting twitter conversations about it - one with Ryan Schmidt, and the other with Kevin Quigley. Both of them know a lot about these subjects; I recommend checking the threads out.

Photos from a visit to CCAT

Added on by Spencer Wright.

A few months back I had the pleasure of visiting the Connecticut Center for Advanced Technology, which is located on the UTC/Pratt & Whitney East Hartford campus. CCAT began as a facility focused on researching laser drilling, but has moved deeper into 3D printing, and specifically directed energy deposition, in the past few years. 

In addition to a full subtractive (manual and CNC) shop, CCAT has a few cool additive tools that I was particularly interested in. The first is an Optomec 850R LENS system. The 850R is a large format directed energy deposition machine which can be used for both new parts and repairs. It's also useful for material development, as DED machines can create parts with a small amount of powder (while powder bed fusion machines generally require a large amount of powder).

(Click on the photos for larger versions + descriptions)

The other thing I was excited to see was their Kuka HA30 robot, which has a coaxial laser cladding head attached to it. This robot can be used for either etching/engraving or cladding, meaning that it can either subtract or add material to a part. Especially when combined with the two-axis rotary table shown below, this thing can create some really complex parts.

It was really cool seeing these specialized technologies being used in real life. Thanks to CCAT for having me!

On Optimization

Added on by Spencer Wright.

As I've explored further into the obscure regions of design for additive manufacturing, I've been thinking a lot about the philosophical underpinnings of optimization, and the role that design optimization can play in product development. Optimization is in the air today; the major CAD vendors all seem to have an offering which purports to create "the ideal part" with "optimum relation between weight, stiffness and dynamic behavior" and "the aesthetics you want." These promises are attractive for seemingly obvious reasons, but it's less clear how design optimization (at least as it exists today) actually affects the product development process.

Product development inherently involves a three-way compromise between quality, cost, and speed. The most critical trait of a product manager is the ability to establish a balance between these three variables, and then find ways to maintain it.

Understanding the strengths and limitations of manufacturing processes is, then, invaluable to me as a product manager. Given infinite resources, people are pretty good at making just about anything that can be designed; there are designers out there who make very successful careers just by pushing the boundaries of what is possible, and employing talented manufacturing engineers to figure out how to bring their designs into existence. But in my own experience, the more I understand and plan for the manufacturing process, the easier it has been to maintain a balance between quality and cost - and hence to create an optimal end product.

All of which makes me feel a strange disconnect when I encounter today's design optimization software, which always seems to focus specifically on creating Platonically perfect parts - with no regard for manufacturability or cost.

To be fair, traditional CAD programs don't usually have a strong manufacturability feedback loop either. Inventor, SolidWorks, and NX are all perfectly happy with me designing a fillet with a radius of .24999995" - when a 1/4" radius would work just fine and cost much less to manufacture. In this way, traditional CAD requires the user to have an understanding of the manufacturability of the features that she designs - a requirement which, given the maturity and nature of conventional manufacturing methods, is not unreasonable.

But the combination of additive manufacturing on one hand, and generative design on the other, produces vastly different effects. No longer does a designer work on features per se. There's no fillet to design in the first place, only material to move around in 3D space. Moreover, the complex interaction between a part's geometry and its orientation on the build platform produce manufacturability problems (overhanging faces and thermal stresses, to name two) that are difficult to predict - and much harder to keep in mind than things like "when you design fillets, make their radii round numbers."

The remarkable thing about AM design optimization software, then, isn't that it allows me to create expensive designs - it's that these kinds of manufacturing factors (orientation to the build platform, and the structural and thermal effects that it produces) aren't treated as things which need to be optimized for at all.

The purpose of optimization should be to help me, as a product manager, design optimal *products* - not to chase some Platonic ideal.

So: Give me a way to incorporate build orientation, overhanging faces, and slicing data into my designs. Those variables are critical to the balance between cost, quality, and speed; without them, the products I design will never be optimal. 

3D reverse engineering process chain

Added on by Spencer Wright.

Big thanks to Michael Raphael and Peter Kennedy, of Direct Dimensions, for their help with the 3D scanning - the key part of this process. Thanks also to Ryan Schmidt (of MeshMixer) and Bradley Rothenberg (of nTopology) for their ongoing support in designing 3D lattice structures.


As I hinted to a few months back, I've been scheming for a while to create an integrated design for a seatpost/saddle support to be printed in titanium. As a first step along this path, I decided that it'd be easiest to use an existing saddle shell, and design a part that would adapt the shell to fit a piece of carbon fiber tubing.

The saddle I chose consists of a carbon fiber shell, some minimal padding, and five female threaded bosses: three in back, two in the front. The bosses fit through the shell, so that they protrude through the underside; they will be my part's connection points. As you can see below, the saddle comes with (and isn't meant to be separated from; this is a decidedly off-label use of this part) a loop shaped rail part; I'll be discarding that and building my own 3D printed titanium part instead.

The first step in my design process is pure reverse engineering. I need to understand where each of those bosses is in 3D space, so that I can design a part that fastens to them securely. In order to do this, I worked with Direct Dimensions to scan - and then reconstruct - the part to a point where I could design around it.

Reverse engineering via 3D scanning is a process of interpolating, smoothing, and in the end often guessing the design intent behind an observed feature. The same is the case with basically any form of reverse engineering, of course; if you measure (via calipers, for instance) a feature to be 100.005mm, you'll generally assume that it was intended to be 100mm. With simple rectilinear parts this process is relatively straightforward, but with more complicated ones - especially ones that include a combination of complex curvature and manual fabrication methods - it can look a lot like art.

Regardless, the first step is to acquire some data on where exactly the part in question *is.* Direct Dimensions started by laser scanning my part with a Faro Edge arm and an HD probe:

This is an interesting hybrid system: the arm itself knows where it is, and the non-contact laser scanning probe knows how far away (and in what direction) the thing it's pointing at is. When combined, the single-point repeatability of the system is below .1mm.

From the point cloud generated by the probing system, Direct Dimensions was able to create a raw polygon mesh:

This mesh is a representation of the underside of the saddle shell; you can see the five bosses as well. It's a start, but not particularly useful for designing a mechanical assembly. To get there, Direct Dimensions used two methods:

First, they used a method called "rapid NURBS" to wrap a NURBS surface to fit the complex shape of the saddle. This is a fairly quick method (an hour or two of work) and results in something that fits all the weird contours and fine features pretty accurately. As you can see here, there's pretty high feature resolution in the model, which can be useful if I need to make sure to avoid (or fit closely to) something. On the other hand, though, the surface is difficult to manipulate and a little hard (due to its complexity) for me to even open up and play with in Inventor.

For a more useable (but less detailed) model, Direct Dimensions made a CAD surface for me as well. This is a much longer and more manual process, taking most of an afternoon. Here, individual surfaces are modeled and stitched together to create a shell that represents all of the necessary feature geometry accurately, but with a bit less precision than the rapid NURBS model. You can see roughly how the model was created below:

At this point, I finally had a model that I could begin to design around. I started by creating a quick lofted part that would stand in (just visually) for the saddle's exterior surfaces:

Then I placed the saddle (my lofted exterior + Direct Dimension's underside) into an assembly in Inventor, and added a carbon fiber seatpost to connect to. 

At this point I'm finally ready to start designing. I begin by creating a new part in Inventor that represents the design space available for my lattice:

Then I bring an STL of the design into MeshMixer and make the mesh way, way less precise. This process involves selectively remeshing (and reducing the mesh quality of) face groups one at a time. Eventually I'll record a time lapse video of the whole thing, but for now you can see a little of the process below:

From this low resolution mesh I'm finally able to create my lattice. I export an OBJ file, bring it into nTopology Element, and create a surface lattice with beams at each one of every triangle's edges.

Next, I create a volume lattice on the inside of the part. I've chosen a large cell size and a vertex-centroid cubic cell structure. When I generate the lattice, nTopology Element only creates the lattice cells whose centers fit within the part. In order to make sure the whole volume is at least partly filled, I step the volume lattice out a few levels, and then warp it to conform to the volume. Then I trim the outlying cells, leaving only the beams that lie fully within the design space.

Now I go into the lattice utilities and set the surface lattice as an attractor. I select the volume lattice as the one whose nodes I want to move, increase the snap range to 50mm and valence to 5 (I want basically all of the volume lattice's nodes to move, except those that have 6 connections), and then move the nodes:

Now I've got a merged structure: A surface lattice and a volume lattice, and they share nodal connections so the whole thing is tied together. I'm ready to thicken the lattice and see what it actually looks like. As before, I've added attractors in the areas where the design has mechanical features. I set the thickness range from .5mm to 1.2mm, and let it run:

Here, you can see both the internal and external structures:

spencer-wright-saddle-fixture-lattice-model.gif

And here it is with the saddle and seatpost attached:

As it's designed now, the lattice part is 18141 mm^3. In titanium 6/4, the weight of the part is 81.76g.

That's light.

Now, this part still isn't really manufacturable - there are too many overhanging faces. It also hasn't been run through FEA, and its distribution of mass probably needs some adjustment.

But it's a pretty good start :)

More soon.

Lattice design workflow, part 3: Integrating full mechanical features

Added on by Spencer Wright.

Note: As before, thanks to Bradley Rothenberg (of nTopology) and Ryan Schmidt (of MeshMixer/Autodesk) for their continued help on this workflow.

As documented previously (1, 23, 4), I've been working on a multi-step workflow to create printable lattice structures for mechanical parts. In earlier posts, I described some of the techniques I used to generate the lattice itself, and at this point I'm ready to refine the mechanical features and evaluate the end result.

I've made a few changes to my remeshed surfaces since my last post, so I start this process today in MeshMixer. Here I've got three parts: The stem body itself, a surface that's designed to reinforce the threaded portions of the faceplate bolt holes (this is mostly hidden inside the stem body, but you can see its border still), and the faceplate itself. 

From this, I export three separate OBJ files and import the into nTopology Element. There, I generate simple surface lattices: each edge in the OBJ is turned into a beam in the new lattices.

Next, I create a set of attractors that I'll use to control the thickness of my lattice. The locations of these attractors were taken directly from Inventor; I know the XYZ locations of the general areas that I want to thicken, and so put the attractors right where I want them. Then I control each attractor's size and falloff curve to thicken just the areas I want. In the shots below I have every attractor on a cosine falloff; the bolt attractors are 12mm in size, and the clamp cylinder attractors are just a few mm bigger than the diameter of the cylinder.

Once I've got the attractors set up, I go through each part and thicken the lattice. The grey appearance is just where nTopology is showing me a wireframe, and the density of the mesh is really high:

You can see here that each part has some degree of variation in its beam sizes. In the bolt areas the mesh is dense and the beams are thick; in the middle of the stem body the mesh is sparse and the beams are thin.

At this point, I export each of the three lattices and bring them back into MeshMixer. Here you can see them overlaid on the original meshes:

Now, I import meshes that correspond with the mechanical features I want to preserve in the part. I've taken these directly from Inventor: I created an assembly file containing the original IPT and then created a new IPT that refers directly to the mechanical features. I export that as an STL, bring it into MeshMixer, and then select it and flip all of its normals so that it's inside out. Here you can see those boolean parts - first as red bodies in Inventor, then as meshes in MeshMixer, then as inside-out meshes:

Now I select the three lattice objects, combine them into one, and run the inspector tool and fix all of the mesh problems. Then I run "Make Solid" on the whole object. I run this in "Accurate" mode and turn the "Solid Accuracy" and "Mesh Density" settings *way* up in order to keep the whole thing smooth:

Now I've got a single lattice object that's fully solid and ready to have its mechanical features taken back out. Pretty rad. I combine the lattice and the mechanical features into one object and run "Make Solid" again, again at high density and accuracy:

I select the result, run the Inspector tool, and fix any errors. Then I look around the lattice and evaluate it. Inevitably there are a bunch of areas that are cut off, thin, or chunky - places where the lattice was thin once the mechanical features were removed, and the meshing operation rounded over the resulting isthmus. Unfortunately, that's not something that I can go back and fix; I need to move individual nodes back in my original lattice in MeshMixer. But at least I know that now, and going back through the workflow actually isn't as painful as it sounds. And anyway, the part that I have now is actually pretty good:

I should note here that I got a *lot* of help on the Boolean operations from Ryan Schmidt. Ryan also recorded a full video showing how to reintroduce the mechanical features even if you didn't have the ability to create them in Inventor. Although I went a slightly different route, there's a lot here that's super useful - and it shows the really powerful features that are built into MeshMixer:

Now that I've gone through the full process from start to finish, I see a few aspects of my design that still need some work. I also know that I still need to reduce the number of overhanging features in my design (which will probably be built on its end, with the handlebar side up). I'm also excited to test out the lattice utilities that are built into the most recent build of nTopology Element - especially in the area where the handlebar bolt reinforcements interface with the rest of the stem body. Bradley describes the process here:

I also, for what it's worth, need to do some actual FEA on my part. But by focusing on a repeatable workflow for even designing parts like this - and keeping a mind towards some basic manufacturability constraints - I've got something here that shows some promise. More soon :)

DMLS vs EBM titanium parts

Added on by Spencer Wright.

Note: Below, I use the term "DMLS" to refer to laser metal powder bed fusion. Some will have issues with this usage; I encourage readers to ignore the (possibly trademarked) terms themselves and focus on the information contained within them.

Over the past few months I've spent a lot of time trying to determine whether DMLS or EBM would be a more suitable technology for the titanium bike parts I'm working on. Early on (in my collaborations with DRT and Layerwise) I focused on DMLS, and more recently I've worked with Addaero on EBM. These two technologies are in many ways complementary, and in truth I expect to work with both of them - but their design constraints and total manufacturing process chain are a bit different, and I wanted to spend some time understanding how that will affect the cost and quality of the parts I'm working on.

In the video below, I show some of the basic differences in surface quality and support structures. Of course there are many other factors that are worth exploration, starting with minimum feature size and built-in stress, probably; I'll get to those in future updates.

Incidentally, I'm *really* interested to see the differences between DMLS and EBM in printing the lattice structures I've been working on. More soon :)