|
Guest editorial by Roopinder Tara
|
|
On proud display at last year’s Autodesk University, the biggest CAD conference in the world, was a VW Microbus retrofitted with wheels like none we have ever seen. The wheels looked as if they were made of twigs painted a bright orange. (See figure 1.) Similar were several equally orange and odd structures in and about the vehicle, boldly holding on the side view mirrors, propping up a rear seat, and attaching the steering wheel to the steering column.
Figure 1: Wheel designed with generative design
What looked like twigs proved to be generatively-designed shapes, the output of generative design algorithms available in Autodesk’s Fusion 360, then cast in metal. The generative design had saved 18% the weight of the previous designs, according to VW.
A Lightweight Hero?
The orange wheels were an apparent success in automobile light-weighting. Generative design aims to create new shapes, including shapes you may never have thought of, shapes that offer a weight advantage over traditional shapes by efficiently putting material where it is needed and removing it where it is not.
But staring at the orange wheel, we wondered if generative design came up with the right answer. And we questioned if changing the shape of the time-honored wheel was the right decision. For lightweighting, our first thought is to change the material. Swapping aluminum for steel, for example, while regenerating the design could be as much as 60% lighter.
The VW Microbus drew a constant stream of visitors after it was promoted from the main stage. You can count on a geeky design and engineering crowd to pick up on anything automotive or aerospace related, especially the unusual. Plus the VW Microbus had a certain nostalgic attraction for the boomers among us, those who had lived through the 1960s. Pictures of the time often included a VW camper painted with peace sign and flowers – but with nondescript steel wheels with hubcaps.
The VW Microbus on display, said to commemorate the 20-year anniversary of the VW Innovation and Engineering Center California in Belmont (south of San Francisco), had the right blend of retro and future. Dutifully taking pictures and filing stories were an easily impressed media. You may have read any one of a number of stories touting generative design with the orange wheels as the most recent shining example, along with the associated claims of how much stronger and lighter it is.
The media blitz that descended on the VW Microbus should be enough to make the orange twiggy wheels the most recent poster project of emerging technologies -- generative design and 3D printing, in particular. In 2018, it was GM’s seat belt bracket that achieved saturation level coverage. (See figure 2.) The year before, it was GE’s jet fuel nozzle.
Figure 2: Seat belt anchor designed with generative design (image source Autodesk)
The seat belt bracket (40% lighter, 20% stronger) was one of 30,000 experimental parts GM produced in its Warren Tech Center. Whether it will see the light of day as a production part is doubtful, given the expense, speed, and other issues of 3D printing. Consumer products that rely on mass production and assembly have had ample time to optimize stamping, bending, casting, and molding parts in great quantity at the least cost.
Aerospace, with razor thin safety margins, can ill afford to replace a proven and tested titanium forging with a 3D metal printed part that could contain voids, stress concentrations, or other imperfections produced by using a relatively new manufacturing process or material. So, with few 3D printed parts emerging from big name manufacturing -- and even fewer generatively-designed parts -- especially in the most glamorous automotive and aerospace industries, can you really fault the industries behind emerging technologies to stretch their mere presence of these parts as victories?
So, Let’s Call it Art
The VW Microbus wheels are cool, we have to admit. Take that with a grain of salt, as engineering is a profession that tries in vain to shake its image as staid, serious, and decidedly un-hip. We thought ditching the pocket protectors would help, but people can still spot us in a crowd.
In return, we engineers put “cool” in its place. “Function before form,” we say disdainfully at things that are trying to be cool. We look down on the public at large, those who have branded us less than cool, those softies who buy cars only for their shine and shape. Real engineers don’t do that. We buy the car by its specs, its gas mileage, data from crash reports, and so on. If there is any beauty we can admire, it is the beauty of simplicity, the quest of an optimum shape, for example.
A Much Simpler Optimum Wheel
The most optimal load-carrying structure is a straight member in tension. It can be a thread, a wire, a cable. This is why spider webs are so strong, why suspension bridges are the most elegant. The load of the suspension bridge’s deck hangs on thin cables. Members in compression on a truss bridge are thick to avoid buckling. Comparing a suspension bridge to a truss bridge is like comparing Beauty to the Beast.
Take a spoked bicycle wheel, for instance. (See figure 3.) There has been no other wheel design that optimizes for weight, strength, and cost. Spokes on a bike wheel are structural supports. To simplify matters, think of the weight of the bike and rider supported totally by the vertical spokes between the wheel hub and the wheel rim. The spoke is in pure tension, which lets it support a tremendous load. The shape of a simple spoke is smooth and straight, and has a round section. Quite unlike the twiggy shape in the retro VW Microbus.
Figure 3: Spokes (image source bike24)
The spoke is smooth and straight not just because of the method of manufacture (it is cut from wires) but simply because smooth and straight has been found to be the optimum. Any lumps on the spoke add superfluous weight. Any bend to the spokes and the bent shape could not resist the slightest tension without plastic deformation.
One might counter by saying the VW wheel twigs are made thick so they could bear tensile and compression loads even as they are bent, but that is hardly optimal use of material. Also, a sharp bend in thick structural members will result in stress concentration factors.
A VW Microbus Backfires
To call the VW Microbus’ orange wheel a "successful design" makes engineers question the criteria of success. If novelty is a criterion, the wheels are without question successful. If weight-saving is a criterion, the comparison should with other lightweight designs, such as spoked and solid wheels. For generative design to be taken seriously as a technology of the future, software vendors should resist offering “winning” designs that win in one regard but lose in every other.
Generative is touted loudest when offering weight savings as it has been successful in producing prototypes that work for a particular load case. For example, the GM’s seat belt restraint appears as if it would have a better strength-to-weight ratio when the seatbelt is loaded (crash situation), which would put its long thin members in tension. However, in compression, such as when it is crushed by being sat on, long thin members won’t work. In fact, no commercial generative design we have seen seems to be capable of reacting to buckling loads in beams or plates.
Another glaring deficiency in most generative design algorithms is the inability to produce shapes that can be manufactured by conventional manufacturing means. Autodesk's Fusion 360 may be an exception, constraining shapes to what can be manufactured with 2.5-axis milling and die casting.
Shape optimization in generative design seems 100%-based on bone growth algorithms, and so produces bumpy shapes. Bone growth, specifically growth between two pieces of a bone fracture, is a result of fibers that grow out of both ends of the bone, then meet, usually at odd angles (anything but straight) and, miraculously, start knitting together, making a bump when the healing is complete. But over time, and if the patient is not too old, the bone remodels itself and removes the bump.
This would lead one to believe generative design's bone growth algorithms are stopped before they can remodel themselves into a smooth shape, probably in the interest of time. Theoretically, the same algorithms could keep running and removing every bit of material where it sees no stress -- like in the bump -- and adding it where the stress is high, such as in the area behind the lump. Eventually it might create a straight, long member. But this would mean a simulation for many more iterations; we would do well to remember that each iteration is a full stress analysis with many elements. Multiply that by the number of members in a part and you quickly have an untenable solution, even on HPC [high performance computing].
Therefore, most generative designs end up with a shape that can only be 3D printed. But 3D printing is not always available, or the shapes are too big for the 3D printer, or a number of other reasons interfere. Bumpy shapes are used as “inspirations” for final designs, a euphemism for a designer laboriously remaking the part bit by bit, substituting for each bumpy member, one that is straight/round/smooth so it can be manufactured by conventional production methods.
[Roopinder Tara is director of content for ENGINEERING.com and has a Masters degree in engineering science. This article first appeared on engineering.com and is printed with permission.]
|
|
Re: Upon Onshape Turning 100 Updates Old
I think your readers would have benefited if your latest article mentioned that Onshape goes beyond CAD in the cloud. It also addresses PDM/PLM [product data management, product lifecycle management] needs. In fact, I suspect that Onshape makes PDM/PLM for small- to medium-size companies a non-issue, because it addresses the data management needs from within user design activities."
- Leonid Raiz
The editor replies: That is a good point. Thank you for raising it, because I tend to ignore PDM/PLM as I am a CAD kind of guy.
- - -
In last week’s upFront.eZine, you refer to windows CAD systems: "Solidworks was... the first serious CAD program to run only on Windows [in 1995]."
However, on your worldcadaccess.com/blog/2009/02/microgds-has-new-owners-again.html article, you point out that MicroGDS came out in 1992, which followed from WinCAD, which was from the late 1980s. GDS was developed in the late 1970s to run on Pr1me, DEC VAX, and Sun mini-computers, and so it was an early and long-standing CAD system. MicroGDS only ran on Windows:
I’m still using it and, in many respects, it is still superior to more modern CAD systems. Bet you don’t publish this!
- Neil Harris
The editor replies: I should have been more specific and called it the "first serious 3D MCAD program," which is what I was thinking. Thank you for reminding me of MicroGDS.
- - -
I tried to do some investigative reporting on one of your sponsors. I read something about their history, then submitted a question to them.
"I read your page 'Why so many users' and I am curious about this statement: Our software is highly subsidized and hence we pass over small fees to each new or upgrading user'. Who is subsidizing your firm, please?
The firm responded: "Can I ask why this may be important to yourself as this isn't a question which has been asked of anyone of the last 32 years."
I replied, "I am curious because in the USA, the term subsidized has come to mean government-funded, which has a checkered history to be sure.
The firm responded: "Our software has been highly subsidized since 1992 to keep its final cost under the $1000 glass ceiling price point. You'll notice that no other company can offer such software as we do at our low prices. The software has also remained the same price for over 20 years or more even though inflation is 3% or more, compounded yearly. So, yes, all of our software is highly subsidized by various sources, including the government, as otherwise it would just not exist."
- Peter Lawton
The editor responds: Even though government funding is available for Canadian publishers. such as me, I am proud to say I have never taken any, because it is poor business to rely on subsidies. A day will come when they are reduced or withdrawn, as has already occurred to certain sectors of the Canadian economy.
Mr Lawton responds: I thought it was funny that no one has asked the question in the 32 years that they have been in business. Can he plan to go to corporate re-hab to wean his company off of this addiction to taxpayer money?
How do other Canadian software companies feel about their tax dollars going to support Okino? As an investor, does the government get a dividend form the company profits?
Government subsidies seem like training wheels, temporary support that should come off the bike once the company is up and running. His claim that “otherwise it would just not exist” is correct in this sense: it would not exist as it is today, as it would have to be far more efficient, and but would that be a bad thing?
This exchange piqued my curiosity about government subsidies in general. How do other countries influence the free market by subsidizing private companies? Here is the answer for USA: goodjobsfirst.org/subsidy-tracker. I am still looking for an international version.
The editor replies: it is an irritant to Canadians that our taxes go to subsidize specific corporations. Bombardier is one of the worst, getting billions over the years. Movie production houses get big tax breaks.
Taxes should be reduced so that all companies benefit, as well as consumers, as we saw with the tax cuts in USA. My supposition is that companies getting subsidies are ones known to flow the savings back to the coffers of political parties -- but I may well be wrong.
Mr Lawton responds: I can see where that might be very difficult for companies trying to compete with ones from other countries, where subsidies are even larger. Perhaps a rating system can become popular with the general public: a company can have a ‘taxpayer burden’ rating, showing a company’s tax footprint. Smaller is better, of course.
The editor replies: I checked some CAD vendors and found they have received the following subsidies from local and federal US governments. 'Not listed' means the firm is not listed in the database, and so may have received no subsidies.
Autodesk $1.6 million
Bentley Systems not listed
Dassault (Aviation received subsidies, not the CAD vendor)
DataCAD not listed
IMSI/Design not listed
Intergraph not listed
IronCAD not listed
Kubotek/CADkey not listed
Onshape not listed
PTC not listed
Siemens $1 billion (probably for energy, not CAD)
Solidworks not listed
SpaceClaim not listed
Trimble $20 million
Vectorworks not listed |
|
|
|
Recent Comments