Love talking shop with folks.Thanks for sharing that video! VERY interesting! Being an R&D engineer (med devices) I too have had to do a ton of testing, one of which was an accelerated 30 year product life test. I had to design and build a test fixture to cycle a device for the stomach compression over 3 million cycles in about 9 days. Side note, it passed!
One thing I noticed is that you had a hard stop of the compression cycle. Is that how it would be on a vehicle? Is it possible to make sure the suspension will not over compress? I'm assuming if the bump stop cycles too many times in over compressing, it'll start to get too hot and break apart.
I know TPU is an amazingly strong and durable material, in almost any durometer, but truly impressed with what you and your team has been able to do!
What FDM printers are you using? Did you have to design and build your own hoppers and feed system for the printers or was it an off the shelf system? I have not heard of any off the shelf pellet/hopper FDM printers, but then I'm only using the hobbyist grade, sub-$1,000 printers. I think the next big evolution in FDM printing will be going to pellet/hopper setups for many reasons:
- Material is cheaper (but the manufacturers will have to start selling in 1 or 2 pound bags instead of 50 lbs at a time)
- Ability to mix and match materials together, maybe a little PETG with PLA, or TPU with PETG or ABS? or...?
- Mix your own colors.
- No more clogged extruders with filament getting into the gears.
- Not having to deal with where to place filament rolls to feed into the bowden tubes.
- Not having to feed filament through long bowden tubes.
The notion of an "ultimate stop" is a misnomer and gets tossed around a lot in the community. In reality, the spring rate just continues getting exponentially higher, so you eventually draw a line in the sand, and call the product "stopped" at a point, as the Force/Displacement curve is near-vertical. For Toyota IFS vehicles, I've found that to be between 1500 and 2000lbs. If you're exceeding that amount of load on the bump stop, you're really thrashing on the truck. For that cycle test, I set it to the max that the 3 horsepower motor could compress the part to.
You nailed the heat point. In real world use, they see intermittent, high rate impacts, allowing them to cool down. Not constant repetitive high speed impacts. Because my product actually dissipates energy, much like a shock, they heat up. Hence the cycle rate for the longevity test was low to allow the part to reach a reasonable steady state temperature.
I build/retrofit my own machines. It's a ton of work... they're based on the voron motion system, as it's the best open source platform that I could find with a good motion system, and buy pre-assembled motion systems. I used to use pellet extruders from a fellow hobbyist, but I do so much machining to their product to make it meet my requirements, that I eventually just designed my own extruders and build them in house.
My product, is my process - I just happen to build bump stops. But there's a few more things In the works
Advantages are all correct - although mixing materials doesn't really happen. The biggest reason I think there's so few folks doing this is because the MOQ (min order quantity) for my material is 3000lbs. Hard to get a 3D printing company big enough to consume that much material and make it worthwhile.
I throw away a lot fewer empty spools nowadays.
