Of all FDM filament types, flexible ones such as TPU invite a whole new way of thinking, as well as applications. Case in point the TPU-based bellows that the [Functional Part Friday] channel on YouTube recently demonstrated.
The idea is quite straightforward: you print TPU and PLA in alternating layers, making sure that the TPU is connected to its previous layer in an alternating fashion. After printing, you peel the PLA and TPU apart, remove the PLA layers and presto, you got yourself bellows.
There were some issues along the way, of course. Case in point the differences between TPU from different brands (Sainsmart, Sunlu) that caused some headaches, and most of all the incompatibility between the Bambu Lab AMS and TPU that led to incredibly brittle TPU prints. This required bypassing the feed mechanism in the AMS, which subsequently went down a rabbit hole of preventing the PTFE tube from getting sucked into the AMS. Being able to print TPU & PLA at the same time also requires a printer with two independent extruders like the Bambu Lab H2D used here, as both materials do not mix in any way. Great news for H2D and IDEX printer owners, of course.
As for practical applications for bellows, beyond printing your own 1900s-era camera, accordion or hand air bellows, you can also create lathe way covers and so on.
Great idea for all those soft robot actuators!
Those sound like enclosed volumes of PLA. With channels in the PLA support, can it be rinsed out?
https://www.researchgate.net/post/In_which_green_solvents_does_PLA_dissolve_easily_and_efficiently sounds almost plausible
Maybe printing only thin strips of PLA for support will help, then you can crush them and get them out through small holes. Or make a “closeable” actuators, made from two parts.
Does TPU work with PVA?
PVA dissolves in water, but TPU absorbs water :( so not ideal
How do you think they should seal the parts together? I feel like the seams would be weak and cause leaks :(
I was able to achieve a similar part without dual nozzles or the use of PLA. Designed a shock boot cover out of TPU, printing it in “VASE Mode” (Prusa Slicer, ie single wall thickness). The caveat being the top could not have an overhang.
It worked perfectly right off the printer, no post processing or waste. VERY flexible l, where the boot could be compress to near flat, then rebound to its native shape.
Thanks for posting the video – a different approach for a different application.
did you print the folds horizontally like in the video? not sure how you would be able to achieve that without PLA layers (but I would love to know!)
I wonder if water soluble filament like PVA could be used instead of PLA. Won’t be able to verify this anyway with P1S, but interesting project for the future.
If you’d ever used PVA, then you’d know the answer. Have a professional cleaning station along with an Ultimaker at work – nightmare process to dissolve and clean up the messy gunk. I’d rather cut my arm off with a pen knife.
TPU absorbs water so I wouldn’t recommend PVA!
Glad there’s a definition else I was going to print out some AI.
Just in time. I was looking for a solution for protecting the bearing rods on my new cnc machine. Perhaps a custom bellow of TPU might work.
Time to print an accordion!
Weird Al would be proud.
The geometry of the “conventional” bellows replicated here in 3D printing lends itself to manual fabrication with folds and cuts and seams. But 3D printing allows all sorts of novel geometries — It seems boring and unimaginative simply to replicate a shape that was originally chosen largely for ease of manual fabrication and limitations of the materials used.
So, this opens a whole new space for fabrication of functional compliant enclosures. I look forward to seeing what people’s imaginations (or generative design or AI minions) can come up with.
Most of the geometry constraint comes from needing to fold down and collapse. There’s a lot of bellows components out there that are made in other ways than with sewn seams (some are casted for instance) and they use the same geometry, because it’s pretty ideal.
Is it ideal though? For example, the volume ratio from full-extended to fully-compressed is pretty awful — lots of dead volume in that core space. Would there be other fold geometries that would satisfy that criterion better? (yes, there are) What are the tradeoffs?
It’s an interesting problem space to explore.
Do you have any better fold geometries in mind?
Would be cool for those old field cameras
As mentioned in the last paragraph.
Just be sure not to use transparent TPU…
Black PLA is transparent in the near infrared. If that’s true for TPU too, you’ll want to consider that for camera use (i.e., don’t use an near infrared-sensitive detector).
Nice stuff for protecting my lathe & mill from chips (both types ;-) ). thx for the tip !