3D printing TPU solids, and welding them to fabric,how to& implications for MYOG

[fred L]

Hello there! This post has some length to it, hopefully it contains something useful.

Intro

3d printing is most known for solid plastic, however, I want to discuss a less used 3d printing material (flexible TPU) and how it can be used for MYOG projects.

Unique to TPU is that it is a thermoplastic that can be welded to fabrics with suitable but common coatings. This is how sleeping pads , tents, pack rafts and many jackets  are sealed. Usually it is two coated fabrics getting stuck together, here I am talking about sticking a custom shape object to such a fabric.

Welding TPU solids to TPU fabrics industrially is not new. However, Today a 140 dollar 3d printer can create any custom shape object in great detail in TPU, and it can be welded to nylon/polyester fabrics covered with regular PU or TPU.

This brings MYOG a bit closer into an area that otherwise is only available to large scale industrial producers of gear, as injection molding is noutoriously hard to pull off at home!. Until now, my imagination has mainly revolved around replicating some industrially made solutions that previously was not really possible in home environments,  Potentially, someone could create new applications that have not been done yet.

Applications:

Valve housings for low pressure inflatable structures. I have not tried to print a mouth valve, but a valve housing can be printed that accommodates commercially available sleeping pad valves (similar to the one on the picture below). Cascade designs for example sell spare valves for their thermarest pads for 8 dollars. The housing is not purchasable, but by printing it, the entire valve system on thermarest pads can be recreated at home and be added to any custom inflatable structure. The complexity of the structure that you can welded at home is off course still limiting, so you will not be making your own X-lite. However this is an example of how custom inflatables can get easier to make in MYOG conditions, with 3d printing expanding the list of good parts that are  available.

Valve housings for high pressure applications. I have created parts that interface with silicone and PU air hoses that then attach a bicycle valve (dunlop/woods, shrader or presta all work). Tiny cheap bike pumps weighing 1 ounce exist, which I use for inflation. My application is to make a replica of the discontinued Klymit Airbeam frame sheet. It seems it was never a commercial success, however I like them. And I want anotherone for a backpack I am sewing. It seems to me that the proprietary valve that Klymit chose is the culprit for most of the leaks that occur, not the fabric getting pierced. What I like about airframes is that now when I can make them myself, I can make a framed backpack, from scratch, at home. This then slightly increases the motivation for making MYOG packs as in general, as there is a framed option.

This is a 3d printed valve housing I welded to a TPU nylon fabric with a dunlop/woods valve attached through a silicone hose. (dont mind the lego). There is a hole in the housing with a diameter of 1.8mm allowing the air to go in. This design will go into my attempt to make a pack airbeam frame sheet. If the tube was given a bigger hole, a commercial replacement mouth blow up valve could be fitted to it, creating a lower pressure inflatable.

 

 

 

ideas for other applications – tarps, tents, packrafts, packs

Packrafts could benefit, as mounts for any item imaginable could be welded straight to the raft wall, even protruding into the raft itself. Say a gopro, GPS, fishing gear, I don’t know what pack rafters use really ;) I guess they could use somewhere to stick their paddles on the side. Clamps for paddles would be really easy to print and weld.

Tents and tarps have fewer applications I believe. Anchors, reinforcement and attachment points could be printed, but they can also be sewn in, or welded from fabrics.

This is about how far my imagination has reached so far. I would love to see others come up with other applications.

Process.

Only general TPU welding skills and tools are required. Sealing custom prints is really no different from welding seam sealing tape to a PU fabric. For general knowledge of welding I therefore refer to guides at diypackraft.com, this is where I learned a lot of it. This is just a short addition for what is specific to to 3d prints.

TPU 3d printed parts stick to both TPU and also to the PU fabrics I have tried.

TPU fabrics are usually made to be airtight with a thick layer, which means that the part can be directly welded with good strength. Because lightweight PU fabrics generally have a thin layer just to keep it watertight, a layer of TPU should be added in between to get good strength to the fabric. This can be a regular seal seaming tape for example. 3d printed parts are air and watertight. Welds to 3d prints reach max strength, meaning that if it is pulled off the fabric with force, the bond between the part and the TPU/PU layer is stronger than the bond between the laminated layer and its fabric.

Usefulness / Limitations.

3d printing of the flexible TPU likely holds different usability for MYOG than hard solid prints, as most useful hard solid parts are already injection molded and widely available. The applications of TPU in the industry is way fewer, but they are almost never freely availiable for purchase.

The usefulness of this technology is mainly determined by how it compares to sewing. A lot of solids can already be attached to fabrics by sewing, such as buckles and other hardware. I believe that anything that can be easily sewn, should be sewn and not welded. However welds are potentially much stronger than seams, as the adhesion is achieved over a two dimensional area. Also when welded, a solid becomes part of that fabric, not just attached to it.

For water and air tight solutions, the other competing means of adhesion is by glue. Welding is in most cases preferable to gluing, as it creates a more consistent and replicable bond, and does not introduce another material into the bond. Gluing TPU is messy and curing times range to up to 24 hours. Therefore I do see reasons for this avenue of MYOG to be explored.

Designs can be shared and reproduced anywhere by anyone. I recon probably up to 30 valve housings could be printed in a single go, although it would likely take something like 24 hours to do that. Material cost for the valve housing on the image is about half a US cent.

An obvious downside is that this does not work on anything silicone or cuben fiber.

Cheers!, I just want to share this as it likely holds usefulness for some select applications. If you come up with Ideas, please share them!

 

[Mike B]

I should not read stuff like this when I am at work…………..gets me thinking about other things….

Thank you for this it makes me want to add a camera mount to a pack raft and a small flyrod holder to clip in my flyrod when I am rowing across the lake. I have no idea how a 3d printer works but I think the table is fixed and the head moves in x/y/z axis? If that is the case can you print directly on the fabric and get a full bond or would it better to use a cement and bond the 2 together  after they are printed?

[Jerry Adams]

rather than tent poles you could make a tube from plastic filled with air.

[R]

A compelling combination of tech.  Wishing I had a similarly compelling use case.

The first thing that pops in to mind is printing zippers, but I don’t think TPU is the right material for it.  There may be potential for welding prints to small pieces of heavy fabric which would then be sewn to the final application. Which is more or less what a zipper is :)

Is printed TPU too flexible for cord hooks or loops?  Could you print snaps?  Low profile, high volume valves like on my S2S pillow (Exped may be similar)? A zip-loc style closure for a roll top or dry bag? Vent hem stiffeners for tents. Pole sockets for trekking pole shelters. A sew on friction slider to attach your quilt to a pad strap (inspired by a commercial product I’ve forgotten the brand of). A hydration hose keeper for shoulder straps? Would anyone want a camera mount for their pack/shoulder-strap or raft? A snap-in mount for a coin cell LED light?

 

[fred L]

Mike, I have printed straight on fabric, it makes for a good bond, However, on my printer (Creality Ender 3) the plate moves in the x axis , while the y and z is on an arm. This means that the piece of fabric would need to be strapped to the printer and moving throughout the process.

It is much more practical to print it separately and then heat seal it to the fabric afterwards. Only heat and pressure is needed, no cement.

I could give it a go to print a female go pro mount in TPU and see how it goes, the design might need to be altered a bit, I dont have a male go pro clip right now, so I would not be to test it. A standard camera screw should be possible to make, I recon the metal threads would require some aquaseal to be glued in place.

I dont know how firm packrafts get ? Would there be a risk that the entire mount would rock back and forth with the motion of the paddles, and make rather shaky image? That would largely depend on how heavy the cam is, where the mount is placed, and how firm the boat gets.

Jerry, Tent airbeams exist comercially, they are just far from lightweight. They have a diameter of about 6-7cm I believe. Usually they are used in car camping where the entire skeleton is blown up with a compressor. They require very high pressures. To deal with that they have an inner tube which is filled with air, and an outer layer that provides compression. For the commercially made ones, weight is the issue, as the easiest and cheapest way to get such high pressures contained in a mass produced product is to using very thick and heavy grades of materials. I believe this is the only profitable way for companies to make and sell such structures. I do recall that NEMO has a product with an UL solution. https://sectionhiker.com/nemo-gogo-elite-1-person-inflatable-bivy-tent-review/.

Does anyone here have experience with it ? I have never heard of anyone who has one. Makes me think that was never a big commercial success. However I dont think that commercial viability neccesarily is a good metric for how useful something can be, it just means it did not appeal to the broad masses of consumers, and the company could not make a profit from selling it.

I believe any attempt to make a tent airbeam like the one in that NEMO would have to use a two layer design. I have tried to create some single layer tubes with packraft fabrics that I pumped up, however the nylon weave is not made to provide compression at such pressures, so the structure expands as pressure increases. When that happens the TPU layer also gets thinner, and more pouous, and stops being airtight. So more constriction would be needed. Perhaps a constricting layer of cuben could be used for that purpose. It would be strong since it is taped in sheer, and also lightweight.

The main issue that I see is that the compressed air would expand in hot weather, and shrink in when cold. I assume this would mean that the structure would have to be over inflated in the evening to stay up all night, and then if the tent was left out in the sun the next day it would put great stress at the beams. Potentially however, dyneema fabrics would be at their strongest in this compression applicaiton, as they can be taped in sheer, and have excellent tensile strength. Perhaps as long as the TPU bladder was constricted, a light one would remain airtight under high pressures.

In the end, carbon fiber and aluminium definately provide simpler solutions of erecting a tent :)

Rene, a lot of cool ideas, I only have time to consider a few of them right now, i’ll get back to it later ;) Zippers already exist and are cheap and reliable in their mass produced form, so I dont think a printed zipper adds new value.However, given how successful zip locs are in other commercial applications, they could potentially provide useful for backpacks too! Right now I have no idea of how printable they are, what weight they would end up with and if they would provide value beyond current solutions such as water resistant zippers and roll tops.

[James Marco]

While any new technique/technology for making things has it’s problems, 3D printing definitely has potential. Making plastic fabrics for tents, in a seamless tapered design, as one panel is one such. Current technology really doesn’t allow for the creation of fabrics, or, complex structures involving the use of several different plastics. Resolution is a problem. Flexible, stiff, shafts can be made with internal web reinforcements for example, bypassing the need for air. (Think “Skin and Foam Core” materials, but designed for stiffness/strength.)

Anyway, the technology is great and can be used for small additions, as it sits. Two part epoxies, high temp metal deposition, etc are all possible in the future, the thick buildups of metals are possible today with correctly applied electroplating techniques. Rather than think of cuben fiber cloth, think spectra reinforced plastics, for another example. But, it does need more research…

 

[Craig B]

Lots of good ideas!  In my experience, 3-d printing is best at structural type things, not things that require flexures or really tight tolerances.  For instance a button snap would probably not work so well.  I don’t think you’d have much luck with a zip-lock type closure either.  A few years ago I tried to 3d print a quarter-turn coin cell battery door with an o-ring seal, and it just was not up to the task.  The beauty of 3d printing to me is that I can easily make something to connect two other commercially available parts that would be difficult to print, but someone else has already gone to the trouble of mass producing.

There’s a lot of capital going into the 3d printing space though.  The company I work for started at a tech incubator, and there were two other companies there trying to do 3d printing applications;  one was doing metal, the other carbon fiber.  After we graduated from the incubator, I would occasionally see one of the guys from the carbon fiber print company, and he said they made a working prototype and were shipping trial parts to customers!

[fred L]

I agree Craig, the ability to connect items into new applications and the creative freedom is enabling when pursuiting new solutions. Beyond this, I believe an item makes sense to print when it is not commercially availiable. Other than the flexible valve mounts, i believe the other item no one could sell me have been custom webbing mounts for one off applications such as this one (in hard plastic).

Craig, yes rigid plastics are probably what is printed 99% of the time. These do not flex, they shatter and should not be used for any flex application. TPU behaves more or less the opposite to a solid plastic, as it returns to its original form after being deformed, can not be broken with a hammer but is easy to cut with a blade. I have found that TPU can also be sewn, it behaves much like leather when it has a thickness less than say 2 mm.

[Craig B]

Yeah, if you can’t find something specific and you can design and print it, that’s definitely a great use of the technology!  Making flexible prints certainly opens up new possibilities for integrating with fabric stuff.  So is the piece pictured above strong, and have you pull tested it?  I’ve been impressed with the strength of FDM parts (like most consumer grade printers) in general relative to SLA.  That’s the other great thing about prints is that you can iterate quickly to find out how much material you need to satisfy a given load requirement!

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