I'm a layman engineer who's decided to take another step forward in my research and work with McKibbens Pneumatic Artificial Muscles. I’m new to creating custom rubber components and laser cutting, so please bear with me. My intent is to be able to order sheets of rubber, which can then be cut in a laser cutter into strips. I would then like to melt the long edges of the strip and fold the rubber strip onto itself, connecting the edges to form a rubber tube. The melting part is for fusing the two sides together. I was wondering what types of rubber would be best suited for this? I was thinking natural or silicone rubber, but again I’m new to making my own rubber components.

  • $\begingroup$ I’m not an expert, but I don’t think most rubbers melt. You might want to try thermoplastic elastomers as these can be melted. $\endgroup$ – Eric S Feb 3 at 17:59
  • $\begingroup$ The laser "cuts" by burning away material. It will leave a burnt edge. My impression is that thermal welding of most rubbers is not possible although I don't know how vulcanising works. I would be very surprised if silicone could be heatsealed. If rubber can be heatsealed then the next question is can burnt rubber be heatsealed? $\endgroup$ – Transistor Feb 3 at 19:11

There are silicone specific adhesives, as silicone does not adhere well to any other material. Appropriately, there are rubber adhesives for genuine rubber as well. The method you describe is going to severely test the adhesion of the material, as it places the most stress along the weakest points in the system.

Have you considered using surgical rubber tubing as the foundation of the system build? I've used this tubing for elastic properties as in a slingshot, but also in an inflation mode (without the sleeve). It works well in the latter instance, as long as the system is not exposed at length to sunshine or chemical fumes of any sort to degrade the silicone. The inflation mode was with water and the resulting rupture was more amusing than dangerous.

A "finger-trap" sleeve as reference in the documentation I've found would help with the longevity of the system.

McMaster-Carr carries such tubing from inside diameters of 1/16" to 1" and 2 mm to 8 mm.

Response to comments: If joining surfaces is preferred to adhesives, your method of heating the surfaces will determine the strength and is likely to be stronger if the process is done properly.

The information I've seen in this respect use a heated blade. It's typically mounted in a jig which directs the "tubular" form of material in such a way as to contact the heated blade simultaneously, while the jig compresses the shape at the contact point.

It's critical to have sufficient energy imparted to the blade to continually compensate for the heat removed by the melting process and to have a well-regulated speed over the blade.

I've laser cut silicone sheet and the mechanical characteristics of the sheet were not changed, although the edges were "cleaner" as a result. I've not cut latex rubber but a quick search indicates that it is not a problem. Cutting any product containing polyvinyl chloride compounds is dangerous, but latex rubber should not have such a compound.

Consider to edit "patters" to "patterns" as I didn't understand at first the reference, not having read all the papers found for this item you desire to construct.

Another option you may wish to consider is to create your specific shapes using 3D printed molds and casting the latex rubber within. This would provide for your custom modifications as well as reduce/eliminate adhesives and bonding complications. The realm of possibilities with a 3D printed mold is exhaustive.

I use OpenSCAD for creating 3D models, which is useful for repetitive mathematical designs, although many of the CAD programs such as Fusion 360 permit parametric modeling as well.

Due to the flexibility of the rubber, you'd be able to create molds that might otherwise not release the part. Alternative methods would include using a water soluble support filament such as PVA which washes away with water, for more complex designs. Vacuum processing during the mold pour may be necessary for more intricate models, but I'm getting ahead of myself.

Even though marked as accepted, additional thought of the matter also suggests that one may want to consider 3D printed versions using TPU filament. It's very "stretchy" and would allow for infinitely complex structures. I've not tested porosity but the substance melts during the printing process and does not delaminate when stretched.

  • $\begingroup$ So what I'm hearing is it would be best to use an adhesive rather than melt the two sides to fuse them together? If so, how might (if at all) the adhesive interfere with the elastic properties of the material? And the weakness in the method that you described seems to be specific to the method of adhering the two pieces together, is that correct? Laser cutting the rubber shouldn't have an effect on the properties of the material, correct? $\endgroup$ – Kirkland Jan 31 at 0:58
  • $\begingroup$ Also, I have not thought of surgical, or latex, rubber for this application. The sleeve it's placed in should have it always protected from sunlight, and I don't expect any gasses outside of the compressed oxygen from contacting it, so it might work so long as the elastic properties function well with the overall intent of the application, experimentation would be required as I don't recall any research that I've read thus far which used latex rubber. $\endgroup$ – Kirkland Jan 31 at 1:00
  • $\begingroup$ Finally, I'm aware that you can get rubber tubes of all types from all sorts of places, however I'm trying to experiment with custom patters, such as a pocketed quilting pattern on the interior structure of the tube, to overcome some issues with the minimum retracted length with PAMs, to make it mimic the behavior of the striated muscles more closely. Also, I'd like to experiment with creating a McKibbens PAM heart, which will require shapes other than a simple tube. Another reason why I'm looking at making my own from scratch. $\endgroup$ – Kirkland Jan 31 at 1:02
  • $\begingroup$ Let me look into Latex Rubber some more and see what I might be able to find... $\endgroup$ – Kirkland Jan 31 at 1:02
  • $\begingroup$ added a ton in the original post, response to comments $\endgroup$ – fred_dot_u Jan 31 at 2:56

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