|The gauntlet on this prosthetic hand was fitted precisely to its user using thermoforming, the process of using heat to make plastic temporarily malleable and shaping as needed before it cools and sets. Image courtesy of Maker Zoo Bangkok, Thailand.|
An Instructable entry by engineer and artist Andreas Bastian titled Thermoforming 3D Printed PLA for Use in Prostethics offered several options for thermoforming (changing the shape of a piece using heat) PLA printed parts. These included using a toaster oven, a heat gun, and a microwave. The last option requires a dish and just enough water to completely submerge the part.
The test part was a parametric version of a gauntlet used in the open source e-NABLE prosthetic limb project. Laying completely flat, it takes much less time to print. Bangkok-based makerspace, Maker Zoo attempted to tackle this project using an induction hot plate and a stainless steel pot (used for soap making, not food) to heat the part evenly.
|From the Instructable (files are included for those who'd like to print out and try this design), one can see the parametric 3D printed gauntlet before and after the thermoforming process.|
Using a cloth placed over a test subject's arm, being careful and using gloves, the piece was fitted in place and allowed to cool by running cold water over it. The process of thermoforming PLA can be done repeatedly, and in this case it was done 3 times before a final fit was made.
Using a thermometer, a temperature of around 70 degrees Celsius or more was required to get the piece evenly pliable. The thermometer seems not to be an accurate way to measure the actual temperature of the PLA piece, so you may have to go over the temperature of its discrete glass transition temperature in order to actually reach it.
Since then, Maker Zoo has acquired a heat gun for more precise and easier heating of parts. Their e-NABLE design may now feature a hand that also uses a thermoformed part to fit around users' limbs. A user with a particularly difficult case has come to Maker Zoo to help develop a new version of 3D printed prosthetic limbs and this process might be the only way to manage this case, and all others regarding such a wide range of challenges.
With parametric (flat) designs, not only is it quicker and cheaper to 3D print, but adding in aesthetic touches can be done much easier as well. Modifications in length and width can also be made on the flat designs much easier than curved shapes in 3D design software. The software being used to develop Maker Zoo's prosthetic limb is SketchUp.
We may never know exactly how much time Andreas Bastian saved others looking into this technique with his Instructable, but it is because of an emerging open source paradigm and selfless contributions like that of Andreas' that are helping move real progress along at an exponential rate.
Thank you Andreas. And if others are interested in thermoforming PLA for any reason, not just prosthetic limbs, but perhaps even wearables or other projects, please check out his well-documented Instructable here.
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