Recently, I’ve been playing around more with 3D-printed thermoforming tools. After having some limited success earlier in the year making 2-part thermoforming molds using SolidWorks’ mold tools, I decided to try something a little more complex: a 3-part mold, incorporating a spring-loaded pinch plate. By pinching the sheet against the upper half of the mold, the pinch plate is intended to allow heated plastic sheets to be directly placed in the mold, without needing a custom frame.
Some images of the prototype mold:
– Hot off the printer:
– Mold Parts:
– Mold and product:
I tested the mold with .030 scratch-resistant acrylic (hard to form) as well as .020 and .030 clear PETG. Some lessons learned:
– The pinch plate concept only works passably. The compressive force provided by the springs I included isn’t consistent across the pinch plate, and the guide pins require me to punch holes in the plastic sheet or shape it strangely, making the tool less easily adapted to different plastic sheets.
– Additionally, heating thermoforming sheets without a frame isn’t reliable. It seems to work acceptably with Kydex, but both the acrylic and PETG tended to curl or warp, especially when there were holes or uneven cuts in the material.
– Finally, this particular mold had a few issues that are particular to it. The part I was trying to form is a straight-sided cup, which has a very low draft angle (0.5 deg), leading to a lot of friction between the mold and the sheet during the press. Additionally, the core tool was printed with a 10% infill, which is too low for this particular geometry – the protruding part of the core compressed significantly, around 3-5 mm, before the two halves of the mold met. The cup that was produced looks nice, but is consequently about 5 mm too short.
Recently at work, we’ve been wrestling with the problem of custom covers for prototype parts. I’ve tried epoxied-together plastic sheets and FDM printing, but haven’t gotten anything to look decent. I’ve also tried molding thermoformable plastic by hand, which looks terrible (and is a burn risk).
However, combining two of these ideas – thermoforming and 3D printing – does seem to be showing some promise. I used SolidWorks’ mold tools to create cavity and core forms for a small test part, and printed them in ABS on a MakerBot Rep2X. I then gently heated Kydex (in .060 and .029 thicknesses) to 170C for a few minutes, draped it over the core, and pressed the cavity down with an arbor press.
So far, the test parts have come out pretty well! I had to cut the test parts out on a bandsaw, which wasn’t terribly clean. Next, I’m going to try designing core/cavity tools with shear blades built in, to automatically cut out the shape.
Two fun things I’ve been playing around with recently:
– 3D Printing: I’ve started work on my own Printrbot 3D printer! I’ve got most of the non-electronic hardware, save the build platform (which is proving to be a nightmare to get…), and am hoping to pick up the motors/driver board/extruder/etc. around Christmas. Here it is now:
– Dual-Booting iPhone: This is just to show that yes, mechanical engineers CAN figure out these newfangled computer-thingys sometimes. Damn kids and their damn “SSH” and whatnot…
Just finished printing a replacement locking clip for the turn signal housing on my girlfriend’s car!
The Engineering department at Swarthmore just got a uPrint 3D printer, which I’ve been itching to try out. After the little plastic tab that held the turn signal housing in place broke (causing the assembly to fall out while driving and swing around by its wires), I figured I had a pretty good project. It’s pretty incredible to think that for 30 minutes in Solidworks (well, and 10k for a industrial 3D printer, but whatever), I can repair a part that I’d otherwise have to throw away. Of course, I’ve still got to install it…