Well This Sucks
So, the foam failed. We needed a new manufacturing method. Back when we were originally deciding how we were going to approach this, we had thought about vacuum forming plastic, but had rejected it because we didn't have a heat source. As it turns out, a friend of ours had a couple 550 Watt heat lamps that we could borrow, so I ordered up some 0.060" white styrene and we built a 2'x4' vacuum table to run off the dust collection system for the CNC mill. We decided we could use the foam parts we had already made and finished as forms for the plastic, and it should be pretty easy.
Here was the setup:
We fired up the lamps, and discovered that we couldn't really get the styrene to its glass transition temperature. It got a little bit soft, but only right under the strip of lamps. We needed more heat. We found some pretty cheap 1500W quartz lamps online and I ordered 2. 3000W of power has to be enough, right?
Well, this time we were able to get large sections of the styrene to a good temperature for forming. We couldn't quite get enough of the corners warm to do a big piece, so we decided to try the knee pieces that I had carved forms for. The positive curves came out beautifully, but there wasn't quite enough vacuum to suck the edge of the part to the table:
The gaping holes came from when we tried to use a heat gun to heat an area and make the corner nice and crisp. We decided we needed 2 things: more lamps so we could heat a larger area and thinner styrene. The dust collector has a lot of airflow, but not much actual vacuum pressure. Our hope was that the airflow was enough and that with thinner plastic it would suck down fine. So, it was off to the internet for 0.030" styrene and two more of the heat lamps. For those of you keeping track at home, that's 6000W total. The setup was getting pretty ridiculous at this point.
The good news is that it worked better than the earlier attempts. Trying to pull the same knee pieces, we got better definition:
As you can see, though, the interior corners are still nowhere near vertical. We'd actually need more vacuum pressure to do this, and we didn't have a good way of getting it. We also tried forming a body piece with similar results:
The bigger problem was that the molds weren't taking the heat well at all. The body mold was doing especially bad:
A closeup of some of the damage:
At this point, we were almost back at square one. We didn't have a manufacturing method, and the pieces we had made so far were pretty much trash. All we had was firsthand knowledge of two methods that wouldn't work.