Here you see the finished diffuser nicely separated from the mold.
I made it at the TechShop in Menlo Park! Here is a picture of the light diffuser in the vacuum forming machine as it is being formed. This machine uses a plug mold to vacuum form plastic parts like this. This machine does not work with a cavity mold because the vacuum does not seal until the mold platform is all the way up.
After it has cooled down, I push the RELEASE button on the vacuum forming machine to inject air to release the diffuser from the mold. In this example, the plastic is too thick and stiff so the part did not release using this method.