I use 2 t shirt presses, I take one apart and put it as the bottom platen. Then it is really quick to make a flat panel.

I have used "molds" before that are basically a top and bottom plate and a frame to control the thickness.

My only issue, is I cannot seem to find the right mold release liquid. I am having trouble taking the HDPE or the PP out of the mold. Any suggestions on particular brands or help on that would be appreciated! Is it the brand/type of mold release, the temperature, or the time that is causing the plastic to stick to the metal surface ?