I was doing research on this topic because I am making the mini metal foundry from Grant Thompson and have a Pla 3D printer (from XYZ). I haven seen anybody pour metal directly onto the plastic so I don't know if it will work or not, but that's what I will find out. I plan on posting my results here, since it is one of the first places I looked, and I hope more people will see my results and be educated. My concerns are that 1. The metal (I will most likely use aluminum) will not vaporize the pla and something bad will happen, and 2. The pla will have moisture trapped inside of it, since that is a trait of pla, and will 'explode' like concrete does when hot metal is poured on it. Hopefully, though, the metal will be hot enough and the results will be similar to if I was using a foam or wax positive buried in sand. I am hopeful since aluminum's melting point is 660 degrees Celsius and pla's melting point is 175 degrees Celsius. As I said, I will post my results here. I expect to be doing this within 2 weeks, but, depending on school and life, that may increase. I'll be back, Skullngloves. (One thing I forgot to mention is that I will be using a low infill and shell density so there is less plastic. That, I believe, will give me the best results.