How can I optimize my print for casting in metal? A fellow maker has tried printing a 3D model in clear PLA (&lt;5% infill, 1 or 2 perimeters), burying it most of the way into casting sand, and then pouring molten aluminum. This melts and burns the PLA, and the aluminum takes the space that the printed model used to take.

There's plenty of room for improvement in his process, but I'm asking about what he can do in terms of the 3D printing process to make his prints more casting-friendly.

What print settings are (generally) best for use in this sort of casting?

What materials, if any, would work better than unpigmented PLA? (Must be a material that a typical thermoplastic FDM printer can handle.)

Any other tips or considerations?
Print a two part negative (mold) of your objects.
http://www.thingiverse.com/thing:31581

https://pinshape.com/blog/how-to-generate-a-3d-printed-mold-for-an-object/

Melt and pour wax into the mold. Praffin wax melts at only 37C, not an issue for both PLA and ABS.
Use the wax object for casting, not ABS/PLA/etc.
The mold is also reusable this way.

To prevent the wax from sticking to the mold, something might be applied to the surface. Oil maybe?