<p>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.</p>

<p>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.</p>

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

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

<p>Any other tips or considerations?</p>

I believe casting typically uses a wax for the positive when using casting sand. So, I would suggest using
wax filament
in your 3D printer.
I would try to shy away from hard polymers like PLA/ABS/Nylon (all typical 3D printing filaments) if the goal is to "melt it away" because a certain amount of the plastic material will either bind itself with the metal or large chunks of plastic will cause inclusions in your part. Both of these side effects will potentially degrade the quality/strength of your part.
I haven't personally used wax filament, so I can't tell you what the correct setting are. However, you can get most of the necessary information from whichever supplier you go through. I might suggest running your machine slower when using a low-melting filament such as wax or PVA (water soluble).