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A fellow maker has tried printing a 3D model in clear PLA (<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?

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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?

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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).

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  • $\begingroup$ From my experience with lost-wax casting for jewelry, the process is to melt the wax out, then increase temperature and burn out the remaining wax / residue. Casting wax is supposed to leave behind little or no residue after the burning process, but I don't know about PLA/ABS/nylon. I would bet that they leave behind more mess and would thus result in more inclusions. $\endgroup$ – Martin Jan 14 '16 at 18:35
  • $\begingroup$ Yeah, I would think that the hard plastics would have a hard time fully melting, depending on the metal you're using and its melting temperature. $\endgroup$ – tbm0115 Jan 14 '16 at 19:20
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Typical procedure on the casting is to use the lost-wax method, and using PLA is absolutely fine.

  • Print your part at around 101% - 103% size
  • Attach flues to the part (or have them part of the model)
  • Cast the part in a mixture of sand and plaster of paris
  • Once set, burn out the PLA in a furnace.
  • Clean the mould of debris
  • Pour your metal of choice

For a more detailed reference, check out the following:
https://www.youtube.com/watch?v=WWVVSZP3Au4

Regarding the printing itself, my only advice is to use a small layer height and carefully clean up the part before casting

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