Silicone Molds for Stove-Top Metal Casting

Casting metal parts from 3D-printed plastic or Styrofoam models is all the rage these days, and for good reason — casting is a way to turn one-offs into mass-produced parts. Seems like most of the metal casting projects we feature are aluminum in sand molds, though, so it’s refreshing to see a casting project using silicone molds to cast low-melting point metals.

Don’t get us wrong — sand-cast aluminum is a great method that can even be used to build a lathe from scratch. But not everyone wants to build a foundry and learn the sometimes fussy craft of creating sand molds. [Chris Deprisco] wanted to explore low-melting point bismuth alloys and set about making silicone rubber molds of a 3D-printed Maltese falcon. The bismuth-tin alloy, sold as a substitute for casting lead fishing weights, melts on at 281°F (138°C) and is cool enough for the mold to handle. Initial problems with bubbles in the cast led to a pressure vessel fix, and a dull, grainy surface was fixed by warming the mold before the pour. And unlike sand molds, silicone molds are reusable.

Of course if aluminum is still your material of choice, there’s no need for a complicated foundry. A tuna can, a loaf of bread, and a handful of play sand is all you need to make custom parts.

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