Aug 10, 2017 | By Benedict

Maker Chris DePrisco has posted a YouTube guide to low-temperature metal casting using 3D printed parts, an air compressor, and a pressure vessel. The method uses silicone molds to cast metals with a low melting point, such as bismuth alloys.

Not many of us have the funds or the basement space to install a metal 3D printer at home. But that doesn’t mean you can’t use a 3D printer to create metal parts.

Chris DePrisco, a hacking and machining expert from the U.S., recently posted a video tutorial showing you how to achieve low temperature metal casting using 3D printed parts, an air compressor, and a pressure vessel. The process will only work using metals with a low melting point, but gives makers a whole new way to fabricate useful objects.

In the 14-minute video, DePrisco experiments with 3D printing and air pressure tools to create a silicone mold for a Maltese falcon. His molten metal of choice is a bismuth alloy, which can be melted 138°C, which is hot, but cool enough for the silicone mold to withstand.

The process, which DePrisco demonstrates with neat close-ups of his equipment and actions, involves first 3D printing a standard model of the falcon using PLA. This is nothing compared to the final metal version, but it’s essential for creating the silicone mold.

When the PLA falcon is printed, DePrisco makes an airtight box out polycarbonate and puts the falcon inside. The box is then filled with a silicone mix, which sets overnight.

“The next day I can remove the mold and see what’s inside,” DePrisco explains. “The silicone easily separates from the part but all the nooks and crannies make removing the part a little more difficult.”

In the end, the maker is able to pull the PLA falcon out from its squishy silicone surroundings without having to make any incisions to the silicone. This leaves behind a perfect silicone mold with a detailed, falcon-shaped hole in the center.

Next comes the pouring of the molten metal into the mold. DePrisco chose to use the bismuth 10 281 alloy, which is 40 percent bismuth and 60 percent tin, and which melts at 138°C.

Once the bismuth had cooled down within the silicone mold and could be pulled out, the metal falcon looked “not great,” in DePrisco’s words, because of bubbles in the cast.

This led DePrisco to attempt using a pressure vessel and air compressor at 60-80 Psi to “crush the bubbles” out of the falcon model. This equipment helped to produce a much better model, though there were still some small metal “balls” on the outside of the bird. This, the maker realized, was caused by air bubbles in the silicone mold, not the bismuth.

Accordingly, DePrisco re-made a silicone mold, only this time he used the pressure equipment.

With air pressure used to make both the silicone mold and the metal cast, DePrisco was able to produce a nice-looking bismuth-tin falcon that was near-identical to the PLA 3D printed model.

“Well, I think that turned out pretty nice,” DePrisco fairly concludes.

So there you have it. While you might not have air compression equipment to hand, DePrisco’s process shows that you can turn cheap 3D printed parts into metal replicas without a metal 3D printer. We think that’s pretty neat.

Check out the tutorial in full in the video below.

 

 

Posted in 3D Printing Application

 

 

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