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3D Printing + Centrifugal Investment Casting
by jonathan goff
One of my employees at Altius Space Machines recently bought a $600 3D printer (A SolidDoodle 3D Printer, 2nd Generation, Pro Model), and we’re hoping in a few months to add a ~$3k B9 Creator as well. I’ve been following 3D printing for almost a decade now, and we’ve been using a lot of 3D printing over the past several months with our DARPA projects and other things we’ve been working on, and decided it was worth having at least a few lower-end systems in-house to save time/money.
I recently had a crazy idea for how to make low-end 3D printers even more valuable for space startups, which I started describing via Twitter when I remembered–YHABFT (You Have a Blog For That)!
Basically, a lot of the 3D printers coming out recently have the ability to print in lost-wax castable resins. For those of you not familiar with the process, lost-wax casting (aka investment casting) is a process where you make a wax model of what you want to make into metal, you coat the wax with a multilayer ceramic/sand shell, melt the wax out while cooking the ceramic, pour the molten metal into now-hollow ceramic shell, and then break the ceramic shell off once the metal has cooled. Investment casting can produce very fine and intricate geometries with smooth surface finishes, and very tight dimensional stability.
Polished stainless steel investment casting. – Prototype Casting, Inc.
Centrifugal Investment Casting places the mold and molten-metal crucible at one end of an arm mounted on a shaft, with a counterweight on the other side. The metal is melted in the crucible, then the shaft is spun at a couple hundred RPM, and centrifugal forces cause the metal to flow into the mold. Higher density metal with low porosity is forced out radially away from the shaft, and lower density metal and dross “float” to the top–typically where the feed sprues are located. Centrifugal casting tends to yield parts with much better quality than other casting methods, in some cases being nearly as good as forged pieces.
A complex stainless steel casting design. – RapidProtoCasting
When you combine the three methods (3D printing, investment casting, and centrifugal casting), you get a process that can potentially take a CAD model and turn it into an aerospace grade metal part within a day. The material quality can often be quite a bit better than you could get with a 3D metal printing process like DLMS, and you have a wider range of materials available.
It looks like a few shops actually offer a service somewhat like this (such as these guys, these guys, and these guys). But most of them still take 2+ days to turn the parts around, and none of them seem to be doing Centrifugal Investment Casting, just normal investment casting (though I could be wrong).
It would be neat if someone could develop a low-cost setup that small companies could buy that would enable small-component Centrifugal Investment Casting of 3D printed parts. Not sure if this is at all feasible within the price range of something that could be done as a Kickstarter, but I’d sure be interested in such a setup.
Jonathan Goff writes the popular space blog Selenian Boondocks at those rare times he can tear himself away from his day job as CEO of Altius Space Machines.
Moonandback
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Source: http://moonandback.com/2013/08/25/3d-printing-centrifugal-investment-casting/
