YHABFT: 3D Printing + Centrifugal Investment Casting

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. 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.

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.

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Jonathan Goff

Jonathan Goff

President/CEO at Altius Space Machines
Jonathan Goff is a space technologist, inventor, and serial space entrepreneur who created the Selenian Boondocks blog. Jon was a co-founder of Masten Space Systems, and is the founder and CEO of Altius Space Machines, a space robotics startup in Broomfield, CO. His family includes his wife, Tiffany, and five boys: Jarom (deceased), Jonathan, James, Peter, and Andrew. Jon has a BS in Manufacturing Engineering (1999) and an MS in Mechanical Engineering (2007) from Brigham Young University, and served an LDS proselytizing mission in Olongapo, Philippines from 2000-2002.
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15 Responses to YHABFT: 3D Printing + Centrifugal Investment Casting

  1. Ben Brockert says:

    Almost all of the cheapest printers are using open source software for slicing. I wonder how much work it would be to re-do their support printing algorithms to make the supports suitable for use as gates, runners, and sprues.

    Are you thinking the system would be electric? Making it run off a normal outlet would either make the batch time long or small.

  2. A_M_Swallow says:

    I was expecting a 3D printer that can be used on a spaceship. Molten metal will be an ‘interesting’ thing to have flying around.

    The rotating arm may allow the casting to work in micro-gravity. Now if we can just get the equipment to work in a vacuum so it can live outside the spacestation.

  3. Jonathan Goff Jonathan Goff says:

    Ben,
    That’s an interesting idea. If you could have the supports double as gates, runners, and sprues, that would be great. I had been thinking about something electric, but you have a good point–it may need to be a 220AC plug socket instead of a normal 110AC to keep the times reasonable.

    AM,
    I wasn’t thinking about in-space 3D printing, but 3D printing here on earth for aerospace and robotics companies.

    ~Jon

  4. Peter Lykke says:

    Don’t make it more complicated than necessary. If you leave out the rotating bit, the technique is described here:
    http://3dtopo.com/lostPLA/
    Note the texture on the finished part – to me it seems that it is the FDM part that is the limiting factor. But maybe it is different with a B9 Creator – someone will have to find out.
    Anyway, on earth it is only a good idea for parts that cannot be milled. In space, forget it, IMHO.

    – Peter

  5. HH says:

    Most low rate production investment castings, especially for aerospace, are made from SLA patterns these days. Centrifugal castings can also be made using graphite tooling on the outside to generate a contour.

  6. jstults says:

    I agree with Peter, the FDM layers on the part is the lim fac on surface finish. We’ve done lost foam (manually cut model) and lost PLA (printed on a Prusa Mendel) at our hackerspace in Dayton. A simple propane burning furnace is what we use to melt the aluminum (cans). Very simpel/cheap technology. The cool thing with the slicing software for RepRaps (well supported now in the mainline Linux distros) is that you can just dial down the infill density, so there’s less material to burn out of the mold and less trouble with ash fowling up the casting.

  7. Let me ask a more general question:

    With a good 3d printer I go grab a part design from wherever, press “print” and expect something to show up on the table some time later. Is there anything like that for metal parts?

    I imagine you’re not getting a machine like that for $3k.

  8. Trent,
    Yeah, there is at least one process for printing metal that is “Tea, Earl-Grey, Hot” like that–it’s the DLMS technique Paul Breed has used for some of his parts in the past. A machine will only set you back probably somewhere in the $50-100k range (I ought to price one out). What I’m proposing here would have more manual steps than that, at least at first. I might be able to make an automated version of most of it–but that would likely drive the price out of the kickstarterable range.

    ~Jon

  9. Jonathan Goff Jonathan Goff says:

    Peter, jstults,

    I guess for me, being a former rocket guy, I care a lot about the actual material properties of the end part, not just the surface resolution. Normal investment casting with a better 3D printer (like a B9Creator) can get you much better resolution, but I want a system that can consistently, and with low maintenance, produce high-strength prototype parts. You might need to put more effort into QC for a final flight-quality part, especially if you don’t want to have to give it huge margins, but if you can make prototype parts quickly in your shop that have nearly flight-grade material properties, I think that would be a game changer in many industries.

    ~Jon

  10. Peter Lykke says:

    Jon,
    If material properties is what you are after, then laser sintering is the way to go. Lots of different high- performing materials and fine precision, say 20 micron layer thickness. For example here: http://www.eos.info/en
    But it doesn’t come cheap, of cause. 100k is not enough for a machine, not yet anyway.

    And I think – hope – you are right about the “game changer” issue. This could be our chance to compete with the chinese some day.

  11. Jonathan Goff Jonathan Goff says:

    Peter,
    Exactly–if you have over $100k for your setup, definitely go buy the laser sintering or DLMS machine. Their materials are reasonably good, though the selection is pretty skimpy. But if you’re a small startup doing stuff, and don’t want to deal with long turnarounds for metal parts, I think that te type of approach I described would be useful.

    ~Jon

  12. Doug Jones says:

    Jon, When I get home this evening I’ll take some photos of my wife’s centrifugal casting machine. It’s a dentist’s model, suitable for fairly small objects such as dental crowns, but it shows the idea. It’s actually spring powered (!), and you just wind it up, place the mold, then insert the crucible and release the catch. The metal cools enough in just a few seconds to stay in place as the centrifuge spins down.

  13. Doug,
    Yeah, one of my employees was telling me about a similar rig. I’d love to see a picture of your wife’s setup though. I’ve seen a few pictures online, but they didn’t show a lot of detail.

    I’d like to build basically a scaled-up version that can do up to say 1 Liter of molten metal, and can hold a say 25x25x25cm mold. Preferably a setup that included a way to keep a shield gas over the molten metal until it has gone into the mold so you don’t get excessive oxidation on aluminum.

    If I can make one of these work, would XCOR want to buy one? 😉

    ~Jon

  14. James Robertson says:

    Jon,

    How do you like the SolidDoodle and B9 Creator?

  15. Jonathan Goff Jonathan Goff says:

    Hey James!

    So far, I haven’t really had a chance to try out the SoliDoodle. One of my employees bought it with his Friday time money, so while it’s still technically owned by the company, I want to give him first stab at trying to make it work, and so far he’s been out on vacation or travel for our DARPA/JPL contract for all but two days since the machine arrived. I think he was having some issues getting the first layer to stick properly, but that’s a common issue apparently when the machine is new–sounds like it’s typically a quick fix.

    As for B9Creator, I haven’t had the money to get one yet, but I want to. I met Mike Joyce at a “Boulder is for Robots” meetup about a year before he kickstartered the thing, and I got to see some of the early prints. I really like the machine, and think it has a lot of potential. Hopefully I’ll get a chance soon to add one of those to our toolkit.

    ~Jon

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