3D Printing Rocket

Rockets are perfect for 3D printing technologies, well at least parts of rockets. Bodytubes, maybe not so much, control electronics, also a no, but rocket engines – there’s the ticket. They are relatively small parts with complex internal features and are manufactured in low quantity. Now for the bad news: they get very hot and very cold; they have small features; they are highly stressed. This means, in general, you can only use metal as a material. This limits us to DMLS, Casting and Infused metal.

DMLS is awesome; you send out a part as an stl file and you get a solid metal part back in a couple of weeks. While I have built various 3D printed parts, sadly none of them are mine to show, so instead check out this awesome work at Rocket Moonlighting. For rockets, DMLS materials are usually Inconel or PH 15-5 with other high temperature alloys such as Cobalt Chrome available as well as lightweight aluminum.

Infused metal is somewhat different from DMLS in that a porous version of the model is made, then infused with another alloy. Usually this is 420 SS fill with bronze. It is cheaper and quicker turn around than DMLS but at the expense of detail, only going down to around 40 mil holes vs DMLS 16 mil. Infused metal is also better with overhangs than DMLS. For these reasons, we are using Infused Metal for our igniter and injector, but if we were to make a regen engine we would probably use DMLS.

3D printed (infused metal) igniter as printed. Spark on top; from left to right fuel, pressure, oxidizer.
3D printed (infused metal) igniter as printed. Spark on top; from left to right fuel, pressure, oxidizer.

Casting is just like any other casting method, but it uses 3D printed wax. This technology has been around for decades now and is very common in low volume parts. It is a good technology, but it has a hard time dealing with long passages and thin walls, as well as only being commercially used with easy-to-cast alloys so we are not using it.

Rules of thumb:

If you can machine it, just machine it; it will probably be better, cheaper, and most likely faster.

Infused metal seems to build up more than the stl; allow for a ~4 mil growth.

You will have to tap most threads and, frankly, the surface finish is much improved by taping.

O-rings work fine with any of the 3D printed parts.

On DMLS, limit overhangs to 45 degrees or live with added supports during build.

ASK YOUR VENDOR about what post machining / supports they are adding.

Have a build direction in mind when you design the model; it really helps.

Surface finish isn’t great on DMLS or infused.

Long small holes are much more likely to clog than short small holes.

Make sure you have flats for post machining or wrench tightening.

That’s about it; give it a shot. Nothing says I’m living in the future like 3D printed metal parts arriving in the mail.

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