I'm not sure. They are either printing it out of high-temperature metal, or they are printing lost-wax molds and then using them to cast the engines.
It's pretty exciting, though. The most efficient engines are those that use expansion nozzles that are entirely fabricated out of thin-walled tubing. This is what was used on all the manned space flights, including the Space Shuttle. Unfortunately, these are quite expensive.
If they can be made by 3-D printing, it's a huge breakthrough. This is one of the angles the big guys are looking at.
3-D printing using liquid metals is a hot field. In more ways than one.
We could build spaceships in space using 3D printing....It is an amazing thing.
“The most efficient engines are those that use expansion nozzles that are entirely fabricated out of thin-walled tubing.”
I think I remember reading about that. It was based on an innovation someone came up with to use the fuel that was being routed to the engine as coolant for the engine itself, right?
NASA Tests Limits of 3-D Printing with Powerful Rocket Engine Check
http://www.nasa.gov/exploration/systems/sls/3d-printed-rocket-injector.html
Aug. 27, 2013
The component was manufactured using selective laser melting. This method built up layers of nickel-chromium alloy powder to make the complex, subscale injector with its 28 elements for channeling and mixing propellants.
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SPACEX LAUNCHES 3D-PRINTED PART TO SPACE, CREATES PRINTED ENGINE CHAMBER
http://www.spacex.com/news/2014/07/31/spacex-launches-3d-printed-part-space-creates-printed-engine-chamber-crewed
JULY 31, 2014
On January 6, 2014, SpaceX launched its Falcon 9 rocket with a 3D-printed Main Oxidizer Valve (MOV) body in one of the nine Merlin 1D engines. The mission marked the first time SpaceX had ever flown a 3D-printed part, with the valve operating successfully with high pressure liquid oxygen, under cryogenic temperatures and high vibration.
The more things change, the more they stay the same: my mother's cousin was a 3-D printer in the 40s & 50s: ran a linotype machine.