NASA has taken another step forward in 3D printed rocket engines by manufacturing and testing an igniter prototype using two distinct metal allows. Using an advanced laser printing method, engineers led by senior engineer Robin Osborne of ERC Inc produced the component in a way that could one day reduce the costs by a third and speed up the process by half.

3D-printed rocket engine components have been around for a while, but until now they've been made out of a single metal using relatively conventional printing methods. In the latest NASA project, engineers at the Marshall Space Flight Center in Huntsville, Alabama, worked with a commercial vendor to produce a rocket engine igniter – a key part used at the moment of ignition.

Igniters tend to be very complex and involve bonding together different metal alloys. The usual way of bonding such alloys has been to braze them. That is, to heat the two pieces of metal with a filler metal between them, causing them to weld strongly together and form a bimetallic component. The trouble is, this is a highly skilled, labor intensive process that takes significant time.

The NASA approach eliminates the brazing step by using a hybrid 3D printing process called automated blown powder laser deposition. This process sees a stream of metallic powder blown into the focus of a laser, which sinters the particles in midair and fuses them to the object being made. Here, it was the prototype igniter made of copper alloy and Inconel – a nickel-chromium-based superalloy.

By using this method in a hybrid machine made by DMG MORI that combines 3-D printing and computer numerical-control machining capabilities, it was possible to make the igniter in one piece instead of the previous four, and also create the complex interior shape of the 10-in (25-cm) tall, 7-in (18-cm) wide igniter. In addition, the two alloys intermixed and fused directly to form a strong bond that stood up to 30 low-pressure hot-fire tests last July.

"Eliminating the brazing process and having bimetallic parts built in a single machine not only decreases cost and manufacturing time, but it also decreases risk by increasing reliability," says Majid Babai, project lead at Marshall's Materials and Processes Laboratory. "By diffusing the two materials together through this process, a bond is generated internally with the two materials and any hard transition is eliminated that could cause the component to crack under the enormous forces and temperature gradient of space travel."

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