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19 Sep 2017
First prototype component to be produced from two different metal alloys using laser additive technique.
Engineers at NASA say that laser 3D printing key components for launch rockets made from different metal alloys could cut the cost of future engines by a third – with the time required to make them slashed by half.
A team at the agency’s Marshall Space Flight Center in Huntsville, Alabama, has for the first time been testing new parts based on two different alloys – said to be more difficult to produce with laser additive manufacturing than the single-alloy parts that they have focused on until now.
This summer, a first multi-alloy igniter prototype – made by a commercial partner - was tested more than 30 times in a low-pressure, hot-fire environment. After that, researchers at the University of Alabama in Huntsville chopped up the part and examined the bimetallic interface under a microscope. They found that the two metals had inter-diffused, described by NASA as a phenomenon that helps create a strong bond.
Start sequence
The job of a rocket engine igniter is to initiate the engine’s start sequence, and it is one of many complex parts made of many different materials.
Traditionally, they are made by brazing – a way to join two types of metals by melting a filler metal into a joint, creating a bi-metallic component. However, brazing requires a significant amount of manual labor, meaning higher costs and longer manufacturing time.
Majid Babai, NASA’s advanced manufacturing chief at the Materials and Processes Laboratory within Marshall, said: “Eliminating the brazing process and having bi-metallic parts built in a single machine not only decreases cost and manufacturing time, but it also decreases risk by increasing reliability.”
“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.”
NASA says that with the new prototype igniter, the two metals - a copper alloy and Inconel (a nickel-chromium alloy) - were joined together using a “unique” hybrid 3D printing process that they call automated blown powder laser deposition.
Using the laser additive technique means that the prototype igniter is made as one single part, instead of four different parts then brazed and welded together as normal.
In this case, the bi-metallic part was created using a hybrid machine made by DMG MORI in Hoffman Estates, Illinois. The new machine integrates 3D printing and CNC machining capabilities.
‘Ship in a bottle’ technique
Preston Jones, director of NASA’s engineering directorate at Marshall, said: “It is a technological achievement to 3D print and test rocket components made with two different alloys. This process could reduce future rocket engine costs by up to a third and manufacturing time by 50 per cent.”
Although the igniter is a relatively small component, measuring only 10 inches in height and 7 inches in diameter at its widest point, the new approach means that a much larger part can be made, and its interior machined during manufacturing. NASA likens that novel process to making a ship inside a bottle, where the exterior of the part is the “bottle” enclosing a detailed, complex “ship” with invisible details inside.
Steve Wofford, manager for the Space Launch System (SLS) liquid engines office at Marshall, concluded: “We’re encouraged about what this new advanced manufacturing technology could do for the SLS program in the future. In next-generation rocket engines, we aspire to create larger, more complex flight components through 3-D printing techniques.”
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