Hot-fire tests show 3D printed rocket parts rival traditionally manufactured parts

July 25, 2013
Left: 3-D printed rocket injector as it looked immediately after it was removed from the selected laser melting printer. Right: Injector after inspection and polishing. Credit: NASA/MSFC

What can survive blazing temperatures of almost 6,000 degrees Fahrenheit without melting? What did not break apart at extreme pressures? What is made by a new process that forms a complex part in just one piece? What takes less than three weeks to go from manufacturing to testing? What can reduce the costs of expensive rocket parts by 60 percent or more?

Answer: 3-D printed parts

Engineers know that 3-D printed rocket parts have the potential to save NASA and industry money and to open up new affordable design possibilities for rockets and spacecraft. But until recently, no one had tested rocket parts critical to in a hot-fire environment.

NASA engineers at the Marshall Space Flight Center in Huntsville, Ala., not only put rocket engine parts to the test but also were able to compare their performance to parts made the old-fashioned way with welds and multiple parts during planned subscale acoustic tests for the Space Launch System (SLS) heavy-lift rocket. In little more than a month, Marshall engineers built two subscale injectors with a specialized 3-D printing machine and completed 11 mainstage hot-fire tests, accumulating 46 seconds of total firing time at temperatures nearing 6,000 degrees Fahrenheit while burning and .

"We saw no difference in performance of the 3-D printed injectors compared to the traditionally manufactured injectors," said Sandra Elam Greene, the propulsion engineer who oversaw the tests and inspected the components afterward. "Two separate 3-D printed injectors operated beautifully during all hot-fire tests."

Post-test inspections showed the injectors remained in such excellent condition and performed so well the team will continue to put them directly in the line of fire. In addition to the SLS acoustic tests, Greene and her team tested a more complex assembly of a 3-D printed injector and thrust chamber liner made by Directed Manufacturing, Inc., of Austin, Texas. Marshall engineers transferred a second 3-D printed injector to NASA's Stennis Space Center in Mississippi, where it will continue to accumulate hot-fire time to test its durability.

"Rocket engines are complex, with hundreds of individual components that many suppliers typically build and assemble, so testing an engine component built with a new process helps verify that it might be an affordable way to make future rockets," said Chris Singer, director of the Marshall Center's Engineering Directorate. "The additive manufacturing process has the potential to reduce the time and cost associated with making complex parts by an order of magnitude."

Traditional subscale rocket injectors for early SLS acoustic tests took six months to fabricate, had four parts, five welds and detailed machining and cost more than $10,000 each. Marshall materials engineers built the same injector in one piece by sintering Inconel steel powder with a state-of-the-art 3-D printer. After minimal machining and inspection with computer scanning, it took just three weeks for the part to reach the test stand and cost less than $5,000 to manufacture.

"It took about 40 hours from start to finish to make each injector using a 3-D printing process called selective laser melting, and another couple of weeks to polish and inspect the parts," explained Ken Cooper, a Marshall materials engineer whose team made the part. "This allowed the propulsion engineers to take advantage of an existing SLS test series to examine how 3-D printed parts performed compared to traditional parts with a similar design."

Since additive manufacturing machines have has become more affordable, varied, and sophisticated, this materials process now offers many possibilities for making every phase of NASA missions more affordable. The SLS injector tests are just one example of NASA's efforts to fabricate and test 3-D printed parts in relevant environments similar to those experienced during NASA missions. The SLS injector test series complements a series of liquid oxygen and gaseous hydrogen rocket assembly firings at NASA's Glenn Research Center in Cleveland, which hot-fire tested an additively manufactured, select laser melted injector developed through collaboration of industry and government agencies. A J-2X engine exhaust port cover made at the Marshall Center became the first 3-D printed part tested during a full-scale engine hot-fire test at NASA's Stennis Center. Marshall materials engineers are currently making a baffle critical for pogo vibration mitigation; it will be tested at Marshall and Stennis and is a potential candidate for the first SLS mission in 2017. Marshall engineers are finishing up ground tests with Made in Space, a Moffett Field, California company working with NASA to develop and test a 3-D printer that will build tools on the International Space Station next year. NASA's Johnson Space Center in Houston is even exploring printing food in space.

"At NASA, we recognize ground-based and in-space additive manufacturing offer the potential for new mission opportunities, whether printing rocket parts, tools or entire spacecraft," Singer said. "Additive manufacturing will improve affordability from design and development to flight and operations, enabling every aspect of sustainable long-term human space exploration."

Explore further: NASA, industry test additively manufactured rocket engine injector

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4 / 5 (4) Jul 25, 2013
it took just three weeks for the part to reach the test stand and cost less than $5,000 to manufacture.

"It took about 40 hours from start to finish to make each injector using a 3-D printing proces..."

Would be interesting no know how much time/money one of the 'old-fashioned' parts require.

Though I don't think the design time should be counted as that is likely equal for both approaches...maybe even less for the 3D parts as you don't have to consider manufacturing process interfaces. So a pure comparison of build-times/manpower required would be the ticket.

But as a whole the article is pretty awesome. I always thought that 3D printed parts would be lacking when it came to even slightly specialized tasks with somewhat elevated material property requirements. But
The future for 3D printing has always seemed bright. And this has upped the lumen count considerably yet again.
3.7 / 5 (3) Jul 25, 2013
What can survive blazing temperatures of almost 6,000 degrees Fahrenheit without melting?

Not the 3D printed part. It's an injector - it's cooled down by the fuel that passes through it.

If the part was actually made from a material that can withstand 6000 F without melting, you wouldn't be able to melt it in the 3D printer. I know of no 3D printer actually capable of forming parts out of tungsten, which melts at 6192 F.
4 / 5 (4) Jul 25, 2013
you wouldn't be able to melt it in the 3D printer

Why not? E.g. we have a partner who 3D prints patient-specific titanium implants via laser sintering titanium powder layer by layer (the machine is about the size of a wardrobe). While that 'only' requires temperatures in excess of 1650C at the point of focus of the laser I'm pretty sure one could get a similar process going for material that melts at 3500 degrees by upping the laser power without substantial changes to the method.
1 / 5 (6) Jul 25, 2013
"We could not weld it, for weeks and weeks we could not weld it." - Bob Schwinghamer of the Apollo program, two minute video from the Science Channel documentary "Moon Machines":
1 / 5 (1) Jul 26, 2013
Why not?

I would hazard that the power density would be so high that it simply blasts the powder around instead of melting it. After all, you have to concentrate tremendous amounts of energy in a confined spot in a very short amount of time. For one thing, any lower melting point impurities would simply turn to gasses and blow off.

Casting or welding tungsten is notoriously difficult, so high purity tungsten parts are typically made by sintering from powder or forging/drawing in a process similiar to wrought iron.
1 / 5 (3) Jul 28, 2013
Casting and welding Tungsten is so easy - we even give the job to the apprentices, in their first day on the job.

"Here is the mop and bucket, clean up these floors over here. Oh by the way, in the corner is a ton of tungsten and coal, a box of matches and a nice hammer each, can you knock us up a few ton of rocket engine parts before you knock off? There is a good Ladde and Laddette."
4 / 5 (1) Jul 28, 2013
I would hazard that the power density would be so high that it simply blasts the powder around instead of melting it.

Looks like there's a company already solved the problem. They first use a binder and then a short pulse laser system to 3D print tungsten
not rated yet Jul 29, 2013
Cool! How about a set of drawings for an anti-drone missile?
not rated yet Jul 29, 2013
Old style method: cost is $10,000
New method: cost is $5,000

Okay, I appreciate they are still testing the process, and the cost will probably come down further, but a 50% cost reduction is not "an order of magnitude", unless you're working in binary...
not rated yet Aug 28, 2013
Looks like there's a company already solved the problem.

Nope. They haven't, yet. That's just their marketing spin.

The advertisement actually says: "Eventually, additional material sets can be printed on the M-FLEX, including tungsten..."

The problem still is, that your binder will evaporate into gas well before the tungsten starts to fuse. Typically binder based metal printers use a lower melting point metal that seeps into the binder and replaces it, effectively soldering the metal powder together. E.g. steel powder with bronze, which means the part is nominally steel, but will disintegrate at temperature where the bronze melts.

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