The U.S. Army is working assiduously to flight-qualify engine parts it has redesigned using additive manufacturing (AM). One such component—an inlet swirl frame for a turbine engine—illustrates the intense appeal of AM: “We reduced the number of its parts from somewhere around 150 to somewhere around 25,” said Amy Lawrence, manufacturing science and technology division chief, U.S. Army Combat Capabilities Development Command, Aviation and Missile Center.
The Army hopes the inlet swirl frame will be up in the air as standard fare in five years, said Lawrence, one of five experts Smart Manufacturing gathered recently at Auburn University for an exclusive panel on AM for mission-critical parts.
A broader goal, she added, is DFM (design for manufacturability): getting closer to the designer’s original intent up front without having to make costly revisions. AM is breathing new life into the decades-old DFM movement.
“Design for additive manufacturing (DFAM) brings over a whole new world of possibilities,” Lawrence said.
NASA is “just at the beginning stages of producing ‘safety-critical’ items,” John Vickers, principal technologist for AM at NASA’s Marshall Space Flight Center, said at the roundtable. “For our human space-flight, rocket-propulsion systems, we don’t have any safety-critical components that are qualified for flight. But we’re developing a process and material standards that will allow us to qualify those: It’s been almost 10 years in the making. We probably have another couple of years before we are actually able to fly those.”
NASA already flies “hundreds, maybe thousands of additive parts on NASA hardware for NASA missions, but those are not safety-critical,” he noted.
On the mission-critical parts menu, NASA first selects simpler components that “aren’t under high load, aren’t in the most extreme environments” in order to prove the safety of AM, Vickers said. But it is eager to use 3D printing for more complex parts that cost a fortune.
“Some of these liquid rocket engines are extremely expensive,” he said, “so we’re trying to cut the cost of those, shorten the development cycle and improve performance, as well.”
The move into high-value hardware—like the injector systems for liquid rocket engines in which the Huntsville, Ala.-based Marshall Space Flight Center specializes—“will all happen in a cascading fashion, very quickly,” Vickers predicted.
More broadly, NASA is considering 3D printing for “manufacturing in-space telescopes and rovers that might go to Mars—we’re looking at components for all of those systems.”
In December 2015, General Electric began producing 3D-printed, fuel-nozzle interiors at its factory in Auburn, Ala. Today, the six-year old factory has 46 printers making fuel-nozzle interiors for the LEAP jet engine, which it developed with Safran Aircraft Engines.
The GE fuel nozzle story was a watershed moment in the history of AM: GE used to make the same part using 20 little pieces of metal. “With additive as an enabler, we make it as one part,” said Ricardo Acevedo, leader of GE Aviation’s Auburn plant.
“Additive gave us a magnificent amount of efficiency from an inventory standpoint, because now you’re only carrying one part, so your inventory gets reduced 70-80%,” he said. “And it gave us five times the durability compared with what a conventional fuel nozzle would have given us, on top of 25% weight reduction and 30% cost efficiency compared with conventional methods.”
Having made 60,000 pieces via AM, GE Aviation is still “paving the way,” Acevedo said. “We have to evolve our inspection systems, for example: A lot of the complexity of the part is inside the part. So we have to develop inspection systems that go along with it.”
GE and NASA today find themselves using very expensive volumetric computed tomography (CT) scanners to inspect 3D-printed parts.
“It’s really the only way today that we can interrogate the inside of the parts in a thorough enough manner for us to evaluate and qualify those parts,” Vickers said. “If we build 1,000 parts or 40,000 parts, we have to use CT to look at every one of those parts.”
To get to “design for manufactured systems and subsystems and components, and manufacturing those with qualified processes,” the industry needs to in the next five years focus intently on open standards and specifications, Lawrence said.
“For us, standards are critical for adoption of AM technologies,” NASA’s Vickers said, noting that Auburn University is working on standards with NASA, the U.S. Department of Defense, some international partners and ASTM International (formerly called the American Society for Testing and Materials).
“At NASA, for these first safety-critical parts, we had to develop our own standards,” he said. “We would rather not be in the standards-development business. But we had to because standards did not exist.”
Additionally, manufacturers need to concentrate on “material databases, the digital thread, cultural change, in situ monitoring and alloy development,” Lawrence said.
In part because of the Manufacturing USA institutes America Makes and NextFlex, manufacturing has reached an inflection point that gives urgency to these initiatives, said Nima Shamsaei, director of the National Center for Additive Manufacturing Excellence (NCAME) in Auburn University’s Samuel Ginn College of Engineering. “At minimum, the potential for AM technology has been realized, both in government agencies and in industry.”
So, he added, academia must quickly adapt to supply the talent needed by government and industry. “And in the last few years, we’ve seen almost every single university trying to get into this. We see activities all around the country, all around the world. In terms of symposia and workshops, we see a lot of participation from different industries, as well as universities.” (Auburn’s NCAME this year secured a $5.2 million R&D contract from NASA to work on regeneratively cooled thrust chamber assemblies for liquid rocket engines.)
The issue of design tools alone illustrates the elaborate work to be done, Shamsaei said. “Additive is a complex process. Think about laser/material interaction, thermal phenomenon, solidification, microstructural evolution, defect formation and more. There is a lot of knowledge we need to generate before we can have validated design tools for additive.”
Greg Harris, director of the Southern Alliance for Advanced Vehicle Manufacturing at Auburn’s engineering college, said another problem that must be addressed is “culture of specific disciplines of discovery, which is everybody thinking, ‘My data is what I need, and I’m not going to share it with anybody else’.”
“If we have a full digital thread, and we’ve captured all of the data about the material, the process, the geometry and the test evaluation and I can see that in real time—while it’s being made—and John can see that in real time—while it’s being made—now we have a trusted source of what that part looks like,” he said.
“Not only that, I can also identify that specific part with that set of data. So now I know lineage, I know everything about this material coming in. When it arrives for assembly, they can pull it in, scan it, say, ‘Look, this is that part. Here’s all the data that goes with that’.”
A scenario like this would allow for predictive capabilities, as well as generative design. In generative design, a designer enters design goals for a part, along with variables like cost constraints, into software that generates an array of possible designs. The software can learn from each query so that it generates more useful design options with more queries.
“We cannot do that today,” Harris said. “We’re moving in that direction. But we have issues in doing this that deal in lack of interoperability between systems.”
Along with the digital thread, open standards, such as STEP, the Standard for the Exchange of Product model data, are again very important.
“The lack of standards is huge right now,” Harris said. “Standards help us develop reliability. And reliability in our materials, processes and geometry are necessary if we are going to have reproducible parts. Reproducible parts are required to achieve certification.
“The things that we’re doing here in additive (at Auburn) are great: We’re gathering great data on materials and processes. But we’re still doing it on an individual, experimental basis. Until we get to a point where we can start to standardize, because we have enough data on the processes and on the materials to be able to do data analytics in a way that makes sense, we’re not really going to get to a point where we can trust those standards that John says he needs to have to qualify a part for flight.”
Standards work underway
One challenge in developing the standards for AM is the fact that the standards-setting process is consensus-based and volunteer, Shamsaei noted: “It’s relatively new technology, and a lot of knowledge is generated in different industrial sectors. I’m sure GE knows a lot about AM, but that’s their IP. They’re not coming into the room and sharing all their secrets.”
“We share,” said Acevedo, noting that GE regularly works with Auburn engineering students on senior design projects and is part of an America Makes-funded AM project that Auburn leads. But it is limited to data on the testing of raw materials—for which open standards would lower basic development costs for any company “jumping into additive” the way GE has, he added.
Nonetheless, ASTM is funding research in support of the standards—some of it at Auburn.
Shamsaei’s crew at Auburn plans to next month present a set of R&D results, funded by ASTM and some U.S. government agencies, to an ASTM standards committee in Paris, he said.