Additive manufacturing holds potential for many possible new frontiers in the aerospace industry, and manufacturers in aviation and space flight are reaching for those new vistas. But they’re held back at less than warp speed due to a lack of awareness, unmet technological needs and the absence of a formal regulatory process in their highly regulated industry.
The additive manufacturing (AM) method offers advantages in maintenance and repair; lightweighting parts; optimizing design, including parts consolidation and flow optimization; accelerating design-to-production time; enabling on-demand replacement parts production, reducing or eliminating the need to warehouse spare parts; and making design traceability and storage digital instead of physical.
These advantages, as well as the leadership and transparency on AM developments shown by large companies such as Airbus, Boeing and GE, which 3D prints close to two dozen parts for its LEAP engine, have helped motivate and inspire others to continue their efforts to make progress.
“The fact that somebody like GE is not using additive as a backup but actually doing that on an important new engine program indicates their faith in the technology and that it can build high-quality components at a reasonable cost that give a performance benefit,” said Richard Grylls, technical director for SLM Solutions NA Inc. (Wixom, MI).
New Applications on the Way
While aerospace companies have exploited the new opportunities AM offers for noncritical flight components, such as brackets, shrouds and ductwork, the method also offers advantages in engine and body work.
“I expect to see many new applications in aircraft engines, especially as it relates to part consolidation and flow optimization,” said Bob Yancey, director of manufacturing industry strategy at Autodesk Inc. (San Francisco), citing GE’s LEAP engine fuel nozzle as an example.
GE’s designers figured out a fluid flow path for the fuel that solved some efficiency and maintenance issues with traditionally manufactured fuel nozzles, he said. The benefit AM offers for fluid control devices—which can include liquid as well as air—is the ability to design and make flow paths that could not be created using traditional manufacturing. What results is more efficient fluid and/or thermal control.
Even with the growing body of demonstrated advantages to additive, the method’s advocates still have a lot of educating to do.
“There’s still a tremendous lack of knowledge for what you can do, which is holding back expansion of AM in aerospace,” said Bryan Hodgson, advanced aerospace applications lead for 3D Systems Inc. (San Diego). “If it’s a new part, it allows you more design freedom. If it’s a low-volume part, it allows you lower cost of ownership. And if it’s an old part, it allows you to replicate the same part with less investment.”
What’s needed, Hodgson said, is a culture change. Designers must shift their thinking on parts design and consider all the new possibilities in designing for AM. Manufacturing engineers need to involve themselves early in the design process.
Stephen Anderson, business development manager for additive manufacturing at Renishaw Inc. (West Dundee, IL), agreed: “What AM really does is bring the designer and the production engineer, the manufacturing engineer, very close together, perhaps more now than ever before.
The Need for Higher Speed
Technologically, AM needs improved and more robust processes, including more in-process monitoring; ramped up R&D on new materials; and increased speed.
“What they’re chasing is how fast can you build a part and make it a good part,” said Gene Granata, Vericut product manager, CGTech (Irvine, CA). “That’s one of the things that holds the technology back because the build rate for a part on these machines is typically slower, compared to creating the same part in the machining world. So, while you can make fantastic parts and detailed parts, the production rate is a little challenging until you can make it higher.”
A component’s build is just one part of the process, though.
“If we could increase the speed, the actual speed of the process, setting things up and getting them ready for the machine, the speed of postprocessing and the speed of getting from an idea through production, if we speed these things up it opens up the possibilities of what is economically feasible to build with the technology,” said Grylls. “Right now, there are a number of components that are economically feasible, and if the industry speeds up all those things, the opportunities just explode.”
At ME’s request, Grylls applied SLM Solutions’ build calculator to a case study part featured on its web site, a spacecraft valve body made of titanium 64 that measures 8.74 × 8.66 × 12.21″ (22.2 × 22.0 × 31.0 cm). The part took 6.5 days to make on SLM Solutions’ twin-laser 400W SLM 280 machine, compared with more than the six months it would take for traditional tooling, casting and machining of a billet.
AM production time would drop to about 4.1 days using a 700-W twin-laser machine; 3.2 days with a 400-W quad-laser; and 2.1 days with a 700-W quad-laser (available in the SLM 500 and the SLM 800, which has a higher Z axis than the 500. The 800 should be available commercially later this year, according to an SLM Solutions spokeswoman).
“There are many variables that make this type of analysis a bit dodgy, but the bottom line is that 3× faster per part is not unreasonable,” Grylls wrote with his results.
Scott Killian, business development manager for aerospace, EOS North America (Novi, MI), stressed the need for more material development. “We have a very limited selection of aluminum materials today. None of them really match the aerospace-grade aluminums [manufacturers] would like to use. So, there’s kind of a gap there. That includes the additive manufacturing powder bed platform in general.”
And on the regulatory side, progress is held back in part by the absence of a well-defined design, material and process qualification system by the US Federal Aviation Administration (FAA) and the European Aviation Safety Agency (EASA). The agencies acknowledge the need for a system, but indicators are it will take years to put in place.
“To date, the certification of aerospace parts is on a case-by-case basis, so there clearly needs to be a more streamlined and defined process for AM to grow,” said Yancey. At least qualification operates on a two-for-one basis: “FAA and EASA work hand-in-hand on these issues, so whatever one develops, the other will follow,” he said.
You Can’t Make a Whole Airplane Out of Plastic
For many years, metal AM has focused on a limited number of materials, and the aerospace industry did little to change that, according to Grylls, who holds a doctorate degree in metallurgy.
“There are a number of reasons, but a lot of it was just that for the people in the aerospace industry, every ounce of their engineering resources was going into ‘how do we introduce this new technology [AM]?’, ” he said. “And if you try to introduce a new technology, doing it with a known material is just a good idea because it gives people comfort that they’re dealing with something they really understand well.”
Among the early additions to the list of metals that aerospace introduced were Inconel 718 and Inconel 625, two well-known and understood alloys in terms of incorporating them into an assembly, heat treatment, and machining, such as drilling.
“So, choosing those for early introduction was a brilliant idea,” Grylls said.
In the last couple of years, as different companies have gotten used to AM, new aluminum alloys and nickel alloys are becoming available, and new titanium alloys are in development, along with other materials.
Autodesk collaborated with Airbus for an interior partition in its A320s made of scalmalloy, an aluminum, magnesium, and scandium alloy that is “as ductile as titanium, as light as aluminum,” according to the web site of its developer, APWorks, an Airbus subsidiary. Using scalmalloy, AM and Autodesk’s generative design technology, Airbus reduced the component’s weight by 45%, said Yancey. The part is currently undergoing the FAA qualification process.
EOS is also developing new materials, including plastics and aluminum.
The 6000 and 7000 series aluminums are the most widely used in aerospace, but they’re difficult to weld, said Killian. Also, aluminum is notorious for building up internal stresses and cracking during the AM process. EOS is looking at ways to change the chemistry of the aluminum and developing new process technologies to solve the cracking problem, he said.
EOS is also working on qualifying more types of aluminum for aerospace and other industries, in part through NextGenAM, a large-scale, serial manufacturing collaboration with automaker Daimler and aerostructures supplier Premium Aerotec.
One of EOS’ legacy plastics, FR-106, a fire-retardant Nylon 11, was the first fire-retardant AM material approved by the FAA for commercial aircraft, said Killian.
“The next evolution of that is taking place now with Boeing, using high-temp plastics … PEEK and PEKK,” he said. “ALM [Advanced Laser Materials (Temple, TX)], a company acquired by EOS in 2009 to advance material development] worked with Boeing for about five years to develop a carbon-filled PEKK material that’s now approved and just started going into production for commercial aircraft last year.”
Like FR-106, the carbon-filled PEKK is used to make air handling ductwork and replaces traditional carbon fiber layup and, in some cases, machined aluminum. Also, Boeing is using carbon-filled PEKK to make more than 600 parts previously made from titanium and aluminum for the CST-100 Starliner space capsule.
“It looks like when those things finally do go to space there’ll be a lot of parts made on EOS machines out of that material,” Killian said.
Also on the plastics side, 3D Systems recently introduced DuraForm ProX FR1200, a flame-retardant, Nylon-12-based interior cabin plastic that delivers FAR 25.853 compatibility. The new plastic is 10% lighter than standard ABS aviation plastic, said Hodgson.
3D Systems printed an economy class video monitor shroud for Boeing 777s purchased by the Dubai-based airline Emirates using the new plastic and a new printer designed to work with it, the ProX SLS 500.
Another aeronautics company, Metro Aerospace (Dallas), used 3D Systems’ DuraForm GF, a glass-filled nylon, to 3D print microvanes, devices attached to an aircraft’s fuselage to reduce drag. Such plastics can sometimes be used to replace aluminum to make parts lighter in weight.
“Obviously, you can’t make a whole airplane out of plastic, but there are certain cases where it makes sense to transition from an aluminum to plastic,” Hodgson said.
Engineers Monitor Internal Geometry
Along with developing new materials, AM companies are also emphasizing in-process monitoring to verify part and material quality in real time, said Autodesk’s Yancey. The information gathered from monitoring can eventually lead to machine analytics and machine learning for continuous process improvement.
In most cases, this includes sensors on the machine to monitor position, temperature, humidity, layer integrity, voids, and other factors, Yancey said. The goal is to predict material quality from the machine sensor data. Currently, test coupons are often printed with the parts and then tested to measure the material properties. They aren’t entirely representative, but in most cases, they’re close, he said.
The goal is to correlate sensor readings and resulting machine data with the tested material properties so engineers can predict material properties during the build. From the analytics, the machine is continually learning and, as it learns, the build parameters are changed to improve the process.
Renishaw knows what Yancey’s talking about.
The company recently launched InfiniAM Spectral software to provide feedback on laser energy input and emissions from AM build processes. It works with the company’s proprietary hardware, which includes in-line optics and an infrared photodiode that monitors the wavelength of the laser’s modulated beam. Together, the software and hardware provide valuable information about part quality during a build.
By being able to put measurement instrumentation into the machine, engineers can analyze every single laser spot weld the laser makes. They can check that the amount of energy intended to go into the build actually did, and that the shape of the melt pool is as they would expect. The system reports on every spot on every layer of an AM part, assembling millions of data points about the internal geometry of the component as it’s built.
“This is incredibly powerful for aerospace customers because it allows them to review, basically, all of that internal geometry as they’re building the part,” said Anderson. “Not after it’s built, but as they’re building it.”
As a result, engineers can correct any problems on the next build or, increasingly, during the same build.
Simulation also offers information about the build process.
“One of the funny things about additive is you can make a part that looks pretty good, but by the time you saw it up or stress analyze it, take a look at what’s going on in the inside [checking for voids], and determining the properties for strength, sometimes you learn that the current process doesn’t create a part that will function as it was designed to,” said CGTech’s Granata.
In addition to protecting additive machines from expensive collisions, simulation can help identify problem areas where additive NC programs don’t apply material correctly to build the desired part. Applying too much heat to metal during the additive process can also cause distortion and affect the material’s properties, or in the case of hybrid machines, zones affected by hot-cold cycling.
“On the CAD side, simulation software would give you analysis of your build process and suggest where your heat buildups are going to be, and suggest some sense of where things are going to fail,” Granata said.