Industrial Engineering

Beyond Niche: Alternative Manufacturing for Aerospace Parts

https://www.pacaf.af.mil/News/Photos/igphoto/2001272900/
Smart Manufacturing Engineering April 2019
By Kip Hanson

From commuter jets to communications satellites, the aerospace industry continues to embrace non-traditional manufacturing processes.

A typical commercial jetliner contains millions of discrete components, yet provided the plane arrives at its destination safely, on schedule, and hopefully without a screaming baby behind them, most of the flying public could care less how any of those parts were made. Airline passengers might care more about their plane’s construction, however, if they knew that the manufacturing methods used to build it have a direct effect on everything from ticket prices and aircraft durability to passenger comfort and Planet Earth’s air quality.

These methods have changed greatly over recent years, thanks in large part to an airline industry that demands improved fuel efficiency in order to reduce fuel costs, and government-mandated, increasingly stringent limits on fuel consumption. The argument for lighter, more fuel-efficient vehicles of all kinds has, in turn, led to adoption of new materials and manufacturing technologies that were unheard of even a few decades ago and, in some cases, far more recently.

Consider additive manufacturing, better known as 3D printing. What was once a novel, prototyping-only manufacturing method has since blossomed into the preferred, oftentimes only way to produce cost-effective aerospace components and tools. “Additive manufacturing has disrupted the industry,” said Adam Broda, senior production engineering manager for additive manufacturing at Chicago-based Boeing Co.

Recent trends in aerospace-based additive manufacturing (AM) have been aimed at using it to reduce long lead times in component and tool fabrication, he said, and for cutting the part cost of complicated designs. But it has also kick-started a design and simulation software revolution, one that will help aerospace manufacturers optimize their designs.

For example, design optimization software, together with AM parts and tooling, has helped Boeing teams cut costs while reducing aircraft weight and improving performance. “Another advantage of moving toward additive manufacturing is that Boeing produces less waste material,” he noted. “It will also enable the company to reduce the number of large tools it has in storage since Boeing will only need to store the individual file to be printed instead of the tool itself.”

Boeing’s facility in Auburn, Wash., uses DMLS (Direct Metal Laser Sintering), FFF (Fused Filament Fabrication), and in the future expects to implement polymer powder bed technology. According to Broda, these methods offer a good balance between cutting-edge efficiency and production-hardened technology.

Someone with a vested interest in the aerospace giant’s success is Scott Killian, business development manager for aerospace at EOS North America, Pflugerville, Texas, makers of the DMLS metal-printing equipment just mentioned as well as various polymer printing technologies. “Polymer continues to play a large role in aerospace, but the platform that has received the most attention and is responsible for the explosive growth over the past five or six years has been 3D metal printing, particularly powder bed fusion,” he said. “Aerospace was really one of the first industries to discover all that metal printing can do.”

AM That’s Fast Enough
There’s an oft-repeated saying within the AM community: complexity is free. This in large part explains 3D printing’s appeal to anyone trying to launch spacecraft, drones and commercial aircraft, as what better method to reduce vehicle weight and increase performance than one with complete freedom when designing critical componentry?

At the same time, 3D printing’s relatively slow build speeds—at least compared to traditional manufacturing techniques—are still plenty fast for companies producing anywhere from a few to a few hundred aircraft per year. And while neither polymer nor metal-based AM has yet reached the speeds needed to meet automotive or consumer product volumes, rest assured, they’re getting there.

“Because 3D printing is still a fairly new technology, the available print speeds and part accuracy are improving rapidly,” Killian explained. “And when you consider the potential of combining what would otherwise require multiple pieces into a single part, or the ability to easily print shapes that were previously impossible to produce, 3D printing will continue to play an important role in the aerospace industry; future successes will come from finding those applications where its higher entry cost and slower production rates provide a win versus traditional manufacturing methods.”

3D Systems Inc., Rock Hill, S.C., is another AM systems provider with an eye on the aerospace prize. Bryan Newbrite, an aerospace engineer responsible for the company’s Advanced Aerospace Application team, pointed out that “3D printing” means many different things.

“We offer eight different types of additive manufacturing technology and seven different types of additive-related software, and that’s just a small percentage of all that’s available today, so when people say 3D printing, it can refer to any number of things,” he said. “It’s more meaningful to look at specific applications and goals, whether they are improvements to fluid dynamics, weight reduction through optimized topology, or simplifying the supply chain because fewer parts are now needed.”

In that same vein, what does “aerospace” really mean? Newbrite said that companies such as Boeing and Airbus have hundreds and, in some cases, thousands of printed parts in their various aircraft, but noted that the military and especially the space industry have easily been 3D printing’s fastest adopters, simply because they have the clearest return on investment.

“If you can reduce the weight of a geostationary satellite by just one kilogram, for instance, you’ll save between $30,000 and $50,000 in launch costs that can now be devoted to additional satellite functionality,” he said. “Another huge benefit made possible with 3D printing is improved heat exchange on rocket engines, turbines and even microprocessors, not unlike what’s being done with conformal cooling channels in plastic injection molds.”

The fly in the ointment with each of these developments comes from the design side. Newbrite and others will tell you that additive success begins at the drawing board. “If you attempt to print parts designed for subtractive manufacturing, you’re squeezing a square peg into a round hole—even in the best case, you’re going to build something slightly less functional and probably far more expensive.”

Robert Yancey, director of manufacturing and production industry strategy and business development at Autodesk Inc., San Francisco, added that designing for additive is a far different animal, one that the industry overall is still grappling with.

“With any manufactured product, designers must concern themselves with the part shape and geometry, the raw materials used to make it, and the actual manufacturing processes,” said Yancey. “It’s this triad that determines what the final part will look like and how it will perform, but how you navigate all of that is very different when you’re talking about machining something from a billet vs. building it one layer at a time.”

Design complexity may be free with 3D printing, but that freedom has a cost. There are more variables to consider with AM, Yancey said, and a key part of the overall process is finding a way to calculate the best balance between design options and build parameters such as layer thickness, support structures, laser power, print speed, cost, and so on.

“This is why generative design technology and other advanced software functionality has become so important to the additive manufacturing community, as it not only does a lot of the heavy mathematical lifting but also provides various business and engineering tradeoffs to explore all the different options available to designers,” he said.

Yancey was quick to point out that AM is nothing new. Composite layup—additive’s alter ego—has been used for more than 40 years in aerospace applications, and he suggested that today’s new generation of 3D printed product designers can learn some valuable lessons on part qualification and certification from those experienced in what is now a mature, albeit increasingly automated, manufacturing process.

Directional Composites Rule

Andrew Purvis has that experience. The manufacturing engineering project manager for composites automation at Electroimpact Inc., Mukilteo, Wash., Purvis said that much of the aerospace industry has adopted composites for use in aircraft wing panels, horizontal stabilizers, negative control surfaces, and fuselage structures, and will probably never go back to metals.

“The new directional composites boast such a high modulus of elasticity and strength-to-weight ratio that some of these components simply wouldn’t function if they were made of metallic materials,” he said. “That, and the advancements we’ve made in automated tape layup (ATL) and advanced fiber placement (AFP) have made composite manufacturing very predictable and cost-competitive.”

Purvis said the commercial shift toward composites began after the military started using ATL technology for some of its aircraft. In this scenario, the need for high performance in the face of extreme speeds, G-forces, and service temperatures—never mind the need for stealthy planes—justified what was then a much higher price. Since then, Boeing and others have felt similar pressures for high-performing aircraft, making composites the material of choice.

Purvis and the Electroimpact team deal with many of the same challenges as any other additive manufacturer. “There are a number of things that need to come together in order for all this to work properly,” said Purvis. “We have design, programming and simulation software that must do its job. There’s the machine tool and the print head that deposits material. Then there are the humans who operate the equipment. It’s quite complex, but it’s a mature, well-understood process that will continue to grow in its capabilities.”

Jets for Jets
Though it may seem that way by now, not all alternative aerospace manufacturing technologies are additive in nature. Simon Kenworthy, business development manager at Shape Technologies Group in Kent, Wash.—a leader in ultrahigh-pressure and abrasive waterjet (AWJ) equipment including Flow International Corp. and other brands—said the cutting technology is used for a wide variety of aerospace needs. These include trimming of forged workpieces, stripping thermal coatings from engine components, de-gating of investment-cast parts, and a process that Electroimpact’s Purvis can relate to, machining of composite aircraft components.

“Abrasive waterjet cutting provides the best method of trimming composite materials, mainly because it leaves a very clean edge,” Kenworthy said. “There’s zero delamination, no exposed fibers, no fiber pull-out or buckling, and no unfriendly thermal effects to the substrate. Compared to mechanical technologies such as milling and drilling—even those specifically designed for composite cutting—it’s by far a more effective technology.”

As anyone who’s machined composite materials will tell you, it’s abrasive stuff. Diamond-tipped, diamond-coated, or diamond-veined tools are typically used, as edge wear is unacceptably high with conventional carbide tooling. Aside from their higher cost and performance, though, these tools still can create the same problems Kenworthy just mentioned, any of which can lead to premature component failure.

A similar though slightly different argument can be made for using AWJ to cut the heat-resistant superalloys found in jet engines. Though less abrasive than composites, the extreme toughness of HRSAs is enough to test the mettle of any machinist. By comparison, AWJ doesn’t care how tough, hard or thick a material is, as the machining is done with tiny bits of sharp garnet that have been injected into an ultra-high pressure (up to 94,000 psi) stream of water. There’s no tool wear and no cutting forces; all that’s needed is patience.

As with most machining processes today, AWJ has also become highly automated. The CNC machine tools now boast up to five axes of motion, allowing complex angled surfaces to be cut, while robotic loading and unloading provide unattended and cost-effective machining. “Certainly with some of the smaller components like engine blades, cycle times are best measured in seconds,” Kenworthy said.

Mixing Traditional and New Technologies
Even in what are otherwise traditional machine shops, decidedly untraditional technologies are being used to improve aerospace machining operations. Stuart Weiler, director of PLM at Elite Aerospace Group Inc., an aircraft component design, engineering, and manufacturing firm based in Tustin, Calif., said the company relies on a mix of five-axis machining centers, Swiss-style CNC lathes, and even some 3D printing for its customers in the satellite, aircraft, and “new space”
(privately-owned space launch) industries.

But this five-year-old company is pushing well beyond the norms with its embrace of Industry 4.0 technologies. It has connected its machine tools to the corporate network and developed dashboards for remote monitoring and production analyses using PTC ThingWorx. It is experimenting with augmented reality in hopes of improving its assembly operations, and for sharing information with aerospace customers. It operates a separate business division that offers contract CNC programming and engineering services. And as a result of its own in-house use of ThingWorx and PLM software from PTC Corp., it has since become a value-added reseller of those products.

“To be honest, I can’t point to any new manufacturing business that we’ve won as a result of our relationship with PTC, but it’s definitely given us greater shop floor efficiency and made us a bit more competitive overall,” explained Stuart, who is responsible for the software. “We’ve even given some of our customers access to our dashboards so they can check on their parts without going through us. And of course, having a PLM system firmly checks the documentation box required by anyone doing aerospace work—without that, it’s almost impossible to win any significant projects. We’re still a young company, but we recognize that the aerospace industry is changing and that we need to stay abreast of all the new technologies that are coming along if we’re to continue serving it.”

As “alternative” becomes mainstream, aerospace manufacturers are helping to advance these key new technologies while learning to use them effectively.