A rule of thumb in the airline business is that every kilogram that can be shaved off the mass of an airframe saves at least $3500 in fuel costs over the aircraft's life span, not to mention concomitant reductions in emissions of carbon dioxide.
Engineers at Airbus's parent, EADS, are using a new 3-D printing technology to make fully operational, "geometrically optimized" aerospace components of titanium, stainless steel, and aluminum alloys that are as much as 65% lighter than traditional machined parts, but just as strong and resistant to fatigue.
The method, an advance in additive layer manufacturing (ALM), is now starting to find use in low-volume production of components for aircraft, satellites, and racecars after first cutting its teeth on customized health-related items such as dental implants, hearing-aid casings, and hip implants, said Jon Meyer, ALM Research Team Leader at EADS Innovation Works, the company's R&D arm in Filton, U.K, near Bristol.
"In recent seasons, for example, quite a number of ALM parts have been installed in Formula One racecars," he noted, adding that the first operational ALM-made aerospace part will fly later this year on an Astrium (an EADS subsidiary) satellite. The hold-and-release mechanism, which keeps the orbiter's solar panels folded during launch, replaces a six-part assembly.
"ALM enables us to work with high-value engineering materials, including titanium alloys, nickel-based stainless steels, and specialist, high-strength aluminum alloys that cannot otherwise be processed easily," Meyer said. He predicted that the performance of ALM parts will improve as metallurgists develop alloys that are tailored for the process. The technique can work with epoxy and other thermopolymer powders.
Growing components in situ
In concept, the ALM process resembles 3D Systems' stereolithography and other 3-D printing techniques that fabricate design and engineering models layer by layer from cross-sectional slices in CAD files, he said. But ALM differs in that it typically employs 200- to 400-W fiber lasers or 1-kW electron-beam guns to directly melt successive layers of metal powders to form operational parts. The fabrication usually takes place in environmental chambers that contain a vacuum or inert (argon) atmosphere and that are usually heated to just below the powder's melting temperature.
Innovation Works researchers have been developing the process in-house for only a few years, so the technique is still relatively immature. But Meyer’s team is confident of its eventual practicality. For although ALM remains a relatively high-cost, batch-manufacturing process, the fact that numerous components can be created simultaneously and that production speeds are rising steadily has led it to foresee the technology as a real-world manufacturing approach.
"We think that it's a good bet that the process will in time become mainstream," he asserted.
And unlike previous laser sintering-based 3-D printing processes, ALM's powders contain no sintering binders that can yield part defects and thus require removal in secondary steps. In addition, any residual stress from the targeted heating (which can make them warp when welded) can be relieved with subsequent annealing, whereas for some parts the preheating avoids residual stress in the first place.
The other main impetus for adoption is the process's unique ability to create extremely complicated shapes—a flexibility that enables engineers to optimize part geometry like never before.
"The technology charges no extra cost for complexity," Meyer said. "It allows a degree of freedom that's never existed previously, which opens up the possibility of novel solutions. And even though it's not that cost-effective at present, it becomes much more so for unique or [left- or right-]handed objects and complex things—items for which the barriers to entry is lower."
Real, working parts
In the aerospace industry, ALM was first used to make wind-tunnel models, but practitioners soon realized the potential for employing it for real-world components. Other early uses included unique components including drill and jig fixtures with integrated workpiece-extraction features, and niche applications such as tooling for polymer manufacturing.
More recently, "we've been looking at things such as steel and titanium engine nacelle hinges for A320 airliners, where we've demonstrated the potential to achieve a 60% weight reduction with the same strength and fatigue endurance," said Meyer. His group is currently evaluating the fire-zone components in representative certification fatigue and static tests. This project, which is being conducted in collaboration with Bombardier, the Canadian aerospace company, is funded by the U.K. Technology Strategy Board.
Another promising effort revolves around the hyperjoint concept, a strong, robust interface between metal and composite, or composite and composite, parts.
"First, you grow an array of small, arrowhead-like pins on the surface of a titanium part, which you then can imbed in the surface of an uncured composite panel without breaking any of the fibers," Meyer explained. "Then you cure the assembly and you get a co-cured metal-composite mechanical joint with the robustness of a fastened joint."
The approach eliminates many steps such as assembly and fastening operations.
The Innovation Works team also recently unveiled the Airbike, a working bicycle that was grown in-situ from nylon, as "a demo item to get the ALM process across to average people." The bike incorporates several notable features including integrally built, "preassembled" components such as wheel bearings and difficult-to-construct, complex truss structures in the frame and seat.
The new process can also provide less tangible benefits.
"It offers, for instance, the potential to build the first few aircraft sets of parts before you switch over to castings or forgings, which can reduce the risk of design changes down the line," Meyer said. "Otherwise, you might get locked into, say, die-tooling designs that were frozen early on before you had all the load data, which can have important implications on overall weight and interface configurations. Such complications can have large knock-on effects."
Other benefits can accrue from ALM. "There are no labor or tooling costs," Meyer said. "Plus, there’s very little waste," whereas in machined parts, much of the costly workpiece material often gets thrown into the swarf bucket.
He noted that ALM's current costs are mostly related to the speed of the process, which his team is working to increase with faster scanning, more powerful beams that can be split multiple times, changes to the layer thicknesses, and other approaches. To do so, the EADS group is working with process system OEMs, including firms such as EOS, Archem, MTT, Concept Lasers, and 3D Systems.
Both heat sources (lasers and electron-beam guns) are improving in parallel, Meyer observed. As higher-power lasers become available, suppliers are meanwhile refining e-beam systems to provide smoother surface-finish results.
"ALM opens up ever-wider opportunities," Meyer concluded. "In terms of complex products, you reach a crossover point where even at today's speeds batches of 100 to 150 parts become economic. We expect to see it used relatively soon in the marine business and for specialized automotive products."
The 3D-printing technique could, in addition, allow replacement components to be produced in remote regions, perhaps improving logistics in humanitarian relief and military operations. It also offers the potential to fulfill the dreams of enthusiast "makers" everywhere—for objects to be produced quickly and cheaply on affordable "printers" that are located in offices, shops, and even homes.