Meet the Machers: 3D Manufacturing Goes Supersonic

On May 20, 1955, a souped-up version of the B-45 Tornado bomber took off from Schenectady Airport in upstate New York, lowered a brand new supersonic jet engine installed in the bomb bay into the air stream and streaked away at Mach 2, twice the speed of sound. The flight was a milestone in American aviation and the engine design, which was developed by jet propulsion pioneer Gerhard Neumann, helped GE become an aviation powerhouse. GE research in Schenectady has not slowed down. Scientists at GE Global Research Labs (GRC) in nearby Niskayuna have now developed a supersonic manufacturing technique called 3D painting that could make next-generation jet engines lighter and more efficient. 3D painting deposits metal powder flying at velocities of up to Mach 4 on precise models to produce and repair jet engine blades, rotors, and other components without resorting to machining or welding. “This additive technology is like a fountain of youth for machine parts,” says Anteneh Kebbede, manager of the Coatings and Surface Lab at the GRC. Kebbede says that 3D painting is a new take on an older technology called cold spray. Cold spray is using a spray gun to coat parts with a thin layer of material. But 3D painting can build whole new parts with walls as thick as one inch or more. “For manufacturers the potential benefits are enormous,” Kebbede says. “Imagine being able to restore an aging part to its original condition with a tool that looks like a spray gun.” Unlike welding, cold spray coatings do not require heat, which can melt surrounding material and change the mechanical qualities of the part. The 3D painting gun is using pressurized carrier gas zipping through a de Laval nozzle to accelerate powder particles as small as five microns to supersonic velocities. The speed causes localized high-energy collisions when the particles hit the surface, the micro version of bullets hitting an I-beam. “Powder particles slam into the surface and form a diffusion bond with the part,” Kebbede says. “The bond happens on the atomic level. That’s why we are so excited.” Kebbede and his team are using a computer-controlled robot to manipulate the gun. Like 3D printers, the computer works with a 3D image of the part. Engineers program the robot so that it moves in an optimal way to deposit the powder. “All the hard work is in the details,” he says. “The powder selection, the conditions the powder experiences in the gun, the speed of the gun, the gun distance from the part, and its angle relative to the part are just some of the inputs that lead to a good bond. That’s the trick. The same process that can cause build-up can also cause erosion.” In the past, engineers used cold spray to clad everything from electronics to cooking pots with soft materials like copper. But Kebbede’s team is now working with superalloys with applications anywhere from heavy-duty gearboxes for oil and gas machinery, to gas turbine rotors and jet engine blades. Who knows, maybe one-day supersonic painting will add a few Machs to the jet engines of the future. SOURCE: GE Reports