GE Global Research Center, Niskayuna, N.Y., reports that engineers at the GE Aviation subsidiary Avio Aero used supersonic cold spray to repair a gearbox from the world’s most powerful jet engine, the GE90. Cold spray, like 3D printing, is one of several additive manufacturing methods in which parts are built by adding material, rather than by cutting it away.
In most 3D printers for metals, lasers melt titanium and other metal powders, fusing them to build parts layer by layer. That technique works well for printing new components directly from a computer file.
However, heating an existing part can alter its crystalline structure and mechanical properties. “When you heat up metal and then cool it again, it changes in the same way powder snow can become a sheet of ice after a warm spell,” says Gregorio Dimagli, repair development manager at Avio Aero, which is located in Bari, italy.
In the cold-spray process at Avio Aero, a metal chamber the size of a walk-in refrigerator holds the part to be repaired and a robotic arm with an attached nozzle. This nozzle sprays metallic powder particles as small as five microns at supersonic speeds onto the piece that needs to be rebuilt. The particles strike the surface with so much energy that they form a diffusion bond with the part.
“Every single metal particle from the powder-charged gun attaches to the component due to the effect of the kinetics,” explains Giulio Longo, the lead repair development engineer.
While traditional 3D printers build parts from computer files, the cold-spray machine is based on digital scans of actual jet engine parts to accurately reconstruct the broken part.
The work is the result of a seven-year partnership between Avio Aero and the Polytechnic University of Bari. At the Apulia Repair Development Center, located on the Bari campus, GE engineers work with professors and experts in mechanical engineering to create new ways to build, maintain, and repair aircraft parts.
