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Fraunhofer

Researchers at the Fraunhofer Institutes for Mechanics of Materials IWM and Production Systems and Design Technology IPK in Germany have developed a way to use shot peening to straighten thin, distorted ceramics for parts such as leaf springs. They fire shot or small pellets at the surface of a component with a blasting gun. The shot strikes the surface and alters the shape of the thin, outermost layer. By moving the gun over the ceramic part along a precisely calculated path, researchers counteracted warping. “Shot peening is common for working metals,” says IWM manager Wulf Pfeiffer. “But it has not been feasible for ceramics because they are too brittle and would shatter.”

Researchers analyzed which size shot might work on ceramics. Pellets that were too big would destroy the surface. Pellet speed was also a factor because hitting the material too fast damages it while hitting it too slowly does not change the surface shape enough. Before making a new component, researchers determined what to expect of particular ceramics. They fired shot and measured the stresses to see what sort of deformation is feasible and how the beam should be directed.

Ceramics are useful in industry because they are lightweight, rigid, resist corrosion, and withstand higher temperatures than metal (over 500°C). Until now, however, ceramics could only be machined using costly diamond tools. And machining creates tensions in the material’s surface, which distort the finished part as soon as it is removed from the machine.

Fortunately, the capability to shot peen the material has let researchers create various prototypes, including a ceramic leaf spring and a concave mirror. The technique is now advanced enough to serve in series production for simple components. Researchers have developed a computer simulation that will let components be worked in multiple axes. They also hope to automate the process using a robot.

© 2012 Penton Media, Inc.