Peen forming of ceramics - A new chipless shaping technique

Thin ceramic components are often distorted during production due to anisotropic shrinkage and/or residual stresses due to machining. If unwanted distortion is detected in a component in its final shape, me distortion cannot be eliminated by additional material removal. Such ceramic components are usually discarded since their brittleness does not permit further flattening. Ceramic parts with complex shapes must be fabricated by, for example, sintering close to the desired shape followed by a costly 3D machining process. This paper describes the first successful experiments aimed at shaping ceramic specimens using shot peening. Strips of different thicknesses made of silicon nitride ceramic were shot-peened using different shot peening parameters. The residual stress-depth distributions were determined using X-ray diffraction. Based on the experimentally-determined stress states, the curvatures of the strips were determined analytically and using Finite Element (FE) calculations. Silicon nitride flat springs and a concave mirror could be peen-formed without the need of additional hard machining. FE calculations demonstrated me capability of designing peen forming processes on basis of experimentally-determined peening stresses.