what is shot peening

Shot peening is a cold working process used to produce a compressive residual stress layer and modify the mechanical properties of metals and composites. It involves striking a surface with shot (round metallic, glass, or ceramic particles) with enough force to create plastic deformation. Shot peening is used to add strength and reduce the stress profile of components, and it can increase fatigue life up to 1000% depending on the part geometry, part material, shot material, shot quality, shot intensity, and shot coverage. Shot peening is similar to sandblasting, but its purpose is not to remove material. Instead, it employs the mechanism of plasticity to achieve its goal, with each particle functioning as a ball-peen hammer. Shot peening is used on gear parts, cams and camshafts, clutch springs, coil springs, connecting rods, crankshafts, gearwheels, leaf and suspension springs, rock drills, and turbine blades. It is also used in foundries for sand removal, decoring, descaling, and surface finishing of castings such as engine blocks and cylinder heads. Shot peening may be used for cosmetic effect, and it is often called for in aircraft repairs to relieve tensile stresses built up in the grinding process and replace them with beneficial compressive stresses.