Shot Peening

Author:  Heaton, Robert B.
Source:  Metal Finishing, July 1989
Doc ID:  1989012
Year of Publication:  1989
Abstract:  
Shot peening is a cold working process in which the surface of a metal part is bombarded with spherical particles (or shot) formed from cast iron, cast steel, stainless steel, ceramic or glass. Most often, peening is used to create a uniform compressive stress layer on or near the surface of metals that prolongs service life under cyclical loading conditions by resisting fatigue failures. For this purpose, peening is applied to leaf and coil springs, gear fillets, drive shafts, torsion bars, axles, oil well drilling equipment, turbine blade root and foil sections, and many other metal components exposed to cyclical stresses. Although shot peening is certainly not a new process, many of the finer points related to the effects of peening variables on the performance of metals remain open to continuing scientific investigation and debate. Research published during the 1980s, for instance, places new emphasis on the significance of shot size and questions the traditionally assumed correlation between Almen strip deflection and compressive residual stress. Likewise, test methods, such as X-ray diffraction, have been studied as alternatives to destructive mechanical methods for assessing peening effects and developing optimum peening parameters. The point here is that the file on theories and test methods used to establish shot peening specifications is definitely not closed. As a consequence this article will avoid theoretical controversies and will instead focus on the production end of peening, including where and why the process is applied, how processing variables are controlled, and the types of automated peening systems currently available.