High Strength and Compactness of Gears by WHSP (Double Hard Shot Peening) Technology

Shot peening is one technique used to enhance the fatigue strength of gears and springs. There have been, however, many uncertain aspects of the relationship between hardness and residual stress distribution provided by shot peening on one hand and the fatigue strength that can be derived from them on the other. Improving the conventional shot peening method, a two-stage peening technology (Double Hard Shot Peening [WHSP] technology) has been developed, whereby fine shot balls less than 0.1 mm in diameter are blasted, in addition to peening by shot balls of 0.8 mm in diameter as at present. The new technology provides high hardness and compressive residual stress directly below the surfaces of the gears, thereby, significantly improving their fatigue strengths. This paper reports on the WHSP technology and application examples of the same.