Investigation of the effects of surface roughness and shot peening on the tooth root bending strength of case-carburized gears

Past studies have demonstrated the positive effects of shot peening, superfinishing, and polish grinding on the flank load-carrying capacity of gears. However, there have as yet not been any thorough investigations into the effects of superfinishing or polish grinding with or without prior shot peening on tooth root bending strength. An extensive experimental study was carried out to investigate the effect of various finishing processes on tooth root bending strength and to determine whether the familiar positive effects of shot peening are maintained after such finishing processes. Smooth surfaces due to superfinishing and polish grinding do not significantly influence the tooth root bending strength of case-carburized gears, assuming that other geometric, metallographic and radiographic properties are unaffected. The increased tooth root bending strength of shot peened and superfinished or polish ground gears demonstrates that the positive effect of shot peening is maintained in combination with superfinishing and polish grinding, if compressive residual stresses are present near the surface of the material.