Influence Factors of Shot Peening Intensity and Its Effect on Residual Stress in Herringbone Gears

Shot peening intensity is a key parameter for evaluating process stability and the strengthening effect of shot peening. However, it is governed by the coupled effects of shot size, shot hardness, shot velocity and other process variables, and its relationship with the residual stress state of complex gear surfaces remains unclear. In this study, a residual stress to arc height calculation model for Almen strips was established and validated using dimple-size measurements and arc-height tests. The effects of S110, S170 and S230 cast steel shots, two shot hardness levels and different air pressures on shot peening intensity were then investigated. A sequentially coupled discrete element model—finite element model (DEM-FEM) method was further used to obtain the impact information and residual stress distribution on a herringbone gear tooth surface, and the effects of shot peening intensity on surface residual stress, maximum compressive residual stress, peak stress depth and compressive residual stress layer depth were analyzed. The results show that shot peening intensity increases with shot velocity, shot diameter and shot hardness. When the shot peening intensity increased from 0.158 mmA to 0.395 mmA, the depth of maximum compressive residual stress increased from 15 μm to 55 μm, and the compressive residual stress layer depth increased from 50 μm to 160 μm. In contrast, the surface residual stress and the magnitude of maximum compressive residual stress did not show a monotonic trend. The findings provide guidance for selecting shot peening parameters and evaluating the strengthening quality of herringbone gears.