Optimizing the Surface Integrity of Gears: Combined Effects of Peening and Superfinishing Processes

Abstract

Copyright © (2025) by American Gear Manufacturers Association. All rights reserved.Increasing the load capacity of agricultural transmissions presents the challenge of enhancing fatigue resistance while maintaining or reducing the size of rotating components. In this context, processes that define the surface integrity properties have been considered as a possibility for optimizing gear flanks. This study addressed the combined effect of gear flank optimization on the residual stress state and topography. Case hardened gears were submitted to a shot peening process to induce compressive residual stress, followed by an isotropic superfinishing process to homogenize the peaks and valleys of the gear's contact surface. Among the groups evaluated, the shot peening (SP), isotropic superfinishing (IS) processes, and the combined effect of both (SP+IS) were examined. Roughness, profile deviation, residual stress, hardness, and microstructure tests were conducted to assess the surface. These evaluations were used to classify the heterogeneity of the surface integrity achieved by the different manufacturing processes. It was found that the SP+IS samples exhibited more compressive residual stresses and lower roughness, along with a reduction in intergranular surface oxidation. The surface also showed a slight variation in its manufacturing quality class, changing from a status of DIN class 7-8 to a class range of 8-9. By evaluating the residual stress states of different manufacturing routes, it was observed that the IS process preserved the heterogeneity of residual stresses previously established by the SP process.