Modeling of multipass grinding effect on residual stresses distribution and surface integrity of D2 thread rolling dies

Abstract

Three questions were raised in this study: Can residual stresses after multipass grinding be predicted? What will be their superposition relationship between initial and final residual stresses distributions? Is there a method to predict and optimize surface integrity of the material after certain number of passes in order to improve the tools life? The procedure followed included a nested factorial experiment. The experimental protocol consisted of six steps, which included microstructural investigation, hardness, roughness, relative cold work, surface and subsurface residual stresses evaluation. All the main effects, including heat treatment, type of grinding operation, and multipass grinding technique and their interactions were found to be significant at a 0.05 level. Experimental significance was summarized with a second order model representing the grinding dynamics. The model was selected among four other candidates since it provided the least predicting errors and the most parsimonious structure with only one explanatory parameter, the damping ratio. The prediction of the complex nature of the residual stresses was achieved in two-folds. First, given the multipass grinding operation preceded by heat treatment, the damping ratio would change based on the experimental data. Then, this thesis provides the prediction on how the residual stresses pattern at different depth would change due to the damping ratio parameter. The contribution of this study was characterization of heat treatment and grinding effects on the surface integrity factor of D2 thread-rolling dies and development of a plausible methodology and potential theory in describing the memory relationship among multipasses during grinding operations.