HOOK SHAPED RESIDUAL STRESS: THE EFFECT OF TOOL PLOUGHING AND THE ANALYSIS OF THE MECHANICAL AND THERMAL EFFECTS

摘要

To investigate the unique hook-shaped residual stress profile generated from hard turning process, an improved orthogonal (2-D) Finite Element (FE) model is established to include the ploughing effect of cutting edge. The model is further decomposed into two FE sub-models (sub-model 1 and sub-model 2) to determine the thermal and mechanical effects on the residual stress profiles by saw-tooth chip formation process and honed-edge ploughing process respectively. The two FE sub-models are sequentially adopted to evaluate the compression effect induced by chip formation process and ploughing effect resulted from honed-edge cutting tool on residual stress profile. Their separated and integrated effects on residual stress hook-shape profile are addressed by comparing the predicted residual stresses by sub-model 1, sub-model 2, the two sub-models' superposition, and the whole improved FE model. The results show that chip formation effect on residual stress profile happens earlier than the ploughing effect. Chip formation effect provides a foundation for the finalized residual stress profile by determining the maximum depth and magnitude of the compressive residual stress. Ploughing process generates much more thermal load to produce the tensile residual stress in hard turned surface and sequentially drives the final resultant residual stress into an obvious hook-shaped by modifying the previous compressive residual stress profile. The location with the maximum compressive residual stress is identified as the critical position to separate the mechanical load and thermal load generated from ploughing effect. The decomposition methodology on mechanical and thermal effects is proposed and thoroughly discussed in the paper.