A micromechanics based simulation and experimental approach to predict surface integrity in precision hard turning.

摘要

Hard turning involves large strain, high strain rate, high temperature, microstructures, and potential loading history. An internal state variable (ISV) plasticity model has been incorporated into finite element analysis (FEA) of hard turning AISI 52100 steel (62 HRc) to understand the nature of material deformations. It was found that the material properties obtained from a compression test may better reflect the overall cutting responses.;The rotation of second phase particles of AISI 52100 steel during turning and grinding was characterized. In addition, a microscale FEA model was developed to incorporate the random microstructures in micromachining conditions. The micromachining phenomena such as size effect, high stress concentration and low temperature in the microstructure region were recovered by the simulation model.;A hybrid FEA model was developed with the concept of plowed depth to predict residual stress profiles. Residual stress was predicted by simulating a dynamic turning process followed by a stress relaxation process. The predicted residual stress characteristics agreed with the experimental ones. A transition of residual stress profile was recovered at the critical plowed depth. The effects of cutting speed, friction coefficient and inelastic heat coefficient on residual stress profiles were also studied.;The contribution of tool/work friction and material plastic deformation to cutting temperature was decoupled by the FEA model. It showed that a relative large plowed depth recovered the hook shaped residual stress profile by turning at low tool/work friction, while small plowed depths recovered the pattern of residual stress profile by grinding. Only a very large plowed depth recovered the hook shaped residual stress profile at large tool/work friction. Compared to residual stress with a rigid tool, the predicted residual stress profile using tool properties showed an increased compressive residual stress at the surface and shifted the maximum compressive residual stress from the subsurface to the surface. The plastic deformation of work material contributed the majority of cutting temperature, while tool/work friction contribution was secondary. Residual stress reversal from subsurface maximum residual stress to surface maximum residual stress may occur when tool/work friction increases.