Research On Mechanism Of Microstructure On Residual Stress And Procss Optimization During Grinding

Maraging steel is widely used in national defense,aerospace and other fields because of its high strength,toughness and good weldability.During processing maraging steel,the grinding,as the last manufacturing procedure,can not only ensure workpiece the accuracy of size and shape,but also meet the final performance requirement.Due to the high temperature,heating rate and the high strain rate,the grinding process often makes the microstructure largely change.The microstructure effect on grinding flow stress in the process of formation and affect the mechanical load and thermal load,which lead the change in residual stress and ultimately influence the performance of the workpiece.Therefore,it is necessary to explore the influence and mechanism of microstructure on residual stress to optimize the grinding quality.In this study,as the starting point,the change of dislocation density and texture are used to represent the microstructure evolution.Through martensitic aging steel 3J33 experiment,the variation law of dislocation density and texture before and after grinding was analyzed,and the prediction model of grinding force,grinding temperature and residual stress was established considering dislocation and texture evolution.The key factors in the surface integrity such as residual stress,roughness and hardness were analyzed from the optimization performance,and a comprehensive optimization scheme was proposed.The main research results of this paper are as follows:(1)Based on the material testing results,the relationship between texture and Taylor factor,as well as the relationship between grain size and dislocation density,was firstly sorted out.Based on the influence and analysis of heating rate,strain rate and temperature on dislocation density,the dislocation density prediction model was constructed.The parameters in dislocation density prediction model are modified according to the analysis of different inputting value.A flow stress model considering dislocation density and Taylor factor is constructed.The grinding arc is divided into three parts: cutting formation zone,plowing zone,and rubbing zone.Based on the relationship between microstructure evolution and flow stress in adjacent grinding arcs,a grinding force model considering dislocation and texture and superimposed heat source grinding temperature are constructed.Compared with the experimental values,the grinding force prediction model has an average error of 5.4% and 14.69% in the tangential and normal directions,respectively,and the average error of the predicted grinding temperature is 8.82%.(2)Furthermore,based on the grinding force and temperature prediction model considering dislocation and texture changes,a mechanical stress and thermal stress model considering the effect of dislocation density and texture changing was constructed,and the rolling-slip contact model and plane strain model were used to calculate the assumptions.The mechanical load and thermal load acting on the microstructure are determined by the Mc Dowell algorithm model and the Von-mises yield criterion.The residual stress distribution after unloading is finally obtained.The residual stress prediction model,which consider the influence of dislocation density and texture could effectively predict the magnitude and distribution of grinding residual stress.The average error of residual stress is 14.32% in the X direction and 14.32% in the Y direction is11.21%.(3)Finally,the influence of grinding parameters on residual stress,hardness and roughness is analyzed.The surface integrity process optimization which considers the residual stress and surface quality is proposed.The results show that the effect of dislocation density on the residual compressive stress is positively correlated,while the influence of Taylor factor is negatively correlated.Increasing the wheel speed could increase the surface residual compressive stress,surface hardness and roughness.In order to obtain a larger residual compressive stress on the surface,the primary optimization objective was to control the content of texture evolution,and the roughness and hardness were the secondary optimization objectives.The final optimization parameters were determined.