Simulation And Experimental Study On The Residual Stress In The Surface Of Pre-heating Grind-hardening

The grind-hardening technology is the result of transformation from austenite to martensite by rapid heating and rapid cooling of workpiece surface material in the process of grinding,at the same time,the surface of the workpiece is deformed by sliding,ploughing and chip forming.And the surface strengthening is achieved under the action of force thermal phase transformation coupling.The subject of this project is to obtain a better grinding harden layer with higher stability by pre-heating method.In this paper,the influence of pre-heating grinding on the residual stress distribution of workpiece surface is studied.As one of the indexes to measure the performance of the workpiece,the study of residual stress plays an important role in effectively controlling the surface quality of workpiece and promoting the development and application of grind hardening process.In this thesis,the grinding force,temperature field and stress field in the process of room temperature and pre-heating grinding are analyzed theoretically and experimentally.The main contents of this thesis are as follows:The experimental equipment and testing methods involved in grinding strengthening experiments are introduced,and the influence of pre heating temperature on the deformation of workpiece is analyzed.In this thesis,the grinding force,the strengthening layer depth and the residual stress of 40Cr steel are studied experimentally,and the effects of grinding parameters on grinding force,strengthening layer depth and residual stress are studied.Experimental results show that the grinding force increases with the increase of the depth of grinding;with the increase of grinding temperature,the depth of the harden layer increases obviously.The empirical formula of grinding force under four variables,including pre-heating temperature,workpiece speed,grinding depth and wheel speed is established,while the actual change law of grinding force is analyzed.A grinding temperature simulation based on piecewise variable force to predict the temperature field is put forward,and the necessity of the segmentation of grinding force and the variety of grinding force are expounded.So the finite element analysis of the temperature field of 40Cr quenched and tempered steel during the grinding process is carried out by the piecewise variable force method.The disciplinarian of temperature field and node temperature with time is obtained,and the distribution of the strengthening layer along the grinding direction of the workpiece is obtained.By comparing the simulation results with the actual change of the depth of strengthening layer,the feasibility of simulation of the segmented grinding force is verified.The influence of grinding parameters on the depth of grind hardening layer is studied by simulation.The residual stress of the workpiece during the pre-heating grinding process is analyzed by APDL command in the universal FEM analys is software ANSYS,in the simulation process,the actual grinding force is applied according to the triangle load,by changing the thermal expansion coefficient during the process of cooling,the simulation of phase change process is realized,and the residual stress field based on the force-thermal-phase coupling is obtained.The correctness of the simulation is verified by experiments and residual stress tests,Finally,the influence of the grinding parameters on the grinding residual stress is studied by simulation.