Research On The Effect Of Pre-stress Timeliness On The Workpiece Residual Stress Of Grinding

With the rapid development of machinery manufacturing industry in modern society,higher requirements are put forward on the anti-fatigue,anti-corrosion and surface integrity of mechanical products in various fields.Grinding is a common means of obtaining higher surface quality.The residual stress on the workpiece surface after grinding is one of the key factors affecting the surface fatigue performance and corrosion performance of the workpiece.Pre-stressed hardened grinding(PSHG)technology,which combines green manufacturing with anti-fatigue manufacturing,is a new machining process that results in the workpiece being hardened on the grinding surface.At the same time,the residual stress on the surface of the workpiece can be controlled.According to the research status quo,the influence mechanism of the pre-stress timeliness on the residual stress of the workpiece is not clear.This paper takes 45 steel workpiece as the research object.Based on the influence of pre-stress timeliness on mechanical-thermal stress and phase-transformation stress,combined with the deformation heat treatment technology,the theoretical analysis of the model,the experimental study and the finite element simulation method,the research on the effect of pre-stress timeliness on the workpiece residual stress of grinding is carried out.The main research work includes:(1)The basic theory of pre-stress hardened grinding is analyzed,and the interaction between grinding heat,grinding force and each stress in the grinding process are analyzed emphatically.The microstructure transformation of the material in the process of hardened grinding is analyzed in detail,especially the martensite phase transition has been focused on research.This has provided a theoretical basis for the carry out the follow-up test and simulation.(2)With 45 steel as the material,pre-stress timeliness of hardened grinding workpiece test was carried out.In the experiment,the pre-stress and the unloading time of pre-stress after the grinding was controlled,multiple sets of tests were carried out The surface residual stress and the cross-section metallographic structure of the workpiece after the test were measured and collected.The influence of pre-stress and pre-stress unloading time on the residual stress and the change of the micro structure were studied,while preparing for the subsequent phase transition stress analysis.(3)Analyze the temperature field of hardened grinding,and then write APDL program of ANSYS to simulate the temperature field to get the temperature change of the workpiece.According to the cooling conditions and phase change node to determine the pre-stress unloading time.And then coupling the thermal and mechanical to analysis the mechanicalthermal stress.Drawing curve of the mechanical-thermal stress of workpiece along the surface and depth direction with the pre-stress unloading time to study the mechanicalthermal stress with different pre-stress under different unloading time,and analyze its effect mechamism.(4)According to the measured residual stress and the mechanical-thermal stress obtained from the simulation,the phase transformation stress under different pre-stress and unloading time can be obtained.Combined with the metallographic structure obtained in the experiment,the analysis of the phase transformation stress with the pre-stress unloading time is carried out,and analyze its effect mechanism.The results show that the surface residual stress of the workpiece after the pre-stress hardened grinding is the residual compressive stress.With the increase of pre-stress unloading time,the mechanical-thermal stress on the workpiece surface gradually decreases and the phase transformation stress becomes smaller gradually.Therefore,the residual stress of the workpiece gradually reduced.So it is easier to obtain that people can get the required residual stress by unloading the pre-stress after workpiece has been cooled to room temperature.