Thermo-Mechanical Coupling Analytical Modeling And Numerical Analysis For Grinding Hardening Process

The grinding process is the last step of precision machining,which is usually used to guarantee the accuracy and surface integrity requirements of workpiece.A lot of heat and pollutes generate in the traditional grinding process due to the action of the coolant.The grinding hardening process is a kind of heat treatment method for workpiece by grinding heat,which integrates the grinding process and the heat treatment.It not only shortens the processing cycle of parts,but also reduces the waste of resources.It is a green process.In order to analyze the influence of grinding hardening process on workpiece performance,the paper is investigated by combining experiment with analytical simulation.The main researches are as follows:Firstly,the characteristics of grinding process are analyzed,and meanwhile the analytical model of the grinding force for the grinding system is established according to the characteristics of grinding process.The average grinding force is calculated by establishing the cutting model of abrasive particles,It includes the three grinding processes,the distribution of undeformed chip thickness and the dynamic abrasive density as well.Grinding experiments are carried out to obtain the grinding forces under different technological parameters.Moreover,the experimental results are compared with the simulation results.Then the hardened layer metallographic structure of the hardened workpiece is observed accordingly.Secondly,based on heat transfer theory and convection heat transfer theory,two-dimensional and three-dimensional finite difference heat transfer equations between grinding wheel and workpiece are established by using partial differential equation of heat conduction;The distribution of two and three dimensional temperature field at different time in the machining process of workpiece is obtained.Furthermore,the distribution law of temperature in the workpiece is analyzed.Thirdly,according to Hertz contact theory,Timoshenko thermoelastic theory and phase transformation theory,the thermal stress,mechanical stress and phase transformation stress in machining process are solved.The Von-Mises elastic-plastic yield theory and generalized Hooke's law are used to solve the elastoplastic stress-strain increment during the grinding process.After the processing is completed,the stress-strain release process is performed according to the plane stress boundary conditions.Based on the above process,it is possible to predict the residual stress distribution inside the workpiece once the machining is completed.Forthly,based on the established residual stress prediction model,the residual stress distribution inside the workpiece is obtained.The influence of machining parameters on the residual stress distribution is analyzed.The results show that the force,temperature field and residual stress model based on analytical method can well reflect the characteristics of grinding and hardening process.The grinding hardening process can change the micro-structure of workpiece and produce needle-like martensite structure.It can generate residual compressive stress and reduces residual tensile stress.In order to improve the distribution of residual stress of workpiece,the lower wheel speed,smaller grinding depth and larger workpiece feed speed should be selected in the grinding hardening process.