Study On Coupling Stress Field Of Rack Form Grind-hardening

Grind-hardening is a new integrated machining technology with considerable potential applications which utilizes grinding heat to quench the non-quenched steel directly. The theoretical analysis, numerical simulation and experimental methods are synthesized in this paper, which provide a reliable way to research the application of grind-hardening in the process of rack forming. The basis for selection of grinding parameters is established and the contents of research are as follows:A set of form grind-hardening experiments are performed. The grinding force and surface hardness are measured. The hardness penetration depth is calculated, and the residual stress is obtained with X-ray diffraction method. The relationship between residual stress and processing parameters is discussed.The model of form grinding force which is the basis of heat flux calculation, is established on the basis of statistical probability results of the grains and the formula of plane grinding. The error between the prediction and experiment is less than 15 percents.The latent heat and heat transfer coefficient are calculated with iterative solution. The numerical model of the temperature field for form grind-hardening is established based on the heat transfer theory. The temperature field is simulated and the temperature history of the node is obtained considering the latent heat, convection and the thermal properties of materials changed with the temperature. The hardness penetration depth is calculated in good agreement with experimental results.The thermal elastic-plastic constitutive relation is deduced during the form grind-hardening on the basis of yield criterion, flow rule and the law of strain hardening. The finite element model of stress field is established based on the thermal-structural coupling theory. Thermal stress and thermal-mechanical stress field are simulated and the conclusion is found that the influence of grinding force for stress field is just a little.The residual stress in hardened layer is calculated considering the phase change and the error with the experimental results is less than 15%. The residual stress on the rack surface is compressive, and the value is gradually decreased and converted to tensile stress.The steps of process parameters selection for form grind-hardening rack are proposed on the assumption that the grinding depth and workpiece speed are variables and the other grinding conditions fixed. The relationship between grinding parameters and the hardness penetration depth is established based on the simulation of temperature field and the constraint of critical heat flux. The process parameters are initially identified according to the technical requirements of the rack. The better grinding parameters are determined by the analysis of residual stress. The processing parameters of form grind-hardening rack whose module is 2mm are determined.