Prediction Modeling Of Residual Stress In Titanium Alloy Milling

With the rapid development of precision machining technology,the functional requirements of the final product need to consider the product performance indicators(including the surface physical characteristics,metallurgical,chemical and biological characteristics)in addition to the geometric characteristics of the machined parts.The distribution of surface residual stress will significantly affect the fatigue life and corrosion resistance of the workpiece.This paper mainly studies the effect of cutting parameters on the distribution of residual stress in the machined surface,and the effect of constitutive model parameters on the prediction of milling force and residual stress distribution in the machined surface.The current work aims to propose a prediction model of residual stress in ideal milling state to assist the subsequent research of residual stress in thin-walled parts.First of all,the processing characteristics and plastic behavior of Ti6Al4 V titanium alloy are analyzed.The significance of constitutive model in cutting simulation is introduced.The difference between Hyperbolic tangent(TANH)constitutive model and Johnson Cook(J-C)constitutive model and the physical meaning of each correction coefficient of TANH constitutive model are analyzed.Secondly,based on the TANH constitutive model,a milling force prediction model considering the thermal coupling effect is established.Among them,the thermo-mechanical coupling algorithm is proposed based on the geometric relationship under orthogonal cutting.The cutting temperature is generated due to the cutting force by cutting temperature model.Then,according to TANH constitutive model,the change of cutting temperature will lead to the change of material flow stress,resulting in the change of cutting force,and the change of cutting force will lead to the change of cutting temperature.This coupling relationship is expressed by iterative calculation until the cutting force converges to the allowable range of error.The establishment of milling force prediction model is mainly based on the analysis of the contact relationship and relative motion relationship between the cutter and the workpiece in the process of milling,using the micro element method to separate the cutter,assuming that each micro element cutting edge is oblique cutting;the accuracy of the model is verified by milling experiments.Thirdly,the prediction model of residual stress is established considering the influence of cutting force and cutting temperature.The stress distribution on the workpiece surface caused by cutting force and cutting temperature is calculated by elastic Hertz contact model.The stress in the workpiece is calculated incrementally,and the stress loading and stress releasing stages are calculated respectively by considering the following hardening criterion and Von Mises criterion of the material,finally the predicted value of the residual stress distribution in the machined surface is obtained.The residual stress in the machined surface was measured by X-ray diffractometer,and compared with the simulation results,the accuracy of the residual stress prediction model was verified.Finally,the GUI function of MATLAB is used to develop the residual stress prediction platform in milling.By inputting the tool parameters,material parameters,constitutive parameters and cutting parameters,the residual stress distribution law of workpiece surface can be obtained,which simplifies the operation steps in the simulation process and improves the simulation efficiency.