A Theoretical Model For Residual Stress Prediction On Milled Surface

Residual stress is an important index to evaluate the surface quality of a machined workpiece,which not only has a great influence on the corrosion resistance,fatigue strength,size stability and static strength of the workpiece,but also can be utilized to control distortion problem in machining of large components.However,it is very difficult to accurately determine the machining-induced surface residual stresses,which are affected by factors in machining process,such as tool geometry,cutting parameters,material properties,lubrication conditions and so on.Therefore,it is necessary to analyze the mechanism of residual stress in order to predict and control the residual stress of the machined surface in the production.In this paper,the surface residual stress in milling process is studied.A theoretical model for predicting the residual stress of milling surface is proposed.The experimental verification is carried out.The contents are as follows:(1)Based on the existing stress field model for two-dimensional orthogonal cutting,A new stress field model in loading process for three-dimensional oblique cutting is established.A leap from special to general,form two-dimensional analysis to three-dimensional analysis is achieved,and the application range of the prediction algorithm of cutting stress field is extended.At the same time,the similar method to extend the analytical algorithm of the temperature field of the two-dimensional orthogonal cutting to the three-dimensional oblique cutting is utilized.Then the mechanics of the more complex milling process is carried out.The feed motion of the milling cutter is coupled with the change of internal stress field and temperature field of the workpiece.The prediction of the stress field and temperature field at any time during the milling process is realized.(2)The existing two-dimensional residual stress analysis algorithm is modified.The boundary conditions of the stress and strain in three-dimensional milling process is redefined.Then according to the characteristics of multi cycle loading in milling process,the curve of the internal loading stress field is drawn.Residual stresses are accumulated with the calculation of every loading cycle.(3)The reliability of the analytical model is verified by experiments.In order to obtain the essential parameters of the analytical model,the radius of the tool tip was measured by DSX100 microscope and the cutting force coefficients were obtained by the calibration test with the Kistler9255 B dynamometer.Then,to verify the proposed model in this paper,residual stresses obtained by both finite element simulation and experimental measurement under the same conditions are compared with the ones predicted by the proposed model.The results match well with each other.