Modeling And Experimental Study Of Residual Stress In Micro Milling

Micro milling is a widely used precision machining technology which is suitable for many kinds of materials. This kind of processing method has great flexibility and speed which can process a variety of micro structure. Micro milling is widely used in aerospace, precision optical parts manufacturing and biotechnology. The surface quality has great influence on the performance of micro parts. Among the indexes of surface integrity, subsurface residual stress affects not only the static strength and corrosion resistance but also the fatigue life of parts. It is necessary to make some research on residual stress in micro milling. A residual stress model should be proposed to predict the distribution of residual stress, and the influence of process parameters on the residual stresses should be analyzed.The characteristics of micro milling is analysed and the tool edge radius and material strengthening effects are considered. A micro milling cutting force prediction model is proposed and the cutting force is predicted according to it. NAK80 die steel is used as the workpiece material. The dynamic cutting forces are collected by Kistler9119AA1 dynamometer. The measured results of the cutting force agree with the predicted results of the analytical model. The accuracy of the cutting force model is verified. The cutting forces are predicted by this model, and the influence of processing parameters on the cutting force is analyzed. An imaginary heat source is utilized to build the temperature field prediction model and the features and rules of the temperature distribution in the workpiece is discussed.Under the assumption of plane strain, the sliding / rolling model is adopted to abtain the mechanical stress field in the workpiece based on the cutting force predition results. And the stress field is taken as the mechnical loads experienced by the workpiece. After loading, unloading and strain-stress release, the results of residual stress in micro milling are finally obtained based on the predition of mechanical loads and themal distortion. An analytical model of residual stress in micro milling is proposed. The residual stresses are tested by Proto iXRD X ray residual stress analyzer. The experimental data and predition results of the analytical model are compared in one chart. The validity of the analytical model is verified.The geometric parameters of the tool are measured accurately by the tool microscope, and the J-C constitutive equation of NAK80 is determined according to the orthogonal cutting experiment. The 2D finite element micro cutting model is established based on AdvantEdge FEM. The distribution of physical quantity of cutting process on different cutting parameters are obtained by the model. The finite element simulation results are compared with the analytical model prediction results and the experimental results, which shows the validity of the finite element model.