Modeling And Surface Integrality Prediction For Precision Cutting Of Hardened Steel GCr15

Hard turning is one of the advanced manufacturing technologies in the last two decades. It is applied to precision process of hardened steel because of its high machining efficiency, good machining flexibility, low energy consumption and pollution. However, as for the new technology, there is a lack of systematic and thorough study in its theory, especially in the modeling and prediction of hard turning, which makes the theoretical basis insufficient that can predict and control effectively surface integrality of machined workpiece in hard turning, and prevents its popularization and application to practical production.In this work, the simulation of adiabatic shear behavior, prediction of cutting force, experiment and prediction of surface integrality are studied by means of combining theoretical analysis, experimental study and numerical simulation in high speed precision cutting of hardened steel GCr15 with PCBN tools, which provides an important theoretical basis and technological support for the further development, popularization and application of hard turning process.By using the method of FEM simulation and experiment, under the effect of adiabatic shear behavior, dynamic characteristics of cutting force, distribution characteristics of cutting temperature in adiabatic shear band, formation and deformation characteristics of serrate chip are investigated. The effect of tool edge and cutting parameters on cutting force, cutting temperature, chip morphology and residual stress on workpiece surface is also studied.Based on friction behavior on tool-chip interface, the cutting force model of precision hard turning is built, which involves the research into experimental relationship of cutting force and cutting load on tool-chip friction interface, equivalent transformation of radius cutting edge, transformation between orthogonal cutting and 3D cutting, calculation of cutting force coefficient. The model realizes the transformation from orthogonal cutting to oblique cutting, then to 3D cutting, which can make calculation results of all parameters in orthogonal cutting model transplanted into complex 3D cutting.Based on systematic cutting experiment and theoretical analysis, the effect of cutting parameters, tool parameters and factor interaction on surface roughness of machined workpiece in hard turning is studied. In addition, the effect of tool wear which is under the joint influence of cutting force and temperature in high-speed cutting, on surface roughness, distribution characteristics of residual stress, formation and characteristics of white layer is also investigated. The results are that with the increase of the tool wear and cutting speed, the surface of the machined workpiece tends to generate tensile residual stresses whose depth increases; when cutting speed reaches to 200m/min, there exists white layer on the surface of machined workpiece even though the flank of PCBN tool is in a fresh state, and with the further increase of cutting speed or flank wear of cutting tool, white layer becomes clearly thicker and uneven on the workpiece surface.The prediction model of surface roughness in hard turning of different parameters is built by RSM, and the prediction models of residual stress and white layer on surface are built using BP artificial neural network, which defines tool parameters and cutting parameters as input value, and the values of residual stress and white layer characteristics as output. Finally, MATLAB is used to develop prediction system of the residual stress, surface white layer, and surface roughness in precision hard turning with PCBN tools. The system has realized higher-accuracy prediction of surface integrality in precision hard turning.