Physical Simulation And Experimental Research On The Cutting Process Of Difficult To Cut Metallic Material

The physical simulation of cutting process can predict important physicalvariables such as the cutting force and temperature of tool, residual stress ofworkpiece and chip morphology, which provides a new method to optimize cuttingparameters and tool geometry parameters and largely reduce the cost of trial cutexperiments. To more precisely model the cutting process, two key technologies ofthe physical simulation on cutting process are improved. Then the improved tool/chipfriction model and material failure criteria are used in the physical simulation modelof the turning process on Ti-6Al-4V and the ball end milling process on Cr12MoV,which are both difficult to cut metallic materials. The main research content is:The crack extending energy theory in fracture mechanics is integrated intocutting simulation to act as material damage evolution criteria, which is normativeand conform to the physical essence of cutting process. The tool/chip friction model isimproved by considering the limiting shear stress in tool/chip interface to change withcoefficient of friction and the coefficient of friction to change with temperature.A two dimensional orthogonal plane strain cutting geometry model of titaniumalloy is established through the simplifying of three-dimensional cylindrical turningprocess. Based on the improved material failure criteria, tool chip friction model andthe cutting geometry model, the finite element physical simulation model of turningprocess of titanium alloy is achieved. The turning experiment of titanium alloy andchip metallographical observation experiment are done. Results show that simulationand experimental cutting force and chip morphology coincide well, which proves thatthe turning physical simulation model is accurate in certain range. The effects ofcutting speed and feed rate on segmented chip morphology are analyzed by comparingthe experimental micro chip morphology of different cutting parameter combinations.The effects of tool rake angle on chip local deformation and curling degree, shearangle, chip geometry, tool temperature are predicted through three different rake anglecutting simulations. The distribution and changing trend of workpiece residual stressin cutting process is modeled in four steps: tool advancing, tool retreating, workpieceload-off, workpiece cooling.The physical simulation model of ball end milling process is built based on theCAD model of ball end mill, the improved tool/chip friction model and material failure criteria. The milling experiment on Cr12MoV mould steel is conducted. Theresults show that the error between simulation and experiment milling force is lessthan15%, which indicates that the ball end milling physical simulation model canpredict the milling force accurately. The formula between theoretical prediction valueof ball end milling force and six cutting force coefficients and tool rotation angle isestablished. The three shear force coefficients can be fitted through the predictionforces of certain amount of physical simualation tests under different cuttingparameter combinations, which can overcome the disadvantage of traditionalexperimental method and reduce the cutting experiment cost.