Research On Milling Mechanism Of TC4 Titanium Alloy Based On SPH Method

Titanium alloy is widely used in aerospace,military and other fields due to its low density,high specific strength and excellent performance at high temperatures.With low hardness and high friction coefficient,titanium alloy is very sensitive to damage and a typical kind of difficult-to-machine material.Milling is one of the main methods for processing titanium alloy.Due to the complexity of the milling process,the observation of the removal process and the direct measurement of cutting force and cutting temperature are difficult,and the milling mechanism is not yet clear.It is an economical and effective method to simulate and research by the finite element method(FEM),which usually has problems of grid distortion,difficulty in solving and grid reconstruction.In this paper,considering the shortage of current simulation methods and the status quo that the experimental process is difficult to observe,the smooth particle hydrodynamics(SPH)method is introduced into the real titanium alloy milling simulation field.Combining theory,simulation and milling experiments,the machining mechanism of titanium alloy milling process and the influencing factors of the machining process are studied.The specific works are as follows:The 3D SPH milling simulation model of Ti6Al4 V titanium alloy under different cutting parameters and the 3D SPH-FEM milling model under different cutting tool geometric parameters were established based on the Johnson-Cook constitutive model,and then the changes of stress,cutting force and temperature during milling were analyzed.The simulation results show that the chip flowed plastically along the rake face,and the bottom area flows slowly.Finally,the chips appear curled and take up most of the heat during the milling process.The change period of the cutting force is the ratio of the period of milling to the number of cutter teeth.The cutting force increases with increasing axial cutting depth,radial cutting depth,and feed per tooth.The optimal tool rake angle is 6 ° ~ 12 °,the optimal helix angle is 36 ° ~ 46 °,and the optimal number of teeth for roughing is 3 or 4.Based on the principle of metal shearing,the theoretical model of milling force of titanium alloy is established.The research results show that the increase of the feed per tooth causes the instantaneous chip thickness to increase.When the radial depth of cut continues to increase,the scope of the cutting force on the chip expands.As the axial depth of cut increases,the time it takes for the tool to cut into the workpiece will increase.In addition,as the rake angle and helix angle of the cutter increase,the equivalent rake angle shows an increasing trend.The theoretical model built can well explain the mechanism of cutting parameters and geometric parameters on cutting force.Single factor test and orthogonal test of milling force of TC4 were designed and carried out on Ninghua machine tool.The research results show that milling is an intermittent machining process,the cutting force changes periodically,and curled chips continue to be generated.The cutting force model was established based on the empirical formula,which verified the accuracy of the simulation model.Under the test conditions,the cutting velocity has the smallest effect on the cutting force.The specific order of sensitivity of the cutting parameters to the feed direction cutting force is: radial depth of cut> feed per tooth > axial depth of cut > velocity.The order of sensitivity to axial cutting forces is: feed per tooth > radial depth of cut > axial depth of cut > velocity.The order of sensitivity to radial cutting forces is: feed per tooth > axial depth of cut > radial depth of cut > velocity.The order of sensitivity to surface roughness is: axial cutting depth> velocity > radial cutting depth> feed per tooth.