Research On Machining Characteristics And Surface Quality Of Titanium Alloys In High Speed Milling

Titanium alloys are widely used in aerospace and other fields due to their high strength,low density,good corrosion resistance and high temperature resistance.However,high hardness and poor thermal conductivity make titanium alloys typical difficult-to-machine materials.Conventional cutting generally uses lower cutting speeds to prevent excessive tool wear,resulting in inefficient cutting.In recent years,High Speed Milling(HSM)has been widely used to process difficult-to-machine materials.This technology can improve cutting efficiency while effectively improving machining quality.Studying the changes of chip,milling force and cutting temperature during high-speed cutting is beneficial for analyzing the influence mechanism of surface quality in high-speed cutting.By analyzing the influence of cutting parameters on the surface quality,the cutting parameters can be reasonably selected to obtain a better surface quality.Based on the Orthogonal cutting model and the material constitutive model,the titanium alloy TC4(Ti6Al4V)is selected as the research material.In this research,the formation mechanism of the chip during the Orthogonal cutting process is analyzed,the milling force model considering the spiral lag is constructed,and the workpiece based on the moving heat source method is established.Based on experiment,the effect of milling speed on milling force and workpiece temperature during milling is also analyzed.Finally,based on the orthogonal experiment,the influence of milling parameters on surface roughness and surface hardness is analyzed to address the problem of surface quality.The empirical formula of surface roughness is established by linear regression analysis.The main research contents of the project include:(1)Based on the parallel shear zone model and the J-C constitutive model,the strain,strain rate,temperature and flow stress of the shear zone are studied,and the formation mechanism of the sawtooth chip is analyzed.With the fabricated metallographic samples of the chip,the microscopic morphology of the chip and the change of metallographic structure caused by the change of milling speed are studied.(2)The milling force mechanical model considering the helix angle is established.Based on the single factor milling force experiment,the influence of milling speed on the milling force is analyzed.Based on the linear milling force identification model,the milling force coefficient under different milling speeds is obtained.The fitting effect of the general polynomial and the power function on the milling force coefficient is compared to obtain a function expression of the milling force coefficient with respect to the milling speed.The milling force model considering the influence of speed is established.(3)Based on the moving heat source method,the temperature field model of the milling workpiece considering the spiral edge is established,and the influence of the milling speed on the workpiece temperature is analyzed according to the change of the heat flux density during the milling process.A thermocouple wireless temperature acquisition system is used to record changes in surface temperature of the workpiece during milling.(4)Using the range method,the influence of milling parameters on the surface roughness and the surface hardness of the workpiece in orthogonal experiments is analyzed.An empirical model of surface roughness based on linear regression analysis is established,and the significance of the linear relationship of dependent and independent variables in the regression equation is tested by F method.