Research On Tool Wear And Surface Integrity Of TC21 Titanium Alloy Under Minimum Quantity Lubrication (MQL) Milling

TC21 is a kind of titanium alloy with two kinds of phases,high strength and high toughness.It has high specific strength,good biocompatibility,heat resistance and corrosion resistance.These properties make it have broad application prospects in aerospace fields.However,the low thermal conductivity,high chemical activity and low elastic modulus of TC21 titanium alloy make it a typical difficult-to-machine material.These characteristics not only make the cutting tool wear easily,but also make it difficult to guarantee the surface quality of the cutting titanium alloy workpiece.All these restrict the wide application of TC21 titanium alloy.Minimum quantity lubrication(MQL)is a lubrication method in which a small amount of lubricating oil is atomized by high pressure gas to form a high pressure oil mist,which is then sprayed into the cutting area to cool down and lubricate.Compared with traditional flooding lubrication,minimum quantity lubrication can improve the cutting performance of workpiece with very little lubricant(generally less than 100ml/h),which has good environmental and economic benefits.Therefore,a large number of scholars at home and abroad have studied MQL in recent years.In this paper,the comprehensive milling performance of TC21 titanium alloy has been studied by using TiAlN coated cemented carbide cutters under green lubrication(dry,high pressure air-cooled,MQL).The specific work is as follows:(1)The influence of milling parameters on milling force during milling TC21 titanium alloy was studied,and the influence of lubrication mode and lubrication parameters on milling force and milling temperature was studied by changing the lubrication conditions.Based on experimental data and regression analysis method,an empirical prediction model of milling force on milling parameters under different lubrication modes is established.(2)The wear rule of carbide coated tool GM-4E-D6.0 in milling TC21 titanium alloy workpiece under different lubrication methods was studied.With the help of laser microscope,scanning electron microscope and EDS,the wear surfaces of milling cutters under different lubrication modes were observed and analyzed.The effects of different lubrication modes on the wear patterns and wear mechanisms of milling cutters were found.Finally,the wear curves of milling cutters under different lubrication modes were obtained.The effect of tool wear on milling force,milling temperature and workpiece surface integrity is also studied.(3)The similarities and differences of surface integrity(micro-morphology,surface roughness and micro-hardness)of TC21 titanium alloy milling workpiece under different milling parameters,lubrication parameters and lubrication modes were studied.The variation of surface roughness and micro-hardness of surface layer and micro-defects of TC21 titanium alloy milling workpiece under different conditions were measured or found.(4)In orthogonal test,the independent variables are milling parameters,and the dependent variables are milling force and surface roughness.Based on the experimental data,the grey-Taguchi correlation analysis method was used to optimize the processing parameters with the goal of minimizing the average milling force and surface roughness.With the minimum milling force and surface roughness as the objective,the optimal machining parameters are obtained.