Characteristics of chip formation and its effects on cutting force and tool wear/damage in milling Ti-25 V-15Cr (Ti40) beta titanium alloy

Ti40 burn-resistant titanium alloy is one kind of beta-phase titanium alloy. There exists complex cutting deformation, high cutting temperature, high cutting force and fluctuations, and serious tool wear and damage in the process of cutting Ti40 alloy. In this paper, the chip formation characteristics, chip formation mechanisms, and their relationships with dynamic fluctuation force of Ti40 beta titanium alloy are analyzed. It is shown that a large number of shear bands are formed inside the deformation of each beta phase grain, its chip thickness varies irregularly, and there exist many micro-serrated teeth and micro-cracks on the serrated chips. The chip formation mechanism of Ti40 alloy involves both adiabatic shear and crack initiation theories. With cutting speed increasing, the formation frequency of adiabatic shear bands is lifted, notable serrated teeth are formed, and the sub-grains are formed more obvious and fine among adiabatic shear bands. At peaks of milling force, notable fluctuation is shown, and the fluctuation times and amplitudes corresponded to the number of irregular cutting chip thickness variations or the irregular instant cutting volume and not a formation of every shear band. The fluctuation of milling force is caused by adiabatic shear and cutting direction change due to vibration. Meanwhile, the effect of chip formation on tool wear/damage is analyzed and compared with Ti6Al4V alloy.