Chip Formation Mechanism In Multi-step Machining Of Ti6Al4V Titanium Alloy

Titanium alloys are widely used in aerospace,medical,metallurgical,chemical and other industries.Due to its low thermal conductivity,large chemical activity,and small deformation coefficient,it is often seen in the cutting process that vibrations in the cutting system,severe work hardening,and excessive cutting forces.In this thesis,the formation mechanism of serrated chip and the multi-step machining of titanium alloy were analyzed by the combination of experiment and simulation,and the chips formation mechanism in multi-step machining of titanium alloy was revealed.Firstly,the orthogonal cutting experiments of titanium alloys were carried out to study the influence of cutting speed and cutting thickness on cutting forces and chip shape.The results show that with the increase of cutting speed,the serration degree of the chip increases and the cutting force decreases.With the increase of the cutting thickness,the serration degree of the chip increases and the cutting force increases.The mechanism of serrated chip formation in the titanium alloy cutting process was analyzed using shear angle theory..The titanium alloy cutting process is simulated using Abaqus finite element software.The finite element model was verified by the chip shape and cutting force obtained in orthogonal cutting experiments.The variation of the residual stress along the depth direction with the cutting speed and the tool rake angle is analyzed.The results show that the residual stress on the machined surfaceprocess is the result of the combined effect of thermal load and mechanical load in the machining.A multi-step cutting experiment of titanium alloys was carried out.The variation of the hardness of the machined surface with cutting speed and cutting thickness was studied.The effects of cutting speed and cutting thickness on the surface hardness in different cutting steps were analyzed,and the macroscopic shape of the chips in different cutting steps was analyzed.The results show that the surface hardness decreases with the increase of the thickness of the first cutting step,but there is no obvious change with the increase of the first step when the cutting speed and cutting thickness of the second cutting step are fixed.The finite element cutting model was used to simulate the formation process of serrated chips in titanium alloy machining,and the simulation and analysis was conducted for multi-step machining of titanium alloy.The results show that with the increase of the cutting speed in the first cutting step,the stiffness damage equivalent and the equivalent plastic strain of the reference unit gradually decrease in first-step machined surface,while the Mises stress gradually increases,resulting in the serrated degree of the second-step chip decrease with the increase of the first-step cutting speed.