Modelling orthogonal cutting of Ti-6Al-4 V titanium alloy using a constitutive model considering the state of stress

The excellent mechanical and physical properties of Ti6Al4V titanium alloy make it a good candidate material for a broad range of applications, with special relevance for the aerospace industry. As a difficult-to-cut alloy, it represents a great challenge to improve its machinability and surface integrity while simultaneously avoiding the high time consuming and cost of the experiments. Modelling and simulation of the machining process offer a cost-effective method to investigate the machining process. In this work, an orthogonal cutting model of Ti-6Al-4 V alloy was developed and used to simulate the major cutting outcomes, including: forces, temperature distribution, chip geometry, chip compression ratio and residual stresses in the machined surface and subsurface. This cutting model includes a constitutive model accounting for the state of stress and the strain-rate effects on the mechanical behaviour (plasticity and damage) of Ti-6Al-4 V alloy in metal cutting. In addition, Zorev contact model is used to simulate the contact stresses at both tool-chip and tool-workpiece interfaces. The proposed cutting model could predict relatively well the major cutting outcomes for seven cutting conditions. The difference between simulated and experimental cutting forces is less than 14%, but the predicted thrust force is underestimated about 53% in maximum. The difference between simulated and measured maximum compressive residual stresses in cutting and transversal directions can reach in average about 17% and 36%, respectively. The maximum difference between predicted and measured thicknesses of the layer affected by residual stresses is less than 19%. This study highlights several critical points affecting the thrust force and the residual stress predictions, which should be considered in future developments of cutting models.

Automated summary

The excellent mechanical and physical properties of Ti6Al4V alloy make it suitable for a wide range of applications, especially in the aerospace industry. However, its difficult-to-cut nature poses challenges for improving its machinability and surface integrity. This study develops a cutting model that simulates the major outcomes of the machining process, including forces, temperature distribution, chip geometry, chip compression ratio, and residual stresses. The model shows good predictions for most cutting conditions, but underestimates the thrust force and shows differences in residual stress predictions. The study highlights critical points that should be considered in future developments of cutting models.