Investigation on effects of single- and multiple-pass strategies on residual stress in machining Ti-6Al-4V alloy

Residual stresses in the surface and subsurface of the machined part are important factors for surface integrity, which can significantly influence its performance and service life. Generally, the final machined surface could be finished by single- or multiple-pass cutting operation and the formation of residual stresses in each process have been widely studied, however few studies pay attention to the differences of residual stress generated by single- and multiple-pass strategy on the final machined surface. In single-pass cutting, the original unprocessed surface is often employed as initial state. While in multiple-pass, the previous cut often cause accumulated strain/stress and temperature on the machined surface/subsurface, which will affect the cutting forces, thermal distributions, plastic deformation in the subsequent cuts and eventually influence the final residual stresses. Thus this paper investigates the cutting forces, temperatures and residual stresses distributions in machining Ti-6Al-4V with the special emphasis on the differences between the single- and multiple-pass strategies. Coupled Eulerian-Lagrangian (CEL) method is used in FE modelling and experiments are also implemented. Good agreements were found between the experimental and numerical results, then further discussions based on the FE results can draw the conclusions that, the first cut in multiple-pass cutting strategy can lead to a decrease in cutting force and surface tensile residual stress in the second cut. The multiple-pass cutting strategy can result in a lower magnitude and depth of compressive residual stress in subsurface, and this is more obvious when a smaller ap is implemented in the sequential cut. This work can provide practical guidance for optimizing the cutting parameters to get the desired residual stress.