Material constitutive model and chip separation criterion influence on the modeling of Ti6Al4V machining with experimental validation in strictly orthogonal cutting condition

Abstract

The titanium alloy Ti6Al4V, although widely used in machining, is a hard-to-machine material, particularly due to the production of saw-toothed (or segmented) chips. The phenomena leading to this kind of chips are still an ongoing problem in the current literature, as well experimentally as numerically. An experimental orthogonal cutting setup on a milling machine is presented as a benchmark to validate finite element models. Its ease of implementation and near-to-zero cost should enable it to be used for any material, as long as the cutting speed is achievable by the feed rate of the machine. In addition to the study of chip formation, this setup could also allow to carry out long, although interrupted, machining tests to analyze tool wear. A numerical finite element model is then introduced to model the chip formation in the same cutting conditions. The comparison of the numerical results with the experiments shows that the level of the forces is mainly influenced by the material constitutive model, while the chip morphology is mostly impacted by the chip separation criterion. Either experimentally or numerically, the mechanism leading to the formation of a Ti6Al4V saw-toothed chip, for the cutting conditions of this study, is the conjunction of the adiabatic shear band in the primary shear zone, followed by the propagation of a crack into it.