Investigation of shear instability in orthogonal machining of TI6AL4V alloy using the finite element method

Abstract

During orthogonal cutting of Ti6Al4V alloy the chip is segmented, suggesting the emergence of some kind of instability during plastic deformation of the material. The segmented chip formation occurs from low cutting speeds and persists even at very high speeds, but with a notable change of the chip morphology. Considerable research efforts have been conducted worldwide to explain the underlying physical mechanisms of the segmented chip formation, and several theoretical models have been proposed. Theoretical models based on thermally aided shear instability which results to adiabatic shear bands formation proposed to explain the plastic instability of the material at high deformation rate s. Unfortunately, these models cannot provide answers at low deformation rates. On the other hand, fracture models which consider machining as a mechanism of ductile or brittle fracture explain the segmented chip formation as a periodic crack generation mechanism . Despite the above theoretical approaches, the phenomenon is still not well understood. The objective of this work is to investigate the mechanisms of catastrophic shear instability during orthogonal cutting of Ti6Al4V alloy based on coupled thermomechanical rigid viscoplastic finite element simulations in a wide range of cutting speeds