Finite Element-based Modeling of Machining-induced Residual Stresses in Ti-6Al-4 V under Finish Turning Conditions

Abstract

Residual stresses (RS) imparted during the finishing stages of machining constitute an essential measure of surface integrity and an acceptance criterion for the safety of critical aerospace parts. To build a predictive tool for machining-induced residual stresses in titanium alloy Ti-6Al-4V, a finite element-based model of orthogonal cutting is developed using DEFORM-2D. A full factorial orthogonal cutting experiment is conducted using sharp tools to investigate the effect of feed rate (f) and cutting speed (v) on residual stresses under finish-turning conditions. For every cutting condition, machining forces are measured using a piezoelectric dynamometer, surface temperatures in the vicinity of the cutting zone are captured with an infra-red camera, and surface residual stresses in the cutting direction are measured by X-ray diffraction (XRD). Experimental results for forces, temperatures and RS are used to validate the finite element model. Once a high confidence level in finite element predictions is obtained, a numerical investigation of the effects of cutting tool edge radius (r) and cutting speed on RS is carried out. Within the investigated range of parameters, residual stresses are found to be compressive in nature. It is observed that residual stresses become more compressive with increasing feed rate and less compressive with increasing edge radius or cutting speed.