Thermal-mechanical responses of Ti-6Al-4V during orthogonal cutting process

Abstract

Orthogonal metal cutting process involves large plastic deformation accompanied by excessive heat generation. This work addresses the thermal-mechanical responses of the workpiece material at the tool-workpiece contact. In this respect, the orthogonal cutting process of Ti-6Al-4V using CVD diamond tool is simulated using finite element method. The cutting condition consists of cutting speed, K=180 m/min, feed rate, t=0.125 mm/rev and width of cut of 1.25 mm. Eulerian formulation with coupled thermal-mechanical analysis is employed in the model. The JohnsonCook constitutive equation is employed for Ti-6Al-4V workpiece material to accurately simulate the formation of shear bands. The stick-slip friction condition is modeled at the tool-chip interface. The sliding coefficient of friction of 0.8 and the limiting shear stress of 700 MPa for stick-slip condition are determined experimentally. Results show that high temperature and temperature gradient concentrate in the primary shear zone and the contact area between the tool rake face and the chip. A primary shear band is predicted in the workpiece ahead of the tool-workpiece contact face while the secondary shear band is formed in the chip. This highly-deformed shear band is revealed in the microstructure of etched chips. The predicted high strain rate results in build-up edge at tool cutting edge-chip contact. Low cutting condition of V=150 m/min, t=0.125 mm/rev promotes stagnant zone formation that helps preserve the cutting edge of the tool. The maximum predicted temperature at the cutting edge is in excess of 700°C Such high temperature level facilitates diffusion of carbon elements into the chips and conversely, elements of titanium into the CVD diamond tool.