Influence of Cutting Tool Wear on Contact Stresses and Temperature Distribution in Titanium Alloy Machining

Abstract

This paper analyses the results of experimental research of contact stresses distribution over an artificial flank wear-land and temperature distribution in a cutting wedge in a free orthogonal turning of the disk made from titanium alloy (Ti-6Al-2Mo-2Cr) by a cutter with a sharp-cornered edge and with a rounded cutting edge. The investigation was carried out by the method of “split cutter” (sectional tool) and method of variable length of an artificial flank wear land. Experiments with variable feed rate and cutting speed show that in titanium alloy machining with a sharp-cornered cutting edge, the highest normal contact stress over the flank land (σh max = 3400…2200 MPa) is observed immediately at the cutting edge, and the curve has a horizontal region with a length of 0.2…0.6 mm. At larger distance from the cutting edge, the value of normal contact stress is dramatically reduced to 1100…500 MPa. The character of normal contact stresses for a rounded cutting edge is different: it is uniform and its value is approximately 2 times smaller as compared to machining with sharp-cornered cutting edge. In author’s opinion it is connected with generation of a seizure zone in chip formation region and explains working capacity of very worn-out cutting tools in machining titanium alloys. The results of experimental research of temperature distribution in the cutting tool wedge show that temperature reaches 1000 °С at essential wear over the flank surface. Such high value of temperature on the contact surface causes softening of work material, and explains the small value of tangential contact stresses (τh = 800…200 MPa) and reduction of normal contact stresses σh far from the cutting edge for a sharp-cornered cutting edge.