Drill life optimisation when drilling TI-6AL-4V with HSS drills

Relatively low machinability of titanium and its alloys is caused mainly by their poor thermal conductivity, low modulus of elasticity, chemical reactivity with cutting tool materials at high temperatures and work bardening characteristics that produce high chip loads near the tool cutting edge of the tools. However, the widespread use of titanium and its alloys for critical components in many applications, bas attracted significant attention for investigations on machinability resulting in a number of recommendations. In many instances, particularly for small production runs of deep-hole drilling in titanium alloy components, drilling operations are carried out by using HSS drills. Not much literature is available concerning this aspect of driIIing. This paper presents an investigation wherein cutting forces, acoustic emissions and chip formation were examined during deep-hole drilling of Ti-6M-4V at various cutting speeds and reed rates and optimum drilling parameters were detennined. Then a CNC program that incorporated the optimum cutting speed and feed parameters, along with a series of chip brealer and full relief steps, was developed. The CNC program was observed to provide a trouble-free deep drilling operation on Ti-6M-4V bars with high-speed steel drills