Hybrid cryogenic MQL highspeed machining of Ti-6Al-4V alloy

Grade 5 titanium alloy, Ti6Al-4V, has high specific strength and is extensively used in aerospace industry. It has the highest strength to weight ration among all structural metals up to 550°. Superior mechanical properties coupled with low thermal conductivity has notoriously made Ti-6Al-4V a difficult to machine material. Machining titanium alloys is associated with short tool life, poor surface integrity and low productivity. Specifically, in aerospace and medical industries, machining titanium imposes a bottleneck in the manufacturing systems. In this paper, a novel hybrid machining environment comprising of liquid nitrogen (LN2) cryogenic coolant and rapeseed oil minimum quantity lubrication (MQL) is investigated for end milling Ti-6Al-4V alloy. The effect of this hybrid machining environment on tool life, tool wear and surface roughness is compared with conventional flood cooling and state of the art cryogenic machining. The results showed that the new hybrid machining environment reduces tool wear growth rate by a factor of 4 resulting in 3.8 times increased tool life as compared with flood cooling. Moreover, surface roughness of 0.25μm is generated by hybrid machining environment as opposed to 0.43μm and 0.57μm for flood cooling and cryogenic machining respectively. This paper clearly demonstrated that using hybrid machining environment, high speed machining of titanium can be realised using solid tungsten carbide cutting tools.