Hybrid cryogenic MQL for improving tool life in machining of Ti-6Al-4V titanium alloy

It is estimated that there is a need for 37,000 new passenger aircrafts until 2037. About 15% of the modern aircrafts are made of titanium alloys due to their high strength to weight ratio. In typical aerospace manufacturing, there is a buy-to-fly ratio of 6:1 for titanium parts which indicates significant machining requirements. Machining titanium alloys is generally associated with short tool life, poor surface integrity, low productivity and high manufacturing costs. These issues have made Ti-6Al-4V a difficult to machine material. In this study, a new hybrid cryogenic MQL cooling/lubrication technique is proposed for end milling Ti-6Al-4V using coated solid carbide tools. The effect of the proposed system on machinability of Ti-6Al-4V was studied at various cutting speeds and compared with flood, minimum quantity lubrication (MQL) and cryogenic cooling. Tool life, tool wear and surface roughness were thoroughly investigated as key machinability metrices and a new model for tool life based on tool wear is proposed. The analysis indicates a significant shift in CNC milling performance, as the new hybrid cryogenic MQL technique shows an increased tool life of 30 times is achieved together with a 50% improvement in productivity compared to state-of-the-art flood coolant machining.