Effects of cooling air temperature on cryogenic machining of Ti–6Al–4V alloy

This paper presents experimental investigations on influence of different coolant strategies such as dry, wet, minimum quantity lubrication (MQL) and MQL with cooling air on performance in milling of the Ti–6Al–4V alloy with uncoated cemented carbide inserts. Cutting force, tool wear, surface roughness and chip morphology are experimentally studied to compare the effects of different cooling air temperatures. The results showed that minimum quantity lubrication (MQL) with cooling air significantly reduces cutting force, tool wear and surface roughness. Unfortunately, MQL (without cooling air) condition cannot produce evident effect on cutting performance, and flaking wear on the flank surface of the insert has been found under this condition. Four different cooling air temperatures are used to investigate the effects of cooling air temperature on the machinability characteristics of Ti–6Al–4V alloy. Based on the experimental results, MQL with cooling air of −15 °C provides more favourable effects compared to other cooling air temperatures (0 °C, −30 °C,−45 °C). Short chips are produced under MQL with cooling air conditions due to the high velocity of cooling air enhances the chip brittleness for easy chip breaking, and the effective penetration of lubricant to the chip–tool interface results in lower friction. However, due to the dramatic increase in chip hardness at lower temperature, MQL with cooling air environments cannot promote chip curl to some extent.