Influence of CO2-snow and subzero MQL on thermal aspects in the machining of Ti-6Al-4V

Abstract

Having a low thermal conductivity, the aerospace alloy Ti-6Al-4V is well-acknowledged as to retain an elevated thermal state in machining and shows poor machinability. An enhanced heat transfer during cutting is hypothesized to reduce the high cutting temperature and result in improved machining performance. Conventional flood cooling is reported as an ‘ineffective’ method to remove heat properly. As such, the advanced novel systems like carbon dioxide snow (CO2-snow) and subzero minimum quantity lubrication (MQL) spray have the potential to pacify the hot cutting zone. The present study investigates the heat transfer capability of CO2-snow and subzero MQL. Afterward, their thermal behavior has been related to the critical machinability metrics such as cutting temperature, cutting force, surface roughness, tool wear, chip analysis, and residual stresses with reference to conventional flood cooling to underscore their overall benefits. The statistical analysis has shown that a higher value of the coefficient of heat transfer (1347 W/m2C) was attained under CO2-snow compared to subzero MQL spray (486 W/m2C). Moreover, the order of overall better machinability has derived as CO2-snow > flood cooling > subzero MQL. Furthermore, the relatively superior heat transfer behavior of CO2-snow in machining resulted in reduced tool wear (i.e., prolonged tool life), and an improved surface finish. In summary, the CO2 snow showed promising results to warrant its application in the machining industry.