Cooling and lubrication performance of supercritical CO2 mixed with nanofluid minimum quantity lubrication in turning Ti-6Al-4 V

Due to low thermal conductivity and high chemical reactivity, the aerospace alloy Ti-6Al-4 V has a high cutting temperature and poor machinability in metalworking operations. It results in poor workpiece quality and low tool life, which increases the processing costs. Therefore, an efficient cooling-lubrication technique is requested to solve this problem. Herein, a new system, supercritical CO 2 mixed with nanofluid minimum quantity lubrication (SCCO 2 -NMQL), is used for the cutting process. Supercritical CO 2 (SCCO 2 ) produces a low-temperature jet field because of the Joule–Thomson effect after injection and delivers the nanofluids deep into the cutting zone for cooling and lubricating during the cutting process. In this work, the effectiveness of SCCO 2 -NMQL cooling-lubrication in turning Ti-6Al-4 V was compared with that of other lubrication conditions (i.e., dry cutting, SCCO 2 , and supercritical CO 2 mixed with minimum quantity lubrication (SCCO 2 -MQL), respectively), in terms of cutting zone temperature, cutting force, surface roughness, and tool wear. In comparison with dry cutting, SCCO 2 , and SCCO 2 -MQL, the cutting temperature drops of SCCO 2 -NMQL are more than 25%, 15%, and 12%, respectively. The use of SCCO 2 -NMQL cooling conditions provides lower cutting force and a superior surface finish. Moreover, the SCCO 2 -NMQL cooling condition has the potential to offer a sufficient cooling-lubrication function to tool wear. Results of the work indicate that SCCO 2 -NMQL can act as an efficient cooling-lubrication technique.