Influence of supercritical CO2 cooling on tool wear and cutting forces in the milling of Ti-6Al-4V

Ti-6Al-4V is known as a difficult-to-machine alloy due to its low thermal conductivity which limits the material’s machinability causing rapid tool wear. Supercritical CO2 is an environmentally friendly alternative cooling technique that can improve the machinability of Ti-6Al-4V enabling higher productivity. This study investigates the variation in tool life and cutting force coefficients when milling Ti-6Al-4V with scCO2, scCO2 combined with minimum quantity lubrication and flood coolant. Results from cutting trials carried out at 60 m/min have shown that when the chip load is controlled, substantial improvement in tool life can be obtained with scCO2+MQL compared to flood coolant with no significant change in cutting force coefficients. However, it has been found that the capabilities of scCO2 are limited outside the practical speed and feed range resulting in no additional benefit in tool life and sharp increase in cutting force coefficients due to higher thermal gradient and excessive tool wear.