Machinability of Ti-6Al-4 V in the milling process using cryogenic cooling and nanofluid MQL

Titanium alloys, valued for their lightweight properties, are increasingly in demand as advanced materials in the aerospace industry. However, they are classified as difficult-to-machine due to their heat resistance and elastic characteristics, necessitating further research. Additionally, conventional lubrication methods present challenges related to the working environment and operator health, underscoring the need for alternative solutions. This study focuses on the milling process of the titanium alloy Ti-6Al-4 V, aiming to optimize the machining environment to enhance key performance metrics such as cutting temperature and surface quality. Experimental results indicate that hybrid nMQL (nanofluid minimum quantity lubrication) combined with cryogenic cooling significantly reduces tool wear. While cryogenic environments tend to produce microcracks, debris, and cutting marks, the nMQL environment is primarily associated with cutting marks and microcracks. Notably, surfaces processed under the combined nMQL + cryogenic environment exhibit greater stability than those produced under other machining conditions. Moreover, when cryogenic cooling is used in conjunction with nanofluid lubrication (nMQL), surface residual stress is reduced by up to 76.6 %, and cutting temperature decreases by as much as 25 % compared to other machining setups. Residual stress measurements, conducted using the hole drilling method with strain gauges, confirmed a significant reduction in surface stress under hybrid lubrication conditions. Additionally, while cutting temperature varies with cutting speed, it was observed to decrease by up to 25.8 % when the hybrid method was applied. The improved performance is attributed to the compressive surface residual stress induced by the elasticity and heat resistance of Ti-6Al-4 V. Consequently, the reduction in residual stress under the cryogenic + nMQL environment enhances tool wear resistance, surface quality, and temperature control, outperforming other machining conditions.