Lubrication Mechanism of scCO₂-MQL in the Assisted Machining of Titanium Alloys

Cutting fluids are often used in the machining of titanium alloys to reduce processing temperature and maximize quality and productivity. The permeability of the cutting fluid in the capillary tube directly influences the effect of lubrication on cooling performance. In this study, supercritical carbon dioxide cryogenic micro-lubrication (scCO(2)-MQL) is used for the auxiliary machining of titanium alloys. A capillary model for scCO(2)-MQL-assisted cutting is proposed and established while considering the characteristics of three-phase states produced during the decompression release of scCO(2). The injection temperature and characteristics of scCO(2) are experimentally investigated, and the dynamic process of scCO(2)-MQL penetration into the capillary is analyzed. The results show that under the applied experimental conditions, the injection temperature of scCO(2)-MQL ranges from approximately -45 degrees C to 60 degrees C. Because scCO(2) presents good solubility in oil, it has the capacity to refine the oil droplets into smaller particles, thus resulting in a higher lubricating oil content in the capillary per unit of time. This leads to enhanced lubricity that can benefit processing applications.