Cutting performance and cutting fluid infiltration characteristics into tool-chip interface during MQL milling

The insufficient infiltration of cutting fluid at the tool-chip contact interface during machining poses a substantial challenge to achieving clean and efficient cutting processes. Key to enhancing the infiltration efficiency of cutting fluids lies in understanding their penetrative characteristics within the tool-chip cutting region. Thus, analyzing the milling performance under varying lubrication environments and cutting parameters forms a fundamental prerequisite to this research. In this study, we experimentally investigated the influences of cutting parameters on cutting force and cutting temperature in dry and minimum quantity lubricant (MQL) milling. In addition, we presented the friction state at the tool-chip interface, incorporating the friction coefficient into our analysis. Moreover, we explored the infiltration characteristics of oil mist fluid within the tool-chip contact region via fluid simulations. The tool wear mechanisms under various lubrication conditions were also elucidated. Subsequently, we established three-stage infiltration models to ascertain the conditions conducive to the formation of stable lubricating films and revealed the internal mechanisms dictating MQL penetration. The results disclose that the cutting force, cutting temperature, and friction coefficient of MQL milling decrease by 10-25%, 9%, and 16% respectively at a cutting speed of vc = 100 m/min, feed rate of fz = 0.4 mm/rev, and axial cutting depth of ap = 0.3 mm. However, as cutting parameters increase, the MQL's ameliorative effect on cutting performance diminishes. The underlying cause for this is the expansion of the tool-chip contact length and the increased chip curling radius, which significantly obstruct the injection of MQL oil mist droplets, resulting in a weakened infiltration effect. In conjunction with the conditions necessary for lubricating film formation, it is evident that an increase in cutting parameters is detrimental to improving the infiltration capacity of the cutting fluid into the capillary.