Physicochemical properties of degradable vegetable-based oils on minimum quantity lubrication milling

With increasing attention being paid to environmental and health problems in metal machining, developing an environmentally friendly cutting fluid is an urgent need. Degradable vegetable oils with non-toxicity and renewability are becoming increasingly popular. However, the mechanism of physicochemical properties of different vegetable oils is not clear on minimum quantity lubrication (MQL) milling. In the study, five typical vegetable oils (i.e., cottonseed, palm, castor, soybean, and peanut) were selected as base oil to experimentally evaluate the lubrication performance of the tool–workpiece interface compared with synthetic cutting fluid. With Grade 45 steel as workpiece material, the lubrication performance was evaluated in terms of milling force, surface roughness and surface morphology, as well as the composition, molecular structure, and viscosity of vegetable oils. Results showed that the vegetable-based oils achieved lower milling force and better surface quality than the synthetic cutting fluid. Among them, palm oil obtained the lowest milling force ( F x = 309 N, F y = 154 N) at 7.76% and 13.6% lower than that of synthetic cutting fluids. The surface quality obtained by vegetable-based oils is superior to that of the synthetic cutting fluid, and the cottonseed and palm MQL acquired the best surface, while soybean obtained the worst surface. Furthermore, the results of surface roughness are consistent with those of surface morphology. Finally, according to the analysis of composition and molecular structure, palm and cottonseed with high content of saturated fatty acids are more suitable as MQL base oils.