Influence of graphite nanoparticle concentration and vegetable oil type in minimum quantity lubrication on the milling performance of SKD11 tool steel

This study investigated the influence of graphite nanoparticles dispersed in castor oil, sunflower oil, and cottonseed oil on minimum quantity lubrication milling of SKD11 tool steel. The machining performance in terms of cutting force, surface roughness/morphology, and cutting temperature was evaluated under four cutting environments: dry cutting, minimum quantity lubrication using each pure oil, and nanofluid minimum quantity lubrication applied with different concentrations of 0.5 and 1.0 wt%. The results demonstrated that nanofluid-minimum quantity lubrication significantly enhanced machining performance compared to dry cutting and pure base oils. Notably, sunflower oil with 0.5 wt% graphite reduced the cutting force by 42.3%, while 1.0% yielded the lowest surface roughness ( R a = 0.64 µm), or reduced by 74%. Thermal analysis showed that cottonseed oil with 1.0 wt% graphite lowered peak cutting temperatures by 66.8%. The layered crystalline structure of graphite and the tribological characteristics of the vegetable-based oils helped reduce friction and increase heat dissipation. Overall, sunflower and cottonseed oil-based nanofluids offer a feasible, sustainable alternative for high-performance minimum quantity lubrication machining, highlighting the need to optimize both oil type and nanoparticle concentration for sustainable machining.