Performances of a tailored vegetable oil-based graphene nanofluid in the MQL internal cooling milling

This study develops a graphene nanofluid based on vegetable oil, integrated with internal cooling and minimum quantity lubrication (MQL) technology, to enhance cooling and lubrication during the machining of 7075 aluminum alloy. Vegetable oil-based graphene nanofluids with varying mass fractions of graphene nanoplatelets were prepared by a two-step method. Oleic acid was added as a surfactant to improve suspension stability and optimize the viscosity of the base fluid. Thermophysical experiments showed that the 0.5 wt% graphene nanofluid exhibited a 23.57 % higher thermal conductivity compared to pure vegetable oil, while maintaining lower viscosity for better cooling performance. In tribological tests, graphene significantly reduced the friction coefficient (6.80 %–17.04 %) and wear, with XPS analysis confirming the formation of a stable carbon film that enhanced wear resistance. MQL milling experiments revealed that the optimized nanofluid reduced cutting temperatures by 11.31 %–20.98 %, cutting forces by 6.75 %–12.83 %, and surface roughness by 7.35 %–20.33 %, while extending tool life by up to 52.9 %. A sustainability evaluation further highlighted the superior environmental compatibility, reduced maintenance demands, improved operator safety, and cost-effectiveness of the nanofluid-MQL compared to conventional cooling methods. These findings demonstrate that the optimized graphene nanofluid significantly enhances machining efficiency, tool life, surface quality, and sustainability.