Influence of Graphene Nanosheets on Thermo-Physical and Tribological Properties of Sustainable Cutting Fluids for MQL Application in Machining Processes

The growing need to increase productivity and pressures for more sustainable manufacturing processes lead to a shift to less harmful lubrication systems that are less harmful to nature and the people involved. The minimal quantity lubrication system (MQL) stands out in this respect, especially in interrupted cutting processes such as milling, due to the cutting interface's highly dynamic and chaotic nature. Using graphene sheets in cutting fluids also increases the efficiency of machining processes. This work investigates the influence on thermophysical and tribological properties of concentrations of 0.05 wt% and 0.1 wt% of graphene sheets in two vegetable-based and one mineral-based cutting fluids. The fluids are first characterized (viscosity, thermal conductivity, diffusivity, and wettability) and tested in reciprocating and ramp milling tests; all experiments are based on norms. The results show that the experiments with cutting fluids (with and without graphene) showed better tribological behavior than those in dry conditions. The graphene sheets alter the thermo-physical and tribological properties of the cutting fluids. The MQL15 vegetable-based fluid showed better lubricating properties in the milling tests, with better conditions for tribosystem chip-tool-workpiece interfaces, which makes the friction coefficient, and wear rate stable. Vegetable-based cutting fluids, even in minimum quantities and with graphene nanoparticles, have a high potential for increasing the efficiency and sustainability of the milling process.