Thermal, rheological, wettability and hard machining performance of MoS2 and CaF2 based minimum quantity hybrid nano-green cutting fluids

Minimum quantity cutting fluids (MQCF) is an alternative for dry machining and flood cooling. However, use of MQCF is limited to mild machining conditions due to high heat generation during machining of hard materials. The applicability of MQCF can be extended in aggressive machining conditions by using vegetable-based green cutting fluids (GCF) with solid lubricant nanoparticles as potential additives. In the present study, hybrid nano green cutting fluids (HN-GCFs) were prepared by mixing different volume concentration of calcium fluoride (CaF2) and molybdenum disulphide (MoS2) solid lubricants in indigenously developed vegetable based GCF. Dispersion stability, thermal conductivity, specific volumetric heat capacity, viscosities and wetting angle of HN-GCFs were measured. In-house fabricated MQCF setup is used to apply minimum HN-GCF across the machining region. Later, the experimentally optimised concentration of both CaF2 and MoS2 based HN-GCFs were selected for machining experiments using MQCF setup. Hard machining experiments were carried out using four different cutting fluids: commercial mineral oil (MO), GCF, 0.3% concentration of CaF2 based HN-GCF (HN-GCF-0.3C) and 0.3% concentration of MoS2 based HN-GCF (HN-GCF-0.3M). Comparative tool wear, workpiece material adhesion and workpiece surface morphology were also investigated. Results show that 0.3% concentration of HN-GCF-0.3M performs better concerning tool-workpiece interface coefficient of friction, cutting force, feed force, and workpiece surface roughness compared to other cutting fluids. During machining with HN-GCF-0.3M, cutting tool experiences 17% and 28% lower cutting as well as feed force, respectively as compared with machining using MO. Also, 11% reduction in tool-chip interface coefficient of friction was observed during machining using HN-GCF-0.3M, and it also produces 37% better workpiece surface finish. Elemental analysis of cutting tool confirms less work material adhesion on the cutting tool rake face using HN-GCF-0.3M