Optimization of Hybrid MQL Nanofluids for Cutting Force and Temperature Reduction in Turning HSLA (High-Strength Low-Alloy) Steel

High-strength low-alloy (HSLA) steel is widely used in structural, transportation, and heavy-duty applications due to its superior strength-to-weight ratio and cost-effectiveness. However, machining such materials typically generates excessive heat and high cutting forces, accelerating tool wear and compromising dimensional accuracy. In this study, a Taguchi L16 experimental design was employed to systematically analyze the effect of nanofluid composition and MQL parameters on machining performance. Four control factors nanofluid composition, concentration, air pressure, and nozzle diameter were examined with respect to tangential force, axial force, and cutting temperature. The results reveal a critical observation that nanofluid composition is the dominant factor influencing all responses, mainly due to the synergistic thermal conductivity and lubricity of hybrid nanoparticles. The optimized condition (50% GNPs, 25% CuO, 25% Al₂O₃ at 2% concentration, 3 bar, and 1 mm nozzle diameter) reduced tangential force to 1024 N, axial force to 456 N, and cutting temperature to 151.88 °C. Compared to dry cutting, this represents more than a 55% reduction in tangential force, a 50% reduction in axial force, and a 35% reduction in temperature, confirming the superior heat-dissipation and friction-reduction capabilities of the hybrid nanofluid. The implications of these findings show that hybrid-nanofluid MQL can notably enhance machining performance of HSLA steel by reducing cutting forces and lowering thermal loads, leading to more stable and efficient cutting conditions. Moreover, the optimized MQL strategy supports sustainable manufacturing by minimizing lubricant consumption while maintaining effective cooling and lubrication.