Nano-Enhanced MQL Optimization for Superior Surface Finish in Hard Milling of 9CrSi Steel

This study explores the optimization of Minimum Quantity Lubrication (MQL) enriched with CuO nanoparticles to achieve exceptional surface quality in the hard milling of 9CrSi alloy steel. Using the Taguchi method with an L9 orthogonal array, the effects of nanoparticle concentration, fluid flow rate, and compressed air pressure on surface roughness (Ra) were systematically investigated. Signal-to-noise (S/N) ratio and analysis of variance (ANOVA) revealed that a nanoparticle concentration of 4 wt%, fluid flow rate of 120 ml/h, and compressed air pressure of 3.5 KG/cm² yielded the lowest surface roughness (Ra = 0.210 µm). Notably, nanoparticle concentration was the most influential factor in surface roughness variation. These findings underscore the transformative potential of nano-enhanced MQL in delivering superior surface finish and sustainable machining for high-hardness alloys.