Multi-response machinability and chip formation analysis in end milling Inconel 718 under diverse lubri-cooling strategies

Nickel-based superalloy machining presents a long-standing obstacle in advanced manufacturing sectors due to the material's low thermal conductivity, high hot hardness, and severe work-hardening tendency, which collectively accelerate tool degradation. This study examines five lubri-cooling strategies: dry machining (DM), compressed air (CA), minimum quantity lubrication (MQL), vortex tube (VT), and flood cooling (FC), during end milling of Inconel 718 with CVD-coated TiN-TiB 2 cemented carbide inserts, filling a critical research gap regarding the under-explored effects of vortex tube cooling in superalloy milling. Machining forces, cutting power, specific cutting energy, surface roughness, chip compression ratio, and chip morphology were assessed across two cutting speeds and two feed rates, with statistical significance verified through ANOVA and Tukey's test. Flood cooling delivered the most favorable technical outcomes, reducing the resultant cutting force by 13.4% , cutting power by 57.2% , and specific cutting energy by 61.2% compared to dry machining. MQL provided intermediate performance, lowering specific cutting energy by 42.9% relative to DM due to enhanced lubrication at the interface. Compressed air and vortex tube cooling exhibited comparable force profiles; however, the thermal pre-cooling effect of VT increased average cutting power by 8.4% compared to DM by raising the mechanical resistance of the workpiece. FC generated the highest surface roughness (Ra = 0.67 μm), while alternative strategies maintained a lower, tighter range (0.33–0.43 μm). VT achieved the lowest chip compression ratio (1.090), marking a significant reduction against DM (1.178). These quantitative insights establish critical engineering boundaries for balancing tool performance and fluid sustainability.