Investigation of cutting temperature, cutting force and surface roughness in turning of inconel 625 superalloy under different eco-friendly cooling/lubrication conditions

Inconel 625 superalloy is widely used in aerospace and energy industries; however, its low thermal conductivity, severe work-hardening tendency, and strong chemical affinity with cutting tools make it difficult to machine. This study systematically investigated the machinability of Inconel 625 under fifteen environmentally friendly cooling/lubrication conditions, including dry machining, high-pressure air cooling (HPAC), vortex air cooling, minimum quantity lubrication (MQL), and hybrid strategies. Machining performance was evaluated using cutting temperature, cutting force, surface roughness, tool wear, total machining cost, and carbon emission. Hybrid cooling/lubrication conditions significantly improved machining performance, reducing cutting temperature by up to 56.04%, cutting force by 11.48%, and surface roughness by 74.08%. Dry machining exhibited the lowest machining cost and carbon emission because no auxiliary cooling/lubrication equipment was employed. Grey Relational Analysis (GRA), integrating technical, economic, and environmental performance indicators, identified the HPAC (14 bar) + MQL (0.90 ml/min) condition as the optimum sustainable machining condition among the tested alternatives. SEM and EDS analyses confirmed that hybrid cooling/lubrication effectively suppressed built-up edge formation and adhesive wear. The proposed experimental framework provides a practical approach for selecting sustainable cooling/lubrication strategies for machining Inconel 625 by simultaneously considering machining performance, economic efficiency, and environmental impact.