Machining performance of Inconel 718 in dry, air-cooling and bio-oil based minimum quantity lubrication environments

Inconel 718 is a widely used superalloy in aerospace, automotive and marine industries due to its high strength and ability to resist high mechanical stresses at high temperatures. However, its low thermal conductivity results in high temperature at the cutting zone during machining that adversely affects the surface quality and tool life. This work explores the machining performance of Inconel 718 alloy by cemented carbide cutting tool in dry, air-cooled and bio-oil based minimum quantity lubrication environments. Putranjiva roxburghii bio-oil was used as a cutting fluid. Emulsions were prepared by varying the water-oil ratio by volume as 100:5, 100:10, 100:15, 100:20, 100:25 and 100:30. The machining input parameters considered were spindle speed, feed rate and depth of cut. Box's evolutionary optimization technique was used to obtain the best combination of machining input parameters. Machining performance was assessed by surface roughness, tool temperature and tool wear. The most favourable machining environment was found to be the minimum quantity lubrication environment. The most desirable surface value of surface roughness obtained was 0.29 µm and the lowest temperatures of the tool and workpiece were 41.1 °C and 31.46 °C, respectively. These were obtained in a minimum quantity lubrication environment at a spindle speed of 180 r/min, feed rate of 16 mm/min and an emulsion ratio of 100:20. Microscopic analysis of the cutting tool revealed less wear indicating minimum quantity lubrication as the preferable environment for machining.