Machinability Assessment in High Speed Turning of High Strength Temperature Resistant Superalloys

Abstract

The paper discusses the effect of cutting parameters and cutting tool material on chip compression ratio, cutting forces and surface roughness in turning of high strength temperature resistant superalloys (HSTR). The experiments were performed in dry cutting environment on precision CNC lathe with fixed depth of cut of 0.5[Formula: see text]mm. Analytical model is developed to determine chip segmentation frequency, shear angle and shear strain and it is correlated with the machining parameters. The machinability of the selected superalloys is assessed in terms of cutting force, chip compression ratio and surface roughness. It is found from the experimental analysis cutting force magnitude is less at higher cutting speed for all the superalloys. Chip compression ratio is found maximum in case of Inconel 718 due to precipitation hardening of alloy and followed by Inconel 600 and Inconel 800. The chip segmentation frequency is high at lower cutting speed for Inconel 600 due significant strain hardening. Serrated chips are produced during machining of three selected superalloys and it is found that serrated tooth spacing decreases with cutting speed. Shear plane angle increases on cutting speed increases which effect tool workpiece contact length during machining resulted thin, short and snarled chips was produced. From analytical modeling it shows that shear strain decreases with cutting speed which indicate that at higher cutting speed material deformed elastically than plastically. The effect of cutting tool material is observed on the surface roughness. The better surface finish is obtained with coated carbide inserts as compared to ceramic inserts for all the selected superalloys. However, Inconel 800 shows higher surface roughness due to combination of (Ni–Cr–Fe) alloying element which is responsible for carburization of surface layer during machining.