Hard turning of AISI 4340 steel using coated carbide insert: Surface roughness, tool wear, chip morphology and cost estimation

Abstract The present study addresses surface roughness, flank wear and chip morphology during dry hard turning of AISI 4340 steel (49 HRC) using CVD (TiN/TiCN/Al 2 O 3 /TiN) multilayer coated carbide tool. Three factors (cutting speed, feed and depth of cut) and three-level factorial experiment designs with Taguchi’s L 9 OA and statistical analysis of variance were performed in order to investigate the effect of these cutting parameters on the tool and workpiece in terms of flank wear and surface roughness. The results shows that surface roughness and flank wear are statistically significant influenced by feed and cutting speed. In fact, increase in cutting speed resulted in better surface finish as well as increase in flank wear. For better understanding of the cutting process, surface topography of machined workpieces, wear mechanisms of worn coated carbide tool and chip morphology of generated chips are observed by scanning electron microscope (SEM). Consequently, MRA was adopted to develop mathematical model for each response, along with various diagnostic tests were performed to check the validity and efficacy of the proposed model. Finally, to justify the economical feasibility of coated carbide tool in hard turning application, a cost analysis was performed based on Gilbert’s approach by evaluating the tool life under optimized cutting condition (suggested by response optimization technique) and estimated that the total machining cost per part is Rs.8.21 for machining of hardened AISI 4340 steel with coated carbide tool.