The effect of cutting speed and work piece hardness on turning performance of nickel based super Alloy-718 using ceramic cutting inserts

Abstract

The present investigation pertains to a series of experiments on plain turning of Inconel 718 with Al–Oxide (620), mixed oxide (6050) and silicon nitride (6190) ceramic cutting tools. The effect of cutting speed and hardness of material (being cut) on flank wear of tools and surface finish of work piece was studied. Inconel 718 with three hardness values (26 HRC, 35 HRC and 45 HRC) was used to assess the turning performance. Three cutting speeds (145 m min−1, 230 m min−1 and 360 m min−1) were used while feed rate and depth of cut was fixed at 0.19 mm min−1 and 0.3 mm respectively. Optical microscopy was used for estimation of tool flank wear and mechanisms of wear were established. Work piece hardness and cutting speed were found to be and also most influencing factors for tool life. Cutting forces observed to be higher for harder work piece and for mixed oxide cutting tool. The influence of cutting speed on chip formation was manifested in the form of continuous chip at a cutting speed of 145 m min−1. Segmented chip at higher cutting speed (above 230 m min−1) was observed for all the three cutting tools. Significant difference in tool flank wear and surface finish was observed for different work piece hardness and cutting speed with different cutting inserts for constant duration of machining time (3 min). Al-Oxide cutting insert provided better surface finish and low flank wear compared to silicon nitride and mixed oxide cutting inserts irrespective of the work piece hardness and cutting speed. Further, 45 HRC Inconel 718 possesses better surface finish and 26 HRC Inconel 718 possess better tool flank wear resistance in turning operation.