Turning of Inconel 718 using liquid nitrogen: multi-objective optimization of cutting parameters using RSM

The objective of this research was to investigate the effectiveness of application of liquid nitrogen (LN2) in turning of Inconel 718 compared to flooded cutting and select suitable LN2 cutting parameters using response surface methodology (RSM). The results of turning experiments conducted by spraying LN2 to the cutting area of Inconel 718 bar showed that using either low or high cutting parameters, cutting performance of Inconel 718 under the cryogenic condition was generally worse than the flooded cutting. However, using the medium cutting parameters, the LN2 cutting performance was as good as that of the flooded cutting both showing a cutting force of 90 N, 60 mu m of flank wear and 0.5-0.6 mu m of surface roughness (Ra). These parameters were further optimized using desirability function of RSM to determine the set of parameters that provided the lowest cutting force, flank wear and Ra values and the highest material removal rate (MRR) under cryogenic cutting. Analysis of variance (ANOVA) performed on the regression models developed showed that cutting speed was the only significant factor on the cutting force. Feed rate was the most influential parameter on the flank wear. Feed rate and depth of cut were significant factors both affecting Ra. Multi-objective optimization showed that a cutting speed of 87 m/min, a feed rate of 0.06 mm/rev and a depth of cut of 0.37 mm constituted the optimum cutting parameters for achieving a cutting force of 78 N, flank wear of 58 mu m, Ra of 0.49 mu m and the MRR of 1.97 cm(3)/min under the cryogenic cutting condition.