Modelling and optimization of selective laser melting parameters using Taguchi and super ranking concept approaches

Nickel super alloy (IN625) widely employed in mechanical moving parts is subjected to sliding contact between mating pairs, which causes wear losses. Wear loss in functional parts causes dimensional inaccuracies, which results in deteriorated performance (vibration and noise) and finally leads to catastrophic failure during their service life. The present work aims at minimizing the wear rate by enhancing the density of IN625 parts printed viz. selective laser melting (SLM) process. SLM parts quality (i.e., density and wear rate) is influenced mainly by process variables (laser power LP, scan speed SS, and hatch distance HD). Taguchi method is employed to study the influencing process variables that could affect the part quality at limited experimental trials and cost. Laser power resulted with highest contribution for both the outputs. Scan speed resulted with least contribution for density and hatch distance for wear rate. Taguchi determined optimal conditions for individual outputs are identical, and this could be because of wear rates' strong dependency on density (i.e., higher the density lesser the wear rate and vice versa). Although the optimal conditions are same, but the percent contribution corresponding to each output variables are found to be different. Therefore, super ranking concept (SRC) method was applied to perform multi-objective optimization and locate optimal conditions. SRC determined optimized conditions (LP: 270 W, SS: 800 mm/s, and HD: 0.10 mm) resulted in lesser wear rate of 0.0031 mg/m and higher density of 8.53 g/cm(3) in SLM parts. The SRC model determined optimized conditions are not the set of Taguchi L-9 experiments and confirmation results revealed the efficacy of the model. SEM analysis on wear track of optimized conditioned parts resulted in minor grooves, coupled with few cracks, and voids. Therefore, Taguchi-SRC model can be applied to analyse and optimize a process for better quality in printed parts at industries.