Parameter optimization of laser transformation hardening by using Taguchi method and utility concept

This paper presents the application of Taguchi method and the utility concept for optimizing the laser process parameters in laser transformation hardening of commercially pure titanium using a continuous-wave 2-kW, Nd:YAG laser. In this study, a set of optimal laser process parameters were evaluated through the Taguchi method of orthogonal arrays and utility concept. Taguchi method and utility concept, a powerful tool to design optimization for quality, is used to find the set of optimal laser hardening parameters such as laser power (LP), scanning speed (SS), and focused position (FP) on two multiple performance characteristics of hardened bead geometries, namely, hardened bead width (HBW) and hardened depth (HD), developed for laser transformation hardening of commercially pure titanium. The utility concept has been employed for the multi-performance characteristics optimization using Taguchi design. The experiments were planned as per Taguchi's L9 orthogonal array. A Taguchi L9 orthogonal array methodology was used to optimize the conditions for laser-hardened bead width and hardened depth. Taguchi tools such as analysis of variance (ANOVA), signal-to-noise ratio, and additive model have been used to analyze, obtain the significant parameters, and evaluate the optimum combination levels of laser transformation hardening process parameters. The optimal levels of the laser process parameters were determined through the analysis of means. The relative importance among the process parameters were identified through ANOVA. The ANOVA results indicated that the most significant process parameters are SS followed by LP and FP, which affect the optimization of multiple performance characteristics. The confirmation tests with optimal levels of laser process parameters were carried out to illustrate the effectiveness of Taguchi optimization method. The optimization results revealed that a combination of higher levels of SS and FP, i.e., increase in defocused beam with negative focal length along with LP in the lower level, is an essential laser hardening parameter to simultaneously minimize the HD and maximize the HBW.