Optimisation and quantitative evaluation of the qualities for Nd-YAG laser transformation hardening

The aim of this paper is to find the optimal process parameters and to evaluate quantitatively the quality characteristics of laser transformation hardening of SNCM 439 steel by a long pulsed Nd-YAG laser beam. The Taguchi methodology and fuzzy evaluation method are used. Using the Taguchi methodology, the surface hardness of the specimen was increased from H_RC52.5 to H_RC63.9. The depth of hardening was also increased from 0.11 mm to 0.21 mm. Moreover, the width of hardening was increased from 0.43 mm to 0.89 mm and the erosion was reduced from 69.55 mg to 40.94 mg. When these four factors are optimised simultaneously, the results show that improvements vary from 19.24% to 97.67% using the Taguchi method. A fuzzy method was also used to analyse and evaluate the processing qualities. The results obtained using the fuzzy method are similar to those obtained using the Taguchi method. The same methodology can be applied to the processing of other high-power laser material. We obtained a significant improvement in the quality of laser transformation hardening by Nd-YAG laser and the quantitative evaluation of the non-discriminating quality factors.