Optimizing multiple quality characteristics via Taguchi method-based Grey analysis

This paper presents and demonstrates the effectiveness of optimizing multiple quality characteristics of Nd:YAG laser welded titanium alloy plates via Taguchi method-based Grey analysis. The modified algorithm adopted here was successfully used for both detraining the optimum settings of machine parameters and for combining multiple quality characteristics into one integrated numerical value called Grey relational grade or rank. The essential machining parameters were identified as (1) shielding gas, (2) laser energy, (3) traveling speed of the workpiece during welding, (4) focusing position, (5) frequency of the impulse laser, and (6) pulse shape of the primary laser beam. Furthermore, the multiple quality characteristics required herein included: (1) high ultimate tension stress, (2) small heat-affected zone, (3) large welding depth to width ratio, and (4) low surface roughness following laser welding. Titanium alloy plates were butt welded under controlled machine parameter settings, machined, and above quality characteristics were measured. The optimized machine parameter settings clearly improved the quality characteristics of welded plates compared to quality levels achieved for conventional machine parameter settings. The tensile stress increased (922 ± 53 to 965.5 ± 46.5 MPa) and the heat-affected zone decreased (0.27–0.22 mm) while the welding depth to width ratio remained the same at 0.76. The new approach increased the surface roughness from Rmax of 14.2 to 34.4 μm.