Parametric appraisal of mechanical and metallurgical behavior of butt welded joints using pulsed Nd:YAG laser on thin sheets of AISI 316

Abstract

In the era of miniaturization, welding of thin sheets find wide spread applications in developing micro-scale products essentially used in bio-medical, aerospace and automobile industries. During welding of thin sheets, welding deformation needs to be addressed to obtain sound and strong joints. Experimental investigation has been made on laser butt welding using pulsed Nd:YAG laser. Specifically, the study attempts to examine the influence of laser parameters such as laser current, pulse width, and scanning speed on weld quality of thin sheets of 0.45 mm. The quality of weld beads have been analyzed by scanning electron microscope (SEM), optical microscope, and radiography and fractographic inspection. Further, mechanical characterization of the weld beads is made by estimating micro-hardness, residual stress, surface roughness, and welding strength. The study indicates that laser current is the most importance parameters in welding of thin sheets because it helps in obtaining good mechanical and metallurgical qualities of welded joints. The welding strength increases with increase in scanning speed to a certain level and then it reduces. Spot overlapping significantly influences on surface integrity (surface roughness) and welding strength of welded joints. Micro-hardness in fusion zone (FZ) is comparatively higher than that in the heat affected zone (HAZ) because of the difference in grain structure (coarseness) attributed to cooling rate. The study further indicates that there is significant effect of laser pulse energy on development of residual stresses in welded joints. The study is extended to develop empirical relationship between laser parameters and welding strength using non-linear regression analysis. The adequacy of the empirical model is checked by comparing the results obtained from empirical model and experimental values. A new meta-heuristic approach known as simple optimization (SOPT) algorithm has been adopted to obtain optimum parametric setting for welding strength. A relative error of 8.79% is obtained when welding strength at optimal parameter setting is compared with confirmatory experiment.