Asymmetry of keyhole and weld pool geometry in PLBW of tailor-welded steel sheets with edge misalignment: Numerical modeling and experimental validation

Abstract

Edge misalignment in butt welded joints is difficult to avoid due to factors such as poor processing accuracy, the presence of assembly tolerances, and welding distortion. It reduces the performance of the joints, which is inextricably associated with molten pool behaviors during the welding process. The purpose of this paper was to investigate the effects of the edge misalignment on weld pool dynamic behaviors by developing a multi-phase CFD model to reproduce the pulsed laser beam welding (PLBW) on a couple of low-carbon steel plates with a thickness of 1.8 mm, which had been verified with experimental weld pool profiles. Both experiments and numerical simulations took into account different scales of edge misalignment. The results demonstrated that the keyhole quickly penetrated the workpiece and remained quasi-steady with the continuous emission before shutting down when the laser intensity was dropped. The flow patterns within the weld pool were characterized by a vertical downward flow near the keyhole, Marangoni flows on both the top and root surfaces, together with a flow from the higher-assembled side to the lower. Those were driven by recoil pressure, surface tension gradient, and gravity, respectively. Moreover, both the weld pool and the keyhole showed a clear inclination toward the assembled lower side, as measured by positive slopes with values ranging from 5 to 25. When the sheet edges became more misaligned, the size of the weld pool shrunk because less laser energy reached the surface of the workpiece. At the termination of the third pulse cycle, the maximum weld width at the top surface (TW) and root surface (RW), as well as the penetration depth, were reduced by 5.281 %, 25.495 %, and 2.303 %, respectively. A larger scale of weld misalignment contributed to a more inclined weld pool, marked by lower slope values.