| Summary: | Productivity rise can be realized at high-speed welding, but in a practice, the constraints emanate from the tolerance welding speed limit beyond which generate humping defects and the likes. These defects are undesirable in welding as they undermined the weld bead integrity and decrease productivity. In this study, an investigation on a lap joint welding using a hybrid Laser-GMAW (L-GMAW) welding process on a carbon steel sheet was undertaken to examine the mechanisms involved in the arc behavior, the droplet transfer, and the weld pool flow dynamics in a hump defect formation at high-speed welding. A variation of the process parameters in the hybrid welding system such as the wire feed speed (WFS), the traveling speed (TS) and the oscillation of the laser beam were used as input signals. A high-speed video camera was used with different viewing positions to capture the sequence of events during the hybrid welding process. The high-speed images of the arc behavior, the weld pool flow pattern with the use of tracer particles in arriving at the root mechanisms were acquired. Based on the experimental resultant, the occurrence mechanisms of the weld defects were proposed. In this study, the key factors in the humping defect formation are the two dominant lateral flows toward the top and bottom sheets, the collision between the weld pool back- and rear-flow and the interruption of the weld pool flow channel. Also, the generation of copious spatter due to the two lateral flows and the swollen buildup towards the hump closure were responsible for the next hump initiation formation. The beam oscillation applied to wet the weld toe angle to delay the outset of the humping defect occurrence was insignificant at higher travel speed. Furthermore, the force of gravity and surface tension were the key forces in this study. Keywords: Hybrid L-GMAW, Lap joint, Arc behavior, Droplet transfer, Hump formation, High travel speed
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