Melt flow regularity and hump formation process during laser deep penetration welding

Abstract

In this study, the relationship between melt flow and hump formation was directly revealed during laser deep penetration welding of transparentmaterial. In partial-penetration welding, the melt flowed obliquely upwards along the bottom of the keyhole to the rear surface of the molten pool. And its flow rate increased first and then decreased with the increase of the welding speed. There was a one-to-one correspondence between the humps formed on the weld surface and the fluctuation of the inclination angle of the front keyhole wall (FKW) near the Brewster angle. The maximum eruption rate of the laser-induced vapor on the FKW exceeded 30 m/s. In full-penetration welding, the melt flow direction changed and humping was suppressed. The laser-induced vapor on the FKW surface can act on the rear keyhole wall, and this is the main reason for melt flow. When the inclination angle of the FKW is close to the Brewster angle, the amount of laser-induced evaporation on the FKW will increase to form a high speed jet of vapor which will drive melt flow in the molten pool behind the keyhole, and this is the main reason for hump formation on the rear surface of the molten pool.