Dropout formation in thick steel plates during laser welding

Laser welding is a promising technique for welding thick metal sheets, which is usually used for achieving full penetration in a single weld pass. However, among the imperfections that can occur, dropout formation becomes an increasingly larger problem when the sheets to be welded get thicker. When the sheets are 15 mm or thicker it is a challenge to suppress and countermeasures to suppress dropouts get less impact. If full penetration is not achieved, the dropout formation cannot be formed and the melt flows to form better weld caps. Therefore a typical method when welding 15 mm and thicker is to use partial penetration from both sides of the joint and thereby achieving full penetration, at a cost of increasing plate handling complexities and time losses.If the mechanisms behind the dropout formation can be understood, countermeasures may be developed and applied in order to be able to laser weld thicker plates with full penetration single pass welding. In order to understand the mechanics of the formation of dropout during full penetration welding in 15 mm thick plates, experiments have been conducted using laser hybrid arc welding (LAHW) using the laser in CW mode and also applying power modulation. During the experiments, the root has been observed with High Speed Imaging (HSI) to observe the mechanisms behind the formation. It is determined that the downward flow from the keyhole along with the surface tensional forces of the molten steel and its cooling rate play the most significant roles.Godkänd; 2015; 20151127 (jankar