Product Code: ICA13_1101

Simultaneous Top and Root High Speed Imaging on Droplet Formation in Laser Welding
Authors:
Torbjörn Ilar, Luleå University of Technology; Luleå Sweden
Ingemar Eriksson, Luleå University of Technology; Luleå Sweden
Alexander Kaplan, Luleå University of Technology; Luleå Sweden
Presented at ICALEO 2013

The regular formation of drops, called the humping effect in laser welding has been studied and analyzed by several research groups, however preferably for the top surface. Humping phenomena at the root have been much less investigated, even though they might have similar impact on the mechanical properties of the weld. Root humping is studied based on synchronized high speed imaging of the melt pool at the top and simultaneously at the root side of the weld. Important relations between the dynamics of the two melt pools can be identified, including characteristic dimensions and time scales. Beside explaining the mechanisms, these relations can be suitable for online process monitoring of root drop formation from the more accessible top of the weld. Opening and closure of the keyhole at the root and its accompanying dynamics from boiling is ofimportance. Different measurement and variation analyses of the droplet formation and its relations to the top melt pool are compared and discussed, including the flow pattern visualized by metallurgical analysis of the droplets. Finally a wider theoretical explanation for root humping is derived and measures for its suppression are proposed.