Product Code: ICAL08_1701

Imaging in Cooperation with Modeling of Selected Defect Mechanisms during Fiber Laser Welding of Stainless Steel
Alexander Kaplan, Lulea University of Technology; Lulea Sweden
Elin Westin, Outokumpu Stainless, Avesta Research Center; Avesta Sweden
Greger Wiklund, Lulea University of Technology; Lulea Sweden
Peter Norman, Lulea University of Technology; Lulea Sweden
Presented at ICALEO 2008

Fiber laser welding of stainless steel was studied for different joint configurations and gaps. The higher focusing capability of fiber lasers compared to traditional Nd:YAG- and CO2-lasers creates a different keyhole and melt pool geometry, usually smaller. These geometrical aspects, accompanied by a different laser energy redistribution, are essential for the weld pool dynamics and the resulting joint, with or without defects. Typical defects that were identified during fiber laser welding are spatter, humping, or lack of material at the top or bottom.

High speed imaging enables to observe the geometry and motions of the melt pool surface and keyhole, illuminated by an additional diode laser permitting spectral filtering. Moreover, the metal vapor dynamics can be visualized. Mathematical modeling provides the possibility to estimate and study additional phenomena difficult to measure, like effects inside the melt volume or the impact of surface tension forces on dynamic melt motion. In particular, for recorded melt surface motion images the corresponding surface tension forces and other mechanisms can be estimated by cooperative complementary modeling, enabling to draw conclusions. This advanced method was carried out for the different joint and defect cases studied, resulting in an illustrated theoretical description of the physical phenomena studied.

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