Imaging in cooperation with modeling of selected defect mechanisms during fiber laser welding of stainless steel

Abstract

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 different, usually smaller, keyhole and melt pool geometries. 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 identified during fiber laser welding were spatter, humping, or lack of material at the top or root.High-speed imaging enables observation of the geometry and motions of the melt pool surface and keyhole during welding. This is illuminated by an additional diode laser permitting spectral filtering and also the metal vapor dynamics can be visualized. Mathematical modeling provides the possibility to estimate and study additional phenomena that are difficult to measure, such as effects inside the melt volume or the impact of surface tension forces on dynamic melt motion. For recorded melt surface motion images, in particular, 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 observed physical phenomena.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 different, usually smaller, keyhole and melt pool geometries. 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 identified during fiber laser welding were spatter, humping, or lack of material at the top or root.High-speed imaging enables observation of the geometry and motions of the melt pool surface and keyhole during welding. This is illuminated by an additional diode laser permitting spectral filtering and also the metal vapor dynamics can be visualized. Mathematical modeling provides the possibility to estimate and study additional phenomena that are difficult to measure, such as effects inside the melt volume or the impact of surface tension forces on dynamic melt mot...