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The droplet escape condition in laser welding is established in this paper. A three-dimensional numerical model is developed to study the weld pool convection and spatter formation at full penetration during the fiber laser welding of 5083 aluminum alloy. It is found that when laser power is 9 kW, the bottom of the keyhole is dynamically opened and closed. When the bottom of the keyhole is closed, the molten metal at the bottom of the back keyhole wall flows upwards along the fusion line. When the bottom of the keyhole is opened, few spatters can be seen around the keyhole at the top surface, two flow patterns exists in the rear part of the keyhole: a portion of molten metal flows upwards along the fusion line, other portion of molten metal flows to the bottom of the keyhole, which promote the spatter formation at the bottom of the keyhole rear wall. [ABSTRACT FROM AUTHOR]

The droplet escape condition is established, a three-dimensional numerical model is built to investigate the behavior of the weld pool in fiber laser welding of 5083 aluminum alloy, the shear stress caused by the metallic vapor flow that has great influence on spatter formation is considered. A high speed photography system is used to capture the transient images of the weld pool, the spatter formation is discussed. The numerical and experimental results show that the spatters generate mainly around the keyhole. Two factors are responsible for the spatter formation: the surface tension of the molten metal around the keyhole is low. The recoil pressure caused by evaporation and the shear stress caused by metallic vapor flow accelerate the upward moving melt around the keyhole. Increasing the welding speed and placing the nozzle at the trailing position can decrease the upward momentum of the molten metal around the keyhole, and stabilize the keyhole, which are help to suppress the formation of spatter. [ABSTRACT FROM AUTHOR]