High-speed synchrotron x-ray imaging of the formation of wedge-shaped capillaries during laser-beam welding at high feed rates

In case of high welding velocities, the geometry of the capillary during laser-beam welding elongates in feed direction to a wedge shape. Following to the change of the capillary, the weld pool changes and the melt velocity increases. Therefore, high-speed X-ray imaging to study the time evolution of capillary geometry and weld pool shape during high-speed laser welding was performed at DESY's synchrotron. The investigation addressed the transition of the capillary geometry from a high aspect ratio to a wedge-shape geometry and how the weld pool geometry and the weld flow changed. In order to investigate the melt flow in the weld pool during welding, the movement of tungsten carbide particles was analysed in the acquired image sequences. The tungsten particles were deposited on top of the sample before welding. Further, a simple method to determine the average melt velocity around the capillary without tracking the tungsten particles is shown. A laser spot diameter of 100 mm and feed rates of up to 2 m/s were used to weld in aluminium.