Weld pool oscillations in laser welding

The weld pool oscillations in laser spot welding were investigated experimentally using high speed schlieren photography and probe laser beam reflection technique. Millisecond, 3 kW power pulses from a Rofin-Sinar RS3000 CO2 laser were used for spot welding of SS304 stainless steel samples. A Lexan 95 argon ion laser provided the probe beam for the measurements of the pool oscillation frequency arid high speed schlieren photography of the dynamics of the melt oscillation amplitude during and after the CO2 laser pulse. It was found that for a 3kW 20 ms laser pulse, the frequency of pool oscillations is in the range of 100-300 Hz during the laser pulse. Following the laser pulse, the oscillation frequency increases up to 1.3 kHz over a 20 ms time period. The amplitude of the waves on the melt surface is on the order of 1 mm during the laser pulse. The post pulse decrease of the wave amplitude correlates with the osillation frequency behavior. Comparison of the measured oscillation frequency with the predict...