Influence of intensity distributions on the process dynamics during laser deep penetration welding of pure nickel with a flexible ring mode laser source

Current research results demonstrate the potential of spatter reduction in laser deep penetration welding by using adapted laser beam intensity distributions between a ring and a core intensity. The spatter-reducing effect, resulting from the additional ring intensity, is often attributed to an enlarged keyhole opening. However, it remains a matter of debate how exactly an additional ring intensity influences the process. This study, therefore, investigates the effect of an increasing ring intensity on process dynamics and the spatter formation regime. Laser beam welding experiments were carried out on 2.4068 nickel hidden T-joints at different welding speeds of up to 16 m/min, as well as different intensity distributions, while maintaining a constant weld depth. The tests were evaluated by using two high-speed cameras from different angles to analyze spatter and their formation mechanisms as well as the keyhole opening. Metallographic analyses and x-ray images were used to determine influences on the seam shape and porosity. It was shown that a change in intensity distribution has a significant influence on the melt flow, the resulting amount of spatter, and the porosity, which is comparable across the investigated welding speeds. While a core-based power distribution leads to spatter formation on the rear of the keyhole opening, it was shown that a ring-based power distribution leads to spatter formation on both sides of the keyhole. With an optimal power distribution, spatter formation could be largely prevented. Based on these findings, the single wave regime, a stabilized regime, and a lateral spatter regime were identified.