Pore formation during laser deep penetration welding is closely related to process dynamics. Dynamics occur due to a variety of effects like fluctuations of absorption on the keyhole wall, melt pool flow or inherent power variations from the laser machine. Depending on process parameters different dynamic behavior, especially in the keyhole, could be observed along with different pore formation during welding. The impact of the keyhole behavior on resulting process instabilities is not completely understood yet, but of great interest with regard to opportunities of process stabilization for pore prevention.
This work presents an attempt of defining a stability number based on correlations of dynamic keyhole parameters and pore formation. Therefore, a keyhole model is introduced describing dynamic keyhole properties during the welding process. Welding experiments are conducted in aluminum base material (EN AW 6082) at different laser powers and welding velocities. Pore percentages in the solidified weld seams are measured using x-ray imaging. Calculated keyhole properties are correlated to the resulting pore percentage. Parameters that show a significant influence on porosity are identified. The frequencies and amplitudes of keyhole radius oscillations as well as the spring coefficient have major impacts on the stability of the keyhole. Based on these keyhole parameters a keyhole stability number is defined.