High welding speeds above 8 m/min during laser beam welding of high-alloy steel (AISI 304) lead to spatter formation, resulting in material losses and adhering spatter that significantly degrade seam quality. This effect can be reduced by using a superposition of a main intensity with a second intensity, which increases the melt pool size and decreases melt velocities. To identify the fundamental mechanism of spatter formation, high-speed synchrotron X-ray imaging was utilized to visualize keyhole behavior and the melt flow characteristics using tungsten carbide particle tracking. The addition of the second intensity increases the keyhole geometry and forms a bulge on the rear wall of the keyhole. It also reduces the upward-directed melt flow at the keyhole rear wall and surrounding the keyhole. Thereby minimizing the melt´s kinetic energy and finally, reducing spatter formation.

Monitoring the deep penetration laser welding process is relevant in order to detect deviations in the process and to achieve defect-free welds. This study aims to investigate the influence of the capillary shape on monitoring signals, as the shape and stability of the capillary have a significant effect on both defect formation and the monitoring signals.

X-ray imaging was employed to capture the capillary shape during welding. Simultaneous measurements of the back-reflected laser beam, the thermal emissions as well as depth measurements using optical coherence tomography were conducted. The simultaneous acquisition enables a direct comparison of the monitoring signals with the capillary shapes. Ray tracing simulations were performed to investigate the impact of changes in the capillary shape on the monitoring signals. The comparison between simulated and measured monitoring signals contribute to the advancement of monitoring methods in laser welding based on optical information from the process.

During deep penetration laser welding, a plume of hot metal vapor and particles is emitted from the keyhole, interacting with the incident laser beam through scattering, absorption, and phase front deformation. These interactions affect the caustic of the laser beam, potentially deteriorating weld quality. We present results from a single-shot caustic measurement of a probe laser beam, aligned coaxially with the processing laser beam. This in-situ measurement enables real-time quantification of variations in process-critical beam parameters, including pointing instabilities, focus shifts, and changes in beam quality. By analyzing the mechanisms of interaction between the laser beam and the vapor plume, our findings offer deeper insights into the interdependence of vapor plume dynamics and welding capillary fluctuations, thus advancing the understanding of laser welding processes.

The continuous joining in the rolling gap is used for thin-walled metallic bipolar plates. This development enables high production rates for cost-effective manufacturing. In a new joining process, flexible bipolar half-shells are fed into a rolling gap for welding and bonded in a second step. The challenge arises from the necessary coordination and synchronization of the multiple laser beams and the strip, with feed rates of up to 30 m∙min⁻¹. For this purpose, a multi-beam scanning optic was developed to realize partially complex weld connections using up to four fiber lasers in the flow field and the ports. Sealing is achieved through adhesive bonding in a following process. This joining technology offers advantages over laser remote welding, as significantly less energy is introduced, distortion is minimized, and coated surfaces can be preserved.

Lack of fusion defects, which result from incomplete melting in laser beam welding, present significant challenges specifically for precise applications such as fuel cell manufacturing. These defects compromise weld quality and performance, especially when producing bipolar plates made from austenitic steel. Despite extensive research into thermal, mechanical, and metallurgical factors, a complete understanding of the formation mechanism of hidden lack of fusion defects is still lacking. This review aims to describe these mechanisms by integrating experimental and computational methods such as finite element method (FEM), computational fluid dynamics (CFD), and multi-physics models to understand and mitigate defects. The findings support the development of adaptive real-time control systems and advanced models, enhancing knowledge and skills in addressing the lack of fusion defects in laser welding of austenitic steel.