Laser beam welding is widely utilized across various industries, including the automotive, nuclear power plant, and petrochemical sectors, due to its excellent compatibility with remote control and automation. It enables high-quality welding with a smaller heat-affected zone compared to other welding techniques. However, during high-power laser irradiation, spatter generation commonly occurs, which contributes to defects such as weld wall thinning and porosity.　In our previous study, we determined that spatter generation is caused by fluctuations in the keyhole during laser irradiation in vacuum conditions. To address this issue, this study employed a multi-spot laser approach in laser beam keyhole welding to develop a spatter-free process, clarifying the effects of multi-spot lasers on spatter suppression.

Laser keyhole welding of dissimilar materials, such as aluminum-copper (Al-Cu) and copper-steel (Cu-1.4301), is important for joining electrical components (battery to busbar). However, the joining process remains challenging due to the narrow process window and the formation of brittle intermetallic compounds (IMCs). Beam oscillation superimposed to the weld trajectory has indicated to expand the process window by modifying heat distribution and influencing IMC formation.

This study investigates the effects of spatial and temporal beam shapes created by FlexiBeam-technology. This technology utilizes a galvo scanner for non-stationary beam shaping by means of oscillation in the kilo-Hertz regime. It generates intensity distributions, such as lines, rings, rectangles, and complex patterns (T-shape). Lap-joint configurations of Al-Cu and Cu-Steel1.4301 are analyzed to study weld intermixture and IMC formation. The results show that specific beam shapes improve process stability. They also reduce IMC growth, leading to better joint quality in dissimilar material welding.

The increasing demand for lightweight, high-strength materials has led to the widespread use of aluminum alloys, in various industries. However, welding these alloys, particularly 6082, presents challenges due to their composition, which includes magnesium and silicon. The differing melting points of these elements cause inconsistent melting and solidification, leading to issues such as porosity, cracking, and reduced strength in the heat-affected zone.

This study focuses on: BrightLine and Rotating Bifocal Optics. BrightLine offers remarkable flexibility by allowing the laser power to be directed entirely to the core fibre, the ring fibre, or distributed between both. Rotating bifocal optics using double wedges split the laser beam into two beams that rotate around a specific radius under identical parameters.

The research focuses on optimizing these techniques to improve weldability and reduce defects like cracks and porosity in 6082 aluminum alloys. Both methods were successfully optimized, achieving the desired welding results.

Highly dynamic beam shaping offers enhanced capabilities and flexibility for the optimization of laser welding processes. The application of dynamic beam shaping requires knowledge about the influence of the frequency on the resulting melt flow and melt pool geometry. In the talk, we present an analysis of the effect of highly dynamic beam deflection during welding of stainless steel and aluminum, using a numerical model and high-speed imaging. In order to determine the limits of using highly dynamic beam deflection, the welding process with a static beam shape equivalent to the average dynamic shape was investigated. The results show different regimes of the melt pool and keyhole characteristics depending on the beam deflection frequency. A significant change in melt flow and melt pool geometry was observed when the (quasi-) static limit is reached.

In order to optimize the behaviour of keyhole and melt pool during laser welding, recent beam shaping technologies allow for manipulating the intensity distribution. Dynamic beam shaping by means of coherent beam combining offers almost unlimited flexibility in changing the intensity distribution on the workpiece surface. The intensity distribution can be dynamically modulated at MHz frequencies. The effects of this fast modulation of the beam shape at previously unachievable frequency ranges has not yet been thoroughly investigated. Within the framework of this study we analyzed the frequency-dependent behaviour of the keyhole and melt pool geometry when changing beam shape periodically at different frequencies. The geometric dimensions were determined by means of Highspeed imaging and polarization goniometer. The results specify the frequency related requirements and limits in dynamic beam shaping during laser welding processes, which are of highest significance to design optimization strategies in laser welding processes.

The identification of optimal process parameters is crucial for the development of high-quality laser welding processes. A challenge in laser welding lies in the occurrence of defects such as spatter, undercuts and hot cracks, which result from instabilities in the keyhole and melt pool during the welding process. A recent study demonstrated that dynamic beam shaping using a laser based on Coherent Beam Combining can effectively stabilize the welding process, as shown for copper welding, which can contribute to an improved weld seam quality. However, determining suitable process parameters typically requires extensive and time-consuming experimental investigations, combined with process-specific expertise. In this study, Bayesian optimisation was applied to efficiently identify parameters for welding using dynamic beam shaping, achieving weld seams with defined depths and minimal defects while significantly reducing the number of required experiments, even at high welding speeds. The experiments were conducted on AW5754.