A review of laser beam oscillation for improved metal coalescence: The purpose, methods, outcomes, and future challenges

In recent years, the widespread adoption of laser fusion processes for metal coalescence, including laser welding and laser cladding, is gaining ground due to increased demand for the fabrication of increasingly complex shapes and dissimilar materials. While thermal field management is important for controlled process quality, modulating heat input in laser processing has become a critical challenge. One approach is to control the melting behaviour through laser beam oscillation, which not only avoids the excessive heat input of conventional methods but also enables control of the temperature distribution to manage the metal fusion width and penetration depth, while preventing fusion defects. However, parameter optimisation for beam oscillation has mainly been adopted using experimental approaches (i.e., relying on empirical decisions). Consequently, in recent years, parameter optimisation approaches incorporating multi-physics simulations have also been developed to better understand and control the laser heat input process. This study reviews the recent improvements in laser fusion processes achieved through beam oscillation. It introduces two approaches (“direct problem” and “inverse problem”) that incorporate multi-physics simulation to address the increasing complexity of laser parameter optimisation. The inverse problem still presents several additional challenging modelling considerations, including mathematical boundary conditions, which provide important guidance for improving robustness and efficiency in future practical optimisation frameworks. Finally, this paper outlines future directions by integrating advanced equipment, data-driven simulation optimisation, and sensing systems for closed-loop control, aiming to establish a highly adaptable and efficient laser fusion process with strategies suitable for practical industrial applications.