Influence of Inter-Beam Distance on Keyhole Depth Instability and Weld Seam Coupling in Dual-Beam Welding of CuSn6 Alloy

This study investigates weld seam interaction and keyhole dynamics in dual-beam laser welding of CuSn6 alloy at varying inter-beam distances of 0.3 mm, 0.6 mm, and 0.9 mm. Numerical simulations are validated against experimental cross sections and high-speed synchrotron X-ray images to capture the narrow, intermediate, and wide keyhole regimes. The asymmetry in the weld seam is quantified through the average root-mean -square amplitude oscillation analysis to evaluate dynamic instability and coupling between the seams. Results show that the asymmetry decreases with an increasing inter-beam distance, while stronger asymmetry and seam coupling are observed at a small inter-beam spacing of 0.3 mm. This also reveals a significant transition from strongly coupled melt pool evolution at small beam spacing to structurally independent weld seam dynamics at larger spacing.