Towards high-speed laser beam welding of stainless-steel foils using an adjustable ring mode laser beam source

Laser beam micro-welding is the state-of-the-art technology for the joining of stainless-steel foils. Approaches for improvement include a parallel processing with several scanning optics or increasing the welding speed. However, the latter is limited in the achievable welding speed due to the occurrence of process defects, such as undercuts and humping. Recent investigations showed that a more targeted energy input by means of beam shaping, such as a superimposed core-ring intensity distribution, is beneficial to overcome that challenge. Within the scope of this work, welding experiments were conducted on AISI 316L metal foils with a thickness of 80 µm in an overlap configuration using an adjustable ring mode (ARM) laser beam source. The cause-effect relationships between different process parameters when applying a core-only or core-ring intensity distributions and the resulting weld seam properties were investigated. To assess the weld seam quality, surface measurements as well as metallographic cross-sections were used. Consequently, different regions within the analyzed parameter range were identified, including a parameter window for a stable welding process. An additional focus was placed on the influence of the ring laser beam on the formation of undercuts and humping elevations. A welding speed-dependent undercut limit based on the energy density was identified for different core-ring laser power distributions. Following the first evaluations, the process parameters were iteratively adjusted in areas of particular interest, where the limits for the maximum welding speed were to be expected. It was determined that the possible welding speed for a sound weld seam could be increased to approximately 920 mm/s with the additional ring laser beam before undercut occurred. The conducted research lays the foundation for further investigations of different welding strategies to control the energy input to further increase the possible welding speed.