Blue diode lasers - Understanding and influencing melt pool dynamics in copper

Within the last years an increasing demand of copper components was observed, especially in the fields of energy transition, e-mobility, or digitalization. For joining those components, laser welding has become more and more popular. Infrared lasers are commonly used for metal welding. They are characterized by a low absorptivity in solid copper at room temperature. In contrast, lasers in the blue wavelength spectrum are characterized by a significantly higher absorptivity. This facilitates the initial energy input into the material and makes the welding process more efficient. Further, in the liquid state, the absorptivity change in copper is much smaller for the blue wavelength. This results in a continuous heating of the material, a more stable melt pool and a lower amount of spatter. One supplier of lasers in the visible wavelength spectrum is Laserline. In 2023, they launched a 4 kW blue diode laser, the currently highest available power for this wavelength. It makes accessible a broad variety of applications. But the scientific investigations for the blue wavelength at a power of several kilowatt are still limited. It is the paper's purpose to extend them by analysing welding of copper and its alloys with a blue diode laser. One the one hand, synchrotron trials were performed allowing a look into the material during welding. A special focus was on the transition between heat conduction and deep penetration welding as well as the keyhole behaviour. On the other hand, conventional welding trials were performed analysing the impact of beam shaping on the melt pool dynamics.