Stable keyhole welding of 1 mm thick copper with a 600 W blue laser system

This paper will report on the first full penetration bead on plate tests of a 1 mm thick copper plate with a 600-W blue laser with nominal spatter remaining on the surface. The 600-W continuous wave laser is focused to a spot size of approximately 200 μm, resulting in an average intensity at the surface of the part of 2.1 MW/cm2. This intensity is well above the power density required to initiate and sustain the keyhole in the part. During the welding process, the keyhole is observed to form rapidly, and once full penetration is achieved, the molten puddle exhibits a very stable surface indicating low turbulence in the weld puddle as the weld progresses. The stable welding process is observed over a wide range of welding speeds and with an Ar-CO2 cover gas for suppressing the surface oxidation during the welding process. This ability to create a stable keyhole weld can be attributed to the high absorptivity of copper in the blue [E. Spisz, A. Weigand, R. Bowman, and J. Jack, “Solar absorptances and spectral reflectance's of 12 metals from temperature ranging from 300 to 500 K,” NASA TN D5353 (1969)]. The blue laser light is uniformly absorbed by the walls of the keyhole during the welding process; however, when instabilities in the keyhole arise due to the turbulence in the melt puddle, the heat input is maintained, and the keyhole remains stable.