Product Code: ICA11_804

Modelled Dependency of the Direct Absorption on the Keyhole Wall Waviness during 1 Micron- and 10 Micron-Laser Welding
Authors:
Alexander F. H. Kaplan, Lulea University of Technology; Lulea Sweden
Presented at ICALEO 2011

During keyhole mode laser welding the absorption of the laser beam at the vapour capillary, the keyhole, takes directly place by Fresnel absorption and indirectly during multiple scattering and by plasma absorption of the propagating beam. The direct Fresnel absorption of the laser beam mainly at the front keyhole wall is the controllable contribution, which requires better understanding. A mathematical first order model enables to estimate the dependency of the keyhole shape on the main process parameters. From ultra high speed imaging it was observed, in a certain parameter window, that a train of waves can stream down the keyhole front wall. By introducing a wavy surface to the modelled keyhole front, the dependency of the absorption on the slope of the waves was studied. Even waves of low roughness rapidly cause shadowing, particularly at low welding speed. 1 micrometer-lasers show increasing direct absorptance for higher waviness while CO2-lasers follow the opposite trend, as can be explained by the different angle dependencies of the Fresnel absorption. For the CO2-laser, which operates close to the distinct Brewster-maximum for smooth keyholes, waves introduce highly reflective domains. The sensitivity to waviness decreases with increasing speed for the 1 micrometer-wavelength lasers.