Influence on the efficiency of the heat conduction mode laser beam welding process regarding different laser spot geometries

In heat conduction mode laser beam processes on steel materials only a fraction of the beam energy induces heat in the irradiated material. If the laser emits radiation with a wavelength of . = 1070 nm, 35 % of the beam energy is absorbed. The percentage of the beam energy, which is used for the melting process, is even smaller. A significant amount of this energy is transported into the material by heat conduction and convection without melting the material. With optimized beam spot geometries, optimized intensity distributions respectively, improved energy efficiencies can be achieved. For a heat conduction mode laser beam welding (HCMLB) process it is shown in this paper, that the intensity distribution has an impact on the energy transport mechanisms. Hereby, the welding depth and the overall energy efficiency were enhanced. Single and twin beam spots with Gaussian distributed intensities were used in experiments on stainless steels. The results have been compared for their energy efficiencies and seam geometries. Finite difference (FD) simulations based on experimental conditions were conducted for single beam spots to identify the physical mechanisms, which are responsible for the observed changes of the welding process. For modeling the energy transport phenomena heat conduction, radiation, thermal and Marangoni convection have been taken into account. In addition, non-linear behavior of the surface-tension influencing the Marangoni convection was respected in the FD simulation. The melt pool geometry, flow and the surface-temperature were calculated. Results of the FD simulation have been compared with the experimental data.