Product Code: PIC2008_P223

Derivation of Optimal Processing Parameters for Conduction Mode Laser Beam Welds by Simulation
Authors:
Achim Mahrle, TU Dresden / IOF - LOT; Dresden Germany
Eckhard Beyer, Fraunhofer Iws; Dresden Germany
Presented at PICALO 2008

Conduction-limited laser beam welding processes are characterized by moderate laser intensities below the threshold intensity necessary for keyhole formation. The absorbed energy at the surface of the weld specimen is transferred into the material by heat conduction and convection. These processes are relatively slow. Consequently, the penetration depth of the fusion zone and/or the possible welding speeds are limited to considerably lower values than in deep penetration laser beam welding.

Successful strategies for increasing the achievable weld depths bases on a control of the weld pool mass flow because the resultant convective heat transfer is the dominant heat transfer mechanism within the molten zone of many materials. The melt pool flow is in turn dominated by the Marangoni effect, i.e. the development of a mass flow caused by surface tension gradients at the free surface of a viscous or liquid material. The strength and direction of this mass flow can be controlled either by a control of the concentration of surface-active agents that change the temperature-dependence of the surface tension or by a control of the temperature distribution at the weld pool surface. Both strategies are theoretically investigated by a three-dimensional simulation of the melt pool formation during heat conduction mode laser beam seam welding.