Laser beam welding
To solve demanding joining tasks, it is highly advisable to use welding process simulations. In dependence of the demanded calculation results we have to differentiate between the real process simulation (concerning the physical phenomenon in the interaction of welding heat source and material) and the structure simulation (temperature field, residual stress and distortion of the welding construction). Furthermore we have to consider the material simulation (joint state, hardness, crack propagation within the heat affected zone)[1].
At the LOT we develop such custom-tailored models for the special conditions of laser beam welding. We apply a traditional FEM-software for the structure and material simulation. The description of the energy input takes place via the equivalent heat source model. The form and distribution is detected by experimental investigations for the respectively applied laser system. Fig. 1 exemplarily shows the geometry and mesh of a FE-model for the calculation of the temperature destribution during a seam welding process with consideration of the clamping device.
Fig.1: Geometry and mesh of a FE- model ( left hand side) for the structure simulation during the laser welding. Here the clamping conditions as well as the calculated temperature distribution in the welding sample and clamping device (right hand side) are considered.
Additionally we develop local process models for the description of the physical phenomena within the interaction zone of laser beam and material. One main focus, here, is the melt pool simulation. We can work with corresponding calculation programs for deep welding and conduction welding [2,3]. Figure 2 exemplarily shows the calculated temperature and velocity fields during the spot-welding in the heat conduction mode. Here, the achievable welding depth is mainly determined by the Marangoni effect and thus by the concentration of surface active elements( e.g. sulfur, oxygen).
Fig 2: Calculated flow and temperature fields after t=0.2 s radiation time for different values of the interface activity of oxygen (left side top: 100ppm, right side bottom: 250ppm, right side top 500 ppm).
The present model for heat conducting welding is currently extended to seam welding. Here, the process gases with admixtures of active gas components (carbon dioxide) are considered. Their influence to the surface energy should directly effect the resulting flow field in the melting bath and thus the seam geometry.
Literatur
[1] D. Radaj (1999), Schweißprozesssimulation: Grundlagen und Anwendungen, Düsseldorf: Verlag für Schweißen und verwandte Verfahren DVS-Verlag GmbH.
[2] A. Mahrle, J. Schmidt (2002), The Influence of Fluid Flow Phenomena on the Laser Beam Welding Process, Int. J. of Heat and Fluid Flow, Vol. 23, 288-297.
[3] A. Mahrle, E. Beyer (2005), Transient Behaviour of Laser-Induced Axi-Symmetric Melt Pools, 18th Meeting on Mathematical Modelling of Materials Processing with Lasers, Igls/Innsbruck (A), 19.-21.01.2005.
Contact:
Dr. Achim Mahrle
Phone: +49 (0) 351 463 31993