PRODUCTION PROCESS A 3D transient model of keyhole and melt pool dynamics in laser beam welding applied to the joining of zinc coated sheets M. Geiger Æ K.-H. Leitz Æ H. Koch Æ A. Otto Received: 28 January 2008 / Accepted: 19 December 2008 / Published online: 24 January 2009 Ó German Academic Society for Production Engineering (WGP) 2009 Abstract In order to get a deeper understanding of laser beam welding, a process model was developed at the Chair of Manufacturing Technology. It is based on the continuity equation, the equation of heat conduction and the Navier– Stokes equation. The model includes effects of Fresnel absorption, vapor pressure, surface tension, melting and evaporation enthalpy and energy loss due to evaporating material. This paper presents the results of a three-dimen- sional, transient finite volume simulation of a laser beam deep penetration welding process based on this model. The simulations show periodic keyhole oscillations and the complex fluid dynamics of the melt pool. A comparison of the evaporation rates calculated from the simulations and the experimentally observed process emissions shows good correlation. Furthermore, the simulations show pore for- mation at higher feed rates, the influence of a gap on the welding process and give an explanation for the welding behavior of zinc coated steel sheets. Keywords Laser beam welding  Keyhole dynamics  Zinc coated sheets 1 Introduction In the last years laser beam welding has become more and more important as a joining technology, especially in automotive industries, as it offers high production quality, high automation potential and flexibility. Although the breakthrough of laser beam welding in industrial joining applications has already taken place and it is a commonly used joining technology, the physics of the welding pro- cess is not yet completely understood. The laser beam welding process is very complex and highly dynamic. There is a multitude of physical effects that have to be considered in a description of the interactions between solid, liquid and gas phase. Because of the bright process radiation it is hardly possible to look into the keyhole and make direct observations. X-ray techniques make keyhole observations possible, however, are connected with a complex extensive experimental setup and only offer small spatial and temporal resolution. Other approaches, like glass and ice welding are used to study the dynamics of the keyhole, but have the disadvantage that the material properties, especially the heat conductivity and surface tension, are hardly comparable to metals like steel and aluminum. Simulations do not suffer from these disad- vantages, as they offer arbitrary temporal resolution and the process variables are available every time step. Besides they allow a direct undisturbed look into the welding process. But so far, there are no all-embracing numerical simulations that include realistic models of all important physical effects and phenomena. So far, most simulations concentrate on few effects, do not consider interactions between different phenomena, use strongly simplified models and only few show the complex three- dimensional transient dynamics of the whole system. Ye et al. [1] presented a three-dimensional model of heat transfer and fluid flow, yet assumed a fixed cylindrical keyhole and neglected surface deformation on the top and bottom surface of the melt pool. Ki et al. [2] for the first time presented numerical simulations showing fully M. Geiger  K.-H. Leitz (&)  H. Koch  A. Otto Chair of Manufacturing Technology, University of Erlangen-Nuremberg, Paul-Gordan-Strasse 3, 91052 Erlangen, Germany e-mail: leitz@lft.uni-erlangen.de URL: www.lft.uni-erlangen.de M. Geiger e-mail: geiger@lft.uni-erlangen.de 123 Prod. Eng. Res. Devel. (2009) 3:127–136 DOI 10.1007/s11740-008-0148-7