OptiLas: Optimization in Laser Beam Welding
Hot cracking is one of the challenging problems in laser beam welding. Laser welding is a modern joining technique for new metallic materials and particularly suitable for handling lightweight constructions as they occur, e.g., in automotive, aircraft, rail vehicle and shipbuilding industries because weight is to be reduced and energy is to be minimized. In these industries new materials like aluminium alloys become increasingly important, however their welding can cause severe problems because of the high risk of the appearance of hot cracks. In order to work against hot crack arising one needs suitable models for the quantitative description of the physical phenomena involved in welding. A technique to prevent this undesirable effect is the so-called multi-beam welding which was first suggested in the 70ies. Thereby two additional laser beams are used in order to compensate for the critical tensile strain induced by the main laser beam. In order to guarantee that this technique prevents the initiation of hot cracks in the solid-liquid region, it is important to choose the positions, sizes, and powers of the two additional heat sources optimally. Note that in case of inappropriate choices for these parameters, hot cracking can even be enhanced. Until now these quantities are generally chosen by trial and error. This project aims towards the simulation and optimization of multi-beam laser welding based on models describing the physical phenomena of laser welding.
Besides the optimization of a first simple model, which allows a semi-analytical solution of the temperature field, a FEM-simulation package has been developed for the solution of a very detailed model which includes the description of the temperature field, the thermomechanical deformations and the metallurgical properties of the weld. Here parallel computations have been performed.
Still pending is the development of a hierarchy of medium size models providing the links to the most detailed model. That medium size model for which optimal solutions can be computed in reasonable times yield practically suboptimal solutions which are to be inserted into the simulation package for the detailed model.
Numerical results obtained so far and their experimental validation demonstrate that hot cracking can be eliminated at least on a laboratory scale.
- initial KONWIHR funding: 1/2003-3/2004
- Prof. Dr. Hans Josef Pesch, Lehrstuhl für Ingenieurmathematik, Uni-Bayreuth