Project Description
The use of laser beam welding in industrial production, especially for achieving high welding speeds and low distortion, is indispensable. Nevertheless, there are challenges in the area of thin sheets (< 3 mm) arising in the production of complex structures in the butt joint due to the gap that occurs between the sheets. During the laser beam butt joint welding, the heat input and subsequent cooling of the material leads to shrinkage, which causes the gap to widen. This in turn changes the local and temporal conditions of the capillary (closed to open capillary) and the overall heat input. The practical result is a termination of welding when the gap dimension exceeds a critical value. The use of active devices that induce counter-displacements and thus influence the widening of the gap is possible, but the specific model-based optimization of the gap with regard to distortion during laser beam welding is hardly systematic to date.
A targeted model-based optimization first requires the thermal-mechanical modeling and simulation of laser beam welding. The project will focus on experimentation, modeling and mathematical optimization. A thermoplastic 3D model will developed hierarchically in a finite-element environment and gradually improved in order to ultimately be able to model asymmetrical gaps. The model for the heat input is based on the projection of the given intensity distribution of the laser beam onto the lateral surface of an (inclined) truncated cone. This mimicks the geometry of the vapor capillary and enables the mapping of a differentiated energy input as a function of depth. The model parameters are defined indirectly based on the solution of a mathematical optimization problem. The data for validating and calibrating the model is obtained through experiments. A suitable device is used to determine gap dimensions in terms of location and time and displacements are also determined in the sheet metal using image processing methods (deviations of form). This results in the goal of the proposed research project: the time- and location-dependent description and optimization of the gap in the area of the laser beam/workpiece interaction zone, taking into consideration variable process conditions and their effects on energy coupling and overall distortion during laser beam deep penetration welding of thin sheets.
