Description
Due to their good price-performance ratio, high strength steels are a key element for building lighter products especially for high production volumes. In order to meet the challenges of welding those materials and to avoid seam defects, the welding process has to be adapted. For this purpose, the present thesis investigates the influence of beam oscillation on the melt pool shape as well as the solidification conditions during laser beam welding of high strength steels. The aim is to suppress the appearance of centerline cracks, which are assigned to the category of solidification cracks and can be avoided by means of three strategies which were identified in the state of the art. Accordingly, a reduction of the strain rates during solidification, a redirection of the solidification structures by increasing the angle of solidification fronts of the melt pool and a de-crease of the strains appearing in the process contribute to lessen hot cracking susceptibility. By the primarily determination of critical melt pool geometries and the subsequent analysis of the influence of the parameters oscillation figure, amplitude, frequency, energy per unit length, focal diameter and shielding gas, suitable ways to manipulate the melt pool shape according to the three strategies are determined. Finally, the avoidance of centerline cracks by using beam oscillation in laser beam welding is demonstrated by means of three examples.
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