Fraunhofer Institute for Mechanics of Materials IWM
Due to the high temperature gradients and rapid cooling rates involved in laser welding, complex residual stresses arise that can lead to warping, cracking, or reduced component strength. The challenge lies in precisely measuring and evaluating these residual stresses to ensure the reliability and service life of the welded components.
The materials science requirements in laser welding lie primarily in controlling the residual stresses caused by rapid temperature changes and microstructural transformations in the weld zone. Furthermore, homogeneity of the material in the welded zone must be ensured, as variations in microstructure and chemical composition influence the mechanical properties.
Determining the residual stresses in laser welds is essential for explaining distortions and establishing safe component usage. At Fraunhofer IWM, both stationary and mobile X-ray diffractometers are used for this purpose, enabling measurements on laboratory specimens and complete components. In this process, layer-by-layer measurement of residual stresses is performed via electrolytic etching. Alternatively, residual stress depth profiles can be determined using the borehole method. The experimental data are compared with numerical simulation results to optimize both the process parameters of laser welding and the post-treatment of the components, thereby reducing detrimental tensile stresses.