Fluid dynamic characteristics have direct influence on the quality of the weld and therefore on the formation of solidification cracks. A deep understanding of the laser welding process and, in particular, a precise knowledge of the thermo-fluid dynamic solidification conditions are indispensable in the study of crack initiation. Process simulations with high spatial resolution make an important contribution to the representation of causalities between process parameters and solidification-relevant properties. Experience shows that, due to the complexity of the subject, such simulations require unacceptably long computing times with conventional software. The cooperation of computer science and production engineering enables the implementation of generated process knowledge in a high-performance simulation framework to perform detailed process simulations with high temporal and spatial resolution.
The aim of Subproject 2 (SP2) is to investigate the relationship between process parameters and solidification relevant properties such as the local temperature, the local temperature gradient and the local chemical composition at the solidification front during laser welding. Relating to the resolidification area of the melt pool, the influence of process parameters on shape and spatial characteristics of this area, the so-called mushy zone, will be investigated. Moreover, experiments will be used to examine if breaking or detaching dendrites appear, which act as condensation nuclei and thus influence the further progress of solidification.
In the course of SP 2, preliminary melt pool simulations are performed using the simulation model developed at the Institute of Photonic Technologies. The obtained data will serve as initial parameters for the simulative studies planned in the other subprojects. In close collaboration with the subproject 3 an efficient, highly scalable and sustainable exascale simulation framework for the laser beam welding process will be developed to investigate the described questions. Modeling of the physics involved in the process necessary for setting up the exascale framework will take place within this subproject. Experimentally obtained findings regarding process dynamics and resulting temperature data will be used to validate the model. For a more detailed understanding of the processes during solidification, in situ measurements of the mushy zone are also required. For this purpose, the solidification processes in the material will be analyzed using high energy synchrotron radiation.