Thermo-fluid-dynamic investigation of the keyhole and the melt pool

• Applicant: Professor Dr.-Ing. Michael Schmidt
• Subject Area: Joining and Separation Technology
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 434946896

The objective of this sub-project is to expand the understanding of the process with regard to the influence of thermo-fluid dynamic processes in the melt pool on the thermo-fluid dynamic and optical processes and phenomena in the keyhole and their effect on the formation of solidification cracks. The complex interaction of energy input, keyhole and melt pool dynamics as well as the solidification behavior is analyzed. The focus is on the quantitative recording of the interactions between the laser beam and the metal vapor above and in the keyhole in order to decipher its contribution to the melt pool dynamics, the development of internal stresses and thus the initiation of solidification cracks. A keyhole model is to be developed, which can be converted into an HPC-capable model in cooperation with subproject 3. A multi-stage methodical approach will be pursued. The cracking conditions in nickel-based alloys that are highly susceptible to solidification cracking are characterized in order to quantify the specific types of solidification cracking and their dependence on the process parameters. This is done by means of process observations in which solidification rate, melt pool size and shape as well as melt pool dynamics are investigated. A particular focus is on the direct analysis of the influence of keyhole dynamics on crack initiation and propagation. High-resolution high-speed surface images, metallographic post-mortem methods and X-ray imaging are used for this purpose. The use of nickel-based alloys susceptible to solidification cracking, in which internal local stresses are decisive for crack initiation, is of central importance here. In addition, the laser-material interaction is investigated in detail, in particular between the vapor torch, vapor capillary and laser radiation. The focus is on both the optical and the thermo-fluid dynamic processes in the vapor phase in order to understand their influence on the melting dynamics and the solidification behavior. This work forms the basis for the HPC-capable keyhole model, which is being developed together with subproject 3 of the research group. In addition, experimental and simulative investigations on the influence of energy input and keyhole dynamics on crack formation will be carried out. The extension of the investigations to a further material group also enables the development of a cross-material methodology for predicting solidification crack probabilities within the overall context of the research group.

• DFG Programme: Research Units
• Subproject of: FOR 5134: Solidification Cracks during Laser Beam Welding: High Performance Computing for High Performance Processing
• Major Instrumentation: Transportabler Faserlaser
• Instrumentation Group: 5700 Festkörper-Laser