Simulation of the influence of electromagnetic stirring during laser beam welding of thick-walled steel components with filler material

• Applicant: Dr.-Ing. Marcel Bachmann
• Subject Area: Production Automation and Assembly Technology
• Term: from 2019 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 416014189

In this project, the influence of electromagnetic stirring on the distribution of filler material during high power laser beam welding of steel with thicknesses above 10 mm will be investigated. Hereby, the need for using filler material can be due to an improved gap-bridging capability, a reduction of the hot-cracking susceptibility or ensuring mechanical-technological properties of the weld. An alternative option for improving the filler material mixing is multi-pass welding which is time-consuming thus lowering the process efficiency. The main focus of the project is to gain insights into the principles of the electromagnetic stirring by means of oscillating magnetic fields in high power laser beam welding of steel. To that, numerical calculations will be conducted solving the coupled problem of heat transfer, fluid dynamics and electromagnetics based on temperature-depending material properties. This allows for a quantification of the stirring behavior depending on process parameters (laser power, process speed, filler wire) and parameters of the magnet system (magnetic field strength, oscillation frequency, angle between welding direction and magnetic field lines). The simulations are verified by accompanying experiments. The physical mechanism is based on the induction of eddy currents due to the oscillation of an external magnetic field. The asymmetric setup as well as the electric isolation of the gap in front of the melt pool lead to a concentration of the eddy currents in the melt. Together with the externally applied magnetic field, a Lorentz force distribution is formed which has a rotational component leading to an improved stirring in the melt.The main objective of the project is the promotion of the mixing behavior into the depth of the melt pool during welding of thick-walled components by induced inhomogeneous Lorentz force distributions. In the end, a numerical model is available allowing for a process optimization with regard to the stirring of the filler material and also for an identification and quantification of the physical effects and mechanisms. The results obtained for high-alloy austenitic stainless steels without ferromagnetic properties are then transferred to structural steels with a pronounced magnetic hysteresis.

• DFG Programme: Research Grants
• Co-Investigator: Professor Dr.-Ing. Michael Rethmeier