1. Multiphysics Simulation Story: Magnets Improve Quality of High-Power Laser BEAM Welding
BAM Federal Institute For Materials Research and Testing, GERMANY
M. Bachmann, V. Avilov, A. Gumenyuk, and M. Rethmeier

2. The Challenge
Welding is one of the most critical operations in the construction of reliable metal structures
High-power laser beam welding uses a localized heat source to achieve narrow deep welds and high welding rates
The use of a localized heat source often results in the distortion of metal components
The weld pool is very wide with an unstable surface
Spattering and the ejection of droplets from the weld pool results in underfills, undercuts, craters, blowholes or blowouts
Researchers are looking at the effects of stationary magnetic fields on laser beam welding quality. Simulation helps them find the best choice of magnets.

3. The Solution
A stationary magnetic field is applied to the laser welding process to improve its quality and counteract effects such as spattering
The distribution of the magnetic field required to improve the uniformity of the weld has been determined with COMSOL Multiphysics
Easy-to-use geometry building and meshing within the same software environment, and the availability of pre- defined multiphysics coupling and the possibility to implement your own equations allows for an accurate simulation of this complex process
A photo of actual welds with the COMSOL Multiphysics results superimposed on them. The left image shows a weld without any applied magnetic field and the resulting wineglass shape. The right image shows the case with B = 0.5 T and how the weld has more of a V shape with straight sides as opposed to the wineglass shape on the left.

4. The Simulation
To model and simulate the laser beam welding, heat transfer, fluid dynamics, and electromagnetics were coupled and solved
COMSOL Multiphysics combined with the CFD and AC/DC Modules allowed BAM to accurately model the process by including, for example, Marangoni effects, gravity, latent heat of fusion, and Lorentz forces
Temperature-dependent material properties were also considered, thus allowing for a strongly coupled model
A plot of temperature in the symmetry section of a weld shows that without any magnetic field applied (top), the weld takes on a wine glass shape. With the addition of a 2 T magnetic field (bottom), the shape starts to take on the form of a V.