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Product Code: ICA13_401

Numerical Simulation of Electromagnetic Melt Control Systems in High Power Laser Beam Welding
Authors:
Marcel Bachmann, Bam Federal Institute for Materials Research and Testing; Berlin Germany
Vjaceslav Avilov, Bam Federal Institue for Materials Research and Testing; Berlin Germany
Andrey Gumenyuk, Bam Federal Institute for Materials Research and Testing; Berlin Germany
Michael Rethmeier, Bam Federal Institue for Materials Research and Testing; Berlin Germany
Presented at ICALEO 2013

The availability of laser sources with a powers of 20 kW upwards prepared the
ground for laser beam welding of up to 20 mm thick metal parts. Challenges are
the prevention of gravity-driven melt drop-out and the control of the dynamics
mainly due to the Marangoni flow.

Coupled numerical turbulent fluid flow, thermal and electromagnetic simulations
and experimental validation with aluminum AlMg3 and stainless steel AISI 304
were done for alternating and steady magnetic fields perpendicular to the process direction. The first can prevent melt sagging in full-penetration welding by
Lorentz forces in the melt induced by an AC magnet located below the weld specimen counteracting gravitational forces. The latter controls the Marangoni flow
by Lorentz braking forces in the melt by the so-called Hartmann effect.

The simulations show that the drop-out of aluminum and stainless steel can be
avoided for 20 mm thick full-penetration welds with moderate magnetic flux densities of 70 mT and 95 mT at oscillation frequencies of 450 Hz and 3 kHz, respectively. The experiments are in good agreement but show somewhat larger
values for steel, whose weakly ferromagnetic properties are a possible reason.
The investigations with steady magnetic fields reveal the possibility to mitigate the
dynamics significantly beginning with around 500 mT at laser penetration depths
of approximately 20 mm.

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