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Aachen University of Technology
When an electric welding arc heats an area of metal, a complex series
of phenomena take place. Following heat transfer to the metal, a phase
change from solid to liquid occurs under the arc, forming a weld pool.
Inside the pool, convection currents begin to form, resulting from buoyancy,
Lorentz forces, and shear stresses at the surface under the influence
of volume expansion of the molten metal. Motion of the liquid metal impacts
subsequent heat transfer and melting, and governs the final shape of the
pool. Since it is the shape and temperature of the weld pool that dictates
the quality of the welded joint, a comprehensive analysis of the procedure
can be extremely helpful.
Researchers at the ISF-Welding Institute of Aachen University of Technology
in Germany have used FIDAP software to do this job. In the steady-state
simulation, the position of the interface between the liquid and solid,
called the melting line, was calculated for different welding conditions.
The liquid surface was allowed to deform during the heating and melting
process as a result of pressure from the arc and volume expansion of the
liquid phase. Two cases were studied: one in which a deeper, narrower
weld pool was expected and another in which a wider, shallower pool was
expected. Different liquid currents were found to develop for these cases,
consistent with laboratory observations. The researchers concluded that
FIDAP software was an excellent tool to use for modeling these complex
structures.
The weld pool shape predicted with FIDAP is shown to
agree well with experimental data.
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