Overview
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Electromagnetic forming is a method of forming where a powerful magnetic
field is created with a large current produced instantly in a coil to cause
deformation in the tube when the eddy currents and magnet fields interact.
The behavior of the deformation in electromagnetic forming is known for
being extremely difficult to analyze because the forming is done in a very
short amount of time, and the dynamic deformation is complicated.
In JMAG, the dynamic deformation can be estimated by evaluating the Lorentz
force density that occurs in the tube.
This example analyzes the Lorentz force density produced in a tube when
a current flows in the coil. |
Eddy Current Density Distribution
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The eddy current density distribution that occurs in the tube at 125 μ
seconds is indicated in Fig. 1. The eddy currents are induced in the tube
by creating a strong magnetic field around the tube with a large current
flowing in the coil. The eddy currents are most concentrated at the ends
of the tubes as indicated in Fig. 1. This drastic change is produced by
the magnetic flux focused around the end of the tubes. |
Lorentz Force Density Waveform
The Lorentz force density in the radial direction for each interval, and
the Lorentz force density in the axial direction for each interval, are
indicated in Fig. 2 and Fig. 3. The tube expands with the positive values
of Lorentz force density in the radial direction, and the tube shrinks
with negative values of Lorentz force density.
The Lorentz force that occurs in the radial direction at 65 μs and
125 μs is produced consistently around the center of the tube, and
the ends become drastically larger, as indicated in Fig. 2. This drastic
change is produced by the eddy currents in the end of the tubes. When the
current is decreasing at 187.5 μs, the Lorentz force that occurs shrinks
the ends of the tube.
The Lorentz force density in the axial direction only occurs within a 10
mm range at each end of the tube, and it is distributed symmetrically across
the center position of 0.
The Lorentz force density produced in the tube needs to be evaluated through
simulation at the design stage, because the Lorentz force produced in the
tube doesn't only expand the tube, but also shrinks it, while a current
flows in the coil.
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