Overview
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Resistance heating is one method of heating used to fabricate steel sheets
that uses the electric resistance in a steel sheet.
Resistance heating uses the heat produced by the Joule losses that occur
from the electric resistance when a current flows through a heated body.
This type of heating is used in hot formed pressing because an object can
be uniformly heated. Generally, more than 600 degrees Celsius is required
for hot formed pressing.
The loss distribution obtained with a magnetic field analysis can be used
as the heat source for a thermal analysis in JMAG.
This example presents the use of a coupled thermal and magnetic field analysis
to obtain the temperature distribution of a resistance heated steel sheet
and the difference in the rising temperatures versus the making current.
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Current Density Distribution / Joule Loss Density Distribution
The current density distribution of the steel sheet at 0.1 seconds for
a power supply current of 16 kA is indicated in Fig. 1, and the Joule loss
density distribution is indicated in Fig. 2.
The current density at the ends of the steel sheet is not distributed uniformly,
highest around the ends of the electrode and lowest at the four corners
of the steel sheet, as indicated in Fig. 1, because the width of the electrode
is smaller than the width of the steel sheet. The distribution of the Joule
loss density is the same as the current density because the Joule losses
are losses produced by the electric resistance of the steel sheet. Furthermore,
the distribution around the center of the steel sheet is almost uniform.
The Joule losses are the heat source of the steel sheet. |
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Temperature Distribution / Variation vs. Time
The temperature distribution of the steel sheet with a power supply current
of 16 kA is indicated in Fig. 3, and the temperature verses time is indicated
in Fig. 4.
Heat is generated in the steel sheet by the electric resistance and heated
to 600 degrees Celsius in 2 seconds. Furthermore, the heat is produced
uniformly in areas that do not contact the electrode, and the temperature
can be controlled by the power supply and amount of time for heating. |
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