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 When
designing a tool for resistance welding, it is best to start at
the weld nugget area first then work back to the power supply.
Determine what needs to happen through the work piece first then
decide how this will be accomplished. It is too late if you get
the tools first then determine how you are going to use them. Determine
the amount of current and time needed to do the weld and the force
required across the electrode. Next determine the current carrying
circuit required. Do you simply need to weld nuggets along a flange
or do you need to produce a welds in the middle of wall of a train?
There are very important mechanical concerns in resistance welding.
Proper electrode alignment, proper electrode force with follow-up,
good part and electrode geometry, with sufficient cooling capabilities
are some of the considerations that have to be accounted. The welding
gun will transfer the power to the weld zone thus its capabilities
are of great importance for producing quality welding results.
The work piece electrical resistance that is presented across the
electrodes is measured in micro-ohms. Since the welding current
required may be in the range of a few thousand amperes up to 250,000
amperes, the range of voltage across the work piece would only be
around 0.5 to 1.5 volts. When all considered, the resistance of
the tools that carry the welding current will exceed the work piece
resistance. The integral transformer-gun design above is very efficiently
designed yet its resistance is still higher than that of the work
piece. The welding transformer that is couple to the gun apparatus
may need to be in the order of 4 to 12 volts in order to overcome
the tool resistance. There are situations where an integral transformer-gun
design can not be used. In such cases, the transformer is remote
from the weld gun by means of large current carrying conductors.
This increases the tool resistance and as a result, the output voltage
across such transformers may need to be as high as 30 volts just
to get the 0.5 to 1.5 volts across the work piece.
photo: Centerline (Windsor) Ltd.
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