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How does resistance spot welding work, and where is it used?

The most common type of resistance welding is spot welding

Spot welding (also known as resistance spot welding) is a resistance welding process. This welding process is used primarily for welding two or more metal sheets together by applying pressure and heat from an electric current to the weld area.

Resistance welding utilises the Joule heating effect (I^2.R) of an electric current passing through a resistor. It is most commonly used for welding sheet metals. The most common type of resistance welding is spot welding. Refer to Figure (a).

The most common type of resistance welding is spot welding

The most common type of resistance welding is spot welding

The two pieces to be welded together (workpieces) are clamped together by two electrodes. Then a controlled burst of current is passed between the electrodes. The interface area between the workpieces heats with I^2.R losses where R is the resistance of the interface. The absorbed energy melts the interface area into a nugget which bonds the workpieces together. The process is fast, repeatable and lends itself to automation.

The welding cycle is shown in Figure (b). The steps are:

  • Electrodes are clamped with a preset force either side of the workpieces.
  • A burst of current of controlled magnitude and duration is passed between the electrodes. This produces the melted nugget.
  • After the current has stopped, the pieces are held together for a time to allow the weld to solidify.
  • The electrodes are released and the weld is complete
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