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Spot welding

Spot welding is a quick and simple method of welding steel. It uses two large electrodes which are placed on either side of the surface to be welded, and passes a large electrical current through them that heats up the metal in-between. The result is a small "spot" that is quickly heated to the melting point, forming a small dot of welded metal. Applying the current for too long can burn a hole right through the material.

Spot welding is typically used when welding sheet metal. Thicker stock is difficult to heat up from a single spot, as the heat can flow into the surrounding metal too easily. You can easily identify spot welding on many sheet metal goods, such as metal pails.

Perhaps the most common application of spot welding is in the automobile industry, where it is used almost universally to weld the sheet metal forming a car. Due to changes in the resistance of the metal as it starts to liquify, the process can be monitored in real-time to ensure a perfect weld every time. This allows the spot welders to be completely automated, and many of the industrial robots found on assembly lines are spot welders (the other major use being painting).