How does spot welding work?

Written by victor fonseca
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How does spot welding work?
(Photo courtesy of www.robot-welding.com.)

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Welding Spots

Spot welding works by sending an electrical current through two metal surfaces and thereby welding the surfaces together at that spot, hence the name. Spot welding requires the use of two copper electrodes and a thorough knowledge of how the thickness and density of the joining metals will react to the electrical current. If too little power is sent through the copper electrodes, then the metal will not adhere. If too much electricity is sent through the electrodes, they will burn a hole through the metal.

How does spot welding work?
The Miller MSW-41 Spot Welder.

Three Key Features

Spot welding provides three powerful features: speed, control and automation. Because the current sent through the electrodes moves in a matter of milliseconds, spot welding does not generate massive amounts of heat. It is therefore less dangerous and conserves more energy. The precise control of the spot welding current means stronger and longer-lasting welds. There are portable spot welding units for tradesmen and automotive experts alike, but the most powerful spot welds are performed by robots. This is especially the case in the manufacturing of automobiles. The modern automotive assembly line typically involves a barrage of spot welds delivered by swivelling robotic arms. These robotic welds deliver precise currents and create incredibly strong welds.

A WSI spot welding robotic system.
A WSI spot welding robotic system.

Portable Spot Welding

The typical portable spot welding apparatus includes two electrodes, an electrical source and water (or brine solution) pumps to instantly cool the metal after the weld. The throat of the electrodes is adjusted to accommodate the thickness of the metals to be welded, and the power source is activated. Touching the electrodes to the spot unleashes the current. The welding times vary, according to the types of metals used, but they can range from .01 seconds to .63 seconds. When the electrodes are released and the current switched off, most spot welding tools will instantly douse the spot with either water or brine to cool it. This allows the piece to be handled quickly and the next spot weld prepared.

A hanging-type spot welding gun.
A hanging-type spot welding gun.

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