Spot welding

The process uses two shaped copper alloy electrodes to concentrate welding current into a small "spot" and to simultaneously clamp the sheets together.

The amount of heat (energy) delivered to the spot is determined by the resistance between the electrodes and the magnitude and duration of the current.

[3] The amount of energy is chosen to match the sheet's material properties, its thickness, and type of electrodes.

Applying too much energy will melt too much metal, eject molten material, and make a hole rather than a weld.

[citation needed] The equipment used in the spot welding process consists of tool holders and electrodes.

Tool holding methods include a paddle-type, light duty, universal, and regular offset.

The electrodes generally are made of a low resistance alloy, usually copper, and are designed in many different shapes and sizes depending on the application needed.

The width of the workpieces is limited by the throat length of the welding apparatus and ranges typically from 5 to 50 inches (13 to 130 cm).

In the case of resistance spot welding, there are two main parts of the tooling system, the features of which fundamentally influence the whole process: the gun and its type, and the size and shape of the electrode.

The crack around the weld nugget will be extended under an external load or fatigue to produce a different type of failure.

Welding times are often very short, which can cause problems with the electrodes—they cannot move fast enough to keep the material clamped.

As such, the heat energy distribution in spot welding could be dramatically changed by the fast motion of the melted metal.

The energy storage element allows the welder to deliver high instantaneous power levels.

As electrical energy is delivered to the weld and causes the temperature to rise, the electrodes and the workpiece are conducting that heat away.

The equipment may seek to control different variables during the weld, such as current, voltage, power, or energy.

[14] Micro spot welders, used in a variety of industries, can go down to 1.5 kVA or less for precision welding needs.

It is common for a spray of molten metal droplets (sparks) to be ejected from the area of the weld during the process.

Thicker stock is more difficult to spot weld because the heat flows into the surrounding metal more easily.

Connecting surfaces should be free of contaminants such as scale, oil, and dirt, to ensure quality welds.