Spot welding

A spot welder is much smaller than a stick welder and much easier to handle. It can be used in any position, even upside down. The fast heat-up time also makes it well suited to this task.

How does spot welding work?

The spot welder essentially consists of three parts: the transformer, to which the power supply is connected, the device itself, which contains all the controls and connections required to operate the various electrodes (the electrode holder), and finally the wire lead, which is connected to the transformer. The wire lead is fed through an insulating sleeve so that you cannot get an electric shock if you switch on the device with anything other than your Welding tool or touch your workpiece.

The workpieces are held by the electrode holder, which can be rotated 360 degrees around its base plate so that you can hold your workpiece in any desired position - flat side up, sideways or upside down. The electrode holder also has two adjustable stop bolts that allow you to determine how far it should move forwards or backwards during welding so that you don't accidentally strike material with the arc. The welding rod guide also helps you to support and align your welding rod by keeping it centred in the air gap between the parts to be welded. To operate a spot welder, all you have to do is plug it into a socket, switch on the power supply switch and then press the on button. The transformer supplies power to the wire lead assembly, which is then passed to the electrode holder and the earth clamp. The ground clamp holds your workpiece in place by clinging to metal objects that are close enough for a good connection...

With a 2-wire system, both the hot and return wires are connected together with a jumper terminal, so there is no need for a separate earth wire - this saves time as you don't have any extra connections or wires lying around. Some spot welders may be equipped with 3-wire systems - in these devices, an additional third wire is fed from the electrode holder directly back through the welding cable, where it is connected to another terminal on the handle of the welding gun. This third wire acts as a pilot arc - it provides enough current to ionise the air gap between the welder and the workpiece so that you don't blow out both parts. With 4-wire systems, there is only one wire that is connected directly to the handle. This isolates the electrode holder from possible electric shocks and still delivers an arc for good welds.

With all types of spot welders, you can start spot welding after inserting a rod into the guide tube and switching on the power supply switch...

When you pull the trigger of your welding gun, current flows through the gun to the two parts, which are held together by their respective electrodes (or clamps). Two wires connect each electrode of the spot welder to the transformer unit via the welding cable, where the current is distributed throughout the wire lead assembly. As one of these electrodes is your workpiece, it is welded to the metal object attached to the earth terminal, creating a bond between the two parts being welded. This current flow also strikes an arc across the air gap between the electrode and the workpiece...

The heat generated by this arc melts both surfaces at their point of contact so that they form a solid piece of metal for as long as you hold the trigger down or until you run out of rod. You can also set the duration of the arc using a rotary knob next to the power source switch.