Spot and projection welding machines

On the basis of the mechanical construction, resistance spot welding machines can be of four types viz. rocker arm, press, portable and multiple electrode machines. Usually projection welding machines are of press or multiple electrode type.

Rocker arm machines: This is the simplest form of stationary machines. This machine consists of a frame that houses the transformer and tap switch vertically adjustable lower horizontal horn and an upper horn mounted in a rocker arm that is pivoted at the front top edge of the frame. This type of machine is available in the capacity range of 10 to 300 kVA (throat depths 300 mm to 1.2 m). For job shop work with short production runs, foot operated type rocker arm machines can be used. Air operated type rocker arm machines are used for short or medium production runs where minimum set up time is needed. Motor operated rocker arm machines will be suitable for long production runs.

Press type machines: They have an upper electrode and welding head that move vertically in a straight line. The capacity of these machines vary from 5 to 600 kVA (throat depths up to 1.2 m). Bench type models of this version are used for radio, instrumental, jewelry and dental work. They have throat depths of a few hundred millimeter and are rated below 5 kVA. Either manual, pneumatic or hydraulic controls can be used. Both spot and projection welding machines are available in this type.

Portable machines: They are otherwise called guns. The basic units of this type are:

• Portable welding gun.
• Electrical controls such as welding contactor and a sequence timer.
• Welding transformer.
• Secondary cables and hose needed to carry power between the transformer and the welding gun.

Welding force is applied by air or hydraulic cylinders. In these machines, secondary losses are high and so secondary voltage is two to four times the voltage of the transformers of the other type.

Multiple Electrode Machines: These are special purpose, custom built machines. These are economical in automobile industry. These are multiple transformer type machines. Each of these transformers will have two secondaries and two electrodes are connected to each secondary. This type is popular among projection welding machines.