Metal Inert Gas welding which is known as MAG (Metal active gas) or GMAW ( gas metal arc welding) in USA is the process of a wide utilization for a vast of materials, including ferrous and non-ferrous

The most important thing to this process is the small diameter electrode wire fed into the arc from a coil. This results in producing quick and neat welds over a wide range of joints

Equipment

● DC output power source

● Wire feed unit ● Torch

● Work return welding lead

● Shielding gas supply, (normally from cylinder)

Lets talk about the Power Source

MIG welding machine in India is carried out on DC electrode (welding wire) positive polarity (DCEP). However DCEN is used (for higher burn off rate) with certain selfshielding and gas shield cored wires.

DC output power sources are of a transformer-rectifier design, with a flat characteristic (constant voltage power source). The most common type of power source used for this process is the switched primary transformer rectifier with constant voltage characteristics from both 3-phase 415V and 1- phase 240V input supplies.

The output of direct current after full wave rectification from a 3-phase machine is very smooth. To obtain smooth output after full wave rectification with a 1- phase machine, a large capacitor bank across the output is required. Because of the expense of this, many low cost single phase welding machines omit this component and therefore provide a poorer weld characteristic.

The switches to the main transformer primary winding provide the output voltage steps at the power source output terminals.

Another method of producing different voltages at the power source output terminals is to use a Thyristor or a Transistor rectifier instead of a simple diode rectifier. This system offers continuously variable output voltage, which can be particularly useful on robot installations and the cost of this type of rectifier can be partly offset with no need for primary voltage switch or switches and a single tapped main transformer primary winding. Most MIG power sources have a contactor or relay used to switch the output ON/OFF with operations of the trigger on the MIG torch. The switch off operation of this contactor is normally delayed to allow the welding wire to Burn back out of the molten weld pool. A thermostat is fitted on the hottest point in the power source, in series with the contactor coil to provide thermal protection to the machine. Power source performance is measured by it’s ability to provide a certain current for a percentage of a 10 minute period before “Thermal CutOut”. This is the “Duty Cycle”.

(Source: Internet)