MAG welding with solid wire electrode is the most widely used manually controlled process for factory fabrication work; it is sometimes known as semiautomatic or CO2 welding.
A continuous solid wire electrode is passed through a wire feed unit to a ‘gun’, usually held and manipulated by the operator.
Power is supplied from a rectifier or inverter source along interconnecting cables to the wire feed unit and gun cable; electrical connection to the wire is made in a contact tip at the end of the gun.
The arc is protected by a shielding gas, which is directed to the weld area by a shroud or nozzle surrounding the contact tip. Shielding gases are normally a mixture of argon, carbon dioxide and possibly oxygen or helium.
Good deposition rates and duty cycles can be expected with the process, which can also be mechanised with simple motorised carriages.
The gas shield is susceptible to being blown away by draughts, which can cause porosity and possible detrimental metallurgical changes in the weld metal.
The process is therefore better suited to factory manufacture, although it is used on site where effective shelters can be provided.
It is also more efficient in the flat and horizontal positions; welds in other positions are deposited with lower voltage and amperage parameters and are more prone to fusion defects.
MAG welding with flux cored electrode, process 136 is a variation that utilises the same equipment as MAG welding, except that the consumable wire electrode is in the form of a small diameter tube filled with a flux.
The advantage of using these wires is that higher deposition rates can be used, particularly when welding in the vertical position (between two vertical faces) or the overhead position. The presence of thin slag assists in overcoming gravity and enables welds to be deposited in position with relatively high current and voltage, thus reducing the possibility of fusion-type defects.
Flux additions also influence the weld chemistry and thus enhance the mechanical properties of the joint.