METAL INERT GAS WELDING

With 'flat' volts/amps characteristic an attempted alteration in arc length (volts) will have little effect, hence arc length (volts) remains constant but a significant change in current will result. This is often referred to as the 'self-adjusting arc'. Metal Inert Gas (MIG) welding is a 'flat' arc process (constant) voltage. Also known as Metal Active Gas (MAG); CO2; Metal-arc Gas Shielded, flux core and GMAW (US). MIG can be used on all materials, in all positions, with high productivity and low heat input. There is no CO2 MIG welding with stainless steel. Normally DC positive though some flux core uses DC negative.

Type of Operation. Manual, mechanised, semi-automatic and automated (robotics).

Mode of Operation.An arc is maintained between the end of the bare wire electrode and the work piece. The wire is fed at a constant speed, selected to give the required current, and the arc length is controlled by the power source. The operator is not therefore concerned with controlling the arc length and can concentrate on depositing the weld metal in the correct manner. Hence the name 'semi-automatic' for manual operation, in which wire, gas and power are fed to a hand held gun via a flexible conduit.The process can be operated at high currents (250 - 500 A) when metal transfer is in the form of a 'spray', but, except for aluminium, this technique is confined to welding in the flat and horizontal positions. For vertical and overhead welding special low current techniques must be used, i.e. 'dip' transfer or pulsed arc. The arc and weld pool are shielded by a stream of gas. The electrode can be solid or flux cored.(In mechanised MIG and submerged arc welding the process may also be operated using constant current or drooping arc characteristics).