MIG Welding Process, MIG welders

MIG Welding Overview

Metal Inert Gas (MIG) welding embraces a group of arc welding processes in which a continuous electrode (the wire) is fed by powered feed rolls (wire feeder) into the weld pool. An electric arc is created between the tip of the wire and the weld pool. The wire is progressively melted at the same speed at which it is being fed and forms part of the weld pool. Both the arc and the weld pool are protected from atmospheric contamination by a shield of inert (non-reactive) gas, which is delivered through a nozzle that is concentric with the welding wire guide tube.

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The Welding Process
An electric motor feeds the consumable wire into the arc and the power source keeps the arc length at a preset values as discussed above. The MIG welding process can be operated at currents within 280-500amps for welding plates, thick walled pipes and flat sections, The spray transfer operation is used most often for this type of operation. Welds which are located in positions where metal tends to run out of the joint under the effect of gravity are welded at lower currents say 69-180amps, using the Dip or Pulse transfer operation.

With MIG Welders the wire is pointed in the direction of travel, this is know as the forehand technique. This lets the arc fuse to the parent metal ahead of the weld pool, thus giving the best penetration. The welder control the speed of travel to ensure the weld pool does not run ahead of the arc, which would cause a lack of fusion.

VOLTAGE control in the profile of the weld.

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Wire diameter depend on the current required, below is a guide, but this will vary depending on the material and gas used

Wire speed
0.6 40-100 2-5
0.8 40-150 3-6
1.0 100-280 3-12
1.2 120-350 4-18

The author would like to thank:

BOC Industrial – A Member of the Linde Group –
Taken from Industrial Gases Catalogue 2010.

Telwin Sp.a -
Taken from “The Art of Welding”

Cemont – A brand within Air Liquid Welding –
Taken from 2010 General Catalogue.

Air Products Ltd –
Taken from “Welders Handbook”