GMAW

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GMAW circuit diagram.

Gas Metal Arc (GMAW) welding, also known as Metal Inert Gas (MIG) welding, joins metals by heating them to their melting points via an electric arc. The arc, shielded from atmospheric contaminants by a shielding gas, exists between a continuous, consumable electrode wire and the metal.^[1]

1 Advantages
2 Methods
3 Short-Circuit Transfer
- 3.1 Limitations of Short-Circuit Transfer
4 Globular Transfer
- 4.1 Limitations of Globular Transfer
5 Spray Arc Transfer
- 5.1 Advantages of Spray Arc Transfer
- 5.2 Limitations of Spray Arc Transfer
6 Pulsed-Spray Transfer
7 Equipment
8 References
9 White Papers
10 Spec Sheets
11 Brochures
12 Line Cards
13 News to Use

Advantages

MIG welding is quicker than stick welding techniques. This makes it well suited for softer metals like aluminum.
MIG welding produces a clean weld with very little spatter, due to protective shielding gases around the welding arc.
MIG welding is suitable for a wide variety of metals and alloys.
The use of semi-inert shielding gases like carbon dioxide makes MIG welding both effective and economical. Gases can be purchased pre-mixed in cylinders or can be generated on-site using a gas mixer.^[2]^[3]

Methods

There are three primary methods of MIG welding.

Semiautomatic, or handheld, welding uses equipment to control only the electrode wire feeding. The welding gun is controlled by hand.
Machine welding uses a welding gun controlled by an operator-monitored machine.
Automatic welding occurs when a machine welds without constant operator intervention.^[1]

Short-Circuit Transfer

Short-circuit transfer occurs when an electrode touches a work piece, producing a short circuit and high current. This causes a transfer of metal, which creates the weld.^[4] Wire feed speeds, voltages and deposition rates tend to be lower in short-circuit transfer than in other types of transfer. This allows for welding of thick or thin metals in various positions.^[1] Short-circuit transfer typically produces a crackling sound (like frying bacon) under optimal conditions.

Limitations of Short-Circuit Transfer

Relatively low deposition rates
Lack of fusion on thicker metals
Spatter^[1]

Globular Transfer

Globular transfer occurs when large globs of wire are disconnected from an electrode wire and enter a weld puddle. Welding parameters like voltage, amperage and wire feed speed are somewhat higher in globular transfer than in short-circuit transfer.^[1]

Limitations of Globular Transfer

Spatter
Less attractive weld appearance than spray arc transfer
Restricted to flat positions and horizontal fillet welds
Restricted to metal 1/8 in. (3 mm) or thicker^[1]

Spray Arc Transfer

Spray arc transfer is a method of metal transfer in which a stream of small molten droplets is “sprayed” across an arc between an electrode wire and a base metal. This method uses relatively high voltage, wire feed speed and amperage values compared to short-circuit transfer. True spray arc transfer creates a characteristic humming or buzzing sound under the right parameters. On the other hand when welding thicker metals the spray arc transfer has a fast crackling sound. In this case, spray arc transfer is defined by a minimum voltage and amperage setting by the welding procedure.^[5]

 ^[1]

Advantages of Spray Arc Transfer

High deposition rates
High-quality fusion and penetration
Attractive bead appearance
Able to use wires with larger diameters
Very little spatter

Limitations of Spray Arc Transfer

Limited to materials 1/8 in. (3 mm) and thicker (hand held)
Restricted to flat and horizontal fillet weld positions (with the exception of some spray transfer on aluminum)
Excellent fit-up is required, since there is no open root capability.^[1]

Pulsed-Spray Transfer

Pulsed-spray metal transfer occurs when a pulse is increased and reduced, with metal transfer occurring only during the pulse peak. Benefits of this method include spatter reduction, fewer incomplete fusion defects and applications in challenging welding positions.^[6]

Equipment

Basic equipment for MIG welding operations includes a welding power source, a wire feeder (constant-speed or voltage-sensing models may be used), an electrode wire, a welding gun and a shielding gas cylinder or gas mixer.^[1],^[2] Note: A constant-voltage, direct-current power source is used most often in MIG welding, but constant-current and alternating-current systems may also be used.^[3] In the event of MIG welding soft metals such as Aluminum there is additional equipment needed. The wire feed needs to be either a spool fed gun or a push-pull wire feed system.^[4]