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	MAG welding with Coogar SG.

MIG/MAG Welding

Metal inert/active gas (MIG/MAG) welding is a general purpose semi-automatic welding process which can produce moderate to high weld metal deposition rates. The MIG/MAG process uses a Direct Current (DC) arc struck between a consumable wire electrode and the work piece. The arc is used to melt the consumable electrode (which is fed continuously into the arc zone) and fuse the base metal. A molten weld pool is created which, when solidified, forms the welded joint.

The melting electrode and the weld pool are protected from atmosphere by a shield of either inert or active (oxidising) gas.

• MIG (Metal Inert Gas) welding uses inert gases, e.g. argon and argon/helium mixtures.

• MAG (Metal Active Gas) welding uses active oxidising gases, e.g. argon/O2/CO2 mixtures.

When carbon dioxide shielding gas is used, the process is also known as CO2 welding.

Operation

MIG/MAG welding is suitable for manual, mechanised and automatic (robotic) application.

An electric motor feeds a consumable wire electrode at a controlled speed through the welding gun and into the arc. Here, the tip of the wire electrode melts at a rate which is primarily controlled by the welding current. The power source is designed to maintain a constant arc voltage (arc length) so that the welder/operator is able to concentrate on ensuring complete fusion of the joint.

In manual welding, the melting electrode tip is generally pointed in the direction of the welding (forehand technique). This produces the best fusion characteristics. The welder must also control the speed of travel and all the primary welding parameters in order to obtain a satisfactory weld.

The main parameters and their effects are:

• Current—controls penetration and weld bead size.
• Voltage—controls weld bead shape and penetration.
• Travel speed—controls weld bead size and penetration.

Welding current

There are two key modes of metal transfer in conventional MIG/MAG welding. These are spray transfer and short circuiting (dip) transfer.

Spray metal transfer is used for welding thick section materials and for welding aluminium and its alloys. Spray metal transfer is characterised by a smooth, quiet arc, low spatter levels and deep penetration. A large, fluid weld pool is created and the technique may only be used in the flat and horizontal-vertical positions.

Short circuiting (dip) metal transfer is used for welding thin sheet materials and for welding in all positions. Short circuiting metal transfer is characterised by a noisy arc, some spatter and moderate-low penetration. The inductance of the welding power supply can be used to optimise metal transfer characteristics and minimise spatter levels.

	Synergic pulsed MIG/MAG welding—droplet transfer.

In order to overcome the limitations of both spray transfer and short circuiting (dip) transfer, pulsed and synergic (or controlled transfer) pulsed MIG/MAG welding can be used. This process variant employs advanced welding power supplies to pulse the welding current between high spray transfer levels and low, short circuiting levels. The power source is used to carefully control the frequency of the current pulses and a precision wire feed unit delivers just the right amount of wire to maintain a smooth, stable arc. This technique allows the production of excellent quality welds in all positions, with low spatter levels at optimum welding current.

Gemini™ gases for MIG/MAG welding

The Gemini range of MIG/MAG welding gases enables optimum weld quality to be obtained on the widest range of industrial metals and alloys.

The Coogar™ range of gas mixtures is particularly suited for the spray and short circuiting transfer MAG welding of steels. Coogar 20 is the Gemini gas for spray transfer welding of mild and carbon-manganese steel plate with a thickness of 10mm and upwards. Coogar 5 is the Gemini gas recommended for short circuiting transfer welding of mild steel sheet and chrome-moly steels. Coogar SG is a premier Gemini gas for MAG welding of steels. It can be used for all metal transfer modes and is particularly suited for advanced synergic (or controlled transfer) MAG welding of steels.

The Gemini range of Astec™ gas mixtures, is specifically designed for optimum weld productivity and quality. Astec gas mixtures are available for the MIG/MAG welding of austenitic stainless steels, aluminium and copper.

Recommended Gemini gases for MIG/MAG welding
carbon steels	stainless steels	aluminium & alloys	magnesium & alloys	copper & alloys	cupro- nickel	nickel & alloys	titanium & alloys
Coogar SG Coogar 5 Coogar 20 carbon dioxide	Astec S3 Astec S5 Weldap™ 2	argon Astec 30 Astec 75	argon Astec 75	Astec 75 argon	Astec 75 Astec 30 Astec 50	argon Astec 75 Astec 50	HP argon argon
The selection of the optimum Gemini gas for your application depends upon a number of features, including material thickness, welding position, etc.

 

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MIG/MAG Welding

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