MIG and MAG Welding Fundamentals and Equipment Setup

MIG and MAG Welding Systems

Depending on the system used, Gas Metal Arc Welding (GMAW) is categorized based on the shielding gas:

1. MIG (Metal Inert Gas): Uses inert gases like argon or helium. It is typically used to weld materials sensitive to oxidation, such as stainless steel, copper, aluminum, and sheet metal.
2. MAG (Metal Active Gas): Uses active gases, which include carbon dioxide, oxygen, or mixtures of argon and carbon dioxide. MAG is applied primarily to ordinary steel or low alloy steels.

GMAW Equipment Components

A complete GMAW setup consists of the following essential components:

1. Power Supply

   Provides the necessary electrical current for the arc.

2. Wire Feed Mechanism / Electrode

   This mechanism ensures the continuous feeding of the wire electrode. It is composed of:

   • Spool: Holds the welding wire.
   • Reel and Sheaves: Guide and straighten the wire.
   • Contact Tube: Transfers the current to the wire.

3. Torch and Gun Assembly

   This element is used by the welder to position the filler material at the correct distance and angle.

   • The torch features a swan-neck where the wire changes direction before entering the contact tube.
   • The gun holds the straight wire and is fixed by a cylinder head in the body of the instrument.
   • Key components include the handle, neck, clamping nozzle, spring, microswitch button, and contact tube.

4. Pressure Regulator

   A device located at the cylinder outlet that reduces the high storage pressure to the lower pressure required for welding. It is composed of:

   • A gauge that indicates the pressure remaining in the cylinder.
   • A flowmeter that controls the flow rate of gas needed for welding.

5. Workpiece Clamp (Ground Clamp)

   A device used to close the electrical circuit.

6. Hose Bundle

   A cable bundle and tubes connecting the machine to the torch. Inside the bundle are the current cable, gas supply tube, coolant supply and return tubes (if liquid-cooled), control cable, and wire guide tube.

7. Wire Electrode

   The wire must be of the same material type as the metal being welded. Wires often come with copper plating to prevent corrosion, improve electrical contact, and reduce friction along the feed path.

Shielding Gases

Shielding gases protect the weld pool and electrode from atmospheric contamination.

• Active Gases: Gases that react chemically with the weld material, such as carbon dioxide, oxygen, and argon mixtures.
• Inert Gases: Noble gases (argon and helium) that do not form chemical bonds with the components of the welding material, protecting the electrode and the weld pool.

Weld Metal Transfer Modes

The transfer of the weld metal (fusion of the wire electrode) can occur in several ways:

• Short Circuit Arc Transfer

  This involves the formation of a molten drop at the end of the wire. The electrode touches the workpiece, forming a short circuit. This creates a bottleneck that breaks up and enters the melt, interrupting the short circuit. The wire feed mechanism immediately pushes the wire back out, repeating the process. This is a succession of short circuits.

• Spray Transfer or Long Arc

  The wire melts, dripping continuously and forming a bright cloud of fine metallic drops that spray across the arc.

• Pulsed Arc Transfer

  This technique involves maintaining a constant current during the welding process, but cycling between a high peak current (for transfer) and a low background current (to maintain the arc).

GMAW Welding Process Steps

1. Prepare the edges of the pieces to be joined.
2. Protect surrounding areas from sparks and heat.
3. In vehicles, disconnect the battery to prevent electrical damage.
4. Don protective clothing and safety gear.
5. Regulate machine parameters based on the thickness of the sheets to be joined (voltage, wire feed speed, gas flow, electrode stick-out length).
6. Spray the nozzle and contact tube with anti-spatter compound.
7. Position yourself to clearly view the melt pool, maintaining a torch inclination of approximately 10 degrees.
8. Make tack welds (stippling) to hold the pieces in position.
9. The direction of travel can be either forward (pushing) or backward (pulling).