MIG/MAG Welding Technology: Equipment, Transfer Modes, and Shielding Gases

Gas Metal Arc Welding (GMAW): MIG and MAG Processes

MIG/MAG welding (Gas Metal Arc Welding) is a heat fusion process that joins pieces of metal using an electric arc generated between a consumable electrode wire and the workpiece. The weld pool is protected by a shielding gas, which prevents contamination of the liquid metal.

• MIG (Metal Inert Gas): Utilizes an inert gas (e.g., Argon or Helium) for protection.
• MAG (Metal Active Gas): Utilizes an active gas (e.g., Carbon Dioxide or mixtures) for protection.

MIG/MAG Welding Equipment Components

1. Power Source

   Plugs into the electrical network (220 V or 380 V). It consists of a transformer and rectifier, providing adjustable, continuous DC voltage, which may fluctuate slightly during operation.

2. Electrode Wire Feeding Mechanism

   This system ensures the continuous supply of the electrode wire to the torch.

   • Reel and Axis: Holds the wire coil. A spring brake system slows the coil to prevent rotation due to inertia after welding stops.
   • Guide Tube: Facilitates centering the wire as it enters the roller system.
   • Traction System (Drive Rollers): An electric motor turns the rollers, pushing the wire toward the gun liner.
   • Braking System: Prevents the wire from tangling at the exit of the drive rollers.

3. Electrode Wire and Gas Connector

   The wire diameter is proportional to the thickness of the pieces being welded. The wire exterior features a copper treatment to ensure better electrical contact in the contact tube and protect it from oxidation.

   The electrical connector transmits power to the gun, which has a positive input for the wire.

4. Welding Torch (Pistol)

   The torch ejects the wire and shielding gas necessary to establish the arc.

   • The design allows for easy access to the wire bath.
   • The contact tube conveys the current to the wire just before it exits, ensuring the tip does not adhere to the metal parts.

5. Manometer and Flowmeter

   The manometer reports the internal pressure of the gas bottle, while the flowmeter regulates the protective gas flow rate.

Properties of Shielding Gases

The choice of gas significantly impacts arc stability, penetration, and bead profile.

• Argon (Ar): High density, provides good weld protection, facilitates easy arc priming, and results in narrow weld beads.
• Helium (He): Low density, protects the arc with greater difficulty, offers low stability and low activation, but yields good amperage and deep penetration beads.
• Carbon Dioxide (CO₂): High density and conductivity, provides good protection, amplitude, and deep penetration ranges.

Metal Transfer Modes in MIG/MAG Welding

The method by which molten metal droplets transfer from the electrode to the weld pool depends primarily on current intensity and voltage. The common forms are:

• Short Circuit Transfer (Low Intensity)

  Droplets grow to a large diameter, and the transfer rate is only a few drops per second. The wire repeatedly contacts the weld pool, causing a short circuit.

• Globular Transfer (Medium Intensity)

  Droplet size decreases rapidly, becoming equal to or slightly smaller than the electrode diameter. Transfer occurs at hundreds of drops per second.

• Spray Transfer (High Intensity)

  Very small droplets are transferred at high speed. Separation increases, but the required current intensity also increases significantly.

Intervening Factors in MIG/MAG Welding

• Current Intensity
• Output Voltage
• Wire Feed Speed
• Current Polarity
• Gas Flow Rate

Resistance Spot Welding (RSW)

Spot welding is a fusion welding process used primarily in the assembly of metallic sheet materials for the manufacture and repair of vehicle bodies (carrocerias).

Key Factors in Spot Welding

• Welding Time Duration
• Electrode Pressure
• Welding Power
• Surface Condition of the Materials

Tungsten Inert Gas (TIG) Welding

TIG welding (Gas Tungsten Arc Welding – GTAW) is a gas-shielded arc process that utilizes the intense heat generated by an electric arc between a non-consumable tungsten electrode and the workpiece.