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Metal Inert Gas Welding (MIG)

Process description
Metal Inert Gas Welding, An electric arc is manually created between the workpiece and a consumable wire electrode at the joint line. The parent metal is melted and the weld created with the continuous feed of the wire which acts as the filler metal. The weld area is shielded with a stable stream of argon or CO2 to prevent oxidation and contamination

Materials
Carbon, low alloy and stainless steels. Most non-ferrous metals (except zinc) are also weldable; aluminum, nickel, magnesium and titanium alloys and copper. Refractory alloys and cast iron can also be welded. Dissimilar metals are difficult to weld.

Process variations

  • Portable semi-automatic (manually operated) or fully automated d.c. systems and robot mounted.
  • Three types of metal transfer to the weld area: dip and pulsed transfer use low current for positional welding (vertical, overhead) and thin sheet; spray transfer uses high currents for thick sheet and high deposition rates, typically for horizontal welding.
  • Shielding gases: pure CO2 or argon/CO2 mix commonly used for carbon and low alloy steels, or a mix of argon/helium, also used for nickel alloys and copper. Pure argon is used for aluminum alloys. High chromium steels use an argon/O2 mix.
  • MIG spot welding: used on lap joints.
  • Flux Cored Arc Welding (FCAW): uses a wire containing a flux and gas generating compounds for self-shielding, although flux-cored wire is preferred with additional shielding gas for certain conditions.
  • Limited to carbon steels and lower welding rates.
MIG 300x153 Metal Inert Gas Welding (MIG)

Economic considerations

  • Weld rates from 0.2 m/min for manual welding to 15 m/min for automated setups.
  • Production costs reduced by high weld deposition rates with continuous operation.
  • Well suited to traversing automated and robotic systems.
  • Choice of electrode wire (10.5–11.5 mm) and shielding gas important cost considerations.
  • Economical for low production runs. Can be used for one-offs.
  • Tooling costs low to moderate.
  • Equipment costs low to moderate, depending on degree of automation.
  • Direct labor costs moderate to high. Skill level required is less than TIG.
  • Finishing costs low generally. There is no slag produced at the weld area, however, some grinding back of the weld may be required.

Typical applications

  • General fabrication
  • Structural steelwork
  • Automobile bodywork

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