What Is MIG Welding? How GMAW Works
MIG welding is the common name for Gas Metal Arc Welding (GMAW). It feeds a solid wire electrode continuously through a gun while an external shielding gas protects the weld pool from the atmosphere. The wire melts and becomes the filler metal. MIG is the easiest arc welding process to learn and the fastest for manual welding, which is why it dominates shop fabrication and manufacturing.
How MIG Welding Works
Wire feeds automatically from a spool inside the machine, through a liner in the gun cable, and out through a contact tip at the end of the gun. The contact tip energizes the wire with welding current. When the wire touches the workpiece, it arcs and melts.
Shielding gas flows from a nozzle (cup) around the contact tip, creating a protective envelope over the weld pool. This keeps oxygen and nitrogen out of the molten metal.
The welder controls gun angle, travel speed, and standoff distance (the gap between the contact tip and the work). The machine controls wire feed speed (which sets amperage) and voltage (which sets arc length). These two settings are the primary adjustments on any MIG welder.
Equipment You Need
A MIG setup requires more equipment than stick but is still straightforward: a constant voltage power source with built-in wire feeder, a MIG gun, a gas regulator, a shielding gas bottle (75/25 Ar/CO2 for mild steel is standard), a ground clamp, and a spool of wire.
Smaller machines (110V) work for light fabrication and auto body. Larger machines (220V and above) handle structural and production welding. Most machines come ready to weld out of the box once you add gas and wire.
Shielding Gas Basics
75% Argon / 25% CO2 (called C25) is the standard shielding gas for mild steel MIG welding. It produces a stable arc, minimal spatter, and good bead appearance.
100% CO2 is cheaper and provides deeper penetration, but produces significantly more spatter and a harsher arc. Some shops use it for heavy structural work where appearance does not matter.
Tri-mix (typically 90% Helium / 7.5% Argon / 2.5% CO2) is used for stainless steel MIG welding.
100% Argon is required for aluminum MIG welding.
Gas flow rate is typically 25-35 CFH (cubic feet per hour). Too low and you get porosity. Too high and you create turbulence that pulls air into the gas envelope, which also causes porosity.
Advantages of MIG Welding
Fastest manual welding process. Continuous wire feed means no stops to change electrodes. Deposition rates are significantly higher than stick or TIG.
Easiest to learn. The machine handles wire feed automatically. The welder only needs to control gun position and travel speed. Most beginners produce acceptable welds within hours.
Minimal cleanup. No slag to chip. Just a quick pass with a wire brush if needed.
High deposition rates. MIG puts down more weld metal per hour than stick or TIG, making it the most productive manual process.
Excellent on thin material. MIG can weld sheet metal down to 24 gauge with the right settings and wire size. Short-circuit transfer mode keeps heat input low.
Consistent weld quality. The automatic wire feed produces even, repeatable beads with less operator variability than stick.
Limitations
Requires shielding gas. Wind blows the gas shield away, causing porosity. MIG is impractical outdoors without a windscreen or enclosure. Even a shop fan pointed at your work area can cause problems.
Cannot weld through contamination. Rust, paint, oil, and mill scale cause porosity and poor fusion with MIG. The joint must be clean.
Less portable. A gas bottle and wire feeder add bulk and weight compared to a stick setup.
Gas and wire costs add up. Shielding gas is a recurring expense, and spools of quality wire are not cheap. For occasional use, the consumable cost per weld is higher than stick.
When to Use MIG Welding
MIG is the default for shop fabrication, automotive work, manufacturing, and any indoor welding on clean material where speed matters. It is the backbone of production welding in factories, job shops, and auto body repair.
If you are a hobbyist or beginner, MIG is the fastest path to making good-looking, structurally sound welds. The learning curve is short and the results are forgiving.
MIG is the wrong choice for outdoor work in wind, heavily contaminated material, or remote field work where hauling a gas bottle is impractical. For those situations, use stick or self-shielded flux-core.
Common MIG Wires
ER70S-6 is the most popular MIG wire in the world. The higher silicon and manganese content provides excellent deoxidation, which means it handles light mill scale and surface contamination better than other wires. It works on virtually every mild steel application.
ER70S-3 has less deoxidizer than ER70S-6, which means it requires cleaner base metal. It produces a cleaner weld with less silicon island residue on the surface. Preferred when the steel is clean and appearance matters.
ER70S-2 is triple-deoxidized with silicon, manganese, and titanium/zirconium/aluminum. It produces the highest quality welds of any carbon steel MIG wire and is often used for root passes or critical applications. It also works as TIG filler rod.
Reference data only. Verify all settings against manufacturer documentation and the applicable welding code before use. Amperage ranges are starting points that vary by position, fit-up, and material. Welding involves serious injury risks including burns, electric shock, fume exposure, and fire. This site does not replace proper training, certification, or employer safety procedures. See full terms of use.
Classification system defined by AWS A5.18, general welding process knowledge.