GMAW · Gas Metal Arc Welding
MIG Welding
MIG welding feeds a solid wire electrode continuously through a gun while shielding gas protects the puddle — the fastest process to learn and the standard for production fabrication on clean steel.
- GMAW
- DCEP for all solid-wire GMAW
- 50–350 A depending on wire size and transfer mode
- External shielding gas, so it cannot be used in wind without shelter
How mig welding works
A drive motor pushes solid wire through the gun at a set speed. The wire carries the welding current, arcs to the work and melts into the puddle, so the electrode is both the heat source and the filler. Shielding gas flows from the nozzle to keep the atmosphere off the molten metal. Because the wire feeds continuously, there are no stops to change electrodes and the duty cycle is high.
At a glance
| AWS designation | GMAW — Gas Metal Arc Welding |
|---|---|
| Also called | MIG, GMAW, Wire welding, MAG welding |
| Polarity | DCEP for all solid-wire GMAW |
| Typical amperage | 50–350 A depending on wire size and transfer mode |
| Typical voltage | 16–24 V short circuit, 24–30 V spray |
| Positions | All positions in short-circuit and pulsed transfer; flat and horizontal only in axial spray |
| Deposition rate | High — continuous feed with no stub loss |
| Shielding | External shielding gas, so it cannot be used in wind without shelter |
| Skill level | Easiest of the arc processes to reach a usable weld with |
Metal transfer modes
| Mode | Description | Typical use |
|---|---|---|
| Short circuit | The wire touches the puddle and shorts roughly 100 times a second. Low heat input, all positions, and the go-to mode for sheet and thin plate. Gives the characteristic crackling bacon sound. | Under 1/4 in, all positions |
| Globular | Droplets larger than the wire diameter fall across the arc under gravity. Spattery and hard to control — usually a mode to avoid rather than to select. | Generally avoided |
| Axial spray | Fine droplets stream across the arc. High deposition, deep penetration and almost no spatter, but the puddle is too fluid for out-of-position work. | Over 1/4 in, flat and horizontal |
| Pulsed spray | The machine pulses between a high peak current that detaches a droplet and a low background current that lets the puddle freeze. Gives spray-quality welds in all positions. | All positions, all thicknesses, on machines that support it |
Shielding gas selection
| Gas | Used for | Notes |
|---|---|---|
| 75% Ar / 25% CO2 | Carbon steel, short circuit and spray | The shop default: smooth arc, low spatter, good appearance. |
| 100% CO2 | Carbon steel, short circuit | Cheapest, deepest penetration, most spatter. Cannot support spray transfer. |
| 90% Ar / 10% CO2 | Carbon steel, spray and pulsed | Used on heavier plate where spray transfer is wanted. |
| 90% He / 7.5% Ar / 2.5% CO2 | Stainless short circuit | The classic stainless tri-mix — good wetting with minimal carbon pickup. |
| 98% Ar / 2% CO2 | Stainless spray | Keeps weld carbon low while supporting spray transfer. |
| 100% argon | Aluminium | Standard for aluminium up to about 1/2 in; add helium for thicker sections. |
Starting settings
Starting points only — every machine, joint and position shifts them. Adjust by arc sound and bead profile.
| Thickness | Wire | Amps | Volts | Wfs |
|---|---|---|---|---|
| 24 gauge (0.6 mm) | 0.023 in | 30–40 | 15–16 | 70–100 ipm |
| 18 gauge (1.2 mm) | 0.023–0.030 in | 50–70 | 16–17 | 120–160 ipm |
| 1/8 in (3.2 mm) | 0.030–0.035 in | 120–160 | 18–20 | 230–280 ipm |
| 3/16 in (4.8 mm) | 0.035 in | 170–200 | 20–22 | 300–350 ipm |
| 1/4 in (6.4 mm) | 0.035–0.045 in | 200–250 | 22–24 | 350–420 ipm |
| 3/8 in (9.5 mm) | 0.045 in | 250–300 | 24–28 | 300–400 ipm (spray) |
Advantages
- Fastest of the common processes to learn to a usable standard
- High deposition rate and high operator duty cycle
- No slag to chip between passes
- Works on material from 24 gauge sheet up to heavy plate
- Readily automated for robotic production
Limitations
- Shielding gas blows away in wind above about 5 mph
- Requires clean base metal — rust, paint and mill scale cause porosity
- Equipment is less portable than a stick machine
- Short-circuit transfer can produce cold lap on thick material if settings are wrong
- Aluminium needs a spool gun or push-pull torch
Where it is used
- Automotive body and chassis fabrication
- General shop fabrication and manufacturing
- Robotic production welding
- Sheet metal work and light structural
- Aluminium fabrication with a spool gun
Filler metals for mig welding
ER70S-6
AWS A5.18/A5.18M · Carbon & Mild Steel
ER70S-6 is the default solid MIG wire for carbon steel — high silicon and manganese let it weld over mill scale and…
ER308L
AWS A5.9/A5.9M · Stainless Steel
ER308L is the bare wire and TIG rod for 304 and 304L stainless — the same low-carbon 19Cr-10Ni chemistry as E308L…
ER316L
AWS A5.9/A5.9M · Stainless Steel
ER316L is the molybdenum-bearing bare filler for 316 and 316L stainless — the standard TIG rod and MIG wire for…
ER4043
AWS A5.10/A5.10M · Aluminum
ER4043 is the 5% silicon aluminum filler — fluid, crack-resistant and the default choice for welding 6061 and…
ER5356
AWS A5.10/A5.10M · Aluminum
ER5356 is the 5% magnesium aluminum filler — stronger than ER4043, stiffer to feed, and the choice when the joint…
ER309L
AWS A5.9/A5.9M · Stainless Steel
ER309L is the bare filler for welding stainless to carbon steel — over-alloyed at 23Cr-12Ni so the joint stays…
MIG Welding — common questions
What does MIG stand for?
Metal Inert Gas. The formal AWS name is Gas Metal Arc Welding, or GMAW, which is more accurate since most steel mixes contain CO2 and are therefore not strictly inert.
What gas is used for MIG welding steel?
75% argon / 25% CO2 is the shop standard. Straight CO2 costs less and penetrates deeper but spatters more and cannot support spray transfer.
Is MIG or stick welding better for beginners?
MIG. The gun holds a constant arc length automatically, so a beginner gets a usable bead far sooner. Stick demands manual arc length control from the first minute.
Can you MIG weld outside?
Not without shelter. Wind above roughly 5 mph strips the shielding gas away and the weld goes porous. Use self-shielded flux-cored wire or a stick machine outdoors.
What thickness can MIG weld?
From 24 gauge sheet up to heavy plate. The practical limit on any given machine is its amperage and duty cycle; multi-pass welding extends it further.