MIG (Metal Inert Gas) welding, officially known as Gas Metal Arc Welding (GMAW), is a process that uses a continuously fed wire electrode and a shielding gas to join metals. It is one of the most widely used welding methods because it is fast, easy to learn and suitable for mild steel, stainless steel and aluminium.
This hub guide pulls together everything you need to weld confidently with MIG — how the process works, how to choose the right wire and shielding gas, how to set up your machine, and how to diagnose the most common faults. Use it as your starting point, then follow the links to in-depth sub-topic guides.
What is MIG welding?
MIG welding creates an electric arc between a continuously fed wire electrode and the workpiece. The heat melts both the wire and the parent metal to form a strong welded joint, while a shielding gas protects the molten weld pool from oxygen and moisture — helping to prevent porosity and contamination.
Unlike stick (MMA) welding, MIG uses a continuous wire feed, which allows longer welds with fewer interruptions. That combination of speed and consistent quality makes it ideal for production welding, fabrication, automotive repair, construction and manufacturing.
The quality of the weld depends on selecting the correct wire, shielding gas and machine settings for the material being welded. For general mild steel applications, ER70S-6 solid wire is the industry standard thanks to its excellent arc stability and weld quality.
For a deeper walkthrough of the process, see how MIG welding works and how to set up your machine.
Why choose MIG welding?
MIG welding is one of the fastest and most productive welding processes available. Continuous wire feed reduces downtime, while the shielding gas produces clean welds with minimal slag and little post-weld cleaning.
Key advantages include:
- Fast welding speeds and excellent productivity
- Ease of learning — one of the most accessible processes for newcomers
- Suitability for automation and robotic systems
- Versatility — welds mild steel, stainless steel and aluminium
High-quality welding wire further improves arc stability and reduces spatter, helping to minimise rework and improve overall efficiency.
Choosing the right shielding gas
The correct shielding gas depends on the material being welded:
- Mild steel — an Argon/CO₂ mixture is the most common choice, providing good arc stability, low spatter and excellent weld appearance. Pure CO₂ offers deeper penetration but produces more spatter.
- Stainless steel — specialist Argon-based gas mixtures are recommended.
- Aluminium — pure Argon is normally used.
You can also weld without a gas bottle by using gasless flux-cored wire, which suits outdoor work. Read our full guide to MIG welding shielding gases and gasless welding.
Choosing the right MIG wire
Wire selection is driven by the parent material, its thickness, the mechanical properties you need, the welding position and the shielding gas. Mild steel applications typically use ER70S-6, while stainless steel and aluminium need dedicated filler wires.
- Mild & structural steel — ER70S-6 is the all-round favourite. See our MIG wire selection guide.
- Stainless steel — 308LSi for 304 grades, 316LSi for 316 grades. See choosing stainless steel MIG wire.
- Aluminium — ER4043 for general fabrication, ER5356 for higher strength. See aluminium MIG welding.
Wire is classified to recognised standards such as BS EN ISO 14341 and AWS A5.18 — understanding these helps you select the correct filler. See MIG wire classifications and standards.
Setting up your MIG welder
Start by selecting the correct wire, shielding gas and contact tip for the material. Install the spool, feed the wire through the liner and adjust the drive rollers to prevent slipping or crushing. Set the correct polarity — solid wire with gas normally runs DC Electrode Positive (DCEP) — then adjust the gas flow and select voltage and wire feed speed to suit the material thickness.
Always test your settings on scrap material first and make small adjustments to achieve a smooth, stable arc. The full step-by-step is in how MIG welding works. If you are still choosing the machine itself, our guide to choosing and buying a MIG welder covers duty cycle, output and the features that matter.
Avoiding common faults
Many MIG problems trace back to the same root causes — the wrong wire, the wrong gas, poor machine settings or inadequate material preparation. Defects such as porosity, lack of fusion and excessive spatter can usually be avoided with quality consumables, clean materials and correct parameters.
Our MIG welding defects and troubleshooting guide covers bird nesting, porosity, spatter, burn back, lack of fusion, undercut, distortion, cracking and feeding problems.
MIG vs other welding processes
MIG is faster and easier to learn than TIG or MMA, but each process has its place. TIG offers greater precision for high-specification work, while MMA is more portable and performs better outdoors. Compare them in MIG vs TIG vs MMA welding. If you are unsure which process and machine suit your work, start with how to choose a welding machine.
Buying and storing MIG wire
Choosing a wire that complies with recognised BS EN ISO or AWS standards — and a supplier who offers consistent quality and technical support — has a direct impact on weld quality and productivity. For advice on bulk purchasing, storage and supplier selection, see our guide to buying MIG wire.