MAG Welding Explained: Process, Strengths, Limits
Knowledge · Welding in contract manufacturing
How does MAG welding work?
A wire feeder pushes the electrode (typically 0.8 to 1.6 mm diameter) through the torch at constant speed. The arc burns between wire and workpiece, the wire melts and forms the seam together with the molten base material. The shielding gas is called active because it takes part chemically: pure CO₂ or mixed gases such as M21 (82 % argon, 18 % CO₂) stabilise the arc and shape penetration and seam profile. Depending on parameters, the process runs in short arc (thin sheet, positional welding), spray arc (thick sections in flat position) or pulsed arc, which combines the advantages of both on modern power sources.
Which materials and thicknesses does MAG cover?
Practically all weldable steels from about 0.8 mm upwards, with no practical upper limit thanks to multi-pass welding. Structural steels such as S235JR and S355J2 are the standard case, plus fine-grain steels and, with adapted low-CO₂ gas, stainless steels. MAG is unsuitable for aluminium, copper and brass; those run under MIG or TIG.
Why is MAG the most economical process for steel?
Because deposition rate translates directly into money. The endless wire feed allows several kilograms of weld metal per hour, a multiple of what a TIG welder achieves with a hand-fed rod. On long fillet welds of a machine frame that adds up to hours. A practical tip for designers: fillet weld volume grows with the square of the throat thickness. Specifying a = 3 where statics allow it, instead of a habitual a = 5, cuts welding time, heat input and distortion substantially.
What do EN 1090 and ISO 9606 regulate?
Load-bearing steel components may only be welded by companies certified to EN 1090-1, executing to EN 1090-2; execution class EXC 2 is the usual standard in machine building. Welders prove their skill through EN ISO 9606-1 qualifications, separated by process (135), material group and position, and a qualified welding coordinator is responsible for procedures and supervision. For buyers this means: no certificates, no load-bearing parts.
MAG at a glance
| Feature | Value / classification |
|---|---|
| Process number (EN ISO 4063) | 135 |
| Shielding gas | CO₂ or M21 (82 % Ar / 18 % CO₂) |
| Wire diameter | 0.8 to 1.6 mm |
| Materials | structural steel (S235, S355), fine-grain steels, stainless with adapted gas |
| Strengths | speed, economy, EN 1090 suitability, automation |
| Limits | aluminium/non-ferrous, visible-seam finish, heat input |
| Typical parts | machine frames, beams, brackets, welded assemblies |
Frequently asked questions
What does 135 stand for in MAG welding?
It is the process number to EN ISO 4063, the international classification of welding processes. 131 is MIG, 141 is TIG. Drawings and welding procedure specifications identify the process by this number.
Is MAG welding approved for load-bearing structures?
Yes, MAG is the standard process for load-bearing steel components to EN 1090-2, provided the company is certified, welders are qualified to EN ISO 9606-1 and a welding coordinator supervises execution.
Which gas is used for MAG?
For structural steel usually M21 mixed gas (82 % argon, 18 % CO₂), a good compromise of penetration, low spatter and appearance. Pure CO₂ is cheaper with deeper penetration but more spatter.
How much faster is MAG than TIG?
As a rule of thumb three to five times the deposited weld metal per hour, depending on seam type and position. TIG is therefore reserved for seams that need its quality.