Mixed-Gas MAG Welding: What It Changes on Our Floor
Key takeaways
- Our structural welding uses MAG with an argon-CO₂ shielding gas mix — process 135 with an M21 gas.
- The mixed gas gives a more stable arc than straight CO₂, with noticeably less spatter and better bead shape.
- Less spatter means less post-weld cleaning, and less risk of spatter contaminating surfaces that must be painted.
- Wire, gas and procedure parameters are all specified in writing per joint group rather than set by habit.
Same process name, different result
Ask a workshop what they weld with and most will say "CO₂" or "MIG". Those are not the same thing, and the difference shows up on the finished part: how much cleaning is needed, how the bead sits against the plate, and how reproducible the penetration is from one shift to the next.
We use metal active gas welding — process 135 in ISO 4063 notation — with an M21 shielding gas, an argon-CO₂ mixture to ISO 14175. The active component is still CO₂, but the argon fraction stabilises the arc in a way straight CO₂ cannot. In practice this gives:
| Straight CO₂ | Mixed gas (M21) | |
|---|---|---|
| Arc behaviour | Harsher, more spatter | Stable, finer droplet transfer |
| Bead appearance | Roped, higher reinforcement | Flatter, smoother tie-in to plate |
| Spatter | Substantial | Noticeably reduced |
| Cleaning after welding | Grinding and chipping | Much lighter |
| Sensitivity to parameters | Higher | More forgiving within range |
For a buyer, most of that table converts into two things: the part looks better before it is cleaned, and there is less chance of spatter sitting in places that later have to take paint or a bushing.
Procedure, not preference
The gas choice is only one line in a written welding procedure. Our procedure for a standard bucket also sets the wire standard (ISO 14341), covers plates from 8 to 30 mm, groups parameters into three ranges for light fillet, fill and capping, and heavy or dissimilar joints, and requires the actual values to be recorded on a run sheet during welding. Slag and porosity are removed between passes, and repair of any one location is limited to twice without engineering approval.
The result on a finished bucket is main seams that run the length of the structure, dressed before blasting, with every weld traceable to the welder who made it.
SHOP FLOOR DATA
| Field | Value |
|---|---|
| Process | 135 MAG, ISO 4063 |
| Shielding gas | M21 (Ar + CO₂), ISO 14175 |
| Wire | Solid wire to ISO 14341 |
| Qualified thickness range | 8–30 mm |
| Positions | Flat and horizontal (PA / PB) |
| Inspection after welding | VT 100%; MT on load-bearing welds |
FAQ
Can you weld to our specified procedure? Yes. If you have a qualified WPS, send it and we will work to it; if you need us to write one, that is part of joint development work.
Who signs off the welders? Welders are required to be qualified for the process and positions they work in, and each weld is traceable to the welder who made it.
Can we inspect before shipment? You are welcome to send your own inspector or appoint a third party. We would rather have you look before shipment than have a conversation after arrival.
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