MIG/MAG welding: transfer modes and settings

Processes 131 and 135 in EN ISO 4063, GMAW in the American numbering. A continuously fed wire that is both the electrode and the filler, under a gas shield — the highest-output manual process in most workshops.

The self-regulating arc

The wire feeds at a set speed and the power source holds a constant voltage. If the arc gets shorter the current rises, the wire burns off faster and the arc returns to length; if it gets longer the opposite happens. The arc regulates its own length several hundred times a second, which is what makes the process easy to learn and awkward to control precisely.

The practical consequence is that you do not set the current. You set the wire feed speed, and the current follows — see wire feed speed. The voltage knob sets the arc length, and therefore the shape of the bead.

Three ways the metal crosses the arc

Short arc (dip transfer). Low voltage and current: the wire touches the pool, short-circuits, the tip pinches off and the arc reignites, about a hundred times a second. Low heat, so it suits thin sheet and positional work. It is also the mode with the highest risk of lack of fusion, because there is not much heat behind the arc.

Globular. The awkward middle range and the mode pure CO₂ gives at almost any setting. Large drops detach irregularly and spatter is at its worst. Most procedures avoid it.

Spray. Above a threshold current, in a mixture with no more than about 20 % CO₂, the metal crosses as a fine stream of droplets. The arc is quiet, the bead is smooth, penetration is deep and spatter is almost nil — but the pool is large, so it is a flat and horizontal mode only. Pulsed transfer exists to bring spray-quality droplets to positional work by pulsing the current above and below the threshold.

The gas

Argon with 8 to 25 % CO₂ covers most steel work. More CO₂ means deeper penetration and more spatter; less means a cleaner face and access to spray transfer. Pure CO₂ is cheap, penetrates well and spatters. Stainless takes argon with 2 % CO₂ or oxygen; aluminium takes pure argon. The gas selection calculator gives the mixture with its EN ISO 14175 designation.

Flow rate is 10 to 16 l/min. Turning it higher does not improve matters past a point: the jet goes turbulent and starts pulling air in. Porosity is more often a draught, a leaking hose or a spatter-blocked nozzle than a low setting.

A starting point that works

For 1.2 mm wire in Ar/18 CO₂ on 5 mm steel: about 220 A, which is roughly 7 m/min of wire, at 24 to 26 V, stick-out 12 mm. Listen to the arc — short arc should sound like frying bacon, a steady rapid crackle. A slow irregular popping means the voltage is too high for the wire speed; a harsh stuttering means the opposite.

What goes wrong

Feeding problems dominate the fault list: a worn liner, a contact tip burnt oval, roll pressure set by feel, or a torch coiled into a loop on the floor. Symptoms and cures are in wire feeding problems. The second most common complaint, lack of fusion in short arc mode, is a technique and heat problem rather than a machine one — see lack of fusion and penetration.

Updated: 13 August 2026