MAG Lassen Explained: The Complete Guide to Metal Active Gas Welding (MIG vs MAG, Settings, Gases & Safety)

What Is MAG Lassen? Metal Active Gas Welding Explained

You walk into a busy Dutch or German fabrication shop and someone shouts, “Kun je MAG lassen?” — can you MAG weld? You nod confidently, strike an arc, and halfway through the first bead you notice something is off. The bead sits flatter, bites deeper, and spits a little more than the MIG welds you’re used to. The regulator tells the story: that cylinder isn’t pure argon. It’s an active mix, and that single fact changes everything about how the arc behaves.

So what exactly is MAG lassen? Break the phrase apart and it gets simple fast. Lassen is the Dutch and German verb for welding. MAG stands for Metal Active Gas — a welding method where a continuously fed, consumable wire electrode melts into the joint while an active shielding gas deliberately reacts with the arc and the molten weld pool. That reaction isn’t a flaw. It’s the point. The gas chemistry shapes penetration, bead profile, spatter levels, and ultimately the strength of the finished joint.

Where MAG Fits in the GMAW Family

MAG and MIG are both variants of Gas Metal Arc Welding (GMAW), the process that uses a continuously fed consumable wire electrode protected from the atmosphere by an externally supplied shielding gas. According to TWI, the only real difference between MIG and MAG is the type of shielding gas used — inert versus active.

The numbering system makes the distinction official:

• ISO 4063 process 131 — MIG (Metal Inert Gas), shielded with inert gases such as argon or helium.
• ISO 4063 process 135 — MAG (Metal Active Gas), shielded with reactive gases such as CO2 or argon/CO2 mixes.

In North America, nobody splits hairs at the counter. The whole family is simply called GMAW, and “MIG” has become a catch-all term for all of it. That’s why a cylinder cheerfully labelled “MIG mix” for steel is technically a MAG gas. If you want the full backstory, our history of MIG welding traces how it all began in the late 1940s at Battelle Memorial Institute, where researchers first developed the idea of a continuously fed aluminum wire shielded with argon. The active-gas branch followed quickly once industry realized CO2 was cheap, hot, and readily available.

The Basic Equipment Chain

Every MAG setup follows the same logical path, from wall socket to arc:

1. Power source — supplies controlled voltage and current, usually DC in constant-voltage mode.
2. Wire feeder — pushes the consumable electrode at a set wire feed speed.
3. Torch and contact tip — the tip conducts current into the wire and guides it toward the joint. Worn tips ruin arc stability fast, so our contact tip guide is worth a read.
4. Shielding gas cylinder and regulator — meters the active gas that protects the molten pool.

That’s the skeleton of the process. In the sections ahead we’ll separate MAG from MIG properly, pick apart the shielding gases, walk through transfer modes and settings, cover materials and safety, and finish with a practical practice routine you can actually use on the bench.

MAG vs MIG: The One Difference That Changes Everything

Stand a MIG and a MAG welder side by side and you cannot tell them apart. Same torch, same wire, same trigger. The difference lives in a single cylinder of gas, and it rewrites how the arc behaves, how the pool freezes, and how strong the finished joint is.

Both belong to the same family: gas metal arc welding, or GMAW. TWI’s explanation of MIG/MAG puts it plainly: MIG is Metal Inert Gas, MAG is Metal Active Gas, and the label depends on the shielding gas flowing through the nozzle.

Inert vs Active: What the Gas Actually Does

An inert gas is a chemical bystander. Argon and helium hover over the pool, shove the atmosphere aside, and take no part in the reaction. They do not dissolve into the metal, they do not change its composition, and they leave the weld chemistry exactly as the wire delivered it. That purity is why MIG is the default for aluminium, stainless, copper, and nickel.

Active gases behave differently. Carbon dioxide and oxygen break down inside the arc, splitting into elements that dive into the molten pool and chemically interact with it, introducing oxygen and carbon as described in Kobelco’s GMAW handbook. That sounds like contamination. On steel, in controlled amounts, it is a tuning tool.

Why Pure Argon Fails on Carbon Steel

Try welding mild steel with straight argon and the problem shows up in seconds. The arc wanders and stiffens instead of settling. The bead comes out narrow and ropey, sitting high on the plate with cold, unfused edges where it should have wet out.

Add a small percentage of CO2 or oxygen and the arc transforms. The oxygen stabilises the arc root, lowers surface tension, and lets the pool wet into the toes of the weld. Penetration deepens, the bead flattens into a sound profile, and spatter becomes manageable. This is why CWB Group treats the oxidising component as a deliberate ingredient rather than an impurity.

MIG vs MAG: Side-by-Side

Same Machine, Different Beast

You do not need a new welder to switch from MIG to MAG. On any ordinary GMAW machine you swap the cylinder, purge the lines, and re-tune voltage and wire feed speed. The wire is often identical. Only the atmosphere around the arc changes.

But the machine will not feel the same afterward. Voltage and wire feed speed that ran perfectly on argon now behave sluggishly, so you retune. Spray transfer thresholds shift. Spatter, penetration, and the arc’s sound all change with the blend. That is why a weld that reads clean on one gas can border on a defect on another.

When the arc misbehaves after a gas change, experienced hands check the shielding flow and the contact tip before touching anything else.

Feel it yourself: run the same bead on argon, then on a 85/15 argon-CO2 mix, and the difference in wetting is immediate. That single test belongs in any serious welding practice routine.

In a Dutch or German shop, the question is never a choice between two processes. It is simply lassen: can you weld? The gas is assumed. That is exactly why the MIG/MAG distinction trips people up: a welder who has only run argon on aluminium will find carbon steel on CO2 feels like a different skill.

That is the heart of it. Same machine, same wire, one active reaction in the arc decides everything. The next time someone asks whether you can MAG lassen, you will know the answer depends on which gas you screw onto the regulator.

Shielding Gases for MAG Lassen: CO2, Ar/CO2 Mixes and Tri-Mix

The gas is the whole point of MAG lassen. In MIG welding you use an inert shield that simply blankets the pool. In MAG welding you deliberately add an active gas that reacts inside the arc, and that reaction is exactly what you are paying for. The gas mixture is one of the few variables that reshapes the arc itself, not just the shield. As TWI explains, the active gas becomes part of the electrical and chemical process. The standard active menu for steels is carbon dioxide, argon with 2 to 5% oxygen, argon with 5 to 25% CO2, and three-part blends of argon, CO2 and oxygen.

Getting the mix right controls arc stability, metal transfer, weld profile, penetration and spatter, all from the regulator.

100% CO2: Cheap, Deep and Messy

Straight CO2 is the budget champion and the deepest-penetrating option. It behaves oddly compared with argon: in the hot arc the CO2 molecule dissociates into carbon monoxide and oxygen, then recombines at the colder workpiece. That recombination releases energy right at the weld pool, which produces the deep, broad, “finger” penetration CO2 welding is famous for.

The downside is turbulence. CO2 runs hotter and more violently, so it spatters heavily, produces a rougher bead and, because it lacks argon’s ionisation behaviour, generally only supports dip (short-circuit) transfer. You cannot get a true axial spray arc with pure CO2.

Argon-Rich Mixes: C25, 90/10, 92/8 and 95/5

Add argon and everything calms down. The most common gas mixture for GMAW is “C25”, 75% argon and 25% CO2. It is the default for carbon steel sheet and general fabrication because it balances penetration, bead appearance and cost. Leaner blends such as 90/10, 92/8 and 95/5 push the arc even smoother: less spatter, better wetting and a flatter bead.

Argon share also decides your transfer mode. Axial spray transfer requires CO2 contents below about 18%, so any mix leaner than C25 can reach the spray threshold at high enough current. More argon means a more stable arc, cleaner beads and a wider usable range. This is why 90/10 and 95/5 dominate higher-quality work.

The trade-off is penetration profile. Extra argon widens and shallows the bead; extra CO2 narrows and deepens it. If you fight burn-through, lean the mix toward argon. If you fight lack of fusion, add CO2.

Tri-Mix: Argon, CO2 and Oxygen

Tri-mix blends add a small percentage of oxygen alongside argon and CO2. The oxygen improves arc stability and droplet detachment, which supports spray and pulsed-spray transfer and high deposition rates. Tri-mix is popular on stainless and thin-gauge work where a smooth, controlled arc matters more than brute penetration.

Matching Gas to Metal: Stainless Needs Care

For stainless steel, low-CO2 mixes around 97.5% argon and 2.5% CO2 are the safe default. Too much oxidising gas burns chromium out of the pool, which strips corrosion resistance and sensitises the steel. Never run a carbon-steel Ar/CO2 mix on stainless; the higher CO2 content will oxidise the alloy and ruin the weld’s chemistry.

Gas Flow and Purity

Flow rate and gas quality matter as much as the blend. A practical starting rule is roughly 10 to 12 times the wire diameter, so a 0.8 mm wire runs about 10 L/min. Too little flow leaves porosity and a weak shield; too much creates turbulence that drags in air from outside the gas envelope.

Purity is non-negotiable. CO2 should be at least 99.8 vol% pure and argon at least 99.99 vol% pure. Moisture and impurities cause porosity and other defects, so check your cylinders and keep your lines dry. As The Fabricator notes, shielding gas is one of the five core variables, with amperage, wire feed speed, voltage and travel speed, that decide whether a weld succeeds. Get the gas right and the rest of your setup becomes far more forgiving; get it wrong and no amount of fiddling with voltage will save the bead.

Metal Transfer Modes: Short-Circuit, Globular, Spray and Pulsed MAG

Metal transfer is simply how molten droplets leave the wire electrode and cross the arc into the weld pool. Four modes dominate MAG welding, and which one you get is decided by current density, arc length (set by voltage), wire-feed speed and shielding gas. Change the gas and you shift the thresholds between them.

Short-Circuit (Dip) Transfer

In short-circuit transfer, the wire physically touches the puddle. The arc extinguishes, surface tension pulls a droplet across, the wire retracts and the arc reignites. This cycle can repeat up to 200 times per second, which is why it sounds like a fast, steady crackle. It is the low-heat-input mode of GMAW, typically run with 0.6–1.1 mm (0.025–0.045 in) electrodes shielded with 100% CO2 or a 75–80% argon plus 20–25% CO2 mix. Usable base-material thickness is generally quoted at 0.6–5.0 mm (0.024–0.20 in). Because the arc is short and the puddle freezes fast, it handles vertical-up and overhead work better than any other mode.

Globular Transfer

Globular transfer is the awkward middle child. It appears when current is high enough to melt large, irregular droplets, but not high enough to launch them in a directed spray. Gravity takes over, so metal falls off the wire in unpredictable lumps, throwing spatter and leaving an unstable arc. It is a transitional mode that is generally avoided in production work. Running a CO2-rich mix widens the range where globular appears, so most operators tune straight through it.

Axial Spray Transfer

Axial spray is the mode that makes MAG welding look effortless. With an argon-rich gas and enough current, the arc pinches the wire tip into a fine taper and fires thousands of tiny droplets per second straight down the arc axis. You get a smooth, quiet arc, almost no spatter, deep fusion and very high deposition. The catch is a large, hot, fluid puddle, so spray transfer is restricted to flat or horizontal positions. It also needs enough current to reach the spray threshold, which is why it is rarely used on thin sheet.

Pulsed Spray Transfer

Pulsed spray fixes that limitation. Current alternates between a low background level and a high peak. The peak is strong enough to detach a droplet, but the average current stays low, so heat input drops. This narrows the heat-input window of spray transfer, letting you weld thinner sections and out-of-position joints with far better control. It is the mode behind most modern synergic machines, though gas mix, wire diameter and stick-out still shape the result.

Current, Voltage and Gas Thresholds

Metal transfer is mostly a question of current density. Low current gives short-circuit; add current and the wire melts faster until it reaches globular, then the spray transition current. Voltage controls arc length, and too much voltage at low current tips you into globular. Shielding gas moves the goalposts: argon-rich mixes lower the spray transition current, while CO2-rich mixes raise it and favour short-circuit. The arc is a balance of amperage, WFS, voltage and gas, so tune one variable at a time.

Choosing a Mode by Thickness and Position

Match the mode to the job. Thin sheet under about 3 mm: short-circuit. Thick plate flat on the bench: spray for speed and fusion. Anything vertical or overhead that is too thick for short-circuit: pulsed spray. If the arc turns spattery and the toes of the bead stop wetting out, you have likely slipped into globular — drop voltage and adjust wire-feed speed. Check your results against examples of good and bad MIG welds, and remember that a worn contact tip will throw off current density enough to change the mode itself.

Setting Up a MAG Welder: Voltage, Wire Feed, Gas Flow and Polarity

Walk up to a MAG machine and the temptation is to hunt for one magic number. There isn’t one. Setup is a balancing act between four linked variables: wire-feed speed, voltage, stickout, and gas flow. When they cooperate, the arc almost tunes itself. Fight them and you get spatter, cold lap, or a bead that looks like a rat’s nest.

Constant Voltage and the Self-Correcting Arc

MAG runs on a constant-voltage (CV) power source. The machine holds voltage nearly steady while wire feeds at a constant speed that matches the welding current. Pull the torch away and the stickout grows, arc length stretches, current drops, and burn-off slows until the arc settles back to its set length. Push in closer and current rises, burn-off speeds up, and the arc re-establishes itself. That self-correction mechanism is exactly why GMAW is so forgiving compared with stick or TIG.

Wire-Feed Speed Sets the Amperage

Here’s the counterintuitive part: you never dial amperage directly. Wire-feed speed (WFS) determines amperage, because more wire entering the arc requires more current to melt it. Crank up WFS and you raise heat input and deposition, not just filler delivery. That’s why WFS and voltage must move as a pair, as this welding-variables breakdown makes clear.

Voltage Controls Arc Length and Bead Width

Voltage sets how long the arc is. Higher voltage means a longer arc, a wider arc cone, and a flatter, wider bead that wets in nicely at the toes. Drop it and the bead narrows, crowns up, and can run cold. Voltage and feed speed are a matched adjustment, not two independent dials.

Stickout: Your Hidden Resistor

Contact-tip-to-work distance behaves like a resistor in the circuit. A longer stickout reduces current at the same WFS; a shorter one raises it. Aim for roughly 10–12 mm (3/8–1/2 in) for short-circuit and about 18–20 mm (3/4 in) for spray or pulsed transfer. Wandering stickout is a top cause of inconsistent beads, and a worn or wrong-sized contact tip makes it worse.

Gas Flow and Polarity

Set shielding-gas flow around 12–16 litres/min (roughly 25–35 CFH), enough to cover the arc but not so much that it turbulently pulls in air. On polarity, the GMAW process generally requires DC+ (electrode positive, or DCEP) for solid wire. If polarity confuses you, this polarity primer untangles the terminology quickly. Self-shielded flux-cored wire reverses that convention, which is why flux-core polarity is worth a separate look.

Inductance and Synergic Mode

Inductance (sometimes labelled “arc control”) shapes how sharply current rises during short-circuit transfer. More inductance softens the arc and reduces spatter; less gives a crisper, faster-following arc. Modern synergic machines take most of this off your plate: select material, wire diameter, gas, and thickness, and the voltage maps to WFS automatically.

Starter Settings for Mild Steel (ER70S-6)

For 1/2 in (12.7 mm) A36, roughly 250 A is a good target. With 90% argon / 10% CO₂ you can reach spray transfer at about 26–28 V and 375–420 IPM. Treat these as starting points, then refine by sound and bead shape.

A Simple Tuning Workflow

1. Set polarity to DC+ and confirm gas flow at the nozzle.
2. Pick wire diameter and a starting voltage for the thickness.
3. Set WFS to match, then run a test bead on scrap of the same steel.
4. Read the bead: too much spatter and popping means lower voltage or more WFS; a cold, ropey bead means more voltage.
5. Fine-tune stickout and travel speed until the arc sounds like steady frying, not crackling.

Setup sticks once you internalise the relationship between feed speed and voltage. Build that muscle with deliberate welding practice, and checking good versus bad MIG welds will train your eye fast.

MAG Welding by Material: Carbon Steel, Stainless, and When NOT to Use It

MAG lassen was built for steel. When the base metal is unalloyed, low-alloyed, or high-alloyed steel, your machine is exactly where it belongs — MIG/MAG is the standard approach for welding carbon steel and stainless steel alike. Step outside that family, though, and the active gas that makes MAG so productive starts working against you.

The key word is Active. The shielding gas isn’t a bystander — it reacts with the weld pool, and whether that reaction helps or harms depends on what you’re welding.

Carbon and Low-Alloy Steels: The Home Ground

This is where MAG earns its reputation. A 75% argon / 25% CO2 blend gives deep penetration, a stable arc and clean bead appearance on plain carbon steel, and handles low-alloy and high-strength grades without drama. Bump toward 100% CO2 for heavy sections where you want more burn-in and don’t mind extra spatter.

The active gas does real work. Oxygen released in the arc lowers surface tension so beads wet out and tie in cleanly. That’s why Argon/CO2 combinations are preferred where millscale is an unavoidable welding condition — the arc cuts through oxides that would sabotage an inert-gas process.

Stainless Steel: Keep the CO2 Low

Stainless is MAG-friendly, but only with the right mix. Carbon pickup is the enemy: too much CO2 feeds carbon into the weld, promoting sensitisation and corrosion. The fix is a low-CO2 mix — around 2.5% CO2 in argon — which keeps carbon pickup minimal while still giving enough arc stability for spray and pulsed transfer. Tri-mix blends (argon with small amounts of CO2 and helium) run hotter for better penetration on austenitic stainless.

Aluminium and Non-Ferrous Metals: Switch to True MIG

Here’s where MAG stops. MAG welding produces an intensely hot arc that can split CO2 into carbon monoxide and oxygen, causing partial oxidation of the pool. On steel that’s tolerable. On aluminium it’s a disaster — one reason MAG isn’t used for light aluminium alloys.

Aluminium is the textbook true-MIG application, running pure argon (up to about 10–12 mm) and argon-helium blends for thicker sections, with no active component at all; oxidising gas attacks aluminium aggressively. Our guide to DC welding aluminium covers the setups that work. Copper, nickel alloys and titanium share the rule: inert gas only.

Coated, Dirty and Galvanised Steel

MAG tolerates a lot, but it can’t rewrite chemistry. Rust, oil, paint and heavy millscale release contaminants into the arc, causing porosity, spatter and erratic transfer. Galvanised steel is the classic trap — its zinc coating vaporises at arc temperatures, producing fume, porosity and inconsistent beads unless you grind the coating back and improve ventilation. Clean to bright metal whenever the joint matters.

Why MAG Stays Indoors

MAG is mostly an indoor process. It depends on a shielding gas that wind can disperse, so a stiff breeze outdoors strips the shield and leaves porosity. That’s the opposite of self-shielded flux-cored welding, where flux inside the wire generates its own protective gas and shrugs off wind. Outdoors, build a windbreak or switch process.

Use this table as a starting reference; your machine, thickness and travel speed will shift the numbers.

Why MAG Lassen Boosts Productivity: Benefits, Cost and Real-World Applications

If you run a fabrication business, MAG lassen is a productivity argument as much as a welding one. The same semi-automatic wire feed that makes MIG so easy to teach also supports high deposition rates, and because the arc burns under an active gas, that extra metal lands with deeper fusion than a pure-argon MIG arc typically manages. For shops bidding work by the metre, that combination is the whole game. It is also why the phrase travels so well: a Dutch or German foreman shouting MAG lassen is asking for a fast, cost-effective process, not a hobby machine.

Deposition Rate, Penetration and Fewer Passes

Continuous wire means no stick changes, no stub loss and no stopping to chip slag between passes. Higher current with a CO2-rich gas drives more metal into the joint per hour, and the deeper penetration of active shielding reduces the number of passes needed on thick plate. In practice, a well-tuned MAG setup on 6–10 mm plate often runs a single pass where a stick welder would need two or three, and the operator keeps both hands moving instead of burning electrodes. Fewer passes means less interpass cleaning, less distortion control and lower labour per metre — provided you keep your contact tip and liner in good shape.

Because GMAW processes deliver such high welding efficiency, they dominate steel structures, bridges, automobiles, motorcycles, construction machinery, ships, offshore structures, pressure vessels and pipelines. In the US, GMAW accounts for roughly 34% of welding by material consumed, behind shielded metal arc welding at about 45% — and its share keeps growing on production lines where speed is measured in seconds.

Why the Gas Bill Is Lower

Pure argon is expensive, and argon-heavy MIG mixes push cost up further. Replacing much of that argon with CO2 keeps the arc stable while cutting shielding gas cost. Active gases also improve penetration, suit thicker material, and reduce porosity risk, giving stronger, more reliable joints with less rework — a saving that rarely shows on the gas invoice but always shows in the scrap bin. On long structural runs the difference compounds fast.

Industries That Live on MAG

• Structural steel and infrastructure — beams, columns and bridge work.
• Automotive and transport — bodies, chassis and maintenance.
• Shipbuilding and offshore — plate and long structural runs.
• Pipe and pressure work — pipelines and vessels.
• Heavy equipment and general fabrication — routine job-shop output.

MAG shows up across pipe welding, manufacturing, automotive maintenance and production, construction and infrastructure because it is simply productive.

Automation, Duty Cycle and Filler Efficiency

Both GMAW variants adapt easily to robotic manufacturing and hard automation, which is why MAG lines run unattended through long shifts. A wire spool feeds continuously, so duty cycle stays high and filler efficiency is excellent compared with stick electrodes — you pay for wire, not for stubs. See how far this goes in robotic submerged arc welding, the heavy-duty cousin of the same idea.

The Trade-Offs You Still Pay For

MAG is not free speed. The learning curve is real: reading the arc and tuning wire feed takes practice, which is why a deliberate welding practice routine matters. CO2-heavy mixes throw more spatter, costing cleaning time. And fume exposure rises with higher currents.

MAG Welding Safety and Fume: The Hazards Nobody Warns You About

MAG lassen feels tame. The wire spools quietly, the arc hums, and there’s no slag to chip. But that active shielding gas and the hotter, more aggressive arc do something quiet and cumulative: they generate fume that many welders treat far too casually. If you weld MAG daily in a shop with the door open and a box fan behind you, you are not ventilating the fume — you are stirring it around your face.

What’s Actually in MAG Fume

Welding fume is a complex cocktail of metal oxides formed when the filler and base metal vaporise in the arc and condense into ultra-fine particles. In MAG welding the usual suspects are iron, manganese, and — when you weld stainless — hexavalent chromium and nickel. The shielding gas itself contributes too: CO2 and high heat generate carbon monoxide and ozone, which are gases you can’t see.

Manganese is the one to respect. The ACGIH threshold limit value is 100 µg/m3 for total (inhalable) manganese and just 20 µg/m3 for respirable manganese. In one NIOSH study, 70 welders exceeded the total Mn TLV and 29 exceeded the respirable limit — quiet overexposure is common, not rare. Prolonged manganese fume exposure can produce Parkinson’s-like neurological symptoms, and prolonged welding fume exposure is linked to lung damage and cancers of the lung, larynx and urinary tract.

Stainless is a different problem. OSHA regulates hexavalent chromium, Cr(VI), under 29 CFR 1910.1026 and 1926.1126, with a permissible exposure limit of just 5 µg/m3 as an 8-hour time-weighted average — one of the tightest limits in industry. That tiny number is why stainless MAG demands extraction, not just a draughty shop.

The Invisible Hazard: Asphyxiation

Shielding gases don’t just shield. Helium, argon and carbon dioxide displace oxygen, and in a confined space — a tank, a vessel, a pit, a shipping container — they can turn a breathable atmosphere deadly in minutes without any smell or warning. Carbon monoxide can also form during the process and add its own asphyxiation risk. The NIOSH pocket guide is blunt about it: never weld in a confined space without atmospheric testing and forced ventilation.

Controlling Fume Before You Inhale It

Respirators are the last line of defence, not the first. Engineering controls come first.

• Local exhaust ventilation (LEV) — a hood or extraction arm placed close to the arc captures fume at the source. Keep in-line duct velocities at 3,000 feet per minute or more so particles don’t settle in horizontal runs. Good shop layout builds this in from the start.
• Fume extraction guns — built-in suction at the nozzle is ideal for high-production and stainless work, where Cr(VI) and Mn matter most.
• Positioning — keep your head out of the plume, not bent over it. Fixed hoods and curtains stop fume drifting into the next bay.
• Respiratory protection — a powered air-purifying respirator (PAPR) for stainless, galvanised or confined work where LEV can’t keep up.
• Clean first — strip paint, oil, solvents and galvanising before you strike an arc. Heated coatings create extra toxins you never planned to breathe.

NIOSH research shows why process choice matters: fume generation ranged from about 390 mg/min for spray-mode GMAW down to below 40 mg/min for Cold Metal Transfer, and rates for stick welding were roughly double the next-highest process. MAG sits high on that list — its higher heat and reactive gas make fume control more important than many welders assume.

Finally, don’t forget the arc itself. MAG throws intense UV and infrared radiation that can burn skin and eyes, so cover up and wear proper shade lenses. Our guide to protective eyewear for welding explains lens selection, and if you’re pregnant or welding near someone who is, the risks and safety guide is worth a read. Build the habits early with solid welding practice, and fume control becomes automatic rather than an afterthought.

Common MAG Welding Mistakes and How to Fix Them

Most MAG defects aren’t mysteries — they’re feedback. The arc is telling you which variable drifted out of balance. Read the symptom, trace the root cause, and adjust one thing at a time.

Porosity Is Almost Always a Gas-Shield Problem

When beginners see pinholes in a bead, the instinct is to blame the wire. In reality, most mystery porosity traces back to the gas shield rather than the wire: wrong flow rate, a dirty or clogged nozzle, wind dispersing the shield, or too-long stickout. Check these first, before you touch the wire. A spatter-clogged nozzle or a worn contact tip disturbs gas flow as much as any regulator error, so keep spares on hand and read up on contact tip welding maintenance and troubleshooting. If you’re welding outdoors or near a shop fan, the shield is being blown away and no wire swap will save you. Use a windbreak and bump flow into the 12–18 CFH range for indoor work.

Treating Wire-Feed Speed and Amperage as Separate Dials

On a MAG machine, wire-feed speed (WFS) largely sets the current — they’re linked, not independent, as The Fabricator explains. Turn WFS up and amperage rises; you can’t set them like two unrelated knobs. The second classic error is swapping wire diameter without resetting the feed speed. A thinner wire burns off faster per inch fed, so the whole setup goes wrong even if voltage and gas stay identical. Changing from 0.035 to 0.030 inch wire means recalibrating WFS from scratch.

Matching the Defect to Its Cause

Too little voltage for a given WFS makes the wire stub into the puddle and pop. Too much voltage produces excess spatter and a flat, undercut bead. Spatter itself is commonly caused by WFS or voltage set too high, though low voltage causes it too by stubbing. Lack of fusion — “cold lap” — usually comes from voltage or WFS too low, or travel speed too fast; increase voltage or WFS and keep the arc on the leading edge of the pool.

Burn-through is a heat problem: too much current for the material thickness, or travel too slow letting the pool grow. On thin sheet, drop WFS and speed up, or switch to a short-circuit transfer and smaller wire. Cold lap at the toes of a fillet happens when the arc rides ahead of the molten pool instead of pushing into the joint.

Read the bead shape while you weld. A high crown with a narrow bead points to low voltage or low WFS. A wide, flat bead with undercut points to high voltage or travel too fast. A wandering, unstable arc often means long stickout, a bad ground, or dirty, coated, or rusty metal.

If gasless wire is your setup, polarity errors look like MAG defects but have different fixes; see polarity for flux core welding. When in doubt, stop, inspect, and practice deliberately — a structured routine beats guesswork, as covered in our welding practice guide for building real skills.

Practical MAG Tips, a Practice Routine and the Bottom Line

Everything in this guide comes down to one idea: welding variables relate to one another. Amperage, wire-feed speed (WFS), voltage, travel speed and shielding gas work together to determine weld performance. Change one, and the others shift. So the fastest way to improve is deliberate practice, not guesswork on a real job.

Welders everywhere fight the same five controls, and the experts agree: get the relationship right before chasing a perfect bead. The Fabricator and ESAB both frame setup as a balancing act, not a list of magic numbers.

A Simple Practice Routine

Start on scrap plate before you strike an arc on anything that matters. Follow a disciplined test-coupon routine:

1. Tune WFS first for fusion and deposition rate.
2. Then set voltage for wetting and arc length.
3. Adjust travel speed last, listening for a steady crackle like frying bacon.

Run beads, cut them, and read the cross-section. Look at the penetration profile, toe wetting and spatter level. Then change only one variable at a time so you actually learn what each control does. Build muscle memory for a consistent stickout and travel speed. Many semi-automatic operators settle around 10–12 IPM, while experienced welders run 18–20 IPM. Repetition on scrap is the fastest route to real skills. Compare your coupons against reference photos of good and bad MIG welds so your eye learns what proper wetting looks like.

Pro Tips That Save Time

• Set gas flow at the nozzle: steel MIG/MAG runs around 25 CFH, aluminum 30–40 CFH.
• Keep contact tips and nozzles clean and inspect them for wear; it prevents most gas-shield defects. Most trace back to a dirty nozzle or a worn contact tip: spatter bridges the nozzle, turbulence pulls in air, and porosity follows.
• Push rather than drag for smoother, flatter beads with better shielding; drag only when you need more penetration.
• Prep and clean joints between passes. Remove mill scale, oil and spatter so each pass wets properly.
• On thick plate, run hotter root passes and cooler cap passes to cut grinding and speed structural work.
• Keep a notebook of the settings that worked for each thickness and material.

MAG for Steel, MIG for Aluminum

The decision is simple. MAG, with its active CO2 or argon mix, is the right choice for carbon steel, stainless and most ferrous work. MIG, with inert gas, is the right choice for aluminum and other non-ferrous metals. Use the wrong gas and you fight the arc all day. If you run out of shielding gas, switch to gasless MIG (flux-cored welding) rather than welding with a bare wire.

The Bottom Line

MAG lassen looks like MIG, but that active gas changes penetration, spatter and bead shape. Master the gas mix, the transfer mode and your settings, and you gain a fast, versatile process for steels. Do the reps on scrap, tune one variable at a time, and the results become repeatable and code-compliant. Nothing here is secret; it is repetition with attention. The welders who make it look easy simply practised deliberately. Pick up a coupon, dial it in, and earn that steady crackle for yourself.

Frequently Asked Questions

Is MAG lassen the same as MIG welding?

They are the same family of process — Gas Metal Arc Welding (GMAW) — but MAG uses an active shielding gas (such as CO2 or an argon/CO2 mix) that reacts with the arc and weld pool, while MIG uses inert gases like argon and helium. The equipment is essentially identical, so you can run MAG on an ordinary MIG welder simply by changing the gas and re-tuning the settings.

What does ‘lassen’ mean in MAG lassen?

‘Lassen’ is the Dutch (and colloquially German-influenced) verb meaning ‘to weld’, so ‘MAG lassen’ translates to MAG welding. MAG itself stands for Metal Active Gas, ISO 4063 process number 135, which is used primarily for welding carbon, low-alloy and stainless steels.

Which gas should I use for MAG welding steel?

For general fabrication on carbon steel, an 80/20 to 75/25 argon/CO2 mix is the standard starting point because it calms the arc and reduces spatter while enabling spray transfer. Use 100% CO2 when you want maximum penetration and lowest gas cost on thick sections and can tolerate more spatter and cleanup.

Can I use MAG for stainless steel?

Yes, but you must use a low-CO2 mix, typically around 97.5% argon and 2.5% CO2, or a tri-mix with helium, to minimise carbon pickup and protect corrosion resistance. Never use a standard 18% CO2 carbon-steel mix on stainless if corrosion performance matters, because it can sensitise the heat-affected zone.

Why does MAG welding not work well for aluminium?

Aluminium requires a genuinely inert shield such as pure argon or an argon-helium blend. The active, oxidising gases used in MAG react aggressively with aluminium and would attack the metal and aggravate the oxide problem, so aluminium welding belongs to the MIG branch of GMAW, not MAG.

What is the correct polarity for MAG welding?

The vast majority of solid-wire GMAW and MAG welding uses DC+ (also called DCEP or reverse polarity), with the electrode positive and the workpiece negative. Always confirm the polarity required for your specific wire and process, because flux-cored wires can differ.

Why is my MAG weld full of porosity?

Porosity almost always traces back to the gas shield rather than the wire. Check for insufficient or excessive gas flow, a clogged or damaged nozzle, a long stickout, wind blowing the shield away, or contaminated base metal, and clean or reposition before changing any settings.

Is MAG welding more dangerous than MIG welding?

MAG welding produces more fume and reactive by-products than MIG, and its shielding gases can displace oxygen in confined spaces. Prolonged exposure to welding fume can cause lung damage and cancer, and manganese and hexavalent chromium are particular concerns, so local exhaust ventilation, positioning and respiratory protection matter greatly.

What thickness can MAG welding handle?

With short-circuit transfer, MAG works well on thin sheet from about 0.6 mm up to roughly 5 mm. Switching to spray or pulsed spray on thicker steel plate lets you carry much higher current and deposition, so with the right wire, gas and power source MAG can weld heavy structural sections in multiple passes.

How do I set up a MAG welder quickly?

Start by matching your wire diameter and gas to the material and thickness, set a sensible gas flow, then set wire-feed speed for amperage and voltage for arc length. Run a test coupon in the same joint and position, then tune wire-feed speed first for fusion and voltage second for wetting, adjusting only one variable at a time.

Authoritative Sources & Further Reading

• https://www.twi-global.com/technical-knowledge/faqs/faq-what-is-mig-mag-welding
• https://www.cwbgroup.org/resources/articles/how-is-argon-used-in-mig-welding-and-how-do-mig-and-mag-welding-differ
• https://www.kobelco-welding.jp/images/education-center/pdf/GMAW_5Ed.pdf
• https://www.thefabricator.com/thewelder/article/arcwelding/how-amperage-wfs-voltage-travel-speed-and-shielding-gas-affect-welding
• https://esab.com/us/nam_en/esab-university/blogs/fine-tuning-performance-mastering-mig-welding-machine-settings/
• https://www.osha.gov/sites/default/files/publications/OSHA%5FFS-3647%5FWELDING.pdf
• https://www.osha.gov/welding-cutting-brazing/hazards-solutions
• https://www.cdc.gov/niosh/npg/npgd0666.html
• https://www.cdc.gov/niosh/chemicals/pel88/pell-pages/welding.html
• https://stacks.cdc.gov/view/cdc/199706
• https://stacks.cdc.gov/view/cdc/210292
• https://www.uti.edu/blog/welding/gmaw-mag-welding