How Does MIG Welding Work? A Beginner’s Guide to GMAW

Picture this: Saturday afternoon, a half-finished steel gate frame, and a shiny new MIG welder in the garage. You pull the trigger expecting sparks and a neat bead, and instead you get a hiss, a fat blobby worm of metal, and a puff of orange-brown dust that smells like burnt pennies. That mess isn’t a bad machine — it’s the process telling you exactly what’s happening. To understand why, you need to know what goes on inside a MIG torch in the split second the trigger gets squeezed.

What MIG Welding Is (and What Actually Happens When You Pull the Trigger)

Back to that Saturday garage. The hiss is the shielding gas, the orange-brown dust is oxidised metal, and the fat blobby worm is a wire feed speed that outran your arc. None of that is a broken machine. It is all feedback, and once you can read it, the process becomes predictable.

So, how does MIG welding work? MIG welding is a constant-voltage arc process in which a continuously fed wire acts as both the electrode and the filler metal, while a shielding gas blankets the molten pool to keep air out. The arc between the wire tip and the workpiece melts both the base metal and the wire, and the two merge in the puddle you are watching.

Why It Is Called GMAW, MIG or MAG

The official AWS and ISO name for the process is GMAW, Gas Metal Arc Welding. The everyday names are regional variants, and the real differences are narrow. ISO 4063 lists MIG as process number 131 and MAG as process number 135, and both sit under the GMAW umbrella. MIG stands for Metal Inert Gas, MAG for Metal Active Gas. The only real distinction is the shielding gas: inert mixes such as argon for MIG, and active, CO₂-containing mixes for MAG. Everything else about the machine, the wire and the arc is the same. Americans say MIG almost universally, Europeans tend to say MAG, and you will see both labels on the same equipment. TWI explains the MIG and MAG distinctions in more detail.

Four Things Happening Every Single Second of the Arc

Here is the part that makes people nod along: four separate jobs running at once.

1. The wire is fed. A motor turns drive rolls that push solid wire off the spool, through the gun liner and out through the contact tip at a controlled speed.
2. The wire melts. Arc heat melts the tip of the protruding wire into a single droplet that swells and hangs there.
3. The arc melts the work. The arc heats the workpiece, and the droplet drops into the molten pool, joining filler metal to base metal.
4. The gas shields. A flow of shielding gas pours from the nozzle, displacing air so the white-hot pool cannot react with oxygen or nitrogen.

Take the fourth job away and the weld metal becomes porous and brittle. Take the third away and you have melted wire sitting next to unmelted steel, which is a cold lap. The four jobs are what make the process work at all.

The Complete Circuit

Picture the whole loop: a constant-voltage DC power source feeds the torch through the work lead. The wire runs out of the gun, becomes the live electrode, and the arc jumps from that wire tip to the workpiece. Current passes through the arc, through the molten pool, into the base metal, through the work lead clamp and back to the machine. That clamp is not a formality: it is the return path for every amp you dial in, and where it sits affects arc behaviour. EWI walks through the constant-voltage behaviour that keeps the arc stable and self-adjusting.

Because the machine holds voltage steady and the arc length changes constantly as the puddle moves, the welder is not chasing amperage by hand. The power source meters wire feed, current and gas. What the welder supplies is guidance: angle, speed, position and the decision of when to fill a crater. That is precisely why the process is called semi-automatic. It is automation in the middle of a hand-guided tool.

MIG is the most heavily automated arc process in the world. Fronius describes MIG and MAG as currently the most frequently used welding process, allowing high welding speeds in manual, mechanised and robot-supported applications. Industrial cells weld everything from car bodies to pipe with the same torch geometry you will use in your garage, and the same principle handles stainless, mild steel and, with the right gun and wire, aluminium. Our complete guide to aluminium MIG welding covers the setup that makes that last one work.

One detail worth knowing about the consumable: MIG wire is copper-plated, which resists rusting, improves electrical conductivity and extends contact tip life. It is also why a MIG wire spool looks coppery rather than steel grey.

The Science Inside the Arc: Electricity, Heat and Metal Chemistry

Pulling the trigger starts a process you can actually picture. Every knob on your machine is a direct consequence of something happening at the tip of that torch, and once the arc makes sense, settings stop being magic numbers.

Polarity: why MIG runs on DC+

Nearly every garage MIG gun is wired for DC electrode positive, also called reverse polarity: the torch is positive, the work clamp is negative. The reason is heat distribution. In reverse polarity most arc heat is generated at the workpiece rather than the wire tip, so you get deep penetration into the plate while still melting the filler efficiently. Flip it and the workpiece gets less heat while the wire tip cooks. As the Lincoln Electric GMAW guide notes, GMAW generally requires DC+ (reverse) polarity with the electrode. The exception is self-shielded flux-cored wire, which runs electrode negative because it needs a different heat balance for its own shielding.

Two controls, not four

On a constant-voltage machine the voltage and wire feed dials are not equal partners. Wire feed speed is primary: the more wire you push through the tip, the more the machine raises current to melt it, and that current drives heat input and deposition rate. Voltage is secondary: it sets arc length, and therefore the width and height of the bead profile. ESAB frames it plainly: on constant-voltage machines, wire feed speed controls amperage and therefore heat input and deposition rate, while voltage controls arc length and bead profile.

That is why turning voltage up does not make a hot weld. It makes a longer arc, a wider, flatter bead and a lazier pool. To add heat, move the wire feed speed.

Burn rate versus feed rate

The EWI explanation of MIG current and voltage gives you the mental model worth memorising. For a stable arc, the burn rate, how fast the wire melts, must equal the feed rate, how fast the machine feeds wire. Melt faster than you feed and the wire melts back into the contact tip, giving a stubbing arc that spits and cracks. Feed faster than it can melt and it jams into the pool, the feed stalls and the gun buries itself in the puddle. Most “the welder is broken” complaints are really this balance being off, usually because the voltage does not suit the feed speed and the stickout.

Heat, the pool and the heat-affected zone

Arc heat melts both base metal and filler. The two liquid metals meet, mix and stir in convection currents, then the pool cools and solidifies outward from the fusion boundary, the line where weld metal melted the parent material. Just beyond it is the heat-affected zone, the band of base metal that got hot enough for its microstructure to change without ever melting.

Because MIG travels fast and concentrates heat into a narrow bead, that zone stays small. The CAERT and ISBE welding technology guidance notes that because of MIG’s fast travel speed, the heat-affected zone is smaller than with SMAW, giving less grain growth, less distortion and less loss of temper in the base metal. Coarse grains in the HAZ are a weaker, more crack-prone version of the original steel, so a smaller HAZ is simply a better weld.

Metal chemistry: dilution and clean metal

Molten metal at welding temperature is highly reactive. It grabs oxygen, nitrogen and hydrogen from the air, and those reactions produce oxides, nitrides and trapped gas that later show up as porosity and brittle, weak weld metal. That is why shielding gas keeps flowing for a moment after the arc stops, so the last hot metal stays covered as it cools. Kemppi describes the same mechanism when it explains how atmosphere contamination ruins an otherwise good weld.

Preparation matters for the same reason. TWI notes that with limited deoxidants available in the process, all rust must be removed before welding. Rust is scaled oxide, it holds moisture, and moisture plus heat gives you hydrogen and trapped porosity. Oil and paint burn into the pool as contamination. Clean to bright metal within a couple of inches of the joint and you have solved a third of your welding problems. For aluminium the cleaning step matters even more, which our complete aluminium MIG guide covers in detail.

The last piece is dilution, the deliberate mixing of filler metal into molten base metal. Too much dilution weakens the weld with the base metal’s chemistry; too little leaves hard, cracking filler with no bonding to the parent metal. Wire is chosen to match the base metal’s strength and composition so the joint behaves as one piece of metal rather than two bolted together.

The four variables that shape every weld

Variable	What it controls	If it is too low	If it is too high
Current (via wire feed speed)	Heat input and penetration depth	Shallow bead, cold lap, poor fusion	Burn-through on thin material, heavy spatter
Voltage	Arc length, bead width and height	Stubbing, choppy arc, narrow bead	Long wandering arc, turbulent pool
Contact tip-to-work distance	Wire exposure to the arc and gas coverage	Tip too close, wire melts back into the tip	Tip too far, more spatter, weaker shielding
Travel speed	Heat deposited per unit length	Excess heat, wide convex bead, burn-through	Cold lap, lack of fusion, narrow bead

Hold on to those four variables. Current, voltage, contact tip-to-work distance and travel speed are the whole language of MIG welding, and every setting you dial in and every defect you chase later in this guide comes back to one of them.

The Four Metal Transfer Modes Explained (Short Circuit, Globular, Spray and Pulsed)

The single biggest factor that changes a MIG weld is how the molten metal crosses the arc. The transfer mode isn’t selected from a menu, but is an outcome of arc voltage, welding current, shielding gas composition, and electrode wire diameter. Since most conventional MIG and MAG setups run off a constant-voltage power source, the arc length self-adjusts. As TWI explains MIG and MAG welding, this self-adjusting behaviour is what allows these different transfer modes to exist.

Short Circuit Transfer

Short circuiting is the most common mode for beginners and is often the default for mild steel with a 75/25 argon-CO2 blend. The cycle is rapid: the wire feeds out, touches the molten pool, and shorts the arc. Current spikes, melting the wire back and depositing a droplet into the pool by capillary action. The arc re-strikes, extends again, and repeats dozens of times per second.

With the wire constantly touching the pool, heat input stays low. This makes it ideal for thin material, stainless steel, and all-position work. The sound is a smooth, rapid crackle. According to ESAB, harsh popping means the wire is melting faster than it’s being fed, so the fix is to decrease voltage or increase wire feed speed. For most jobs, .023 or .030 inch solid wire with 75/25 or 80/20 argon blend will cover material from 18 gauge up to around 1/4 inch.

Globular Transfer

Globular transfer sits between short circuit and spray. Droplets are much larger than those seen in spray mode, irregular in shape, and transfer primarily under gravity and electromagnetic forces rather than being forced axially across the arc. This creates a rougher bead with a noticeable amount of spatter.

You’ll see it most often when running 100% CO2 on heavier steel, as the gas doesn’t support as tight or stable of an arc. While still perfectly usable for plate over 1/4 inch where CO2’s penetration is desired, it’s rarely the cleanest option. Typical setups use .035 or .045 inch solid wire with 100% CO2.

Spray Transfer

At higher amperage, the electromagnetic pinch force becomes strong enough to detach very small droplets from the wire tip and accelerate them straight down the axis of the gun. TWI describes spray transfer as metal being deposited by mechanical force at high current, and notes that pulsed currents can be used to achieve the same action.

The tradeoff for this is heat. Spray transfer produces fast travel speeds, deep penetration, a narrow and well-defined bead, and minimal spatter. However, it requires more amperage and gas coverage, and is almost exclusively a flat and horizontal process. For this mode, .035 or .045 inch wire with a 75/25 or 80/20 argon blend is common for plate from roughly 3/16 inch and up.

Pulsed Transfer

Pulsed MIG takes the benefits of spray transfer and tames its heat. Modern inverters alternate between a high peak current, which sprays small droplets across the arc, and a low background current that cools the weld pool between each pulse. This allows for a much lower average current than conventional spray while still keeping droplet detachment consistent.

The result is less spatter, a smaller heat-affected zone, less distortion, and stable control over a much wider range of positions and thicknesses. Many jobs that would burn through in plain spray become manageable, including vertical-up welds. For this versatility, .030 to .045 inch wire with a 75/25 or 90/10 argon blend is used across a range from 24 gauge all the way up to 1/2 inch and beyond.

Some machines take this a step further with a combined arc, pairing a pulsed phase with a short circuit dip phase. As Fronius describes, the pulse provides penetration and heat, while the dip phase cools the pool to make vertical and overhead work much easier to control.

Mode	How the droplet transfers	Typical wire and gas	Best for	Main drawback
Short circuit	Wire touches the pool, shorts, transfers by capillary action, re-strikes	.023 or .030 wire, 75/25 or 80/20 argon blend	Thin sheet, stainless, all-position work	Low deposition rate on thick plate
Globular	Large, irregular drops moved by gravity and electromagnetic forces	.035 or .045 wire, 100% CO2	Heavier carbon steel where CO2 penetration is wanted	High spatter, rough bead, unstable arc
Spray	Small droplets detached and thrown axially across the arc at high current	.035 or .045 wire, 75/25 or 80/20 argon blend	Plate from ~3/16 inch up, flat and horizontal production	High heat input, poor positional control
Pulsed	Peak and background current alternate to detach droplets at low average heat	.030 to .045 wire, 75/25 or 90/10 argon blend	Wide thickness range, including vertical and overhead	Requires a pulsed-capable inverter machine

Equipment Breakdown: Power Source, Wire Feeder, Torch, Gun and Consumables

Most beginners stare at the two knobs on a MIG welder and ignore everything else, so by the time the arc is struck the machine has already made a dozen decisions for you. Knowing the parts turns “my welder is rubbish” into “my contact tip is undersized and my gun cable is kinked.”

A complete MIG setup has seven elements, according to TWI’s guide to MIG/MAG welding: the power source, the wire feeder and hosepack, the torch and cable, the work lead and clamp, the gas supply, the filler wire and the workpiece.

The Power Source: Constant-Voltage DC

A MIG power source is a constant-voltage, direct-current machine. Constant voltage holds arc voltage steady and adjusts current to the wire’s burn rate; direct current makes the workpiece negative (electrode negative, DC-), so roughly two-thirds of the heat lands on the work and MIG penetrates deeply.

Older units step mains voltage down with a transformer and rectify it to DC. Miller’s portable MIG welders are typically DC constant-voltage machines using transformers and rectifiers to modulate line voltage for arc stability and clean arc starts. Inverters chop AC into high-frequency DC instead, and Miller’s basic MIG setup guidance spells out what that changes: less spatter, a more forgiving arc start and the ability to weld thinner material with heavier wire.

Two nameplate specs matter most:

• Duty cycle. The share of a ten-minute cycle the machine can weld without overheating, at a given amperage. Rated 20 percent at 130 amps, it runs 2 minutes on and 8 off; a 60 percent machine is a shop machine. That is why a cheap 115V welder trips a breaker on 1/4-inch plate while a 230V machine sails through.
• Input power and phase. A 115V single-phase machine plugs into a normal outlet and is limited to roughly 130 amps of output. A 230V single-phase shop machine is the jump for heavier plate; three-phase 460V machines belong in production shops and robotic cells.

The Wire Feeder and Hosepack

The feeder is what actually meters the wire: a spool on a spindle plus drive rolls (four on better machines, two on cheap ones) that grip the wire and push it toward the torch at a controlled speed. A motor drives the rolls, and a scale sets feed speed in inches per minute.

Knurled drive rolls grip harder and suit hard, copper-coated wire, while V-groove rolls hold softer wire such as aluminium better and cut the “shaving” on soft wire. The hose pack between feeder and torch holds a liner guiding the wire its whole length; a rusty, kinked or contaminated liner wrecks feeding no matter how good the machine is.

The Torch (or Gun) and Its Consumables

Americans call it a torch, British and European shops call it a gun. A MIG torch is a bent steel gooseneck with four parts inside:

1. Liner. The narrow tube the wire slides through, held by a spiral or nut at the torch neck.
2. Gas diffuser. Behind the contact tip, spreading shielding gas evenly around it. Clogged ports starve gas flow and cause porosity.
3. Contact tip. A copper or copper-plated nozzle the wire runs through, carrying current to the wire. It is sized to the wire and stamped with that size, so a .030 tip may read “.030” or “10-20”.
4. Nozzle. The ceramic or copper outer cup that shapes and directs the gas. Straight nozzles suit flat work; tapered nozzles concentrate gas for narrower beads and positional work.

Copper plating matters because Lincoln Electric notes that copper-plated solid wire improves electrical conductivity and extends contact tip life and arc performance. Plain copper wire is softer and less conductive, so tips wear faster.

Contact Tip to Work Distance

The contact tip-to-work distance, or CTWD, is the gap between tip and workpiece, not the same as stickout, the wire protruding past the nozzle. Too close and the tip overheats into the puddle; too far and the arc is long, unstable and spattery, with gas diluted before it reaches the pool. Keep the tip 1/4 to 3/8 inch from the work.

Work Lead, Clamp, Gas Supply and Workpiece

The work lead and earth clamp complete the circuit. Clamp to the workpiece or an electrically connected fixture, and keep the clamp off rusty, painted or greasy surfaces, which cause arc blow. The gas side is a cylinder, regulator and flowmeter: the regulator drops cylinder pressure to a working level, and the flowmeter shows the litres per minute reaching the torch, so a floating-ball flowmeter beats guessing. The workpiece must be clean, dry steel with mill scale, rust, oil, paint and moisture removed.

Spool Guns and Push-Pull Torches

Soft aluminium wire struggles to push through a long gun cable: it kinks, bird-nests and shaves against the liner. A spool gun is a small self-contained feeder on the torch handle, so the wire travels only inches from spool to tip. A push-pull torch puts drive rolls in front of and behind the wire, gripping rather than pushing it, which makes long feeds stable, and modern 2-in-1 push-pull torches combine feeder and torch in one barrel.

Because aluminium is where this matters most, read up first: the complete practical guide to aluminium MIG welding and how to prep aluminium properly for welding. For thinner or cosmetic work, aluminium flux core welding sidesteps the gas supply entirely.

Choosing a Wire Diameter

Wire diameter dictates your settings and the material you can handle: .025-inch wire suits 24-gauge material, while .030-inch deposits faster and handles 1/8 to 1/4 inch.

Wire diameter	Typical material thickness	Notes
.023 (0.6 mm)	24 to 18 gauge sheet	Thin sheet; needs fine control
.025 (0.6 to 0.7 mm)	24 gauge up to 1/8 inch	Easiest all-rounder for beginners
.030 (0.8 mm)	1/8 to 1/4 inch	Most common general-purpose size
.035 (0.9 mm)	1/4 to 1/2 inch	Heavy plate and production work
.045 (1.2 mm)	1/2 inch and thicker	Structural and thick-section work

Match the liner to the wire. Liners are colour-coded by diameter, so a red .030 liner in a .035 machine will bind and cause feeding problems. When in doubt, change the whole front end: liner, contact tip, gas diffuser and nozzle.

Shielding Gas: The Variable That Decides Whether Your Weld Is Sound

Gas isn’t an accessory for MIG welding, it’s the process. Without it, even the best machine settings and technique won’t save your weld. As TWI explains, MIG and MAG welding rely on a gas supply to shield the arc, unlike stick welding which uses flux. That gas directly affects arc stability, metal transfer, weld profile, penetration, and spatter, making it just as important as voltage.

Why Molten Steel Needs a Gas Blanket

When steel reaches welding temperatures, it actively reacts with oxygen and nitrogen from the air. Oxygen creates oxides that can become trapped or expelled from the pool, whilst nitrogen dissolves into the weld metal. Together, they create a brittle, crack-prone bead. A shielding gas blanket simply blocks that reaction from ever happening.

The defects that follow are very specific. Porosity leaves trapped gas holes throughout the weld. Excessive spatter is caused by oxidised particles shooting out of the arc. Brittle weld metal can look perfectly sound, yet snap under load. On stainless steel, impaired corrosion resistance is a particular concern, as trapped oxides can become rust points later on.

The Gases and Mixes You Need to Know

Choosing the correct mix comes down to balancing penetration, spatter, appearance and cost. The breakdown below covers the most used options for MIG and MAG work:

Gas or Mix	Behaviour	Best For	Main Drawback
100% CO2	Deep penetration, aggressive arc, rougher bead	Heavy carbon steel, structural work	Most spatter out of the common options
75% Ar / 25% CO2	Balanced arc with added CO2 for penetration and stability	Most mild steel fabrication, wide range of thicknesses	More spatter than higher-argon blends
80/20, 85/15, 90/10 Ar/CO2	Smoother bead with less spatter	Thin sheet, stainless, cosmetic welds	Reduced penetration at higher argon content
100% argon	Very stable and clean with no oxidation	Aluminium, copper, titanium, some stainless. See our aluminium MIG welding guide for specifics	Poor penetration and unstable on plain carbon steel
Argon / helium mixes	Broader, hotter arc with increased heat input	Stainless steel, aluminium, thicker stainless sections	Expensive and can be sluggish on thin material

For thinner carbon and mild steel, ESAB highlights an 82% argon / 18% CO2 blend. When run in short-circuit transfer, it can provide the lowest spatter, the best bead appearance and improved burn-through prevention, often without needing to drop wire speed drastically.

Flow Rate, Timers, Leaks and Wind

Even the correct mix will fail if the flow rate is off. As a general rule, ESAB recommends around 10 to 12 litres per minute for typical wire diameters in a sheltered area. If porosity is present or there’s any breeze, raise this to roughly 15 LPM. Going above 15 creates turbulence, which pulls outside air into the gas column and breaks your shield. Imperial values sit around 25 to 40 CFH for the same window.

Two timer settings are easy to overlook. Pre-flow ensures gas is established before the arc strikes, protecting the very start of the weld. Post-flow keeps a blanket over the hot, oxidising metal as it cools, which is especially important for stainless and aluminium. Check for leaks at the regulator, hose connections, gun body and gas diffuser. A quick test is to block the nozzle, increase the flow and watch for any drop on the flowmeter.

Outdoors is the greatest enemy to a stable shield. As noted by Kemppi, drafts are a core drawback of MIG and MAG welding. A wind screen can help, but a fully sheltered position is always better. For sustained outdoor repairs, this is precisely why self-shielded flux-cored wire, much like stick welding, is often the more reliable choice.

Setting the Machine: Wire Feed Speed, Voltage, Gas and Polarity

A beginner staring at the front panel of a MIG welder sees a wall of labels: WFS, voltage, wire size, gas, polarity, inductance, spot mode. It looks like a puzzle with no right answer. It is not. On mild steel with solid wire and a 75/25 gas mix, you can go from a cold machine to a decent bead in ten minutes if you set things in the same order every time.

The trick is to stop treating the panel as a list of independent settings. On a constant-voltage machine, wire feed speed is the master control and voltage is the trimmer. Get that relationship straight and the rest follows.

Step 1: Let Material Thickness Set the Current

Start with the steel in front of you, not the machine. Miller’s rule of thumb is that each .001 inch of thickness requires 1 amp of output, so .125-inch plate wants roughly 125 amps and 3/16-inch plate about 180 amps. It is a starting point, not a law; joint design, position and travel speed will nudge it, but it stops you guessing. Miller’s guide to setting MIG parameters walks through the same logic step by step.

Step 2: Pick the Wire Diameter

Now match the wire to amperage. .030-inch is the sweet spot for most home and shop work, handling everything from 1/16-inch up to 1/4-inch. .023 and .025 keep heat low on thin sheet, .035 and .045 suit heavier plate. If your machine’s wire speed scale cannot deliver the speed your amperage needs, go to thinner wire rather than a machine that cannot keep up.

Step 3: Set the Wire Feed Speed

With .030-inch wire, Miller’s chart method is simple: multiply the amperage by 2 to get wire feed speed in inches per minute. So 125 amps means about 250 ipm. Everything follows from that one number: higher WFS equals higher current equals more heat input and higher deposition rate. Wire feed speed is a heat dial in disguise.

Step 4: Set Voltage for Arc Length

Voltage controls arc length and therefore bead shape. ESAB notes that higher voltage gives a longer arc and a flatter, wider bead, while lower voltage gives a shorter arc, a narrow bead and deeper penetration. Practically: if the arc stubs into the workpiece, increase voltage; if it is erratic and burns back at the tip, reduce it.

Here is the part beginners miss. Wire feed speed and voltage are not independent. On a constant-voltage machine the wire feed speed drives current, and the voltage you dial in holds that arc length steady. Turn WFS up and you usually need a little more voltage to keep the arc from stubbing; turn voltage down too far and the wire jams into the pool.

Polarity: DCEP for Solid Wire

Solid MIG wire runs DC electrode positive (DCEP), the setting on nearly every modern machine and usually marked “MIG” on the mode switch. Self-shielded flux-cored wire runs electrode negative instead, because the tube and its flux supply their own shielding. Get it wrong and you get a sputtering, foul-smelling mess. If you are running self-shielded flux-cored wire, see how aluminum flux core welding handles the polarity and feed differences before you start.

Travel Speed: The Fourth Variable

Even with the machine frozen on one setting, moving the gun faster changes heat input, because heat per inch of weld drops as travel speed rises. Keep travel speed steady, and when something looks wrong, change one variable at a time. Change two and you will never know which mattered.

For vertical and overhead work, ESAB recommends reducing wire feed speed and voltage relative to flat position, and favours pulsed or short-circuit transfer, since both control the pool better than plain spray. None of these numbers travel well to aluminium, where feedability becomes the deciding factor; the aluminum MIG welding guide covers that side in detail.

How to Read the Bead

• Good weld: a uniform bead, slightly convex or flat, with even ripples, clean fusion at the toes and no spatter.
• Voltage too high: poor arc control, inconsistent penetration, a turbulent pool that keeps spitting, plus a wide flat bead.
• Voltage too low: stubbing, a harsh buzzing sound, poor fusion and a narrow, lumpy bead.
• Wire feed speed too high: excessive heat, burn-through on thin material, a fat convex bead and heavy spatter.

Material Thickness	Amps	WFS (.030 wire)	Voltage	Notes
1/16 in	~60 A	~120 ipm	17-18 V	Short circuit, thin sheet
1/8 in	~125 A	~250 ipm	18-19 V	Good all-round setting
3/16 in	~180 A	~360 ipm	20-21 V	Spray or globular
1/4 in	~250 A	~500 ipm	22-24 V	Heavy plate, needs a 250 V machine
3/8 in	~375 A	~750 ipm	24-26 V	Shop machine territory

Starting points for .030-inch solid wire with 75/25 gas, not a substitute for your machine’s own chart and manual.

Technique: Gun Angle, Travel Speed, Stickout and Position

Machine settings tell only half the story. Two welders can run identical amperage, voltage and wire feed speed and still produce a clean bead one way and a lumpy caterpillar the other. The difference is technique, and nailing these four clears up many defects in the MIG troubleshooting guide.

Gun Angle and Work Angle

The work angle is the angle the joint presents; the gun angle is how far you lean the torch off it. Miller recommends 0 to 15 degrees of tilt, with the arc aimed at the leading edge of the pool. Aim into the pool and the arc pushes molten metal forward; trail it and you drag metal behind you, widening the bead and lowering penetration.

Guides from Miller Electric put lack of fusion down mainly to improper gun angle or incorrect travel speed, so fix those before touching the machine knobs. Miller also lists excessive gun angle and overextended wire as causes of porosity, because a steep angle blows the arc across the pool surface and draws in air.

Push or Drag?

Push means the gun leads the puddle, tilted away from travel direction. Drag means the gun follows it, tilted into the puddle.

• Flat and horizontal fillets: drag keeps the puddle small and improves your view of the toe.
• Vertical and overhead: push gives more control, since the arc pushes molten metal back into the puddle instead of letting gravity run it out.
• Thin sheet flat: push cuts burn-through risk on light material.

Whichever you pick, commit: switching mid-weld changes bead shape and heat input without you noticing.

Travel Speed

Travel speed interacts with heat input constantly. Too fast gives a narrow cold lap: the wire lands on metal only just melted, so the puddle never merges with the base metal and the bead overlaps the toes instead of fusing to them. Miller notes that increasing travel speed helps prevent cold lap.

Too slow floods the pool, leaving a wide, flat, convex bead with poor penetration, and on material under 1/8 inch (about 12 gauge) you burn straight through. Beginners crawl along thin edges, so slow the parameters and move faster. Kemppi puts it neatly: excessive current or too low a welding speed floods the pool ahead of the arc, meaning insufficient penetration.

Stickout Length

Stickout is the length of unconsumed wire sticking out past the nozzle. Use no more than about 1/2 inch of wire extended past the nozzle. More extension burns more wire into spatter and pushes the gas column away from the pool, so shielding coverage suffers. Short stickout gives a tighter bead and cleaner metal. A wire poking out far is fed but never melting fast enough, and the fault is usually on the machine side: a worn liner, a slipping drive roll or a gun dragging on the work.

Weaving, Puddle Control and Crater Fill

For flat and horizontal fillets, a simple up-and-down or circular weave spreads heat into the legs of the joint. Weave slowly and keep the arc on the leading edge of the puddle. Puddle control means watching the pool: a small, tight, glossy puddle means your heat is right, while a large, dull, flat one means you are about to flood or burn through, so speed up or back off the parameters.

Do not snap the trigger off at the end of a run; that leaves a deep crater that contracts as it cools and cracks. The FAA advisory circular on aircraft maintenance welding notes that crescent cracks occur at the end of a weld run when the pool is not properly filled, which is why crater fill is standard practice. Crater fill ramps wire feed down and voltage up as you release the trigger, keeping the arc alive long enough to fill the crater; you can also feather the trigger manually at the end of the pass.

Between passes, grind out spatter and remove the oxide layer so the next pass fuses to fresh metal; skip it and you get lack of fusion that looks like a settings problem.

Tack Welding Technique

Tacks hold the parts in place, and bad tacks cause bad welds. Tack at the corners or ends of the joint, not the middle, so you can check fit before committing. Keep tacks small, use slightly lower heat than your final pass, and put them where they can be ground out or buried in the weld. Tack both sides of a square tube frame so the joint does not shift as it cools, then chip the tacks apart and re-fit if needed.

Worked Example: A 3/16-Inch Mild Steel Square Tube Frame

Four pieces of 3/16-inch (about 5 mm) square tube, two 36-inch and two 24-inch, forming a simple rectangular frame.

1. Joint prep. Cut square, deburr and bevel a plain butt, then clean off mill scale, oil and rust. Dirty structural tube can be run as flux core welding, though a square tube frame still calls for MIG control.
2. Fit-up. Clamp and tack with the frame square, checking diagonals first. A frame out of square stays out of square.
3. Flat welds first. Tack the frame on a bench, top side up. Set parameters for 3/16-inch steel on .030-inch wire with a 75/25 mix, then use drag technique, the gun at about 10 degrees, at a steady travel speed around the perimeter.
4. Vertical and overhead. Flip the frame for vertical joints and switch to push with a slight upward angle. Overhead, set parameters low (less wire feed speed and voltage than on flat), use push, and work in short passes so the pool stays small.
5. Clean and inspect. Grind tacks out, dress the beads and check for undercut, cold lap and cracks before painting.

One more thing to carry forward: if the arc drifts sideways or pushes the bead, that is arc blow, fixed by moving the earth return clamp, keeping the arc short, lowering current, or angling the gun against the blow.

Troubleshooting: Reading the Defect and Fixing the Root Cause

Most welding defects are not mysteries. They are messages, and reading them saves scrap metal and whole afternoons.

Welding imperfections are classified in ISO 6520-1: any discontinuity in the weld metal or a deviation from the assumed weld geometry. Acceptable limits come from weld class in ISO 5817, which grades joints B (strictest), C and

Troubleshooting: Reading the Defect and Fixing the Root Cause

Most welding defects are not mysteries. They are messages, and reading them saves scrap metal and whole afternoons.

Welding imperfections are classified in ISO 6520-1: any discontinuity in the weld metal or a deviation from the assumed weld geometry. Acceptable limits come from weld class in ISO 5817, which grades joints B (strictest), C and D (most forgiving). Grade C suits general mechanical work, grade B demanding production. A flaw you shrug off on a gate frame can still fail inspection on a certified job.

Porosity

Porosity is among the most common MIG welding defects: gas trapped in the weld metal instead of escaping, as Miller Electric describes. It shows as round holes, ragged cavities or orange-peel pitting, and looks like sponge on a fracture.

Cause	What to check
Flow	Ball floating at your set rate; cylinder gauge matching the regulator. Full at the regulator, empty at the wand, means a downstream leak or restriction.
Leaks	Pinholes in the hose and failed regulator O-rings steal shielding gas.
Drafts	An open garage door strips the gas blanket off the pool in seconds. Hang a curtain or screen.
Nozzle	Too small a bore cannot feed the arc at high amperage, and spatter chokes it. Clean with a comber or brass brush.
Contact tip	Recess it a few millimetres behind the nozzle end. A proud tip lets gas swirl the arc.
Base metal	Oil, paint, rust, moisture and cutting fluid under the bead gas out as they vaporise. Clean to bright metal.
Wet cylinder	A cylinder stored in a damp shed carries moisture into the gas, showing as fine dispersed porosity.
Gun angle and stickout	Excessive angle distorts the shield; wire too far past the nozzle pushes the arc out of the blanket.

Aluminium has its own list, since the oxide re-forms instantly. Our guide to aluminium cleaner for welding covers the prep steps that make the difference.

Lack of Fusion and Cold Lap

Lack of fusion means the weld metal never bonded to the base metal; cold lap is the milder cousin, where molten filler rides over the cold joint without melting in. Both look fine on the surface and split open in a bend test. Causes are heat and geometry: travel too fast, or a gun angle that pushes the arc off the leading edge. Kemppi’s fixes: clean the joint faces, weld vertical-up so the pool has time to flow into the joint, use a shorter arc with less voltage, and raise heat input.

Undercut

Undercut is a groove melted into the base metal at the toe of the bead, and it acts as a stress riser. It comes from too much current, a long or high-voltage arc, or too much travel angle. Bring the current down, trim voltage to shorten the arc, and keep the gun over the joint instead of trailing off to one side.

Burn-Through

Burn-through is melt-through of the base metal, usually on thin sheet: a hole opens and molten metal drops through. It is excess heat. Drop amperage, drop wire feed speed to match, and speed up travel. On very thin material use smaller wire in pulse or short-circuit mode, and put a backing bar or scrap plate underneath.

Excessive Spatter

Spatter is the small globules of metal that fly off the weld. A little is normal in short-circuit transfer; heavy spatter means energy is going somewhere other than the bead.

• Not enough gas: the arc is not fully enclosed, so droplets detach and oxidise in flight.
• Dirty or rusty wire: feed from the spool end, not the stick end, and keep the spool covered.
• Voltage or travel speed too high: a long, fast arc throws metal off the pool.
• Excessive stickout: keep no more than about half an inch of wire past the nozzle. Longer extension weakens gas coverage.
• Wrong contact tip: size it to the wire diameter and recess it a few millimetres. An oversized tip acts like a nozzle inside the nozzle.

Convex and Concave Beads

Shape faults, not structural faults, but on visible work they separate a professional result from a beginner’s. A convex bead is humped with poor toe fusion, the sign of cold running: not enough heat for the filler to reach the edges. Raise voltage and heat input slightly. A concave bead is scooped in the middle because the pool was too fluid and slow-moving; lower the parameters or speed up travel. A slightly convex bead with clean toes is the goal on most structural work.

Wire Feeding Problems

If the wire will not feed, the arc never starts and everything downstream is confusing.

• Bird-nesting: the wire kinks leaving the drive rolls, from excess feed force, worn or mismatched rolls, or a badly routed liner. Match the groove to the wire and knurl it for soft wire.
• Liner wear: a rough, oversized or flattened bore drags on the wire. Replace liners often; they are cheap.
• Drive roll mismatch: a V-groove roll paired with a knurled roll will not feed soft wire. Replace the pair as a set.
• Slipping gun: a bent or jammed liner, or a kinked cable behind the gun, stops the wire even though the rollers turn.

Aluminium is the worst offender, because soft wire gets scraped rather than gripped. Spool guns and push-pull torches exist for that reason, and our complete aluminium MIG welding guide covers the setup.

Arc Blow

Arc blow is magnetic deflection of the arc to one side of the joint, caused by the self-induced field of the current in the workpiece. The arc lunges at the toe and spits, worse on thicker material or higher current. Move the ground clamp as close to the weld as possible, on the same side as the work lead, and clamp it to the workpiece rather than a distant frame. If you cannot move it, angle the work so the field does not push the arc into the joint.

Cracks

Crater cracks form at the end of a bead as the pool shrinks when you release the trigger; fill the crater with the crater-fill feature or feather in extra wire. Longitudinal cracks along the bead centre are usually hot cracking from restraint, a wide V, high travel speed or excessive heat. Transverse and toe cracks are usually metallurgical or hydrogen issues: dirty or wet base metal, high sulfur or phosphorus in the weld metal, or an unsuitable filler. Check preheat and interpass temperature on restrained joints and match the filler to the base metal.

A Systematic Diagnostic Routine

Randomly changing settings wastes afternoons. Miller’s method is simpler: when a defect appears, identify what changed during the weld, parameter or technique, then work through those variables as remedies.

Check four categories in order, each eliminating a larger set of causes than the next:

1. Gas: flow rate, leaks, drafts, cylinder and nozzle condition.
2. Consumables: contact tip size and recess, liner condition, nozzle bore, wire condition and diameter.
3. Parameters: wire feed speed, voltage, amperage, travel speed, polarity, gas mix.
4. Technique: gun angle, travel angle, stickout, weaving, work position, joint preparation and fit-up.

Ask one question first: what changed? A new cylinder, nozzle size, wire diameter, tip or setting makes that the prime suspect. If nothing changed and the job starts misbehaving, the environment changed, most often weather, gas supply or worn consumables.

One habit saves more money than any setting: cut the defect out properly instead of welding over it. A grinder and flap disc remove it and its causes faster than any parameter change, and give you a clean restart.

MIG vs TIG vs Flux-Cored vs Stick: Choosing the Right Process

No single process is “the best.” Each creates its arc, protects the weld, and feeds filler metal differently, and picking the wrong one wastes time, consumables, and money. Here is how the four most common arc processes compare and where each one earns its keep.

Understanding the Fundamental Differences

The split comes down to the electrode and the shielding method:

• MIG (GMAW) uses a consumable solid wire that acts as both electrode and filler metal, with external shielding gas protecting the weld.
• TIG (GTAW) reverses that: a non-consumable tungsten electrode creates the arc, and filler metal is added separately by hand.
• Flux-Cored (FCAW) uses a tubular consumable wire filled with fluxing agents and deoxidizers. The flux can generate its own shielding gases as it burns, so no external gas is required for self-shielded variants.
• Stick (SMAW) uses a flux-coated consumable stick electrode. The burning flux forms its own protective slag and shielding gas, making the process entirely self-contained.

Head-To-Head Comparison

Factor	MIG (GMAW)	TIG (GTAW)	Flux-Cored (FCAW)	Stick (SMAW)
Electrode/Filler	Consumable solid wire (electrode & filler)	Non-consumable tungsten, separate filler rod	Consumable tubular flux-cored wire	Consumable flux-coated stick electrode
Shielding	External shielding gas	External inert gas (usually Argon)	Internal (self-shielded) or external gas + flux	Flux produces shielding gas and slag
Speed & Deposition	Very fast, high deposition	Slowest, low deposition	Very fast, very high deposition	Moderate, moderate deposition
Spatter	Moderate to high (more than TIG)	Minimal to none	High (especially self-shielded)	Moderate
Positional Capability	Great flat/horizontal, capable with spray/pulsed, trickier overhead	Excellent in all positions with practice	Excellent, especially with all-position flux-cored wires	Excellent in all positions
Typical Materials	Mild steel, stainless, aluminum	Thin steel, stainless, aluminum, exotic alloys	Mild and carbon steels, structural work	Mild steel, carbon steel, some cast irons
Learning Curve	Easy for beginners	Most difficult	Moderate	Moderate, with slag removal to learn
Cost Per Metre	Low to moderate	Highest	Low	Very low
Typical Applications	Fabrication, automotive, and production work	Cosmetic welds, pipe, and thin gauge work	Structural steel, repairs, and outdoor jobs	Construction, field repairs, and rusty/dirty steel

When To Choose Each Process

As TWI notes, MIG is faster than TIG, meaning shorter production times and lower costs. TIG remains the precise choice for small and thin materials that need a clean, cosmetic bead. ESAB echoes this: MIG is fast and easy to learn, but it lacks TIG’s precision, throws more spatter, and is less effective on very thin material.

On aluminum the split is sharper. For medium-thick aluminum and long welds, MIG is a major productivity boost, but the soft wire is prone to bird-nesting, kinking, and surface shaving, so read the Aluminum MIG Welding: The Complete Practical Guide first. That is exactly why spool guns and push-pull torches exist: they fix wire feedability. For ultra-thin aluminum or cosmetic work, TIG still wins, and prep matters, so using an aluminum cleaner for welding before striking an arc is crucial.

For work outdoors in the elements, flux-cored is king. Self-shielded flux-cored arc welding is used primarily for mild steel applications outdoors and tolerates a strong breeze far better than gas-shielded MIG, making it the go-to on job sites where wind and rust would otherwise ruin a gas shield.

Honest Limits: When Not To Choose MIG

MIG can be operated semi- or fully automatically with no risk of trapped slag, but it is not a cure-all. Its main limitations:

• Thin material: burn-through is a constant risk on very thin sheet without precise parameters.
• Wind sensitivity: any significant breeze disrupts the shielding gas and invites porosity. Flux-cored handles this far better.
• Cleanliness required: MIG is far less forgiving of heavy rust, oil, or paint than stick or self-shielded flux-cored.
• Precision: less precise than TIG for intricate or cosmetic welds, with more spatter to clean up.
• Aesthetics: not ideal where a slag-free, show-quality bead is the priority. TIG is usually worth the extra time there.

The smartest approach is versatility, not loyalty. Keep MIG for speed and production, TIG for precision, flux-cored for the elements, and stick for the grimiest repairs. Choosing based on your environment rather than popularity will give you the cleanest and strongest result.

Safety, Beginner Mistakes and Your First Steps Forward

Nothing ruins a first MIG welding project faster than an injury or a house fire, and both are preventable. Get the safety habits down, learn what to practise, and the process goes from mysterious to enjoyable fast.

Protecting your eyes, skin and lungs

Every welding regulation agrees: wear a helmet or hand shield during all arc welding. OSHA 1910.252 is non-negotiable, and it is specific about shade numbers for a reason. The arc throws intense visible light plus invisible ultraviolet and infrared radiation, so a fraction of a second of exposure causes arc eye, a painful corneal inflammation that takes days to heal. The helmet must cover your face, neck and ears.

The OSHA filter shade guide lists gas-shielded arc welding on ferrous materials at shade 12 and gas-shielded arc welding on nonferrous materials at shade 11, but treat those as starting points. Auto-darkening helmets start light and darken as the arc strikes, so many beginners settle on shade 10 or 11 on mild steel for easier visibility. Pick a shade dense enough to see your work with no strain, and make sure the auto-darkening speed beats your trigger pull.

Beyond the helmet, wear flame-resistant cotton, leather gloves and safety boots. MIG spatter is hot and it flies, so snug-cuffed sleeves and a leather apron are the minimum, and skip polyester fleece, because melted spatter sticks to skin.

Fire prevention and the fire watch rule

Welding sparks travel. They land on wood, rags, sawdust extraction systems and the car in the next bay. Welding is the top cause of structural fires in industrial settings, and it is almost always poor housekeeping, not poor skill.

OSHA 1910.252 is clear: remove combustible material before you start, keep fire extinguishers available and working, and designate a fire watch whenever appreciable combustible material lies within 35 feet (10.7 m) of the work, or wall and floor openings expose combustibles within that radius. The part people forget: the fire watch must be maintained for at least a half hour after welding is completed, because smouldering fires in sawdust and wall cavities routinely take 20 to 30 minutes to catch. The watch needs a working extinguisher and the authority to stop the job.

NIOSH’s welding research flags used drums, tanks and containers. OSHA requires hollow spaces and containers to be vented before welding, and cleaning used drums of flammable material is non-negotiable. Never weld a fuel tank without purging, which means flooding it with an inert gas such as argon or nitrogen to displace the flammable atmosphere while venting the displaced gas away from your breathing zone. Get that wrong and you get an explosion, not a burn.

Fumes, ventilation and manganese

Welding fume is the fine metal oxide particles produced when the arc vaporises the workpiece, and it carries substances that are dangerous over time. OSHA requires local exhaust or general ventilation to keep toxic fumes, gases and dusts below the maximum allowable concentration listed in 1910.1000 (Table Z-1).

Manganese is the one to understand: welding steel releases it into the fume. NIOSH reports that prolonged exposure above 1 mg/m³ may lead to manganism, a Parkinsonian syndrome that mimics Parkinson’s disease, and it also identifies welder’s anthrax, a rare but serious disease linked to metal fume exposure. Confined spaces make it dramatically worse, because there is nowhere for the fume to go, so entry procedures, atmospheric testing and an attendant are mandatory in shipyards and industrial plants.

Exposure limit for manganese	Value
OSHA PEL	5 mg/m³ ceiling
NIOSH REL	1 mg/m³ TWA, 3 mg/m³ STEL
ACGIH TLV	0.02 mg/m³ respirable, 0.1 mg/m³ inhalable

The TLV sits far below the OSHA ceiling, and that ceiling is a legal backstop, not a comfortable workplace. Use a fume extraction arm or local exhaust hood positioned 12 to 18 inches from the arc, and wear a properly fitted respirator if ventilation is poor. The alloy steel welding electrode safety guide applies the same logic to stick welding consumables, and ANSI Z49.1 is why your wire spool warns against use without adequate ventilation.

The ten mistakes every beginner makes

1. No PPE, or the wrong shade. Auto-darkening helmet, shade 10 to 12, leather gloves, FR sleeves.
2. Welding dirty metal. Rust, oil, paint and moisture cause porosity. Grind to bright metal first.
3. Wrong gas mode. A flux-core machine fed a shielding gas hose spatters. Check the setting.
4. Wrong polarity. Solid wire runs DC positive, flux-cored wire DC negative. Read the label.
5. Guessed arc length. Set the voltage, then trim by ear. Long arc sizzles, stubby arc pops.
6. No chipping hammer or brush. Stop, chip, brush, restart. Keep them at the work.
7. Dragging the torch. Guide the gun along the joint, arc on the leading edge.
8. Ignoring gas flow. 10 to 12 LPM indoors, more in a breeze, always pre-flow first.
9. Old paint or galv. Grind back to clean metal, change the nozzle. Galv fumes badly.
10. Rushing the first hour. Practise on scrap coupon metal until a good arc sounds familiar.

Your first steps forward

Work through a deliberate sequence. Start with bead-on-plate: run a straight bead on flat mild steel and learn what a steady sizzle sounds like versus a spitting, crackling mess. Then flat butt welds on 3/16 and 1/4 inch plate, tacking first so you can practise filler control without managing a gap at the same time. Next fillet welds, because vertical-up and overhead fillets are what you are paid for, and only then positional work. Always practise on scrap coupon metal before touching a real project: a 12 inch length of 3/16 inch plate costs nothing and teaches more than a finished gate frame.

Keep the shopping list simple and buy quality where it matters: a 200 to 250 amp MIG welder with a stable constant-voltage power source, a spool gun if aluminium is planned, a solid regulator and flowmeter, .030 inch ER70S-6 wire and decent consumables. Spend on the welding equipment and gas supply essentials rather than a cheap machine with a missing wire feeder, and read the aluminum MIG welding guide first for aluminium, where the gun and consumables differ completely from steel work. Buy safety gear first, then the machine, then the wire and gas.

Once you can lay a consistent flat bead, consider certification. The aluminium welding course breakdown shows how structured training works and what it costs, and AWS credentials such as D1.1 structural steel or D1.2 aluminium are what move welders into better-paid shop work.

Conclusion

So how does MIG welding work? A constant-voltage power source pushes a continuously fed consumable wire through a contact tip, forming the electrode. The arc melts wire and base metal into a single molten pool, shielding gas blankets the pool so air cannot oxidise it, and as you move the torch the pool cools and solidifies into a fusion bond. The machine meters the wire, gas and current; you steer the gun. That is why the process is called semi-automatic. Respect the safety rules, practise on scrap until the arc sounds right, and the rest follows.

Frequently Asked Questions

How does MIG welding actually work, in simple terms?

A constant-voltage power source creates an electric arc between a continuously fed welding wire and the workpiece. The arc melts the wire tip and the base metal, forming a molten pool that fuses them together, while shielding gas floods the area to keep air away from the hot metal. The wire is fed automatically at a set speed, so the welder only has to steer the gun and manage the puddle.

Is MIG welding harder to learn than TIG welding?

No — MIG is generally considered the easiest arc welding process to learn, because the machine meters wire feed, current and gas and the welder only steers the gun. TIG gives finer control and cleaner cosmetic welds but takes considerably longer per weld and requires two-handed coordination with a filler rod. If your goal is thick steel and production work, MIG is the faster path to competence.

What shielding gas should I use for MIG welding mild steel?

For most home and shop mild steel work, a 75% argon / 25% CO2 blend is the standard choice because the CO2 helps stabilise the arc and aid penetration. For thinner sheet where you want less spatter and a tidier bead, 85/15 or 90/10 argon-dominant mixes work well. Pure CO2 is cheaper and penetrates deeply but produces more spatter and a rougher bead.

Do I need shielding gas for MIG welding?

Only if you are using solid wire. Self-shielded flux-cored wire generates its own protective gas from the core as it burns, so it needs no cylinder — which is why it is the standard choice for outdoor and field welding. It does leave a slag layer to chip away, and it spatters more than solid-wire MIG.

What amperage should I use for MIG welding 1/8-inch steel?

The usual rule of thumb is about 1 amp for every .001 inch of material thickness, so 1/8-inch (0.125-inch) steel calls for roughly 125 amps. From there, size your wire to the machine — .030-inch solid wire works well in that range on most 230V shop machines, while .025-inch suits thinner material and lighter welders.

Why is my MIG weld full of porosity?

Porosity means gas got trapped in the weld metal, and in MIG welding it almost always points to the shielding gas rather than the machine settings. Check flow rate at the nozzle, look for leaks in the hose and torch fittings, confirm the nozzle is the right size and not spatter-blocked, keep the wire extension to about 1/2 inch, and shield the area from wind. Dirty or rusty base metal is the other common culprit.

Can you MIG weld aluminum?

Yes, but you need 100% argon and the right hardware. Aluminium wire is soft and prone to kinking and bird-nesting in the feed system, so a spool gun or push-pull torch is usually required. It also conducts heat far more than steel, so you must keep travel speed up and heat input down to avoid melting through the base metal.

Why is my MIG gun spitting wire and making a mess?

That is usually a feed problem, not a welding problem. The most common causes are a worn or wrong-sized drive roll, a mismatched liner, tension set too high, a dirty or rusty spool of wire, or a contact tip that is too small and stripping the coating. Work through the gun from the spool outward: clean the wire, check the drive roll size marking, inspect the liner for burrs, then check the tip.

What safety gear do I need before MIG welding?

At minimum a properly rated auto-darkening welding helmet with the correct shade filter (OSHA’s guide puts gas-shielded arc welding on ferrous work at shade 12), flame-resistant clothing, leather gloves, and safety boots. You also need ventilation or a fume extractor, a fire extinguisher, and a screen if anyone else is working nearby.

Should I learn MIG or flux-cored first?

Learn solid-wire MIG first if you have access to a shop with gas, because the arc is more forgiving, produces no slag and gives you cleaner feedback while you learn puddle control and travel speed. Add flux-cored when you need to weld outdoors or on rusty, dirty structural steel — the technique differs slightly because the drag angle and spatter behaviour are different.