Electric Arc Welding Process: A Complete Guide

The first time most people see an arc weld up close, they are usually standing three metres away from a puddle of glowing steel, wearing a plastic face shield and half-convinced they have made a terrible mistake. That reaction is normal — an electric arc welder melts metal at temperatures far beyond the melting point of steel, throws off sparks, and fills a small shop with a smell that is genuinely unpleasant. But underneath the noise and the glare, the electric arc welding process is one of the most predictable and controllable joining technologies humans have ever built. This guide walks through how the arc actually works, how the five main arc processes differ, how to set up your machine, how to stay safe while doing it, and how to fix the handful of defects that trip up nearly every beginner.

What the Electric Arc Welding Process Actually Is

The first time you watch an arc weld up close, the noise and glare make it look more like metalworking than joinery. Strip away the sparks and you find a simple chain of events: electricity, an arc, and metal that melts and becomes one piece.

Here is the definition. The electric arc welding process is a fusion joining process: an electric arc is struck between an electrode and the workpiece, and the heat of that arc melts the base metal and, where filler metal is used, the filler as well. The molten metal flows together and solidifies as a single continuous joint. Nothing is glued, nothing is pressed together under force, and nothing is melted in a separate pot before it reaches the joint. The base metal itself becomes part of the weld.

That is the whole idea. Every machine, process designation and trick of the trade in this guide is detail layered on one mechanism.

Three Jobs Every Arc Process Has to Do

The American Welding Society organises arc processes around a framework you can see in the AWS codes and standards library. Every process on the market answers the same three questions.

1. Create and sustain the arc. You need a continuous, stable column of plasma between electrode and workpiece, one that survives a moving hand, a moving torch and a part that is not perfectly still.
2. Shield the molten pool from the air. Molten steel reacts badly with oxygen and nitrogen. Protection comes either from a stream of shielding gas (MIG and TIG) or from a flux that breaks down into a protective slag blanket (stick and most flux-cored work). Self-shielded flux-cored wire carries its protection inside the wire.
3. Add filler metal if the joint needs it. Thin sections, wide gaps and load-carrying joints are filled with a consumable electrode or wire that melts into the pool. Plenty of welds need none at all.

The Machine Behind the Arc

An arc welder is, at heart, a transformer or an inverter. Its job is to take your shop voltage and step it into a high, tightly controlled current delivered through two cables: a work lead clamped to your part, and an electrode holder or torch carrying the consumable. That clamp is not decoration. It completes the circuit, and the arc exists because current needs a path back to the source.

That gives you the whole mental model:

• Base metal — the steel or alloy you are joining, which becomes part of the finished weld.
• Filler metal — the consumable electrode or wire that adds material, chosen to match or slightly outrun the base metal in strength.
• Arc — the plasma column carrying the current and doing the heating.
• Slag — the solid waste that floats on a flux-shielded pool and gets chipped off afterwards.
• Shielding — the gas or flux that keeps air away from the hot metal.

One number frames everything. Steel melts at roughly 2,800°F (1,540°C), and the arc itself is far hotter than that. That surplus heat is why an arc welder can cut, braze and join metal in a single pass, and why controlling heat, not controlling the arc, is the real skill the process demands.

Picture it in a two-car garage on a Saturday. Clamp the ground lead to a 3/8 in steel bracket, strike an arc with a 7018 electrode, and the electrode melts into the joint while a slag blanket forms over the puddle. Chip the slag, paint it, done. Swap in a MIG machine and bare wire feeds from the spool as you push the torch, laying a smooth bead with no slag at all. Different consumable, different shielding method, identical physics: electricity, an arc, molten metal, a cooled joint.

What Makes It “Electric”

The name comes from the heat source. In oxy-fuel gas welding, the heat comes from a burning gas flame. In resistance welding, current passes through a clamped joint, which heats up and fuses under pressure. Arc welding takes its heat from an electric arc sustained between an electrode and the work. All three join metal, but only one is defined by electricity running through a plasma column.

It is also not brazing or soldering. Those processes join metal with a filler that melts at a temperature below the base metal’s melting point and wets the surface without melting it. The base metal stays solid, and that changes the joint’s strength, the filler you pick and the heat you are allowed to apply. Air acetylene torch work covers the brazing and soldering side of that fence. OSHA draws the same line in its general requirements for welding, cutting and brazing.

What to Expect From Here

One principle, five standard processes. Stick (SMAW), MIG (GMAW), flux-cored (FCAW), TIG (GTAW) and submerged arc (SAW) all solve the same three problems in different ways, whether you are working in an aerospace fabrication shop or a farm field. Why stick welding still wins so many jobs is really a story about which of those three answers suits the conditions. The rest of this guide covers the process map, the physics a welder actually feels, safety, setup and the defects that trip up beginners.

The Five Main Arc Welding Processes Compared

Which arc welding process should you use? It depends on the material, thickness, position, environment and machine budget. Each of the five core processes solves the same three problems: create an arc, protect the molten pool from air, and add filler metal.

SMAW: Shielded Metal Arc Welding (Stick)

SMAW is what most people picture when they hear “arc welding”: you tap a coated consumable electrode against the work, and it melts as it feeds into the puddle. The coating supplies the shielding atmosphere and adds elements to the weld metal. Because the electrode is a thick, self-contained stick, no gas and no wire feed are needed, making SMAW the most portable process there is. It runs on constant current, works in every position including vertical and overhead, and tolerates dirty, rusted and painted steel better than any other process, so it dominates field repair, structural erection and shipbuilding. The cost is speed: constant electrode changes, a less efficient arc and slag to chip off between passes. It suits jobs where a gas cylinder is inconvenient, as the advantages of stick welding shows.

GMAW: Gas Metal Arc Welding (MIG)

GMAW is the production workhorse. A continuous solid wire feeds automatically from a spool through the torch while shielding gas blankets the arc, keeping air off the molten metal. The wire is usually copper-coated steel; aluminium and stainless exist too. GMAW needs external gas, typically argon, carbon dioxide or an argon/CO2 blend, and runs on a constant-voltage source. For steel the standard setup is DCEN, putting heat into the workpiece rather than the wire for deeper penetration and a cleaner arc. It is fast, produces very little slag and automates easily, so it dominates production welding. It handles thin material down to about 20 gauge and thicker plate with flux-cored wire. Its weakness is wind, which blows the shielding gas away. Softer alloys need their own settings, covered in the aluminium MIG welding guide.

FCAW: Flux Cored Arc Welding

FCAW looks like MIG, but the wire is a tube filled with flux. Depending on the wire type, the core either provides its own shielding atmosphere or dumps slag-forming compounds into the arc. Self-shielded flux-cored wire needs no gas cylinder, which makes it enormously popular for structural steel erection, pipeline work, ship repair and outdoor field welding, where wind would destroy a gas-shielded arc. Gas-shielded flux-cored wire adds external gas for cleaner welds on thinner material, sitting between GMAW and self-shielded FCAW. It runs on constant voltage, usually electrode positive for many self-shielded wires. The downsides are heavy spatter, more slag than solid wire and a rougher bead. A GMAW torch often runs flux-cored wire unchanged, since the wire feed and gun are the same hardware, as aluminium flux core welding shows.

GTAW: Gas Tungsten Arc Welding (TIG)

GTAW uses a non-consumable tungsten electrode for the arc, with a separate filler rod fed by hand and the pool protected by an inert gas, almost always argon or a helium blend. Manual filler addition and precise amperage control give you outstanding control over heat input and bead shape. TIG is the standard for thin sections, stainless steel, aluminium, copper and cosmetic work where the bead has to look machined, plus repair work on thin or heat-sensitive parts a sloppy MIG pass would ruin. The cost is speed and skill: it is the slowest mainstream process, carries the highest labour cost per weld, and controlling heat on thick material needs a foot pedal and real technique. Aluminium TIG work also demands careful preparation, covered in the guide to cleaning aluminium correctly before welding.

SAW: Submerged Arc Welding

SAW runs under a blanket of granular flux that covers the arc entirely. The flux does the shielding, and because the arc is buried there is no arc light, no fume and very little spatter. That quiet environment allows very high current and very high deposition rates, and the process is easy to automate. SAW is for long, straight, flat or horizontal seams on heavy plate: pressure vessels, large structural sections, pipeline and shipyard work. It needs a flux delivery system, flux recovery and usually a positioner or tractor, so it is a specialised industrial setup rather than a home shop machine.

Side-by-Side Comparison

Process	Trade Name	Consumable	Shielding	Power Source	Best Fit	Watch Out
SMAW	Stick	Coated electrode	Coating, no gas	Constant current	All-position field work, heavy plate	Slow, slag, low deposition
GMAW	MIG	Solid wire	Ar, CO2 or blend	Constant voltage	Production work, thin material	Wind sensitive, less precise
FCAW	Flux-cored	Tubular flux-core wire	Self- or gas-shielded	Constant voltage	Structural and outdoor work	Spatter, slag, rough bead
GTAW	TIG	Tungsten, hand-fed filler	Inert Ar or He	Constant current	Thin gauge, stainless, aluminium	Slowest, highest skill cost
SAW	Submerged arc	Solid wire	Granular flux blanket	Constant voltage	Long seams on heavy plate	Industrial gear only

Nearly every steel shop runs more than one of these processes, and the choice changes with the day. A fabricator might use MIG for a stainless tank, TIG for a visible corner and stick to tack a 20 mm plate in place. Learn two of them well and you can handle nearly any job that walks in the door.

How the Arc Works: Power Sources, Polarity and Heat Input

The electric arc may look simple, but its behaviour comes down to three things: the power source, the direction of current, and the heat going into the joint. Get any of these wrong and even a good joint can become a bad one.

Constant Current vs Constant Voltage

The biggest split in arc welding machines is between constant current (CC) and constant voltage (CV).

A constant current (CC) machine, often called a drooping power source, holds the amperage you set while voltage changes with arc length. Move the electrode closer and voltage drops. Pull it back and it rises. This self-correcting response is ideal for stick and TIG, as both rely on the welder to control arc length by hand. It’s this control that makes Why SMAW still wins in the field so relevant for outdoor and repair work.

A constant voltage (CV) machine does the opposite. You set the voltage, and the wire feeder determines amperage based off of wire feed speed. Since MIG and flux-cored use a continuously fed wire, the machine keeps a steady arc voltage while faster wire feed brings more amps and more heat. This pairing is what allows for consistent beads over long runs.

Polarity: Where the Heat Goes

Polarity dictates which side of the arc takes the majority of the heat. DCEP (direct current electrode positive) puts around two thirds of the heat into the base metal and one third into the electrode. DCEN (direct current electrode negative) flips this, putting most of the heat into the workpiece and keeping the electrode cooler.

Process	Normal Polarity	Why
SMAW (stick)	DCEP	Maximises base metal penetration
GMAW (MIG)	DCEN	Concentrates heat in the workpiece with minimal spatter
GTAW (TIG)	DCEN	Keeps the tungsten cool to avoid melting or contamination
FCAW	DCEN for gas-shielded, often DCEP for self-shielded	Follow the specific wire and flux type

Open-Circuit Voltage

Open-circuit voltage is the voltage present at the leads when the arc isn’t struck. It’s the shock hazard welders work around daily. To limit that hazard, OSHA 29 CFR 1910.254 caps manual arc welding equipment to 80 volts on AC and 100 volts on DC, and limits automatic or mechanised arc welding equipment to 100 volts.

Heat Input: The Number That Governs Your Weld

Heat input is an approximate measure of energy delivered per inch of travel. The formula used in most shops is:

Heat input (kJ/in) = (Volts × Amps × 60) ÷ travel speed in inches per minute ÷ 1,000

For example, running GMAW at 26 volts and 230 amps at 40 ipm gives roughly 9.0 kJ/inch. Dropping to 30 ipm with the same settings raises that to about 12.0 kJ/inch, a change that can decide whether a restrained joint cracks or not.

• More heat input: Deeper penetration, wider beads, more distortion, higher residual stress, and an increased risk of hydrogen-assisted cracking.
• Less heat input: Less distortion, but a higher risk of lack of fusion, cold lap, or incomplete penetration, especially on thick or dirty steel.

Arc length plays a large role here. A longer arc raises voltage, widens the bead, increases spatter, pulls more nitrogen from the air, and reduces penetration. A short arc concentrates heat but risks stubbing, toe cold lap, or slag trapping. This is exactly why TIG allows for such tight control, a practice covered in the aerospace TIG welding guide.

Where the Code Gets Involved

Heat input isn’t just a preference. AWS D1.1/D1.1M:2025 ties preheat and heat input to diffusible hydrogen and the steel being joined. Under the 2025 edition, prequalified welding of A913 Gr80 without preheat is only allowed when the ambient temperature is above 32°F (0°C) and the electrode has a diffusible hydrogen content of 8 mL/100 g (H8) or less. Below that, or with a higher-hydrogen electrode, preheat becomes mandatory. Voltage, amperage, travel speed, wire or rod diameter, and preheat all feed this calculation, all of which are verified against AWS structural codes by a qualified inspector.

Choosing the Right Arc Welding Process for Your Job

Choosing a process sounds technical, but it comes down to a few honest questions about the job in front of you. One solid process with good fundamentals covers most of what you will ever be asked to weld.

Ask these seven questions first

1. What is the material? Mild steel is forgiving. Stainless, aluminium and cast iron are not, and each narrows your choices fast.
2. How thick is it? Thickness drives both the process and the consumable you buy.
3. What kind of joint? Butt, lap, fillet or full pipe changes access and heat control completely.
4. Will you be welding out of position? Overhead and vertical work suit stick and flux-cored far better than MIG or TIG.
5. How good must it look? Cosmetic stainless or aluminium is a TIG job, not a close call.
6. Where are you welding? A clean shop, a windy site or a confined space rewrites the shielding rules.
7. What is the budget? Gas, wire and power add up, but so does the time you spend chipping slag.

Where each process earns its keep

Stick (SMAW) is the field welder’s first choice. No gas cylinders, excellent all-position control, and it handles 1/8 in plate and heavier without drama. It also tolerates rust, mill scale and dirty steel. The trade-off is speed and slag, as why SMAW still wins explains.

MIG (GMAW) is the production workhorse. It is efficient from about 1/8 in to 1/2 in, lays down a fast, clean bead, and pairs with a huge range of wire and gas combinations. In a clean shop with steady throughput, nothing else matches it.

TIG (GTAW) becomes the practical choice below 1/8 in (1/16 in, 20 to 22 gauge) and for non-ferrous work. Heat input sits under a fingertip, which is why it rules cosmetic stainless and aluminium.

Flux-cored (FCAW) earns its keep on thick structural plate and outdoor work, where it out-deposits stick and tolerates wind better than gas-shielded MIG.

By thickness:

Material thickness	Go-to process	Why
1/16 in (20–22 gauge) and thinner	GTAW	Too thin for stick, spatters with MIG, no heat control elsewhere
1/8 in to 1/4 in	GMAW	The sweet spot: fast, clean, easy filler control
1/4 in to 1/2 in	GMAW or FCAW	FCAW for structural, GMAW for throughput
3/8 in and heavier	FCAW or SMAW	FCAW wins on speed, SMAW on field versatility

Matching the filler metal

Process is half the decision. The consumable has to match the base metal and the strength you need. AWS classification numbers look cryptic but are logical once you know the code. In E7018, the 70 is tensile strength in ksi, the 1 means all-position, and the 18 denotes a low-hydrogen iron-powder electrode. For GMAW, ER70S-6 is the common solid mild steel wire, where the S means single-pass, multi-purpose.

Special cases that change the plan

• Galvanised steel: grind back to bright metal, then use self-shielded flux-cored wire or a 25% argon / 75% CO2 blend, and expect zinc fume in the first passes.
• Stainless steel: carries a hexavalent chromium (Cr(VI)) fume hazard that OSHA regulates separately under 29 CFR 1910.1026. Keep heat input low, use ER308L, and purge thin stainless with backing gas.
• Aluminium: spooled ER4043 or ER5356 wire, or ER4043 / ER5356 TIG rods, with argon or argon-helium. It demands thorough cleaning and steady AC or DCEN. Start with the aluminium MIG guide and prepping aluminium properly.
• Cast iron: nickel-iron consumables with preheat and a slow cool, or brazing for low-stress repair jobs.
• Coated, painted or primed surfaces: grind back to clean metal before the arc strikes. OSHA’s welding fume fact sheet advises cleaning surfaces of coatings that could create toxic exposure.

When a job should not be arc welded at all

Some work should be bolted, brazed, or handed to a shop with the right equipment. Walk away from arc welding when the base metal is unknown, when the joint needs a code-compliant weld and you are not qualified to AWS D1.1 requirements, when the part is heat-sensitive and distortion would ruin it, or when a fastener does the job cheaper. Knowing when not to weld is a skill too.

Safety: Fume, Fire, Electricity and Heat

Ask any experienced welder what scares them most about arc welding and you will rarely hear “the arc.” You will hear about fume rolling into their face and a fire watch who wandered off. The four hazards below cause nearly all serious welding injuries, and each is already governed: OSHA 1910.252 covers fire prevention, 1910.254 covers the electrical side.

1. Fume: The Hazard Nobody Sees

Welding fume is not ordinary smoke but an ultrafine aerosol of metal oxides plus gases, formed as the arc vaporises base metal, filler metal and coatings. The particles are small enough to reach deep lung tissue and stay there. OSHA’s fact sheet FS-3647 describes metal fume fever, the classic short-term reaction: fever, chills, cough and chest tightness that can start within hours of exposure and clear once the welder leaves the area.

• Chromium VI. Stainless and chrome-bearing alloys release Cr(VI), a confirmed carcinogen. OSHA’s PEL is 5 µg/m³ as an 8-hour TWA, action level 2.5 µg/m³. Above the action level, employers must run exposure determinations and provide medical surveillance; above the PEL, respiratory protection is required on top of engineering controls.
• Manganese. All mild steel fume contains it. OSHA’s PEL is 5 mg/m³ as a ceiling; ACGIH’s TLV is far lower at 0.02 mg/m³ respirable and 0.1 mg/m³ inhalable as an 8-hour TWA; NIOSH’s REL is 1 mg/m³ TWA with a 3 mg/m³ short-term limit. NIOSH reports neurological effects below 0.2 mg/m³: mood and short-term memory changes, slowed reaction time, reduced hand-eye coordination, manganism above 1 mg/m³.

Fume is a mixture, and IARC classifies welding fumes and welding-produced UV radiation as Group 1 carcinogens, meaning sufficient evidence of carcinogenicity in humans. Welder’s anthrax, a skin and lung infection from soil-borne spores in contaminated areas, is rare but serious.

Confined spaces change the arithmetic. 1910.253 requires cylinders and welding machines outside the space, an attendant with a preplanned rescue procedure at the entrance, and adequate ventilation before entry. In a tank or duct, fume concentrates right around the welder.

2. Fire and Heat

Arc welding produces intense heat, sparks and molten spatter. The most cited rule in OSHA 1910.252 is simple: move combustibles at least 35 ft (10.7 m) from the work where practicable. If you cannot move them, protect them with fire-resistant covers, or post a fire watch.

A fire watch is required when appreciable combustibles sit within 35 ft, when sparks can reach the floor, or when welding happens in a confined space with limited escape. The watch must be a competent person who can see the work area and the path to an exit, with access to an extinguisher, and must stay on the job at least 30 minutes after welding finishes. Many fires start in smouldering insulation, underfloor voids and cable trays long after the arc stops.

• Used containers. Only approved, labelled, closed containers for hot electrode holders, slag and stubs.
• Prohibited areas. No welding near flammable gases and fuels where the hazard is not properly controlled.
• Protection. Fire blankets, fire-resistant curtains and metal splash guards where you cannot move the combustibles.

Heat also means burns, and shop burns far outnumber the injuries that reach the paperwork. Gloves, sleeves and a leather apron are not optional near a live arc.

3. Electricity

Welding current is industrial current running through a metal object you may be holding. The rules in 1910.254 exist because the failure modes are predictable.

• Ground the machine. Ground it to the work table or workpiece, and ground frames or enclosures when connected.
• No splices within 10 ft (3 m) of the electrode holder. A splice under load creates heat and arcing. Replace the cable, do not tape it.
• Never carry current through chains, wire ropes, cranes, hoists or elevators. Disconnect the holder before moving a suspended load.
• Never coil the electrode cable around your body. One turn around the forearm creates a serious shock path if insulation fails. Hang the cable on a hook or roller.
• Wet machines. Dry and test anything that gets wet before returning it to service.

Store holders off hot surfaces and out of standing water, and hang cables where a forklift cannot crush them.

4. PPE, Hot Work and Eye Protection

OSHA requires helmets or hand shields for all arc welding or arc cutting operations except submerged arc welding. A helmet with the correct shade number is the most effective thing you can own, and the one item a welder should never cheap out on or share.

• FR clothing. Flame-resistant cotton or aramid, sleeves down, no synthetic shirts that melt into skin.
• Gloves. Leather welding gloves, leather apron and sleeve protectors for spatter and heat, gauntlets over the forearm.
• Boots. Safety-toe leather with no exposed laces. A dropped electrode finds a canvas sneaker.
• Respirator. A fitted N95 or P100 handles particulate; for fume you want supplied-air or powered protection where ventilation cannot keep levels down. Tight-fitting respirators need medical evaluation and fit testing.
• Hearing and visibility. Ear plugs or defenders in noisy shops, and glasses or goggles under the helmet for grinding, chipping and slag breakout.

Finally, treat every welding job as hot work. If nobody has shown you the site-specific permit, the fire watch drill and the emergency procedure, ask. For how consumables change the risk profile, our guide to alloy steel welding electrodes covers what is actually in the rod you are burning.

Setting Up the Job: Joint Prep, Fit-Up and Technique

Most disappointing welds are made by a decent welder working on a badly prepared joint, with sloppy fit-up, a contaminated surface and a ground clamp in the wrong place. Setup decides more than technique does.

Step 1: Clean the steel

Grind, wire-brush or degrease the joint faces and the metal either side of them. Mill scale, rust, paint, oil and even a fingerprint end up as slag or porosity in the bead. Clean until the metal looks bright and uniform across the area you will heat. Aluminium needs solvent cleaning plus mechanical prep, covered in the guide to prepping aluminium for welding.

Step 2: Fit-up beats technique

Align and gap the joint before welding. A 1/8 in (3 mm) misalignment twists the part, so check with a straightedge and a square, then clamp the pieces into a rigid fixture. For GMAW on 3/8 in (9.5 mm) steel, a root gap of roughly 1/16 to 1/8 in (1.5 to 3 mm) is a workable starting point. Too tight and you burn through, too wide and you pour filler metal into a hole.

Tack first, then re-check alignment, because tacks move. Keep tacks small, or grind them flush if they sit inside the final weld.

Step 3: Preheat and interpass temperature

Preheat slows cooling, lowers hardness and helps hydrogen escape the weld. Interpass temperature is the highest temperature the steel reached before the next pass. A 3/8 in mild-steel bracket usually needs neither, but AWS D1.1 sets minimum preheat and maximum interpass temperatures by thickness, carbon equivalent and diffusible hydrogen level, and many rows cap interpass at 350 °F (175 °C). Read the row that matches your material rather than guessing.

Step 4: Ground the work properly

The work clamp goes directly onto the part you are welding, close to the joint, and into the machine’s work terminal. Not onto a table, scaffold, ladder or unpainted surface. A clamp biting into paint or dirt will arc, burn the part and starve the process of a stable path. OSHA 1910.254 covers grounding requirements for portable electric welding equipment. Put the clamp on a sacrificial spot if the finish matters.

Step 5: Consumables and how to store them

Low-hydrogen electrodes such as E7018 must be kept dry. A damp electrode puts moisture back into the weld as hydrogen and drives cold cracking, which is why structural shops use a rod oven or heated holding oven instead of a bucket. Buy smaller boxes if you cannot store them warm. Handle them with clean, dry gloves and read the classification on the box, as explained in the all-position welding rod guide. Wire needs the same care: keep it sealed and dry, and match the liner and contact tip to the wire diameter.

Step 6: Shielding gas flow

Set gas flow at the torch, not at the cylinder. For steel MIG on a 75/25 argon-CO2 blend, around 20 cfh is a sound starting point. Too little and the arc drinks air, giving rust-coloured spatter and porosity. Too much and the jet turns turbulent, dragging the arc around and spitting wire. Wrong mixes are worse: too much CO2 on stainless or aluminium causes porosity and colour problems. Cylinder handling basics are in the air gas welding supply guide.

Step 7: Travel technique and adding filler

Stringer welds, with no side-to-side weaving, deposit a narrower bead that is easier to clean and less likely to trap slag or undercut the toes. Weave beads suit wide fillets, but every pass over cold metal risks oxide and undercut, so keep them shallow. Back-stepping, welding a short segment then stepping back along it, spreads heat and reduces distortion. Chip slag and brush between passes; trapped slag becomes an inclusion.

Keep the rod or wire in the puddle and feed from the side of the joint rather than plunging it in. TIG tungsten prep and filler technique are a skill of their own, covered in the TIG technique and training guide.

Worked example: a 3/8 in mild-steel bracket

Process	GMAW (MIG), short-circuit transfer
Wire	0.045 in ER70S-6 solid wire
Gas	75% argon / 25% CO2 (C25) at about 20 cfh
Settings	Around 300 A and 26 V, near the rough 1 A per 0.001 in thickness rule of thumb
Consumables	0.045 contact tip, 1/2 in nozzle
Fit-up	1/16 to 1/8 in gap, tacked at both ends, re-checked with a straightedge
Technique	Stringer beads in roughly 2 in segments, back-stepped, slag chipped and brushed between passes

Common Arc Welding Defects and How to Fix Them

Every welder produces bad welds. The difference between a beginner and a pro is not whether defects happen, but whether the welder can name what went wrong and fix it. Read a weld the way an inspector does: symptom first, cause second, corrective action third.

Defect	What it looks like	Likely causes	How to fix it
Undercut	Groove melted into base metal at the bead toe	Fast travel speed, high amperage, wrong work angle, long arc	Slow down, cut amps, fix torch angle, short arc
Porosity	Round gas voids, pinholes or foamy bead surface	Dirty or damp base metal, contaminated gas or wire, oil or paint	Clean the joint, check gas and flow, shorten the arc
Slag inclusion	Dark grey or brown slag trapped in the bead	Poor interpass cleaning, wrong travel angle, too much weave	Grind or chip between passes, sweep slag, correct torch angle
Spatter	Metal globs thrown from the puddle onto the plate	Voltage too high for wire size, wire feed too fast, wrong polarity	Set correct voltage and wire feed, check polarity, clean up
Excessive reinforcement	Tall, proud bead standing above the plate	Slow travel speed, excess filler, wide weaving	Travel faster, lay less filler, or grind and blend
Incomplete fusion	Bead sits on the surface with little penetration	Low heat, fast travel speed, poor fit-up, dirty joint	Add heat, slow down, improve fit-up, clean the joint
Burn-through	Hole melted through the plate or root	Too much heat, too little material, poor restraint, gap too large	Reduce heat, add backing, close the gap, use a lower-heat process
Overlap	New bead rolls over the previous one	Slow travel speed, too much wire, arc too short	Speed up slightly, reduce filler feed, steady arc length
Cold lap	Dull, cold bead that did not melt into the base metal	Arc too short, travel too fast, no dwell on the joint	Hold the arc at the puddle edge, slow down, add heat
Excessive penetration	Root blown out past the other side of the joint	Too much heat for the thickness, incorrect gap, no backing	Reduce amperage and travel speed, use backing, control the gap
Arc strike	Crater-like spot where the arc was struck on the plate	Stray arc start, poor grounding, clumsy electrode handling	Grind out smoothly and inspect, especially on pressure work

Undercut: the most common defect you will ever make

Undercut is a groove melted into the base metal at the toe of the bead. Causes are travel too fast, too many amps, a work angle that aims the arc into the plate edge, or too long an arc. Slow down, trim the amps, angle the torch so arc force runs along the joint, and keep the arc short. It is not cosmetic: the groove removes cross-section and creates a stress raiser, a classic crack starter in fatigue-loaded steel, so grind it out and reweld.

Porosity: gas voids that weaken the joint quietly

Porosity shows up as round voids, pinholes or a foamy, sponge-like bead. Hydrogen, nitrogen and oxygen get into the pool and freeze into trapped bubbles. Usual suspects are contaminated shielding gas, dirty or damp base metal, oil or paint near the joint, an arc too long for air to be drawn in, and a wet wire spool on GMAW or FCAW. Voids and inclusions break the load path and act as stress concentrators, which is why the AWS D1.1 structural welding code treats them as rejectable conditions based on size and extent.

Incomplete fusion and burn-through are opposites

Incomplete fusion means the weld metal never melted into the base metal, visible as a bead sitting on the surface with a seam line where the two should have merged. Causes are low heat, fast travel speed, poor fit-up or a contaminated joint. Burn-through is the opposite: too much heat or too little material, so the root melts out and you punch a hole through the plate.

Excessive reinforcement and arc strikes

Excessive reinforcement is a bead standing proud of the plate, often normal on fillet welds where the drawing specifies a convex fillet. It becomes a problem when the drawing calls for a flush or nearly flush profile, such as a flange face or sealing surface that must be ground back into the parent metal. Weld a wider, flatter bead if grinding is planned.

An arc strike is a stray start of the arc, often from tapping the electrode against the plate, leaving a small hard quenched crater and a hardened heat-affected zone. Grind it out on ordinary work. On pressure equipment and structural steel the crater can hold hard spots and micro-cracks, and strikes outside an approved area are grounds for rejection.

Ugly but passing versus an actual failure

A wide, lumpy bead with light spatter can be strong, fully penetrated and acceptable on a structural joint, while a smooth, shiny ribbon can hide porosity, incomplete fusion or a crack underneath it. What counts is penetration, fusion, no voids or cracks, and conformance to the acceptance criteria. Cosmetic welding is a separate skill, and it takes practice.

That is where inspection comes in. Dye penetrant, magnetic particle, ultrasonic and radiographic methods find defects no eye will catch, which is why coded work gets third-party review. For anyone moving into that side of the trade, AWS offers certification and education pathways including the Certified Welding Inspector program.

Our guides to stick welding technique and aluminium MIG welding cover the prep habits that prevent many of these defects, and aluminium punishes a dirty joint and a contaminated torch. When a weld fails, change one variable at a time: amperage, travel speed and arc length interact, so changing all three teaches you nothing.

Managing Distortion, Residual Stress and Weld Quality

A flat plate can bow like a canoe after one pass of filler metal. Machine, wire and beads were all fine, yet the part moved anyway. That is distortion, and once you know why, it stops being mysterious.

Why Welds Move

Distortion comes from non-uniform heating. Metal near the arc heats fast and tries to expand while the steel around it stays rigid, putting the hot zone under compressive stress. When it cools, it wants to shrink but the plate restrains it, so the part bows or twists.

• Too much filler metal. A fat, slow bead deposits more heat and shrinkage than a small, fast one, so size the weld to the load.
• Bad fit-up. A wide gap or mismatched edge forces the pool to bridge, pulling the pieces out of alignment.
• Poor restraint. Rigid clamping can make the weld look fine while pushing distortion into residual stress you cannot see.

A second, invisible problem rides along: residual stress. As weld metal shrinks while constrained by the plate, that force locks into the joint and stays after cooling. It is the hidden reason a weld that passes inspection can still crack months later, or why a part bows after machining.

The Anti-Distortion Toolbox

• Plan the sequence first. Weld toward the end of the joint so the part shrinks toward a free end; on closed frames, work outward from the middle.
• Back-step. Weld a short segment, step back over the gap, then continue, spreading heat over the same area longer.
• Alternate sides on balanced parts, so symmetric sequencing cancels the push in one direction.
• Keep the bead size tight. Smaller welds shrink and distort less, and excess reinforcement invites cracks.
• Preheat to flatten the gradient by warming ahead of the arc. On heavy or high-carbon sections, preheat is about cracking.
• Fixture strongly, but let it move. Over-restraint turns movement into residual stress.
• Tack deliberately: few, well-placed tacks, not a row of them, with their shrinkage controlled.

Quality Control: What You Can See and What You Cannot

Every inspection method finds some defects and misses others. Knowing each blind spot makes an inspection program sensible rather than decorative.

Method	Finds	Misses
Visual (VT)	Surface cracks, undercut, overlap, bad profile	Anything buried inside the weld
Dye penetrant (PT)	Fine surface-breaking cracks	Subsurface defects; dirty or porous surfaces
Magnetic particle (MT)	Surface and near-surface cracks in ferrous material	Non-ferrous metals like aluminium or stainless
Ultrasonic (UT)	Internal flaws, lack of fusion, cracks	Fine surface detail; needs trained interpretation
Radiographic (RT)	Internal defects on film or digital detectors	Some surface conditions; cost and safety controls

Visual inspection remains the backbone of weld quality control because it is fast, cheap and catches most problems, but it only shows what you can see. NDT comes in when a hidden flaw carries real consequences, such as pressure equipment, critical structures or aerospace work, and code-required examinations often combine methods because each covers the gaps of the others.

Safety rules matter too. Radiography uses radioactive sources and requires controlled areas, monitoring and licensing, and OSHA’s welding provisions set safety expectations around hot work and equipment, including 1910.253 for welding, cutting and brazing equipment.

The Code Baseline

AWS D1.1/D1.1M:2025-AMD1, now in its 25th edition, sets requirements for welding structural steel, including qualification and inspection. It is written by more than 200 technical committees with about 1,500 volunteer engineers, and its standards are ANSI accredited. Acceptance criteria are not opinion: the contract points at a clause, and the inspector points at the clause.

Visual inspection quality is judged against written criteria, not against how a weld feels. A bead that looks heavy may be a reject if the code sets a maximum reinforcement and minimum profile, while a thin-looking one may still pass. Read the spec before you weld.

Welder Qualification and Inspection Careers

Welder qualification under AWS D1.1 proves a welder can deposit sound welds in a defined process, position, thickness range and supporting material. Certified Welding Inspector (CWI) is the AWS credential for administering welding quality programs. The AWS certification and education programs outline both paths, and this guide to welding careers explains how the roles differ.

Control distortion by controlling heat and sequence. Detect what you cannot see with the right inspection method. Code your work to a written standard rather than memory.

Equipment and Consumables: Building a Setup That Fits Your Work

Sticker price is not the number that matters. What matters is the arc behaviour your material demands, whether you can service the machine with consumables you can find on a Tuesday afternoon, and the five-year running cost.

Constant Current vs Constant Voltage

A constant current (CC) machine, also called a drooping-voltage welder, suits stick (SMAW) and TIG (GTAW): you set amperage, and the power source holds it by dropping voltage as arc length changes, so the arc stays steady even when a beginner wobbles. A constant voltage (CV) machine suits MIG (GMAW) and flux-cored (FCAW): you set voltage, and a strong feeder with a 4-roll drive matches wire speed to it, so wire feed speed sets arc length, not your hand.

Type	Processes	You set	Arc behaviour
Constant current (CC)	SMAW, GTAW	Amps	Forgiving; a stubby drag keeps its heat
Constant voltage (CV)	GMAW, FCAW	Volts and wire feed speed	Length tied to voltage; wire speed sets deposition
Multi-process	All four	Mode switch	One box, several jobs, fewer machines on the truck

Inverter vs Transformer/Rectifier

Transformer/rectifier machines are heavy, bulky and slow to respond. Inverters dominate new purchases for faster arc response, easier striking, better heat control on thin material and far lower weight. Responding thousands of times per second, they can be hot-started and controlled in ways a transformer cannot, which matters on thin material and stainless, where a short arc that will not burn through is critical, and on 6010/7010 electrodes.

One inverter runs stick, MIG, TIG and flux-cored, and many add a spool gun for aluminium. If aluminium is on the horizon, check for an aluminium-capable mode and spool-gun acceptance; our aluminium MIG welding guide shows what that takes in practice.

Power, Duty Cycle and Field Work

Most machines take single-phase 240 V, with 208 V and 120 V models for lighter work; three-phase 480 V units dominate industrial shops because they run bigger power sources without single-phase load spikes. On three-phase supply, a single-phase machine needs a phase monitor or it dies when a phase drops.

Duty cycle is the honest spec: a percentage at a given amperage over a stated cycle, such as 60% at 200 A, meaning 6 minutes of welding in every 10 and 4 of cooling. Buy headroom and it stops being a worry. They are also rated for cooling air up to 40°C (104°F) and altitudes up to 3,300 ft (1,005.8 m), and every extra 1,000 ft cuts output, so read the output chart, not the nameplate.

Off the grid, engine-driven welders are standard: diesel runs all day and starts reliably, while a small petrol generator brings surge voltage dropouts and carburettor issues. Size the generator to the welder’s input current; surge rating matters more than running wattage.

Consumables and What They Actually Do

Electrodes. The AWS code tells you everything. In E7018 the first digit is tensile strength in thousands of psi (70 ksi), the second is ductility and impact toughness (1 means low, so 6010 and 7010 are not impact-rated), the third is position capability (0 flat and horizontal only, 1 all position, 2 or 3 deeper penetration), and the last digit is coating (8 = low-hydrogen iron powder). Our all-position welding rod guide explains it further.

Wire. Solid wire is clean, virtually slag-free and suits indoor shop work. Flux-cored wire carries its own flux, so it can be self-shielded (no gas cylinder, ideal for field structural work) or gas-shielded for a cleaner, higher deposition weld, with slag to chip between passes.

Tungsten. Pure runs DC only and wanders on AC; ceriated, lanthanated and thoriated are the practical picks. Thoriated carries a little radioactive thorium with an excellent arc, but brings handling and disposal rules, so shops now specify lanthanated or ceriated. Workable lanthanated handles AC and DC.

Shielding gas. CO2 is standard for short-arc GMAW on carbon steel; argon serves TIG and GMAW on stainless or aluminium; argon/CO2 blends (75/25, 85/15) are the workhorses for spray and flat-position carbon steel; helium-argon mixes give a hotter TIG arc on heavy stainless or copper. CO2 is cheaper but splattery, while argon blends cost more and weld cleaner. That choice shapes your gas supplier and cylinder service, so build it before a big job.

Maintenance That Prevents Most Callbacks

Most “bad welder” complaints are consumable and maintenance problems, not machine problems.

• Contact tips and nozzles: swap the tip when wire feeds inconsistently or wears past the nozzle hole. A gouged nozzle spitting wire is a bird’s nest waiting to happen.
• Wire liners: flush and re-lube every few months and whenever you change wire diameter or spool type. A dirty liner is the top cause of “my new gun will not feed.”
• Gas regulators: check for leaks and verify flow with a flow meter. Low flow is a leading cause of porosity.
• Ground clamp: clean the jaws and the metal you clamp to. A clamp on dirty or rusty metal is an arc-strike and shock hazard.
• Cables and leads: inspect for nicks, cracked insulation and loose connectors. OSHA 1910.254 covers grounding, splices and cable routing.

Running Costs and Total Cost of Ownership

Think of a welder as a lease on an hourly rate: the machine is fixed, and every weld costs consumables, gas, electricity and labour. A 25 lb spool of ER70S-6, a cylinder of 75/25 and electrode stubs add up fast, while electricity is the smallest line item in almost every shop. A cheap machine with no spare parts and no service support can cost more over five years than a mid-range unit with a dealer network, so buy for supportability, not price. Check that parts are stocked locally and the unit is standard 120/240 V.

One non-negotiable: OSHA 29 CFR 1910.254(a)(3) requires workers designated to operate arc welding equipment to be properly instructed and qualified on it. A new machine is a training trigger, so budget time to teach it.

Buy the machine that matches your process and your hours, maintain it on schedule, and it will outlast your first five projects. The expensive mistake is overspending on gear that fights your material.

Wrapping Up: A Realistic Path to Competence

Every process here does three jobs: melt the base metal, protect the pool, add filler. What changes between them is how the arc is fed, how the pool is shielded, and how steady the heat is. The rest is practice, and practice you can schedule.

The One-Line Rule for Each Process

If you remember one thing, let it be this table.

Process	The one-line rule
SMAW (stick)	Choose it when the site, weather or workpiece is hostile and you need a stick that tolerates rough handling and all-position deposits.
GMAW (MIG)	Choose it for fast, consistent deposition in a shop with clean mild steel and thinner material.
FCAW (flux-cored)	Choose it for stick penetration at MIG speed, especially outdoors on thick structural steel.
GTAW (TIG)	Choose it for thin gauge, stainless, aluminium, and joints that must look like the parent metal.
SAW (submerged arc)	Choose it for long, straight, heavy factory seams, running under a blanket of flux.

Stick earned its reputation and still earns respect on farm, field, pipeline and repair work. Why SMAW still wins has the reasoning. All are shop-viable, and the right answer is usually the one your hands already know.

A 30-60-90 Day Practice Plan

Window	Focus	Tasks
Days 1 to 30	Own one process	Cut 10 to 15 coupons from 6 mm (1/4 in) mild steel plate. Run bead-on-plate, a fillet, then a butt joint with a back bar. Set up machine, extraction and PPE properly every time, so the habit forms first.
Days 31 to 60	Add a second process	Repeat those three joints in a second process to compare them on the same coupon set. Start a settings log. Borrow a machine at a shared shop or a friend’s garage.
Days 61 to 90	Build something real	Build a steel table frame, trailer bracket, workbench or shelf brackets. Realistic fit-up, tacking, sequencing, distortion control and cleanup. Log the settings.

Scrap coupons cost a fraction of the material and let you experiment with amperage and travel speed without risking a finished assembly. A failed coupon teaches what a failed frame would, without costing you the frame.

The second habit worth building early is logging. Weld quality improves fastest when you record amperage, voltage, wire or electrode size, gas flow and travel speed for each joint, then change one variable at a time. Change three things at once and you cannot tell which one helped.

The Non-Negotiables

• Fume extraction or proper general ventilation. Weld fume is a fine metal aerosol plus gases, and the only reliable control is moving the air. OSHA 1910.252 sets ventilation and fire prevention requirements for arc welding.
• Correct shade eye protection. A shade too light lets you see the puddle and still damage your eyes; 1910.252 includes the filter shade table.
• FR clothing, gloves and boots. Sparks do not stop at your sleeves, and cotton is a poor last line of defence.
• A fire watch when combustibles are within 35 ft. That distance comes from 1910.252, which also requires a watch after work stops.
• A sound ground connection and disciplined cables. No splices within 10 ft of the electrode holder, never carry current through a chain, hoist or crane, never coil cable around your body. OSHA 1910.254 covers this and holder storage.

A Final Checklist to Print

• Material confirmed, joint prepared, edges cleaned, fit-up checked
• Machine set to material and thickness, consumable and gas correct
• Ventilation running before the arc strikes
• Correct shade helmet or goggles, FR clothing, gloves, boots
• Ground clamp on the workpiece, not a rusty structure nearby
• Combustibles moved, or fire watch posted and equipped
• Gas cylinder upright, secured, correct gas
• Settings written down, one variable changed per test

Where to Go Next

For a second process, the material-specific guides are the fastest route. The complete practical guide to MIG welding aluminium covers what changes when the metal changes, and what an aluminium welding course actually teaches gives you a structured route in. For consumable decisions once you are past mild steel, alloy steel welding electrodes is the reference. If your interest turns toward inspection rather than production, the AWS certification and education pathway, including the Certified Welding Inspector programme, is where the formal route runs.

The arc is predictable, the machines are more forgiving than their reputations suggest, and the gap between a first bead and a good one is repetition plus a written record. Start on scrap, keep safety habits on from the first arc, and give yourself ninety days.

Frequently Asked Questions

What is the difference between MIG, TIG and stick welding?

All three are electric arc welding processes that differ in how the arc is created, how the weld pool is protected and how filler metal is added. MIG (GMAW) feeds a solid wire continuously and needs shielding gas; TIG (GTAW) uses a non-consumable tungsten and inert gas for the most precise, cleanest welds; stick (SMAW) uses a flux-coated electrode that creates its own shielding and slag, making it the most portable and forgiving.

Is stick welding harder to learn than MIG welding?

Stick requires more hand coordination because you maintain arc length and travel speed by feel while managing a stick electrode, but it is more forgiving of dirty steel and works in every position. MIG is generally faster and easier to learn for a beginner with a clean shop and a machine that supports flux-free short-circuit transfer, so most hobbyists start with MIG or flux-cored and pick up stick second.

Is electric arc welding safe for a complete beginner to do at home?

It can be, but only with the same discipline a professional applies: local exhaust ventilation or a fume extractor, correct shade-number eye protection, fire-resistant clothing and gloves, a sound ground clamp, and no combustibles within 35 ft of the work. Welding galvanised or stainless material indoors without extraction is the classic mistake, because it can put hexavalent chromium or zinc oxide fume into your breathing zone.

What ventilation is needed when welding indoors?

The goal is to keep fume and gas concentrations below the applicable limits, which OSHA 1910.252 states as keeping toxic fumes, gases and dusts below the maximum allowable concentration in 1910.1000. A fume extractor positioned roughly a foot from the arc, or general ventilation that moves fresh air across the work and keeps fumes away from the welder’s breathing zone, is the standard approach; welding in a closed room with a respirator as your only control is not adequate.

Why do I get undercut when welding, and how do I fix it?

Undercut is a groove melted into the base metal at the toe of the bead, and it is the most common arc-welding defect. It usually comes from too much amperage, too fast a travel speed, dragging the arc along the edge of the joint, or too long an arc length. Slow down slightly, aim the arc slightly toward the centre of the puddle, and use filler rather than letting the arc eat the edge.

Can I weld aluminium with MIG or TIG?

Yes — aluminium is routinely TIG welded with AC and MIG welded with DCEN using spooled ER4043 or ER5356 wire and an argon or argon/helium mix. The challenges are oxide removal and heat control: the metal must be cleaned to bright metal immediately before welding, and a torch that is too cold or a wire that is too fast will leave a dull, contaminated bead.

What is the best arc welding process for thick steel plate?

For plate beyond about half an inch, flux-cored arc welding (FCAW) gives the highest deposition rate and tolerates rust and outdoor conditions, while stick (SMAW) remains the standard for structural and field work where equipment portability matters. Below that thickness, MIG is usually faster, and heavy single-pass seams are frequently made with submerged arc welding in a fabrication shop.

How do I pick the right shielding gas and amperage for my machine?

For carbon steel with GMAW, pure CO2 is cheapest and works at short arc lengths, while an argon/CO2 blend gives a more stable, less spattery arc; use pure argon for TIG and for GMAW on stainless or aluminium. Amperage comes from the machine’s own process setting, then you fine-tune by watching the bead: a narrow, tall, rough bead means the amperage is too high for the wire size, and a wide, flat, cold-looking bead usually means the wire feed and amperage are too low.

Why does my MIG weld keep being porous?

Porosity means gas got trapped in the bead, and the usual causes are contaminated shielding gas (a leaking regulator or an empty cylinder), dirty or oily base metal, damp wire or flux-cored wire left out, and an arc that is too long so shielding gas is blown away from the pool. Check the cylinder and regulator first, then clean the joint back to bright metal, then shorten the arc and re-test on a scrap coupon.

Do I need a licence or certification to weld for other people?

Certification requirements depend on where you are and what you are welding. In many jurisdictions there is no licence to weld generally, but commercial and structural work is usually governed by a contract code such as AWS D1.1, which requires welder qualification tests and qualified procedures. Pressure vessels, pipelines and regulated structures have their own certification schemes, and AWS certification such as the CWI is what employers ask for when you move into inspection or supervision.