There are more than a dozen types of welding in industrial use, and they are not interchangeable. A 3 mm bracket that welds cleanly with TIG warps under stick, and a 40 mm vessel seam that needs six flux-cored passes closes in one submerged arc pass. The sections below give thickness, materials, deposition, distortion and cost position for each process, then a comparison table, a decision matrix, defect causes and inspection methods.
What Are the Main Types of Welding?
Welding splits into five families: arc (MIG, TIG, stick, flux-cored, submerged arc, plasma, stud), resistance (spot, seam, projection), high-energy beam (laser, electron beam), solid-state (friction stir, friction, ultrasonic) and oxy-fuel gas. The family sets how heat reaches the joint, which fixes thickness limits, distortion and cost.
Two variables explain most of the differences. Heat input in kJ per mm decides how much the plate shrinks, which is why submerged arc bows a thin panel. Energy density in W/cm² decides how deep fusion runs, which is why an electron beam seals 50 mm of steel in one pass.
Thickness is the first filter. Convert gauge numbers with the sheet metal gauge chart before choosing, because 0.9 mm and 2 mm sheet do not share a process list.
How Do the Welding Processes Compare?
The table scores the processes used most in contract fabrication on thickness, materials, deposition, finish, distortion and relative cost per meter. The cost index bundles labor, consumables, cleaning and inspection, so read it as a comparison between processes, not a price. Welding is one line in the estimate; the rest of the price build-up is covered in how CNC machining cost is calculated.
| Process | Typical thickness | Materials | Speed | As-welded finish | Distortion | Cost index |
|---|---|---|---|---|---|---|
| GMAW (MIG) | 0.8–12 mm | Steel, stainless, aluminum | 1–4 kg/h | Light spatter | Moderate | 1.0 |
| GTAW (TIG) | 0.5–6 mm | Stainless, aluminum, titanium | 0.2–1 kg/h | Cleanest, no slag | Low | 2.2 |
| SMAW (stick) | 2–25 mm | Steel, cast iron repair | 1–2 kg/h | Slag, spatter | Moderate to high | 1.2 |
| FCAW | 2–25 mm | Steel, some stainless | 2–6 kg/h | Slag, fume | Moderate | 0.8 |
| SAW | 6–100 mm | Steel | 5–25 kg/h | Smooth | High | 0.6 |
| PAW | 0.1–12 mm | Stainless, titanium, nickel | 0.5–3 kg/h | Clean keyhole | Low | 1.5 |
| RSW (spot) | 0.5–3 mm per sheet | Steel, aluminum, coated | 0.1–0.5 s per spot | Tip marks | Very low | 0.5 |
| RSEW (seam) | 0.1–3 mm | Steel, stainless | 1–5 m/min | Roller marks | Low | 0.9 |
| RPW (projection) | 0.5–4 mm | Steel, nuts, studs | Several per stroke | Local dimple | Low | 0.5 |
| OFW (oxy-fuel) | 0.5–6 mm | Steel, copper, cast iron | 0.3–1 kg/h | Scale, wide bead | Very high | 1.4 |
| LBW (laser) | 0.5–6 mm | Steel, stainless, aluminum | 1–10 m/min | Narrow, bright | Very low | 1.8 |
| EBW | 1–50 mm | Steel, titanium, dissimilar | 0.5–3 m/min | Vacuum clean | Very low | 3.0 |
| FSW | 1–25 mm | Aluminum 2xxx–7xxx | 0.1–1 m/min | Tool marks | Low | 2.5 |
| Stud | 3–25 mm stud | Steel, stainless, aluminum | 0.1–1 s per stud | Small fillet | Low | 0.7 |
A 2.2 index can still be cheapest on a 200-part order when it removes a fixture or a machining step.
MIG Welding (GMAW)
MIG welding feeds a continuous wire electrode through a gun while shielding gas protects the pool. It covers 0.8 mm to 12 mm, deposits 1 to 4 kg per hour, and asks less skill than TIG or stick. Short-circuit transfer handles thin sheet, spray transfer flat plate.
Gas mix sets penetration and cost: 75% argon with 25% CO2 for spray transfer, 100% CO2 for cheaper work with more spatter, argon with 2% oxygen for stainless. Wind above about 2 m/s strips the shield and leaves porosity, and so does oil in the joint.
TIG Welding (GTAW)
TIG welding uses a non-consumable tungsten electrode and a separate filler rod, so heat and deposition are controlled independently. It covers 0.5 mm to 6 mm, gives the cleanest bead of any arc process, and suits stainless, aluminum, titanium and thin-wall tube. Deposition is 0.2 to 1 kg per hour.
Polarity does the work: DCEN for steel and stainless, alternating current for aluminum, where the positive half-cycle breaks up oxide. A backing purge protects stainless roots. Above about 8 mm it becomes a labor problem, and any oxide or draft shows up as porosity.
Stick Welding (SMAW)
Stick welding melts a flux-coated consumable electrode that supplies filler, shielding gas and slag together. Electrodes run 1.6 to 6 mm and cover plate from 2 mm to 25 mm, including rusty, dirty or windy sites where gas shielding fails. Deposition is 1 to 2 kg per hour and every pass needs cleaning.
The classification predicts behavior. E6010 is cellulosic and deep-penetrating, used for pipeline roots; E7018 is low-hydrogen and tougher but must stay dry in a rod oven, because moisture drives hydrogen cracking. Sheet below 2 mm burns through, and slag inclusion follows an uncleaned pass.
Flux-Cored Arc Welding (FCAW)
Flux-cored arc welding runs a tubular wire filled with flux, with or without external gas. It deposits 2 to 6 kg per hour, roughly double MIG at the same current, and tolerates mill scale and light rust. Self-shielded wire works in wind; gas-shielded wire runs cleaner and tougher.
Self-shielded wire is standard for field erection and shipyards because no gas bottle is needed. The trade-offs are slag removal between passes, fume that needs extraction, and wire stored dry. It struggles below about 1.5 mm and where slag cannot be reached for cleaning.
Submerged Arc Welding (SAW)
Submerged arc welding buries the arc under granular flux, so there is no visible arc, little fume and no spatter. Current runs 300 to 1,000 A, deposition reaches 5 to 25 kg per hour, and one pass penetrates 6 mm to 25 mm of steel. It works only flat and horizontal.
The trapped heat gives it the highest heat input of the common arc processes, which is why long straight seams run fast and thin restrained panels bow. Pipe seams, vessel shells and beam webs are its work. Damp flux leads to hydrogen cracking.
Resistance Welding: Spot, Seam and Projection
Resistance welding passes a high current through lapped sheets held under electrode force. Heat comes from resistance at the faying surface, and the nugget forms without filler or gas. A spot weld takes 0.1 to 0.5 seconds on 0.5 mm to 3 mm sheet and distorts almost nothing.
Spot welding
Nugget diameter is usually 4 to 5 times the square root of sheet thickness in mm, so 1 mm sheet needs a 4 to 5 mm nugget. Current, time, force and tip condition set the result; a mushroomed tip spreads current into a weak weld.
Seam welding
Roller electrodes replace fixed tips, and overlapping nuggets form a leak-tight seam at 1 to 5 m/min on 0.1 mm to 3 mm sheet. Fuel tanks and radiators use it because it seals as it joins. Speed and current must balance or the seam leaks.
Projection welding
A coined dimple or formed nut concentrates current where the weld is wanted, and several welds form in one stroke. Weld nuts and brackets attach to sheet without a fastener hole, given a parallel press and consistent projection height.
Oxy-Fuel Welding
Oxy-fuel welding burns acetylene in oxygen at a flame near 3,100 °C and melts the joint with a separate filler rod. It covers 0.5 mm to 6 mm steel, needs no electricity, and stays useful for pipework, HVAC, repair and preheating. Distortion is the highest of any process here.
Flame setting decides the result: neutral for steel, oxidizing for brazing. The same torch with a cutting attachment severs plate far thicker than it can weld. Aluminum needs a flux whose chloride residue must be washed off, and titanium is out of reach.
Laser Welding
Laser welding focuses a fiber or disk beam to a spot under a millimeter and melts the seam at power densities above 105 W/cm². Conduction mode handles thin sheet, keyhole mode welds deeper. It joins 0.5 mm to 6 mm at meters per minute with a narrow heat-affected zone.
Fit-up is the constraint: a keyhole will not bridge a gap wider than roughly 10% of sheet thickness without filler wire, so parts must be cut, formed and clamped accurately. Battery tabs, busbars and sensor housings are typical. Aluminum and copper reflect the beam when cold.
Electron Beam Welding
Electron beam welding accelerates electrons into the joint inside a vacuum chamber. Power density reaches 108 W/cm², single-pass penetration runs 50 mm and more in steel, and the heat-affected zone stays under a millimeter. The vacuum excludes oxygen, so titanium welds without flux or gas.
Voltage is typically 30 to 150 kV, and magnetic deflection steers the beam. Pump-down and chamber size set cycle time rather than welding speed. Gear and shaft assemblies, turbine parts and copper-to-steel joints are typical. Oversized or magnetized parts and gapped joints do not work.
Plasma Arc Welding
Plasma arc welding forces the arc through a water-cooled orifice, constricting it into a stiff column with energy density above TIG. Keyhole mode welds 6 mm to 12 mm steel in one pass from one side, while micro-plasma handles foil and 0.1 mm wire. It costs far less than laser.
Two gas flows are needed: plasma gas through the orifice and shielding gas around the cup. The arc punches through and surface tension closes the hole behind it, giving full penetration and a clean root. Standoff must be held constant or the arc wanders.
Friction Stir Welding
Friction stir welding is solid state. A rotating tool with a shoulder and pin stirs plasticized metal along the seam without melting it. It welds aluminum from 1 mm to 25 mm in one pass, makes no fume or porosity, and keeps 70 to 90 percent of parent strength in 6xxx alloys.
The tool needs a rigid machine, a backing anvil and axial force of several kilonewtons on thick plate. Travel is slow by fusion standards, 100 to 1,000 mm/min, but the joint is made in one pass with no filler. Steel wears tools quickly and the retracting pin leaves an exit keyhole.
Stud Welding
Stud welding attaches a fastener in one cycle. Drawn-arc stud welding strikes a pilot arc, withdraws the stud, then plunges it into the molten pool inside a ceramic ferrule in 0.1 to 1 second. Studs run 3 mm to 25 mm diameter, and capacitor-discharge units handle sheet from 0.8 mm.
The ferrule contains and shields the pool, and one trigger pull completes the weld. Capacitor discharge is faster and ferrule-free for small studs. Shear connectors through decking, insulation pins and tapped studs use it because access is needed from one side only.
Robotic Welding
Robotic welding mounts a MIG, TIG or flux-cored torch on a six-axis arm that repeats a path within about ±0.1 mm, usually with a positioner turning the part to keep the weld flat. It raises arc time and holds parameters steady, but pays back only when parts repeat.
The cost is in fixtures and programming, not the arm. A cell needs a fixture locating every part within about a millimeter, a program or offline model, and seam tracking to absorb variation. A few dozen parts a year rarely justify it; a few thousand usually do.
Which Welding Process Fits Your Part?
Choose in this order: thickness, material, joint access, finish, then volume. Sheet under 3 mm goes to MIG, TIG, laser or spot. Plate from 6 mm goes to flux-cored or submerged arc. Aluminum housings go to TIG, friction stir or laser, and fasteners to stud or projection.
| Part and thickness | Annual volume | First choice | Alternative | Avoid |
|---|---|---|---|---|
| Sheet metal enclosure, 1–3 mm | 1–500 | MIG or TIG | Spot for coated sheet | Submerged arc |
| Precision bracket, 0.8–2 mm | 1,000+ | Laser or spot | MIG | Stick |
| Structural gusset, 6–20 mm | 50–1,000 | Flux-cored | MIG multi-pass | Laser |
| Long beam or web, 10–40 mm | 100+ | Submerged arc | Flux-cored | TIG |
| Pressure vessel shell, 8–50 mm | 10–200 | Submerged arc, TIG root | Flux-cored | Oxy-fuel |
| Stainless tube, 1.5–6 mm | 100+ | Orbital TIG | Plasma | Stick |
| Aluminum tray, 1–4 mm | 100+ | Friction stir or laser | Pulsed MIG | Stick |
| Dissimilar section, 5–50 mm | Any | Electron beam | Friction stir | Oxy-fuel |
| Stud on sheet, 0.8–6 mm | 1,000+ | Stud welding | Projection | MIG |
| Body panel, 0.7–2 mm | 10,000+ | Spot | Laser | Flux-cored |
| Cast iron repair, 5–30 mm | 1–20 | Stick, nickel electrode | Oxy-fuel with flux | MIG |
| Foil part, 0.05–0.5 mm | Any | Micro-plasma or laser | TIG | Submerged arc |
Two rules settle the rest: do not specify a process that needs a preparation the part cannot hold, and do not specify one the volume cannot pay for. A supplier running sheet metal fabrication and production welding under one roof also removes a tolerance stack.
Weld Quality Checks and Common Defects
Inspection starts before the first arc: a qualified procedure, a supporting qualification record, and welders qualified to ISO 9606 or AWS D1.1. In process, control fit-up, cleaning, preheat and interpass temperature. After welding, inspect 100 percent visually against ISO 5817 level B or C, then test only the joints the drawing calls critical.
Visual inspection finds more defects than any other method and costs almost nothing. Dye penetrant finds surface-breaking cracks on stainless and aluminum, magnetic particle finds near-surface flaws in steel, ultrasonic finds lack of fusion in thick section, and radiography images porosity and slag. The inspection and quality assurance process adds procedure records, certificates and a CMM report.
Most defects come from four inputs: contamination, wrong parameters, poor fit-up and moisture. Porosity is gas trapped as the pool freezes, lack of fusion is insufficient heat or too fast travel, undercut is excess current or a long arc, and hydrogen cracking comes from moisture in flux or on the plate.
| Defect | Cause | Prevention | Detection |
|---|---|---|---|
| Porosity | Damp flux, oil, lost gas cover | Dry consumables, clean joint | Visual, radiography |
| Slag inclusion | Slag left between passes | Chip and brush each pass | Radiography, ultrasonic |
| Lack of fusion | Travel too fast, current too low | Raise current, grind oxide | Ultrasonic, macro |
| Incomplete penetration | Root gap too small, heat too low | Correct gap, open root | Radiography |
| Undercut | Excess current, long arc | Lower current, shorter arc | Visual, magnetic particle |
| Solidification cracking | High sulfur, deep narrow bead | Filler match, wider bead | Penetrant, radiography |
| Hydrogen cracking | Moisture, high hardness, fast cooling | Dry consumables, preheat | Delayed particle or ultrasonic |
| Lamellar tearing | Through-thickness strain | Joint redesign, buttering | Ultrasonic |
| Distortion | Uneven shrinkage, excess heat | Balanced sequence, backstep | Dimensional check |
| Burn-through | Excess current on thin sheet | Lower current, backing | Visual |
Hydrogen cracking can appear 24 to 48 hours after welding, so structural inspections are often repeated the next day.
How to Specify Welds on a Drawing
A weld callout needs the process and procedure reference, a symbol with size and length, the acceptance level and any post-weld treatment. Use AWS A2.4 or ISO 2553 symbols rather than notes, state the level as ISO 5817 B or C, and add preheat, interpass limit and cleaning.
Symbols translate without ambiguity. A fillet with a 5 mm leg on the arrow side, a length and a pitch tells the welder what to run, and the AWS A2.4 welding symbols guide covers the reference line, arrow, tail and supplementary marks. Name the base metal by standard: ASTM A36 or A572 Grade 50, 304 or 316L, 5052 or 6061.
Give the filler class, such as ER70S-6 or ER308L, or cite a WPS. State the finish order, because welding after coating destroys the film.
Welding Cost Drivers and Lead Time
Cost per welded part comes from arc time, fit-up, fixturing, consumables, inspection and rework, not from the hourly rate alone. A one-meter fillet with a 6 mm leg takes about four minutes of arc time with flux-cored and fifteen with TIG, and labor dominates the difference.
Design moves the number more than process choice. Oversized fillets are the usual waste: a 6 mm leg where 4 mm carries the load adds about 50 percent more weld metal. Welding, stress relief, machining and finishing in that order is what lets a frame hold ±0.005 mm on a bore.
Sheet metal assemblies ship in 5 to 12 business days depending on finishing, and machined parts in 3 to 10 business days after drawing approval. Post-weld assembly is quoted separately when the drawing calls for it.
Frequently Asked Questions About Types of Welding
These five questions come up most often when a drawing reaches a fabricator: process choice for thin sheet, relative cost, aluminum MIG, single-pass depth and distortion control. Each answer gives a working range so you can check it against the comparison table above.
Is TIG or MIG better for thin sheet?
Below about 1 mm, TIG gives the control to avoid burn-through, especially with pulsed current. Between 1 mm and 3 mm, MIG is faster and cheaper per meter, and laser or spot beat both at high volume. Choose TIG for visible or stainless joints, MIG when speed matters more.
What is the cheapest welding process?
It depends on volume. Resistance spot welding has the lowest cost per joint in high-volume production because a weld takes under a second. Submerged arc has the lowest cost per meter on long straight seams. For a handful of parts or field repair, stick wins because the equipment is cheap.
Can you MIG weld aluminum?
Yes. Aluminum MIG uses pure argon or an argon-helium mix, a push angle, and a spool gun or push-pull torch to feed the soft wire. It is faster than TIG above 3 mm. Thin aluminum, visible joints and repair work still favor alternating-current TIG, which breaks up the oxide.
How thick can a single weld pass be?
Electron beam leads at 50 mm and more in steel, followed by laser at roughly 6 to 12 mm depending on power. Plasma keyhole covers 6 to 12 mm, submerged arc 6 to 25 mm, and MIG about 6 to 8 mm without a groove. TIG is limited to 3 to 4 mm per pass.
How do you control distortion?
Reduce heat input, balance the weld sequence around the neutral axis, backstep long seams, clamp the part, and use the smallest leg size the load allows. Pre-setting the part in the opposite direction helps on thin panels. Stress relief after welding removes residual stress before machining.
How Do You Get Welded Parts Made?
Send a drawing that carries weld symbols, the base metal standard, filler class and acceptance level, and state the annual volume. That package lets a fabricator choose the process, confirm the procedure and quote without a clarification round. Lead time follows the finishing route rather than the welding itself.
YC Prime Precision is an ISO 9001-certified contract manufacturer in Qingdao, Shandong, with 20+ years of production experience, 500+ customers and 120+ countries served from 90,000 m² of factory space. MIG, TIG, spot and robotic welding run alongside sheet metal fabrication and CNC machining, with stress relief and finishing in the same plant. CMM inspection, material certificates and inspection reports are available on request. Send the drawing to get an instant quote; sheet metal assemblies typically quote at 5 to 12 business days, machined parts at 3 to 10 after drawing approval.
