Types of Welding: Processes, Advantages, Disadvantages and Applications

There are two broad types of welding: fusion welding, where the edges are melted and fuse together, and solid-state welding, where the metals are joined by pressure, friction or diffusion without melting. Fusion welding is further split by heat source into arc welding (SMAW, MIG/MAG, TIG, SAW, FCAW, plasma), gas welding (oxy-acetylene), resistance welding (spot, seam, projection) and high-energy-beam welding (laser, electron beam). Solid-state welding covers friction, friction stir, forge, cold, ultrasonic and explosion welding.

This page is the overview. Each process gets a short section with its advantages, disadvantages and applications, and a link to our detailed page where one exists. The comparison table and the “how to choose” guide are further down.

How are welding processes classified?

The cleanest way to classify welding is by where the heat (or energy) comes from and whether the metal melts.

Soldering and brazing also join metals, but they are not welding: the base metal never melts, only a lower-melting filler does. See soldering vs brazing and the brazing process for those.

Arc welding processes

Arc welding is the largest and most used family. An electric arc forms between an electrode and the workpiece and melts both; something (a flux, a gas or both) shields the molten pool from oxygen and nitrogen in the air. For the power sources behind these processes (transformer, inverter, CC vs CV output), see welding machine types.

1. Shielded metal arc welding (SMAW, stick or MMA)

A consumable electrode coated with flux is struck against the work. The coating burns to form a gas shield and a slag layer over the weld. It needs only a power source, a holder and a box of rods, so it is the standard process on Indian building sites, fabrication shops and pipelines.

• Advantages: cheap, portable, works outdoors in wind, all positions, suits most steels and cast iron.
• Disadvantages: slow (rods must be changed, slag chipped), spatter, not suited to thin sheet or reactive metals, needs a skilled welder.
• Applications: structural steel, repair and maintenance, pipelines, agricultural equipment.

More: stick welding in detail.

2. Gas metal arc welding (GMAW, MIG/MAG)

A continuous bare wire is fed through a gun, and a shielding gas flows around it. With an inert gas (argon, helium) it is called MIG; with an active gas (CO₂ or argon-CO₂ mixes, common for steel) it is MAG.

• Advantages: fast, no slag, easy to learn, easy to automate and robotise.
• Disadvantages: gas shield blows away outdoors, equipment costs more than stick, risk of lack of fusion if the settings are wrong.
• Applications: automobile and two-wheeler frames, sheet-metal fabrication, robotic production lines, aluminium work.

More: MIG welding.

3. Gas tungsten arc welding (GTAW, TIG)

The arc comes from a non-consumable tungsten electrode, shielded by argon. Filler rod, if needed, is added by the other hand. AC is used for aluminium and magnesium, DC electrode-negative for steel and stainless steel.

• Advantages: the cleanest, most precise arc weld, no spatter or slag, welds almost any metal including titanium, very good on thin sections.
• Disadvantages: slow, low deposition rate, needs high welder skill and clean surfaces.
• Applications: root passes in pipes, aerospace parts, stainless steel food and pharma piping, bicycle frames.

More: TIG welding and welding aluminium.

4. Submerged arc welding (SAW)

A wire electrode is fed automatically, and the arc burns under a blanket of granular flux, so it cannot be seen. Almost no heat escapes, which is why it has the highest thermal efficiency of the arc processes.

• Advantages: very high deposition rate, deep penetration, no arc glare or spatter, consistent quality.
• Disadvantages: only flat and horizontal positions (the flux would fall off), mostly for thicker steel, flux handling and recovery needed.
• Applications: pressure vessels, boilers, large-diameter pipes, ship panels, heavy structural beams, wind towers.

5. Flux-cored arc welding (FCAW)

Like MIG, but the wire is a tube filled with flux. Self-shielded wire needs no gas; gas-shielded wire uses CO₂ or argon-CO₂ as well.

• Advantages: higher deposition than stick, self-shielded wire works outdoors, good for thick sections and positional work.
• Disadvantages: slag to remove, more fume, wire costs more than solid wire.
• Applications: shipbuilding, construction steel, heavy equipment repair.

More: flux-cored welding.

Plasma arc welding (PAW)

A close relative of TIG in which the arc is squeezed through a narrow nozzle, giving a hotter, more concentrated arc. It can weld in keyhole mode and is used for precision tube and thin-sheet work.

Gas welding: oxy-acetylene

Acetylene burns with oxygen at the torch tip to give a flame of roughly 3100-3200 °C, hot enough to melt steel. A neutral flame is used for most steel; an oxidising flame for brass; a carburising flame for some hard-facing.

• Advantages: no electricity needed, cheap and portable, the same set can cut, heat, braze and bend.
• Disadvantages: slow, wide heat-affected zone and distortion, poor for thick sections, cylinder handling risks.
• Applications: thin sheet and small pipe repair, maintenance work, and above all oxy-fuel cutting.

Resistance welding: spot, seam and projection

Two sheets are clamped between copper electrodes and a large current (typically several thousand amperes) is passed for a fraction of a second. The resistance at the sheet interface heats and melts a small nugget (heat = I²Rt), and the electrode force forges it. No filler, flux or gas is used.

• Spot welding: separate round nuggets. A car body-in-white carries thousands of spot welds.
• Seam welding: roller electrodes make overlapping spots, giving a leak-tight seam for fuel tanks, drums and radiators.
• Projection welding: small raised projections concentrate the current, used to weld nuts and studs to sheet.
• Flash butt welding: two ends are flashed, then forged together, used for rails, chain links and wheel rims.

Advantages: very fast (under a second per spot), easy to automate, no consumables. Disadvantages: costly machines, mostly limited to lap joints in sheet, joint quality is hard to inspect.

High-energy-beam welding: laser and electron beam

A laser or an electron beam is focused to a very small spot, giving such high power density that it vaporises a narrow “keyhole” through the joint. The result is a deep, narrow weld with a small heat-affected zone and little distortion.

• Laser beam welding: works in air with a gas shield, easy to put on a robot; used for car body panels, tailored blanks, battery tabs and medical devices.
• Electron beam welding: needs a vacuum chamber, but can weld very thick sections in one pass; used for aerospace, nuclear and precision parts.

Advantages: high speed, minimal distortion, joins some dissimilar metals. Disadvantages: very high equipment cost, tight fit-up needed, safety enclosures (laser light, X-rays from electron beams).

Solid-state welding processes

In solid-state welding the metal never melts, so there is no cast weld structure, no porosity from gas and little change to the base metal. It is also the route for many dissimilar-metal joints (aluminium to copper, aluminium to steel) that cannot be fusion welded well.

Friction welding

One part is spun against the other under pressure. Friction heats the interface to a plastic state, the rotation stops, and a forging force completes the joint, pushing out a ring of flash. Used for drill pipes, axle shafts, engine valves and bimetal joints.

Friction stir welding (FSW)

A rotating tool with a shoulder and pin is plunged into the joint line and moved along it, stirring the softened metal of both plates together. Invented at TWI in the UK in 1991, it is now widely used for aluminium: ship decks, rail coaches, rocket fuel tanks and aircraft panels.

Forge welding and cold welding

Forge welding is the oldest process: a blacksmith heats two pieces to a white heat and hammers them together. Cold welding joins clean, oxide-free metal surfaces by high pressure alone at room temperature; it works best with soft, ductile metals such as aluminium and copper wire. See cold welding.

Other solid-state methods

• Ultrasonic welding: high-frequency vibration under light pressure; used for wires, battery tabs and thin foils (and plastics).
• Explosion welding: an explosive charge drives one plate onto another; used to clad steel with stainless steel, titanium or copper.
• Diffusion bonding: parts are held at high temperature and pressure until atoms diffuse across the interface; used in aerospace.

Thermit welding

Although it is a fusion process, it fits nowhere else. A mix of aluminium powder and iron oxide is ignited in a crucible above a mould around the rail gap; the reaction produces molten steel that runs into the gap. Railways use it to join rails on track, because it needs no power supply.

Comparison table of welding processes

Thickness and cost columns are typical, not limits; they vary with joint design and equipment.

Worked example: heat input for SMAW vs SAW

Heat input tells you how much energy each millimetre of weld receives. It controls the width of the heat-affected zone, the cooling rate and so the hardness and toughness of the joint, which is why welding procedures record it. ISO/TR 17671-1 (the same method is used in EN 1011-1) gives:

Q = k × (V × I × 60) / (1000 × S) in kJ/mm

where V is arc voltage (volts), I is current (amperes), S is travel speed (mm/min) and k is the thermal efficiency factor: 1.0 for SAW, 0.8 for SMAW, MIG/MAG and FCAW, 0.6 for TIG and plasma. The part without k is called the arc energy.

SMAW fill pass: V = 24 V, I = 160 A, S = 150 mm/min, k = 0.8.

• Arc energy = (24 × 160 × 60) / (1000 × 150) = 230,400 / 150,000 = 1.536 kJ/mm
• Heat input Q = 0.8 × 1.536 = 1.23 kJ/mm

SAW pass: V = 32 V, I = 550 A, S = 500 mm/min, k = 1.0.

• Arc energy = (32 × 550 × 60) / (1000 × 500) = 1,056,000 / 500,000 = 2.112 kJ/mm
• Heat input Q = 1.0 × 2.112 = 2.11 kJ/mm

The SAW pass puts about 1.7 times as much heat into each millimetre (2.11 / 1.23), even though it travels more than three times faster, because its current is so much higher and none of the arc heat is lost to the air. That is why SAW fills thick joints in fewer passes, and also why its heat-affected zone is wider and cools more slowly. For the effect on the HAZ, see our welding processes notes.

Tip: in exam problems, check the speed unit. If S is in mm/s, drop the 60: Q = k × V × I / (1000 × S).

How to choose a welding process

• Material: aluminium, titanium and thin stainless point to TIG or MIG; plain carbon steel can use almost anything; dissimilar metals often need friction, friction stir, explosion or beam welding.
• Thickness: thin sheet (under about 3 mm) suits TIG, MIG, spot or laser; thick plate suits SAW, FCAW or multi-pass SMAW.
• Position and site: overhead and vertical work outdoors favours stick or self-shielded flux-cored; SAW is flat and horizontal only; gas-shielded processes need shelter from wind.
• Volume: one-off repair favours stick or oxy-acetylene; mass production favours robotic MIG, resistance spot or laser.
• Quality and looks: TIG for the cleanest visible welds and critical root runs; electron beam or friction stir for the highest-integrity joints.
• Budget and skill: stick has the lowest equipment cost but needs a skilled hand; automated processes cost more but depend less on the operator.

Welding safety

• Eyes and skin: the arc gives off intense ultraviolet light that causes “arc eye” and skin burns. Use a welding helmet with the filter shade the lens maker recommends for your current, plus flame-resistant clothing and gloves. Screens protect people nearby.
• Fumes: use extraction or good ventilation, especially for galvanised, stainless and flux-cored work.
• Electric shock: dry gloves, sound cables and a proper return clamp; take care in wet or confined spaces.
• Fire: sparks travel several metres. Clear flammables and keep an extinguisher ready.
• Gas cylinders: keep upright and chained, use flashback arrestors on oxy-fuel sets, and never let oil touch oxygen fittings.

Further reading: the American Welding Society (AWS), the fusion welding process overview on ScienceDirect, and the manufacturing processes courses on NPTEL.

FAQs

What are the main types of welding?

Welding splits into fusion and solid-state processes. The main fusion types are arc welding (stick, MIG/MAG, TIG, submerged arc, flux-cored), gas welding (oxy-acetylene), resistance welding (spot, seam) and beam welding (laser, electron beam). Solid-state types include friction, friction stir, forge, cold and ultrasonic welding.

Which type of welding is the strongest?

No process is strongest in every case. A correctly made weld with any suitable process can match the strength of the base metal. For critical joints, TIG, electron beam and friction stir welding usually give the fewest defects, while SAW gives sound welds in thick steel.

Which welding process is easiest to learn?

MIG (GMAW) is generally the easiest arc process to learn, because the wire feeds itself and there is no slag. Stick welding is cheap but harder to master, and TIG needs the most hand skill.

What is the difference between fusion and solid-state welding?

In fusion welding the joint edges melt and solidify together, usually with a filler. In solid-state welding the metals are joined below their melting point by pressure, friction, vibration or diffusion, so there is no molten pool.

Which welding is used for car bodies?

Car bodies are mainly joined by resistance spot welding, with robotic MIG welding and laser welding used for some seams and high-strength parts.

Related Topics on EngineeringHulk

• 👉 Welding Machine Types
• 👉 Stick (SMAW) Welding
• 👉 MIG Welding
• 👉 TIG Welding
• 👉 Cold Welding
• 👉 Welding Defects