There are dozens of types of welding processes, but four cover almost all of the work: stick, MIG, TIG and flux-cored. All four strike an electric arc and melt the parent metal. What separates them is how the weld is shielded from the air, and that one difference decides which you can use outdoors, on aluminium, or on rust.
The four arc processes compared
| Process | Shielded by | Best for | Works outdoors | Hardest part |
|---|---|---|---|---|
| Stick (SMAW / MMA, ISO 111) | Flux burning off the electrode | Rust, paint, thick steel, site work | Yes | Striking and holding the arc |
| MIG (GMAW, ISO 131) | Bottled gas, usually argon or a mix | Long clean welds on steel in a shop | No, wind blows the shield away | Setting wire speed against voltage |
| TIG (GTAW, ISO 141) | Bottled argon | Aluminium, stainless, thin wall, visible welds | No | Two hands and a foot at once |
| Flux-cored (FCAW) | Flux inside the wire, sometimes gas as well | Thick steel outdoors at wire-feed speed | Yes, the self-shielded kind | Slag, and a lot of spatter |
The four arc processes you will actually meet
Stick welding (SMAW)
An arc between a flux-coated consumable rod and the work. The flux burns to make its own gas shield and leaves slag over the bead, which you chip off. No gas bottle, no wire feeder, no regulator - which is why it still goes to the top of a structure or out to a field. It tolerates rust, paint and mill scale better than anything else here. Setting the amperage and striking the arc is the whole skill, and the number on the rod tells you the rest.
Where it struggles: sheet metal, aluminium, and anything that has to look good without a grinder. You also stop every time a rod runs out, which is roughly every twelve inches of weld.
MIG welding (GMAW, and MAG)
A motor feeds bare wire through the torch while bottled gas shields the puddle. Pull the trigger and it welds continuously, which makes it the fastest of the four to learn and the fastest to lay down metal. Strictly, MIG uses inert gas and MAG uses an active mix such as argon with carbon dioxide - the gas you choose changes the penetration and the spatter as much as the machine does. Wire speed against voltage is the setting that decides whether it works.
Where it struggles: outdoors. A light breeze pulls the gas shield off the puddle and the weld fills with porosity, and you will not see it until it fails.
TIG welding (GTAW)
A non-consumable tungsten electrode makes the arc; argon shields it; your other hand feeds filler rod into the puddle, usually with a foot pedal controlling the current. It is the slowest process and the most controllable, and the only one of the four that will weld aluminium properly - which needs alternating current to strip the oxide off. If you are buying, our comparison of AC/DC and DC-only TIG machines covers what the numbers on a spec sheet mean, and MIG against TIG is the choice most people are actually making.
Where it struggles: speed, and the learning curve. Two hands and a foot doing three different things is genuinely hard for the first few hours.
Flux-cored arc welding (FCAW)
A wire feeder like MIG, but the wire is a tube with flux inside it. Self-shielded flux-cored needs no gas at all, which gives you wire-feed speed outdoors. Gas-shielded flux-cored adds a bottle and gives a cleaner, stronger deposit on thick steel.
Where it struggles: it makes slag and a great deal of spatter, and it is overkill on anything thin.
The processes behind the ones you meet
These four are not the whole list. Most of the steel in the things around you was joined by a process no hobbyist ever touches.
- Submerged arc (SAW, ISO 121) - the arc runs under a blanket of granular flux, invisible and with no spatter. This is how pipe mills and shipyards lay very long, very thick welds
- Plasma arc (ISO 15) - TIG with the arc squeezed through a constricting nozzle, which makes it hotter and far more concentrated. Also the basis of plasma cutting
- Resistance spot welding - no arc and no filler. Two copper electrodes clamp the sheets and a heavy current through the joint melts a nugget between them. The seams on a car body are thousands of these
- Oxy-fuel welding - a flame rather than an arc, oxygen and acetylene. Largely replaced for welding, still used for cutting, brazing and heating
- Laser and electron beam - very narrow, very deep welds with almost no heat-affected zone. Automotive and aerospace production, not workshops
- Friction stir welding - no melting at all. Invented by Wayne Thomas at TWI in 1991: a rotating profiled tool is plunged into the joint line and traversed along it, heating and softening the metal without melting it. Now used on aluminium in aerospace, rail, shipbuilding and electric vehicle battery trays
Fusion or solid-phase: the distinction that explains the rest
TWI classifies joining processes by one question: does the parent metal melt? In a fusion process, as TWI put it, the edges of a component are melted together to form weld metal. Stick, MIG, TIG, flux-cored, submerged arc, laser and oxy-fuel are all fusion. Friction stir and resistance welding are not: they join in the solid phase, under heat and pressure. And brazing and soldering are not welding at all, because only the filler melts - the line between them is 450 degrees C.
The distinction matters for a practical reason. A fusion weld changes the metal's structure in a band either side of the joint, the heat-affected zone, and that band is where cracks start. A solid-phase process makes a much smaller one, which is why aerospace aluminium is friction stir welded rather than fused.
Which welding process should you learn first?
Watch this before you decide. The Kentucky Welding Institute is an accredited welding school, and seeing the three processes compared does more in a few minutes than any table on this page.
Pick by what you are joining, not by what looks impressive
In order, from the most common answer to the least.
- Mild steel, in a garage, and you want welds this weekend
- MIG. Shortest path from nothing to a sound weld
- Farm gates, trailers, rusty brackets, or anything outdoors
- stick. One machine, a handful of rods, no bottle to rent
- Aluminium, stainless, exhaust tube, anything on show
- TIG. Expect to be bad at it for a fortnight
- Structural steel thicker than a quarter inch, outdoors
- flux-cored
- All four on one machine
- a multiprocess inverter does MIG, stick and DC TIG. It will not do AC TIG, so it will not do aluminium
Frequently asked questions
How many types of welding processes are there?
Dozens are catalogued, and BS EN ISO 4063 gives each a number - 111 for stick, 131 for MIG, 141 for TIG. Four of them cover nearly all manual work: stick, MIG, TIG and flux-cored. The rest are production processes such as submerged arc, resistance spot and laser welding, which run on machines rather than in hands.
Which welding process is the strongest?
None of them, as a property of the process. A sound weld in any of the four is stronger than the steel around it, because the filler is chosen to over-match the parent metal. What differs is how easy each process makes it to produce a sound weld in a given situation - TIG on thin stainless, stick on rusty plate outdoors.
Which is the easiest welding process to learn?
MIG. One trigger, one hand, and the machine feeds the filler for you. Stick is next, and its difficulty is concentrated in the first hour - striking the arc without sticking the rod. TIG is the hardest, because your two hands and one foot each have a different job.
Can one machine do all of them?
A multiprocess inverter will do MIG, stick and DC TIG, and many will run flux-cored wire as well. The gap is AC TIG, which is what aluminium needs; only a machine that says AC/DC will do it. Buying one multiprocess machine is usually cheaper than two dedicated ones and worse at each job than either.
What is the difference between MIG and MAG?
The gas. MIG is metal inert gas, argon or helium, and is what aluminium and stainless need. MAG is metal active gas, usually argon mixed with carbon dioxide, which reacts in the arc and gives deeper penetration on steel. In American usage both are called MIG, and the formal name for both is GMAW.
Sources
- TWI - Welding and joining process classification, and the BS EN ISO 4063 process numbers
- TWI - What is arc welding, and the process types
- TWI - Friction stir welding: invented by Wayne Thomas at TWI in 1991
- TWI - MIG and MAG welding, and the difference between them
- American Welding Society - What is GTA welding
- Kentucky Welding Institute - MIG vs TIG vs Stick, run side by side
In short
Every arc process melts the parent metal; the difference is how it keeps the air out, and everything else follows from that. Flux keeps working in the wind, so stick and self-shielded flux-cored go outside. Bottled gas does not, so MIG and TIG stay in the shop. Choose by what you are joining and where you are standing, and the rest of the list - submerged arc, laser, friction stir - is production equipment you will read about rather than own.