MIG vs TIG welding: what actually differs
One electrode melts, the other does not — and everything else follows from that. Speed, heat, skill, gas, and cost, and which process suits which job.
Ask what separates MIG from TIG and you will get a list: speed, heat, spatter, appearance, price. All of it is true, and all of it is downstream of a single mechanical difference.
In MIG the wire is the electrode, and it melts. In TIG the electrode is tungsten, and it does not. Everything else follows.
The one difference everything else comes from
In MIG — properly GMAW, gas metal arc welding — a spool of wire feeds continuously through the torch. That wire carries the current, strikes the arc, and melts into the joint. Filler and arc are the same thing, arriving at the same time, at whatever rate the feeder is set to. It is a fundamentally fast arrangement, and it needs only one hand and a trigger.
In TIG — GTAW, gas tungsten arc welding — the electrode is tungsten, chosen because it melts at a higher temperature than anything it is welding. It strikes the arc and stays put. Filler, if the joint needs any, comes from a separate rod the welder dips into the pool by hand. Two hands, two rhythms, and complete control over how much metal goes in and when.
That is the whole distinction. The rest of this page is consequences.
Speed and deposition
Because MIG’s filler feeds itself, it deposits far more metal per hour than a welder can dip by hand. Conventional manual TIG sits at the bottom of every deposition chart — around 0.3 kg/hr is typical — while MIG runs several times that.
On thick section and long runs, that gap decides the job. A structural fabricator welding heavy carbon steel is not going to dip filler by hand, and no argument about weld quality will change that.
Heat input and distortion
MIG’s speed comes with heat. More current, more filler, more energy into the part — and heat input is what drives distortion, residual stress and, in corrosion-resistant alloys, loss of the properties the alloy was chosen for.
TIG puts in less. A tighter, more controllable arc and a slower, deliberate fill mean a narrower heat-affected zone and a part that stays closer to its intended shape. On thin wall, that is not a refinement but a requirement — MIG’s heat will blow through material that TIG welds comfortably.
Cleanliness: spatter, slag, and fusion
MIG spatters. How much depends on the transfer mode, the gas, and the settings, but it spatters, and the spatter has to come off. It also carries genuine risks of lack of fusion and poor tie-ins — defects that hide under a bead that looks perfectly acceptable from outside.
TIG does neither. There is no slag, no interpass cleaning, and the weld pool is visible and controllable throughout. That is why TIG is what codes specify for root passes, for pressure work, and for anything that will be radiographed.
Skill
This is where the two diverge most for shops trying to hire.
MIG is quick to learn. A capable welder is productive on it within days, and the process forgives a good deal.
Manual TIG is a genuine craft. Steering the torch, dipping the filler in rhythm, holding a short arc without touching the tungsten and contaminating it — that takes months to learn and years to master at code quality. In a market short of skilled welders, that difference is a business constraint, not a technical footnote.
Shielding gas
MIG uses an active mixture — argon with CO₂ for steel, or small oxygen additions — which stabilises the arc and shapes the bead. The M in MAG stands for active gas.
TIG needs a genuinely inert shield, in practice pure argon. The two are not interchangeable in either direction: MIG’s gas destroys a tungsten electrode, and pure argon makes a poor MIG arc on steel. If that side of the job is what you are working out, the shielding gas guide covers purity, flow rates, and purge gas in detail.
Cost
Equipment cost is similar enough not to decide anything. What differs is what the weld costs once it is made.
MIG wins on arc time and consumables. TIG wins on everything that happens afterwards — no spatter to grind, no slag to chip, no interpass cleaning, and a lower rejection rate on inspected work. On a job with no inspection and forgiving metallurgy, MIG is cheaper. On a job where a rejected weld means cutting it out, the arithmetic reverses.
At a glance
| MIG / MAG (GMAW) | TIG (GTAW) | |
|---|---|---|
| Electrode | Wire, consumed | Tungsten, not consumed |
| Filler | Same as electrode | Separate rod, optional |
| Shielding gas | Ar/CO₂, Ar/O₂ (active) | Pure argon (inert) |
| Deposition | High | Lowest of the common processes |
| Heat input | High | Low |
| Spatter | Yes | None |
| Interpass cleaning | Usually | None |
| Skill to learn | Days | Months to years |
| Typical work | Thick steel, production, structures | Thin wall, stainless, aluminum, titanium, roots, code work |
Which to choose
Choose MIG when throughput is the priority and the metallurgy is forgiving: heavy carbon-steel structures, long runs, high-volume fabrication, jobs where tolerances leave room for distortion and nothing gets radiographed.
Choose TIG when the weld has to be verifiably right: thin wall, stainless and duplex, nickel alloys, aluminum, titanium, root passes on pipe, hygienic surfaces, anything code-driven or inspected.
Most shops that do both do exactly that — MIG where volume rules, TIG where the joint does.
Where the line has moved
The comparison above describes conventional versions of both processes, and one part of it is no longer fixed.
TIG’s deposition rate was always its limitation, and the cause was the cold filler rod: dipping cold metal into the pool chills it and forces slow travel. Hot wire TIG breaks that link. A separate low-voltage source heats the filler close to melting point before it enters the pool, and a feeder delivers it mechanically instead of by hand.
That changes two of the entries in the table at once. Deposition climbs to MIG-class figures — around 4 kg/hr and beyond, depending on the application — while the arc stays a TIG arc, so the heat input, the absence of spatter and the fusion quality stay where TIG has always been. And because the wire is fed rather than dipped, the operator manages torch angle and travel instead of a two-handed rhythm, which shortens the learning curve considerably.
That is the process TIP TIG makes. If you are weighing it against a MIG line you already run, the direct comparison has the numbers side by side.
In short
MIG melts its electrode; TIG does not. From that follows MIG’s speed and heat and spatter, and TIG’s control, cleanliness and skill requirement. Pick MIG for volume on forgiving material, TIG for anything that has to survive an inspector. And note that the deposition gap — the one reason most shops give for not using TIG — is the one part of the comparison that modern hot wire processes have closed.