The Short Answer
MIG for speed and production. TIG for precision and appearance. But if that were the whole story, nobody would need both on the truck.
The real answer depends on material, thickness, position, environment, and what the customer is paying for. Most working welders run both processes and pick based on the job. Here's how to think about it.
How They Work
MIG (GMAW) feeds a consumable wire electrode through a gun with shielding gas (typically 75/25 argon/CO2 for steel, pure argon for aluminum). The wire melts into the joint. You pull the trigger and go. The machine handles wire speed and voltage — you control travel speed, angle, and stick-out.
TIG (GTAW) uses a non-consumable tungsten electrode to create the arc. You feed filler rod by hand with one hand and control the torch with the other. A foot pedal or thumb control adjusts amperage in real time. Shielding gas is pure argon (or helium/argon mix for thicker aluminum). Everything is manual. Everything is precise.
When MIG Wins
Thicker steel. Anything over 1/4" where appearance isn't critical — MIG is faster by a wide margin. Structural steel, equipment repair, trailer frames, heavy plate. You can lay down a 1/4" fillet in a single pass with MIG. TIG on the same joint takes three or four passes.
Production work. If you're running 200 feet of fillet weld on a fabrication job, MIG is the only sane choice. Wire-fed processes have a higher deposition rate — you're putting more metal down per hour, which means lower labor cost per foot of weld.
Vertical and overhead. MIG with the right wire and settings is manageable in position. Short-circuit transfer on vertical-up is a bread-and-butter mobile welding technique. TIG in overhead is doable but slow and brutal on your arms.
Wind. MIG's gas flow rate can be cranked up to compensate for mild wind. In serious wind, neither process works well — but flux-core (FCAW) is self-shielded and handles it. On a mobile rig, wind is a daily reality.
Field repairs. A farmer calls with a broken loader arm. The excavator contractor has a cracked bucket tooth. You're not there to make art — you're there to get iron back to work. MIG gets the repair done and the machine running.
When TIG Wins
Thin material. Anything under 1/8" and especially under 16 gauge — TIG gives you the heat control to avoid burn-through. Sheet metal, tubing, thin wall pipe. The foot pedal lets you feather the amperage as you weld, which is the difference between a good bead and a hole.
Aluminum. TIG on aluminum is the gold standard. AC current breaks up the oxide layer while the tungsten maintains a stable arc. MIG with a spool gun works for thicker aluminum, but for anything cosmetic or structural under 1/4" — TIG is the move. Boat hulls, intake manifolds, aluminum railings, trailer skins.
Stainless steel. TIG produces the cleanest stainless welds with the least discoloration. Back-purging with argon on the root side keeps the sugaring down. For food-grade, pharmaceutical, or architectural stainless — TIG is usually spec'd.
Cosmetic work. Handrails, furniture, gates, art pieces — anything the customer will see. TIG stack-of-dimes beads look professional. MIG beads on visible work look like you were in a hurry, because you were.
Pipe. Open root pipe welding (6G position) is a TIG job. The root pass needs the precision and penetration control that only TIG provides. Fill and cap passes can switch to MIG or stick for speed, but the root is TIG. Pipeline welders know this — it's why certifications distinguish between processes.
Exotic metals. Chromoly, Inconel, titanium, copper-nickel — TIG with the right filler and gas coverage. These materials don't tolerate sloppy heat input or contamination. If someone asks you to MIG weld titanium, walk away.
Head-to-Head Comparison
| Factor | MIG | TIG |
|--------|-----|-----|
| Speed | Fast — 2-4x TIG on equivalent joints | Slow — every bead is hand-fed |
| Learning curve | Moderate — trigger and go | Steep — two-hand coordination + pedal |
| Material range | Steel, stainless, aluminum (spool gun) | Steel, stainless, aluminum, exotics |
| Thickness sweet spot | 16ga to unlimited | Foil to 1/4" (practical limit for efficiency) |
| Weld appearance | Functional — good enough for structure | Beautiful — stack of dimes |
| Heat control | Limited — voltage/wire speed presets | Full — foot pedal real-time adjustment |
| Outdoor use | Workable with higher gas flow | Difficult — argon disperses easily in wind |
| Joint access | Gun is bulky — needs clearance | Torch is compact — fits tight spaces |
| Filler cost | Wire is cheap ($30-80/spool) | Rod is moderate ($15-40/lb) |
| Gas cost | 75/25 mix — $30-50/refill | Pure argon — $30-50/refill |
| Equipment cost | $800-3,000 (machine only) | $1,500-5,000 (machine only) |
| Cleanup | Spatter — needs grinding | Minimal to none |
What About Stick and Flux-Core?
MIG and TIG aren't the only options on a mobile welding rig.
Stick (SMAW) is the original field welding process. No gas bottle, no wire feeder, works in wind and rain. A lot of structural and pipeline work still specs stick. The tradeoff is speed (slower than MIG) and cleanup (slag chipping). But a good stick welder with 7018 puts down as strong a joint as anything.
Flux-core (FCAW) is MIG's outdoor cousin. Self-shielded wire means no gas bottle and no wind sensitivity. Higher deposition than stick, less cleanup than stick, but more spatter than gas-shielded MIG. For heavy outdoor fabrication — pipeline, structural, shipyard — flux-core is often the primary process.
Most mobile rigs carry all four: MIG for general fab, TIG for precision, stick for field emergencies, flux-core for heavy outdoor work. The machine choice (Trailblazer, Ranger, Big Blue) determines which processes you can run.
Cost Difference on the Job
For the customer hiring a mobile welder, the process affects the bill:
- MIG jobs typically run $75-125/hour. Faster completion = lower total bill on most repairs.
- TIG jobs typically run $100-175/hour. Slower process + higher skill = premium rate.
- Aluminum TIG often commands $125-200/hour due to the added difficulty and consumable cost.
A mobile welder who offers both processes gives the customer the right tool for the job instead of making everything fit one process. That's the difference between a welder and a specialist.
The Bottom Line
Don't pick a side. Pick the process that fits the joint.
MIG when you need metal down fast, the material is thick enough to take the heat, and appearance is secondary. TIG when the material is thin, the customer will see the weld, or the metal demands it.
If you're building a rig or hiring a mobile welder, look for someone who runs both and knows when to switch. That's the mark of a welder who's done enough work to know that no single process covers everything.