TIG, MIG, spot: three ways to weld sheet metal, three different results in appearance, strength and cost. Here is how to choose.
The three processes
- TIG (Tungsten Inert Gas): an arc between a tungsten electrode and the part, under inert gas. Precise, clean, slow.
- MIG/MAG (Metal Inert/Active Gas): a continuously fed wire electrode melted under gas. Fast, versatile, productive.
- Spot welding (resistance): two electrodes clamp the sheets and an intense current melts the material at the contact point. Very fast, no filler metal.
Comparison
| Criterion | TIG | MIG/MAG | Spot |
|---|---|---|---|
| Bead appearance | Excellent | Decent | No bead |
| Speed | Slow | Fast | Very fast |
| Ideal thickness | 0.5 to 6 mm | 1 to 15 mm | 0.5 to 3 mm |
| Thermal distortion | Moderate | Significant | Localized |
| Hourly cost | High | Moderate | Low in volume |
| Filler metal | Yes | Yes | No |
When to choose TIG
TIG gives the cleanest, most regular bead. It is the choice for visible parts, quality stainless assemblies, and thin gauges where thermal control is critical. It is also the process for thin aluminum and special steels.
If the bead will be visible on the finished product, or if the part is polished stainless, TIG is the way.
The trade-off: it is slow and requires a highly skilled welder. Cost climbs fast on large runs.
When to choose MIG/MAG
MIG/MAG is the production process. The wire feeds continuously, speed is high, and it handles a wide thickness range. It is the default choice for structures, frames, and assemblies where productivity beats bead aesthetics.
The downside: more spatter, a less clean bead, and more thermal distortion than TIG. Plan for it on large sheets.
When to choose spot welding
Spot welding is unbeatable in volume on overlapping thin-sheet assemblies: bodywork, enclosures, covers, cabinets. No filler metal, no bead, a cycle of a few tenths of a second per spot. Distortion stays very localized.
Its limits: it only suits thin overlapping sheets, and the joint is not watertight. For a continuous or sealed joint, you need a bead.
Designing for welding
A few design rules that make the shop's life easier:
- Provide enough torch access: a bead in a closed corner is very hard to make.
- Limit the number of beads: each one adds time and distortion.
- For spot welding, provide enough sheet overlap.
- Think about bead symmetry to balance thermal distortion.
DRAWLESS and welded assemblies
DRAWLESS aims to cover the full range of sheet metal needs, from single parts to complex assemblies. Accounting for welding constraints — access, overlap, symmetry — is part of the engine roadmap, which evolves every week to handle ever more elaborate parts.