- TIG for visible work, thin sheet and food contact surfaces.
- MIG for structural steel, hidden joints and volume.
- Heat input, not process, is what warps a panel.
TIG and MIG are both gas-shielded arc processes and both will make a sound weld in stainless steel. In the Moorebank workshop the choice is almost never about strength. It is about heat, about how much of the weld will be seen on a Sydney kitchen or a Melbourne shopfront, and about how much of your budget you want to spend on a grinder.
TIG: control, at a price
Tungsten inert gas welding uses a non-consumable electrode and a separately fed filler rod, which means the welder controls heat and filler independently. On 0.9mm and 1.2mm sheet, the thicknesses most benches, sinks and canopies are made from, that control is the difference between a crisp corner and a panel that has pulled into a curve.
- Visible corners, upstands and food contact joints.
- Anything thinner than about 2mm.
- Joints that will be dressed flush and grain-matched.
- Tube and balustrade work where the weld is at eye height.
The trade-off is speed. TIG lays down far less metal per minute than MIG, and on a long structural seam that difference shows up directly in the quote. There is no craft argument for TIG welding a bench frame that will never be seen.
MIG: speed, where speed is the point
MIG feeds a consumable wire continuously, so it deposits quickly and tolerates less-than-perfect fit-up. On mild steel framing, plinths, cages, brackets and any joint that ends up behind cladding or under powder coat, it is the correct process and the cheaper one.
Distortion is a heat problem, not a process problem
Stainless expands roughly half again as much as mild steel for the same temperature rise and conducts heat away more slowly. Put a continuous weld along a 2400mm bench edge and it will bow, whichever gun is in the welder's hand. What keeps a panel flat is sequence and restraint: stitch welding, alternating ends, clamping to a flat table, and letting the work cool instead of chasing the seam.
Whatever the process, the weld is not finished
Welding stainless burns chromium out of the surface either side of the bead. That is the straw and blue heat tint you can see. Until that tint is removed and the surface repassivated, that strip is measurably less corrosion resistant than the parent sheet. Grinding it bright is not enough on its own, because grinding leaves free iron behind. It needs pickling or an equivalent chemical clean, then passivation.
You can tell how a shop treats its stainless by looking at the back of a weld and the edge of a heat tint. Both are places nobody photographs.