Spot welding joins overlapping sheets by clamping them between two copper electrodes and passing a strong current for a fraction of a second. The metal melts only at the spot between the electrodes and forms a small round weld nugget. It is fast, needs no filler or gas, and is the usual way to join sheet-metal cabinets, panels, car bodies and wire mesh.
Quick facts
- Process
- Resistance welding with copper electrodes
- Materials
- Mild steel (CRCA), galvanised steel, stainless; aluminium on special machines
- Typical thickness
- About 0.5–3 mm (0.0197–0.118 inch) per sheet
- Weld time
- A fraction of a second per spot
- Filler or gas
- None
- Usually priced
- Per spot or per part
How it is done
- Sheets are cut, bent and cleaned of heavy oil or rust
- They are overlapped and held in position, often in a fixture
- Electrodes squeeze the sheets, current flows and a nugget forms
- Electrodes hold briefly while the nugget cools
- Spot pitch and size are checked; peel tests on sample pieces confirm strength
Spot, projection or MIG?
| Spot welding | Projection welding | MIG | |
|---|---|---|---|
| Joint | Overlapping sheets | Nuts, studs, embossed points | Any joint |
| Speed | Very fast | Very fast | Slower |
| Marks | Small dents | Small | Weld bead to grind |
| Filler and gas | None | None | Wire and gas |
What to send
- Drawing with spot positions and pitch
- Material, coating and thickness of each sheet
- Whether weld nuts or studs must be projection welded
- Finish: are electrode marks acceptable on the visible face?
- Quantity
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Questions
- How strong is a spot weld?
- A good spot weld is stronger than the sheet around it: in a peel test the sheet tears around the nugget.
- Can galvanised sheet be spot welded?
- Yes, with higher current and more electrode dressing, because zinc sticks to the copper tips.
- What is projection welding?
- A resistance weld through small raised points, used to fix weld nuts and studs onto sheet parts.
The figures on this page are typical values for guidance, written by Diemeco from standard engineering practice. They are not a specification: confirm grades and properties with the relevant standard or the supplier's mill test certificate, and tolerances with your workshop. Last checked 23 October 2026.