Spot Welding
Resistance spot welding (RSW) joins overlapping sheet metal panels by passing high current through copper electrode tips at precise contact points — no filler wire or shielding gas required. With cycle times as fast as 0.1s per spot, RSW is the fastest joining method for high-volume assemblies where lap-joint structural strength matters more than continuous seam appearance.
Spot welding joins overlapping sheet metal by passing a high current through two copper electrodes, forming a weld nugget at the interface in under a second. It needs no filler, no gas and no consumable, which makes it the fastest and cheapest way to join thin sheet assemblies at volume.
What material thickness suits spot welding?
Spot welding works on overlapping sheets from roughly 0.5 mm to 3 mm per side. Below 0.5 mm the nugget burns through; above about 3 mm the current required becomes impractical and the joint is better served by MIG. Dissimilar thicknesses can be welded, but the ratio should stay within about 3:1.
How strong is a spot weld?
A correctly formed nugget in mild steel typically exceeds the strength of the surrounding sheet in shear, which is why automotive bodies rely on thousands of them. Strength falls off sharply if the nugget is undersized, so we set current, time and electrode force per material and verify with peel testing on first-off parts.
Resistance spot welding: process window
| Parameter | Guideline | Note |
|---|---|---|
| Sheet thickness per side | 0.5–3.0 mm | Outside this window use MIG or TIG |
| Thickness ratio between sheets | ≤ 3:1 | Wider ratios shift the nugget off-centre |
| Minimum weld spacing | 3–5 × nugget diameter | Closer spacing shunts current between welds |
| Minimum edge distance | ≥ nugget diameter | Prevents the nugget blowing out at the edge |
| Typical cycle time | Under 1 second per weld | Fastest joining method at volume |
Common questions about Spot Welding
Is spot welding waterproof or airtight?
No. A spot weld is a series of discrete nuggets with gaps between them, so the joint is neither sealed nor continuous. For an IP-rated or liquid-tight enclosure the seam needs continuous TIG or laser welding, or a gasketed mechanical joint. We will tell you which at DFM stage.
Can you spot weld stainless steel and aluminium?
Stainless spot welds well and is common in appliance and enclosure work. Aluminium can be spot welded but needs much higher current, tighter surface preparation and more frequent electrode dressing, so for aluminium assemblies we usually recommend TIG or riveting instead.
How do you check spot weld quality?
We set parameters from the material and thickness, then verify on first-off parts with a destructive peel or chisel test that confirms the nugget diameter. Production parts are checked by weld count, spacing and visual inspection against the approved sample.
Materials we run this process on
Related capabilities and next steps
Specifications
Capabilities
Spot Welding vs Other Joining Methods
Multi-parameter comparison to help you choose the right joining method for your application.
| Parameter | Spot (RSW) | TIG (GTAW) | MIG (GMAW) | Laser |
|---|---|---|---|---|
| Welding Speed | Very fast — 0.1–0.5 s/spot | Slow — manual pace, 50–300 mm/min | Moderate — 1000–3000 mm/min | Very fast — 10–5000 mm/min |
| HAZ Width | Very narrow — <1 mm | Narrow — 1–2 mm | Moderate — 3–5 mm | Ultra-narrow — <1 mm |
| Distortion | Very low | Low | Moderate | Minimal |
| Filler Material | None | Optional | Required | None |
| Automation | Fully automated | Manual / semi-auto | Semi-auto / auto | Fully automated |
| Appearance | Limited — spot marks only | Excellent — smooth stacked-dime bead | Good — minor ripples | Excellent — cosmetic seam |
| Best For | High-volume sheet assemblies | Food-grade, sanitary, visible joints | High-speed structural welds | Precision enclosures, thin-wall parts |
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