⊙ Spot weld
Spot weld · Soldadura en plano · ISO 1101 + ASME Y14.5
Example in plan
How to interpret it
On the drawing, “5 spots Ø5 pitch 30 on sheet joint” states a spot weld requirement.
What controls
Joint formed by discrete spots between two or more overlapping sheets, typically by resistance welding between electrodes, although it can also be done by arc through the top sheet. The symbol is accompanied by the spot diameter (that of the fused core, or nugget, not the electrode imprint), the number of spots and the pitch between them. Each spot is an independent joint; the strength of the assembly is the sum of them, which is why the number and pitch are as mandatory as the diameter.
How to verify
The real process control is periodic peel tests: two sheets of a sample are torn apart and the pulled-out button is measured, which must reach the specified diameter. The surface imprint is no measure of the nugget. In production this is complemented by monitoring the machine parameters and, on critical parts, by ultrasonic testing specific to resistance spot welds. The number of spots and the pitch are checked by counting and measuring with a tape measure.
Common mistakes when interpreting it
- Measuring the diameter of the mark left by the electrode and accepting it: what carries the load is the fused internal nugget, which can be much smaller.
- Confusing it with a plug weld: a spot weld does not need a pre-made hole in the top sheet.
- Making fewer spots than specified because 'it holds just the same': the number and pitch are part of the joint calculation.
How to get it in the workshop / if it comes out of tolerance
It is the thin-sheet process: car bodies, enclosures, deep-drawn assemblies. The spot diameter is determined by the machine parameters (force, current and time) and the condition of the electrodes, not by the operator's hand. Worn or mushroomed electrode tips produce spots that look large on the outside and are small inside, which is the worst possible scenario.
Small spots or stuck welds without fusion: check the condition of the electrode tips, which is the number one cause, and then force and time. Spatter and expulsion of molten material indicate excessive current or low force. If the sheets are not in contact before the spot is made, the material heats up at the interface and the nugget does not grow: check the clamping fixture and cleanliness between the sheets.
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Other symbols in Flat welding
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