Troubleshooting guide › Process troubleshooting › Projection welding problems
Projection welding looks like spot welding but behaves differently: the current is concentrated by the projections on the part, not by the electrode tips, and all projections must collapse together. That changes what goes wrong. The faults below are the ones we are asked about on weld nuts, weld bolts and embossed sheet projections.
Reviewed by the Cruxweld technical team, October 2026. Settings are starting points to confirm on a test piece; acceptance is decided by the code or drawing the job is built to. Checks marked “call” are for our technical team.
| Spot welding | Projection welding | |
|---|---|---|
| Where the current concentrates | Electrode tip face | The projection(s) on the part; electrodes are flat and large |
| Force | Set for the sheet; held steady | Must follow the part as the projections collapse (fast head, low friction); too much force flattens the projection before current flows |
| Time | Longer | Short: typically 5-20 cycles; a long time melts the thread or sheet after the projection is gone |
| Alignment | Tips face to face | Platens parallel, die flat, part square: one tilted nut means one projection takes all the current |
| Number of welds | One nugget | All projections at once (3 or 4 on a weld nut); an unequal number welded is the classic fault |
| Electrode wear | Tips mushroom | Dies pit where projections sit; locating pins wear |
Not all projections fused, or the weld is only a skin: current too low, time too short, force too high (projections flattened cold), part dirty or oily, sheet coated.
Nut tilted on the pin or die, die face worn or pitted, platens not parallel, projections of unequal height (bad nut batch), locating pin too long so the nut sits on the pin instead of the sheet.
Current too high, force too low, locating pin conducting (not insulated or worn), current flowing through the pin instead of the projections, weld started before full force.
Pin picks up spatter, pin not insulated, pin too tight in the nut bore, pin bending under off-centre force.
Platens not parallel, die not flat, head stalling (dry guide, low air), one projection touching first.
Time too long, current too high for the sheet, lower electrode too small so the sheet overheats.
Dies heating up through the batch, air pressure dropping as other machines draw, nut batch mixed, cooling water stopped.
Projection too small or badly formed (wrong tool), projection flattened by force before current, current too low.
Numbers for current and time depend on the machine kVA, the nut size and the sheet; the twist test and the carbon-paper check are the reliable guides, not a table copied from another machine.
Small nuts on thin sheet, sometimes, with flat electrodes and a pin die, but the head of a rocker-arm spot welder is slow to follow the collapse and the arms deflect, so results are inconsistent. A pneumatic projection welder with flat platens is the right machine.
The die has heated up and softened, or the pin has worn and the nut is sitting on it instead of the sheet, or the air pressure has dropped. Check water flow, the pin and the gauge, in that order.
Projection welding needs three things the machine must give: enough current for all projections at once (kVA sized for the nut, not the sheet), a fast-following head so the electrode keeps force on the part while the projections collapse, and flat, parallel platens with dies made for the part. Our pneumatic projection welders have T-slot copper-alloy platens and we make dies to the nut or bolt you use.
Send a photo of the weld or cut, your machine model, consumable and plate thickness. Our technical team replies on WhatsApp with the likely causes and the next checks to make.
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