Frequently Asked Questions
Surface splash and electrode sticking are a result of excessive heating between the electrode and the sheet material being joined. The resistance of the surface or current concentration is likely to be too high.
It is important first to check that the welding conditions are not excessive and that the electrode material is correct for the job being done. New or freshly cleaned electrodes can give sticking on coated steels and often settle down once bedded in with a thin coating on the electrode tip. Higher conductivity electrode materials such as copper/zirconium can give a benefit under these conditions compared to copper/chromium/zirconium. See also What electrode material should I use for resistance spot welding? Do not forget to maintain good water cooling of the electrodes.
The most common causes are:
- Misaligned electrodes: ensure the tip size is correct and that the tips are aligned and applied square to the sheet when the electrode force is applied.
- Electrode force is too low: ensure that the force is suitable for the material being welded and that the squeeze time is sufficient to allow the set force to be reached before the weld current flows.
- Contaminated material surface: dirty material or the presence of surface oxide cause undue surface heating. Some surface treatments such as heavy passivation (particularly if a phosphate treatment is used) also have a high resistance and prevent uniform current flow. Check the weldability of abraded material to verify if this is the cause of the problem.
- Contaminated electrode tip: electrodes normally become oxidised or coated with zinc when welding galvanised steel. However, heavy build-up of contaminant can cause excessive surface heating. Improve the electrode maintenance procedure and, if the electrode contamination is worse than normal, check for possible causes.
Resistance welding of sheet metals - a guide to best practice