Frequently Asked Questions
In an effort to guarantee weld quality, weld parameter settings are often set close to a splash condition. This is done so that small changes in process variables are unlikely to give small welds, but it can lead to expulsion of molten metal from the weld nugget.
The following factors can cause weld splash:
- Unsuitable welding conditions: such as welding current too high or weld time too long.
Recommended: check the suitability of the conditions against guidelines, such as BS 1140, BS EN ISO 14373 or TWI guidelines.
- Small electrode contact due to poor alignment of tips, wrong tip size or tips not square to the sheet.
Recommended: control the electrode tip, and check for equipment and access problems causing misalignment, otherwise weld quality is also at risk.
- Component problems: such as lack of flatness of the component or poor fit-up, requiring substantial force to close gaps between the sheets.
Recommended: wherever possible work towards eliminating presswork problems. Try to eliminate the cause rather than attempt to compensate for the problem. However, longer weld times or pulsed welding condition scan help with thicker or stronger materials.
- Edge welds: welding too close to the sheet edge because of insufficient flange width, misaligned flanges or inaccuracy of placement of the tips on the flange.
Recommended: the centre of the weld made with a tip diameter d should not be less than 1.25d from the edge of the flange or flat contacting area.
- Electrode force problem: splash is more likely at low electrode force levels or if the force has not reached its set value when current flows because the squeeze time is too short.
Recommended: check force level and squeeze time are adequate.
- Surface condition: dirt, oxide or a heavy passivation can lead to a high resistance surface, which generates excessive or localised heat.
References
BS1140: - British Standard specification for resistance spot welding of uncoated and coated low carbon steel.
BS EN ISO 14373 - Resistance welding - Procedure for spot welding of uncoated and coated low carbon steel.
Further information
Resistance welding of sheet metals - a guide to best practice
TWI Guidelines - Settings for resistance spot welding of steels - Practical guidelines
Settings for resistance spot welding of steels - Practical guidelines Tables