What is expulsion?

The phenomenon of expulsion is commonly referred to as spatter, however, the correct description is expulsion in the case of resistance welding. The outer expulsion is generated between electrodes and the object to be welded, and the inner expulsion is generated within the objects to be welded.
Expulsions tend to occur when welding current is higher, weld time is longer, or electrode force is lower than those of the optimal welding parameters.
Expulsions can be reduced by decreasing the weld current, shortening the weld time, or increasing the electrode force. In the case of spot welding, adding upslopes may be effective.
In the case of projection welding, insufficient parallelism of electrodes may cause expulsions. Or in the case of spot welding, external disturbances, such as sheet gaps, may cause expulsions.