What is the role of the basic welding cycle in spot (projection) welding?

普电

The basic welding cycle of spot (projection) welding is mainly composed of four procedures: preloading, welding, maintaining and stopping. Its functions are as follows:
Preloading procedure: it is to pressurize the weldments before power on, and its function is to establish a good contact and conductive path between the weldments, so as to ensure the stability of contact resistance.

Welding procedure: the metal on the contact surface is electrified and heated under the action of electrode pressure to form closed nugget and plastic metal ring.

Maintenance procedure: in the cooling crystallization stage, when the nugget reaches the qualified shape and size, the welding current will be cut off and then enter this procedure, which plays the role of cooling crystallization under the electrode pressure, which helps to reduce the generation of defects such as shrinkage and cracks.

Rest procedure: it means that the cooling crystallization process is over, the pressure is cancelled, the electrode is lifted up, the workpiece is taken out and the workpiece is put in at the beginning of the next cycle.