During the seam forming process (intermittent) seam welding, each solder joint is also subjected to three stages of pre-pressing, electrical heating and cooling crystallization. However, due to the rapid changes in the relative position between the roll electrode and the weldment during seam welding, these three stages are not as distinct as those distinguished by spot welding. Can consider it:

 

1) Under the direct compression of the roller electrode, the metal heated by the electric current is in the "electric heating stage".

 

2) The adjacent metal that is about to enter the roller electrode is subjected to a certain preheating and partial pressure of the roller electrode, and is in the "preloading stage".

 

3) The adjacent metal just exposed from the bottom of the roller electrode begins to cool on the one hand, and is pressed by the roller electrode part in the same way, and is in the "cooling crystallization stage". Therefore, the weld zone below the roller electrode and the metal material on both sides adjacent to it will be in different stages at the same time. For any spot on the weld, the process of passing under the rollers is a three-stage process of "preload - heat - cool to crystallize". Since the process is carried out under dynamic conditions, the pressure in the preloading and cooling crystallization stages is insufficient, the quality of the seam welding head should generally be worse than that of the spot welding, and cracks such as cracks and shrinkage are prone to holes.