Series spot welding method, device for carrying out the method, and electrodes employed in the method or the device

A series spot welding method comprising:

• superimposing a first metal plate and a second metal plate on each other, the first metal plate having a first portion that is in contact with the second metal plate when the first and second metal plates are superimposed on each other, wherein the first portion is not welded to the second metal plate, and at least one pair of second portions that are away from the second metal plate when the first and second metal plates are superimposed on each other, wherein the second portions are flat apex portions formed in the first metal plate and are welded to the second metal plate;
• pressing at least one pair electrodes having spherical leading edges onto the second portions in a direction toward the second metal plate, so as to deform the pair of second portions into a spherical shape wherein the at least one pair of electrodes are on a same surface to be welded;
• and
• causing current to flow between the electrodes, with the deformed second portions in contact with the second metal plate, so as to weld the first and second metal plates to each other.