One-side spot welding method and one-side spot welding apparatus

A one-side spot welding method for causing electrodes to contact a welding portion of a work-piece only from one side of the work-piece to weld the work-piece, the method comprising:

• performing a nugget forming process that causes the work-piece to be fully electrically conducted at a predetermined current value while applying welding pressure to the work-piece by the electrodes from the one side;
• and
• performing a slow-cooling process that causes the work-piece to be electrically conducted at a current value lower than the predetermined current value after the nugget forming process while applying welding pressure to the work-piece by the electrodes from the one side,
• wherein the electrodes include a welding electrode and one or more grounding electrodes, and
• wherein the one-side spot welding method further comprises using a locking mechanism to join the welding electrode to the one or more grounding electrodes for regulating relative vertical positions of the welding electrode and the one or more grounding electrodes in such a way that in the joined condition a welding pressure from the welding electrode to the work-piece in the slow-cooling process is lower than a welding pressure from the welding electrode to the work-piece in the nugget forming process, and
• wherein the locking mechanism includes a latch opening that is provided in an outer circumference surface of the welding electrode, and a latching member that is provided in the grounding-electrode supporting member so as to face the latch opening and is moved, so as to be inserted into the latching opening, in a direction perpendicular to a direction of the working-piece being pressed.