Abstract
The authors have developed an apparatus for varying an electrode force of a spot welding machine. This is equipped with a servomotor by which we can change rotation instantaneously from normal to reverse and vice versa, and also has a display by which we can monitor the change in the electrode force. Lap resistance spot welding was performed on cold rolled steel (SPCC) and temporal changes of the electrode force were compared with those by a conventional process. In the conventional process the electrode force changed complexly with the elapsed time and the changes were divided into three kinds depending on welding current. When we decreased the initial electrode force than that in the conventional process good welds could be obtained even in lower welding current and the decrease in the thickness of the welds could be lowered. In this case the temporal changes of the electrode force could be explained during the expansion and shrinkage of the welds, though the electrode force changed complexly depending on the initial electrode force and welding current.
