Patent ID: 9694437
Date: 2017-07-04
CPC Classifications: B23K

Claim:
1. A one-side resistance spot welding method comprising the steps in the order named of: providing a first electrode and a pair of second electrodes arranged across the first electrode, the first electrode and the pair of second electrodes being disposed mutually close to each other on one side of a workpiece composed of at least two superposed steel sheets, the first electrode having a spherical surface at a tip end thereof; bringing the first electrode and the pair of second electrodes into pressure contact with a surface of an endmost steel sheet of the at least two superposed steel sheets; feeding an electric current having a current value smaller than a current value of a welding current from the first electrode to the pair of second electrodes in a branched manner to preheat the workpiece such that an annular high-temperature region coaxial with the first electrode and having a higher temperature than neighboring parts is created in the workpiece due to resistance heat generation at a position located near the tip end of the first electrode; and feeding the welding current in another branched manner from the first electrode through the workpiece to the pair of second electrodes to thereby form weld nuggets at an interface between the endmost steel sheet and an adjacent steel sheet at positions aligned with the pair of second electrodes, wherein the annular high-temperature region forms a shielded current path due to its high electric resistance and serves to guide the welding current from the first electrode to flow into the adjacent steel sheet via the shielded current path, thereby allowing the welding current to subsequently advance along the adjacent steel sheet and reach the pair of second electrodes via the endmost steel sheet, wherein the electric current is switched to the current value of the welding current from the current value smaller than the current value of the welding current while a resistance value of the workpiece is increased.