Abstract: Exemplary embodiments provide a resistance welding method capable of stabilizing quality or improving efficiency of resistance welding such as spot welding. This resistance welding method comprises a calculating step of calculating resistance ratio X of a second electric resistance value R2 of workpieces to be joined in residual heat after Joule heating stops to a first electric resistance value R1 of the workpieces immediately before the Joule heating stops or vice versa (R2/R1 or R1/R2); a determining step of determining whether the resistance ratio X is equal to or greater than a threshold value Xn, and a reheating step of carrying out the Joule heating again when the resistance ratio X is smaller than the threshold value Xn. Thereby at least part of a welding portion is melted and solidified to reliably form a nugget, and a stably resistance-welded member can be provided.

Abstract: A difference processing circuit receives input of welding images taken by a CCD camera in real time and then differentiates power monitoring images recorded in a memory from welding images to obtain difference processing reflected light images. Due to the difference processing performed by a difference processing circuit, foreign matter images included in welding images and power monitoring images are eliminated and the difference processing reflected light images that are obtained do not include any foreign matter images. A quality judgment device uses the difference processing reflected light images obtained by a difference processing circuit and conducts a quality judgment. As described above, since difference processing reflected light images do not include any foreign matter images, a quality judgment device does not receive any influence from the foreign matter that is adhered to the protective glass and can conduct an excellent evaluation of the welding quality.

Abstract: A resistance welding method according to the invention includes: a melting start time specification process for specifying a melting start time, which is a time at which at least a part of a welding portion of a welding subject starts to melt while being subjected to Joule heating by a power input from an electrode pressed against the welding subject, by detecting a variation in an ultrasonic wave emitted toward the welding portion; a first power amount calculation process for calculating a first power amount, which is an integrated value of the power input into the welding subject via the electrode from the melting start time; a first determination process for determining whether or not the first power amount has reached a first set value; and a heating process for performing the Joule heating from the melting start time until the first power amount reaches the first set value.

Abstract: In a resistance welding method, by controlling the power amount from a melting start time onward, the weld quality may be stabilized efficiently, even when a disturbance is present, because of the correlation between the amount of power input from the melting start start time and a resulting nugget. The resistance welding method includes: pressing an electrode against a workpiece; inputting power to the workpiece through the electrode to subject the workpiece to Joule heating; detecting the melting start time, which is the time at which at least a portion of the faying portion of a workpiece starts to melt when subjected to Joule heating; calculating a first power amount input into the workpiece from the melting start time; and determining whether the first power amount has reached a first set value; and continuing the Joule heating until the first power amount reaches the first set value.

Abstract: This invention aims to provide a resistance welding method capable of stabilizing quality or improving efficiency of resistance welding such as spot welding. This resistance welding method comprises a calculating step of calculating resistance ratio X of a second electric resistance value R2 of workpieces to be joined in residual heat after Joule heating stops to a first electric resistance value R1 of the workpieces immediately before the Joule heating stops or vice versa (R2/R1 or R1/R2); a determining step of determining whether the resistance ratio X is equal to or greater than a threshold value Xn, and a reheating step of carrying out the Joule heating again when the resistance ratio X is smaller than the threshold value Xn. Thereby at least part of a welding portion is melted and solidified to reliably form a nugget, and a stably resistance-welded member can be provided.

Abstract: A difference processing circuit receives input of welding images taken by a CCD camera in real time and then differentiates power monitoring images recorded in a memory from welding images to obtain difference processing reflected light images. Due to the difference processing performed by a difference processing circuit, foreign matter images included in welding images and power monitoring images are eliminated and the difference processing reflected light images that are obtained do not include any foreign matter images. A quality judgment device uses the difference processing reflected light images obtained by a difference processing circuit and conducts a quality judgment. As described above, since difference processing reflected light images do not include any foreign matter images, a quality judgment device does not receive any influence from the foreign matter that is adhered to the protective glass and can conduct an excellent evaluation of the welding quality.