The invention provides a switching electrode which has a small variation in resistance value even when a large amount of current is repeatedly cut off and can carry a stable amount of current even when it is continuously used. In the invention, the switching electrode is used in a switch which includes a first switching electrode tip (21) and a second switching electrode tip (22), brings the first switching electrode tip (21) and the second switching electrode tip (22) into surface contact with each other to carry a current, and separates the first switching electrode tip (21) and the second switching electrode tip (22) to cut off the current. At least one of contact surfaces of the first switching electrode tip (21) and the second switching electrode tip (22) is a flat surface having an uneven portion.

A system and method of welding a workpiece. A predetermined current may be applied through electrodes that engage the workpiece. A resistance profile may be generated based on the predetermined current. A weld profile may be selected based on the resistance profile. The weld profile may then be executed to weld the workpiece.

A system and method of welding a workpiece. A predetermined current may be applied through electrodes that engage the workpiece. A resistance profile may be generated based on the predetermined current. A weld profile may be selected based on the resistance profile. The weld profile may then be executed to weld the workpiece.

The present invention provides a resistance spot welding method. A resistance spot welding method according to the present invention in which a sheet combination of two or more overlapping steel sheets is sandwiched between a pair of electrodes and joined together by applying current while applying pressure, the method including a main current application step in which current application is performed with a current I.sub.w (kA), and subsequently, a post-tempering heat treatment step in which after cooling is performed for a cooling time t.sub.ct (ms) shown in formula (1) below, current application is performed with a current I.sub.t (kA) shown in formula (2) below for a current application time t.sub.t (ms) shown in formula (3) below: 800?t.sub.ct . . . formula (1), 0.5?I.sub.w?I.sub.t?I.sub.w . . . formula (2), and 500?t.sub.t . . . formula (3).

The present invention provides a resistance spot welding method. A resistance spot welding method according to the present invention in which a sheet combination of two or more overlapping steel sheets is sandwiched between a pair of electrodes and joined together by applying current while applying pressure, the method including a main current application step in which current application is performed with a current I.sub.w (kA), and subsequently, a post-tempering heat treatment step in which after cooling is performed for a cooling time t.sub.ct (ms) shown in formula (1) below, current application is performed with a current I.sub.t (kA) shown in formula (2) below for a current application time t.sub.t (ms) shown in formula (3) below: 800?t.sub.ct . . . formula (1), 0.5?I.sub.w?I.sub.t?I.sub.w . . . formula (2), and 500?t.sub.t . . . formula (3).

A resistance spot welding method includes sandwiching metal plates put on top of one another between a pair of electrodes and performing resistance spot welding sequentially on a plurality of welding points close to each other on the metal plates by performing a current application between the electrodes so as to join the metal plates to each other. A welding current value to form a welding nugget at a welding point to be subjected to the resistance spot welding second or later among the welding points is set to be higher than a first welding current value to form a first welding nugget at a first welding point to be subjected to the resistance spot welding first among the welding points.

Object of the present invention is to provide a welding method prevented the fracture at the spot welding zone by recovering the strength of a spot welding zone, namely, the ductility and the toughness in the spot welding zone, and a weld structure manufactured by the method. In the welding method, a spot welding zone provided with a weld nugget is formed by conducting spot welding on the heat treated steel sheets in a stack; the spot welding zone is tempering treated by the high-frequency electrical current application to make the weld nugget have a hardness of 150% or less of the hardness of the heat treated steel sheets, and the heat affected zone surrounding the weld nugget is made to have a hardness of 30% to 90% of the hardness at the weld nugget before the tempering treatment by the high-frequency electrical current application.

Object of the present invention is to provide a welding method prevented the fracture at the spot welding zone by recovering the strength of a spot welding zone, namely, the ductility and the toughness in the spot welding zone, and a weld structure manufactured by the method. In the welding method, a spot welding zone provided with a weld nugget is formed by conducting spot welding on the heat treated steel sheets in a stack; the spot welding zone is tempering treated by the high-frequency electrical current application to make the weld nugget have a hardness of 150% or less of the hardness of the heat treated steel sheets, and the heat affected zone surrounding the weld nugget is made to have a hardness of 30% to 90% of the hardness at the weld nugget before the tempering treatment by the high-frequency electrical current application.

A method for manufacturing a joined member and a joined member manufacturing apparatus which can manufacture a joined member with a joint portion having an appropriate hardness. A method for manufacturing a joined member C by joining a first member D formed of a metal material having a possibility of undergoing quenching and a second member E formed of a metal material, the method includes a contact-placing step S1 of placing the first and second members D and E with joint target portions of the first and second members D and E respectively being in contact with each other; a joining step S2 of joining the first and second members D and E by passing a pulsed welding electric current A1 for joining through the joint target portions J of the first and second members D and E; a first tempering step S3 of tempering a joint portion F, where the first and second members D and E are joined, by passing a first tempering electric current A2 through the joint portion F; and a second tempering step S4 of tempering the joint portion F by passing a second tempering electric current A3 smaller than the first tempering electric current A2 through the joint portion F.

A method of resistance spot welding to join a plurality of overlapping metal sheets, including: dividing a current pattern into two or more steps for welding; before actual welding, performing test welding to store, for each step as a target value, a time variation of an instantaneous amount of heat generated per unit volume and a cumulative amount of heat generated per unit volume; and subsequently, as actual welding, starting welding using, as a standard, a time variation curve of the instantaneous amount of heat generated per unit volume obtained by the test welding, and when a time variation amount of an instantaneous amount of heat generated deviates during any step from the time variation curve by a difference, performing adaptive control welding to control a current passage amount in order to compensate for the difference during a remaining welding time in the step.