A resistance spot welding method includes: performing test welding; and performing actual welding after the test welding, wherein in subsequent current passage in the test welding, current passage is performed by constant current control under a condition: 0.5 ? Vtp/Vtm ? 2.0 when tc<800 ms; 0.5?0.3.Math.(tc?800)/800 ? Vtp/Vtm ? 2.0?0.5.Math.(tc?800)/800 when 800 ms ? tc<1600 ms; and 0.2 ? Vtp/Vtm ? 1.5 when tc ? 1600 ms, and wherein in main current passage in the actual welding, adaptive control welding is performed, and in subsequent current passage in the actual welding, current passage is performed by constant current control under a condition: 0.8.Math.Itp ? Imp ? 1.2.Math.Itp.

A power supply unit for a resistance welding apparatus, said power supply unit comprising a converter circuit adapted to convert an alternating power supply current, AC, applied via a residual current protection circuit to an input of said converter circuit into a pulsed electrical current supplied from an output of said converter circuit to a primary coil of a transformer of said resistance welding apparatus, and at least one switching element provided between the output of said converter circuit and protective earth.

A resistance spot welding method of galvanized high-strength steel with good joint performance, wherein: three welding pulses are used within one spot welding schedule; a first welding pulse and a second welding pulse are used for generating a nugget and suppressing the generation of liquid metal embrittlement (LME) cracks, wherein the first welding pulse generates a nugget having a diameter of 3.75T-4.25T in which T represents a plate thickness; the second welding pulse causes the nugget to grow slowly; and a third welding pulse which is a tempering pulse is used for improving plasticity of a welding spot. A time t1 of the first welding pulse is set and a welding current I1 of the first welding pulse is obtained through tests, and the welding current I1 of the first welding pulse is a welding current upon generating the nugget having the diameter of 3.75T-4.25T; and a welding current I2 and a time t2 of the second welding pulse, and a welding current I3 and a time t3 of the third welding pulse are calculated by the welding current I1 and the time t1 of the first welding pulse. By the resistance spot welding method of galvanized high-strength steel, the liquid metal embrittlement cracks during the spot welding of the high-strength steel galvanized plates can be effectively suppressed, meanwhile, the plasticity of the welding point is improved, and the probability of button pullout failure of the welding point during broken testing is increased. Therefore, the joint by spot welding of the high-strength steel galvanized plates with more reliable quality and more excellent performance is obtained, and a useful guidance can be provided for the welding production of the high-strength steel galvanized plates.

A welding apparatus for resistance-welding a tubular member and a bar member includes: a positioning jig configured to make contact with the bar member from one side of the bar member in a direction perpendicular to an extending direction of the bar member; a first power supply jig configured to press the bar member from the other side of the bar member in the direction; a second power supply jig provided on an anti-bar member side of the tubular member and configured to apply pressure to contact surfaces of the bar member and the tubular member; and means for supplying, with the bar member pressed between the positioning jig and the first power supply jig and the second power supply jig applying pressure to the contact surfaces, electric current to the first power supply jig, the bar member, the contact surfaces, the tubular member and the second power supply jig.

Embodiments of a welding power supply include an engine adapted to drive a generator to produce a first power and a energy storage device adapted to discharge energy to produce a second power. The welding power supply also includes control circuitry adapted to detect a commanded output. The control circuitry is adapted to meet the commanded output by controlling access to power from the energy storage device to produce the second power when the commanded output is below a first predetermined load level. The control circuitry is further adapted to meet the commanded output by controlling access to power from the engine and the energy storage device to produce the first power and the second power when the commanded output is above a second predetermined load level.

By superposing a plurality of steel sheets including a high tensile steel sheet and performing pulsation conduction by an inverter DC type spot welding power supply and controlling the conduction time of the current pulses, intervals of the current pulses, that is, conduction idle time, and weld current applied at the current pulses in a variable manner, the optimum weld conditions are obtained. For resistance spot welding of the hot stamped steel sheet, resistance spot welding with a minimum weld current of a second pulsation step higher than the maximum weld current at a first pulsation step is used to suppress the occurrence of outer spatter and inner spatter and secure a broad suitable current range even if using an inverter DC power supply.

By superposing a plurality of steel sheets including a high tensile steel sheet and performing pulsation conduction by an inverter DC type spot welding power supply and controlling the conduction time of the current pulses, intervals of the current pulses, that is, conduction idle time, and weld current applied at the current pulses in a variable manner, the optimum weld conditions are obtained. For resistance spot welding of the hot stamped steel sheet, resistance spot welding with a minimum weld current of a second pulsation step higher than the maximum weld current at a first pulsation step is used to suppress the occurrence of outer spatter and inner spatter and secure a broad suitable current range even if using an inverter DC power supply.

This seam-welding device carries out seam welding while repeating one cycle comprising a melting period, an interruption period, and a heating period implemented either before or after the interruption period. A welding current is applied between a pair of roller electrodes so as to form a welded part between workpieces during the melting period, the application of the current between the roller electrode pair is interrupted so as to solidify the welded part during the interruption period, and a heating current smaller than the welding current is applied between the roller electrode pair so as to heat the laminated body within a solidification temperature range of the welded part during the heating period. Consequently, even when the welding speed is increased, formation of cracks and spatter is effectively suppressed such that a high-quality joined product is obtained.

This seam-welding device carries out seam welding while repeating one cycle comprising a melting period, an interruption period, and a heating period implemented either before or after the interruption period. A welding current is applied between a pair of roller electrodes so as to form a welded part between workpieces during the melting period, the application of the current between the roller electrode pair is interrupted so as to solidify the welded part during the interruption period, and a heating current smaller than the welding current is applied between the roller electrode pair so as to heat the laminated body within a solidification temperature range of the welded part during the heating period. Consequently, even when the welding speed is increased, formation of cracks and spatter is effectively suppressed such that a high-quality joined product is obtained.

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.