Abstract: A resistance welding method according to the present invention includes a current control step of sequentially performing a first control for maintaining a welding current being a direct current at a current value I1 (first target value) or in the vicinity of the current value I1, a second control for raising the welding current from the current value I1 to a current value I2 (second target value, I2>I1) and for subsequently maintaining the welding current at the current value I2 or in the vicinity of the current value I2, and a third control for lowering the welding current from the current value I2 to a value smaller than the current value I1, and the resistance welding method further comprises an energization step of applying the welding current while repeating the current control step plural times until a predetermined energization period of time elapses.

Abstract: The vehicle roof structure includes: a closely facing section that abuts or is adjacent to a side outer panel; a negative curved-surface section that is positioned more inwards in the vehicle width direction than the closely facing section of the roof panel, and has a recessed face that is indented downwards; and a mounting surface that is formed in the side outer panel at an inner side in the vehicle width direction to downwards of the vehicle towards, and at which the closely facing section abuts or is adjacent, in which an edge, on a side of the roof panel, of the brazing material that has solidified to join the roof panel and the side outer panel is positioned on the negative curved-surface section.

Abstract: The vehicle roof structure includes: a closely facing section that abuts or is adjacent to a side outer panel; a negative curved-surface section that is positioned more inwards in the vehicle width direction than the closely facing section of the roof panel, and has a recessed face that is indented downwards; and a mounting surface that is formed in the side outer panel at an inner side in the vehicle width direction to downwards of the vehicle towards, and at which the closely facing section abuts or is adjacent, in which an edge, on a side of the roof panel, of the brazing material that has solidified to join the roof panel and the side outer panel is positioned on the negative curved-surface section.

Abstract: A one-side resistance spot welding method includes a preheating step followed by a welding step. In the preheating step, an electric current having a smaller current value than a welding current is fed from a first electrode to second electrodes such that a substantially annular high-temperature region coaxial with the first electrode and having a higher temperature than neighboring parts is created in a workpiece due to resistance heat generation at a position located near a tip end of the first electrode. In the welding step, the annular high-temperature region forms a shielded current path due to its high electric resistance and serves to guide a welding current from the first electrode to flow into a bottom steel sheet of the workpiece via the shielded current path, thereby allowing the welding current to subsequently advance along the bottom steel sheet and reach the second electrodes via a top steel sheet.

Abstract: A spot welding method and a spot welding apparatus are provided. A stacked assembly of at least three workpieces is gripped between first and second welding tips. An inner workpiece positioned inside of the stacked assembly, of two of the workpieces that exhibit a maximum contact resistance in the stacked assembly, is electrically connected to a ground electrode, or to an electrode having the same polarity as the second welding tip near an outer workpiece positioned adjacent to the inner workpiece and facing outwardly from the stacked assembly, of the two workpieces. Then, electric current is applied from the first welding tip toward the second welding tip. In this case, first, the stacked assembly is pressed under a first pressing force, and then, the stacked assembly is pressed under a second pressing force which is greater than the first pressing force.

Abstract: A one-side spot welding method for causing an electrode to contact a welding portion of a work-piece only from one side of the work-piece to weld the work-piece, the method includes a nugget forming process of applying welding pressure to the work-piece through the electrode, and causing the work-piece to be fully electrically conducted at a predetermined current value, and a slow-cooling process of applying welding pressure to the work-piece through the electrode from the one side, and causing the work-piece to be electrically conducted at a current value lower than the predetermined current value after the nugget forming process.

Abstract: A one-side resistance spot welding method includes a preheating step followed by a welding step. In the preheating step, an electric current having a smaller current value than a welding current is fed from a first electrode to second electrodes such that a substantially annular high-temperature region coaxial with the first electrode and having a higher temperature than neighboring parts is created in a workpiece due to resistance heat generation at a position located near a tip end of the first electrode. In the welding step, the annular high-temperature region forms a shielded current path due to its high electric resistance and serves to guide a welding current from the first electrode to flow into a bottom steel sheet of the workpiece via the shielded current path, thereby allowing the welding current to subsequently advance along the bottom steel sheet and reach the second electrodes via a top steel sheet.

Abstract: A one-side spot welding method for causing an electrode to contact a welding portion of a work-piece only from one side of the work-piece to weld the work-piece, the method includes a nugget forming process of applying welding pressure to the work-piece through the electrode, and causing the work-piece to be fully electrically conducted at a predetermined current value, and a slow-cooling process of applying welding pressure to the work-piece through the electrode from the one side, and causing the work-piece to be electrically conducted at a current value lower than the predetermined current value after the nugget forming process.

Abstract: A spot welding method and a spot welding apparatus are provided. A stacked assembly of at least three workpieces is gripped between first and second welding tips. An inner workpiece positioned inside of the stacked assembly, of two of the workpieces that exhibit a maximum contact resistance in the stacked assembly, is electrically connected to a ground electrode, or to an electrode having the same polarity as the second welding tip near an outer workpiece positioned adjacent to the inner workpiece and facing outwardly from the stacked assembly, of the two workpieces. Then, electric current is applied from the first welding tip toward the second welding tip. In this case, first, the stacked assembly is pressed under a first pressing force, and then, the stacked assembly is pressed under a second pressing force which is greater than the first pressing force.

Abstract: Disclosed are a bonded product, and a manufacturing method and manufacturing device therefor. To obtain a bonded product formed of a solidified material of a molten metal which has been poured into a forming mold with a workpiece, all or part of which is already held therein, or formed of a semi-solidified slurry which is contained in the forming mold together with the workpiece, the semi-solidified slurry or the molten metal is relatively made to flow on the end faces of the workpiece while friction sufficient to break the passive state existing at the surface of the molten metal or the semi-solidified slurry is generated between the workpiece and the semi-solidified slurry or the molten metal.