Joining method

A joining method for joining a first plate material to a second plate material by screwing a self-tapping screw into the first plate material and the second plate material from one direction, the joining method comprising:

• putting the first plate material and the second plate material on top of each other such that a first recessed portion formed in at least one of the first plate material and the second plate material is opened in a contacting face between the first plate material and the second plate material, the first recessed portion being formed in a part into which the self-tapping screw is screwed in the at least one of the first plate material and the second plate material, the first recessed portion having an inner periphery larger than an external-thread outside diameter of the self-tapping screw;
• and
• penetrating the first plate material and the second plate material with the self-tapping screw, the first plate material being placed on a near side in a screw-in direction of the self-tapping screw relative to the second plate material, wherein an excess part generated from the first plate material at a time when the self-tapping screw penetrates through the first plate material flows into the first recessed portion,
• in a case where a third plate material is further provided such that the second plate material and the third plate material are put on top of each other and joined to each other, putting the second plate material and the third plate material on top of each other such that a second recessed portion formed in at least one of the second plate material and the third plate material is opened in a contacting face between the second plate material and the third plate material, the second recessed portion being formed in a part into which the self-tapping screw is screwed in the at least one of the second plate material and the third plate material, the second recessed portion having an inner periphery larger than the external-thread outside diameter of the self-tapping screw,
• wherein, in the case where the third plate material is further provided such that the second plate material and the third plate material are put on top of each other and joined to each other, when the first recessed portion is formed by press molding, the first recessed portion is formed in the first plate material that is a plate material on the nearest side in the screw-in direction of the self-tapping screw, such that the first recessed portion is opened in the contacting face between the first plate material and the second plate material, and the second recessed portion is formed in the third plate material that is a plate material on a deepest side in the screw-in direction of the self-tapping screw, such that the second recessed portion is opened in the contacting face between the third plate material and the second plate material.