Friction spot joint structure

Abstract

In a friction spot joint structure, a first plate member is pressed against a second plate member by using a rotary tool and a receiving member. A concave portion is formed by a rotating pin portion of the rotating tool, with an interface between the first plate member and the second plate member remained. In this time, the first and second plate members are allowed to plastic-flow, so that an annular bulging portion of the second plate member raised into the first plate member is formed around the concave portion.

Description

CROSS REFERENCE TO RELATED APPLICATIONS [0001] This Non-provisional application claims priority under 35 U.S.C. § 119(a) on Patent Application No. 2004-037708 filed in Japan on Feb. 16, 2004, the entire contents of which are hereby incorporated by reference. BACKGROUND ART [0002] 1. Field of the Invention [0003] The present invention relates to a friction spot joint structure in which a plurality of plate members are overlapped and joined by plastic-flowing the plate members. [0004] 2. Description of the Prior Art [0005] It has been known conventionally that light metals, particularly aluminum and the like are unsuitable for fused joint such as arc welding, compared with steels, because they are more conductive and transfer more heat than steels. [0006] Taking the above into consideration, friction spot joint structure has been known in which plate members are point joined by fusing a part thereof by friction, for example, as disclosed in Japanese Patent Application Laid Open Public...

AI Technical Summary

Benefits of technology

[0012] With the above structure, the continuous interface between the first plate member and the second plate member exists. Therefore, the pressed second plate member plastic-flows into the first plate member in a solid phase state when the first and the second plate members interposed between the rotary tool and the receiving member are softened by friction heat caused at the rotating shoulder and pin portions. Thus, that the first plate member and the second plate member are joined to each other mechanically, forming the annular bulging portion around the concave portion. The joint strength depends on the size of a mechanically joined part of the bulging portion, which can be easily adjusted by changing joining conditions such as the pressure and number of rotation of the rotary tool, the joining period and the like. Hence, a target joint strength can be obtained constantly.

[0013] Further, the continuous interface remains between the first plate member and the second plate member at the bottom of the concave portion, and therefore, stress concentration is hard to be invited compared with the case with a discontinuous interface. Accordingly, cracking is prevented and the shear fracture strength is increased. Furthermore, the second plate member is not exposed to the wall face forming the concave portion. Therefore, in the case using a material having an anti-corrosion characteristic as the first plate member, even if the second plate member is inferior in anti-corrosion characteristic, the anti-corrosion characteristic at the joint part is ensured and easy quality management for surface treatment, coating and the like can be attained because the same material exists continuously in the surface portion.

[0014] In the second invention, a protruding portion is formed so as to protrude outward from the annular bulging portion. By this formation, the protruding portion of the second plate member encroaches into the first plate member outward from the bulging portion, whereby, the protruding portion exhibits an effect as an anchor to increase the strength against a load in a direction of force to separate the first plate member from the second plate member.

[0015] In the third and fourth inventions, the first plate member and the second plate member are made of a light metal. In light metals having small specific gravities, such as aluminum, magnesium, plastic flow in a solid phase state is easily caused at comparatively low temperatures. Hence, with the light metal employed, the effects of the present invention are remarkably exhibited.

Problems solved by technology

It has been known conventionally that light metals, particularly aluminum and the like are unsuitable for fused joint such as arc welding, compared with steels, because they are more conductive and transfer more heat than steels.

However, the adjustment is difficult because the relationship between the joint quality and such joining conditions is unclear.

Further, the point joint is performed by fusing plate materials by friction, which requires a considerable time period.

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