Blind rivet

Claim 1

In a blind rivet assembly having a grip thickness within a range bounded by minimum and maximum thickness values for use in gripping at least two sheetlike layers, said rivet assembly including a blind rivet having a mandrel associated, therewith, the improvement comprising: said blind rivet being an integral one-piece body having an elongated shank which is free at one end and is provided with an enlarged head at the other end, said shank at the free end thereof defining thereon an end surface, said shank having a smooth and substantially cylindrical outer surface of substantially uniform diameter throughout the axial extent thereof; said mandrel having an elongated stem which projects through the rivet body and has an enlargement at one end thereof, said enlargement having a substantially flat bottom surface for abutting contact with said end surface of said shank, said enlargement having a maximum cross-sectional dimension which is defined by said bottom surface and is approximately equal to the diameter of said shank, and the bottom surface of said enlargement having an outer edge which directly contacts said end surface; said shank having means associated therewith in the vicinity of the free end thereof for permitting deformation of the shank to create a substantially annular upset portion which at least partially surrounds said enlargement in response to said enlargement and said head being axially moved toward one another for effecting compression of said shank therebetween; said shank also having means associated therewith which is positioned more closely adjacent said head for radially outwardly deforming said shank at a location intermediate the ends thereof to create a substantially annular radially outwardly projecting bead which is created adjacent the rearward side of the layers only when the grip thickness of the layers equals or slightly exceeds the minimum grip thickness, said last-mentioned means being incapable of forming said bead when the thickness of the layers is equal to or only slightly less than the maximum grip thickness; said shank when in an initial nondeformed condition having a first substantially cylindrical bore formed coaxially over a substantial axial extend thereof, said first bore extending inwardly from the free end of said shank and having a smooth substantially cylindrical wall which is of substantially uniform diameter; said shank having a second axially elongated bore formed therein and extending over a substantial axial extent thereof, said second elongated bore extending axially of said rivet body through the head and axially into and partially through the shank for communication with said first bore, said second bore being of larger diameter than said first bore, said shank at the axial intersection between said first and second bores defining thereon an annular shoulder which surrounds said first bore and projects substantially radially outwardly therefrom, said shoulder facing axially toward said head and being at a location which is spaced axially from the underside of the head by a distance which is greater than said minimum grip thickness, whereby said first and second bores each extend over a substantial axial length of said rivet body with said first and second bores together extending over the complete axial length of said rivet body; and said stem of said mandrel having an outer diameter over its length which closely equals the diameter of said first bore so that the stem can be freely axially moved into and through said first and second bores, said stem at a location which is disposed within said shank being provided with a reduced cross section to facilitate breaking of said stem in response to a substantially predetermined tension force being imposed on the stem during deformation of the rivet body.