DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] As set forth above, the self-attaching female fastener element of this invention may be utilized as a self-piercing female fastener or pierce nut wherein the female fastener element pierces an opening in a metal panel and is attached in one stroke of a die press. Alternatively, the self-attaching female fastener may be utilized as a clinch nut, wherein the clinch nut is installed in a prepierced panel opening. The preferred embodiments of the self-attaching female fastener element of this invention may also be formed by conventional cold heading techniques, but provides superior joint integrity, particularly in thin metal applications and may be used to provide a sealed nut and panel assembly by the method of this invention illustrated in FIG. 5 discussed below.

[0015] The embodiment of the self-attaching female fastener element 20 illustrated in FIG. 1 , for example, includes a generally cylindrical body 22 having spaced flats 24 and a tubular barrel portion 26 best illustrated in FIG. 4 . The self-attaching female fastener element further includes a central annular pilot portion 28 having an annular end face 30 and a cylindrical bore 32 which is preferably threaded, as shown. Alternatively, the bore may be unthreaded for receipt of a thread forming or thread rolling male fastener or plug as described below in regard to applications of the self-attaching female fastener of this invention. The female fastener element 20 further includes an annular flange portion 34 surrounding the pilot portion 28 having a planar annular bearing face 36 . Where the self-attaching female fastener element 20 of this invention is utilized as a pierce nut, the annular end face 30 of the pilot portion is preferably planar and the annular bearing face 36 and may be spaced below the plane of the end face 30 as best shown in FIG. 3 or the planar surfaces may be coplanar. An annular groove 38 is defined in the bearing face 36 of the flange portion 34 which includes an inner groove side wall 40 adjacent the pilot portion 28 , which may also form an outer wall of the pilot portion, an outer groove side wall 42 and a bottom groove wall 44 . In a preferred embodiment of the invention, the outer groove side wall 42 is inclined inwardly from the bottom wall 44 toward the pilot portion 28 as best shown in FIG. 3 and the inner groove side wall 40 is inclined outwardly from the bottom groove wall 44 toward the flange portion as also shown in FIG. 3 . Although in a preferred embodiment, both the inner and outer groove side walls are inclined as shown in FIG. 3 to improve retention of the female fastener element 20 on a panel, the inner groove side wall 40 may also be cylindrical. The inclined inner and outer side walls 40 and 42 form a restricted opening of the annular groove 38 , sometimes referred to as a “re-entrant groove” by those skilled in this art.

[0016] In the preferred embodiment of the self-attaching female fastener element 20 of this invention, the bottom groove wall 44 includes a plurality of wedge-shaped circumferentially spaced recesses 46 as shown in FIGS. 1 and 2 . The wedge-shaped recesses 46 each include a recess bottom wall 48 and opposed recess side walls 50 . The recess side walls 50 diverge outwardly, such that the wedge-shaped recesses 46 are narrower adjacent the pilot portion 28 than adjacent the flange portion 34 . In a preferred embodiment, the bottom wall 48 of the wedge-shaped recesses 46 are planar and spaced below the plane of the bottom groove wall 44 . Where the recesses 46 extend from the inner groove side wall 40 to the outer groove side wall 42 , as shown, the circumferentially spaced wedge-shaped recesses 46 thus interrupt the bottom groove wall 44 forming circumferentially spaced segments. An alternative explanation is that the groove includes a plurality of spaced bottom groove walls 48 between adjacent wedge-shaped circumferentially spaced recesses 46 .

[0017] As shown in FIGS. 1 and 2 , the bottom groove wall segments 44 between adjacent wedge-shaped recesses 46 are generally rectangular except for the arcuate inner and outer portions which join the inner groove side wall 40 and the outer groove side wall 42 . The geometry of the generally rectangular bottom groove wall segments 44 and the wedge-shaped recesses 46 is explained in FIG. 2 . As shown in FIG. 2 , the segments of the bottom groove wall 44 between the wedge-shaped recesses 46 are defined by parallel lines A and B tangent to a circle C generated from the axis D of the bore 32 through the end face 30 of the pilot portion 28 . As shown in FIG. 2 , the parallel lines A and B are coincident with the recess side walls 50 of adjacent wedge-shaped recesses 46 , such that the segments of the bottom groove wall 44 are defined by parallel lines defined by the side walls 50 of adjacent wedge-shaped recesses 46 and the recess side walls 50 of the circumferentially spaced recesses 46 diverge outwardly forming wedge-shaped recesses 46 between the generally rectangular bottom wall segments 44 . As will be understood, however, the bottom groove wall segments 44 are actually segments of an annulus having arcuate inner and outer side walls. In the most preferred embodiment, the planar bottom groove wall segments 44 and the wedge-shaped circumferentially spaced recesses 46 are planar, such that the recess bottom walls 48 are parallel to the segments of the bottom groove wall 44 but spaced below the plane of the segments of the bottom groove wall 44 as shown.

[0018] FIG. 5 illustrates the method of installation or method of attaching the self-attaching female fastener element 20 illustrated in FIGS. 1 to 4 , wherein the female fastener element 20 is utilized as a pierce nut. As set forth above, the self-attaching female fastener element 20 may also be used as a clinch nut, wherein the panel metal is pierced prior to attachment. The female fastener element 20 is cross-sectioned in FIG. 5 the same as FIG. 3 .

[0019] As set forth above, the female fastener element 20 may be attached to a metal panel 52 to form a sealed joint with the panel as shown in FIG. 5 . The female fastener element 20 is installed in a panel 52 by a die member 54 commonly referred to as a “die button.” The die button 54 is normally attached to a lower die shoe or die platen of a press (not shown) and the female fastener element 20 is received in an installation head (not shown) in the upper die shoe (not shown). However, as will be understood by those skilled in this art, the orientation of the die button 54 and the self-attaching female fastener element 20 can be reversed. The die button 54 generally includes a cylindrical body portion 56 having a cylindrical opening 58 which receives the panel slug 60 . The die button further includes an annular lip 62 having an inclined or frustoconical outer surface 64 and a radius 66 which joins the inclined outer surface 64 with the end face 68 of the die button. The panel 52 is pierced between the leading edge of the opening 58 through the die button 54 and the end face 30 of the pilot portion 28 . The annular lip 62 then deforms an annular panel portion 70 surrounding the pierce panel opening into the annular groove 38 in the bearing face 36 of the flange portion 34 , as shown. In a preferred embodiment, wherein the self-attaching female fastener element 20 forms a sealed joint with the panel 52 , the internal diameter of the cylindrical opening 58 is less than the external diameter of the pilot portion 28 , such that the inclined inner wall 40 of the annular groove 38 is inelastically and permanently deformed radially outwardly and axially as shown in FIG. 5 , forming an integral annular bead or lip 72 which entraps the annular panel portion 70 in the annular groove 38 and compacts the panel portion 70 beneath the inclined inner and outer side walls 40 and 42 as shown in FIG. 5 forming a sealed joint between the female fastener element 20 and the panel 52 . During the installation, the panel portion 70 is also deformed against the bottom groove wall segments 44 and the recessed bottom walls 48 , substantially filling the wedge-shaped recesses 46 in contact with the recess side walls 50 .

[0020] The female fastener element 20 and panel assembly illustrated in FIG. 5 thus provides a secure sealed female fastener element and panel assembly which may be used for many applications including, for example, an oil pan nut or bung for a container containing a liquid requiring a sealed joint between the female fastener element and a panel. The wedge-shaped circumferentially spaced recesses 46 prevent rotation of the fastener element 20 on the panel 52 , particularly when the annular panel portion 70 is compacted into the annular groove 38 against the recess bottom and side walls 48 and 50 by the integral annular bead 72 and the bead 72 entraps the panel portion 70 and assures full contact with the inclined inner and outer side walls 40 and 42 of the annular groove 38 providing superior push-off strength. The barrel portion 26 increases the length of the threaded bore 32 . In a preferred embodiment, the barrel portion 26 has a diameter substantially less than the diameter of the flange portion 34 to reduce the overall weight of the female fastener element and provides a bearing surface. As will be understood by those skilled in this art, the installation head (not shown) normally attached to the upper die shoe of a die press (not shown) generally includes a plunger 74 which drives the female fastener element 20 into the panel 52 and the die button 54 is retained in a fixture 76 in the lower die shoe as described above.

[0021] As will be understood by those skilled in this art, various modifications may be made to the self-attaching female fastener element 20 , the method of attaching the female fastener element and the fastener element and panel assembly of this invention with the purview of the appended claims. For example, the female fastener element 20 may be utilized in various applications requiring a female fastener in a panel and is not limited to the sealed fastener and panel assembly illustrated in FIG. 5 , wherein the die button 54 deforms the pilot portion 28 , forming the integral radial bead or lip 72 , although this is a preferred installation for a sealed female fastener and panel assembly and provides improved integrity for the joint. Further, although a preferred embodiment of the fastener element 20 includes an inclined inner side wall 40 of the annular groove 38 , the side wall 40 may also be cylindrical. The flats 24 on the cylindrical body 22 assist retention of the fastener element during threading of the bore 32 but are not required, particularly when the bore 32 is unthreaded, as described above. Having described preferred embodiments of the female fastener element, panel assembly and method of this invention, the invention is now claimed as follows.