Self-Threading Female Fastener Elements and Method of Forming Same
A female fastener having a self-threading bore for threaded receipt of a conventional male threaded fastener which forms a substantially continuous female thread without tapping having a prevailing torque. The bore includes a cylindrical internal surface and a plurality of circumferentially spaced concave recesses having a total volume equal to an annulus defined by a major diameter and an inner diameter of the cylindrical surface. A method of forming self-attaching fasteners by rolling a continuous metal strip having a central pilot, piercing spaced self-threading bores through the pilot and either severing the pilot or the strip. Where the strip is severed into discreet fasteners, the fasteners may be interconnected by a frangible connector without reorienting the fasteners.
1 . A female fastener element having a self-threading bore for threaded receipt of a conventional spirally threaded male fastener element, comprising:
a metal body portion having a configured bore therethrough, said configured bore including a generally cylindrical internal surface having an internal diameter approximately equal to a minor diameter of said spirally threaded male fastener element and a plurality of circumferentially spaced concave recesses in said cylindrical internal surface having a total volume approximately equal to an annulus defined by a major diameter of said configured bore measured between a radial outer surface of opposed recesses and an internal diameter of said cylindrical surface less said total volume of said recesses, whereby threading of said spirally threaded male fastener element into said bore deforms metal from said generally cylindrical surface into said recesses forming a substantially continuous female thread in said bore.
2 . The female fastener element as defined in claim 1 , wherein said concave recesses each include a generally cylindrical internal surface.
3 . The female fastener element as defined in claim 1 , wherein said generally cylindrical internal surface of said bore includes an inlet portion receiving said male fastener element having a greater internal diameter than an intermediate portion of said bore.
4 . The female fastener element as defined in claim 2 , wherein said inlet portion is frustoconical having a major internal diameter greater than said intermediate portion of said bore.
5 . The female fastener element as defined in claim 1 , wherein said major diameter of said bore is approximately equal to a major diameter of said spirally threaded male fastener element.
6 . A female fastener element having a self-threading bore for receipt of a conventional spirally threaded male fastener element, said female fastener element including a metal body portion having a configured bore therethrough, said configured bore including a generally cylindrical internal surface having a diameter greater than a major diameter of said spirally threaded male fastener element and a plurality of spaced generally arcuate concave recesses, whereby threading of said spirally threaded male fastener element into said bore deforms metal from said generally cylindrical surface to said spaced recesses forming a substantially continuous spiral female thread in said bore.
7 . The female fastener element as defined in claim 6 , wherein said generally cylindrical internal surface of said bore includes an inlet portion receiving said male fastener element having a greater internal diameter than an intermediate portion of said bore.
8 . The female fastener element as defined in claim 7 , wherein said generally cylindrical internal surface in said inlet portion is frustoconical having a major diameter greater than an internal diameter of said intermediate portion.
9 . The female fastener element as defined in claim 6 , wherein said generally cylindrical surface has an internal diameter approximately equal to a minor diameter of said spirally threaded male fastener element.
10 . The female fastener element as defined in claim 9 , wherein said bore has a major diameter measured between opposed said generally cylindrical recesses approximately equal to a major diameter of said spirally threaded male fastener element.
11 . The female fastener element as defined in claim 6 , wherein a total volume of said plurality of spaced generally cylindrical recesses is approximately equal to a volume of an annulus defined by a major diameter measured between a radial outer surface of opposed generally cylindrical recesses and a diameter of said generally cylindrical surface less said total volume of said recesses.
12 . A threading female fastener element having a configured self-threading bore for receipt of a conventional spirally threaded male fastener element, said female fastener element including a metal body portion having a configured bore therethrough, said configured bore including a generally cylindrical internal surface having an internal diameter generally equal to a minor diameter of said spirally thread male fastener element including a frustoconical inlet portion and a cylindrical outlet portion, and said generally cylindrical internal surface including a plurality of spaced concave arcuate recesses having a total volume approximately equal to an annulus defined by a major diameter of said configured bore measured between a radial outer surface of opposed concave arcuate recesses and a diameter of said generally cylindrical surface less said total volume of said recesses, whereby threading of said spirally threaded male fastener element into said inlet portion of said bore deforms metal from said generally cylindrical surface into said recesses forming a substantially continuous female thread in said bore.
13 . The female fastener element as defined in claim 12 , wherein said major diameter of said bore measured between said radial outer surface of opposed recesses is generally equal to a major diameter of said spirally threaded male fastener element.
14 . A method of forming a continuous strip of self-attaching female fastener elements, said method comprising the following steps:
rolling a metal strip having a cross-section of said female fastener elements including a continuous pilot portion having an end face and continuous flange portions on opposed sides of continuous pilot portion; and
piercing a self-threading bore through said end face of said pilot portion including a generally cylindrical internal surface and a plurality of circumferentially spaced concave recesses in said cylindrical surface having a total volume approximately equal to an annulus defined by a major diameter of said bore measured between a radial outer surface of opposed said recesses and an internal diameter of said generally cylindrical surface less said total volume of said spaced recesses, whereby threading a spirally threaded male fastener element into said bore having a major diameter greater than said internal diameter of said cylindrical surface deforms metal into said recesses forming a substantially continuous female thread in said bore.
15 . The method of forming a continuous strip of self-attaching female fastener elements as defined in claim 14 , wherein said method includes severing said strip and forming discreet self-attaching female fastener elements having a self-threading bore.
16 . The method of forming a continuous strip of self-attaching female fastener elements as defined in claim 15 , wherein said method includes interconnecting said discreet self-attaching female fastener elements with a frangible connector element without reorienting said fastener elements.
17 . The method of forming a continuous strip of self-attaching females fastener elements as defined in claim 14 , wherein said method includes piercing said bore through said end face of said pilot portion and forming a frustoconical opening through a back face of said strip opposite said end face.
18 . The method of forming a continuous strip of self-attaching female fastener elements as defined in claim 14 , wherein said method includes piercing said bore through said pilot portion having substantially cylindrical spaced recesses in said generally cylindrical internal surface.