Self-drilling expansion fastener and method of forming same

#The present invention relates to an expansion fastener integrally formed of a sheet metal material, and more particularly to an expansion fastener capable of self-drilling a hole.

#An expansion fastening device is usually used to fixedly connect multiple sheet workpieces, such as building panels, to one another, and includes a bolt and an expansion fastener. FIG. 1 shows a typical conventional expansion fastener 10, which includes a barrel body 11 having a plurality of longitudinally extended elongated slots 12 formed thereon to define a plurality of laterally spaced middle bars 13; a nut 14 connected to a head of the barrel body 11; and a bottom cover 15 connected to a bottom of the barrel body 11. As shown in FIG. 2, a bolt 16 can be extended through the bottom cover 15 and the barrel body 11 of the expansion fastener 10 to mesh with the nut 14. When the barrel body 11 is subjected to a pull, the middle bars 13 are brought to expand outward and become deformed. The deformed middle bars 13 and the bolt 16 together lock an attached object 17 to a supporting object 18.

#The conventional expansion fastener 10 is disadvantageous in terms of assembling and installation thereof. First, the nut 14 and the bottom cover 15 are connected to the barrel body 11 by welding, which is time and labor consuming to result in high manufacturing cost of the expansion fastener 10. Second, two steps are required to install the conventional expansion fastener 10 on a sheet workpiece, such as a panel or a board. That is, a hole having size corresponding to the expansion fastener 10 must first be drilled on the supporting object 18; and then, the barrel body 11 is driven into the hole with a hammer, for example, so that the barrel body 11 is tightly fitted in the hole without the risk of rotating relative to the supporting object 18. The above installation is apparently troublesome and consumes a lot of time and labor. It is therefore desirable to overcome these disadvantages.

#The structure and the technical means adopted by the present invention to achieve the above and other objects can be best understood by referring to the following detailed description of the preferred embodiments and the accompanying drawings, wherein

#FIG. 1 is an exploded perspective view of a conventional expansion fastener;

#FIG. 2 is a sectional view showing the expansion fastener of FIG. 1 in use;

#The present invention will now be described with a preferred embodiment thereof and with reference to the accompanying drawings.

#Please refer to FIGS. 3 to 6. A self-drilling expansion fastener 20 according to a preferred embodiment of the present invention is integrally formed of a sheet metal material, and includes an expansion structure 21 and a drill structure 30 located at a head of the expansion structure 21. The expansion structure 21 has a front portion formed into an internally threaded body portion 22 and a rear portion formed into a barrel body portion 23. The internally threaded body portion 22 is a cylindrical hollow body and defines a plurality of internal threads 24.

#The barrel body portion 23 is a hexagonal hollow body and internally defines a hex bore. The barrel body portion 23 includes a plurality of laterally spaced force-distributing bars 25. Once the barrel body portion 23 is subjected to an axial pull, stress occurs at the force-distributing bars 25. In other words, the force-distributing bars 25 together form a weakening zone. In the preferred embodiment as shown in FIG. 5, there are six axially extended force-distributing bars 25 being laterally equally spaced on the barrel body portion 23, such that a spacing slot 26 is formed between any two adjacent force-distributing bars 25. Further, the barrel body portion 23 includes at least one retaining wing 27. In the illustrated preferred embodiment, as shown in FIG. 5, there are two retaining wings 27 formed on the barrel body portion 23 by stamping, so that these retaining wings 27 are outward protruded from a wall surface of the barrel body portion 23 and are slant at a fixed angle relative to a horizontal rear end of the barrel body portion 23. And, the barrel body portion 23 includes at least one stopper 28 formed on the rear end thereof.