Self-drilling expansion fastener and method of forming same

Abstract

A self-drilling expansion fastener is integrally formed of a sheet metal material for locking two or more sheet workpieces together, and includes an expansion structure and a drill structure. The expansion structure has a plurality of internal threads and force-distributing bars. The drill structure has a chip guard for covering a head of the expansion structure, and a drill forward projected from the chip guar for self-drilling a hole. When an externally threaded element is screwed into the expansion structure to mesh with the internal threads, the force-distributing bars are brought to expand outward and are finally compressed into a folded state to thereby tightly lock the sheet workpieces to one another. A method of forming the self-drilling expansion fastener is also disclosed.

What is claimed is: 
     
         1 . A method of integrally forming a self-drilling expansion fastener from a sheet metal material through a series of punching and stamping, comprising the following steps:
 obtaining a sheet metal material having dimensions required for forming the self-drilling expansion fastener, and defining an expansion structure zone and a drill structure zone on the obtained sheet metal material;   stamping the expansion structure zone at a specified location, which is defined as a thread forming zone, to obtain threads having required dimensions;   punching the expansion structure zone at a specified location, which is defined as a barrel body forming zone, to obtain a plurality of force-distributing bars;   punching the drill structure zone at a predetermined location to obtain a required chip guard;   punching the drill structure zone at a predetermined location to obtain a required drill; and   stamping the thread forming zone and the barrel body forming zone to obtain required configurations for these two zones.   
     
     
         2 . The self-drilling expansion fastener forming method as claimed in  claim 1 , wherein the chip guard includes two side covers and the drill includes two drill bits. 
     
     
         3 . The self-drilling expansion fastener forming method as claimed in  claim 1 , wherein the barrel body forming zone is stamped at a predetermined location to obtain at least one outward protruded retaining wing, and the retaining wing being slant at a fixed angle relative to a horizontal rear end of the barrel body forming zone. 
     
     
         4 . The self-drilling expansion fastener forming method as claimed in  claim 1 , wherein the thread forming zone is stamped into a near-cylindrical hollow body, and the barrel body forming zone is stamped into a hexagonal hollow body internally defining a hex bore. 
     
     
         5 . The self-drilling expansion fastener forming method as claimed in  claim 1 , wherein the barrel body forming zone is punched at a predetermined location to obtain at least one stopper. 
     
     
         6 . The self-drilling expansion fastener forming method as claimed in  claim 1 , wherein the expansion structure zone is punched at a specified location to obtain at least one coupling device for coupling two longitudinal sides of the expansion structure zone to each other to complete the forming of the self-drilling expansion fastener.