Captivated fastener assembly with post-formed retention feature and method for forming the same

Abstract

A captivated fastener assembly is provided along with a technique for captivating a fastener in a workpiece. The assembly includes a fastener having a head, a shank extending from said head that has an upper unthreaded shank portion and a lower threaded shank portion, wherein the diameter of the outer tips of the threads of the lower threaded shank portion exceed the diameter of the upper unthreaded shank portion. The assembly further includes a workpiece having a sleeve with an internal bore with a diameter slightly larger than the diameter of the fastener shank so that the sleeve can be received over the shank. The sleeve also includes segments that deform inwardly in response to a predetermined compressive force, thereby forming a plurality of deformed segments that protrude inwardly. Thus, the plurality of deformed segments provide an inner diameter that is less than the diameter of the outer tips of the threads of the lower threaded shank portion, thereby holding the fastener captive.

What is claimed is:  
     
         1 . A captivated fastener assembly comprising: 
 a fastener having a head, a shank extending from said head, said shank having an upper unthreaded shank portion and a lower threaded shank portion, wherein the diameter of the outer tips of the threads of the lower threaded shank portion exceed the diameter of the upper unthreaded shank portion;    a workpiece having a sleeve with an internal bore with a diameter slightly larger than the diameter of the fastener shank so that the sleeve can be received over the shank, said sleeve having a plurality of deformed segments that are deformed inwardly responsive to a predetermined compressive force after the fastener is inserted into the sleeve, thereby forming a plurality of deformed segments protruding inwardly, wherein the diameter provided by said plurality of deformed segments is less than diameter of the outer tips of the threads of the lower threaded shank portion, thereby holding it captive.    
     
     
         2 . The assembly of  claim 1 , wherein said sleeve has a wall thickness that is substantially uniform.  
     
     
         3 . The assembly of  claim 1 , wherein said sleeve has a substantially straight- walled configuration before being inwardly deformed in response to said predetermined compressive force.  
     
     
         4 . The assembly of  claim 1 , wherein said unthreaded shank portion of said fastener can move axially relative to said plurality of deformed segments.  
     
     
         5 . The assembly of  claim 1 , wherein said plurality of deformed segments includes two deformed segments positioned diametrically opposite to each other.  
     
     
         6 . A method of captivating a fastener within a workpiece having a sleeve with an internal bore, the fastener having a threaded shank portion and an unthreaded shank portion each defining a given diameter, said method comprising: 
 sliding the workpiece sleeve over the shank of the fastener such that the sleeve slides freely along the length of the fastener thereby forming a fastener pre-assembly;    inwardly deforming a plurality of segments of the workpiece sleeve to create deformed segments, thereby reducing a portion of the internal bore size of the sleeve to a diameter less than that of the outer tips of the threads of the shank,    whereby the fastener can move axially relative to said sleeve diameter reduced portion about the unthreaded shank portion while engagement of the threads with the sleeve reduced diameter deformed segments prevents separation of the fastener from the workpiece.    
     
     
         7 . The method of  claim 6  wherein the workpiece sleeve has a substantially straight-walled configuration prior to inwardly deforming the plurality of segments of the workpiece sleeve.  
     
     
         8 . The method of  claim 6  wherein the workpiece sleeve has a radial thickness that is sufficiently thick to prevent deflection of the sleeve diameter reduced portion against said unthreaded shank portion to such an extent that it would prevent axial movement of the fastener relative to the workpiece sleeve.  
     
     
         9 . An apparatus for transforming a fastener and a workpiece sleeve into a captivated fastener assembly, wherein the arrangement comprises: 
 a carrying roller adaptable to receive and support the fastener assembly; and    a crimping roller positioned adjacently to said carrying roller, wherein said carrying roller and said crimping roller cooperate to provide a compressive force on the workpiece sleeve such that a plurality of deformed segments are formed, thereby captivating the fastener within the workpiece sleeve.    
     
     
         10 . The arrangement of  claim 9 , further comprising a feeding mechanism adaptable to transport the fastener assembly onto said carrying roller.  
     
     
         11 . The arrangement of  claim 10 , wherein said feeding mechanism is adaptable to slide the workpiece sleeve over the fastener.  
     
     
         12 . The arrangement of  claim 9 , wherein a plurality of pockets are formed on the carrying roller to accept and support the fastener assembly.  
     
     
         13 . The arrangement of  claim 12 , wherein each of said plurality of pockets includes a crimping dowel adaptable to engage a non-deformed segment of the workpiece sleeve to provide deformation thereof.  
     
     
         14 . The arrangement of  claim 9 , wherein the crimping roller includes an annular rim that engages a portion of the workpiece sleeve such that a compressive force is applied to provide deformation thereon.