Abstract:
A blind setting rivet assembly capable of permanently fastening one or more sheet metal work pieces or the like together is disclosed. The rivet assembly may be self polishing and self tapping and may also provide a hollow cylindrical threaded bolt head onto which a nut may be affixed to provide a means to removably attach other work pieces, components or the like. The rivet assembly comprises a rivet body having a hollow tubular sleeve and an enlarged flattened head. The rivet body surrounds a mandrel that may have a weakened area of reduced diameter to allow detachment of the mandrel shaft following application of sufficient axial force to the shank. This application of force sets the rivet by causing a tapered shoulder section of the mandrel to deform the rivet sleeve. The mandrel shank may be terminated in a screw tip. This screw tip punctures, spreads, self-taps, and self-polishes an aperture in the work pieces through which the rivet sleeve passes. The mandrel&#39;s shank may have a weakened area of reduced diameter adjacent to the screw tip that allows detachment of shaft following application of sufficient axial force to the shank. This application of force causes the tapered shoulder section of the screw tip to compress and deform the rivet sleeve setting the rivet.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    The present application claims the benefit under 35 U.S.C. §119(e) of U.S. Provisional Application No. 60/261,650, filed Jan. 12, 2001. Said U.S. Provisional Application No. 60/261,650 is herein incorporated by reference in its entirety.  
       INCORPORATION BY REFERENCE  
       [0002]    The following related commonly owned patents are incorporated herein by reference in their entirety:  
                                           Inventor   U.S. Pat. No.   Issue Date   Filing Date                   Aasgaard   5,741,099   April 21, 1998   July 12, 1996       Aasgaard   5,762,456   June 9, 1998   July 12, 1996       Aasgaard   5,915,901   June 29, 1999   October 27, 1997                  
 
     
    
     
       FIELD OF THE INVENTION  
         [0003]    The present invention generally relates to the field of fasteners such as rivets and the like, and more particularly to a self-polishing and tapping rivet assembly.  
         BACKGROUND OF THE INVENTION  
         [0004]    Blind setting rivets are typically used to fasten sheet metal work pieces or the like together when access is available to only one side of the work pieces. However, application of blind setting rivets may at times be cumbersome. For example, in many applications, special jigs must be used to maintain exact alignment of the work pieces from the time the hole is drilled until the rivet can be applied.  
           [0005]    Because of these and other limitations, self-drilling blind setting rivets were developed. These rivets employ specialized drill heads which may be difficult to manufacture and are thus prohibitively expensive for many applications. Further, such rivets may leave a burr on the outer layer of the work piece materials. This burr may prevent proper seating of the rivet and may cause fractures in work pieces as it is applied, resulting in a weak joint. Known to the art are self-drilling rivets having deburring ears to remove burrs during the drilling operation. However, the drill bit of such rivets removes work piece material to create a hole for the rivet shank. This removed material may fall within an enclosed area creating a possible nuisance or hazard.  
           [0006]    Typical drills have spirals designed to help the metal edges cut and spiral the shrapnel out. In a typical self-drilling rivet the spirals are designed to help the cut metal edges to create shrapnel which requires that high torque be placed on the mandrel of the rivet assembly.  
           [0007]    U.S. Pat. No. 5,915,901 describes the use of the excurvations formed during application to increase application strength. However, in some applications, a polished aperture is desirable. Consequently, it would be advantageous to provide a blind setting rivet that would be both self-tapping and self-polishing instead of only self drilling (using a drill bit) or only self-tapping (using a screw tip). Such a self-tapping, self-polishing rivet would remove all excurvations that would leave a clean aperture. Additionally, a self-tapping and self-polishing rivet would be less expensive and easier to manufacture than the self-drilling rivets (using a drill bit) and would require less torque during application.  
         SUMMARY OF THE INVENTION  
         [0008]    Accordingly, the present invention is directed to a self-tapping and self-polishing blind setting rivet assembly capable of permanently fastening one or more work pieces or the like together and/or to another object. In one embodiment, the rivet assembly may further include a hollow cylindrical threaded bolt head onto which a nut may be affixed to provide a means to removably attach other work pieces, components or the like.  
           [0009]    In exemplary embodiments of the invention, the self-tapping and self-polishing blind setting rivet assembly comprises a rivet body having a hollow tubular sleeve and an enlarged flattened head. The rivet body surrounds a mandrel having a weakened area of reduced diameter to allow detachment of the mandrel shaft following application of sufficient axial force to the shank. This application of force sets the rivet by causing a tapered shoulder section of the mandrel to deform the rivet sleeve. The mandrel shank is terminated in a self-tapping and self-polishing auger that punctures, spreads, self-taps and self-polishes an aperture in the work piece(s) through which the rivet sleeve passes. The self-tapping and self-polishing auger includes a generally longitudinally formed groove providing one or more cutting edges that incrementally shave or carve small amounts of work piece material allowing torque to be dispersed over several small cutting edges simultaneously.  
           [0010]    It is to be understood that both the forgoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention as claimed. The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate an embodiment of the invention and together with the general description, serve to explain the principles of the invention. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    The numerous advantages of the present invention may be better understood by those skilled in the art by reference to the accompanying figures in which:  
         [0012]    [0012]FIG. 1 is a side elevational view illustrating a self-tapping and self-polishing blind setting rivet assembly in accordance with an exemplary embodiment of the present invention;  
         [0013]    [0013]FIG. 2 is a partial cross-sectional side elevational view illustrating the self-tapping and self-polishing blind setting bolt rivet assembly shown in FIG. 1;  
         [0014]    [0014]FIG. 3 is a side elevational view illustrating the mandrel of the rivet assembly shown in FIG. 1;  
         [0015]    [0015]FIG. 4 is a side elevational enlarged view illustrating the self-tapping and self-polishing head of the mandrel shown in FIG. 3;  
         [0016]    [0016]FIG. 5A and 5B are a front elevational views further illustrating exemplary self-tapping and self-polishing augers in accordance with the present invention;  
         [0017]    [0017]FIGS. 6A, 6B and  6 C are side elevational view illustrating alternative self-tapping and self-polishing augers in accordance with exemplary embodiments of the invention;  
         [0018]    [0018]FIG. 7 is a partial cross-sectional side elevational view of the rivet assembly shown in FIG. 1 depicting the rivet assembly at the beginning of application;  
         [0019]    [0019]FIG. 8 is a partial cross-sectional side elevational view of the rivet assembly shown in FIG. 1 depicting the rivet assembly following the separation and folding of an aperture through the work piece materials by the screw tip;  
         [0020]    [0020]FIG. 9 is a partial cross-sectional side elevational view of the rivet assembly shown in FIG. 1 depicting the rivet assembly after the application of a rearward force on the mandrel shank;  
         [0021]    [0021]FIG. 10 is a partial cross-sectional side elevational view of the rivet assembly shown in FIG. 1 illustrating separation of the upper shank from the screw tip and shoulder section;  
         [0022]    [0022]FIG. 11 is a partial cross-sectional side elevational view of an alternative embodiment of the present invention depicting the detachment of the auger and shoulder section following application;  
         [0023]    [0023]FIG. 12 is a partial cross-sectional, side elevational view illustrating a self-tapping and self-polishing blind setting rivet assembly in accordance with a second exemplary embodiment of the present invention;  
         [0024]    [0024]FIG. 13 is a side elevational view illustrating the mandrel of the rivet assembly shown in FIG. 12;  
         [0025]    [0025]FIG. 14 is a partial cross-sectional side elevational view illustrating a self-tapping and self-polishing blind setting bolt rivet assembly in accordance with an exemplary embodiment of the present invention, wherein the bolt rivet assembly is shown following application of rearward force on the mandrel shank causing separation of the upper shank and the screw tip;  
         [0026]    [0026]FIG. 15 is a partial cross-sectional side elevational view illustrating a self-tapping and self-polishing blind setting bolt rivet assembly depicting with a threaded enlarged flattened head in accordance with an exemplary embodiment of the present invention, wherein the bolt rivet assembly is shown following completion of self-tapping and self-polishing of an aperture prior to application; and  
         [0027]    [0027]FIG. 16 is a partial cross-sectional side elevational view illustrating a self-tapping and self-polishing blind setting bolt rivet assembly in accordance with an exemplary embodiment of the present invention, wherein the bolt rivet assembly is shown following application. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0028]    Reference will now be made in detail to the presently preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings.  
         [0029]    Referring generally now to FIGS. 1 through 11, a self-tapping and self-polishing, blind setting rivet assembly  100  in accordance with an exemplary embodiment of the present invention is described. As shown, rivet assembly  100  comprises a rivet body  102  having a hollow tubular rivet sleeve  104  and an enlarged flattened head  106  surrounding a mandrel  108  having a self-tapping and self-polishing auger  110 , a shoulder section  112 , and a shank  114 . In exemplary embodiments, the rivet body  102  may be made of steel, aluminum, plastic, composite, or other desirable rivet material. The mandrel  108  may be made of steel, aluminum, plastic, composite, or other material, which is preferably of higher tensile strength than the rivet body material.  
         [0030]    Self-tapping and self-polishing auger  110  is comprised of a generally conical barrel having a self-tapping and self-polishing tip  116 , a cutting portion  118 , and optionally a polishing portion  120 . A weakened area of reduced diameter  122  may be formed in the mandrel shank  114  rearward from shoulder section  112 . This weakened area  122  is preferably sized to fracture upon application of a predetermined tensile force to the shank  114  allowing self-tapping and polishing auger  110  and shoulder section  112  to be detached from shank  114  following completed application of the rivet assembly  100 . Likewise, an area of enlarged diameter  124  may be formed in mandrel  108  between shoulder section  112  and weakened area of reduced diameter  122 . This area of enlarged diameter  124  retains mandrel  108  within rivet body  102  until sufficient force is applied to the shank  114  during application to set the rivet body  102  and cause the area of reduced diameter  122  to fracture. In one embodiment, this enlarged area  124  also retains the self-tapping and polishing auger  110  and shoulder section  112  within sleeve  104  following application of the rivet assembly  100  by creating an interference with the inner surface of the sleeve  104  as the sleeve  104  is deformed during application of the rivet. Moreover, in embodiments of the invention, mandrel  108  may include a grommet or like seal for providing a liquid and gas impermeable seal between the shank  114  and the rivet body  102 . As shown in FIGS. 2 and 3, lengths or spaces  126  &amp;  128  of mandrel  108  may be provided between shoulder section  112  and enlarged portion  124  and between enlarged portion  124  and weakened area  122 . However, in some applications these spaces  126  &amp;  128  may be eliminated.  
         [0031]    In embodiments of the invention, weakened area  122  may be positioned on mandrel  108  so that a length of shank  114  remains in rivet body  102  after separation of the rear portion of the shank  114 . Preferably, this length is predetermined to allow shank  114  to fracture at a point that is substantially flush with the outer surface of enlarged flattened head  106 . In this manner, the remaining part of shank  114  substantially fills the hollow portion of the rivet body  102 , increasing its strength.  
         [0032]    It will be appreciated that the areas of reduced diameter  122  and enlarged diameter  124  may have different cross-sectional shapes depending upon factors such as, for example, the material from which the mandrel  108  is made, the types of work piece material(s) in which the rivet assembly  100  is being applied, the amount of fracture strength required for the area of reduced diameter  122 , and the holding strength of the area of enlarged diameter  124 . For instance, in FIGS. 2 and 3, the area of reduced diameter  122  and enlarged diameter  124  are shown as having generally curved cross-sectional shapes. However, in other embodiments, these areas may have a V-shape, a rectangular shape, a faceted shape, or the like.  
         [0033]    During application of rivet assembly  100 , self-tapping and polishing auger  110  is held substantially normal to the surface of a work piece while rotary motion is applied to shank  114 . This rotary motion threads the auger  110  into the work piece materials and expands them. In this manner, the auger  110  pulls itself through the work piece materials while simultaneously smoothing the aperture it forms. Preferably, self-tapping and self-polishing tip  116  is pointed or angled to facilitate piercing of the outer surface of the work piece.  
         [0034]    In exemplary embodiments, the rear portion of the shank  114  may be designed for use with a specialized chuck or various types of power or hand tools to provide rotary motion and axial retraction to the mandrel  108 . Preferably, the outer diameter  130  of shoulder section  112  is slightly larger than outer diameter  132  of rivet sleeve  104  allowing the sleeve to pass through the hole or aperture formed by self-tapping and self-polishing rivet head  110 .  
         [0035]    Referring now to FIG. 4, the self-tapping and self-polishing auger  110  of mandrel  108  is described. As described in the discussion of FIGS. 1 through 3, self-tapping and self-polishing auger  110  is comprised of a generally conical barrel having a self-tapping tip  116 , a cutting portion  118 , and optionally a polishing portion  120 . In the embodiment illustrated, self-tapping tip  116  includes a point  134  for piercing the surface of a work piece. Point  134 , which may be centered on the longitudinal axis of auger  110  or offset therefrom, extends into one or initial contact edges  136  suitable for forming a hole or aperture by puncturing, separating and then scraping or carving work piece material. Initial contact edges  136  may be angled and may be offset to assist in separating and tapping the work piece material(s). In this manner, self-tapping and self-polishing tip  116  facilitates initial insertion (tapping) of the rivet assembly  100  allowing the rivet assembly  100  to be more easily started in the work piece.  
         [0036]    As shown in FIG. 4, a groove  138  is formed generally longitudinally in the cutting portion  118  of auger  110 . Groove  138  may extend to various depths in auger  110  and may have a variety of shapes depending on factors such as, for example, the material of the work piece for which the rivet assembly  100  (FIG. 1) is to be used (e.g., steel, aluminum, plastic, etc). For example, as shown in FIGS. 4 and 5, groove  138  may have a generally half-conical shape extending from self-tapping and polishing tip  116  to shoulder section  112  so that the depth of groove  138  increases uniformly through cutting portion  118 . However, it will be appreciated that groove  138  is not limited to this shape, but may have other shapes depending the materials of the work pieces in which the rivet assembly  100  (FIG. 1) is being inserted, and the like. For example, in one embodiment, groove  138  may extend only partially from shoulder portion  112  of auger  110  to tip  116  while in another embodiment groove  138  may have a constant depth between tip  116  and shoulder portion  112  or may vary in depth or width in a non-uniform manner.  
         [0037]    Staged leading cutting edges  140  and trailing edges  142  may be formed in the cutting portion  118  of self-tapping and self-polishing auger  110  along groove  138 , rearward of self-tapping tip  116 . Preferably, leading cutting edges  140  incrementally remove work piece material(s) by shaving or carving the materials from the wall of the aperture being formed. The removed materials may then be channeled away from the aperture by groove  138 . In this manner, the amount of torque required for inserting or tapping rivet assembly  100  through a work piece is substantially reduced compared to conventional self-boring rivet assemblies.  
         [0038]    In the exemplary embodiment shown, leading cutting edges  140  and trailing edges  142  may be substantially parallel to the longitudinal axis  144  of self-tapping and self-polishing auger  110 . Alternately, as shown FIG. 6A, any or all of leading cutting edges  140  and trailing edges  142  may be angled, thereby forming an angle (a) with respect to longitudinal axis  144 . As shown in FIG. 4, leading cutting edges  140  and trailing edges  142  are generally parallel to longitudinal axis  144 , angle (a) is substantially zero (0). Further, either or both of leading cutting edges  140  and/or trailing edges  142  may be curved.  
         [0039]    A polishing leading edge  148  may be formed in the polishing portion  120  of self-tapping and self-polishing auger  110  along groove  138  rearward of cutting portion  118  and forward of shoulder portion  112 . Similarly, a polishing trailing edge  150  may be formed in the polishing portion  120  along groove  138  opposite leading edge  148 . Preferably, polishing leading and trailing edges  148  &amp;  150  remove any excurvations (e.g., material bored away from work piece by auger  110 ) leaving a clean, substantially burr free aperture formed in the work piece(s) through which rivet sleeve  104  (FIGS. 1 and 2) may pass. Further, either or both of polishing leading edge  148  and/or polishing trailing edge  150  may be curved.  
         [0040]    In the exemplary embodiment shown, polishing leading edge  148  and polishing trailing edge  150  may be substantially parallel to the longitudinal axis  144  of auger  110 . Alternately, as shown in FIG. 6A, either one or both of polishing leading edge  148  and polishing trailing edge  150  may be angled, thereby forming an angle (β) with respect to longitudinal axis  144 .  
         [0041]    By angling cutting edges  140 , trailing edges  142 , polishing leading edge  148  and/or polishing trailing edge  150 , the amount of material removed during each turn of auger  110  may be controlled. Generally, by selecting a larger value of angle (α) for an auger having a given length (l), a smaller amount of work piece material is removed by each leading cutting edge  140 . Likewise, by selecting a larger value of angle (β) for an auger  110  having a given length (l), a smaller amount work piece material is removed during each turn. Thus, it will be appreciated that the selection of angles (α) and (β) will depend on factors such as the application in which rivet assembly  100  is to be used and the material properties of the work pieces in which rivet assembly  100  is to be inserted, the amount of material to be removed by cutting and polishing edges  140  &amp;  148 , and the like. For example, in the embodiment shown in FIG. 4, wherein polishing edges  148  and polishing trailing edge  150  are generally parallel to longitudinal axis  144 , angle (β) is substantially zero (0). Conversely, in the embodiment shown in FIG. 6A, polishing edges  148  &amp;  150  are formed with an angle (β) equal to the taper of the cutting portion  118  of self-tapping and self-polishing auger  110 . According, the polishing edges  148  &amp;  150  shown in FIG. 4 would remove more material from the work piece(s) during each turn of auger  110  than the polishing edges shown in FIG. 6A.  
         [0042]    Referring now to FIGS. 5A and 5B, self-tapping and self-polishing auger  110  may include multiple grooves  138  and thus multiple sets of leading cutting edges  140  and trailing edges  142  spaced about its circumference. Moreover, leading cutting edge  140  may extend outwardly from longitudinal axis  144  (FIG. 4) further than trailing edge  142  depending on the application in which rivet assembly  100  is to be used, the material properties of the work pieces in which rivet assembly  100  is to be inserted, and the like. Similarly, polishing leading edge  148  may extend outwardly from longitudinal axis  144  (FIG. 4) further than polishing trailing edge  150 . FIG. 5B illustrates an auger  110  wherein grooves  138  are angled with respect to the longitudinal axis  144  (FIG. 4) of the auger  110 , while FIG. 5A illustrates an auger  110  wherein the grooves  138  are substantially straight (not angled).  
         [0043]    Turning again to FIG. 4, threads  154  may extend substantially about the barrel of self-tapping and self-polishing auger  110 . Threads  154  may extend between each leading cutting edge  140  and trailing edge  142  along the length of cutting portion  118 , thus, separating each leading cutting edge  140  and trailing edge  142  from longitudinally adjacent leading cutting edges or trailing edges. Preferably, as auger  110  is inserted into a work piece, threads  154  pull the head through the work piece material, reducing the amount of force required to drive the head through the work piece. Shoulder section  112  may have a convex surface for providing less resistance to rivet sleeve  104  (FIG. 1).  
         [0044]    In exemplary embodiment of the invention, polishing portion  120  may be tapered. Threads  154  may blend smoothly into polishing portion  120  or, alternately, shoulder section  112  to provide a smooth transition for polishing of the aperture formed. FIGS. 4, 5A, and  5 B illustrate threads  154  as having a generally helical cone shape and extending between tip  116  and polishing portion  120 . However, it will be appreciated that those of skill may employ other thread designs in the art without departing from the scope and spirit of the present invention. For example, the size and pitch of threads  154  may be varied, or the width or spacing of threads  154  may be increased or decreased as they progress along cutting portion  118  away from tip  116 .  
         [0045]    In embodiments of the invention shown in FIGS. 6B and 6C, threads  154  may extend only partially along the length of the barrel of auger  110  from tip  116  to polishing portion  120  (as shown in FIG. 6B), or may be eliminated entirely (as shown in FIG. 6C) so that single leading cutting edges  140  and trailing edges  142  are formed. In FIG. 6C, polishing edges  148  &amp;  150  (FIG. 4) are also eliminated so that leading cutting edges  140  and trailing edges  142  extend the length of auger  110  from tip  116  to shoulder portion  112 . As shown in FIG. 6C, auger  110  may optionally include protruding finishing edges  152  which, in softer metals such as aluminum and the like, will function to remove any burr created by leading cutting edges  140  as the aperture in the work piece is formed.  
         [0046]    [0046]FIGS. 7 through 11 illustrate the application or insertion of a self-tapping and self polishing rivet assembly  10 , described in connection with FIGS. 1 through 5, to join two or more work pieces (two work pieces  156  &amp;  158  are shown). FIG. 7 depicts the rivet assembly  100  near the beginning of application. Preferably, the self-tapping and self polishing auger  110  is held substantially normal to the outer work piece surface  160  while rotary motion is applied to the shank  114  of mandrel  108 . For instance, as described in the discussion of FIG. 1, the rear portion of the shank  114  may be placed in a specialized chuck (not shown) and various types of power or hand tools (not shown) may be used to provide rotary motion and axial retraction to the mandrel  108  (see FIG. 9, 10 and  11 ).  
         [0047]    Rotary motion applied to mandrel  108  causes self-tapping tip  116  to tap a hole or aperture in adjacent work pieces  156  &amp;  158 . As the self-tapping tip  116  punctures, spreads and cuts the work piece materials, removed material on the inner surface  160  of the innermost work piece  152  is separated and scraped or carved away from the work piece. The rotary motion further drives threads  154  of head  110  into the work pieces  156  &amp;  158 , pulling the auger  110  though the work pieces where cutting edges  140  &amp;  142  incrementally shave or carve material from the surface of the aperture being formed. This removed material may then be channeled away from the aperture via groove  138 . In this manner, the amount of torque required to insert or tap auger  110  through a work piece is substantially reduced compared to that required by augers of conventional self-boring rivet assemblies. Further, the material removed by auger  110  may be more easily removed since it is channeled to the outer surface  160  of work piece  156 .  
         [0048]    [0048]FIG. 8 illustrates rivet assembly  100  following the creation of an aperture through the work piece materials ( 156  &amp;  158 ) by the self-tapping and self-polishing auger  110 . As polishing portion  120  of auger  110  passes though the aperture formed in work pieces  156  &amp;  158 , the rotary motion applied to shank  114  further causes polishing edges  148  &amp;  152  to shave or carve additional material, burrs caused by leading cutting edges  140  and the like from the inner surface of the aperture, smoothing the aperture prior to insertion of rivet sleeve  104 . Preferably, the outer diameter  130  of the shoulder section  112  is slightly larger than outer diameter  132  of rivet sleeve  104  allowing the sleeve to pass through the aperture formed. Once the aperture is formed in work pieces  156  &amp;  158 , rivet sleeve  104  may be inserted into the aperture until enlarged flattened head  106  abuts the outer surface  160  of the outer work piece  156 .  
         [0049]    [0049]FIG. 9 depicts rivet assembly  100  following the application of a rearward tension force on shank  114  setting the rivet assembly  100 . To set the rivet assembly  100 , the rear portion of the shank  114  may be grasped by a riveting tool, a grasping tool, or the like, and axially retracted away from the outer surface  160  of work piece  156 . This axial retraction causes shoulder section  112  to deform rivet sleeve  114 . As shoulder section  112  (and self-tapping and self-polishing head  110 ) is drawn into rivet sleeve  104 , the tapered upper face of shoulder section  112  spreads the sleeve  104  radially. This action causes the rivet sleeve  104  to be spread until it will no longer pass through the aperture created in the work pieces  156  &amp;  158 . Further, the deformed portion of rivet sleeve  104  is pulled against the inner surface  162  of the innermost work piece  154  tightening the rivet to the work pieces  152  &amp;  154 . Preferably, the weakened area of reduced diameter  118  is sized to break at a predetermined tensile load greater than the tensile load required to cause deformation of hollow tubular sleeve  104 , allowing the sleeve  104  to be fully deformed prior to separation of shank  114 .  
         [0050]    [0050]FIG. 10 depicts rivet assembly  100  following separation of shank  114  and setting. In the embodiment shown, self-tapping and self-polishing auger  110  and shoulder section  112  are retained in rivet sleeve due to an interference between enlarged area  124  and the inner surface of the sleeve  104 . This interference may be created by deformation of the rivet sleeve  104  during application. In embodiments of the invention, the tapered upper face of shoulder section  112  may further deform the rivet sleeve  104  to at least partially encircle the head  110  to provide additional retention of the head  110  after application of the rivet assembly  100 .  
         [0051]    [0051]FIG. 11 illustrates a rivet assembly  200  in accordance with an alternative embodiment of the present invention wherein the self-tapping and self-polishing head and shoulder section detach from the rivet body following application of the rivet assembly. In such embodiments, wherein self-tapping and self-polishing auger  202  is allowed to drop off, the shoulder section  204  of mandrel  206  may have a face  208  comprising a tapered inner section  210  and a flat-plate outer section  212 . Preferably, the tapered inner section  210  initially spreads the lower end of rivet sleeve  214 . The flat-plate outer section  212  then flattens the sleeve  214  against the inner surface  216  of the innermost work piece  218  allowing the self-tapping and self-polishing head  202  and shoulder section  204  to drop off following separation of shank  220 . Shoulder section  204  may further include etchings or serrations  222  about its perimeter for smoothing and polishing the aperture formed by auger  202 .  
         [0052]    Referring now to FIGS. 12 and 13, a rivet assembly  300  employing a self-tapping and self-polishing head in accordance with a second exemplary embodiment of the present invention is described. Rivet assembly  300  comprises a rivet body  302  having a hollow tubular rivet sleeve  304  and an enlarged flattened head  306  surrounding a mandrel  308  having a shank  310  having a self-tapping and self-polishing auger  312 . The self-tapping and self-polishing auger  312  is comprised of a generally conical threaded barrel  314  having a self-tapping tip  316 , a cutting portion  318 , and optionally a polishing portion  320 . In the embodiment illustrated, self-tapping tip  316  is pointed (i.e., it does not include initial contact edge  136  (FIG. 4)) or has an initial contact edge  136  of nominal size) for forming or tapping an aperture in work piece by puncturing and separating work piece materials allowing the rivet assembly to be more easily tapped or started in the work piece.  
         [0053]    A groove  322  is formed generally longitudinally in the cutting portion  318  of barrel  314 . Groove  322  may extend to various depths in barrel  314  and may have different shapes depending on the material of the work piece for which the rivet assembly  300  is designed. For example, as shown, groove  322  may have a generally V-shaped cross-section extending from self-tapping tip  316  to shoulder section  320  wherein the depth of groove  322  increases longitudinally along barrel  314  from tip  316  to shoulder section  324 .  
         [0054]    Staged leading cutting edges  326  and trailing edges  328  may be formed in the cutting portion  318  of auger  312  along groove  322 , rearward of self-tapping tip  316 . Like cutting edges  140  &amp;  142  of FIGS. 1 through 5, leading cutting edges  326  incrementally remove work piece material(s), which may then be channeled away by groove  322 . In this manner, the amount of torque required to insert rivet assembly  300  through a work piece is substantially reduced compared to conventional self-boring rivet assemblies. Further, like cutting edges  140  of FIGS. 1 through 5B, leading cutting edges  326  and trailing cutting edges  328  may be substantially parallel to the longitudinal axis  330  of auger  312  or may be angled with respect to the longitudinal axis  330  depending on the application in which rivet assembly  300  is to be used, the material properties of the work pieces in which rivet assembly  300  is to be inserted, the amount of material to be removed by each cutting edge  326 , and the like.  
         [0055]    Similarly, polishing leading edge  332  and trailing edge  334  may be formed in the polishing portion  320  of self-tapping and self-polishing auger  312  along groove  322  rearward of cutting portion  318  and forward of shoulder portion  322 . Like polishing edges  148  &amp;  150  of FIGS. 1 through 5B, polishing leading and trailing edges  332  &amp;  334  remove any excurvations (e.g., material bored away from work piece by head  110 ) leaving a clean, substantially burr free, aperture through the work piece(s) through which rivet sleeve  304  may extend. Further, like polishing edges  148  &amp;  150  of FIGS. 1 through 5, polishing edges  332  &amp;  334  may be substantially parallel to longitudinal axis  330  or may be angled with respect to the longitudinal axis  330  depending on the application in which rivet assembly  300  is to be used, the material properties of the work pieces in which rivet assembly  300  is to be inserted, the amount of material to be removed by each polishing edge  332  &amp;  334 , and the like.  
         [0056]    [0056]FIGS. 14 through 16 illustrate bolt rivet assemblies in accordance with exemplary embodiments of the present invention. The bolt rivet assemblies  400 ,  500  &amp;  600  comprises a hollow rivet body  402 ,  502  &amp;  602  surrounding a mandrel  404 ,  504  &amp;  604 , respectively. As shown, each of the rivet bodies  402 ,  502  &amp;  602  includes a hollow tubular sleeve  406 ,  506  &amp;  606  and a threaded bolt head  408 ,  508  &amp;  608  separated by an enlarged flattened head or flange  410 ,  510  &amp;  610 . The rivet body  402 ,  502  &amp;  602  may be made of steel, aluminum, plastic, composite, or other desirable rivet material. The mandrel  404 ,  504  &amp;  604  may comprise a self-tapping and self-polishing head  412 ,  512  &amp;  612  (e.g., head  110  shown in FIGS. 4 and 5 or, alternately, head  312  shown in FIGS. 12 and 13), a shoulder section  414  &amp;  514  and a shank  416 ,  516  &amp;  616 . The mandrel  404 ,  504  &amp;  604  may be made of steel, aluminum, plastic composite, or other material that is preferably of higher tensile strength than the rivet body material.  
         [0057]    In certain applications, it may be desirable for the threaded portion of bolt head  408 ,  508  &amp;  608  to have multiple sets of threads. A separate head may be fashioned so that these multiple threads may strip its internal threads as it is being threaded onto the rivet body. Thus, once threaded onto the threaded portion, the head cannot be removed. In this fashion, the head may be tightened onto the rivet body and permanently retained. A second nut may be fashioned having a thread pattern corresponding to that of the rivet body so that it will not be stripped and consequently may be removable. Nuts suitable for use with bolt rivet assemblies  400 ,  500  &amp;  600  may vary from six-sided or hex head nuts and wing nuts to various special shapes as required by the application. Additional work pieces, other components, or the like (not shown) may be removably attached to the threaded bolt head and secured by the nut.  
         [0058]    [0058]FIG. 14 depicts a rivet assembly  400  comprising a rivet body  402  including an enlarged flattened head or flange  410  having a concave inner face  418  and convex outer face  420 . Preferably, as the rivet assembly  400  is applied, axial retraction of the mandrel  404  pulls the enlarged flattened head  410  against the outer surface  422  of the outer work piece  424 , compressing and flattening its concave inner face  418 . When the weakened area  426  on mandrel  404  fractures and the shank  416  is released, the concave inner face  418  attempts to retain its original shape causing the rim  430  of the inner face  418  to apply a spring-like force to the outer surface  422 . This force holds the work pieces ( 424  &amp;  432 ) snugly between the head  410  and deformed portion of the rivet body&#39;s sleeve  406 . As a result, the head  410  may increase application strength and prevent rotation of the rivet body  400  with or without a locking washer or serrated inner surface.  
         [0059]    The head or flange of the rivet body  402 ,  502  &amp;  602  may be part of a single piece rivet unit (e.g., enlarged flattened head  410 ) or it may be removable (e.g., removable heads  510  &amp;  610 ). In FIG. 15, a rivet body  500  is depicted formed from a single tube  518  having a threaded portion  520  abutting the sleeve portion  506  and forming bolt head  508 . Enlarged flattened head  510  includes a threaded aperture  522  so that it may be threaded onto threaded portion  520 , and is thus removable. In exemplary embodiments, enlarged flattened head  510  may have a six-sided or hex design similar to a standard nut, or, may alternatively be cylindrical. Additionally, enlarged flattened head  510  may have serrated inner  524  (and outer) surfaces depending upon application requirements. These serrated surfaces  524  may function to increase surface friction between the rivet head  510  and the outer surface  526  of the work piece  528  to prevent rotation of bolt rivet assembly  500  eliminating the need for a lock washer (FIG. 14). The serrated surfaces  524  may further function to prevent rotation of the bolt rivet assembly  500  during loosening and/or tightening of a nut onto the bolt head  508 . Alternately, as shown in FIG. 16, a lock washer  616  may be utilized in place of serrated surfaces for preventing rotation of the rivet assembly  600  and removal of the head  608 . Lock washer  616  may encircle rivet sleeve  606  and be trapped between the enlarged flattened head and the upper surface  618  of a work piece  620 .  
         [0060]    In the embodiment shown in FIG. 16, weakened area  626  is positioned on mandrel  604  so that a length  628  of shank  616  remains in rivet body  602  after separation of the rear portion of the shank  616 . Preferably, length  628  is predetermined to allow shank  616  to fracture at a point that is substantially flush with the end of bolt head  608 . In this manner, the length  628  substantially fills the hollow portion of the rivet body  602 , increasing its strength.  
         [0061]    [0061]FIGS. 1 through 16 illustrate augers designed to be rotated clockwise during insertion. However, it will be appreciated by those of skill in the art that the augers illustrated herein may alternately be designed to be rotated counterclockwise during insertion without departing from the scope and spirit of the present invention. Similarly, in FIGS.  14  though  16 , bolt heads are shown having clockwise threads. However, bolt heads in accordance with the present invention may also be reverse threaded (i.e., may have counterclockwise threads).  
         [0062]    It is believed that the self-polishing and tapping rivet assembly of the present invention and many of its attendant advantages will be understood by the forgoing description. It is also believed that it will be apparent that various changes may be made in the form, construction and arrangement of the components thereof without departing from the scope and spirit of the invention or without sacrificing all of its material advantages. The form herein before described being merely an explanatory embodiment thereof. It is the intention of the following claims to encompass and include such changes.