Abstract:
A blind setting rivet assembly capable of permanently fastening sheet metal work pieces or the like together 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 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 coring head that cores an aperture in the workpieces through which the rivet sleeve passes. The mandrel shank includes 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. 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 components.

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. 60/468,188, filed May 5, 2003, which is herein incorporated by reference in its entirety. 
     
    
     
       INCORPORATION BY REFERENCE  
         [0002]    The following related commonly owned patents and patent applications are incorporated herein by reference in their entirety:  
                                           Inventor   Pat./App No.   Issue Date   Filing Date                   Aasgaard   10/719,748       Nov. 11, 2003       Aasgaard   10/050,084       Jan. 14, 2002       Aasgaard    5,741,099   Apr. 21, 1998   Jul. 12, 1996       Aasgaard    5,762,456   Jun. 9, 1998   Jul. 12, 1996       Aasgaard    5,915,901   Jun. 29, 1999   Oct. 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 rivet assembly having a blind-setting coring head.  
         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 drill bits 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. Alternatively, 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 larger, polished aperture is desirable. Consequently, it would be advantageous to provide a blind setting rivet that would be capable of self-tapping and coring an aperture instead of only self drilling (using a drill bit) or only self-tapping (using a screw tip). Such a self-tapping, coring rivet should retain material removed from the workpiece and would leave a clean, polished aperture.  
         SUMMARY OF THE INVENTION  
         [0007]    Accordingly, the present invention is directed to a self-tapping and blind setting coring rivet assembly. In basic embodiments, the rivet assembly is suitable for permanently fastening two or more workpieces, or the like, together. In other embodiments, the rivet assembly may further include a threaded bolt head onto which a nut may be affixed for removably attaching objects or components to one or more workpieces.  
           [0008]    In exemplary embodiments of the invention, the blind setting coring rivet assembly comprises a rivet body having a hollow tubular sleeve and a generally flattened, enlarged head. The rivet body surrounds a mandrel comprising a coring tip and a shank having a weakened area for allowing detachment of the shaft from the coring tip following application of sufficient axial force to the shank. This application of force sets the rivet by causing a tapered shoulder section joining the coring tip and the shank of the mandrel to deform the rivet sleeve. The coring tip, which in embodiments of the invention may be self-tapping, cores an aperture in the work piece(s) through which the rivet sleeve passes, retaining material cored from the workpiece(s) within the coring tip. The coring tip includes a serrated leading edge having one or more cutting teeth and may further include a generally longitudinally formed groove providing polishing edges that shave or carve small amounts of work piece material from the cored aperture for polishing the aperture.  
           [0009]    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  
       [0010]    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:  
         [0011]    [0011]FIG. 1 is a side elevational view illustrating a self-tapping, blind-setting coring rivet assembly having a coring head in accordance with an exemplary embodiment of the present invention;  
         [0012]    [0012]FIG. 2 is a partial cross-sectional side elevational view illustrating the rivet assembly shown in FIG. 1;  
         [0013]    [0013]FIG. 3 is a side elevational view illustrating the mandrel of the rivet assembly shown in FIG. 1;  
         [0014]    [0014]FIGS. 4 and 5 are end elevational and side elevational views, respectively, of the coring head of the rivet assembly shown in FIG. 1;  
         [0015]    [0015]FIGS. 6 and 7 are end elevational and side elevational views, respectively, of a coring head in accordance with an alternative exemplary embodiment of the present invention;  
         [0016]    [0016]FIGS. 8, 9,  10 ,  11  and  12  are side elevational views illustrating a blind-setting, coring rivet assembly in accordance with an exemplary embodiment of the present invention being applied to a workpiece or workpieces; and  
         [0017]    [0017]FIGS. 13, 14 and  15  are side elevational views illustrating exemplary blind- setting, coring bolt rivet assemblies in accordance with exemplary embodiments of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0018]    Reference will now be made in detail to the presently preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings.  
         [0019]    Referring generally now to FIGS. 1 through 15, self-tapping and blind setting coring rivet assemblies  100  in accordance with exemplary embodiments of the present invention are described. As shown in FIG. 1, rivet assembly  100  comprises a rivet body  102  having a hollow tubular rivet sleeve  104  and a generally flattened head  106 . The rivet body  102  surrounds a mandrel  108  having a coring tip or head  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.  
         [0020]    As shown, coring head  110  is comprised of a generally barrel shaped body portion  116  having a serrated leading edge  118 , and optionally a self-tapping central tip  120 . During application of rivet assembly  100 , coring head  110  is held substantially normal to the surface of a work piece while rotary motion is applied to shank  114 . This rotary motion causes the coring head  110  to penetrate into the work piece materials, cutting or coring an aperture therein. In this manner, the cutting head  110  forms an aperture through the work piece materials.  
         [0021]    A weakened area (e.g., an area of reduced diameter, an etched area, or the like)  122  may be formed in the mandrel shank  114  rearward from shoulder section  112 . This weakened area  122  is preferably designed to fracture upon application of a predetermined tensile force to the shank  114  allowing coring head  110  and shoulder section  112  to be detached from shank  114  following completed application of the rivet assembly  100 . Similarly, a restrictor or area of enlarged diameter  124  may be formed in mandrel  108  between shoulder section  112  and weakened area  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 cutting head  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. In embodiments of the invention, mandrel  108  may further 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.  
         [0022]    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.  
         [0023]    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.  
         [0024]    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 . The shank  114  may be cylindrical in cross-section as illustrated, or alternately may have any other desired shape (e.g., square, hexagonal, octagonal, or the like) required by the rivet setting tool employed. Preferably, the outer diameter of shoulder section  112  is slightly larger than the outer diameter  132  of rivet sleeve  104  allowing the sleeve  104  to pass through the hole or aperture formed by coring head  110 .  
         [0025]    Referring now to FIGS. 4 through 7, exemplary coring heads  110  in accordance with the present invention are described. Each coring head  110  is comprised of a generally cylindrical or barrel shaped body portion  116  having an inner diameter (d i )  130 , an outer diameter (d e )  132  an external length (l e )  134  and an internal length or depth (l i )  136  terminated in internal wall portion  138 . The opposite end of body portion  116  from internal wall portion  138  is terminated in a serrated leading edge  118  comprised of a plurality of angled cutting teeth  140  arranged tangentially about the leading edge  118 . In exemplary embodiments, each of the cutting teeth  140  includes a leading face  142  and a trailing face  144  meeting at an angle to form a cutting edge  146 . In the embodiment illustrated, self-tapping tip  116  includes a self-tapping central tip  120  for piercing the surface of a work piece. It will be appreciated by those of skill in the art that internal wall portion  138  may be substantially flat as illustrated in FIGS. 4 and 6, or alternatively, may have other shapes without departing from the scope and intent of the present invention.  
         [0026]    By adjusting the angle and length of leading and trailing faces  142  &amp;  144  with respect to the longitudinal axis of the coring head  110 , cutting edge  146  may be shaped so that the depth of cut during each turn of coring head  110  may be controlled, thereby controlling the torque required to insert rivet assembly  100  through a workpiece or workpieces. Moreover, by adjusting shape and orientation of the cutting edge with respect to the body portion, the type of cut made in the workpiece material may be closely controlled. For example, by angling the cutting edges  146  outward, away from the longitudinal axis of the coring head  110 , material cut from the workpiece is forced outward from the cored section. Conversely, by angling the cutting edges inward, toward the longitudinal axis of the coring head  110 , material cut from the workpiece is forced inward toward the cored section. It will be appreciated that teeth  140  or groups of teeth  140  may further be alternately angled inward and outward to provide additional control of the cut dynamics without departing from the scope and spirit of the present invention. Similarly, cutting edges  146  of teeth  140  may extend beyond the external diameter (d e )  132  of the body portion  116  so that teeth  140  take a more aggressive cut or bite from the workpiece material. Conversely, cutting edges  146  of teeth  140  may be formed to not extend beyond the diameter (d e )  132  of the body portion  116  in order to take a less aggressive cut or bite from the workpiece material. Again, it will be appreciated that the cutting edges  146  of teeth  140  or groups of teeth  140  may alternately extend beyond the external diameter (d e )  132  of the body portion  116  and remain within the external diameter (d e )  132  to provide an aggressive bite or cut, while forming an aperture that remains substantially smooth, requiring less polishing than would an aperture having all teeth extending beyond the external diameter (d e )  132 . Thus, it will be appreciated that the selection precise shapes for teeth  140  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 maximum torque available for insertion of the rivet assembly  100 , and the like. Moreover, the external length (l e )  134  and/or internal length or depth (l i )  136  of body portion  116  may be selected depending on the thickness of the workpiece or workpieces through which the rivet assembly is to be inserted.  
         [0027]    As shown in FIGS. 4 and 5, coring head  110  may include a self-tapping central tip  120 , which is preferably centered on the longitudinal axis of coring head  110 , and extends from the internal wall portion  138  beyond leading edge  118 . In exemplary embodiments of the invention, self-tapping central tip  120  includes an initial point  148  suitable for piercing the surface of the workpiece. In such embodiments, piercing point  148  may extend into one or more initial contact edges  150  suitable for forming a guide hole or aperture in the workpiece by puncturing, separating and then scraping or carving work piece material from the surface of the workpiece. Initial contact edges  150  may be angled and may be offset to assist in separating and tapping the work piece material(s). In this manner, self-tapping central tip  120  facilitates initial insertion (tapping) of the rivet assembly  100  allowing the rivet assembly  100  to be more easily started in the work piece. In other embodiments, as shown in FIGS. 6 and 7, coring head  110  may be fabricated without self-tapping central tip  120 .  
         [0028]    As shown, initial contact edges  150  may transition into a thread  152  extending at least substantially about self-tapping central tip  120 . Preferably, as central tip  120  is inserted into a work piece and a guide hole is started by piercing point  148  and initial contact edges  150 , thread  152  pull the central tip  120 , and body portion  116 , through the work piece material, reducing the amount of force required to tap the coring head though the workpiece. It will be appreciated that those of skill in the art may employ thread designs other than those specifically illustrated and described without departing from the scope and intent of the present invention. For example, the size and pitch of threads  152  may be varied, or the width or spacing of thread  152  may be increased or decreased.  
         [0029]    As shown in FIGS. 4 through 7, one or more grooves  154  may be formed generally longitudinally in barrel shaped body portion  116 . Each groove  154  may extend to various depths in barrel shaped body portion  116  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, in exemplary embodiments, groove  154  may have a generally half-conical or elliptical shape extending from leading edge  118  to shoulder section  112 . However, it will be appreciated that groove  154  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, the size and shape of teeth  140 , and the like. For example, in one embodiment, groove  154  may extend only partially from shoulder portion  112  of coring head  110  to leading edge  118  while in another embodiment groove  154  may vary in depth or width uniformly between leading edge  118  and shoulder portion  112  or may vary in depth or width in a non-uniform manner. It will be appreciated that coring head  110  may also be fabricated without groove  154 , without departing from the scope and intent of the present invention.  
         [0030]    A polishing leading edge  156  and polishing trailing edge  158  may be formed along one or more of grooves  154 . Preferably, polishing leading and trailing edges  156  &amp;  158  remove any excurvations (e.g., material bored away from work piece by coring head  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. In the embodiment illustrated polishing leading and trailing edges  156  &amp;  158  are illustrated as being straight or linear edges. However, either or both of polishing leading edge  156  and/or polishing trailing edge  158  may be curved or curvilinear without departing from the scope and intent of the present invention. In the exemplary embodiment shown, groove  154 , polishing leading edge  156  and polishing trailing edge  158  may be substantially parallel to the longitudinal axis  144  of auger  110 . Alternately, any or all of groove  154 , polishing leading edge  156  and polishing trailing edge  158  may be angled, thereby forming an angle with respect to the longitudinal axis. Moreover, leading polishing edge  156  may extend outwardly from the longitudinal axis further than trailing polishing edge  158  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.  
         [0031]    [0031]FIGS. 8 through 12 illustrate the application or insertion of a rivet assembly  100 , described in connection with FIGS. 1 through 7, to join two or more workpieces (two work pieces  160  &amp;  162  are shown). FIG. 8 depicts the rivet assembly  100  near the beginning of application. Preferably, the coring head  110  is held substantially normal to the outer work piece surface  164  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 and power or hand tools (such as the rivet setting device described in U.S. patent application Ser. No. 10/719,748) may be used to provide rotary motion and axial retraction to the mandrel  108  (see FIGS. 9, 10 and  11 ).  
         [0032]    Rotary motion applied to mandrel  108  causes self-tapping central tip  120  to tap a hole or aperture in adjacent work pieces  160  &amp;  162 . As the self-tapping central tip  116  punctures, spreads and cuts the work piece materials, removed material on the inner surface  164  of the innermost work piece  160  is separated and scraped or carved away from the work piece  164 . The rotary motion further engages leading edge  118  into the surface  164  of work piece  160 . For example, in the embodiment illustrated, central tip  120 , once tapped in workpiece  162 , pulls body portion  116  toward inner surface  164  until leading edge  118  is brought into contact with surface  164 . Leading edge  118  then engages the surface  164  cutting in turn though workpiece  160  and workpiece  162  so that a generally cylindrical section of each workpiece is removed. Preferably, this section is retained within the body portion  116  by central tip  120  and/or interference between the section and the inner surface of body portion  116 . However, it will be appreciated that in embodiments of the invention, the generally cylindrical section cored from the workpiece may alternately be removed from body portion  116  if, for example, removal of the section is necessitated by application requirements, or the like.  
         [0033]    [0033]FIG. 9 illustrates rivet assembly  100  following the creation of an aperture through the work piece materials ( 160  &amp;  162 ) by the coring head  110 . As body portion  116  of coring head  110  passes though the aperture formed in work pieces  160  &amp;  162 , the rotary motion applied to shank  114  further causes polishing edges  156  &amp;  158  to shave or carve additional material, burrs caused by leading edge  118  and the like from the inner surface of the aperture, smoothing the aperture prior to insertion of rivet sleeve  104 . Preferably, the outer diameter of the shoulder section  112  (see FIG. 2) is slightly larger than outer diameter of rivet sleeve  104  allowing the sleeve to pass through the aperture formed. Once the aperture is formed in work pieces  160  &amp;  162 , rivet sleeve  104  may be inserted into the aperture until enlarged flattened head  106  abuts the outer surface  164  of workpiece  160 .  
         [0034]    [0034]FIG. 10 depicts rivet assembly  100  following the application of a rearward tension force on shank  104  setting the rivet assembly  100 . To set the rivet assembly  100 , the rear portion of the shank  114  may be grasped by a rivet setting tool (such as the rivet setting device described in U.S. patent application Ser. No. 10/719,748), a grasping tool, or the like, and axially retracted away from surface  164  of workpiece  160 . This axial retraction causes shoulder section  112  to deform rivet sleeve  114 . As shoulder section  112  (and coring 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  160  &amp;  162 . Further, the deformed portion of rivet sleeve  104  is pulled against the surface  166  of work piece  162  tightening the rivet to the work pieces  160  &amp;  162 . Preferably, the weakened area  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 .  
         [0035]    [0035]FIG. 11 depicts rivet assembly  100  following separation of shank  114  and setting. In the embodiment shown, coring head  110  and shoulder section  112  are retained in rivet sleeve due to 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 .  
         [0036]    [0036]FIG. 12 illustrates a rivet assembly  100  in accordance with an alternative embodiment of the present invention wherein the coring head  110  and shoulder section  112  detach from the rivet body  104  following application of the rivet assembly  100 . In such embodiments, wherein polishing head  110  is allowed to drop off, the shoulder section  112  of mandrel  106  may have a face  168  comprising a tapered inner section  170  and a flat-plate outer section  172 . Preferably, the tapered inner section  170  initially spreads the lower end of rivet sleeve  104 . The flat-plate outer section  172  then flattens the sleeve  104  against the inner surface  166  of the workpiece  162  allowing the coring head  110  and shoulder section  112  to drop off following separation of shank  114 .  
         [0037]    [0037]FIGS. 13 through 15 illustrate bolt rivet assemblies in accordance with exemplary embodiments of the present invention. Bolt rivet assemblies  200 , like rivet assemblies  100  illustrated in FIGS. 1 through 12, comprises a hollow rivet body  202  surrounding a mandrel  204  having a coring head  206  in accordance with the present invention (e.g., employing any or all of the features of coring head  110  described in FIGS. 1 through 12). As shown, each of the rivet bodies  202  includes a hollow tubular sleeve  208  and a threaded bolt head  210  separated by an enlarged flattened head or flange  212 . The rivet body  202  may be made of steel, aluminum, plastic, composite, or other desirable rivet material. The mandrel  204  may comprise coring head  206 , a shoulder section  216  and a shank  218 . The mandrel  204  may be made of steel, aluminum, plastic composite or other material that is preferably of higher tensile strength than the rivet body material.  
         [0038]    [0038]FIG. 13 depicts a rivet assembly  200  comprising a rivet body  202  including an enlarged flattened head or flange  212  having a concave inner face  220  and convex outer face  222 . Preferably, as rivet assembly  200  is applied, axial retraction of the mandrel  204  pulls the enlarged flattened head  212  against the surface  224  of workpiece  226 , compressing and flattening the concave inner face  220 . When the weakened area  228  on mandrel  204  fractures and the shank  218  is released, the concave inner face  220  attempts to retain its original shape causing the rim  230  of the inner face  220  to apply a spring-like force to surface  224 . This force holds the work pieces ( 226  &amp;  232 ) snugly between the head  212  and the deformed portion of the rivet body&#39;s sleeve  208 . As a result, the head  212  may increase application strength and prevent rotation of the rivet body  202  with or without a locking washer or serrated inner surface.  
         [0039]    As shown in FIGS. 13 through 15, the head or flange of the rivet body  202  may be part of a single piece rivet unit (e.g., as shown in FIG. 13) or it may be removable (e.g., as shown in FIGS. 14 and 15). In FIGS. 14 and 15, a rivet body  202  is depicted formed from a single tube  234  having a threaded portion  236  transitioning to the sleeve portion  208  and forming bolt head  210 . In this embodiment, flattened head  212  includes a threaded aperture  238  so that the head  212  may be threaded onto threaded portion  236 , and is thus removable. In exemplary embodiments, flattened head  212  of FIGS. 14 and 15 may have a six-sided or hex design similar to a standard nut, or, may alternatively be cylindrical. Additionally, as shown in FIG. 14, flattened head  212  may have serrated inner (and additionally or alternatively outer) surfaces  240  depending upon application requirements. These serrated surfaces  240  may function to increase surface friction between the rivet head  212  and the surface  226  of the work piece  226  to prevent rotation of bolt rivet assembly  200  eliminating the need for a lock washer (see FIG. 15). The serrated surfaces  240  may further function to prevent rotation of the bolt rivet assembly  200  during loosening and/or tightening of a nut onto the bolt head  210 . Alternately, as shown in FIG. 15, a lock washer  242  may be utilized in place of serrated surfaces for preventing rotation of the rivet assembly  200  and removal of the head  212 . Lock washer  242  may encircle rivet sleeve  204  and be trapped between the enlarged flattened head  212  and the surface  226  of the work piece  228 .  
         [0040]    Additionally, in the embodiment shown in FIG. 15, weakened area  244  is positioned on mandrel  204  so that a length  246  of shank  218  remains in rivet body  202  after separation of the rear portion of the shank  218 . Preferably, length  246  is predetermined to allow shank  218  to fracture at a point that is substantially flush with the end of bolt head  210 . In this manner, the length  246  substantially fills the hollow portion of the rivet body  202 , increasing the strength of the rivet body  202 .  
         [0041]    [0041]FIGS. 1 through 15 illustrate coring heads  110  and  206  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 intent of the present invention. Similarly, in FIGS.  13  though  15 , 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).  
         [0042]    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.