Abstract:
A blind rivet  200  comprises a mandrel  214  having a deformable mandrel head  218  such that when the blind rivet is received in a pair of aligned apertures of dissimilar sizes in a pair of components  220, 222  to be joined, the mandrel head is adapted to be deformed and cause deformation of a rivet body  202  such that the blind rivet engages the inner surfaces defined by both of the apertures before the mandrel and its head are pulled free of the rivet body.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 61/236,270, filed on Aug. 24, 2009, which is incorporated by reference herein. 
     
    
     BACKGROUND AND SUMMARY 
       [0002]    The present invention relates to blind rivets, and relates particularly to a blind rivet having a mandrel with a deformable mandrel head. 
         [0003]    Manufacturing processes such as automotive manufacturing processes use blind rivets as a means of joining parts together since this is a cost effective method avoiding costly and labour intensive tasks which arise when nut and bolt or screw fastenings are used. Blind rivets, which are well known in the art, are used to attach two pieces of material together by means of access to one side of the material.  FIGS. 1   a - d  illustrate a blind rivet  100 , known as a break stem rivet, used to join together two pieces of material  102 . The blind rivet  100  has a cylindrical rivet body portion  104  with a flange  106  at one end. A mandrel  107 , which has an elongated mandrel stem  108  and a head portion  110  at one end, is fed through the rivet body portion  104  such that the head portion  110  of the mandrel  107  engages the opposite end of the rivet body portion  104  to that from which the flange  106  extends. 
         [0004]    With reference to  FIG. 1   a  the blind rivet  100  is fed through two overlapping apertures in the pieces of material  102  to be joined together such that the flange  106  engages one of the pieces of material  102 . A force F 1  is applied to the mandrel stem  108  in a direction away from the pieces of material  102 , and a force F 2  is also applied to the flange portion  106  in an opposite direction to that of force F 1 . With reference to  FIGS. 1   b  and  1   c , the force F 1  applied to the mandrel stem  108  causes the mandrel head  110  to exert a force on the rivet body portion  104  of the blind rivet  100 . Such a force causes deformation of the rivet body portion  104  as the mandrel head  110  is pulled towards the pieces of material  102  being joined together, resulting in the creation of an additional flange portion  114 . 
         [0005]    The mandrel head  110  is pulled through the rivet body portion  104  of the blind rivet  100  until the additional flange portion  114  engages the material  102 . Typically the mandrel head  110  is made of harder material than the mandrel stem  108  such that the mandrel stem  108  breaks away from the mandrel head  110  on further application of the force F 1  after the additional flange portion  114  engages the material  102 . Following this process the two pieces of material  102  are therefore joined together and held in place by the flange  106  and additional flange portion  114 . 
         [0006]    Pull through blind rivets are also known in the art. Pull through rivets differ from break stem rivets described also in that the mandrel stem does not break away from the mandrel head, and the mandrel head is pulled entirely through the rivet body portion of the blind rivet, and is disposed of with the mandrel stem. U.S. Pat. No. 4,497,603 discloses such a pull through blind rivet. 
         [0007]    A problem with conventional break stem and pull through blind rivets, however, is that it is difficult to reliably join pieces of material having dissimilar sized apertures extending therethrough. With further reference to  FIG. 1   d , for example, if one of the pieces of material  102  had a slightly wider aperture than the other, the rivet body portion  104  of the blind rivet  100  would not engage the entirety of the inner surface defined by the wider aperture. This may then allow the piece of material having the slightly wider aperture to move in a transverse direction. Conventionally this problem would be rectified by drilling a wider aperture in the piece of material  102  having the smaller aperture such that the apertures in the two pieces of material  102  to be joined are of substantially the same size. This complicates and increases the cost of a manufacturing process. Preferred embodiments of the present invention seek to overcome one or more of the above disadvantages of the prior art. 
         [0008]    According to the present invention there is provided a blind rivet comprising: 
         [0009]    a rivet body having a flange for abutting a work piece and an elongated portion extending from said flange, wherein said elongated portion has a bore for receiving a mandrel head of a mandrel; and 
         [0010]    a mandrel having a mandrel head adapted to be located in said bore, and a mandrel stem extending from said mandrel head; 
         [0011]    wherein the rivet is adapted to be received in an aperture in a work piece in a first direction such that said flange engages said work piece, and said mandrel head is adapted to be deformed and to cause deformation of said elongated portion as a result of pulling said mandrel head out of said rivet body in a second direction opposite to said first direction. 
         [0012]    The use of a deformable mandrel head provides the advantage that a blind rivet can be used to fixably attach pieces of material together having dissimilar sized apertures extending therethrough. In another preferred embodiment said mandrel head has a tapering cross section. In a preferred embodiment said mandrel head has a substantially part-conical cross-section. This allows the mandrel head to slightly enter the rivet body portion prior to its deformation providing the advantage that the rivet body portion is evenly deformed around the aperture extending through it. 
         [0013]    In a further preferred embodiment said elongated portion has a plurality of first ribs arranged on an outer surface thereof for engaging an aperture in a work piece. This increases the grip of the rivet on the work piece thereby providing the advantage of minimizing rotation of the work piece relative to the rivet and vice versa. In a preferred embodiment a plurality of said first ribs extends substantially parallel to a longitudinal axis of said elongated portion. 
         [0014]    In another preferred embodiment said flange has a plurality of second ribs arranged thereon for engaging an edge of an aperture in a work piece. This increases the grip of the rivet on the work piece thereby providing the advantage of minimizing rotation of the work piece relative to the rivet and vice versa. In a further preferred embodiment a plurality of said second ribs extend transversely to a longitudinal axis of said elongated portion. In a preferred embodiment said bore extends the entire length of said elongated portion. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    Preferred embodiments of the invention will now be described, by way of example only and not in any limitative sense, with reference to the accompanying drawings in which: 
           [0016]      FIG. 1  illustrates a plurality of cross-sectional views of a break stem blind rivet of the prior art in use; 
           [0017]      FIG. 2  illustrates a perspective view of a blind rivet of the present invention; 
           [0018]      FIG. 3  illustrates a plurality of cross sectional views of the blind rivet in  FIG. 2  in use; and 
           [0019]      FIG. 4  illustrates a plurality of perspective views of different rivet body portions which may be used in the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0020]      FIG. 2  illustrates a pull through blind rivet  200  embodying the present invention. The blind rivet  200  has a cylindrical rivet body portion  202  having a bore  204  extending entirely through it along an axis  206 . The rivet body portion  202  has a flange portion  208  extending from it at one end, and has a partially ribbed outer surface  210 . The flange portion  208  also has a ribbed surface  212  on the side of the flange facing the direction of the rivet body portion  202 . A mandrel  214  having an elongated mandrel stem  216  and a deformable mandrel head  218  extends through the bore  204  in the rivet body portion  202 . The mandrel head  218  is wider than the bore  204  extending through the rivet body portion  202 . The mandrel is secured to the rivet body prior to setting by an interference fit between the stem and the bore of the rivet body. 
         [0021]    The operation of the blind rivet  200  in  FIG. 2 , will now be described with reference to  FIG. 3 . As shown in  FIG. 3   a , the pieces of material  220 ,  222  having large and small apertures  221 ,  223 , respectively extending therethrough, are placed in engagement with one another such that the apertures extending therethrough are aligned. The blind rivet  200  is then fed through the aligned apertures in the pieces of material  220 ,  222  such that the flange portion  208  abuts the surface of the material  222  having the smaller of the two apertures. A force F 1  is then applied to the mandrel stem  216  in a direction away from the rivet body portion  202  along axis  206 , and a force F 2  is applied to the flange portion  208  in the direction of the rivet body portion  202  in a direction opposite to that of force F 1 . The force F 1  pulls the mandrel stem  216  away from the rivet body portion  202  and causes the mandrel head  218  to be pulled into the bore  204  extending through the rivet body portion  202 . The tapered surface on the side of the mandrel head  218  adjacent the mandrel stem  216  is brought into engagement with the rivet body portion  202  as the mandrel  214  is pulled away from the rivet body portion  202 . 
         [0022]    Referring to  FIG. 3   b , as the mandrel  214  is pulled away from the rivet body portion  202 , the mandrel head  218  exerts a force on the mandrel body portion  202  which thereby causes it to deform, resulting in the creation of an additional flange portion  224 . As the mandrel head  218  is pulled further through the bore  204  in the rivet body portion  202 , the situation illustrated in  FIG. 3   b  occurs, where the additional flange portion  224  comes into engagement with the surface of material piece  220 . At this point, the pieces of material  220 ,  222  are joined and held together by flange portion  208  and the additional flange portion  224  of the tail or blind end of the rivet body. However there exists a gap  226  between the rivet body portion  202  and the inner surface of the apertures extending through both of the pieces of material  220 ,  222 . 
         [0023]    In order for the mandrel head  218  to be pulled further through the bore  204  in the rivet body portion  202 , the mandrel head  218  must deform so as to fit through the larger aperture in material piece  220 , which is narrower than the width of the mandrel head in its initial state.  FIG. 3   c  illustrates the mandrel head  218  having deformed a sufficient amount to fit through the larger aperture in material piece  220 . As the mandrel head  218  is pulled through this aperture, the mandrel body portion  202  deforms further such that it is brought into engagement with the inner surface defined by the aperture in material piece  220 . At this point however, there still exists a gap  226  between the rivet body portion  202  and the inner surface of the smaller aperture extending through material piece  222 . 
         [0024]    As the mandrel head  218  is pulled further through the bore  204  in the rivet body portion  202 , the mandrel head  218  deforms further such that it can fit through the smaller aperture in material piece  222 , which is narrower than the width of the mandrel head  218  after being pulled through the larger aperture in material piece  220 . The mandrel head  218  is therefore deformed a sufficient amount such that it may be pulled through the smaller aperture in material piece  222 , and as it is pulled through this aperture, the mandrel body portion  202  is again further deformed such that it is brought into engagement with the inner surface defined by the smaller aperture in material piece  222 . The mandrel stem  216  and mandrel head  218  are then pulled such that they are completely separated from the rivet body portion  202  as illustrated in  FIG. 3   d.    
         [0025]    Following this process, the two pieces of material  220 ,  222  are joined together in such a way that they can not move relative to each other. The ribs  210  (see  FIG. 2 ) on the outer surface of the rivet body portion  202  engage the inner surfaces of the apertures in both material pieces  220 ,  222  so as to increase the grip of the rivet body portion  202  on the pieces of material  220 ,  222  and thereby prevent rotation of the joined pieces of material  220 ,  222  about the rivet body portion  202 . As the mandrel head  218  is pulled out of the bore  204  in the rivet body portion  204 , the outer surface of the rivet body portion  202 , and therefore the flange  208  extending from it, deform in such a way that the ribbed surface  212  (see  FIG. 2 ) of the flange  208  is forced against the material piece  222  thereby preventing rotation of the rivet body portion  202  relative to the material piece  222 . The rivet body is thereby permanently fastened to the workpieces during normal use. 
         [0026]    If the pieces of material being joined by a blind rivet  200  of the present invention are electrical conductors, the blind rivet  200  is able to form a joint between the two pieces of material which has earth or grounding continuity. For example, workpiece  220  is a conductive metal eyelet attached to an electrical wire and workpiece  222  is a stamped steel panel of an automotive vehicle or electronic cabinet, such as a computer or server chassis. The panel workpiece  222  acts as a grounded electrical conductor if electricity flows to it from conductive eyelet  220 . Alternately, workpiece  222  may be the eyelet and workpiece  220  may be the grounding panel whereby ribs  212  of flange  208  dig into and deter eyelet  222  from rotation. In these examples, it is desirable to deter rotation of the conductive eyelet relative to the adjacent panel by way of the blind rivet ribs  210  and  212 . 
         [0027]      FIG. 4  illustrates various other rivet body portion  202  outer surface configurations. In particular,  FIGS. 4   a  and  4   d  illustrate a rivet body portion  202 ′ having a partially splined outer surface, and  FIGS. 4   b ,  4   c ,  4   e  and  4   f , illustrate a rivet body portion having a partially ( 202 ″) and entirely ( 202 ′″) ribbed outer surface, respectively. In the embodiment of  FIGS. 4   b  and  4   e , the outer surface of the rivet body section is free of discontinuities (i.e., circular-cylindrically smooth) between the axially elongated ribs on the body section and the laterally elongated ribs on the underside of the flange. 
         [0028]    It will be appreciated by persons skilled in the art that the above embodiments have been described by way of example only and not in any limitative sense, and that various alterations and modifications are possible without departure from the scope of the invention as defined by the appended claims. For example the blind rivet of the present invention may be used to join more than two pieces of material together.