Abstract:
A blind rivet comprises a sleeve, a body, and a mandrel. The sleeve includes a barrel with a hexagonal cross-section, a flange, and a through-hole. The rivet body includes a base, a barrel with slits extending in the axial direction, and a through-hole. The mandrel includes an elongated stem and a head. During the setting process, the barrel of the rivet body is pushed open by the head of the mandrel, and the objects to be fastened are fastened between the opened portion of the barrel and the flange of the sleeve. The mandrel is then pulled further and the polygonal vertices of the sleeve barrel are compressed by a round squeezing hole in a nosepiece. The compression of the sleeve barrel forces the inner circumference of the barrel into non-sliding engagement with the mandrel.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority from Japanese Patent Application No. 2011-052372, filed on Mar. 10, 2011, the disclosure of which is incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates to a blind rivet. The present invention relates more specifically to a blind rivet and fastening method thereof in which the shear strength between the sleeve and the mandrel is high without increasing the load used to squeeze the sleeve in a squeezed rivet-type blind rivet. 
         [0003]    In well-known blind rivets, there is a hollow metal rivet having a rivet barrel and a flange on one end of the rivet barrel, and an enveloped metal mandrel in which a stem extends through the rivet and from the flange of the rivet barrel. A blind rivet has the advantage of being able to fasten a plurality of panels using an operation performed on one side. 
         [0004]    A blind rivet is a rivet with two separate components: a sleeve with a flange, and a rivet body. A slit is formed in the rivet body in the axial direction, and the portions of the rivet body separated by the slit are pushed outward by the mandrel and fastened. 
         [0005]    In such a blind rivet, the through-hole in the sleeve is aligned with the through-hole in the rivet body, the stem of the mandrel is inserted into the aligned through-holes in the sleeve and the rivet body, the head of the mandrel is arranged near the end of the rivet body, and the blind rivet is assembled so that the stem of the mandrel extends from the rivet body and the sleeve. 
         [0006]    When members to be fastened are fastened using a blind rivet, the stem of the mandrel in the assembled blind rivet is inserted into the nosepiece of a fastening machine until the barrel of the sleeve comes into contact with the nosepiece. With the stem held by a gripping member, the head of the mandrel is inserted into a mounting hole of a member to be fastened such as a panel, and the flange on the sleeve is brought into contact with the portion of the member to be fastened surrounding the mounting hole. Next, when the fastening machine pulls strongly on the stem of the mandrel from the barrel side of the sleeve, the barrel of the rivet body is deformed so that it is folded, bent and opened by the edge of the mounting hole in the member to be fastened. The barrel of the sleeve is squeezed by the fastening machine, and engaged by the engaging portions of the mandrel in the through-hole of the sleeve. The mandrel is broken off at the slender breakable portion of the stem, and the members to be fastened such as panels can be fastened between the flange of the sleeve and the opened barrel of the rivet body. 
         [0007]    After the blind rivet has been fastened, the squeezed barrel of the sleeve and the engaging portions of the mandrel in the through-hole of the sleeve have to be secured strongly so that they do not easily come off. In a blind rivet with a sleeve, the sleeve is squeezed and the shear strength is increased where the engaging portions of the mandrel engage the threading. In order to do so, the diameter of the sleeve barrel is enlarged and the amount of squeezing increased or the length is extended. When the diameter or length of the sleeve barrel is increased, the load needed to squeeze the sleeve barrel is increased when the blind rivet is fastened. Thus, the shear load on the breakable portion of the mandrel has to be increased. However, when the shear load on the breakable portion of the mandrel is increased, the extraction strength of the fastening machine has to be increased, and larger machinery is required. It also becomes more difficult to stably fasten the blind rivet. 
         [0008]    Therefore, it would be desirable if an increase in the sleeve squeezing load could be prevented even when the shear strength between the sleeve and the mandrel is increased. 
         [0009]    Patent Document 1 relates to a blind rivet which is easy to fasten from below while facing the ceiling of a building. In the blind rivet of Patent Document 1, a suspended member is arranged between an expandable portion for caulking a member and the enlarged head of a tensile rod so as to cooperate with the head of the sleeve body. When the suspended member is inserted elastically into a mounting hole in the member, it is restored and keeps the rivet body from falling out. 
         [0010]    Patent Document 2 relates to a blind rivet that is easy to remove after fastening. The blind rivet in Patent Document 2 includes a rivet body having a trunk and a rivet head on one end of the trunk, a plug having a stem tail, an easy-to-bend connecting portion, and a spiral-shaped groove, and a stem having an end head. When the blind rivet is fastened, the material from the rivet head enters the spiral-shaped groove and is fastened. The fastened rivet can be released fairly easily by rotating the rivet head. 
         [0011]    In Patent Document 1, the purpose of the invention is to keep the rivet body of a blind rivet from falling out. In Patent Document 2, the purpose of the invention is to allow a blind rivet to be easily removed after fastening. Neither one mentions reducing the load used to squeeze the sleeve of the blind rivet. 
         [0012]    Therefore, it would be desirable if an increase in the sleeve squeezing load could be prevented even when the shear strength between the sleeve and the mandrel is increased.
   [Patent Document 1] Published Unexamined Patent Application No. 2000-213516   [Patent Document 2] Published Unexamined Patent Application No. 63-254212   
 
       SUMMARY OF THE APPLICATION 
       [0015]    Therefore, a purpose of the present invention is to realize a blind rivet in which the shear strength between the sleeve and the mandrel is increased and the sleeve squeezing load is not increased by partially squeezing the sleeve deeply. 
         [0016]    In order to achieve this purpose, in a first aspect of the present invention, the cross-section of the barrel of the sleeve has a hexagonal shape before fastening. The cross-section of the squeezing hole for squeezing the barrel of the sleeve in the fastening machine has a round shape, and the inner diameter of the squeezing hole becomes somewhat smaller so as to be shorter than the distance between vertices with respect to the barrel of the sleeve with a hexagonally shaped cross-section and to be substantially equal to the distance between opposing sides of the hexagonal shape. When a barrel of a sleeve with this shape is combined with the squeezing hole and the barrel of the sleeve is squeezed, the barrel of the sleeve is squeezed only in the vicinity of the vertices of the hexagonal shape. The vicinity of the central portion of the sides of the hexagonal shape is hardly squeezed at all. This reduces the sleeve-squeezing load to that which is necessary for squeezing. As a result, the shear strength between the sleeve and the mandrel can be increased without increasing the sleeve-squeezing load, even though the amount of sleeve being squeezed is partially increased. 
         [0017]    A first aspect of the present invention is a blind rivet for fastening a plurality of members to be fastened having a mounting hole, characterized in comprising: 
         [0018]    a sleeve having a barrel, a flange formed on one end of the barrel, and a through-hole formed so as to pass through the interior, 
         [0019]    a rivet body having a through-hole formed so as to pass through the interior, and 
         [0020]    a mandrel having an elongated stem, and a head having an outer diameter greater than the inner diameter of the through-holes in the sleeve and the rivet body, 
         [0021]    the various components being combined so the head of the mandrel is arranged near the end of the rivet body, and the stem of the mandrel passes through the through-holes in the rivet body and the sleeve and extends from the end of the sleeve; 
         [0022]    wherein the blind rivet is inserted from the head of the mandrel into through-holes in the members to be fastened, the surface of the flange in the sleeve makes contact with the portion of a member to be fastened surrounding the mounting hole, 
         [0023]    the barrel of the sleeve contacts the entrance to a squeezing hole in a nosepiece having a different cross-sectional shape from the outer shape of the barrel of the sleeve, the rivet body is pushed and deformed by the head of the mandrel when the stem of the mandrel is pulled, the barrel of the sleeve is pulled into the squeezing hole, the cross-section of the barrel of the sleeve is squeezed by the shape of the squeezing hole, and the inner diameter of the inner circumference of the through-hole in the barrel of the sleeve becomes smaller and engages the engaging portions of the mandrel, and 
         [0024]    the members to be fastened becoming fastened between the deformed rivet body and the flange of the sleeve. 
         [0025]    When a sleeve is squeezed by a squeezing hole in the nosepiece having a different cross-sectional shape from the barrel of the sleeve, the squeezing area is smaller and the sleeve-squeezing load is smaller than a case in which the same thickness is squeezed around the entire periphery. 
         [0026]    Optionally, the rivet body has a base, and a barrel formed at an end of the base having a slit extending in the axial direction, and the barrel of the rivet body is pushed by the head of the mandrel to open the barrel at the position contacting the edge of the mounting hole in a member to be fastened, and the members to be fastened are fastened between the opened portion of the barrel in the rivet body and the flange in the sleeve. 
         [0027]    Because the slit makes the rivet body easier to open, the members to be fastened can be fastened stably. 
         [0028]    Preferably, the mandrel is broken off in the breakable portion of the stem with a small diameter, and the section from the breakable portion to the head remains in the fastened section when the members to be fastened are fastened. 
         [0029]    Optionally, the cross-section of the barrel in the sleeve has a hexagonal shape, the cross-section of the squeezing hole in the nosepiece has a round shape, and the cross-section of the barrel in the sleeve is squeezed into a round shape. 
         [0030]    Optionally, the cross-section of the barrel in the sleeve has a round shape, the cross-section of the squeezing hole in the nosepiece has a polygonal shape, and the cross-section of the barrel in the sleeve is squeezed into a polygonal shape. 
         [0031]    Optionally, the polygonal shape is a hexagonal shape. 
         [0032]    Optionally, the cross-section of the barrel in the sleeve has a round shape, the cross-section of the squeezing hole in the nosepiece has a round shape with protrusions at equal intervals in the circumferential direction, and the cross-section of the barrel in the sleeve is squeezed into a round shape with recesses at equal intervals in the circumferential direction. 
         [0033]    A second aspect of the present invention is a blind rivet for fastening a plurality of members to be fastened having a mounting hole, characterized in comprising: 
         [0034]    a sleeve having a barrel with a cross-section having a polygonal shape, a flange formed on one end of the barrel, and a through-hole formed so as to pass through the interior; 
         [0035]    a rivet body having a through-hole formed so as to pass through the interior; and 
         [0036]    a mandrel having an elongated stem, and a head having an outer diameter greater than the inner diameter of the through-holes in the sleeve and the rivet body; 
         [0037]    the various components being combined so the head of the mandrel is arranged near the end of the rivet body, and the stem of the mandrel passes through the through-holes in the sleeve and the rivet body and extends from the end of the sleeve. 
         [0038]    When the stem of the mandrel is pulled while the barrel of the sleeve in the blind rivet is being squeezed by the through-hole in the nosepiece having a cross-section with a round shape, the cross-section of the barrel of the sleeve is squeezed into a round shape, and the blind rivet is fastened. 
         [0039]    A third aspect of the present invention is a method for fastening members to be fastened using a blind rivet, characterizing in comprising the steps of: 
         [0040]    preparing a sleeve having a barrel with a polygonal cross-section, a flange formed on one end of the barrel, and a through-hole formed so as to pass through the interior, 
         [0041]    a rivet body having a base, a barrel formed at an end of the base having a slit extending in the axial direction, and a through-hole formed so as to pass through the interior, and 
         [0042]    a mandrel having an elongated stem, and a head having an outer diameter greater than the inner diameter of the through-holes in the sleeve and the rivet body; 
         [0043]    combining the various components so the head of the mandrel is arranged near the barrel-side end of the rivet body, the stem of the mandrel passes through the through-holes in the sleeve and the rivet body and extends from the barrel-side end of the sleeve, and a blind rivet is prepared; 
         [0044]    inserting the blind rivet from the head of the mandrel into through-holes in the members to be fastened, the surface of the flange-side end of the sleeve contacting the portion of a member to be fastened surrounding the mounting hole; 
         [0045]    bringing the barrel-side end of the sleeve into contact with the entrance to a squeezing hole having a round cross-section in the nosepiece of a fastening machine; and 
         [0046]    pulling the stem of the mandrel from the barrel side of the sleeve so that the barrel of the rivet body is pushed by the head of the mandrel to open the barrel at the position contacting the edge of the mounting hole in a member to be fastened, the members to be fastened are fastened between the opened portion of the barrel in the rivet body and the flange in the sleeve, 
         [0047]    the barrel in the sleeve is squeezed by the squeezing hole in the nosepiece, the outer diameter at the vertices of the barrel with a polygonal shape is reduced, the inner circumference of the through-hole in the barrel engages the engaging portion of the mandrel, and 
         [0048]    the mandrel is broken off in the breakable portion of the stem with a small diameter. 
         [0049]    Thus, in the present invention, a blind rivet can be obtained in which the sleeve squeezing load is not increased, and in which the shear strength between the sleeve and the mandrel is high. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
         [0050]      FIG. 1  is a partially cutaway front view of the blind rivet in a first embodiment of the present invention. 
           [0051]      FIG. 2  ( a ) is a partially cutaway front view of the sleeve of the blind rivet in  FIG. 1 , and  FIG. 2  ( b ) is a right side view of the same. 
           [0052]      FIG. 3  ( a ) is a partially cutaway front view of the rivet body of the blind rivet in  FIG. 1 , and  FIG. 3  ( b ) is a right side view of the same. 
           [0053]      FIG. 4  is a front view of the mandrel of the blind rivet in  FIG. 1 . 
           [0054]      FIG. 5  ( a ) is an enlarged view of section A of the mandrel in  FIG. 4 , and  FIG. 5  ( b ) is an enlarged view of section B of the same. 
           [0055]      FIG. 6  is a partially cutaway front view of the blind rivet in  FIG. 1  inserted into holes in members to be fastened. 
           [0056]      FIG. 7  is a partially cutaway front view of the step in which the blind rivet in  FIG. 1  is set in the fastening machine used to fasten the members to be fastened. 
           [0057]      FIG. 8  is a partially cutaway front view of the step in which members to be fastened are fastened by the blind rivet in  FIG. 1 . 
           [0058]      FIG. 9  is a partially cutaway front view of the members fastened by the blind rivet in  FIG. 1 . 
           [0059]      FIG. 10  is a right side view of the sleeve when the members have been fastened by the blind rivet in  FIG. 9 . 
           [0060]      FIG. 11  is a right side view of the sleeve when members have been fastened by the blind rivet in a second embodiment of the present invention. 
           [0061]      FIG. 12  is a right side view of the sleeve when members have been fastened by the blind rivet in a third embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0062]    The following is an explanation of the blind rivets in embodiments of the present invention with reference to the figures. 
         [0063]      FIG. 1  is a partially cutaway front view of the blind rivet in a first embodiment of the present invention. This blind rivet includes a sleeve  10 , a rivet body  20 , and a mandrel  30 . The through-hole in the rivet body  20  is aligned with the through-hole in the sleeve  10 , the stem of the mandrel  30  is inserted into the aligned through-holes, and the head  33  of the mandrel  30  is arranged near the slitted end  24  of the rivet body  20 . 
         [0064]    The following is an explanation of the sleeve  10 , rivet body  20 , and mandrel  30  constituting the blind rivet with reference to  FIG. 2  through  FIG. 4 . 
         [0065]      FIG. 2  ( a ) is a partially cutaway front view of the sleeve  10 , which is a component of the blind rivet in this embodiment of the present invention, and  FIG. 2  ( b ) is a right side view of the same. The sleeve  10  includes a cylindrical barrel  11 , and a flange  12  formed at one end of the barrel  11  and having a larger diameter than the barrel  11 . The cross-sectional outer shape of the barrel  11  is a hexagonal shape, and the end with the barrel  11  is the barrel-side end  14 . The outer shape of the flange  12  is a round shape, and an end with the flange  12  is the flange-side end  15 . The outer diameter of the flange can have a hexagonal shape. 
         [0066]    A through-hole (bore)  13  with a round cross-section extends between the barrel-side end  14  and the flange-side end  15  of the sleeve  10 . The inner diameter  13   d  of the through-hole  13  is large enough to allow insertion of the stem  31  of the mandrel  30 , but is smaller than the outer diameter  33   d  of the head  33  of the mandrel  30 . 
         [0067]    The sleeve  10  is made out of a softer material than the mandrel  30  such as aluminum or an aluminum alloy. Alternatively, it can be made out of the same material as the mandrel  30  such as steel. 
         [0068]      FIG. 3  ( a ) is a partially cutaway front view of the rivet body  20  of the blind rivet in  FIG. 1 , and  FIG. 3  ( b ) is a right side view of the same. 
         [0069]    The rivet body  20  has an overall round cylindrical shape and includes a round cylindrical base  21  and a barrel  22  continuing from the base  21 . The end of the base  21  in the axial direction is the base end  26 , and the end of the barrel  22  is the barrel-side end  24 . Slits  25  are formed in the barrel  22  at equal intervals in the circumferential direction which extend to the barrel-side end  24  in the axial direction. There are four slits in this embodiment. A through-hole (bore)  23  which extends in the axial direction is formed inside the rivet body  20 . The inner diameter  23   d  of the through-hole  23  is substantially equal to the inner diameter  13   d  of the through-hole  13  in the sleeve  10 . The inner diameter is large enough for the stem  31  of the mandrel  30  to be inserted, but is smaller than the outer diameter  33   d  of the head  33  of the mandrel  30  so that the head  33  comes into contact with the barrel-side end  24  and stops. 
         [0070]      FIG. 4  is a front view of the mandrel  30 , which is a component of the blind rivet in this embodiment of the present invention. The mandrel  30  includes an elongated stem  31 , and a head  33  at one end of the stem  31 . The outer diameter  33   d  of the head  33  is larger than the inner diameter  13   d  of the through-hole  13  in the sleeve  10 , and is larger than the inner diameter  23   d  of the through-hole  23  in the rivet body  20 . The outer diameter  33   d  of the head  33  is smaller than the inner diameters  43   d ,  44   d  of the mounting holes  43 ,  44  in the members to be fastened  41 ,  42  so that the head can pass through the mounting holes  43 ,  44 . The portion of the stem  31  continuing from the head  33  is a tapered portion  32  which is inclined so that the outer diameter becomes smaller on the stem  31  side. In this embodiment, the angle α forming the tapered portion is 90 degrees. 
         [0071]    The stem  31  is column-shaped, and can be inserted into the through-hole  13  in the sleeve  10  and into the through-hole  23  in the rivet body  20 . The length of the stem  31  is greater than the total length of the through-hole  13  in the sleeve  10  and the through-hole  23  in the rivet body  20 . The stem  31  of the mandrel  30  is inserted into the through-hole  13  in the sleeve  10  and the through-hole  23  in the rivet body  20 . When the head  33  is adjacent to the barrel-side end  24  of the rivet body  20 , the tip  37  of the stem  31  protrudes from the barrel-side end  14  of the sleeve  10 . 
         [0072]    From the tapered portion  32  continuing after the head  33 , the stem  31  of the mandrel  30  includes a column-shaped portion  34 , an engaging portion  38 , a breakable portion  35 , a gripped portion  36 , and a tip  37 . The column-shaped portion  34  is adjacent to the tapered portion  32 . 
         [0073]    The engaging portion  38  is adjacent to the column-shaped portion  34 .  FIG. 5  ( b ) is an enlarged view of the engagement portion  38  of the mandrel  30  (Section B in  FIG. 4 ). Circumferential grooves  38   g  are formed at a predetermined interval in the engaging portion  38 , forming engagement ridges  38   r  between the grooves. When the blind rivet is fastened by a fastening machine, the barrel  11  of the sleeve  10  is pushed by the nosepiece of the fastening machine from the outer periphery, and its inner diameter becomes smaller. The engagement ridges  38   r  of the engaging portion  38  are pressed into and engage the inner circumference of the through-hole  13  when the barrel portion  11  of sleeve  10  is radially compressed and become secured so the mandrel  30  portion does not fall out of the sleeve  10 . Screw-like threaded grooves can also be formed in the engaging portion  38 . 
         [0074]    The breakable portion  35  is adjacent to the engaging portion  38 .  FIG. 5  ( a ) is an enlarged view of the breakable portion  35  of the mandrel (Section A in  FIG. 4 ). The outer diameter of the breakable portion  35  is smaller than the engaging portion  38  or the gripped portion  36 , so that the stem breaks off at the breakable portion  35 . When the blind rivet is assembled, the breakable portion  35  is received in the through-hole  13  of the sleeve  10 . When the stem  31  of the mandrel  30  is pulled out by the fastening machine and a certain pulling force is exceeded, the stem breaks off at the breakable portion  35 . 
         [0075]    A gripped portion  36  with a diameter greater than that of the breakable portion  35  is adjacent to the breakable portion  35 . Multiple levels of engagement grooves  36   r  are formed in the gripped portion  36  so that the gripping member of the fastening machine does not slip when gripping the gripped portion. The tip  37  is at the end of the stem  31 . 
         [0076]    The mandrel  30  can be made from a material such as steel. 
         [0077]      FIG. 6  is a partially cutaway front view of the blind rivet in  FIG. 1  inserted into mounting holes  43 ,  44  in members to be fastened  41 ,  42 . The left side of  FIG. 6  is the blind side, and the blind rivet mounting operation is performed from the right. 
         [0078]    The members to be fastened  41 ,  42  overlap so that the position of the mounting hole  43  in one member to be fastened  41  is aligned with the position of the mounting hole  44  in the other member to be fastened  42 . 
         [0079]    The blind rivet in  FIG. 1  assembled from the sleeve  10 , the rivet body  20 , and the mandrel  30  is inserted into the mounting holes  43 ,  44  in the members to be fastened  41 ,  42  from the right in  FIG. 6 , and the flange  12  on the sleeve  10  is brought into contact with the surface of the member to be fastened  41  surrounding the mounting hole  43 . 
         [0080]    The following is an explanation with reference to  FIG. 7  through  FIG. 9  of the operation performed to fasten the members to be fastened  41 ,  42  using the blind rivet in this embodiment of the present invention. 
         [0081]      FIG. 7  is a partially cutaway front view of the step in which the blind rivet in  FIG. 6  is set in the fastening machine used to fasten the members to be fastened  41 ,  42 . The nosepiece  50  of the fastening machine has an end face  51  on the blind rivet side, and the central portion has a squeezing hole  52  having a round cross-section. The inner diameter  52   d  of the squeezing hole  52  is slightly smaller than the distance  11   d   1  between the vertices of the hexagonally shaped barrel  11  in the sleeve  10 , and is substantially equal to the distance  11   d   2  between the hexagonal sides of the barrel  11 . An inclined portion (tapered bore)  53  is formed near the end face  51  of the squeezing hole  52 . When the stem  31  of the mandrel  30  is inserted into the squeezing hole  52  of the nosepiece  50 , the barrel-side end  14  of the sleeve  10  makes contact with the inner circumference of the inclined portion  53  of the nosepiece  50  and stops. The inner diameter  52   d  of the squeezing hole  52  can be slightly shorter than the distance  11   d   2  between the hexagonal sides of the barrel  11  in the sleeve  10  if the squeezing load is not increased. 
         [0082]    Next, the gripped portion  36  of the mandrel  30  is gripped by the gripping member  55  and is pulled out (to the right in  FIGS. 6 and 7 ). The tapered portion  32  of the mandrel  30  adjacent to the head  33  makes contact with the barrel-side end  24  of the rivet body  20 . By gripping the gripped portion  36  of the mandrel  30  and pulling out, the tapered portion  32  folds, bends, and opens the slit  25  portions of barrel  22  at the position where the barrel  22  of the rivet body  20  makes contact with the edge of the mounting hole  44  in the member to be fastened  42 . 
         [0083]    The nosepiece  50  moves to the left in  FIG. 7  relative to the sleeve  10 . Thus, the barrel  11  of the sleeve  10  is squeezed and radially compressed around engaging part  38  by the inclined surface  53  and squeezing hole  52  in the nosepiece  50  of the fastening machine. 
         [0084]      FIG. 8  is a partially cutaway front view of the step in which the gripped portion  36  of the mandrel  30  is pulled out, and the members to be fastened  41 ,  42  are fastened by the blind rivet. While the barrel  11  with the flange  10  is being pulled from the outer circumference, the squeezing hole  52  in the nosepiece  50  deforms the six vertices  11   v  of the hexagonally shaped barrel  11  so that the distance  11   d   1  between the vertices becomes smaller and the reduced distance  11   d   1 ′ between the deformed vertices becomes substantially equal to the inner diameter  52   d  of the squeezing hole  52 . The smaller distance  11   d   1 ′ between the vertices is substantially equal to the distance  11   d   2  between the sides of the hexagon. As can be seen in a comparison of the barrels  11  in  FIG. 7  and  FIG. 8 , the outer diameter of the barrel  11  after deformation by the squeezing hole  52  has no hexagonal vertices and is substantially round shaped. 
         [0085]    At this time, by squeezing the outer circumference of the barrel  11 , the diameter of the inner circumference of the through-hole  13  becomes radially compressed and smaller than the inner diameter  13   d  before fastening, and the inner surface of through-hole  13  deforms and engages the engagement ridges  38   r  in the engaging portion  38  of the mandrel  30 . 
         [0086]    When the end face  51  comes into contact with the flange  12  of the sleeve  10 , the nosepiece  50  stops. 
         [0087]    The blind rivet clamps the members to be fastened  41 ,  42  between the opened barrel  22 ′ in the rivet body  20  and the flange  12  in the sleeve  10 . Afterwards, when the mandrel  30  is pulled out strongly, it breaks off at the breakable portion  35 , and the fastened section of the mandrel from the breakable portion  35  to the head  33  remains inside rivet body  20  and sleeve  10 . Because the inner surface of compressed through-hole  13  in the sleeve  10  engages the engaging portion  38  of the mandrel  30 , the section of the mandrel  30  remaining in the blind rivet does not fall out of the blind rivet. Because the remaining section of the mandrel  30  is securely fixed to the barrel  11  in the sleeve  10 , high fastening strength can be obtained. Afterwards, the nosepiece  50  is withdrawn to the right in  FIG. 8 , and the fastening is completed. 
         [0088]      FIG. 9  is a front view of the members to be fastened  41  and  42  after fastening by the blind rivet in  FIG. 8 . In this figure, a portion of the rivet is cut away. The members to be fastened  41 ,  42  are fastened between the opened barrel  22 ′ of the rivet body  20  and the flange  12  of the sleeve  10 . 
         [0089]      FIG. 10  is a right side view of the sleeve  10  when the members to be fastened have been fastened by the blind rivet in  FIG. 9 . In  FIG. 10 , the rivet body  20  and the mandrel  30  are not shown. In the barrel  11  of the sleeve  10 , the hexagonal vertices are deformed by the hole  52  in the nosepiece  50 , and the barrel becomes substantially round shaped. Because the outlet to the squeezing hole  52  in the nosepiece  50  has an inclined portion  53 , the portion of the barrel  11  adjacent to the flange  12  has uncrushed vertices and retains its hexagonal shape. 
         [0090]      FIG. 11  is a right side view of the sleeve  10 ′ when members to be fastened  41 ,  42  have been fastened by the blind rivet in a second embodiment of the present invention. In  FIG. 11 , the rivet body  20  and the mandrel  30  are not shown. In the first embodiment, the cross-section of the barrel  11  in the sleeve  10  is hexagonally shaped, and barrel  11  is squeezed by a squeezing hole with a round-shaped cross-section. In the second embodiment, the cross-section of the barrel  11 ′ in the sleeve  10 ′ is round shaped before the fastening operation, and the cross-section of the squeezing hole  52 ′ in the nosepiece  50 ′ of the fastening machine is hexagonally shaped. A barrel  11 ′ with a round-shaped cross-section is squeezed by a squeezing hole  52 ′ with a hexagonally shaped cross-section to produce a barrel  11 ′ with a round-shaped cross-section. The distance  11   d   1 ′ between opposing vertices of the hexagonal shape after squeezing is nearly equal to the diameter of the barrel  11 ′ before squeezing, and the distance  11   d   2 ′ between the opposing sides of the hexagonal shape is smaller than the diameter of the barrel  11 ′ before squeezing. The opposing sides of the hexagonal shape after squeezing have been squeezed, but the vertices of the hexagon shape have hardly been squeezed at all. This reduces the sleeve squeezing load. 
         [0091]      FIG. 12  is a right side view of the sleeve  10 ″ when members to be fastened  41 ,  42  have been fastened by the blind rivet in a third embodiment of the present invention. In  FIG. 12 , the rivet body  20  and the mandrel  30  are not shown. In the third embodiment, the cross-section of the barrel  11 ″ in the sleeve  10 ″ before fastening is round shaped just as in the second embodiment. In the third embodiment, the cross-section of the squeezing hole  52 ″ in the nosepiece  50 ′ has six protrusions formed circumferentially at equal intervals. When a barrel  11 ″ with a round-shaped cross-section is squeezed by a squeezing hole  52 ″ with this shape, recesses  18 ″ are formed at six locations in the cross-section of the barrel  11 ″. The diameter  11   d   1 ″ outside of the recesses  18 ″ is substantially equal to the diameter of the sleeve  11 ′ before squeezing. Because the portions outside of the recesses  18 ″ are hardly squeezed at all, the sleeve squeezing load is reduced. 
         [0092]    In the first through third embodiments of the present invention, a blind rivet can be obtained in which the sleeve squeezing load is not increased, and in which the shear strength between the sleeve and the mandrel is high. 
         [0093]    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.