Abstract:
A method and apparatus for riveting metal members, and particularly, metal sheets is disclosed. The apparatus includes a rivet assembly for driving rivets into stacked metal sheets and a die assembly for assisting in supporting the sheets during driving of the rivets and for assisting in securing the rivets to the sheets. The rivet assembly, the die assembly or both in combination provide energy to at least a portion of the metal sheets prior to riveting. In turn, the energy elevates the temperature of the portion of the sheets such that the rivets can be more effectively driven into the sheets and such that the sheets are fastened to each other with greater ease and consistency.

Description:
TECHNICAL FIELD  
         [0001]    The present invention relates to a method and apparatus for riveting metal members together for assembling automotive vehicle structures.  
         BACKGROUND OF THE INVENTION  
         [0002]    It is known that the manufacture of automotive vehicles often requires that metal members be attached to each other to form automotive vehicle structures. Pierce riveting is one potential method of attaching such members, particularly, metal sheets. Pierce riveting typically requires a sharpened end portion of a rivet to pierce through a first of two stacked metal sheets, and through at least a portion of a second of the stacked sheets. During such piercing, the sharpened end portion of the rivet is typically deformed or bent to secure the rivet to the sheets. For conventional pierce riveting processes, however, large amounts of force may be required to pierce through the sheets. Moreover, for higher strength sheets, the rivets may deform prior to proper piercing of the sheets or the sheets may be undesirably cracked during the riveting process. Thus, there is a need for improved pierce riveting techniques, apparatuses or both, for achieving high integrity attachment of metal members, particularly, sheets formed of refractory or high strength to weight metals such as those based on aluminum, magnesium, iron, high strength steel or the like.  
         SUMMARY OF THE INVENTION  
         [0003]    The present invention meets these needs by providing an improved method of riveting a first metal member to a second metal member, with particular utility in the formation of components for an automotive vehicle. The method involves providing a piercing rivet having a central axis, a generally disk-shaped head portion and an annular portion extending outwardly from a bottom surface of the head portion, the annular portion including a sharpened piercing edge. For riveting, a first metal member is stacked on a second metal member, wherein each of the members has a first side and a second side, and at least a portion of the second side of the first member is in overlapping contact with at least a portion of the first side of the second member for forming an overlapped region. The first and second metal members are placed between a rivet assembly and a die assembly, the rivet assembly including a punch surrounded by a first electrode for contacting the first member, the die assembly including a die surrounded by a second electrode for contacting the second member, the die having a cylindrical cavity with a protrusion extending into the cavity, the first and second electrodes each connected to an electrical energy source. Thereafter, an electrical current is induced with the electrical energy source, the current flowing between the first and second electrodes and through the first and second metal members for heating the overlapped region of the first member and the second member to a more ductile condition. The rivet is driven through the first metal member and partially through the second metal member in the overlapped region such that the annular portion of the rivet is deformed radially away from the central axis to interferingly secure the rivet to the members thereby attaching the members to each other.  
           [0004]    The present invention also provides an apparatus for riveting a first metal sheet to a second metal sheet. The apparatus includes a rivet assembly for driving a rivet through the first metal sheet and partially through the second metal sheets while the first sheet is stacked upon the second sheet. The rivet assembly includes a cylindrical punch moveable between at least a first position and a second position for driving the rivet through the first sheet and partially through the second sheet. The rivet assembly also includes a generally cylindrical binder clamp that is cylindrical about a centrally located axis, the binder clamp having a cylindrical hole that is coaxial with the axis and extends down the center of the binder clamp for receiving the punch. A cylindrical first electrode surrounds at least a portion of the binder clamp, the first electrode for contacting and supplying electricity to the metal sheets to heat the sheets prior to driving the rivet into the sheets. An insulator is disposed between the first electrode and the binder clamp for electrically separating the first electrode from the binder clamp. The apparatus also includes a die assembly for at least partially supporting the first and second sheets as the rivet assembly drives the rivet into the sheets, the die assembly. The dies assembly includes a central cylindrical die having a central cylindrical cavity defined by a circular bottom surface and an annular surface, the circular bottom surface defining a centrally located protrusion extending into the cavity. The die assembly also includes a cup shaped second electrode for conducting electricity with the first electrode, the second electrode having a generally cylindrical cavity for receiving the die. A cup shaped insulator electrically separates the second electrode from the die, the insulator receiving the die in a cavity within the insulator, the insulator being receivable within the cavity of the electrode. The apparatus also include an energy source for inducing an electrical current across the electrodes.  
           [0005]    The present invention thus provides an improved riveting apparatus and riveting technique for providing securing piercing rivets in stacked sheets thereby more securely fastening the sheets together. The ability to locally control the temperature of the members being joined makes this invention particularly advantageous for the joining of high strength to weight metals or materials with ordinarily low ductility. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]    These and other aspects and advantages of the present invention will become apparent upon reading the following detailed description in combination with the accompanying drawings, in which:  
         [0007]    [0007]FIG. 1 is a sectional view of a riveting apparatus prior to riveting a pair of stacked metal sheets to each other;  
         [0008]    [0008]FIG. 2 is a sectional view of the riveting apparatus of FIG. 1 during riveting of the pair of stacked metal sheets to each other;  
         [0009]    [0009]FIG. 3 is a sectional view of the riveting apparatus of FIG. 1 further along in the riveting of the pair of stacked metal sheets to each other;  
         [0010]    [0010]FIG. 4 illustrates the riveting apparatus of FIGS. 1, 2 and  3  with a robot arm and an energy source; and  
         [0011]    FIGS.  5 ( a ) and  5 ( b ) illustrate perspective views of a preferred rivet. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0012]    Referring to FIGS.  1 - 4 , a first metal member (depicted as a sheet  10 ) is riveted to a second metal member (depicted as a sheet  12 ) with a piercing rivet  14  that is driven into the sheets  10 ,  12  by a riveting apparatus  16 . The riveting apparatus  16  includes a rivet driving assembly  18  for driving the rivet  14  through the first sheet  10  and into the second sheet  12  and a die assembly  22  for supporting the metal sheets  10 ,  12  and for assisting in securing the rivet  14  to the sheets  10 ,  12 .  
         [0013]    The rivet assembly  18  includes a clamp  24  (e.g., a generally elongated metal binder) having an opening  26  extending down a length of the binder clamp  24 . A punch  28  (e.g., an elongated cylindrical steel punch) of the assembly  18  is received in the opening  26  and the punch  28  is moveable along a length of the opening  26  between at least a first position, as shown in FIG. 1, and a second position, as shown in FIG. 3. The punch  28  may be moved hydraulically, mechanically, electrically, pneumatically or otherwise.  
         [0014]    An electrode  34  (e.g., a copper electrode) of the rivet assembly  18  is generally annular and surrounds at least a portion of the binder clamp  24  and the hole  26  through which the punch  28  moves. A generally annular insulator  36  of the rivet assembly  18  is disposed between the binder clamp  24  and the electrode  34  to electrically separate the electrode  34  from the binder clamp  24  and the punch  28 . The insulator  36  may be formed of an insulative material such as a plastic, polymer, ceramic, or the like. In one preferred embodiment, the insulator  36  is a laminate formed with a fabric or paper molded with a synthetic resin.  
         [0015]    In FIGS.  1 - 3 , the punch  28 , the opening  26 , the insulator  36  and the electrode  34  are generally cylindrical, coaxial or both about a central axis  38  extending centrally along their lengths. Preferably, a housing (not shown) can be used to fasten the electrode  34 , the insulator  36 , and the binder clamp  24  together. Alternatively, other conventional fasteners or fastening techniques may be used.  
         [0016]    The die assembly  22  includes a generally cylindrical die  44  having a central cylindrical opening or cavity  46  defined by a bottom circular surface  48  and a peripheral annular wall surface  50 , which may be integrated into a single continuous surface. Preferably, the die  44  includes a protrusion  52  that extends into the cavity from the center of the circular surface  48 . Alternatively, the die  44  may be formed in a variety of sizes or with a variety of cavity shapes depending upon the rivet  14  to be driven into the sheets  10 ,  12 , the properties of the sheets  10 ,  12 , the thickness of the sheets or a combination thereof.  
         [0017]    The die assembly  22  further includes a generally cup shaped electrode  60  with an annular portion  62  and a base portion  64  that cooperatively define a cavity for receiving the die  44 . Preferably, the die assembly  22  also includes a generally cup-shaped insulator  68  with an annular portion  70  and a base portion  74  defining a cavity wherein the insulator  68  is formed of a material similar to the material of the insulator  36  of the rivet assembly  18 . As shown, the insulator  68  fits within the cavity (preferably flush) of the electrode  60  and the die  44  is received in the cavity of the insulator  68  for electrically separating the die  44  from the electrode  60 . By changing the dimensions of the insulator  68 , the die  44  or both, a variety of different dies having a variety of different sized or shaped cavities may be interchanged within the cavity of the electrode  60  if desired. The components of the rivet assembly  18  and the die assembly  22  may be fastened together as desired by conventional fasteners, adhesives, a housing or the like.  
         [0018]    The rivet assembly  18 , the die assembly  22  or both may be mounted to various apparatus for moving the rivet assembly  18  or the die assembly  22  relative to each other, such as robots, C-frames and hard tooling such as a die set, or the like. In the exemplary embodiment shown in FIG. 4, the rivet assembly  18  is attached to a robot arm  84  that can move the rivet assembly  18  as desired. The die assembly  22  is stably positioned adjacent the robot arm  84 .  
         [0019]    An energy source  86  such as a transformer or other energy source is electrically coupled to the electrodes  34 ,  60  of the rivet assembly  18  and the die assembly  22  for providing electricity (e.g., current or voltage) to those electrodes  34 ,  60 .  
         [0020]    Now with reference to FIGS.  5 ( a ) and  5 ( b ), the piercing rivet  14  is substantially symmetrical about a central axis  88  and includes a head portion  90  and a body portion  92  with a sharpened edge portion  94 , that is adapted to both pierce a material and deform during piercing for forming an interlock. As shown, in one example, the head portion  90  is generally disk-shaped with a substantially flat top surface  96  and a bottom surface  98 . The body portion  92  is generally annular and extends outwardly away from the bottom surface  98  of the head portion  90 . Preferably, the head portion  90  extends radially outwardly away from the central axis  88  further than the body portion  92 .  
         [0021]    The rivet  14  may be formed of a variety of high strength to weight metals such as aluminum or magnesium alloys. Preferably, however, the rivet  14  is formed of a refractory metal such as high strength steel. Optionally, the rivet  14  may be coated with a suitable protective coating, such as with an anti-corrosion agent, or may be selectively hardened at certain portion for achieving a hardness gradient in the rivet.  
         [0022]    In alternative embodiments, various other piercing rivets may be used. As an example, a rivet having an adhesive may be used such as the rivets disclosed in commonly owned copending application titled “A Rivet and Method for Riveting Metal Sheets Therewith”, Attorney Docket No. GP-301717, filed on the same date as the present application and fully incorporated herein by reference for all purposes.  
         [0023]    Referring additionally to FIGS.  1 - 3 , the piercing rivet  14  is positioned within the rivet assembly  18  for allowing the punch  28  to drive the rivet  14  into the sheets  10 ,  12 . As shown, the top surface  96  of the rivet  14  is contacted substantially flush against the punch  28 . The rivet  14  may be temporarily secured against the punch  28 , such as by magnetic forces, with a securing member (not shown), or otherwise.  
         [0024]    The first metal sheet  10  and second metal sheet  12  each include a first side  110  and a second side  112 . The first sheet  10  is stacked upon the second sheet  12  such that at least a portion of the second side  112  of the first sheet  10  is in substantially continuous contact with at least a portion of the first side  110  of the second sheet  12  to form an overlapping portion or region for receiving the rivet  12 . The sheets  10 ,  12  may be formed of several metals. Preferably, the sheets  10 ,  12  are formed of a high strength or refractory metal such as an aluminum alloy, a magnesium alloy, a high strength steel or the like with thicknesses ranging between 0.6 mm and 3.0 mm, although thicker of thinner sheets may also be used.  
         [0025]    The stacked sheets  10 ,  12  are placed between the rivet assembly  18  and the die assembly  22  of the riveting apparatus  16 . Preferably, the sheets  10 ,  12  are placed upon the die assembly  22  such that the second side  112  of the second sheet  12  contacts the die assembly  22 . Thereafter, the rivet assembly  18  is contacted with first side  110  of the first sheet  10  (e.g., using the robot arm  84  or another apparatus) to clamp the sheets  10 ,  12  between the rivet assembly  18  and the die assembly  22 .  
         [0026]    When the sheets  10 ,  12  are clamped between the assemblies  18 ,  22 , the electrode  34  of the rivet assembly  18  is in contact with the first side  110  of the first sheet  10  and the electrode  60  of the die assembly  22  is in contact with the second side  112  of the second sheet  12 . The energy source  86  induces an electric current that flows between the two electrodes  34 ,  60  through each of the sheets  10 ,  12 . Advantageously, the current may be applied for as short as about {fraction (1/30)} of a second using about 20 kiloamps of electricity for aluminum, however, different levels of energy may be used for different amounts of time depending on the application. The current provides energy to the sheets  10 ,  12  thereby elevating the temperature of (i.e., resistive heating) at least a portion of each of the sheets  10 ,  12  (i.e., the overlapped region) to a desired temperature. Preferably, the heated portion is the overlapping region of the sheets  10 ,  12  in which the rivet  14  is to be driven.  
         [0027]    Thereafter, the punch  28  is moved from its first position shown in FIG. 1 to its second position as shown in FIG. 3 to drive the rivet  14  at least partially through the overlapping region of the sheets  10 ,  12 . As shown, the sharpened piercing edge  94  of the rivet  14  pierces entirely through the first sheet  10  and partially through the second sheet  12 .  
         [0028]    During driving of the rivet  14 , the rivet  14  urges a portion  120  of the first and second sheets  10 ,  12  into contact with the protrusion  52  of the die  44  thereby pinching the portion  120  between the rivet  14  and the protrusion  52 . In turn, the protrusion  52  places a force on the portion  120  of the sheets  10 ,  12  and the force is transmitted to the annular portion  92  of the rivet  14 . This force at least partially bends or deforms the annular portion  92 , starting with the sharpened edge  94 , radially away from the central axis  88  of rivet  14  to interferingly secure the rivet  14  to the sheets  10 ,  12  thereby attaching the sheets  10 ,  12  to each other. Preferably, the rivet  14  is driven through the first sheet  10  and into the second sheet  12  until the top surface  96  of the head portion  90  is substantially flush with the first surface  110  of the first sheet  10 .  
         [0029]    Advantageously, heating of the sheets  10 ,  12  increases the ductility of the overlapping portion of the sheets  10 ,  12 . Thus, the rivet  14  can be driven through the first sheet  10 , and partially through the second sheet  12  relatively easily and preferably without any undesired deformation of the rivet  14  or undesired cracking of the sheets  10 ,  12 . In preferred embodiments, the ductility of the overlapping region can be doubled, tripled or even quintupled.  
         [0030]    Although, the assemblies shown use electrodes coupled to an electrical energy source, it is contemplated that other energy sources suitable for locally heating the sheets, such as lasers (e.g., carbon dioxide or Nd:Yag lasers) may be attached to or form part of the rivet assembly  18 , the die assembly  22  or both. It is further contemplated that the electrodes  34 ,  60  may not surround the punch  28  or die  44 , but may be otherwise associated with or adjacent the punch  28  or die  44  or that the electrodes  34 ,  60  may be integrally formed as the punch  28  or die  44 .  
         [0031]    The method and apparatus described above may be used for attaching several different automotive components that have sheet metal or sheet metal portions. Examples include peel joints, lap joints, various vehicle panels such as door panels, decklids, hoods, sunroof applications or the like. Furthermore, the overlapped regions of the sheets may be continuously bonded or intermittently bonded over some or all of its area.  
         [0032]    Advantageously, riveting according to the present invention is inexpensive, can improve the consistency of rivet formation, and can extend the life of tooling used to drive and deform the rivets.  
         [0033]    It should be understood that the invention is not limited to the exact embodiment or construction which has been illustrated and described but that various changes may be made without departing from the spirit and the scope of the invention.