Abstract:
A method of joining parts together with a flow drill screw or with a clinch joint. A first part formed of metal or a composite material is joined to a second part that includes a fiber-filled layer and a resin matrix layer. The flow drill screw extends through the first part and the second part into the second part. The resin matrix layer prevents fibers from the fiber filled layer from being forced through the back of the second panel. A clinch joint may be formed into the first part and the second part but does not penetrate completely through the resin matrix layer. When the clinch joint is formed, the resin matrix layer inhibits the fiber filled layer from pushing through the second layer of the second panel.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation-in-part of U.S. application Ser. No. 13/448,464 filed Apr. 14, 2012, the disclosure of which is incorporated in its entirety by reference herein. 
     
    
     TECHNICAL FIELD 
       [0002]    This disclosure relates to riveting, clinching or flow drill screwing parts or panels to a composite part formed from a layered resin and a fibrous filler material. 
       BACKGROUND 
       [0003]    As the automotive industry continues to focus on reducing the weight of vehicles to meet customer expectations on fuel economy and CAFE requirements, interest in alternative materials including carbon fiber composite applications has increased. In body-in-white structures, joining methods have traditionally relied on resistance-spot welding (e.g., in steel structures). In the case of aluminum intensive vehicles and other mixed metal joining applications, self-piercing rivet (SPR) technology prevails. One advantage of SPR technology is that it is a high production volume assembly process. Further, it is compatible with adhesive, where both methods can be used in conjunction. The challenge often faced with SPR however, is that the substrate material must be ductile enough to form a “button”, i.e., protrusion, which is the result of creating the joint and the necessary deformation to provide mechanical interlock. When composite parts do not have sufficient ductility to form a button on the obverse side, fibers may be exposed through cracks in this surface. Surface cracking and fiber displacement are undesirable, as they may reduce the durability of the joint and result in premature failure. 
         [0004]    In addition to SPRs, other joining technologies are available for joining parts to fiber reinforced composite parts. Flow drill screws may be driven through a part, either a first metal or composite part and into the fiber reinforced composite part. As the flow drill screw is driven through the part, an extruded bushing is formed on the exit side of the second composite part and can expose fibers. The exposed fibers can reduce the robustness of the joint. Clinch joints may be used to join parts to a fiber reinforced composite part but the clinching operation may result in fibers being pushed through the back side of the composite part and the resin may fracture as the fibers are pushed through the back side. 
         [0005]    Composite materials, such as carbon fiber, glass fiber or natural fiber composites, can be limited in application due to challenges relating to joining parts together. Frequently, these composites have limited ductility and are not well adapted to large displacements and deformation required to produce a button or bushing on the back side of the composite part. While adhesive has been used extensively in the past to join composite parts together, adhesive joining is a lower volume production method when used in isolation and is susceptible to displacement (i.e., movement between the parts to be joined) until the adhesive is cured. Blind rivets may be used to fasten parts to a composite component but it is necessary to first drill or pre-form a hole through the parts to insert the blind rivet. Assembly operations for drilling holes, aligning the holes, inserting the blind rivet and affixing the rivet add to the cost of assembly and the cost of tooling. A joining solution is needed that meets high volume production requirements and enables joining in a low ductility material. 
         [0006]    This disclosure is directed to overcoming the above problems and other problems associated with the use of composite parts in applications where other parts are joined to a composite part. 
       SUMMARY 
       [0007]    One method of joining a part to a composite part is to drive a flow drill screw (hereinafter “FDS”) through the part and into a composite part with a flow drill screw driver. The FDS approach may be performed when access to the assembly of parts is provided on only one side of the assembly. 
         [0008]    An alternative method of joining a part to a composite part is to form a clinch joint. Clinch joints are formed by a set of tools that include a clinch punch and a back-up die. Clinch joints may be used only if access is provided to two sides of the assembly. 
         [0009]    According to one aspect of this disclosure, a method of joining a part to a composite material part is disclosed. According to the method, a first part is selected and a second part is selected that includes a first layer of a resin matrix that is reinforced with a filler material and a second layer of a resin matrix that does not include the filler material on at least part of one side of the second part. The first and second parts are secured together with a FDS or a clinch joint formed by a punch tool and a back-up. The first layer of the second part that includes resin and reinforcement fibers is contained by the second layer of the second part that includes resin but no added reinforcement fibers. The second layer prevents the reinforcement fibers in the first layer from penetrating the second layer. 
         [0010]    According to other aspects of the disclosure, the method further comprises forming the second part in a compression molding die by placing the filler material including a fiber reinforcement and a resin matrix into the compression molding die. The method may further comprise depositing the resin matrix into the compression molding die in two steps. In one step, the resin is deposited in the compression molding die to encase the filler material in the first layer. In another step, the resin is deposited in the compression molding die in the second layer. In another approach, the method may further comprise providing a textured surface on a predetermined portion of the compression molding die where the second layer is formed. The textured surface inhibits the filler material from becoming part of the second layer. Following either approach, the second layer may be more than 3 microns thick. 
         [0011]    According to another aspect of the disclosure, an assembly may be provided that includes a first part and a second part formed of a composite material that is joined together with a FDS or a clinch joint. The FDS extends through the first part and the second part. The clinch joint does not include a fastener but joins the parts by driving a portion of the first part into the second part, creating a mechanical interlock between the two parts. The mechanical interlock is formed by the punch and back-up die geometry. The second part has a first layer of a resin matrix that is reinforced with filler and a second layer of a resin matrix that does not include the filler on at least part of one side of the second part. 
         [0012]    The filler material is not exposed on a side of the second part that is opposite the first part after insertion of the FDS or formation of the clinch joint. The filler may be a fiber reinforcement that is randomly deposited or aligned in the resin matrix. The second layer of the second part may be provided in localized areas on the first layer where the FDS or the clinch joint is formed. 
         [0013]    These and other aspects of the disclosure will be better understood in view of the attached drawings and the following detailed description of the disclosed embodiments. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]      FIGS. 1A-1D  are a series of diagrammatic views illustrating the manufacturing process for inserting a self-piercing rivet with a self-piercing rivet tool into two panels beginning with the initial set up through completion of the riveting process; 
           [0015]      FIG. 2  is a diagrammatic view showing one rivet in position to be inserted into a metal part and a composite part; 
           [0016]      FIG. 3  is a fragmentary cross-sectional view showing a self-piercing rivet inserted through a first panel and into a second composite material panel having added resin matrix; 
           [0017]      FIG. 4  is a perspective view partially in cross section showing the obverse side of a pair of panels joined with self-piercing rivets in areas having additional resin matrix material; 
           [0018]      FIG. 5  is a diagrammatic view showing FDS in position to be inserted into a metal part and a composite part; 
           [0019]      FIG. 6  is a fragmentary cross-sectional view showing a FDS inserted through a first panel and into a second composite material panel having added resin matrix; 
           [0020]      FIG. 7  is a diagrammatic view showing a clinch joint forming tool in position prior to joining a metal part and a composite part; and 
           [0021]      FIG. 8  is a fragmentary cross-sectional view showing a clinch joint made through a first panel and into a second composite material panel having added resin matrix. 
       
    
    
     DETAILED DESCRIPTION 
       [0022]    A detailed description of the illustrated embodiments of the present invention is provided below. The disclosed embodiments are examples of the invention that may be embodied in various and alternative forms. The figures are not necessarily to scale. Some features may be exaggerated or minimized to show details of particular components. The specific structural and functional details disclosed in this application are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art how to practice the invention. 
         [0023]    Referring to  FIGS. 1A-1D , a self-piercing rivet tool is generally identified by reference numeral  10 . The self-piercing rivet tool  10  is used to insert a self-piercing rivet  12  (hereinafter “SPR”) into a first panel or part  16  and a second panel or part  18 . The first panel may be a steel, aluminum or other metal panel or may alternatively be a composite part, such as, an SMC composite panel including a fiber reinforced resin. The second panel or part  18  is a composite panel that is preferably provided with additional matrix material on the lower side of the panel  18 . The structure of the second panel  18 , or part, is described more specifically with reference to  FIGS. 2-4 . 
         [0024]    The first and second panels  16  and  18  are shown in  FIG. 1A  to be retained between a blank holder  20  and a die  22  that engage opposite sides of the stack of panels. Additional panels may be provided of various compositions. This disclosure is intended to include stacks of three, four or more panels of various thicknesses and compositions. The die  22  backs up the panels  16  and  18  as the punch  24  drives the rivet. 
         [0025]    Referring to  FIG. 1B , the first part of the riveting process is illustrated wherein an indentation  26  is formed in the panels  16  and  18  that are driven into a pip  28  formed in the die  22 . While a pip  28  is shown in the illustrated embodiment, a die  22  having a flat surface could also be employed in the disclosed process. The rivet  12  includes a hollow tubular portion  30  that is driven into the first and second panels  16  and  18  to join the panels together. 
         [0026]    Referring to  FIG. 1C , the rivet  12  is shown fully inserted into the first and second panels  16  and  18  with the punch  24  driving the rivet  12  until it is flush with the first panel  16 . The blank holder  20  continues to apply pressure to the first panel  16  while the tubular portion  30  of the rivet  12  is driven through the first panel  16  and into the second or composite panel  18 . A slug  32  is separated from the first panel  16  and retained within the hollow tubular portion  30  of the rivet  12  when the self-piercing rivet is inserted into the panels  16  and  18 . The hollow tubular portion  30  is shown in an expanded condition after it is driven over the pip  28  that is covered by the second panel  18 . 
         [0027]    Referring to  FIG. 1D , the blank holder  20  and punch  24  are shown being lifted off the first panel  16  after having inserted the rivet  12  through the first panel  16  and into the second panel  18 . A button  34  is formed by the rivet  12 . The button  34  is formed by the rivet  12  as it is inserted through the first panel  16  and partially through the second panel  18 . The rivet  12  and joined panels  16  and  18  are shown in position to be removed from the die  22 . 
         [0028]    Referring to  FIG. 2 , a single rivet  12  is shown above two panels  16  and  18  that are ready to be joined by insertion of the rivet  12 . A fiber filled layer  36  includes randomly distributed fibers and filler. The fiber filled layer  36  may include a carbon fiber, glass fiber, mica, or natural fiber filler material that may be arranged as a random composite or loose filler material. The fiber filled layer  36  is encased in a resin matrix. The resin matrix may be a thermoplastic or thermoset resin. A matrix layer  38  is provided adjacent the fiber filled layer  36  on the obverse side  40  of the second panel  18 . The term “obverse side” as used herein is intended to identify the side of the stack of panels that is opposite the side through which the rivet  12  is inserted. The matrix layer  38  is preferably three microns or more in thickness to provide a flexible non-brittle layer into which the tubular portion  30  of the rivet  12  may extend. A top layer  44  may be provided above the fiber filled layer  36  that may be approximately 1 to 2 microns thick. As illustrated, the thickness of the layers  38  and  44  are exaggerated to be visible in the drawings. The top layer  44  is provided to assure a smooth surface on the panel, as required. 
         [0029]    A textured surface  46  may be provided on the obverse side  40  of the second panel  18 . The textured surface  46  may serve to prevent fiber filler material from moving too close to the obverse side  40  in the molding or panel forming process. The textured surface  46  permits additional resin accumulating to 3 microns or more to form a relatively pure matrix mix adjacent the obverse side  40 . The textured surface  46  may be provided over the entire surface of the second panel  18  or may be provided in localized areas. 
         [0030]    Referring to  FIG. 3 , a rivet  12  is shown inserted through a first panel  16  and into the second panel generally indicated by reference numeral  18 . The second panel  18  is preferably a composite material, such as an SMC, injection molded, compression molded, or Vartum liquid vacuum assist manufactured panel. As the rivet  12  is inserted, a slug  32  is severed from the first panel  16 . The slug  32  locks the tubular portion  30  of the rivet  12  into an expanded condition and interlocks with the fiber filled layer  36  of the second panel  18 . The matrix layer  38  facilitates forming a smooth button  34  on the obverse side  40  of the second panel  18 . Fibers in the fiber filled layer  36  may be displaced upon insertion of the tubular portion  30  of the rivet  12  but any displaced fibers are held within the panel by the matrix layer  38 . 
         [0031]    Referring to  FIG. 4 , a first panel  16  is shown below a second panel  18 . The first and second panels are inverted in comparison to the other views presented above to illustrate the two areas having added matrix material in localized areas. An edge area  52  is shown in which additional resin is provided to permit joining the two panels together with rivets  12  (shown in  FIGS. 1-3 ). The rivets  12  upon insertion form buttons  34  on the edge area  52 . In a similar manner, a single rivet area  54  is shown that is partially or wholly circular and may be provided in a particular localized area to receive a single rivet  12  (shown in  FIGS. 1-3 ). By providing only localized areas  52 ,  54  of added matrix, the weight of the second panel  18  may be minimized while providing a matrix layer  38  in which well-formed and smooth buttons  34  may be formed on the obverse side of the second panel  18 . 
         [0032]    Referring to  FIG. 5 , a FDS  62  is shown above two panels  16  and  18  that are ready to be joined by insertion of the FDS  62 . The fiber filled layer  36  includes randomly distributed fibers and filler. The fiber filled layer  36  may include fiber filler material as previously described that may be arranged as a random composite or loose filler material. The fiber filler is encased in a resin matrix that may be a thermoplastic or thermoset resin. The matrix layer  38  is provided adjacent the fiber filled layer  36  on the obverse side  40  of the second panel  18 . The matrix layer  38  provides a flexible layer through which the FDS  62  may extend. The thickness of the layers  38  and  44  are exaggerated to be visible in the drawings. The top layer  44  is provided to assure a smooth surface on the panel, as required. 
         [0033]    Referring to  FIG. 6 , a FDS  62  is shown inserted through a first panel  16  and through the second panel  18 . As the FDS  62  is inserted, the tip of the screw  64  frictionally heats the panels  16  and  18  until the threaded shaft  66  of the FDS  62  is received by the panels  16  and  18 . A bushing  68  is formed on the matrix layer  38  of the second panel  18  and internal threads  70  are formed by the self-tapping action of the threads of the FDS  62 . The bushing  68  receives the FDS  62  and interlocks with the fiber filled layer  36  of the second panel  18 . The matrix layer  38  provides the bushing  64  with a smooth surface on the obverse side  40  of the second panel  18 . Fibers in the fiber filled layer  36  may be displaced upon insertion of the FDS  62  but any displaced fibers are held within the panel by the matrix layer  38 . 
         [0034]    A clearance hole  71  is provided in the first panel  16  that may be provided if the first panel is relatively thick or has substantial yield strength properties. However, it should be understood that depending on the thickness and material properties of the top layer  16  no clearance hole  71  may be necessary. 
         [0035]    Referring to  FIG. 7 , a clinch joining tool  72  is illustrated that includes a punch  74  on one side of the first panel  16  and the second panel  18 . A die  76  is positioned on the obverse side  40  of the second panel  18 . 
         [0036]    Referring to  FIG. 8 , the panels  16  and  18  are shown to be joined together with a clinch joint  78 . The punch  74  (shown in  FIG. 7 ) is driven into the first panel  16  to displace a circular portion  80  of the first panel  16  into a corresponding displaced portion  82  of the second panel  18 . The reaction force applied by the die button  76  creates an undercut area  84  that is formed on the second panel  18  that locks the two panels  16  and  18  together. 
         [0037]    The matrix layer  38  restrains the reinforcement fibers in the fiber filled layer  36  from being forced through the obverse side  40  of the second panel  18 . As a result, the displaced portion  82  of the second panel  18  remains smooth even after the clinch joint  78  is formed. 
         [0038]    While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention. Additionally, the features of various implementing embodiments may be combined to form further embodiments of the invention.