Abstract:
A composite part including a resin matrix and fibers reinforcing the resin matrix in a first portion of the matrix. A second portion of the resin matrix is substantially devoid of fibers. The fibers may be in the form of a woven mat that defines an opening. Alternatively, the fibers may be loose fibers that are deposited in a mold that includes predetermined areas that are shielded from the deposit of the loose fibers. A method of making the composite part is disclosed in which a woven mat having an opening is filled with resin. Another method is also disclosed in which loose fibers are shielded from being deposited in a portion of the mold that is subsequently filled with resin.

Description:
TECHNICAL FIELD 
     This disclosure relates to reinforced composite parts and methods of making reinforced composite part assemblies with improved fastening performance. 
     BACKGROUND 
     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. 
     Other joining techniques that may be used to join metal parts and composite fiber reinforced parts include flow-drill screws, clinch joints and flow drilling processes. With each technique the fibers in the area where the fastener is inserted or the joint is to be formed may result in surface cracking or fiber displacement. 
     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 join parts together. 
     Adhesives are used extensively 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 glue is cured. 
     Other methods, such as 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. 
     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 
     According to one aspect of this disclosure, a composite part is disclosed that comprises a resin matrix having a predetermined location for receiving a fastener. Fibers reinforce the resin matrix in a first portion of the resin matrix. A second portion of the resin matrix is substantially devoid of fibers at the predetermined location. 
     According to other aspects of this disclosure as it relates to a composite part, the fibers reinforcing the resin matrix may further comprise a woven mat that defines an opening in the mat provided at the predetermined location. Alternatively, the fibers reinforcing the resin matrix may be loose fibers that are dispersed in the first portion of the resin matrix, but that are not dispersed in the second portion of the resin matrix. 
     The composite part may be provided in combination with an assembled part that is assembled to the composite part with the fastener that is inserted through the assembled part and through a first side of the composite part. The combination may further comprise a protrusion disposed on a second side of the composite part that is opposite the point of insertion on the first side of the predetermined location. 
     According to another aspect of this disclosure, a method of making a fiber reinforced composite part is disclosed that comprises providing a fiber mat defining an opening. The fiber mat is inserted into a mold with the opening in a predetermined location in the mold. A liquid resin is supplied to the mold and envelopes the fiber mat. The resin is then hardened, or cured, in the mold. The resin fills the opening to provide a substantially fiberless fastener receptacle area on the fiber reinforced composite part in the predetermined location. 
     According to other aspects of the disclosure, the method may further comprise assembling a second part to the fiber reinforced composite part. The fiber reinforced composite part and the second part are joined together at the predetermined location. The step of joining the fiber reinforced composite part and the second part may further comprise forming a clinch joint in the second part and the fastener receptacle area in the fiber reinforced composite part. Alternatively, the step of joining the fiber reinforced composite part and the second part may further comprise inserting a fastener through the second part and into the fastener receptacle area in the fiber reinforced composite part. The fastener may be a rivet, a self-piercing rivet, a self-tapping screw, or a flow drill screw. 
     According to another aspect of this disclosure, an alternative method is disclosed for making a fiber reinforced composite part with loose fiber material. The alternative method comprises shielding a predetermined portion of a mold while depositing a loose fiber material in the mold so that the loose fiber material is not deposited in the predetermined portion of the mold. A liquid resin is supplied to a mold that encapsulates the loose fiber reinforcement material and fills the predetermined portion of the mold. The resin is then hardened to form a substantially fiberless fastener receptacle area in the fiber reinforced composite part. 
     This disclosure is directed to solving the above problems and other problems as will be more specifically described below with reference to the attached drawings of the illustrated embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an exploded perspective view of a part that is to be fastened with a fastener to a fiber reinforced composite part having a fastener receptacle area that is not reinforced with fibers. 
         FIG. 2  is a fragmentary cross-sectional view of the mold that has a fiber mat that defines an opening and is disposed in the mold. 
         FIG. 3  is a fragmentary cross-sectional view of the mold filled with a resin matrix material and the fiber mat. 
         FIG. 4  is a fragmentary cross-sectional view of a mold including a pin that is movable between an extended position to prevent loose fibers from being deposited in a predetermined area of the mold and subsequently backfilled with resin when the pin is retracted. 
         FIG. 5  is a fragmentary cross-sectional view of the mold including the pin that is movable between an extended position and a retracted position in the refracted position showing the loose fibers deposited around the predetermined area. 
         FIG. 6  is a fragmentary cross-sectional view of the mold filled with a resin matrix material and including the pin that is movable between an extended position and a retracted position in the refracted position showing the loose fibers deposited around the predetermined area. 
         FIG. 7  is a cross-sectional view of a part assembled to a fiber reinforced composite part with a self-piercing rivet in position to be inserted into the parts. 
         FIG. 8  is a cross-sectional view of the part assembled to the fiber reinforced composite part with the self-piercing rivet fastening the parts together. 
         FIG. 9  is a cross-sectional view of a part assembled to a fiber reinforced composite part with a flow drill screw in position to be inserted into the parts. 
         FIG. 10  is a cross-sectional view of the part assembled to the fiber reinforced composite part with the flow drill screw fastening the parts together. 
         FIG. 11  is a cross-sectional view of the part assembled to a fiber reinforced composite part with a clinch joint forming tool in position to join the parts. 
         FIG. 12  is a cross-sectional view of the part assembled to the fiber reinforced composite part with a clinch joint fastening the parts together. 
     
    
    
     DETAILED DESCRIPTION 
     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. 
     Referring to  FIG. 1 , a composite part assembly  10  is shown to include an aluminum part  12  that is positioned to be joined to a fiber reinforced composite part  14  by a self-piercing rivet  16 . The self-piercing rivet  16  is shown aligned with a fastener receptacle area  18  in the fiber reinforced composite part  14 . Assembly of the parts with the self-piercing rivet  16  is described below with reference to  FIGS. 7 and 8 . 
     Referring to  FIG. 2 , a mold  20  is illustrated that includes a mold cavity  22 . A woven fiber mat  26  defines an opening  28  in a predetermined area that corresponds to the desired location of the fastener receptacle area  18  (shown in  FIG. 1 ). The woven fiber mat  26  is loaded into the mold cavity  22  with the opening  28  in the predetermined area. 
     Referring to  FIG. 3 , the mold  20  is shown with the mold cavity  22  filled with the woven fiber mat  26  and a resin matrix  30  that is poured, injected or otherwise supplied to the mold cavity  22 . The resin matrix fills interstitial spaces within the woven fiber mat  28  and also fills the opening  28  in the fiber mat  26 . The resin matrix  30  in the opening  28  comprises the fastener receptacle area  18  (shown in  FIG. 1 ). 
     Referring to  FIG. 4 , an alternative embodiment of a mold  32  is illustrated that includes a mold cavity  34  in which a pin  36  is disposed. The pin  36  is shown in its extended position in  FIG. 4 . Loose fibers  38  are supplied to the mold cavity  34  while the pin  36  is in its extended position. The pin  36  in the extended position prevents the loose fibers  38  from being deposited in the space within the mold cavity  34  with the pin  36  in its extended position is disposed. The pin  36  in its extended position shields the portion of the mold cavity  34  from the deposit of the fibers  38 . 
     Referring to  FIG. 5 , the alternative mold  32  is shown with the pin  36  in the refracted position. The mold cavity  34  includes the loose fiber throughout except where the void  40  is defined within the loose fibers  38  and above the pin  36 . It should be understood that the void  40  may include a limited number of fibers  38  because there is no partition preventing the fibers  38  from being inadvertently deposited within the void. 
     Referring to  FIG. 6 , the alternative mold  32  is shown with the mold cavity  34  filled with loose fibers  38  that are now encapsulated in a resin matrix  42 . The resin matrix  42  fills the interstitial areas between the loose fibers  38  and also fills the void  40  (shown in  FIG. 5 ). The resin  42  in the void  40  comprises the fastener receptacle area  18  (shown in  FIG. 1 ). The resin  42  and the void  40  may include some inadvertently deposited fibers  38 . However, the density of the fibers  38  should be markedly less than the void area  40  with a fiber density of less than 10% of the fiber density in the other parts of the resin matrix  42 . 
     It should be understood that the resin  42  may be injected as a two-step resin injection with a two-step cure. For example, with the pin extended, the mold may be filled with loose fiber. Resin may be injected into the mold  32  and partially cured. 
     Referring to  FIG. 7 , an aluminum part  12  and a fiber reinforced composite part  14  are shown in a position to be assembled together by the insertion of a self-piercing rivet  16 . The self-piercing rivet  16  is aligned with the fastener receptacle area  18  within the fiber reinforced composite part  14 . 
     Referring to  FIG. 8 , the self-piercing rivet  16  is driven through the panels  12  and  14  by a rivet punch  44 . A back-up die  46  backs up the fiber reinforced composite part  14  in the fastener receptacle area  18 . Insertion of the self-piercing rivet  16  results in a button-shaped protrusion  48  being formed on the obverse side of the fiber reinforced composite part  14 . 
     Referring to  FIG. 9 , a flow drill screw  50  is aligned with an aluminum part  12  and a fiber reinforced composite part  14 . The flow drill screw  50  is shown ready to be inserted into the aluminum part  12  and is in alignment with the fastener receptacle area  18  provided by the fiber reinforced composite part  14 . The flow drill screw  50  is driven through the aluminum part  12  first by rapidly rotating the flow drill screw  50  while applying pressure to drive the flow drill screw  50  through the aluminum part  12 . After initial penetration by the flow drill screw  50 , the speed of rotation of the flow drill screw  50  is reduced and the threads on the flow drill screw  50  form a tapped hole in the aluminum part  12  and the fiber reinforced composite part  14 . 
     While the aluminum part  12 , as shown in  FIG. 1 , does not include a clearance hole, it should be appreciated that a clearance hole may be provided through the aluminum part  12 . If so, the clearance hole (not shown) should be aligned with the fastener receptacle area  18  in the fiber reinforced composite part  14 . The thickness of the aluminum part  12  and the material properties of the aluminum part  12  are factors that must be assessed in determining whether a hole must be provided in the aluminum part  12  for the flow drill screw  50 . 
     Referring to  FIG. 10 , the flow drill screw  50  is shown securing the aluminum part  12  to the fiber reinforced composite part  14 . The flow drill screw  50  integrally forms a bushing area  52  on the fiber reinforced composite part  14 . The flow drill screw  50  is inserted through the fastener receptacle area that is substantially void of fiber. The bushing  52  is substantially free from fiber penetration, cracks or splits that would ordinarily be formed by the flow drill screw  50  being inserted through a fiber reinforced composite part  14  that does not include a fastener receptacle area  18 . 
     Referring to  FIG. 11 , a clinch joint punch  56  is shown aligned with a clinch joint back-up die  58 . The fastener receptacle area  18  of the fiber reinforced composite part  14  is disposed between and aligned with the clinch joint punch  56  and the clinch joint back-up die  58 . 
     Referring to  FIG. 12 , a composite part assembly  10  is shown with the aluminum part  12  assembled to the fiber reinforced composite part  14  by a clinch joint  60 . The clinch joint  60  is formed in the fastener receptacle area  18  that is substantially void of reinforcing fibers. Reinforcing fibers in the fiber reinforced composite part  14  reinforce the part  14  while the absence of fibers in the fastener receptacle area  18  allow the clinch joint  60  to be formed without cracking or splitting caused by fibers being forced through the obverse side of the fastener receptacle area  18  of the fiber reinforced composite part  14 . 
     While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms of the disclosed apparatus and method. 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 disclosure as claimed. The features of various implementing embodiments may be combined to form further embodiments of the disclosed concepts.