Patent Publication Number: US-10328643-B2

Title: Apparatus for fabricating composite fasteners

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional application of U.S. patent application Ser. No. 13/773,042, filed Feb. 21, 2013, now U.S. Pat. No. 9,623,612. This application is related to U.S. patent application Ser. No. 13/773,120 filed concurrently herewith on Feb. 21, 2013, and now U.S. Pat. No. 9,238,339 which is incorporated by reference herein in its entirety. 
    
    
     BACKGROUND INFORMATION 
     1. Field 
     The present disclosure generally relates to fasteners, and deals more particularly with a method and apparatus for fabricating high strength composite fasteners. 
     2. Background 
     Plastic fasteners such as threaded bolts and screws have been developed for use in several applications because of their light weight, compared to metal fasteners. Plastic fasteners may be fabricated using injection molding, extrusion or compression molding techniques. It is known that plastic fasteners may be strengthened by incorporating reinforcement fibers in a plastic resin, however these reinforced plastic fasteners may nevertheless be weaker than metallic fasteners due to their relatively low fiber volume in relation to the plastic resin. In one approach, long, continuous axially aligned reinforcing fibers infused with a polymer resin are formed by a molding process. Although providing additional strength in the axial direction of the fastener, the fastener may be substantially anisotropic, rendering it unsuitable for some applications. Additionally, known reinforced plastic fasteners are difficult to fabricate, especially in high volume because of the need to layup and align continuous fibers in a mold. 
     Accordingly, there is a need for a method and apparatus for producing fiber reinforced, plastic fasteners that have a high fiber volume and exhibit quasi-isotropic properties. There is also a need for a method and apparatus of the type mentioned above which permits fabrication of high-strength plastic fasteners quickly and in high-volume Further, there is a need for threaded fasteners which incorporate fibers in the threads to increase thread strength. 
     SUMMARY 
     The disclosed embodiments provide a method and apparatus for fabricating fiber reinforced, high-strength thermoplastic fasteners which exhibit quasi-isotropic properties, and which may be manufactured rapidly and in high-volume using compression molding equipment. The fasteners have a high fiber volume in relation to the thermoplastic resin volume and can be molded to near net shape, in any of a variety of geometries. Light weight, high-strength fasteners may be produced which are suitable for use in high-performance applications such as airframes for aircraft. 
     According to one disclosed embodiment a method is provided of producing a composite fastener. The method comprises introducing thermoplastic resin infused fiber flakes into a reservoir, heating the infused fiber flakes in the reservoir to the melting temperature of the thermoplastic resin, resulting in a mixture of melted thermoplastic resin and fiber flakes, and flowing the mixture of the melted thermoplastic resin and fiber flakes into a mold having the shape of the fastener. The method may further comprise providing a fiber pre-preg having a relatively high fiber content, and chopping the fiber pre-preg into the infused flakes. The fiber pre-preg may include bidirectional reinforcing fibers. The method also comprises measuring a charge of the infused fiber flakes to be introduced into the reservoir, wherein the charge corresponds to a volume when melted that substantially matches the volume of a plurality of mold cavities in the mold. The method may further comprise compressing melted thermoplastic resin and the infused fiber flakes in the mold. Flowing the mixture into the mold includes randomly orienting the fiber flakes in the mixture. 
     According to another disclosed embodiment, a method is provided of producing fiber reinforced thermoplastic fasteners, comprising producing thermoplastic resin infused fiber flakes, and placing a charge of the infused fiber flakes into a reservoir. The method also includes heating the infused fiber flakes within the reservoir until resin in the infused fiber flakes melt and become a flowable mixture of thermoplastic resin and fibers, flowing the flowable mixture from the reservoir into each of a plurality of mold cavities in a mold, each of the mold cavities having the shape of a fastener, and compression molding the flowable mixture into a plurality of fasteners. Producing the infused fiber flakes is performed by cutting fiber pre-preg, which may be accomplished by chopping strips of unidirectional pre-preg tape. The method may further comprise forming a charge of the infused fiber flakes having a volume, when melted, that substantially corresponds to the volume of the mold cavities. Flowing the flowable mixture into the mold cavities is performed such that fiber orientations of the fiber flakes are random substantially throughout each of the mold cavities. The method may also comprise allowing the fasteners to cool and solidify within the mold cavities, and removing the fasteners from the mold cavities. 
     According to still another disclosed embodiment, apparatus is provided for producing a plurality of composite fasteners, comprising a mold having a plurality of mold cavities respectively defining fasteners, and a reservoir for containing thermoplastic infused fiber flakes, the reservoir being coupled with the mold cavities and adapted to be heated to melt the thermoplastic infused fiber flakes. The reservoir is integrated with the mold, and the mold optionally includes a wall separating the reservoir from the mold cavities, and a flow control opening in the wall for controlling the flow of melted, infused fiber flakes from the reservoir into the mold. The apparatus may further comprise heater elements for heating the mold and the reservoir. The reservoir has a substantially open top, and the apparatus further comprises a male die adapted to be displaced into the reservoir and force melted fiber flakes to flow from the reservoir into the mold cavities. The mold includes a wall separating the reservoir from the mold cavities, and the wall includes an opening therein through which the melted fiber flakes may flow from the reservoir into the mold cavities. The wall is spaced from the mold cavities to form a flow region through which the melted fiber flakes may be distributed to the mold cavities. In one variation, the reservoir is located above and is directly open to the mold cavities. 
     The features, functions, and advantages can be achieved independently in various embodiments of the present disclosure or may be combined in yet other embodiments in which further details can be seen with reference to the following description and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The novel features believed characteristic of the illustrative embodiments are set forth in the appended claims. The illustrative embodiments, however, as well as a preferred mode of use, further objectives and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment of the present disclosure when read in conjunction with the accompanying drawings, wherein: 
         FIG. 1  is an illustration of a functional block diagram of apparatus for producing high-strength composite fasteners according to one disclosed embodiment. 
         FIG. 2  is an illustration of a mixture of fiber flakes thermoplastic resin used to fill mold cavities forming part of the apparatus shown in  FIG. 1 . 
         FIG. 3  is an illustration of a flow diagram of a method of making the high-strength composite fasteners using the apparatus of  FIG. 1 . 
         FIG. 4A  is an illustration of a longitudinal side view of one form of the high-strength composite fastener. 
         FIG. 4B  is an illustration of end view of the fastener shown in  FIG. 4A . 
         FIG. 5A  is an illustration of a longitudinal side view of another form of the high strength composite fastener. 
         FIG. 5B  is an illustration of an end view of the fastener shown in  FIG. 5A . 
         FIG. 6A  is an illustration of a longitudinal side view of a another form of the high-strength composite fastener. 
         FIG. 6B  is an illustration of an end view of the fastener shown in  FIG. 6A . 
         FIG. 7  is an illustration of exemplary shapes of the thermoplastic fiber flakes used to mold the composite fasteners. 
         FIG. 8  is an illustration of a thermoplastic fiber flake having bidirectional reinforcing fibers. 
         FIG. 9  is an illustration of a sectional view of a one embodiment of the mold forming part of the apparatus shown in  FIG. 1 . 
         FIG. 10  is an illustration similar to  FIG. 9 , but showing the mold having been placed in a compression molding machine and filled with a charge of thermoplastic resin fiber flakes. 
         FIG. 11  is an illustration similar to  FIG. 10 , but showing a male die beginning to compress a heated charge in the mold. 
         FIG. 12  is an illustration similar to  FIG. 11 , but showing the male die having compressed the heated charge and force it to flow into the mold cavities. 
         FIG. 13  is an illustration of a flow diagram of aircraft production and service methodology. 
         FIG. 14  is illustration of a block diagram of an aircraft. 
     
    
    
     DETAILED DESCRIPTION 
     Referring first to  FIGS. 1 and 2 , the disclosed embodiments relate to a method and apparatus for producing high-strength composite fasteners  30  having a high fiber volume and exhibiting quasi-isotropic properties. Fasteners  30  may be produced which have any of a variety of sizes, geometries and features. For example, as shown in  FIGS. 4A and 4B , the fastener  30  may have a  12  point wrenching head  30   a , a shank  30   b  and a threaded tip  30   c . Another example of the fastener  30 , shown in  FIGS. 5A and 5B , is provided with a countersunk head  30   b  having a screwdriver recess  30   e . Still another example of the fastener  30 , shown in  FIGS. 6A and 6B , is provided with a hex head  30   f . The fasteners  30  shown in  FIGS. 4A-6B , should not be interpreted as limiting, but rather are merely exemplary of a wide variety of fastener geometries and features that may be manufactured using the disclosed method and apparatus. The particular fastener design that is selected will depend on the application, and specific fastener performance requirements. 
     Referring again to  FIGS. 1 and 2 , the fasteners  30  are compression molded in a compression molding machine  44 , although other molding equipment and techniques may be possible. A preselected charge  24  of randomly oriented, thermoplastic infused fiber flakes  32  is loaded into a material reservoir  34  from a material supply  36 . The infused fiber flakes  32  are heated  28  within the material reservoir  34  until the resin in the infused fiber flakes  32  melts and becomes flowable, resulting in a flowable mixture  29  of melted resin and fiber flakes  32 . The flowable mixture  29  of melted resin and fiber flakes  32  is directed through channels  38  or other flow areas within a partable mold  42 , into a plurality of individual fastener mold cavities  40  in the mold  42 . Each of the mold cavities  40  has a geometry defining a fastener  30 . As will be discussed below in more detail, the material reservoir  34  may be integrated into the mold  42 . 
       FIG. 3  illustrates the overall steps of a method of producing high-strength composite fasteners using the apparatus shown in  FIG. 1 . At step  46 , a reservoir  34  is filled with a charge  24  of thermoplastic resin infused fiber flakes  32 . The charge  24  may be premeasured to correspond to a volume, which, when melted, substantially matches the volume of the mold cavities. At  48 , the infused fiber flakes  32  are melted by heating  28  the charge  24  within the reservoir  34 . At step  50 , the melted fiber flakes  32  are flowed into a mold  42  having at least one mold cavity  40  defining a fastener  30 . Although not shown in  FIG. 3 , optionally, a quantity of resin may be added or removed from the melted charge  24  before the charge  24  is flowed into the mold cavity  40  in order to adjust the fiber fraction of the finished fastener  30 . At  52 , the molded fastener  30  is allowed to cool and solidify, and at step  54 , the mold  42  is parted and the fastener  30  is removed from the mold cavity  40 . 
     In one embodiment, the mold charge  24  may comprise fiber flakes  32  that are formed from unidirectional fibers pre-impregnated with a thermoplastic resin. Fasteners  30  produced by the disclosed method may achieve a high fiber content by employing pre-preg fiber in which the fiber content is relatively high, for example, and without limitation, at least approximately 60% fiber content or higher. In this embodiment, the source of the thermoplastic resin which forms that fastener  30  is derived solely from the resin contained in the infused fiber flakes  32 . Alternatively, however, it may be possible to use tackified dry fiber flakes  32  that may not be pre-impregnated with resin, in which case a premeasured quantity of thermoplastic resin may added to the mold charge  24 . It should be noted here that in some embodiments, satisfactory performance results may be obtained where the fiber content of the fastener  30  is substantially less than 60%. 
     The fiber flakes  32  may have one or more specific shapes which may aid in maintaining a substantially uniform distribution and random orientation of the reinforcing fibers  33  (see  FIGS. 3 and 4 ) within the melted mixture  29  of resin and fiber flakes  32  as the mixture  29  flows into the mold cavities  40 . The specific shapes of the fiber flakes  32  may also assist in imparting quasi-isotropic mechanical properties to the fastener  30  by incorporating various lengths of fiber reinforcement within the mixture  29 . The thermoplastic resin may comprise a relatively high viscosity thermoplastic resin such as, without limitation, PEI (polyetherimide) PPS (polyphenylene sulphide), PES (polyethersulfone), PEEK (polyetheretherketone), PEKK (polyetheretherketone), and PEKK-FC (polyetherketoneketone-fc grade), to name only a few. The reinforcing fibers  33  ( FIG. 7 ) in the fiber flakes  32  may be any of a variety of high strength fibers, such as, without limitation, carbon, metal, ceramic and/or glass fibers. It may also be possible to reinforce the fastener  30  by adding metallic and/or ceramic particles or “whiskers” to the mold charge  24 . 
     The fiber flakes  32  may be formed, for example and without limitation, using a rotary chopper to chop fiber pre-preg tape, or by die cutting individual shapes from a roll or strip of pre-preg tape (not shown) having a high fiber content or from a sheet of pre-preg having a high fiber content. Alternatively, as previously mentioned, it may be possible to form the fiber flakes  32  from a tackified dry fiber perform (not shown), as by die cutting or other techniques. It may also be possible to form the fiber flakes  32  using other production processes. 
     The fiber flakes  32  may be substantially flat and may have any of various outline shapes. For example, as shown in  FIG. 7 , the fiber flakes  32  may have the shape of a square  56   a , a rectangle  56   b , a circle  56   c , an equilateral triangle  56   d , a trapezoid  56   e , a hexagon  56   f  or other polygon (not shown), an ellipse  56   g  or a diamond  56   h . Other shapes are possible. In some embodiments, fiber flakes  32  with two or more of the shapes  56   a - 56   h  may be mixed together. 
     The presence of fibers  33  having differing lengths in the mixture  29  may aid in achieving a more uniform distribution of the fiber flakes  32  in the fastener  30 , while promoting isotropic mechanical properties and/or strengthening the fastener  30 . Fiber flakes  32  having shapes such the circle  56   c , triangle  56   d , hexagon  56   f , ellipse  56   g  and diamond  56   h , may be particularly useful in improving the isotropic mechanical properties of the fastener  30  because of the fact that these shapes result in each fiber flake  32  having differing fiber lengths. Accordingly, a combination or mix of long and short fiber lengths within a single fiber flake  32  may be particularly desirable. Generally, the size and shape of the fiber flakes  32  may be selected to optimize the flow, strength and finish quality of the fastener  30 . While the fiber flakes  32  illustrated in  FIG. 7  employ unidirectional reinforcing fibers  33 , the fiber flakes  32  may comprise resin infused bidirectional fibers  60  as shown in  FIG. 8 . The bi-directional fibers  60  may be intertwined with each other by weaving, knitting or other techniques. 
     Attention is now directed to  FIG. 9  which illustrates additional details of one embodiment of the mold  42  previously discussed in connection with  FIG. 1 . In this example, the mold  42  includes an integrated reservoir  34  in the form of a recess  35  in the top of the mold  42 . The top of the reservoir recess  35  is open to allow a charge of the infused fiber flakes (not shown in  FIG. 9 ) to be placed in the reservoir  34 . The reservoir  34  may be separated from a flow region  64  in the mold  42  by a separation wall  68  having a centrally located flow control opening  62  therein which allows a melted mixture  29  of resin and from the reservoir  34  to flow readily into the flow region  64 . The mold  42  further includes a plurality of mold cavities  40  therein, beneath the flow region  64 . As previously described, the size and geometry of each of the mold cavities  40  corresponds to, and defines one of the fasteners  30 . In some embodiments, all of the mold cavities  40  may be substantially identical, whereas in other embodiments, the mold cavities  40  may be different from each other in order to produce fasteners  30  having differing sizes, shapes, and/or features. Moreover, some embodiments of the mold  42  may not employ the separation wall  68 , in which case the reservoir  34  is above and is directly open to the mold cavities  40 . In those embodiments employing the separation wall  68 , a measured charge of the resin infused fiber flakes is placed in the reservoir  44  that substantially matches the volume of the mold cavities  40 , plus the volume beneath the separation wall  68 . In embodiments that do not employ the separation wall  68 , a measured charge of the resin infused fiber flakes is placed in the reservoir  44  that substantially matches the volume of the mold cavities  40 . 
     The mold  42  may also include integrated heating elements  66  both in the area of the reservoir  34  and the mold  42 . The heating elements  66  function to both heat the infused fiber flakes  32  within the reservoir  34  to their melting temperature, and to maintain the elevated temperature of the resin as it flows into the mold cavities  40 . In some embodiments, the mold  42  may not employ heating elements  66 , in which case the mold  42  may be heated by placing it in an oven (not shown) where it is heated it to the required temperatures, following which it may be transferred to a hydraulic compression press where the molding operation is carried out. In either case, it may be useful in some applications to preheat the mold  42  in an oven prior to carrying out molding operations. 
     Referring now to  FIG. 10 , the mold  42  is placed in a compression molding machine  44  that includes a heated male die  70  coupled with a power operated ram  72 . The male die  70  is axially aligned with and is forced into the reservoir recess  35  by force F generated by the ram  72  during a molding operation.  FIGS. 11 and 12  illustrate sequential progress of the male die  70  as it is forced into the reservoir recess  35 . As shown in  FIG. 11 , the male die  70  may be partially displaced to initially compact the charge  24 , as the charge  24  is being heated to the melt temperature of the resin. Heating elements  66  integrated into the male die  70  may assist in accelerating heating of the charge  24  to the melt temperature of the resin. In other embodiments, the charge  24  may be heated to its melt temperature before the male die  70  is forced into the reservoir recess  35 . Melting of the infused fiber flakes  32  while in the reservoir  34  assists in randomizing the fiber orientations of the fiber flakes  32 , before they are flowed into the mold cavities  40 . 
     Referring particularly to  FIG. 12 , when the resin in the infused fiber flakes  32  melts, the mixture  29  of the resin and the fiber flakes  32  becomes flowable. Continued displacement of the male die  70  further into the reservoir recess  35  compresses and causes the mixture to flow  76  through the flow control opening  62  into the flow region  64 . Continued pressure applied by the male die  70  results in the mixture  29  flowing into the mold cavities  40 , thereby compressing and molding the fasteners  32  to near net shape. The random fiber orientations of the fiber flakes  32  flowing into the mold cavities  40  results in the molded fasteners  30  exhibiting substantially quasi-isotropic properties. Moreover, the relatively high fiber content of the fasteners  30  achieved by use of high fiber content pre-preg results in fasteners  30  that are high in strength. Following molding as described above, the mold  42  is allowed to cool, following which the mold  42  may be parted and the fasteners  30  may be removed. Depending upon the application, it may be necessary or desirable to perform post mold machining or other finish work on the fasteners  30 . 
     Embodiments of the disclosure may find use in a variety of potential applications, particularly in the transportation industry, including for example, aerospace, marine, automotive applications and other applications where high strength, lightweight fasteners are used. Thus, referring now to  FIGS. 13 and 14 , embodiments of the disclosure may be used in the context of an aircraft manufacturing and service method  78  as shown in  FIG. 13  and an aircraft  80  as shown in  FIG. 14 . Aircraft applications of the disclosed embodiments may include, for example, without limitation, fasteners that are used in the airframe  96  or in the interior  100  ( FIG. 14 ) of the aircraft  80 , to name only a few. During pre-production, exemplary method  78  may include specification and design  82  of the aircraft  80  and material procurement  84 . During production, component and subassembly manufacturing  86  and system integration  88  of the aircraft  80  takes place. Thereafter, the aircraft  80  may go through certification and delivery  90  in order to be placed in service  92 . While in service by a customer, the aircraft  80  is scheduled for routine maintenance and service  94 , which may also include modification, reconfiguration, refurbishment, and so on. 
     Each of the processes of method  78  may be performed or carried out by a system integrator, a third party, and/or an operator (e.g., a customer). For the purposes of this description, a system integrator may include without limitation any number of aircraft manufacturers and major-system subcontractors; a third party may include without limitation any number of vendors, subcontractors, and suppliers; and an operator may be an airline, leasing company, military entity, service organization, and so on. 
     As shown in  FIG. 14 , the aircraft  80  produced by exemplary method  78  may include an airframe  96  with a plurality of systems  98  and an interior  100 . Examples of high-level systems  98  include one or more of a propulsion system  102 , an electrical system  104 , a hydraulic system  106 , and an environmental system  108 . Any number of other systems may be included. Although an aerospace example is shown, the principles of the disclosure may be applied to other industries, such as the marine and automotive industries. 
     Systems and methods embodied herein may be employed during any one or more of the stages of the production and service method  78 . For example, components or subassemblies corresponding to production process  86  may be fabricated or manufactured in a manner similar to components or subassemblies produced while the aircraft  80  is in service. Also, one or more apparatus embodiments, method embodiments, or a combination thereof may be utilized during the production stages  86  and  88 , for example, by substantially expediting assembly of or reducing the cost of an aircraft  80 . Similarly, one or more of apparatus embodiments, method embodiments, or a combination thereof may be utilized while the aircraft  80  is in service, for example and without limitation, to maintenance and service  94 . 
     The description of the different illustrative embodiments has been presented for purposes of illustration and description, and is not intended to be exhaustive or limited to the embodiments in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art. Further, different illustrative embodiments may provide different advantages as compared to other illustrative embodiments. The embodiment or embodiments selected are chosen and described in order to best explain the principles of the embodiments, the practical application, and to enable others of ordinary skill in the art to understand the disclosure for various embodiments with various modifications as are suited to the particular use contemplated.