Abstract:
The present invention provides a 3-D printed scaffold tailored to a particular hybrid composite material to receive the reinforcement components and support them during application of a secondary composite material. The printed scaffold may provide for retention features that locate and hold the reinforcement components in a variety of different configurations and may incorporate a microstructure having vacuum diffusion properties to assist in composite material lay-up. The invention contemplates either that the scaffold may be sacrificial (retained in hybrid composite) or constructed to permit disassembly and reuse. The 3D printed scaffold may also provide shapes or profile surfaces serving as layup forms that give shape to the woven fiber mat during assembly.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 62/206,609, filed Aug. 18, 2015. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The present invention rotates to hybrid composite materials and in particular to a hybrid composite and a manufacturing process using a 3-D printed element in the fabrication of the hybrid composites. 
         [0003]    Hybrid composites are materials constructed from two different materials, one of which is a composite (for example, a fiber reinforced polymer with a metal, or two different fiber reinforced polymer matrices). The use of hybrid composites simplifies the design and manufacture of specialized materials by allowing pre-manufacture of one composite element having particular strength properties and then permitting the composite element to be assembled into a secondary composite to augment the strength of that secondary composite in a way that would be difficult to manufacture monolithically. For example, a reinforced shape, such as a rod or bar may be advantageously pre-manufactured by extrusion or pultrusion to provide axial alignment of the fiber reinforcements. The pultruded shape may then be incorporated into a secondary composite laid up with woven fiber mats. Each manufacturing process contributes its particular advantage. 
         [0004]    During the manufacturing process of a hybrid composite, the pre-manufactured reinforcement components must be properly aligned and retained for integration into the completed structure. Supporting the components of a hybrid composite material during integration can be difficult. 
       SUMMARY OF THE INVENTION 
       [0005]    The present invention provides a 3-D printed scaffold tailored to the particular hybrid to receive the reinforcement components and support them during application of a secondary composite material. The printed scaffold may provide for retention features that locate and hold the reinforcement components in a variety of different configurations and may incorporate a microstructure having vacuum diffusion properties to assist in composite material lay-up. The invention contemplates either that the scaffold may be sacrificial (retained in hybrid composite) or constructed to permit disassembly and reuse. The 3D printed scaffold may also provide shapes or profile surfaces serving as layup forms that give shape to the woven fiber mat during assembly. 
         [0006]    These particular objects and advantages may apply to only n e embodiments falling within the claims and thus do not define the scope of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  is a flowchart of the manufacturing process of the present invention together with a cross-sectional view of an example 3-D scaffold for a hollow rectangular tube as it is used. to construct a hybrid composite element; 
           [0008]      FIG. 2  is a fragmentary detail of the scaffold of  FIG. 1  showing in an enlarged further detail a microscopic pore structure for vacuum diffusion; 
           [0009]      FIG. 3  is a perspective view of the scaffold as attached to the reinforcement components and showing an air path through the walls of the scaffold for assisting in lay-up of the secondary composite material; 
           [0010]      FIG. 4  is a cross-sectional view through a printed scaffold similar to that of  FIG. 1  as attached to reinforcement components prior to incorporation into a secondary composite material, Where the printed scaffold is assembled from multiple printed elements using a water-soluble glue or the like; 
           [0011]      FIG. 5  is a figure similar to that of  FIG. 4  showing the reinforcement components incorporated into a secondary composite and the disassembly of the scaffold for removal; 
           [0012]      FIG. 6  is a fragmentary view with several layers of cutaway showing a scaffold for a fiber tow support; 
           [0013]      FIG. 7  is a top plan view, partially exploded, of scaffold for the manufacture of a bumper using the principles of the present invention showing reinforcement components prior to assembly on the scaffold; 
           [0014]      FIG. 8  is a fragmentary perspective view of the scaffold of  FIG. 7  with reinforcement components installed and showing the use of an internal threaded rod for assembly of scaffold components together; 
           [0015]      FIG. 9  is a cross-sectional view of the scaffold before assembly of the reinforcement components; 
           [0016]      FIG. 10  is a cross-section similar to that of  FIG. 9  showing installation of the reinforcement components on the scaffold and application of the secondary composite material; 
           [0017]      FIG. 11  is a top fragmentary view of the bumper scaffold of  FIG. 7  showing application of a reinforcing fabric sleeve around the scaffold and reinforcing components as part of the secondary composite material and showing a retainer ring that may fit around ends of the fabric sleeve to corral frayed edges of the sleeve; and 
           [0018]      FIG. 12  is a perspective fragmentary view of a protective sheath that may alternatively or in addition cover the fabric layer as an additional protective element. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0019]    Referring now to  FIG. 1 , the present invention provides a manufacturing method in which a 3-D printed scaffold  10  is prepared, as indicated by process block  12 , that will serve as a mold and retaining fixture in the construction of a hybrid composite material. The scaffold  10  may be printed by a variety of different 3-D printing technologies including, for example, those using extrusion processes such as the extrusion of a molten plastic filament (fused deposition modeling) and those using photo polymerization (stereolithography) or sintering (e.g., selective laser sintering) or the like. Importantly the material of the scaffold  10  may have relatively modest physical properties far beneath those required of the final hybrid composite product allowing a wide variety of materials to be used including, for example, low temperature or brittle polymers. The material of scaffold  10  may also have relatively stronger physical properties far above those of the hybrid composite polymers. 
         [0020]    Referring now also to  FIG. 2 , the scaffold  10  may include pockets  14  and  16  for receiving and retaining reinforcement materials with a predetermined spatial location. For example, in the construction of an elongated rectangular hybrid composite tube, the scaffold  10  may have a generally rectangular cross-section. At each corner of the scaffold  10 , the scaffold  10  may provide first pocket  14  that may receive reinforcement components  15  in the form of a pultruded fiber-composite rod having a circular cross-section. The reinforcement components  15  may extend along the axial length of the scaffold  10  at each corner to provide enhanced strength to the ultimately produced product. 
         [0021]    In this regard, the pockets  14  of the scaffold  10  may include retention features, for example, pocket lips  18 , which project so that the pocket  16  extends in close contact over more than 180 degrees around the circumference of the reinforcement components  15 . As a result, the pocket lips  18  must flex outwardly to receive the rod-shaped reinforcement components  15  and then to spring inward to retain the reinforcement components  15  within the pocket  14  with a snap-like action possible with resilience of the material of the scaffold  10 . 
         [0022]    Similarly, pocket  16  may provide a shallow trough sized to receive a reinforcement component  19 , the latter in the form of a pultruded fiber-reinforced bar of generally rectangular cross-section. Pocket  16  may also include retention features  20  allowing the reinforcement component  19  to be press fit into the pocket  16  and retained by inward force through the retention feature  20  relying on the elasticity of the retention feature  20  or its support in the scaffold  10 . 
         [0023]    In this way the scaffold  10  may receive the reinforcement components  15  and  19  per process block  22  and may locate and retain the reinforcement components  15  and  19  in a desired relationship to each other and the other surfaces of the scaffold  10 . 
         [0024]    As indicated by process block  24 , a secondary composite  26  may then be applied around the outside of the scaffold  10  in contact with the reinforcement components  15  and  19  to integrate the latter therewith to form the completed hybrid composite element  31 . The secondary composite  26 , for example, may be a fiber mat impregnated with a curing polymer material or may be a wound fiber tow within an adhesive matrix or other composite material. 
         [0025]    Referring now also to  FIGS. 2 and 3 , the scaffold  10  may incorporate micro-channels  28  leading from a center lumen  30  within the scaffold  10  to outer surfaces of the scaffold  10 . The micro-channels  28  may be readily formed during the three-dimensional printing process which admits to such complexity without substantially increasing the cost of the part. Upon completion of the scaffold and the insertion of hybrid components per process block  22 , plugs  32  may be installed at either end of the scaffold  10  to cover the central lumen  30 . One plug  32  may communicate with a vacuum hose  34  drawing air out of the central lumen  30  so that replenishing air  35  passes diffusely through the walls of the scaffold  10  and around the inserted reinforcement components  15  and  19  to help pull secondary composite  26  into tight contact with the reinforcement components  15  and  19  and to remove any trapped air. In this example, the scaffold  10  may remain within the completed hybrid composite element  31  or may be removed by melting, dissolving, or other destruction of the scaffold  10 . 
         [0026]    Referring again to  FIGS. 1 and 4 , in an alternative embodiment, after the scaffold  10  is printed, in an optional step  36 , the printed elements of the scaffold may be assembled together into the final scaffold  10  used at process block  22 . This assembly may employ, for example, mechanical detent elements like snaps or hooks built into the components of the scaffold  10  or, for example, the application of a releasable adhesive  38  to joints between scaffold elements  40 . For example, the releasable adhesive  38  may be a water-soluble glue or the like allowing it to be released by exposing scaffold  10  to water introduced through the lumen  30 . 
         [0027]    In this case the reinforcement components  15  and  19  may also be attached to the scaffold elements  40  by means of releasable adhesive  38 . This will allow the scaffold elements  40  to be more easily removed from the reinforcement components  15  as will be discussed below. 
         [0028]    In the example of  FIG. 4 , the scaffold  10  is constructed of six interconnected elements including left and right sidewalls  40   a  and  40   b  which have wedge-shaped quadrilateral cross-sections to present a smaller outer face at the outside of the scaffold  10  and a larger interior face near the lumen  30 . This configuration will assist in withdrawing the elements  40   a  and  40   b  away from the secondary composite  26  as will be discussed. The left and right sidewalls  40   a  and  40   b  are joined to upper and lower scaffold plates  42  each being mirror images of the other and each formed of left scaffold portion  42   a  and right scaffold portion  42   b  attached by water-soluble adhesive  38  along a vertical midline of the scaffold  10 . The left scaffold portion  42   a  and right scaffold portion  42   b  contact the left and right sidewalls  40   a  and  40   b  along outwardly sloping interfaces that permit the left and right sidewalls  40   a  and  40   b  to separate from the left scaffold portion  42   a  and right scaffold portion  42   b  as they move inward which in turn allows the left scaffold portion  42   a  and right scaffold portion  42   b  to also be removed from the secondary composite  26 . 
         [0029]    Referring now to  FIG. 5 , and as indicated by process block  50 , after the application, of the secondary composite  26 , the scaffold  10  may be disassembled after softening the adhesive  38  through a water bath introduced through the lumen  30 . As noted above, this allows the left and right scaffold portions  42   a  and  42   b  and left and right sidewalks  40   a  and  40   b  to be drawn inward and then be withdrawn from the lumen  30  along an axis of the completed hybrid composite element  31  for reuse. 
         [0030]    Referring now to  FIG. 6 , the scaffold  10  may work with a flexible hybrid component, for example, a fiber tow  60  which may be wound in locating grooves  62  on the scaffold  10  to provide for controlled strength augmentation to a superficially applied secondary composite  26 . In this case, tension on the tow  60  retains it against the scaffold  10  without the need for mechanical retaining elements or the like. 
         [0031]    Referring now to  FIGS. 7 and 8 , in an example use of the present invention, a bumper  64  may be assembled from a set of 3D printed scaffold elements  66   a - 66   f  that are interconnected to make a scaffold  10 . This interconnection may be accomplished by providing for a central bore  70  running axially through a center of each of the scaffold elements  66  that will receive an short length of an oversized threaded rod  72  (serving to cut its own threads within the bore  70 ) allowing the scaffold elements  66  to be assembled together by relative rotation of the scaffold elements  66  about the threaded rod  72 . For this purpose, adhesive may be applied to the threaded rod  72  after receipt by one of the scaffold elements  66  to prevent its further engagement with that scaffold elements  66  upon mutual rotation of the scaffold elements  66  to tighten together along the joining threaded rod  72 . 
         [0032]    The use of multiple scaffold elements  66  that may be assembled together allows the size of the printed scaffold  10  to be arbitrarily increased beyond the size capacity of a particular 3D printing machine. In some embodiments, seams  67  between the scaffold elements  66  may be spanned by the axially extending reinforcement components  19  during assembly for greater strength. The reinforcement components  19  may be attached to the scaffold elements  66  by an adhesive. 
         [0033]    Referring to  FIGS. 8 and 9 , in this example, the scaffold  10  provides a substantially square cross-section having axially extending pockets  14   a  in each of the corners of the square around the central bore  70  for the receipt of reinforcement components  19   a,  the later being, for example, solid rods of a pultruded carbon fiber material. Faces of the square cross-section of the scaffold  10  may also have axially extending pockets  14   b  receiving tubular reinforcement components  19   b  being, for example, pultruded carbon fiber tubes. 
         [0034]    Referring to  FIG. 10 , upon assembly of the reinforcement components  19   a  and  19   b  on the scaffold  10 , a secondary composite  26  may be applied around the outside of the scaffold  10  in contact with the reinforcement components  19   a  and  19   b  and the scaffold  10  to integrate them into a completed hybrid composite element  31 . In this case, the scaffold  10  is retained within the hybrid composite element  31 . The secondary composite  26 , for example a matt of woven fiber impregnated with a hardening polymer material, may provide for a continuous extent that spans the seams  67  between the scaffold elements  66  and between the reinforcement components  19 . 
         [0035]    Referring now to  FIGS. 10 and 11 , the secondary composite  26  covering the assembled scaffold  10  and reinforcement components  19  of  FIG. 10  may include a fabric sleeve  74 , for example, of a woven or nonwoven carbon fiber mesh, that may be impregnated with a polymer matrix material  75  hardening around and within the fabric sleeve  74  to provide the reinforced secondary composite  26 . The frayed ends  76  of the fabric sleeve may be finished by means of a 3-D printed retainer ring  78  conforming closely to the outer dimensions of the scaffold  10  near the frayed ends  76  with an allowance for the thickness of the fabric sleeve  74 . The retainer ring  78  covers a frayed end  76  eliminating a need for an additional manufacturing step of trimming the fibers of this frayed end  76 . The retainer rings  78  may be integrated with the composite material  26  by the same impregnating polymer matrix material  75  to provide a fully integrated assembly. 
         [0036]    Referring now to  FIG. 12 , in an alternative embodiment, a 3-D printed sheath  80 , for example, fabricated in two inter-fitting halves  80   a  and  80   b  may be 3-D printed to have an internal cavity  82  closely conforming to the scaffold  10  as assembled to the reinforcement components  19  with an allowance for the fabric sleeve  74 . This sheath  80  may, but need not be, adhered to the secondary composite  26  and serves to protect finished composite and in particular the fabric sleeve  75  from impact damage, punctures, or cuts by sharp objects. 3-D printing allows the complex cavity  82  to be easily formed on a custom basis. The printed sheath  80  may be used with or without the retainer ring  78 . 
         [0037]    Certain terminology is used herein for purposes of reference only, and thus is not intended to be limiting. For example, terms such as “upper”, “lower”, “above”, and “below” refer to directions in the drawings to which reference is made. Terms such as “front”, “back”, “rear”, “bottom” and “side”, describe the orientation of portions of the component within a consistent but arbitrary frame of reference which is made clear by reference to the text and the associated drawings describing the component under discussion. Such terminology may include the words specifically mentioned above, derivatives thereof, and words of similar import. Similarly, the terms “first”, “second” and other such numerical terms referring to structures do not imply a sequence or order unless clearly indicated by the context. 
         [0038]    When introducing elements or features of the present disclosure and the exemplary embodiments, the articles “a”, “an”, “the” and “said” are intended to mean that there are one or more of such elements or features. The terms “comprising”, “including” and “having” are intended to be inclusive and mean that there may be additional elements or features other than those specifically noted. It is further to be understood that the method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed. 
         [0039]    It is specifically intended that the present invention not be limited to the embodiments and illustrations contained herein and the claims should be understood to include modified forms of those embodiments including portions of the embodiments and combinations of elements of different embodiments as come within the scope of the following claims. All of the publications described herein, including patents and non-patent publications, are hereby incorporated herein by reference in their entireties.