CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a divisional application of patent application U.S. Ser. No. 11/927,003, entitled “Apparatuses, Systems, and Methods for Manufacturing Composite Parts,” filed Oct. 29, 2007, which is, in turn, a divisional application of patent application U.S. Ser. No. 10/953,670, entitled “Apparatuses, Systems, and Methods for Manufacturing Composite Parts,” filed Sep. 29, 2004. All of which are hereby incorporated by reference into the present disclosure. 
     
    
     BACKGROUND INFORMATION 
       [0002]    1. Field 
         [0003]    The following disclosure relates generally to composite part manufacturing and, more particularly, to apparatuses, systems, and methods for laminating fiber-reinforced resin materials on female tools. 
         [0004]    2. Background 
         [0005]    Fiber-reinforced resin materials, or “composite materials” as they are commonly known, offer a number of advantages over conventional metal materials including high strength-to-weight ratios and good corrosion resistance. Conventional composite materials typically include glass, carbon, or polyaramide fibers in woven and/or non-woven configurations. In the raw material stage, the fibers can be pre-impregnated with resin or left dry. If dry, the fibers can be infused with resin after lay-up on a mold surface. Heat and/or pressure can be applied to the resin-impregnated fibers on the mold surface to cure the resin and harden the laminate in the shape of the mold. The heat and pressure can be applied with an oven, an autoclave, a heated flat or contoured forming tool, or a combination of methods including the use of a vacuum bag. 
         [0006]    Composite parts can be formed in the above manner on both male and female tools. With male tools, the fiber plies are applied to an exterior mold surface that forms an inner mold line of the part. Adding plies to the lay-up on a male tool increases the thickness of the part and changes the outer mold line, but the inner mold line remains unchanged. Conversely, with female tools, the fiber plies are applied to an interior mold surface that forms an outer mold line of the part. Adding plies to the lay-up on a female tool increases the thickness of the part and changes the inner mold line, but the outer mold line remains unchanged. 
         [0007]    Female tools are desirable when the mating surface is located on the exterior of a part because female tools allow the outer mold line (i.e., the exterior surface) to be tightly controlled. Female tooling (also known as “outer mold line tooling”) is also desirable when making multiple parts having the same external dimensions but different thicknesses. Aircraft fuselages, for example, often have multiple frames with the same external dimensions but different thicknesses. In this situation, all of the frames can be made with a single female tool because the tool allows the thickness to vary without changing the external dimensions. If future growth of the aircraft requires further thickening of the frames, this can be achieved without changing tooling. Conversely, if male tooling were used, then a separate tool would be required for each different frame thickness. 
         [0008]    One problem that arises when manufacturing composite parts with female tooling, however, is that the fiber plies tend to bridge and/or wrinkle across internal radii on the mold surface.  FIG. 1 , for example, illustrates a cross-sectional end view of fiber material  110  laid up on a portion of a female tool  102  in accordance with the prior art. The female tool  102  includes an interior mold surface  104  having a first side region  103  spaced apart from a second side region  105  by a radius region  106 . A vacuum bag  120  is positioned over the fiber material  110  and evacuated to compress the fiber material  110  against the mold surface  104 . As the vacuum bag  120  is being evacuated, the outside air pressure presses the fiber material  110  firmly against the side regions  103  and  105 , resisting movement of the fiber material  110  into the radius region  106 . This resistance causes the fiber material  110  to bridge across the radius region  106 , thereby reducing the fiber density in this region. The reduction in fiber density in this region can compromise the structural integrity of the finished part. 
       SUMMARY 
       [0009]    The present invention is directed generally toward apparatuses, systems, and methods for manufacturing composite parts and other laminated parts with female tools. A caul configured in accordance with one aspect of the invention includes a base portion positioned between first and second corner portions. The term “caul” is used throughout this disclosure to refer broadly to a device or piece of material configured to apply pressure in laminating. The base portion of the caul has a curved shape when it is in a relaxed state, but moves to a flatter shape when it is subjected to pressure during lamination. Flattening the base portion in this manner causes the first and second corner portions to move outwardly and away from the base portion. 
         [0010]    A system for manufacturing a laminate in accordance with another embodiment of the invention includes a tool having a mold surface configured to support the laminate. The mold surface can include a side region positioned between first and second transition regions. The system can further include a caul configured to apply pressure to the laminate on the mold surface. The caul can include a curved base portion positioned between first and second corner portions. Pressing the base portion of the caul toward the side region of the mold surface causes the base portion to flatten and drive the first and second corner portions outwardly toward the first and second transition regions, respectively, of the mold surface. 
         [0011]    A method for manufacturing a fiber-reinforced resin part in accordance with a further aspect of the invention includes positioning a plurality of fibers on a mold surface of a tool, and positioning a curved base portion of a caul over a first portion of the fibers. The method further includes pressing the curved base portion toward a side region of the mold surface. Pressing the curved base portion in this manner flattens the base portion against the first portion of fibers and compresses a second portion of the fibers against a transition region of the mold surface. 
         [0012]    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 
         [0013]    The novel features believed characteristic of the advantageous embodiments are set forth in the appended claims. The advantageous 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 advantageous embodiment of the present disclosure when read in conjunction with the accompanying drawings, wherein: 
           [0014]      FIG. 1  is a cross-sectional end view of a prior art system for laminating fiber material on a female tool. 
           [0015]      FIG. 2  is an exploded isometric view of a system for laminating material on a female tool in accordance with an embodiment of the invention. 
           [0016]      FIGS. 3A-3D  include isometric and cross-sectional end views illustrating various stages in a method for manufacturing a laminated part in accordance with an embodiment of the invention. 
           [0017]      FIG. 4  is an isometric view of a caul for applying pressure in laminating in accordance with an embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0018]    The following disclosure describes apparatuses, systems, and various methods for manufacturing composite parts. Certain details are set forth in the following description and in  FIGS. 2A-4  to provide a thorough understanding of various embodiments of the invention. Other details describing well-known structures and systems often associated with composite parts and composite part manufacturing, however, are not set forth in the following disclosure to avoid unnecessarily obscuring the description of the various embodiments of the invention. 
         [0019]    Many of the details, dimensions, angles, and other features shown in the Figures are merely illustrative of particular embodiments of the invention. Accordingly, other embodiments can have other details, dimensions, angles, and features without departing from the spirit or scope of the present invention. In addition, further embodiments can be practiced without several of the details described below. 
         [0020]    In the Figures, identical reference numbers identify identical or at least generally similar elements. To facilitate the discussion of any particular element, the most significant digit or digits of any reference number refer to the Figure in which that element is first introduced. For example, element  230  is first introduced and discussed with reference to  FIG. 2 . 
         [0021]      FIG. 2  is an exploded isometric view of a manufacturing system  200  for laminating a plurality of fiber plies  210  together in accordance with an embodiment of the invention. In one aspect of this embodiment, the manufacturing system  200  includes a female tool  202  having a mold surface  204  configured to support the fiber plies  210  during lamination. The mold surface  204  can include a first side region  203  spaced apart from a second side region  205  by a first transition region  206   a , and a third side region  207  spaced apart from the second side region  205  by a second transition region  206   b . In the illustrated embodiment, the transition regions  206  include surfaces defining internal radii. In other embodiments, however, the transition regions  206  can have other shapes without departing from the spirit or scope of the present invention. Such shapes can include, for example, beveled surfaces, partially beveled surfaces, and curved surfaces having elliptical, oval, and other curved components. 
         [0022]    In another aspect of this embodiment, the manufacturing system  200  can further include a release layer  230 , a flow media or medium  240 , and a caul  250 . The release layer  230  acts as a separator between the fiber plies  210  and the flow medium  240 . Various materials known in the art are suitable for this purpose, including materials that do not bond to epoxies and other resins such as fluorinated ethylene propylene (FEP), high density polyethylene (PE), and nylon. 
         [0023]    The flow medium  240  can have an uneven surface texture that facilitates the diffusion of resin through the fiber plies  210  when the plies are sandwiched between the caul  250  and the mold surface  204 . In one embodiment, for example, the flow medium  240  can include a plurality of grooves formed on an exterior surface. In another embodiment, the flow media can include a plurality of ridges arranged in a grid or other pattern. In further embodiments, the flow medium  240  can be formed from screen, mesh, weave, and/or other perforated materials. These embodiments of the flow medium  240  can be manufactured from various materials including polypropylene, polyethylene, nylon, polyester, thermoplastic, and polyvinylchloride. 
         [0024]    The caul  250  is a tooling aid having a base portion  253  positioned between a first corner portion  252   a  and a second corner portion  252   b . In the illustrated embodiment, the base portion  253  includes a curved or cambered web portion extending between the two corner portions  252 . In other embodiments, the caul  250  can have other shapes, including other more linear shapes. For example, in another embodiment the base portion  253  can have an inverted V shape, or a partial-inverted V shape. 
         [0025]    The base portion  253  is configured to be positioned proximate to the second side region  205  of the mold surface  204 . The first corner portion  252   a  is configured to be positioned proximate to the first transition region  206   a  of the mold surface  204 , and the second corner portion  252   b  is configured to be proximate to the second transition region  206   b . Once the caul  250  has been positioned on the tool  202  in the foregoing manner, the sealing layer  220  can be placed over the caul  250  and evacuated. As explained in greater detail below, the resulting pressure flattens the base portion  253  against the fiber plies  210  and presses the plies against the mold surface  204 . In other embodiments, other types of pressure, e.g., mechanical and/or manual pressure, can be used to flatten the base portion  253  against the fiber plies  210 . 
         [0026]    The caul  250  can be manufactured from any number of suitable materials that flex under external pressure. Such materials can include materials that behave elastically through a range of deflections. In one embodiment, for example, the caul  250  can be formed from sheet metal, such as stainless steel. In another embodiment, the caul  250  can be formed from thermoplastic materials using a rotomolding process, a vacuum forming process, and/or other known processes. One advantage of using thermoplastic materials is that they are easily formed and relatively inexpensive. As a result, the caul  250  can be disposed of after a single use without incurring significant costs. 
         [0027]    The manufacturing system  200  can be used in accordance with embodiments of the invention to laminate fiber plies that are initially dry or pre-impregnated with resin. If the fiber plies  210  are initially dry, then the manufacturing system  200  can include a resin infusion system  260  to infuse the plies  210  with resin after the plies  210  have been arranged on the mold surface  204  in, e.g., a “preform.” In this embodiment, the resin infusion system  260  can include a resin fill pot  262  and a resin drain pot  264  (shown schematically in  FIG. 2  and not to scale). As described in greater detail below, resin from the fill pot  262  flows into the plies  210  via a perforated inlet runner  266  positioned toward one side of the female tool  202 . Excess resin then flows out of the plies  210  and into the drain pot  264  via a perforated outlet runner  268  positioned toward an opposite side of the female tool  202 . 
         [0028]      FIGS. 3A and 3B  are isometric views, and  FIGS. 3C and 3D  are cross-sectional end views, illustrating various stages of a method for manufacturing a composite part with the manufacturing system  200  described above with reference to  FIG. 2 . Referring first to  FIG. 3A , this view shows the fiber plies  210  after they have been arranged on the mold surface  204  of the female tool  202 . In  FIG. 3B , the release layer  230  is laid over the fiber plies  210 , and the flow medium  240  is in turn laid over the release layer  230 . Next, the caul  250  is positioned over the flow medium  240  so that the base portion  253  is positioned proximate to the second side region  205  of the mold surface  204  and the first and second corner regions  252   a  and  252   b  are positioned proximate to the first and second transition regions  206   a  and  206   b , respectively. Referring next to  FIG. 3C , the sealing layer  220  is laid over the caul  250  and sealed around the outside of the tool  202  using a suitable method known in the art. Next, the space under the sealing layer  220  is evacuated to compress the caul  250  against the fiber plies  210 . 
         [0029]      FIG. 3D  illustrates the manufacturing system  200  after the sealing layer  220  has been evacuated. As shown, the resulting external pressure causes the base portion  253  of the caul  250  to flex downwardly compressing the fiber plies  210  against the second side region  205  of the mold surface  204 . Flexing the base portion  253  downwardly in this manner drives the corner portions  252  outwardly toward the corresponding transition regions  206  of the mold surface  204 . The corner portions  252  press the fiber plies  210  into the transition regions  206  with sufficient force to prevent fiber bridging and/or wrinkling in these areas. Thus, use of the caul  250  in the foregoing manner can help ensure that the finished part has sufficient fiber/resin density in the transition regions. 
         [0030]    As mentioned above, the manufacturing system  200  can be used in a number of different embodiments to laminate both pre-impregnated fiber plies and fiber plies that are initially dry. If pre-impregnated plies are used, then there is no need to infuse the plies with resin after they have been compacted against the mold surface  204  as described above. In such embodiments, the fiber plies  210  can be cured after compacting by the application of heat and/or pressure in a suitable oven or autoclave. 
         [0031]    Alternatively, if the fiber plies  210  are initially dry, then resin can be infused into the plies at the perform stage using a number of different methods. In one method, for example, the fiber plies  210  are first compressed against the mold surface  204  as described above with reference to  FIGS. 3A-3D . Next, a valve  260  is closed and the resin drain pot  264  is evacuated to a first pressure P 1  of, e.g., from about 0 PSIA to about 2 PSIA. The resin fill pot  262  is left at a second pressure P 2  of, e.g., about ambient pressure, that is, about 14.7 PSIA. The valve  260  is then opened and the pressure differential between the drain pot  264  and the fill pot  262  causes resin to flow from the fill pot  262  into the compressed fiber plies  210  (i.e., into the “preform”) via the inlet runner  266 . After the resin has diffused through the fiber plies  210 , it flows into the drain pot  264  via the outlet runner  268 . 
         [0032]    A potential disadvantage of flowing resin into the fiber plies  210  in the foregoing manner is that the resin pressure in the plies  210  tends to equalize with the external pressure once the plies  210  are saturated. As a result, the external pressure alone may be insufficient to adequately compress the fiber plies  210  during cure. One way to avoid this problem is to use a supplemental mechanical device (not shown) to apply an external force to the caul  250  after resin infusion and during cure. Another approach is to re-evacuate the sealing layer  220  after the resin infusion process. 
         [0033]    Yet another method for avoiding the pressure equalization problem described above is to hold the resin fill pot  262  at a partial vacuum pressure during the resin infusion process, rather than letting it come up to ambient pressure. For example, in one embodiment, the fill pot  262  can be held at a partial vacuum pressure of about one-half an atmosphere, e.g., about 7 PSIA, while the resin drain pot  264  can initially be evacuated to, e.g., from about 0 PSIA to about 2 PSIA. In this way, the fiber plies  210  will have a net external pressure of about 7 PSIA exerted on them after the resin infusion process and during cure. 
         [0034]    The various fill and drain pot pressures described above are provided by way of example. In other embodiments, one or more of these pressures, and/or one or more of the resulting pressure differentials, may differ from those described above without departing from the spirit or scope of the present invention. 
         [0035]    Suitable methods for infusing fiber plies with resin are described in detail in co-pending U.S. patent application Ser. No. 10/485,725, entitled “Controlled Atmospheric Pressure Resin Infusion,” filed May 28, 2003 as PCT Application PCT/US03/16794, and incorporated herein in its entirety by reference. In addition, various mechanical, pneumatic, and/or hydraulic devices for applying pressure to material plies during lamination are disclosed in co-pending U.S. patent application Ser. No. 10/899,660, entitled “Methods and Systems for Manufacturing Composite Parts with Female Tools,” filed Jul. 26, 2004, and incorporated herein in its entirety by reference. 
         [0036]      FIG. 4  is an isometric view of a caul  450  configured in accordance with another embodiment of the invention. Various aspects of the caul  450  can be at least generally similar in structure and function to the caul  250  described above with reference to  FIGS. 2-3D . 
         [0037]    In one aspect of this particular embodiment, however, the caul  450  includes an exterior portion  470  having an uneven (i.e., a non-smooth) surface texture. For example, in the illustrated embodiment, the exterior portion  470  includes a plurality of ridges  472  arranged in a grid pattern. In another embodiment, the exterior portion  470  can include a plurality of grooves arranged in a grid or other pattern. In further embodiments, the exterior portion  470  can include other features giving it an uneven surface texture. Such features can include, for example, bumps, channels, spikes, ribs, perforations, etc. 
         [0038]    One feature of the caul  450  is that ridges  472  can facilitate the diffusion of resin through compressed fiber plies in a manner similar to the flow medium  240  described above with reference to  FIG. 2 . One advantage of this feature is that the flow medium  240  can be omitted when laminating with the caul  450  in certain embodiments. Omitting the flow media can reduce cost and simplify the manufacturing process. 
         [0039]    From the foregoing, it will be appreciated that specific embodiments of the invention have been described herein for purposes of illustration, but that various modifications may be made without deviating from the spirit and scope of the invention. For example, aspects of the invention described in the context of particular embodiments may be combined or eliminated in other embodiments. Further, while advantages associated with certain embodiments of the invention have been described in the context of those embodiments, other embodiments may also exhibit such advantages, and no embodiment need necessarily exhibit such advantages to fall within the scope of the invention. Accordingly, the invention is not limited, except as by the appended claims.
Tooling aids for applying pressure in laminating, and methods for their use, are described herein. In one embodiment, a caul for applying pressure in laminating includes a base portion positioned between first and second corner portions. The base portion can have a curved shape when it is in a relaxed state, but it moves to a flatter shape when subjected to pressure during lamination. Movement of the base portion to the flatter shape causes the first and second corner portions to move outwardly and away from the base portion. In this manner, the caul can be used to compact laminating materials into corner regions of a corresponding female mold surface.