Patent Publication Number: US-2007108646-A1

Title: Method of fabricating a composite structure with details

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
      Not Applicable  
     STATEMENT RE: FEDERALLY SPONSORED RESEARCH/DEVELOPMENT  
      Not Applicable  
     BACKGROUND  
      The present invention relates to a method of fabricating a composite part having integral structural details.  
      Fiber composite parts may be generally formed into a wide variety of shapes. For example, composite fibers may be shaped as a fairing. However, due to fiber composite parts being generally more flexible in bending and less stiff compared to steel or aluminum, the solid laminate fairing fabricated of composite fibers may not be capable of withstanding high wind gusts thereby deforming the fiber composite fairing while the airplane is in motion. Wind gusts may buckle and stress the fiber composite fairing thereby ultimately possibly destroying the fiber composite fairing. As such, solid laminate fiber composite parts may have limited applicability to highly stressed conditions where the structure is subjected to bending loads.  
      Stiffeners may be incorporated into the fiber composite fairing to increase the stiffness of the fairing for withstanding the air gust and air pressures applied to the fairing as the airplane flies through the air. However, manufacturers of fiber composite parts have been unsuccessful in incorporating stiffeners into fairings in a cost efficient manner. Moreover, manufacturers of fiber composite parts have been unsuccessful in reliably incorporating stiffeners into an airplane fairing in a unitized fashion. One reason is that the resin may not flow through the fiber completely prior to resin cure thereby leaving dry areas of fiber. Another reason is that pooling of resin may occur as resin flows through the fiber. The state of the art requires that the stiffeners be fabricated separately and subsequently joined or assembled to the parent molded surface.  
      Accordingly, there is a need in the art for an improved method of fabricating a fiber composite part which incorporates structural details in a single unitized structure.  
     BRIEF SUMMARY  
      The present invention addresses the needs discussed above and discussed herein as well as those that are known in the art. As will be discussed in detail below, a method of fabricating a part with integral structural details will be discussed in relation to a fairing with stiffeners. However, the example (i.e., fairing with stiffeners) used to describe the method is not meant to limit the scope of this disclosure. Accordingly, it is contemplated that the description of the method may be variously embodied and employed to other types of parts such as trusses with integral structural details.  
      A fairing may define a control surface. The control surface may have a smooth curved configuration bounded by an upper horizontal edge, opposed curvilinear lateral edges, and a lower arc shaped interface which mates with an adjacent part of an assembly. On a rear side of the fairing, a plurality of horizontal and vertical stiffeners may be formed behind the control surface to stiffen the control surface.  
      The control surface may be formed by laying fiber on a molding surface of a tool mold. The molding surface may have a corresponding negative configuration of the control surface of the fairing. The tool mold may also have other surfaces for defining the upper horizontal edge, lateral opposed edges and the lower arc shaped interface.  
      The stiffeners may be fabricated by wrapping a plurality of detail molds, assembling the wrapped detail molds onto the molding surface, flowing resin through the fiber and curing the fiber. In particular, an interface surface and a detail surface of the detail mold may be wrapped with fiber. A top surface of the detail mold may be absent fiber such that the detail mold may be removed from the assembly after the resin has flowed through the fiber and the composite part is cured. The detail molds may be collectively assembled onto the tool mold in a jig saw configuration. Fibers laid on detail surfaces of adjacent detail molds may collectively form the stiffeners along the adjacent boundaries.  
      The fibers laid on the detail mold may be engaged to the detail mold via vacuum bagging. A plurality of detail molds wrapped with fiber may be inserted into a first vacuum bag. A continuous cloth material may be laid over each of the detail molds, and more particularly, the fiber wrapped about the detail molds. The cloth may also extend continuously to an output port of the first vacuum bag. The first vacuum bag may be sealed and a vacuum applied to the vacuum port. Air may be evacuated out of the first vacuum bag, and the first vacuum bag may apply pressure uniformly onto the fiber so as to compress the fiber onto the detail mold. After sufficient time has elapsed, the detail molds are removed from the first vacuum bag and assembled on the tool mold in the jig saw configuration.  
      The detail molds and the tool mold may be enclosed in a second vacuum bag. The second vacuum bag may have a plurality of resin input ports and at least one resin output port to flow resin through the fiber wrapped about the detail molds and fiber laid on the tool mold.  
      The second vacuum bag may be connected to a manifold and a resin reservoir via the resin input port. Also, the second vacuum bag may be connected to a vacuum pump via the resin output port. To flow resin through the fiber, the vacuum pump may be activated thereby evacuating the air from the vacuum bag. Resin may be drawn from the resin reservoir to the manifold. The manifold distributes the resin to the resin input ports of the second vacuum bag. Resin flows through the fibers wrapped on the detail molds and fibers laid on the tool mold. The resin is evacuated from the second vacuum bag via the resin output port(s) of the second vacuum bag. The resin drawn from the second vacuum bag may be collected in resin reservoirs. Since the resin is drawn into the second vacuum bag through the plurality of resin input ports, the resin flows uniformly throughout the fibers wrapped about the detail molds and the fibers laid on the tool mold. The reason is that flow of resin through the fiber is managed in smaller controllable portions.  
      The resin also flows uniformly through each of the detail molds via a system of resin input and resin channels formed integrally with each of the detail molds. The resin input may be formed at a central location of a top surface of the detail mold. The resin input may be a circular aperture which extends through the detail mold from the top surface to a bottom surface of the detail mold. The resin input may be in fluid communication with a plurality of resin channels integrally formed on the bottom surface of the detail mold. The plurality of resin channels may have a star burst configuration to promote a uniform flow front of resin toward the fibers laid on the interface surface of the detail mold. When resin flows through the second vacuum bag, resin flows through the resin input and through the resin channels. When the resin reaches the distal end of the resin channel, a back pressure is created to force or promote the resin flow front to reach the fiber uniformly. The resin flow front reaches the inner periphery of the fiber laid on the interface surface uniformly thereby promoting a resin flow through all of the fiber.  
      In another aspect of the method, a manifold may be placed on top of the assembled detail molds. A bottom surface of the manifold may have a mating configuration with the aggregate of top surfaces of the detail molds. The manifold bottom surface may have a system of resin channels that connect a resin input of the manifold to the resin inputs of the detail molds. When the manifold is laid on the top surfaces of the detail molds, a resin conduit is formed. The detail molds, tool mold and the manifold may be inserted into a second vacuum bag with a manifold resin input alignable to a resin input port of the second vacuum bag. Resin may be flowed through the resin input port through the manifold resin input which distributes the resin to the plurality of resin inputs of the plurality of detail molds. The second vacuum bag may also have an output port for drawing excess resin out of the second vacuum bag.  
      In another aspect of the method, a manufacturing output rate of a composite fiber part manufacturer may be increased with the method disclosed herein. The reason is that the method divides the labor required to build or fabricate the part into a plurality of more separate and manageable parts. For example, a first employee may wrap fiber about a first detail mold, a second employee may wrap fiber about a second detail mold, and a third employee may lay fiber on the tool mold.  
      The method discussed herein for fabricating the part with the detail has the following advantages. First, resin is distributed to a plurality of input ports and detail molds. This provides control of resin flow on smaller more manageable areas increasing the likelihood that the fiber is flowed with resin and pooling is less likely. This distributed flow of resin also reduces the rate of exotherm associated with the overall volume of resin, to allow for a longer infusion time prior to gelling of the resin and also enabling larger parts to be fabricated The method discussed herein may be referred to as affordable feature integration. Affordable feature integration facilitates parallel production flow resulting in faster throughput, reduced turn around times and reduced costs. Additionally, the manifold which distributes the resin into the plurality of resin input of the detail molds is configurable to fit any configuration of resin inputs. The detail molds may also be located on the tool mold using a third plate located by an external datum. Furthermore, this location of the detail molds provides precise positioning of the details thereby establishing control of the external surfaces of the part and “detolerancing” the internal location of the fiber layers. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      These and other features and advantages of the various embodiments disclosed herein will be better understood with respect to the following description and drawings, in which like numbers refer to like parts throughout, and in which:  
       FIG. 1  is a front view of a fairing fabricated via a method of wrapping fibrous material about a plurality of detail molds, laying fibrous material on a molding surface of a tool mold, assembling the detail molds and tool mold in a jig saw configuration, flowing resin through the fibrous material, and curing the resin;  
       FIG. 2  is a rear view of the fairing shown in  FIG. 1 ;  
       FIG. 3  is a first truss structure fabricated with the steps used to fabricate the fairing shown in  FIGS. 1 and 2 ;  
       FIG. 4  is a second truss structure fabricated with the steps used to fabricate the fairing shown in  FIGS. 1 and 2 ;  
       FIG. 5  is a perspective view of a tool mold with a portion thereof laid with fibrous material and a portion thereof not laid with fibrous material;  
       FIG. 6  is a flow chart of the method of fabricating a part with a detail;  
       FIG. 7  is a plurality of detail molds assembled on top of a molding surface of the tool mold;  
       FIG. 7A  is a cross-sectional view of a stiffener shown in  FIG. 6 ;  
       FIG. 8  is a bottom view of a detail mold illustrating fibrous material wrapped about an interface surface and a detail surface, and resin channels in a star burst configuration leading from a resin input, and dash lines showing a progression of a resin flow front;  
       FIG. 9  is a top view of the detail mold shown in  FIG. 7  illustrating a resin input at a central portion thereof;  
       FIG. 10  is a plurality of detail molds wrapped with fibrous material and inserted into a first vacuum bag for compressing the fibrous material onto the detail mold;  
       FIG. 11  is a system view of a resin distribution system, the resin distribution system has a resin reservoir filled with resin in fluid communication with a manifold which distributes the resin to a plurality of input ports of a second vacuum bag, the resin flows through the fibrous material laid on the detail molds and the tool mold and excess resin is evacuated from the second vacuum bag into resin reservoirs;  
       FIG. 12  is a top view of a manifold with a plurality of resin channels which distributes resin to the plurality of resin inputs of the detail molds; and  
       FIG. 13  is a cross-sectional view of the manifold and detail molds shown in  FIG. 12 . 
    
    
     DETAILED DESCRIPTION  
      Referring now to  FIGS. 1 and 2 , front and rear views of a fairing  10  fabricated with the method of the present invention are shown.  FIG. 1  illustrates the control surface  12  of the fairing  10 , and  FIG. 2  illustrates a plurality of stiffeners  14   a, b  on a back side  16  of the fairing  10 . The stiffeners  14  provide stiffness to the control surface  12  of the part  10 . It is also contemplated that the method of the present invention may be employed and embodied to fabricate parts other than a fairing  10 . By way of example and not limitation, the method of fabricating a part may be employed and embodied to fabricate truss structures  18   a, b,  as shown in  FIGS. 3 and 4 . Accordingly, the drawings and the descriptive portion of this disclosure is not meant to limit the scope of the present invention but is merely provided as an example of various embodiments and aspects of the present invention.  
      Referring now to  FIG. 5 , a tool mold  20  of the fairing  10  is shown. A molding surface  22  of the tool mold  20  may have a smooth exterior surface. More particularly, the molding surface  22  of the tool mold  20  may have a negative configuration of the control surface  12 . The molding surface  22  of the tool mold  20  may have a different configuration based on the function of the part to be fabricated.  
      Fibrous material  24  may be laid on the molding surface  22  of the tool mold  20 . The fibrous material  24  may be provided in a sheet form and cut to size to fit the molding surface  22  of the tool mold  20 . Additionally, a curved lower portion  26  (see  FIG. 1 ) of the fairing  10  may be fabricated by laying an arc shaped fibrous material layer  28  on a corresponding bridge  30  formed on the tool mold  20 . The entire molding surface  22  of the tool mold  20  may be laid with one or more fibrous material layers  24  depending on the specific application of the part to be fabricated. The fibrous material  24  laid on the tool mold molding surface  22  defines the control surface  12  of the fairing  10  and the back surface  16  of the fairing  10  as well. Stiffeners  14 , and more generically, details may be fabricated on the back surface  16  of the fairing  10  to increase the stiffness of the fairing  10 . These stiffeners  14  may be co-cured with the fairing  10 /control surface  12 . The stiffeners  14  represent one embodiment of the detail that may be fabricated on the part. It is also contemplated that other types of details may be fabricated with the part having various configurations and functions.  
      Referring to  FIG. 6 , the stiffeners  14  are fabricated with the control surface  12  by providing a plurality of detail molds  200 , providing a tool mold  202 , wrapping fibrous material  204  about the detail molds, laying fibrous material  206  on the molding surface of the tool mold, arranging  208  the detail molds on the tool mold so as to collectively form the details, flowing resin  210  through the fibrous material, co-curing  212  the resin and detaching  214  the detail molds and tool mold from the fibrous material. For example, a first detail mold  32   a  (see  FIGS. 7 and 7 A) and a second detail mold  32   b  (see  FIGS. 7 and 7 A) disposed adjacent to each other may define one of the stiffeners  14  (see  FIG. 7A ). As shown in  FIG. 7A , the first detail mold  32   a  may have fibrous material  24   a  wrapped about an interface surface  34   a  and a detail surface  36   a.  The fibrous material wrapped on the detail mold  32 A may have a reversed L-shaped configuration. Likewise, the second detail mold  32   b  may have fibrous material  24   b  wrapped about the detail surface  36   b  and the interface surface  34   b  with an L-shaped configuration. The fibrous materials  24   a, b  wrapped on the interface surfaces  34   a, b  may be disposed adjacent to the molding surface  22  of the tool mold  20 . The fibrous materials  24   a  wrapped on the detail surface  36   a  of the detail mold  32   a  may be disposed adjacent to fibrous material  24   b  wrapped on the detail surface  36   b  of adjacent detail mold  36   b.  Resin may be flowed through the fibrous material  24   a, b  wrapped about the first and second detail molds  32   a, b  as well as the fibrous material  24   c  laid on the molding surface  22  of the tool mold  20  and co-cured. When the resin is cured, a strong bond is formed between the fibrous materials  24   a, b  wrapped on the first and second detail molds  32   a, b  and the fibrous materials  24   c  laid on the molding surface  22 .  
      In another example, as shown in  FIG. 7 , the first detail mold  32   a,  the second detail mold  32   b,  a third detail mold  32   c  and fourth detail mold  32   d  may be disposed adjacent to each other with a corner of each mold  32   a - d  at a common point to collectively define an intersection  38  of the horizontal stiffener  14   a  and the vertical stiffener  14   b.  The interface surface  34  and the detail surface  36  of each of the detail molds  32   a - d  may be wrapped with fibrous material  24  thereabout. The interface surface  34  may be disposed adjacent to the molding surface  22  of the tool mold  20 , whereas, the detail surface  36  may be disposed adjacent to detail surfaces  36  of adjacent detail molds  32 . The fibrous materials  24  wrapped on the detail molds  32  and the fibrous materials  24  laid on the molding surface  22  of the tool mold  20  collectively have a configuration of the details.  
       FIGS. 8 and 9  are a bottom view and a top view, respectively, of the detail mold  32  wrapped with fibrous material  24 . More particularly,  FIG. 9  illustrates a top view of the detail mold  32 . A center of the top surface  40  may be formed with an aperture or resin input  42  that extends through to the interface surface or bottom surface  34  of the detail mold  32 , as shown in  FIGS. 8 and 9 . As shown, the resin input  42  extends through the entire thickness of the detail mold  32 . Moreover, a plurality of resin channels  46  are formed with a star burst configuration. (See  FIG. 8 ). The resin channels  46  extend toward but do not extend to the inner perimeter  48  of the fibrous material  24  laid on the interface surface  34  of the detail mold  32 . The fibrous material  24  may be wrapped on the interface surface  34  as well as the detail surface  36 . As shown in  FIG. 8 , the fibrous material  24  may be wrapped about the entire periphery of the detail mold  32  on the interface surface  34  as well as the detail surface  36 .  
      Referring now to  FIG. 10 , the plurality of detail molds  32   d - f  wrapped with fibrous material  24  may be inserted into a first vacuum bag  50  with a continuous cloth member  52  extending from a vacuum port  54  of the first vacuum bag  50  to each of the detail molds  32   d - f.  The first vacuum bag  50  may be hermetically sealed and a vacuum applied to the vacuum port  54  to evacuate the air from the first vacuum bag  50 . Upon evacuation, the first vacuum bag  50  applies uniform pressure on the fibrous material  24  to compress the fibrous material  24  onto the interface surface  34  and the detail surface  36  of the detail molds  32   d - f.  After sufficient time has elapsed for the fibrous material  24  to engage the detail molds  32   d - f,  the detail molds  32   d - f  may be collectively arranged in a jig-saw style manner on the molding surface  22  of the tool mold  20 , as shown in  FIG. 7 .  
      Resin may be flowed through the fibrous material  24  wrapped on the detail mold  32  and laid on the tool mold  20  and co-cured together to form the fairing  10  with stiffeners  14 . In particular, the tool mold  20  and the detail molds  32  may be placed or inserted into a second vacuum bag  56 , as shown in  FIG. 11 . The second vacuum bag  56  may have a plurality of resin input ports  58  that are alignable to the resin inputs  42  of the detail molds  32 , as shown in  FIG. 11 . The second vacuum bag  56  may also have a plurality of output ports  60  for applying a vacuum to draw resin  62  through the resin input ports  58  to the output ports  60 . When the resin  62  is flowed from the resin input port  58  to the resin output port  60 , resin  62  flows through the fibrous material  24  laid on the tool mold  20  as well as the fibrous material  24  wrapped on the detail molds  32 .  
      More particularly, the second vacuum bag  56  may be laid on an outer periphery  64  of the tool mold  20 , as shown in  FIG. 11 . A periphery  66  of the second vacuum bag  56  shown in  FIG. 11  may be hermetically sealed to the periphery  64  of the tool mold  20  thereby forming a vacuum-tight cavity wherein the fibrous materials  24  laid on the tool mold  20  and the detail mold  32  are trapped therein. In the alternative, the second vacuum bag  56  may entirely enclose the tool mold  20  and the plurality of detail molds  32 . The plurality of input ports  58  may be attached to a plurality of resin hoses  68  which are in fluid communication with a resin reservoir  70  filled with resin  62 . The plurality of output ports  60  may be connected to a flexible tube  72  in fluid communication with a vacuum pump  74 . When the second vacuum bag  56  is sealed, the vacuum pump  74  may be activated to create a vacuum within the second vacuum bag  56 . At this point, resin  62  may flow from the resin reservoir  70  to a manifold  76  which distributes resin  62  to the plurality of input ports  58 . The resin input ports  58  are aligned to the resin inputs  42  formed in the detail molds  32 . The resin  62  then proceeds through the resin inputs  42  of the detail molds  32  and flows through the resin channels  46  (see  FIG. 8 ) toward the fibrous material  24  wrapped on the interface surface  34  and the detail surface  36  of the detail molds  32 . When the resin  62  reaches the distal end  78  of the resin channels  46 , as shown in  FIG. 8 , a back pressure is created to thereby squeeze out the resin  62  with a uniform flow front  80   a, b  shown in  FIG. 8  by the dashed lines. Flow fronts  80   a  and  80   b  shows the uniform development of the flow front  80  as the resin  62  flows under the detail mold  32 . The resin flow front  80   a, b  proceeds toward the fibrous material  24  laid on the interface surface  34  of the detail mold  32  and flows upward into the fibrous material  24  laid on the detail surface  36 . The vacuum draws the resin  62  through the resin output ports  60  and into a resin reservoir  82 . Prior to the flow of resin  62  through the fibrous material  24 , the fibrous material  24  may be heated to an operating temperature based on the selection of the fibrous material  24  and the resin combination. It is also contemplated that a resin/fibrous material combination may be matched such that the resin  62  is flowed through the fibrous material  24  and then raised to a cure temperature to co-cure the part with the detail.  
      In the alternative, as shown in  FIG. 12 , a manifold  84  having a single resin input  86  and a plurality of resin channels  88  may be placed on top of the plurality of assembled detail molds  32  wherein the resin channels  88  of the manifold  84  provides a resin flow path from the resin input  86  of the manifold  84  to the resin input  42  of the detail molds  32 . In particular, as shown in  FIG. 13 , a bottom surface  90  of the manifold  84  may mate with the top surfaces  40  of the detail molds  32  so as to form a resin flow path  92  through the resin channels  88  of the manifold  84 . The resin reservoir  70  may be in fluid communication with the resin input port  58  of the second vacuum bag  56  which is alignable to the resin input  86  of the manifold  84 . When vacuum is applied to the second vacuum bag  56 , resin  62  flows from the resin reservoir  70  through the resin input port  58  of the second vacuum bag  56  and through the resin input  86  of the manifold  84  and distributes the resin  62  to the resin inputs  42  of the detail molds  32  via the resin channels  88  of the manifold  84 . The manifold  84  may be fabricated from a formable material such as glass or a rigid material such as aluminum based on the contour of the top surfaces  40  of the detail molds  32 .  
      The manifold  84  may also serve the purpose of locating the detail molds  32  with respect to the tool mold  20 . In particular, if the detail molds  32  are merely laid on top of the molding surface  22  of the tool mold  20 , the location of the detail molds  32  may be considerably varied based on a contention that the detail molds  32  are designed to have some space therebetween when they  32  are disposed on the tool mold  20  in the jig saw configuration. To more accurately locate the detail molds  32  with respect to the tool mold  20 , as shown in  FIG. 12 , the manifold  84  may be fixed to a datum  94  via pins  102 . Pin apertures  98  (see  FIGS. 12 and 13 ) may also be formed in the manifold  84  above each of the detail molds  32  and a pin hole  100  (see  FIGS. 12 and 13 ) aligned to the pin aperture  98  may be formed in each of the detail molds  32 . The pin  102  (see  FIGS. 12 and 13 ) may be inserted into each of the pin apertures  98  of the manifold  84  and respective pin holes  100  of the detail molds  32  to locate the detail molds  32  with respect to the datum  94 . In this manner, the detail molds  32  are located with respect to the datum  94  via the manifold  84  and not merely placed on top of the molding surface  22  and positioned by an interference fit therebetween.  
      In another aspect of the method disclosed herein, the method of fabricating a part having a detail enables a business to divide the labor of fabricating the part having the detail. The method permits a plurality of employees to work on respective detail molds  32  and tool mold  20 . In particular, as discussed above, there may be a plurality of detail molds  32  and a tool mold  20  which may be wrapped and laid with fibrous material  24  and assembled together, flowed with resin  62 , and co-cured to produce a part having a detail. Advantageously, each of the detail molds  32  may be worked on by different employees, and also, the tool mold  20  may be worked on by a different employee than those working on the detail molds  32 . As such, a plurality of employees may work on a single part having details thereby dividing the labor to fabricate the part having the detail. For example, if the part having the detail requires four detail molds  32  and one tool mold  20 , and each detail mold  32  requires one man hour to finish and the tool mold  20  requires two man hours, then the total number of man hours required to fabricate the part would be six man hours. Accordingly, a business having one employee working on the detail molds  32  and the tool mold  20  of the part may fabricate one part every six hours. Advantageously, with the method discussed above in fabricating the part having the detail, the business may have three employees working on the detail molds  32  and the tool mold  20 . Two employees may each work on two of the detail molds  32  thereby completing the work required on four detail molds  32  in two hours. The third employee may work on the tool mold  20  and complete work on the tool mold  20  in two hours. Accordingly, the business may fabricate one part having the details every two hours. By this simple illustration, the output of the business may be increased threefold.  
      The above description is given by way of example, and not limitation. Given the above disclosure, one skilled in the art could devise variations that are within the scope and spirit of the invention disclosed herein. Further, the various features of the embodiments disclosed herein can be used alone, or in varying combinations with each other and are not intended to be limited to the specific combination described herein. Thus, the scope of the claims is not to be limited by the illustrated embodiments.