Patent Publication Number: US-2023158712-A1

Title: System and method of forming a fiber preform for use in manufacturing a component made of a composite material

Description:
GOVERNMENT CLAUSE 
     This invention was made with government support under Grant No. DE-EE0009204 awarded by the U.S. Department of Energy. The Government has certain rights in this invention. 
    
    
     INTRODUCTION 
     The information provided in this section is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure. 
     The present disclosure relates to systems and methods for forming a fiber preform for use in manufacturing a component made of a composite material. 
     Composite materials are used for buildings, bridges, and structures such as boat hulls, swimming pool panels, shower stalls, bathtubs, storage tanks, sinks, and countertops. In the automotive industry, composite materials are used for interior trim components, structural components, underbody components, and closure parts. Composite materials are also used for components on spacecraft and aircraft. 
     Components made of composite materials are manufactured from fiber preforms constructed from yarns or fiber tows and formed into three-dimensional (3D) shapes. The fiber preforms are typically made using a 3D weaving process, a 3D braiding process, or a 3D lay of short fibers. One or more fiber performs are inserted into a mold, a resin is applied to the fiber preform(s), and the fiber preform(s) and the resin are molded into a composite component. 
     SUMMARY 
     The present application discloses a method of making a preform for use in manufacturing a component made of a composite material. In a first example, the method includes stitching fibers onto a film to form a fiber bed in a two-dimensional shape, removing the film from the fiber bed, and adjusting the fiber bed into a three-dimensional shape to form the preform. 
     In one aspect, the method further includes determining an amount by which the fibers are deformed when the fiber bed is adjusted from the two-dimensional shape to the three-dimensional shape, and determining, based on the fiber deformation amount, at least one of an orientation of the fibers within a plane of the fiber bed, a number of the fibers per unit area of the fiber bed, a material of stitches securing the fibers to the film, a number of the stitches per unit area of the fiber bed, and a length of the fibers between a pair of adjacent ones of the stitches. 
     In one aspect, the method further includes determining a first area of the fiber bed in which the fiber deformation amount is greater than the fiber deformation amount in a second area of the fiber bed, and stitching the fibers onto the film such that the fiber length in the first area of the fiber bed greater than the fiber length in the second area of the fiber bed. 
     In one aspect, the method further includes placing a piece of foam onto the film in the first area of the fiber bed before stitching the fibers onto the film to increase the fiber length in the first area. 
     In one aspect, the method further includes determining a first area of the fiber bed in which the fiber deformation amount is greater than the fiber deformation amount in a second area of the fiber bed, stitching the fibers onto the film using a first set of the stitches in the first area of the fiber bed, stitching the fibers onto the film using a second set of the stitches in the second area of the fiber bed, and melting the stitches in the first area of the fiber bed after removing the film from the fiber bed and before adjusting the fiber bed to the three-dimensional shape. The stitches in the first set are made of a first material, and the stitches in the second set are made of a second material that has a higher melting point than the first material. 
     In one aspect, the method further includes determining a first area of the fiber bed in which the fiber deformation amount is greater than the fiber deformation amount in a second area of the fiber bed, stitching the fibers onto the film in the second area of the fiber bed, and not stitching the fibers onto the film in the first area of the fiber bed. 
     In one aspect, the film is water-soluble, and the method further includes removing the film from the fiber bed by dissolving the film. 
     In one aspect, the film is paper, and the method further includes removing the film from the fiber bed by tearing the film. 
     In a second example of a method of making a preform for use in manufacturing a component made of a composite material, the method includes stitching first fibers onto a first film to form a first fiber bed in a first two-dimensional shape with a first dart, forming a lacing that extends across the first dart, and pulling the lacing to close the first dart and adjust the first fiber bed into a first three-dimensional shape. 
     In one aspect, the method further includes forming the lacing using the first fibers. 
     In one aspect, the method further includes loosening stitches securing the first fibers to the first film along edges of the first dart after forming the lacing and before pulling the lacing. 
     In one aspect, the method further includes removing the first film after stitching the first fibers onto the first film and before pulling the lacing. 
     In one aspect, the method further includes forming the first dart in the first two-dimensional shape of the first fiber bed by stitching the first fibers onto the first film in an area surrounding the first dart without stitching the first fibers onto the first film in an area of the first dart. 
     In one aspect, the method further includes determining a stress in the first fibers when the first fiber bed is adjusted from the first two-dimensional shape to the first three-dimensional shape, and forming the first dart in an area of the first fiber bed in which the fiber stress is greater than the fiber stress in another area of the first fiber bed. 
     In one aspect, the method further includes stitching second fibers onto a second film to form a second fiber bed in a second two-dimensional shape with a second dart, closing the second dart in the second fiber bed to adjust the second fiber bed to a second three-dimensional shape, and overlaying the first and second fiber beds so that (i) the second fiber bed covers the first dart in the first fiber bed and (ii) the first fiber bed covers the second dart in the second fiber bed. The first and second fiber beds form the preform. 
     In a third example of a method of making a preform for use in manufacturing a component made of a composite material, the method includes stitching fibers to a film to form a fiber bed having a two-dimensional shape, and adjusting the fiber bed to a three-dimensional shape to form the preform. Stitching the fibers to the film includes stitching the fibers to the film using a first number of stitches per unit area in a first area of the fiber bed, and stitching the fibers to the film using a second number of the stitches per unit area in a second area of the fiber bed. The first number is less than the second number. 
     In one aspect, the method further includes determining a stress in the fibers when the fiber bed is adjusted from the two-dimensional shape to the three-dimensional shape, and stitching the fibers to the film using the first and second numbers of stitches per unit area in the first and second areas of the fiber bed, respectively. The fiber stress in the first area is greater than the fiber stress in the second area. 
     In one aspect, the method further includes stitching a third number of the fibers per unit area to the film in the first area of the fiber bed, and stitching a fourth number of the fibers per unit area to the film in the second area of the fiber bed. The third number is less than the fourth number. 
     In one aspect, the method further includes removing the film after stitching the fibers to the film and before adjusting the fiber bed to the three-dimensional shape. 
     In one aspect, the first area of the fiber bed corresponds to a dart in the two-dimensional shape, and the method further includes loosening the stitches along edges of the dart after removing the film, and pulling those of the fibers extending across the dart to close the dart and adjust the fiber bed to the three-dimensional shape. 
     Further areas of applicability of the present disclosure will become apparent from the detailed description, the claims and the drawings. The detailed description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present disclosure will become more fully understood from the detailed description and the accompanying drawings, wherein: 
         FIG.  1    is a flowchart illustrating a first example of a method for forming a fiber preform according to the principles of the present disclosure; 
         FIGS.  2  through  7    are perspective and planar views of an example of a fiber preform, or a shape thereof, at various stages of the method of  FIG.  1   ; 
         FIG.  8    is a flowchart illustrating a second example of a method for forming a fiber preform according to the principles of the present disclosure; 
         FIGS.  9  through  14    are perspective and planar views of an example of a fiber preform, or a shape thereof, at various stages of the method of  FIG.  8   ; 
         FIG.  15    is a flowchart illustrating a third example of a method for forming a fiber preform according to the principles of the present disclosure; 
         FIGS.  16  through  20    are perspective and planar views of an example of a fiber preform, or a shape thereof, at various stages of the method of  FIG.  8   ; and 
         FIGS.  21  through  25    are perspective and planar views of an example of a fiber preform, or a shape thereof, at various stages of a fourth example of a method for forming a fiber preform according to the principles of the present disclosure. 
     
    
    
     In the drawings, reference numbers may be reused to identify similar and/or identical elements. 
     DETAILED DESCRIPTION 
     Some fiber preforms are initially formed in a two-dimensional (2D) shape by stitching fiber tows to a stabilizing fabric to form a fiber bed, and then adjusted to a 3D shape. The stabilizing fabric serves as a base layer to which the fiber tows are stitched. The stabilizing fabric is typically a plain weave or non-woven material that cannot stretch to match the contours of a complicated part. In addition, the multitude of stitches securing the fiber tows to the material cause the force required to shear the material to be high relative to regular non-crimp fabric or woven fabrics. In turn, it is difficult to shear the material to match the contours of a target component. 
     To address this issue, it may be desirable to remove the stitching in an area that needs to be sheared. However, this task is difficult for an operator to perform once the preform is manufactured, as the stitches are in multiple layers of the preform. Therefore, pieces of the preform are cut out and replaced with larger, more formable patches. This leads to inefficient use of the reinforcing materials, requires the preforms to be thicker than necessary, leads to racetracking during the molding process, adds cost to the overall operation, and slows the production of preforms. Racetracking occurs when a fiber perform does not uniformly fill a mold, which results in a gap to which resin races instead of filling up the entire composite part. 
     A method of forming a fiber preform according to the present disclosure addresses the above issues in one or more ways. In one way, the method uses a water-soluble film, or a film that is easily torn (e.g., newsprint paper), as the base layer to which the fiber tows are stitched so that the film may be dissolved or torn away from the fiber bed after the fiber bed is formed. Removing the film improves the formability of the fiber preform, which enables adjusting the fiber preform from its 2D shape to its 3D shape without damaging the fiber preform. 
     In another way, the method varies one or more parameters in areas of the fiber preform that are subjected to high shear when the fiber preform is adjusted from its 2D shape to its 3D shape. In one example, the method minimizes the number of stitches used to secure the fiber tows to the base layer in the high shear areas, does not stitch the fiber tows to the base layer in the high shear areas, and/or uses meltable stitches in the high shear areas. In another example, the method reduces the number of fiber tows crossing the high shear areas, or forms darts or gaps in the high shear areas so that the fiber tows do not extend across the high shear areas. 
     In another example, if darts are formed in the fiber preform, the method forms lacings that extend across the darts, and the method pulls the ends of the lacings to close the darts and adjust the fiber preform from its 2D shape to its 3D shape. The lacing may be formed from the fiber tows. The fiber tows forming the lacings may be stitched to the base layer along the edges of the darts using wider stitches with less thread tension relative to stitches in other areas to enable the fiber tows to slide. 
     Referring now to  FIG.  1   , a method of forming a preform  48  shown in  FIG.  6    begins at step  10 . At step  12 , the method analyzes the shape of the preform  48  to identify areas of high fiber deformation. For example, referring briefly to  FIGS.  2  and  3   , the method may determine a desired 3D shape  50  (e.g., a pyramidal frustum) of the preform  48 , and determine a 2D shape  52  (e.g., square) of the preform  48  that can be adjusted (e.g., folded, molded) to the desired 3D shape  50 . The method may then determine the amount of fiber deformation in the preform  48  as the preform  48  is adjusted from the 2D shape  52  to the 3D shape  50 . The method may make this determination using finite element analysis (FEA). 
     Referring again to  FIG.  1   , at step  14 , the method determines a desired orientation of fibers that form the preform  48  and a desired length of the fibers based on, for example, the fiber deformation as the preform  48  is adjusted from its 2D shape  52  to its 3D shape  50 . For example, referring briefly to  FIG.  7   , to form the preform  48  in its 2D shape  52 , fiber tows  54  are stitched to a backing  56 , such as a stabilizing fabric or film, to form a fiber bed  58  within a plane defined by an x-axis  60  and a y-axis  62 . Each fiber tow  54  includes thousands of the fibers bound together. 
     The fibers in the fiber tows  54  may be made of E-Glass, S-Glass, basalt, carbon, Kevlar®, or a combination thereof. The backing  56  may be made of a water-soluble material, such as polyvinyl alcohol, polyethylene glycol, polyvinyl alcohol acetates, polyethylene oxides, or a combination thereof, so that the backing  56  may be dissolved after the fiber bed  58  is formed. Alternatively, the backing  56  may be made of a material such as newsprint paper that is easily torn but stable enough to act as a substrate for the fiber tows  54 . In turn, the backing  56  may be torn away from the fiber bed  58  after the fiber bed  58  is formed. Removing the backing  56  improves the formability of the preform  48 , which enables adjusting the preform  48  from its 2D shape  52  to its 3D shape  50  without damaging the preform  48 . 
     The method may determine the orientation of each fiber tow  54  within the plane of the fiber bed, and determining the length of each fiber tow  54  between adjacent stitches securing the fiber tow  54  to the backing  56 . In the example shown, the orientation of each fiber tow  54  is generally parallel to the y-axis  60 . In addition, if each fiber tow  54  is stitched to the backing  56  at locations  64  where the routing of the fiber tow  54  changes direction, then the length of each fiber tow  54  is equal to a distance  66  between the locations  64 . 
     The method may determine the amount of fiber stress associated with multiple possible orientations of each fiber tow  54  using, for example, FEA, and select the fiber tow orientation that minimizes the fiber stress in areas of high fiber deformation. For example, if a central area  68  of the fiber bed  58  is to be confined or compressed in a depression in a tool to form the preform  48  in its 3D shape  50 , the method may select the fiber orientation that minimizes the fiber stress in the central area  68 . Thus, orienting the fiber tows  54  parallel to the y-axis  60  as shown may minimize the fiber stress in the central area  68  of the fiber bed  58 . 
     Similarly, the method may determine the amount of fiber stress associated with multiple possible lengths of each fiber tow  54  using, for example, FEA, and select the fiber tow length that minimizes fiber stress in areas of high fiber deformation. If the central area  68  of the fiber bed  58  is to be compressed to form the preform  48  its 3D shape  50 , the method may select the fiber tow length that minimizes the fiber stress in the central area  68 . For example, the method may increase the fiber tow length in the central area  68  of the fiber bed  58  relative to the fiber tow length in other areas of the fiber bed  58  as shown, which may minimize the fiber stress in the central area  68 . 
     Referring now to  FIGS.  1  and  4   , at step  16 , the method identifies high shear areas  70  in the fiber bed  58  where stitching is to be omitted or minimized. When the fiber bed  58  is adjusted from the 2D shape  52  to the 3D shape  50 , the amount of fiber deformation (e.g., the amount by which the fibers are bent) is greater in the high shear areas  70  than in other areas of the fiber bed  58 . The method may identify the high shear areas  70  using FEA. 
     At step  18 , the method may place a foam insert  72  onto the backing  56  in an area of the fiber bed  58  where additional fiber tow length is desired. As discussed above, the method may use a greater fiber tow length in areas of high fiber deformation relative to the fiber tow length used in other areas of the fiber bed  58 . Thus, the method may place the foam insert  72  in each of the high shear areas  70  as shown in  FIG.  4    to increase the fiber tow length in the high shear areas  70 . After the fiber tows  54  are stitched to the backing  56 , the foam insert  72  is disposed between the fiber tows  54  and the backing  56  and therefore increases the fiber tow length in the area(s) of the fiber bed  58  in which the foam insert  72  is placed. 
     At step  20 , the method stitches the fiber tows  54  to the backing  56  to form the fiber bed  58 , and the method uses a different stitch density in the high shear areas  70  of the fiber bed  58  when doing so. For example, the method may stitch the fiber tows  54  to the backing  56  using a first number of stitches  74  per unit area in the high shear areas  70  while using a second number of stitches  76  per unit area in all other areas of the fiber bed  58 . The first number is less than the second number. The first number may be zero, in which case the method does not stitch the fiber tows  54  to the backing  56  in the high shear areas  70  of the fiber bed  58 . 
     In addition to or instead of adjusting the fiber tow length and/or the stitch density in the high shear areas  70  of the fiber bed  58 , the method may adjust one or more (e.g., all) of the following in the high shear areas  70 : the fiber tow orientation, the stitch material, and/or the fiber tow density. For example, in the high shear areas  70 , the method may orient the fiber tows  54  perpendicular to fold lines  78  about which the fiber bed  58  is folded when the fiber bed  58  is adjusted from the 2D shape  52  to the 3D shape  50 . In the remainder of the fiber bed  58 , the method may orient the fiber tows  54  parallel to the vertical or horizontal edges of the fiber bed  58 . In addition, the method may route the fiber tows  54  in one layer in a different direction than the fiber tows  54  in another, separate layer to accommodate part complexity. 
     In another example, the method may form the stitches  74  in the high shear areas  70  of the fiber bed  58  from a first material, and the method may form the stitches  76  in all other areas of the fiber bed  58  from a second material. The first material may have a lower melting point than the second material so that the stiches  74  may be melted without melting the stitches  76 . The first material may be low density polyethylene, poly(ethylene adipate), poly(1-butene), poly(trans 1, 4-butadiene), or a combination thereof. The second material may be polyester, polyamide 6, polyamide  66 , glass, basalt, carbon or a combination thereof. 
     In another example, the method may stitch a third number of the fiber tows  54  per unit area to the backing  56  in the high shear areas  70 , and the method may stitch a fourth number of the fiber tows  54  per unit area to the backing  56  in all other areas of the fiber bed  58 . The third number is less than the fourth number. This concept is illustrated in  FIG.  7   , which shows fewer of the fiber tows  54  per unit area in the central area  68  of the fiber bed  58  relative to the number of the fiber tows  54  in the remainder of the fiber bed  58 . Reducing the fiber tow density in the central area  68  of the fiber bed  58  allows the fiber tows  54  to be more spaced in the direction of compression before becoming closely packed. This allows the mechanical properties of the final part to be unaffected in the central area  68 . 
     Referring now to  FIGS.  1  and  5   , at step  22 , the method removes the backing  56  from the preform  48  and, if the foam insert  72  is placed onto the backing  56 , the method removes the foam insert  72  from the preform  48 . The method removes the backing  56  from the preform  48  by dissolving the backing  56  in water or tearing the backing  56  away from the fiber bed  58 . At step  24 , the method dries the preform  48  if the backing  56  has been removed by dissolution. 
     At step  26 , the method melts any stitches, such as the stitches  74 , in the high shear areas  70  of the fiber bed  58 . At step  28 , the method adds a binder to the preform  48 . The binder may be made from an epoxy-based material or a urethane-based material. 
     At step  30 , the method inserts the preform  48  into a preform mold. At step  32 , the method molds the preform  48  into its final 3D shape, which is shown in  FIG.  6   . When the preform  48  is in its final 3D shape, the preform  48  may be inserted into a final mold and molded into a component made of composite material using, for example, high-pressure resin transfer molding (HP-RTM). Instead of adding binder to the preform  48  and inserting the preform  48  into the preform mold, the method may simply insert the preform  48  into the final mold. The method ends at step  34 . 
     Referring now to  FIG.  8   , a method of forming a fiber preform  150  shown in  FIG.  14    begins at step  100 . At step  102 , the method determines a 2D shape, such as a rectangle corresponding to a 2D shape  152  shown in  FIG.  10    without darts  154 , which is adjustable to a desired 3D shape  156  of the preform  150  shown in  FIG.  9   . For example, the method may flatten the 3D shape  156  into the 2D shape  152  using, for example, computer modeling. 
     At step  104 , the method analyzes the stress in the preform  150  when the preform  150  is adjusted from its 2D shape to its 3D shape  156 , and removes material in areas of high stress to form the darts  154  in the 2D shape  152  as shown in  FIG.  10   . For example, the method may form the darts  154  in the area of the fiber bed  164  in which the fiber stress is greater than the fiber stress in other areas of the fiber bed  164 . While the darts  154  have triangular shapes in the example shown, the darts  154  may have other shapes such as another polygonal shape or a shape with curved sides. The darts  154  improve the formability of the preform  150 , which enables adjusting the preform  150  from its 2D shape  152  to its 3D shape  156  without damaging the preform  150 . 
     At step  106 , if multiple ones of the preform  150  are needed to cover gaps, the method may point the darts  154  in different directions. For example, referring briefly to  FIG.  23   , the method may point two of the darts  154  in each preform  150  in a first direction  158  and point two of the darts  154  in each preform  150  in a second direction  160  that is perpendicular to the first direction  158 . In turn, when the preforms  150  overlay one another as shown in  FIG.  24   , the material of one of the preforms  150  covers the darts  154  in the other one of the preforms  150 . 
     Referring now to  FIGS.  8  and  11   , at step  108 , the method stitches fiber tows, such as the fiber tows  54  shown in  FIG.  7   , to a removable stabilizing film  162  to form a fiber bed  164  in the 2D shape  152 . In the example shown in  FIG.  11   , the method places and stitches the fiber tows onto the stabilizing film  162  in areas surrounding the darts  154  without placing or stitching the fiber tows onto the stabilizing film  162  in the areas of the darts  154 . Alternately, the method may place and stitch the fiber tows onto the stabilizing film  162  in the areas of the darts  154 , but decrease the density of the fiber tows in the area of the darts  154  relative to the fiber tow density in the remainder of the fiber bed  164 . 
     The stabilizing film  162  may be made of a water-soluble material, such as polyvinyl alcohol, polyethylene glycol, polyvinyl alcohol acetates, polyethylene oxides, or a combination thereof, so that the stabilizing film  162  may be dissolved after the fiber bed  164  is formed. Alternatively, the stabilizing film  162  may be made of a material such as newsprint paper that is easily torn but stable enough to act as a substrate for the fiber tows. In turn, the stabilizing film  162  may be torn away from the fiber bed  164  after the fiber bed  164  is formed. Removing the stabilizing film  162  improves the formability of the preform  150 , which enables adjusting the preform  150  from its 2D shape  152  to its 3D shape  156  without damaging the preform  150 . 
     Referring now to  FIGS.  8  and  12   , at step  110 , the method adds lacings  166  over the darts  154  using an adjusted stitch width and tension. For example, the width of stitches securing the lacings  166  to the stabilizing film  162  may be within a range from 10 percent to 50 percent greater than the width of stitches securing the fiber tows to the stabilizing film  162 . In another example, the tension of the stitches securing the lacings  166  to the stabilizing film  162  may be within a range from 10 percent to 50 percent less than the tension of the stitches securing the fiber tows to the stabilizing film  162 . The stitches may be formed from a stitching material such as polyester, polyamide 6, polyamide  66 , glass, basalt, carbon or a combination thereof. 
     In the example shown in  FIG.  12   , the method forms the lacings  166  from the fiber tows. The method accomplishes this by extending the fiber tows across the darts  154  and stitching the fiber tows to the stabilizing film  162  at edges  170  ( FIG.  11   ) of the darts  154  without stitching the fiber tows to the stabilizing film  162  in the areas of the darts  154 . The stitching material is only used along the edges  170  of the darts  154  in order to locate fixed points through which the lacings (fiber tows) can slide. The method does not stitch the fiber tows to the stabilizing film  162  in the areas of the darts  154  since the stabilizing film  162  is to be removed, at which point only the lacings are in the dart areas as shown in  FIG.  13   . 
     Referring now to  FIGS.  8 ,  12 , and  13   , at step  112 , the method removes the stabilizing film  162  from the preform  150 . The method removes the stabilizing film  162  from the preform  150  by dissolving the stabilizing film  162  in water or tearing the stabilizing film  162  away from the fiber bed  164 . The method dries the preform  150  if the stabilizing film  162  has been removed by dissolution. 
     Referring now to  FIGS.  8 ,  13 , and  14   , at step  114 , the method closes the darts  154  by pulling on ends  168  of the lacings  166  to draw together or overlap edges  170  ( FIG.  11   ) of the darts  154 . Pulling on the lacings  166  may also adjust the preform  150  from its 2D shape  152  shown in  FIG.  13    to its 3D shape  156  shown in  FIG.  14   . The method may then tie the ends  168  of the lacings  166  to one another to maintain the preform  150  in its 3D shape  156 . After forming the lacings  166  and before pulling the lacings  166  to close the darts  154 , the method may loosen the stiches securing the lacings  166  to the fiber bed  164  along the edges  170  of the darts  154  to enable the lacings  166  to slide through the stiches. 
     At step  116 , the method adds a binder to the preform  150 . The binder may be made from an epoxy-based material or a urethane-based material. At step  118 , the method inserts the preform  150  into a preform mold. At step  120 , the method molds the preform  150  in its final 3D shape, which is shown in  FIG.  14   . When the preform  150  is in its final 3D shape, the preform  150  may be inserted into a final mold and molded into a component made of composite material using, for example, HP-RTM. Instead of adding binder to the preform  150  and inserting the preform  150  into the preform mold, the method may simply insert the preform  150  into the final mold. The method ends at step  122 . 
     Referring now to  FIG.  15   , a method of forming a fiber preform  50  shown in  FIG.  20    begins at step  200 . At step  202 , the method determines a 2D shape, such as a rectangle corresponding to a 2D shape  252  shown in  FIG.  17    without darts  254 , which is adjustable to a desired 3D shape  256  of the preform  250  shown in  FIG.  16   . The method may flatten the 3D shape  256  into the 2D shape  252  using, for example, computer modeling. 
     At step  204 , the method analyzes the stress in the preform  250  when the preform  250  is adjusted from its 2D shape to its 3D shape  256 , and removes material in areas of high stress to form the darts  254  in the 2D shape  252  as shown in  FIG.  17   . For example, the method may form the darts  254  in the area of the fiber bed  264  in which the fiber stress is greater than the fiber stress in other areas of the fiber bed  264 . While the darts  254  have triangular shapes in the example shown, the darts  254  may have other shapes such as another polygonal shape or a shape with curved sides. The darts  254  improve the formability of the preform  250 , which enables adjusting the preform  250  from its 2D shape  252  to its 3D shape  256  without damaging the preform  250 . 
     At step  206 , if multiple ones of the preform  250  are needed to cover gaps, the method may point the darts  254  in different directions. For example, briefly referring to  FIG.  23   , the method may point two of the darts  254  in the preform  250  in a first direction  258  and point two of the darts  254  in the preform  250  in a second direction  260  that is perpendicular the first direction  258 . In turn, when the preforms  250  overlay one another as shown in  FIG.  24   , the material of one of the preforms  250  covers the darts  254  in the other one of the preforms  250 . 
     Referring now to  FIGS.  15  and  18   , at step  208 , the method stitches fiber tows  266  to a removable stabilizing film  262  to form a fiber bed  264  in the 2D shape  252 . In the example shown in  FIG.  18   , when stitching the fiber tows  266  to the stabilizing film  262 , the method uses less stitches per unit area in the area of the darts  254  relative to the number of stitches per unit area used in the remainder of the fiber bed  264 . In addition, the method uses fewer of the fiber tows  266  per unit area in the area of the darts  254  relative to the number of the fiber tows  266  per unit area used in the remainder of the fiber bed  264 . Each fiber tow  266  includes thousands of fibers bound together. 
     The fibers in the fiber tows  266  may be made of E-Glass, S-Glass, basalt, carbon, Kevlar®, or a combination thereof. The stabilizing film  262  may be made of a water-soluble material, such as polyvinyl alcohol, polyethylene glycol, polyvinyl alcohol acetates, polyethylene oxides, or a combination thereof, so that the stabilizing film  262  may be dissolved after the fiber bed  264  is formed. Alternatively, the stabilizing film  262  may be made of a material such as newsprint paper that is easily torn but stable enough to act as a substrate for the fiber tows. In turn, the stabilizing film  262  may be torn away from the fiber bed  264  after the fiber bed  264  is formed. Removing the stabilizing film  262  improves the formability of the preform  250 , which enables adjusting the preform  250  from its 2D shape  252  to its 3D shape  256  without damaging the preform  250 . 
     Those of the fiber tows  266  that extend across the darts  254  form lacings over the darts  254 . The fiber tows  266  that form the lacings are stitched to the stabilizing film  262  along edges  270  ( FIG.  18   ) of the darts  254 . The fiber tow density and the stitch density in the areas of the darts  254  may be within a range from 50 percent to 90 percent less than the fiber tow density and the stitch density, respectively, in all other areas of the fiber bed  264 . 
     Referring now to  FIGS.  15 ,  18 , and  19   , at step  210 , the method removes the stabilizing film  262  from the preform  250 . The method removes the stabilizing film  262  from the preform  250  by dissolving the stabilizing film  262  in water or tearing the stabilizing film  262  away from the fiber bed  264 . The method dries the preform  250  if the stabilizing film  262  has been removed by dissolution. At step  212 , the method loosens the stiches securing the lacings  266  to the stabilizing film  262  along the edges  270  of the darts  254  to enable the lacings  266  to slide through the stiches. 
     Referring now to  FIGS.  15 ,  19 , and  20   , at step  214 , the method closes the darts  254  by pulling on ends  268  of the lacings  266  to draw together or overlap the edges  170  of the darts  154 . The ends  268  of the lacings  266  are formed by cutting the fiber tows forming the lacings  266  on one side of each dart  254  along cut lines  269  ( FIG.  18   ). Forming the ends  268  of the lacings  266  in this way ensures that, after the stabilizing film  262  is removed, the portions of the lacings  266  adjacent to the ends  268  can slide while the portions of the lacings  266  on the other sides of the darts  254  are fixed. Pulling on the lacings  266  may also adjust the preform  250  from its 2D shape  252  shown in  FIG.  13    to its 3D shape  256  shown in  FIG.  14   . The method may then tie the lacings  266  to one another to maintain the preform  250  in its 3D shape  256 . After forming the lacings  266  and before pulling the lacings  266  to close the darts  254 , the method may loosen the stiches securing the lacings  266  to the stabilizing film  262  along the edges  270  ( FIG.  18   ) of the darts  254  to enable the lacings  266  to slide through the stiches. 
     At step  216 , the method adds a binder to the preform  250 . The binder may be made from an epoxy-based material or a urethane-based material. At step  218 , the method inserts the preform  250  into a preform mold. At step  220 , the method molds the preform  250  in its final 3D shape, which is shown in  FIG.  20   . When the preform  250  is in its final 3D shape, the preform  250  may be inserted into a final mold and molded into a component made of composite material using, for example, HP-RTM. Instead of adding binder to the preform  250  and inserting the preform  250  into the preform mold, the method may simply insert the preform  250  into the final mold. The method ends at step  222 . 
     Referring now to  FIGS.  21  through  25   , a method of forming the fiber preform  300  shown in  FIG.  25    is illustrated. The method of  FIGS.  21  through  25    is illustrated using preforms that are shaped similar to the preform  150  shown in  FIGS.  9  through  12    and the preform  250  shown in  FIGS.  15  through  20   . Therefore, the reference numbers for both of these preforms, and features thereof, are reused to describe the method of  FIGS.  21  through  25   . 
       FIG.  21    shows the desired 3D shape  156  or  256  of the preform  300 .  FIG.  22    shows the 2D shape  152  or  252  that is adjustable to the 3D shape  156  or  256 . The method may determine the 2D shape  152  or  252 , and determine where and how to form the darts  154  or  254  therein, in the manner described above with reference to steps  102 ,  104 , and  106  of  FIG.  8    or to steps  202 ,  204 , and  206  of  FIG.  15   . Once the 2D shape  152  or  252  is determined, the method forms the preform  150  or  250  in the manner described with reference to steps  108 ,  110 , and  112  of  FIG.  8    or to steps  208 ,  210 , and  212  of  FIG.  15   . 
       FIG.  23    shows two of the preforms  150 , two of the preforms  250 , or one of the preform  150  and one of the preform  250 . As discussed above, the preforms  150  and  250  have complementary patterns (e.g., the darts  154 ,  254  in the preforms  150  and  250  point in different directions).  FIG.  24    shows two of the preforms  150  overlaying one another, two of the preforms  250  overlaying one another, the preform  150  and the preform  250  overlaying one another. Since the preforms  150  and  250  have complementary patterns, the material in one of the preforms  150  or  250  covers the gaps (e.g., the darts  154 ,  254 ) in the other one of the preforms  150  or  250  when the preforms  150  or  250  overlay one another. The method may adjust the preforms  150   or  250  to their 3D shapes  156 ,  256  by, for example, pulling the lacings  166  or  266 , before arranging the preforms  150  to overlay one another. 
       FIG.  25    shows two of the preforms  150 , two of the preforms  250 , or the preform  150  and the preform  250  collectively forming the preform  300  in its 3D shape  156  or  256 . To form the preform  300 , the method may add binder to the preforms  150  or  250 , insert the preforms  150  or  250  into a preform mold so that the preforms  150  or  250  overlay one another, and then mold the preforms  150  or  250  into the preform  300 . The preform  300  may be inserted into a final mold and molded into a component made of composite material using, for example, HP-RTM. 
     The foregoing description is merely illustrative in nature and is in no way intended to limit the disclosure, its application, or uses. The broad teachings of the disclosure can be implemented in a variety of forms. Therefore, while this disclosure includes particular examples, the true scope of the disclosure should not be so limited since other modifications will become apparent upon a study of the drawings, the specification, and the following claims. It should be understood that one or more steps within a method may be executed in different order (or concurrently) without altering the principles of the present disclosure. Further, although each of the embodiments is described above as having certain features, any one or more of those features described with respect to any embodiment of the disclosure can be implemented in and/or combined with features of any of the other embodiments, even if that combination is not explicitly described. In other words, the described embodiments are not mutually exclusive, and permutations of one or more embodiments with one another remain within the scope of this disclosure. 
     Spatial and functional relationships between elements (for example, between modules, circuit elements, semiconductor layers, etc.) are described using various terms, including “connected,” “engaged,” “coupled,” “adjacent,” “next to,” “on top of,” “above,” “below,” and “disposed.” Unless explicitly described as being “direct,” when a relationship between first and second elements is described in the above disclosure, that relationship can be a direct relationship where no other intervening elements are present between the first and second elements, but can also be an indirect relationship where one or more intervening elements are present (either spatially or functionally) between the first and second elements. As used herein, the phrase at least one of A, B, and C should be construed to mean a logical (A OR B OR C), using a non-exclusive logical OR, and should not be construed to mean “at least one of A, at least one of B, and at least one of C.”