Abstract:
A process for the production of a fiber profile ( 32 ) that is designed to fill in a space with a nail-head-shaped or half-nail-head-shaped cross-section that originates from the assembly of preforms in a T shape, of which at least one includes a curvature radius at the junction zone of the preforms, includes: supplying powder-coated fibers ( 28 ) to a preforming station ( 30 ) where the powder is activated and the fibers ( 28 ) move into a passage whose shapes are adapted to those of the desired profile, and then making the preformed fibers move into a shaping station ( 34 ) where the fiber profile ( 32 ) is cooled and shaped by circulating in a cavity whose shapes are adapted to those of the desired profile.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to a process for the production of a profile made of composite material fibers that has a half-nail-head or nail-head cross-section. The invention also relates to the device for the implementation of said process as well as the thus obtained profile. 
     Certain pieces made of composite material are produced from assembled fibrous reinforcement preforms, arranged in a mold and then immersed in a resin matrix. 
     To obtain a T shape, according to a first embodiment that is illustrated in  FIG. 1 , three preforms are assembled: a first preform  10  that is called an essentially flat plate, and then two other L-shaped preforms  12 ,  12 ′ that are arranged symmetrically, each of the L-shaped preforms having a first wing that is flattened against a wing of the other L-shaped preform and a second wing that is flattened against the plate  10 . Since, at the junction of the wings, the L-shaped preforms  12 ,  12 ′ have a more or less significant curvature radius, there is a space  14  that has the shape of a nail head at the junction of the three preforms. In this case, this space  14  has a cross-section with a flat surface and two concave and curved surfaces. 
     According to another embodiment that is illustrated in  FIG. 2 , at least three preforms are assembled: a first preform  20  that is called a plate, essentially flat, a second preform  22  that forms the base of the T of which one edge is flattened against the plate  20 , and at least a third L-shaped preform  24  whose first wing is flattened against the plate  20 , whereby the other wing is flattened against the preform  22 . Since, at the junction of the wings, the preform  24  has a more or less significant curvature radius, there is a space that has the shape of a half-nail head  26  at the junction of the preforms  20  to  24 . In this case, this space  26  has a cross-section with two flat surfaces and a concave and curved surface. 
     To ensure the soundness of the material of the piece that results from proper control of the resin injection, the space  14  or  26  should be filled with fibrous reinforcements. 
     According to one embodiment, an operator forms pre-impregnated or powdered carbon fibers into strands so as to obtain a strand  27  with a circular cross-section. He then positions the strand  27  that is thus produced in the space  14  or  26  using, for example, an adhesive strip, and then he heats it with an iron so that said strand  27  is made integral with the other preforms. 
     This embodiment is not satisfactory because it does not make it possible to achieve optimized filling of the space  14  or  26 , taking into account the essentially circular cross-section of the strand. The unfilled cavities promote the appearance of preferred paths of resin that disturb the filling of the mold and consequently increase the risks of greatly porous zones and/or dry zones. 
     According to another drawback, as illustrated in  FIG. 3 , the surrounding sub-preforms of the strand  27  that is used to fill the space  14  or  26  are deformed during the assembly of the preforms or during the closing of the mold, which affects the mechanical characteristics of the thus produced piece because of the undulations of the fibers. 
     BRIEF SUMMARY OF THE INVENTION 
     Also, the purpose of this invention is to overcome the drawbacks of the prior art by proposing a process for the production of a composite material profile that has a half-nail-head or nail-head cross-section that makes it possible to optimally fill in a space between the preforms that are assembled in a T shape so as to obtain a composite material piece in order to guarantee the required mechanical characteristics of said composite material piece. 
     For this purpose, the invention has as its object a process for the production of a fiber profile that is designed to fill in a space with a nail-head-shaped or half-nail-head-shaped cross-section that originates from the assembly of preforms in a T shape, of which at least one comprises a curvature radius at the junction zone of said preforms, characterized in that it consists in supplying powder-coated fibers to a preforming station where said powder is activated and said fibers move into a passage whose shapes are adapted to those of the desired profile, and then in making said preformed fibers move into a shaping station where said fiber profile is cooled and shaped by circulating in a cavity whose shapes are adapted to those of the desired profile. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other characteristics and advantages will emerge from the following description of the invention, a description that is provided by way of example only, relative to the accompanying drawings in which: 
         FIG. 1  is a cutaway that illustrates a first variant of assembly of preforms that delimit a space with a nail-head shape, 
         FIG. 2  is a cutaway that illustrates another variant of assembly of preforms delimiting a space with a half-nail-head shape, 
         FIG. 3  is a cutaway that illustrates an assembly of preforms with a strand according to the prior art that is used to fill in a space between the preforms as illustrated in  FIG. 2 , 
         FIG. 4  is a perspective view of a device for producing a fiber profile according to the invention, 
         FIG. 5  is a view that illustrates a part of the device of  FIG. 4  that allows the preforming and shaping of a fiber profile according to the invention, 
         FIG. 6  is a cutaway of the preforming means of the device according to the invention, 
         FIG. 7A  is a diagram of the preforming means according to a first variant of the invention that are suitable for obtaining a profile with a half-nail-head-shaped cross-section, 
         FIG. 7B  is a diagram of the preforming means according to another variant of the invention that are suitable for obtaining a profile with a nail-head-shaped cross-section, 
         FIG. 8A  is a diagram of the shaping means according to a first variant of the invention that are suitable for obtaining a profile with a half-nail-head-shaped cross-section, 
         FIG. 8B  is a diagram of the shaping means according to another variant of the invention that are suitable for obtaining a profile with a nail-head-shaped cross-section, 
         FIG. 9  is a diagram that illustrates another variant of the shaping means, 
         FIG. 10  is a perspective view of the means for powdering fibers that are used to produce a fiber profile according to the invention, 
         FIG. 11  is a cutaway that illustrates the means for storing and unwinding fibers that are used for producing a fiber profile according to the invention, 
         FIG. 12  is a fraction that illustrates an assembly of preforms that integrate a profile with a half-nail-head-shaped cross-section according to the invention, 
         FIG. 13  is a diagram that illustrates another variant of the shaping means that make it possible to obtain a curved profile, and 
         FIG. 14  is a diagram that illustrates another variant of the shaping means that make it possible to obtain a curved profile. 
     
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
       FIG. 1  shows a first variant of an assembly of preforms that are arranged in the shape of a T, comprising a first preform  10  that is called an essentially flat plate, as well as two other L-shaped preforms  12 ,  12 ′ that are arranged symmetrically, each of the L-shaped preforms having a first wing that is flattened against a wing of the other L-shaped preform, and a second wing that is flattened against the plate  10 . Since, at the junction of the wings, the L-shaped preforms  12 ,  12 ′ have a more or less significant curvature radius, there is a space  14  that has a nail-head-shaped cross-section at the junction of the three preforms. In this case, this space  14  has a cross-section with a flat surface and two concave and curved surfaces. 
       FIG. 2  shows another variant of an assembly of preforms that are arranged in the shape of a T, comprising a first preform  20  that is called a plate, essentially flat, a second preform  22  that forms the base of the T of which one edge is flattened against the plate  20 , and at least a third L-shaped preform  24  of which a first wing is flattened against the plate  20 , whereby the other wing is flattened against the preform  22 . Since, at the junction of the wings, the preform  24  has a more or less significant curvature radius, there is a space that has a half-nail-head-shaped cross-section  26  at the junction of the preforms  20  to  24 . In this case, this space  26  has a cross-section with two flat surfaces and a concave and curved surface. 
     According to the two variants, at least one of the preforms that are assembled so as to form a T comprises a curvature radius at the junction zone of said preforms. 
       FIG. 4  shows a device that makes it possible to produce a fiber profile with a half-nail-head- or nail-head-shaped cross-section according to the invention. This device comprises powder-coated fiber supply means  28 , a preforming station  30  at a temperature that is greater than or close to the temperature of use of said powder that makes it possible to obtain a fiber profile  32 , and a shaping station  34  that ensures a cooling of the profile  32  to guarantee the required dimensions to said profile. 
     According to one embodiment, the powdered fiber supply means  28  comprise two parts: a first part that comprises several reels  36  of dry fiber rolls  38  (visible in  FIG. 11 ) that are mounted on a support called a creel  40  as well as a second part that comprises means  42  for powdering dry fibers  38 . 
     Preferably, the reel  36  comprises means for adjusting the tension of the fibers to ensure proper operation of the device. According to the example that is illustrated in  FIG. 11 , the reel  36  comprises an axis of rotation  44  that is fixed on the creel  40  as well as a nut  46  that makes it possible to adjust the tightening of the roll. This tightening makes it possible to prevent the rolls from unwinding in an uncontrolled manner under the action of the weight of the fibers at the output of the roll and to obtain a tension of the fibers in the device. This tension is necessary in particular for ensuring proper operation of the powdering means  42 . 
     According to one embodiment, the powdering means comprise at least one powdering station that is illustrated in details in  FIG. 10 . The powdering means can comprise two stations as illustrated in  FIG. 4 . 
     This station comprises a powder storage hopper  48 , a drum  50  to whose surface the powder is brought by a first scraper  52  and against which the dry fibers  38  are flattened. The powder that has not adhered to the fibers falls into a recovery tank  54 . Preferably, a second scraper  56  can be provided for removing excess powder. 
     By way of example, the powder can be a thermosetting resin powder or a thermoplastic resin powder. 
     The powdered fibers  28  then penetrate the preforming station  30  comprising means for activating the powder and means for pressing the fibers  28  against one another so as to obtain a fiber profile  32 . 
     According to an embodiment that is illustrated in  FIGS. 5 ,  6 ,  7 A and  7 B, the preforming station  30  comprises two rollers  58 ,  58 ′ whose axes of rotation are arranged perpendicular to the direction of advance of the fibers  28 , preferably horizontally. 
     At its peripheral surface, at least one of the rollers  58 ,  58 ′ comprises a groove  60  into which the fibers move. 
     Preferably, the lower roller  58  comprises a groove  60 . 
     The rollers are arranged so that their peripheral surfaces are tangent in order to define a passage  62  whose dimensions are adapted to those of the fiber profile that is to be obtained. 
     In the case of a fiber profile with a half-nail-head-shaped cross-section as illustrated in  FIGS. 6 and 7A , the lower roller  58  has a right-angled V-shaped groove, whereas at its peripheral surface, the upper roller  58 ′ has a convex curved shape that is adapted to the concave and curved shape of the fiber profile that it is desired to obtain. 
     In the case of a fiber profile with a nail-head-shaped cross-section as illustrated in  FIG. 7B , the lower roller  58  has a V-shaped groove with curved and convex wings whose shapes are adapted to the curved and concave shapes of the profile that it is desired to obtain whereas the upper roller  58 ′ has an essentially rectilinear peripheral surface. 
     According to the variants, means can be provided for extending closer toward the axes of rotation of the rollers  58 ,  58 ′ so as to exert pressure on the fibers. 
     According to one embodiment, the activation of the powder is achieved by heating by bringing said powder to a temperature that is greater than or close to its temperature of use. In this case, at least one of the rollers comprises heating means, for example a resistor. As a variant, the rollers  58 ,  58 ′ can be placed in a chamber and/or means for blowing hot air can be provided for heating the powdered fibers  28 . 
     According to an embodiment that is illustrated in  FIGS. 5 ,  8 A and  8 B, the shaping station  34  comprises two belts  64 ,  64 ′ that work with one another so as to define a cavity  66  in which the profile of hot fibers leaving the preforming station  30  is arranged. 
     The belts  64 ,  64 ′ each use an essentially rectilinear portion  68 , or  68 ′, stretched between two pulleys  70 , or  70 ′. 
     To the right of these essentially rectilinear portions  68 ,  68 ′, the belts  64 ,  64 ′ work together so as to define a cavity  66 . Means  72  are provided for flattening the belts  64 ,  64 ′ against one another so as to exert pressure on the fiber profile so that the rotation of the belts produces the continuous driving of the fibers and the fiber profile in the device. 
     The shaping station makes it possible to cool the fiber profile and to calibrate it so as to impart to it a cross-section with precise dimensions that are adapted to the space  14  or  26  that is housed between the preforms. 
     In the case of a profile with a half-nail-head-shaped cross-section as illustrated in  FIG. 8A , a belt  64  comprises a cross-section with a hollow right-angled V-shape whereas the other belt  64 ′ comprises a cross-section with a projecting shape with a curved and convex portion that is adapted to the concave and curved shape of the fiber profile that it is desired to obtain. 
     In the case of a profile with a nail-head-shaped cross-section as illustrated in  FIG. 8B , a belt  64  comprises a hollow V-shaped cross-section with curved and convex wings whose shapes are adapted to the curved and concaves shapes of the profile that it is desired to obtain whereas the other belt  64 ′ comprises a cross-section with a flat shape. 
     As appropriate, it is possible to use at least one porous belt  64 ,  64 ′ that is subjected locally to a negative pressure housed in a chamber  74  so as to improve adhesion to the profile, as illustrated in  FIG. 9 . 
     As appropriate, it is possible to obtain a rectilinear profile, as illustrated in  FIGS. 5 and 9 , or a curved profile as illustrated in  FIGS. 13 and 14 . 
     In the case of a curved profile, the shaping station  34  comprises, as above, two belts  64 ,  64 ′ that work with one another so as to define a cavity  66  in which the hot fiber profile that exits from the preforming station  30  is arranged. 
     The belts  64 ,  64 ′ each use a shaping portion  68 , or  68 ′, between two pulleys  70 , or  70 ′. Contrary to the variant that is illustrated in  FIG. 5 , the shaping portions  68 ,  68 ′ are not rectilinear but curved so as to impart a curved shape to the profile. As for the variant that makes it possible to obtain a rectilinear profile, to the right of the shaping portions  68 ,  68 ′, the belts  64 ,  64 ′ work together so as to define a cavity  66 . Means  72  are provided to flatten the belts  64 ,  64 ′ against one another so as to exert pressure on the fiber profile in order that the rotation of the belts produces the continuous driving of the fibers and the fiber profile in the device. 
     In the case of a curved profile, the belts  64  and  64 ′ are curved in the zone where they work together. 
     According to a first variant that is illustrated in  FIG. 13 , the means  72  can come in the form of a friction pad  76  that is made of a material with a low friction coefficient whose surface that is in contact with one of the belts  64 ,  64 ′ (the belt  64 ′ in  FIG. 13 ) has a shape that is adapted to the desired curvature radius of the profile. 
     According to another variant that is illustrated in  FIG. 14 , the means  72  can come in the form of a series of rollers  78  whose pivoting axes are arranged based on the desired curvature radius of the profile. 
     In addition, the device of the invention can comprise means  80  for cutting the profile, for example, at least one flange for tightening the profile and a rotary disk for slicing it. 
     The process of the invention makes it possible to obtain a fiber profile whose shapes are perfectly adapted to those of the space originating from the assembly of preforms. 
     Whereby the space  14  or  26  is perfectly filled in by the fiber profile, the risks of preferred resin paths appearing are reduced, which limits the disturbances during the filling of the mold and consequently the risks of greatly porous zones and/or dry zones. 
     According to another advantage, whereby the profile has shapes that are perfectly adapted to those of the spaces  14  or  26 , the fibers of the preforms that are adjacent to the profile are less disoriented, which also makes it possible to reduce the risks of alterations of the mechanical characteristics of the thus obtained piece. 
     The invention is not limited to a T-shaped preform but can also be applied to other shapes of preforms, in particular to an I-shaped preform that is equivalent to two T-shaped forms.