Abstract:
The invention relates to a compaction assembly comprising a shaping mold ( 24 ) delimiting an upwardly open housing, capable of receiving a woven preform cut out beforehand ( 10   a ), and a vertically moveable compaction tool ( 128 ) and forming, with the shaping mold, ( 24 ), a compaction assembly for said preform placed beforehand in the housing. The compaction tool ( 128 ) includes at least one foot portion ( 128 A). The compaction tool ( 128 ) comprises at least three separate compaction blocks ( 1281 - 1287 ). Application to the manufacturing of composite fan blades for a turbomachine.

Description:
TECHNICAL FIELD 
       [0001]    The present disclosure relates to a method for manufacturing a composite turbomachine blade and to a compaction assembly used in this method. The composite blade may be of the type comprising a preform in three-dimensionally-woven yarns or fibers and a binder maintaining the relative arrangement between the yarns of the preform. Said preform may be formed with warp yarns and weft yarns, the direction of the warp yarns forming the longitudinal direction of the preform. 
         [0002]    In particular, the present method relates to the manufacturing of a fan blade for a turbomachine, notably a turbojet engine. However, the manufacturing of a blade intended for a low pressure compressor is also contemplated, where the attained operating temperatures are compatible with the thermomechanical strength of this type of blade. Also, the manufacturing of open rotor blades or blades with integrated platform is contemplated. 
       BACKGROUND 
       [0003]    Customarily, fan blades made in a composite material, in particular in carbon fibers, are made from a stack of pre-impregnated unidirectional plies which are placed in a mold by orienting the successive plies differently, before compaction and polymerization in the autoclave. This very delicate technique requires the carrying out of operations for stacking plies manually, which is long and costly. 
         [0004]    The preparation of woven preforms was also proposed, with dry fibers, which are then assembled by sewing, before impregnation with a resin by injection into a closed mold. One alternative consisted of producing a single woven preform which is mounted with one or several solid inserts before injection. These solutions (U.S. Pat. No. 5,672,417 and U.S. Pat. No. 5,013,216) however have the drawback of requiring the assembling of several parts and of generating in these assembling areas, particularly weak sites, for example with respect to delamination, which is very detrimental in terms of mechanical strength, notably for impact resistance. 
         [0005]    In order to overcome these drawbacks, patent document FR 2 861 143 proposed the making of a preform in yarns or fibers woven in three-dimensions giving the possibility of forming with it alone, after optional cutting out and injection of the binder, the final part forming all the portions of the turbomachine blade, without resorting to the use of inserts or of any other added element. 
         [0006]    In particular, the manufacturing method shown in patent document FR 2 892 339 is used, during which the woven and then cut-out preform is shaped in a mold before injecting the binder and proceeding with the curing of the binder. 
         [0007]    However, a certain number of problems related to how this shaping is achieved, persist today. 
       General Presentation 
       [0008]    The present disclosure relates to a compaction assembly with which the above-mentioned drawbacks may be avoided. In particular this compaction assembly allows the preform to be pre-compacted. 
         [0009]    The compaction assembly may be used for a preform obtained by weaving yarns in three dimensions and intended to form a composite turbomachine blade, said preform comprising at the same time the airfoil, the foot of the blade and, between the airfoil and the foot, the root of the blade. 
         [0010]    This compaction assembly comprises a shaping mold delimiting an upwardly open housing, suitable for receiving a woven preform (which may be cut out beforehand), and a vertically moveable compaction tool cooperating with the shaping mold in order to form a compaction assembly allowing compaction of said preform when placed in the housing. The compaction assembly defines a longitudinal direction and a vertical middle plane parallel to the longitudinal direction. 
         [0011]    The compaction tool may comprise at least three separate compaction blocks, among which are a central compaction block passing through said middle plane and two side compaction blocks located at the side edges of said compaction tool, said compaction blocks being adapted to move downwards one by one towards the shaping mold in an independent way, starting with the central compaction block. 
         [0012]    The compaction tool may be configured to go downward in the direction of the shaping mold. 
         [0013]    The present disclosure also deals with a method for manufacturing a composite turbomachine blade, using a compaction assembly. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    Other advantages and features of the invention will become apparent upon reading the following description referring to the appended drawings wherein: 
           [0015]      FIG. 1  is a general perspective view of an example of a preform, after being cut out, 
           [0016]      FIG. 2  illustrates a step of an example of manufacturing method, 
           [0017]      FIGS. 3 and 4  are sectional views along the directions III and IV of  FIG. 2  showing the effect of compaction on the profile of two different portions of the preform, with a compaction assembly according to a first embodiment of the present invention, 
           [0018]      FIG. 5  is a partial view of the preform of  FIG. 1 , showing the foot and the root as an enlargement, 
           [0019]      FIG. 6  is a sectional view similar to that of  FIG. 4 , showing another example of a compaction assembly, 
           [0020]      FIG. 7  is a perspective view of the compaction tool of the compaction assembly of  FIG. 6 . 
       
    
    
     DETAILED DESCRIPTION 
       [0021]    In the following detailed description, it is referred to the accompanying drawings showing examples of compaction assembly or examples of manufacturing process. It is intended that these examples be considered as illustrative only, the scope of the invention not being limited to these examples. 
         [0022]    In an illustrative embodiment, the manufacturing method begins with a first step a) consisting of making a three-dimensional preform  10  by weaving, the woven preform including warp yarns  20   a  and weft yarns  20   b.  In both of these groups of yarns, tracer yarns  22  visually identifiable with respect to the other yarns and regularly located at least at the surface of the preform are provided. 
         [0023]    The warp and weft yarns may belong, for example, to the group formed by carbon fibers, glass fibers, silica fibers, silicon carbide fibers, alumina fibers, aramid fibers and aromatic polyamide fibers. 
         [0024]    The woven preform in one piece is then cut out according to a second step b) of the method. More exactly, this woven preform is outlined by cutting out the contour according to a predetermined three-dimensional abacus provided so that after deformation, the preform observes the geometry of the finished part. This cutting out may be carried out with a water jet and/or with mechanical means (scissors, cutter, saw . . . ) and/or by cutting out with a laser. 
         [0025]    This results in a cut-out preform  10   a  as visible in  FIG. 1 . The portions intended to form the airfoil  12  and the foot  14  of the blade, as well as the root  13  which is the transition portion between the airfoil  12  and the foot  14 . In particular, the warp yarns  20   a  and the weft yarns  20   b  used for weaving in  3  dimensions are carbon fibers (black), and glass or Kevlar fibers (white) form tracer yarns  22  essentially located at the surface of the preform, along the main longitudinal direction parallel to the warp yarns  20   a  and along the transversal direction parallel to the weft yarns  20   b.  In this way, the tracer yarns  22  appear with a white color on the remainder of the preform which is black, and the tracer yarns  22  are therefore very visible. Additionally, these tracer yarns are detectable with conventional non-destructive inspection technologies (X-ray or ultrasonic tomography type) allowing the compliance of the final part to be checked. 
         [0026]    In particular, these tracer yarns  22  are present here at the surface of both faces (respectively intended to form the pressure-side wall  17  and the suction-side wall  18 ) of the blade at predetermined locations in order to be used as a reference point for the positioning with view to the cutting and other steps for treating the preform as this will be discussed hereafter. 
         [0027]    During this cutting step, it is intended to keep a series of tracer yarns  22  located at the surface of the preform along at least one reference face  16 , which, in the illustrated case is the face intended to form the leading edge. 
         [0028]    Next, step c) is carried out in which pre-deformation of the cut-out preform  10   a  is achieved. 
         [0029]    In particular, during step c), said pre-deformation is achieved by placing the cut-out preform  10   a  in a shaping mold  24  ( FIG. 2 ) having different portions delimiting between them a cavity or housing  26  intended to house the cut-out preform  10   a  and having marks used as a reference for positioning at least some of the tracer yarns  22 . 
         [0030]    Different systems for localizing and positioning the cut-out preform  10   a  may be used, in particular a laser projector  27  (see  FIG. 2 ) which projects a light beam to the ideal location of a tracer yarn  22  so that it is then easy to move accordingly the corresponding tracer yarn  22  in order to obtain the predetermined positioning. 
         [0031]    Alternatively or additionally, masks, taking up again the contour and/or the position of all or part of the tracer yarns  22 , may be positioned on the preform in order to check its proper positioning. 
         [0032]    When the cut-out preform  10   a  is positioned in the shaping mold  24 , the cut-out preform  10   a  is placed in a configuration which deforms it by applying a rotation (arrow  25   a  in  FIG. 2 ) around an axis XX′ parallel to its main direction, which has the consequence of twisting the airfoil around this axis. 
         [0033]    In some cases, provision can also be made for the shaping mold  24  to present a moving portion  24   a  that is slidable and designed to come into position against the free end of the root of the preform so as to exert stress (arrow  25   b ), thereby producing the desired deformation of this portion  14  of the preform, or avoiding certain types of deformation in this portion, while deformation is being applied to other portions of the preform  10   b.    
         [0034]    It should be understood that numerous different possibilities can be envisaged for shaping the cut-out preform  10   a  by making use of the tracer yarns  22  as reference elements for positioning the preform  10   a  in the shaping mold  24 . 
         [0035]    The strategy for placing the cut-out preform  10   a  in the shaping mold  24  is also related to the cutting-out or outlining profile made before, according to the selected reference surface(s), in particular from among the foot, the head, the leading edge  16 , the trailing edge  19  or any other predetermined area. 
         [0036]    The cut-out preform  10   a  may be put into place in the shaping mold  24  in a manner that is sufficiently accurate to perform all of the deformations needed in order to achieve the desired final shape. However, it is also possible to perform this step c) as a plurality of sub-steps. 
         [0037]    A binder comprising a thermosetting resin is then injected into said injection mold in order to impregnate the whole preform and to maintain the relative arrangement between the yarns of the preform; said injection mold is heated; and a composite molded part is extracted from the mold, substantially having the shape and the dimensions of said blade 
         [0038]    In a step d) following step c) and before injecting said binder, pre-compaction of at least one portion of the pre-deformed preform  10   b  comprising the foot and preferably the foot  14  and the root  13 , is achieved over the whole width of the pre-deformed preform  10   b.  This pre-compaction blocks certain fibers in an intended position, whence an intermediate geometry of the preform, which still further approaches the intended final shape. 
         [0039]    The compaction tool  28  used for this purpose, schematically and partly visible in  FIG. 2 , may be made by completing the shaping mold  24  with the required pieces of equipment. Indeed, the compaction tool  28  is moveable (up and down) and should be able to be brought to a temperature of the order of 100° C. 
         [0040]    During this step d), the sizing products coating the yarns and which are used for facilitating weaving, are the ones which allow the blocking of the relative position of the fibers of the pre-compacted portion. 
         [0041]    Subsequently, wetting of the pre-compacted preform  10   c  is performed and drying in an oven is performed, by means of which a stiffened preform is provided. In fact, this stiffening will sufficiently set the shape given during step c) to the cut-out preform  10   a,  having become the pre-deformed preform  10   b,  so that it may easily be placed subsequently in the injection mold  24  without substantially changing its shape which corresponds to that of the aforementioned pre-deformation. 
         [0042]    If necessary, it is optionally possible to add a tackifying agent inside the preform, for example a diluted resin, notably of the epoxide type, the whole giving the possibility under the effect of the heat and of the pressure which are exerted during the pre-compaction step d), of having the woven carbon fibers adhere to each other in order to avoid that the pre-deformed preform  10   b  undergoes any subsequent deformation notably during the injection step. 
         [0043]    The compaction tool  28  has a shape and dimensions which allows it to be inserted into the housing  26  of the shaping mold in order to allow compaction of the woven preform to an intermediate fiber volume level relatively to the definitive fiber volume level of the final part. For example, the target volume level of fibers for a compacted preform obtained with the compaction tool  28  is between 35% end 55%, so that the final part, after injection, presents a target volume level of fibers between 50% and 60%. 
         [0044]    Reference is now made to  FIGS. 3 and 4 , illustrating a cross-sectional view of a pre-deformed preform  10   b  and a compaction assembly according to an embodiment (shaping mold  24  and compaction tool  28 ).  FIG. 3  is a cross-sectional view at the foot  14  while  FIG. 4  is a cross-sectional view at the root  13  of the preform  10   b.  These figures illustrate how the pre-deformation is applied on these different portions of the pre-deformed preform  10   b  (dotted lines) in order to obtain the compacted preform  10   c  (solid line). 
         [0045]    For the foot  14  ( FIG. 3 ), the housing  26  of the shaping mold  24  has a rectangular section and the compaction tool  28  has foot portion  28 A, the rectangular section of which is mating that of the housing  26 . 
         [0046]    For the root  13  ( FIG. 4 ), the housing  26  of the shaping mold  24  has a section with a convex bottom  26   a  and flared sides  26   b  towards the aperture of the housing  26 . The compaction tool  28  has a root portion  28 B, the section of which includes substantially vertical sides  28   b  and a bottom  28   a,  intended to come and face the convex bottom of the shaping mold  24 . This bottom  28   a  is concave with a profile having larger radii of curvature than the convex profile of the bottom of the housing  26  of the shaping mold  24 . 
         [0047]    The compaction tool  28  according to this embodiment is in one piece so that during its movement, it moves down (or up) as a whole, into (or from) the housing  26  of the shaping mold  24 , thus compressing the pre-deformed preform  10   b.    
         [0048]    In order to avoid damaging the fibers of the pre-deformed preform  10   b,  and notably to avoid nipping them, the surfaces of the shaping mold  24  and the compaction tool  28 , turned towards the housing, do not have any (protruding or re-entrant) sharp edge but consist of faces with rounded angles by rounded or radially arranged links forming fillets. 
         [0049]    In such a situation, when the compaction tool  28  moves downwards, if the root portion  28 B which will compact the root  13  of the preform ( FIG. 4 ) is considered, firstly the side edges  16   a  and  19   a  of the pre-deformed preform  10   b,  intended to respectively form the leading edge  16  and the trailing edge  19 , are the ones which come into contact with the compaction tool  28  at the location of the side edges  28   c  of the bottom  28   a.  Next, contact is gradually made with the whole surface of the root  13  turned facing the compaction tool  28 , finishing with the central area (strip) of the surface, this central area passing through a middle plane PM of the compaction assembly. 
         [0050]    This middle plane PM, which is not necessarily a plane of symmetry for the compaction assembly and for the preform, is vertical, parallel to the axis XX&#39; oriented along the main direction of the preform, and is found at half distance both between the side edges  26   b  of the housing  26  of the shaping mold  24  and between the side edges  28   b  of the compaction tool  28 . 
         [0051]    This configuration may sometimes have certain drawbacks regarding the pre-deformation of the root  13 : in the case of  FIGS. 4 and 5 , the side edges  16   a  and  19   a  of the pre-deformed preform  10   b  being thinner in thickness on the one hand and undergoing larger flexure than the remainder of the root  13 , the fibers  20  forming the preform undergo buckling, which may be detrimental to the proper thermal mechanical strength of the final blade. 
         [0052]    The areas of the cut-out preform  10   a  which undergo this undesirable buckling, are indicated in  FIG. 5  at both locations Z 1  and Z 2  corresponding to the thin edges of the root  13  located in proximity to the airfoil  12 . 
         [0053]    To avoid the above-mentioned drawbacks, the compaction tool of the compaction assembly includes at least one foot portion and the compaction tool includes at least three separate compaction blocks, among which are a central compaction block passing through said middle plane and two side compaction blocks located at the side ends of said compaction tool, said compaction blocks being able to move downwards one by one towards the shaping mold in an independent way, starting with the central compaction block. 
         [0054]    In this way, the compaction tool may be formed with at least three portions and it is possible to have these portions move down at different moments, starting with the central compaction block which first moves down so that the first contact between the compaction tool and the cut-out preform is made at the central area of the surface of the root turned facing the compaction tool. 
         [0055]    In this way, by means of the compaction assembly of the invention, the side edges of the root of the preform are compacted lastly, which gives the possibility of minimizing or even avoiding the buckling of fibers of these small thickness areas during the pre-compaction step. 
         [0056]    The compaction tool may include an odd number of separate compaction blocks, so as to form a geometry with a central compaction block passing through said middle plane and on either side of this central compaction block, an identical number of other compaction blocks. 
         [0057]    This solution also has the advantage of making it further possible to dose the pre-compaction level exerted by each of these compaction blocks on the preform, which may be measured by the intermediate fiber volume level resulting from this pre-compaction. 
         [0058]    In certain embodiments, said compaction blocks are capable of moving down one by one towards the shaping mold in an order which compacts the whole width of said preform, starting with said central compaction block and then each compaction block adjacent to the one having moved down previously, and this until the side compaction block. 
         [0059]    In certain embodiments, the compaction tool includes only one foot portion. In other embodiments, the compaction tool includes a foot portion  128 A and a root portion  128 B, as illustrated in  FIG. 7 . 
         [0060]    In certain embodiments, said compaction blocks are capable of moving down towards the shaping mold, starting with the central compaction block, and then with all the compaction blocks found on one of the sides of the middle plane, preferably one by one and in series from the central compaction block until the second side compaction block. 
         [0061]    Alternatively, said compaction blocks are capable of moving down towards the shaping mold in a symmetrical way relatively to the middle plane. 
         [0062]    In certain embodiments, the whole compaction tool  128  is divided into at least three separate compaction blocks, among which is a central compaction block  128   1  passing through the middle plane PM of the compaction tool  128 , said compaction blocks being capable of moving down towards the shaping mold  24  independently, starting with the central compaction block  128   1 . 
         [0063]    In the example of  FIGS. 6 and 7 , the whole compaction tool  128  is divided into seven separate compaction blocks  128   1 ,  128   2 ,  128   3 ,  128   4 ,  128   5 ,  128   6 ,  128   7 , distributed around and on either side of the middle plane PM. 
         [0064]    In this way, it is possible to break down the downward movement of the whole compaction tool  128  (foot portion  128 A and root portion  128 B), starting with the central compaction block  128   1  passing through the middle plane PM of the compaction tool  128  (downward pointing arrow Dl and dotted line  128   1 ′ in  FIG. 6 ), and then both compaction blocks  128   2  and  128   3  located on either side of the central compaction block  128   1  (downward pointing arrows D 2  and D 3  and dotted lines  128   2 ′ and  128   3 ′ in  FIG. 6 ), and so forth until both side compaction blocks  128   6  and  128   7  located at the side edges of the compaction tool  128 . 
         [0065]    As illustrated in  FIGS. 7 , optionally, the compacting tool  128  includes at least one window  132  giving the possibility of viewing the position of at least one tracer yarn when the preform is placed in the housing delimited between the shaping mold  24  and the compaction tool  128 . This window  132  for example consists of a portion of the compaction tool  128  made in a transparent material or preferably an aperture passing right through the whole thickness of the compaction tool  128 . This window  132  may be positioned in an area of the root portion  128 B which is adjacent to the foot portion  128 A, preferably at the central compaction block  128   1 . Such a window  132  notably gives the possibility of making sure that the tracer yarn(s)  22  visible through this window (for example the span exit tracer yarn) are properly positioned and remain so during the compaction operation. 
         [0066]    In the example illustrated in  FIGS. 6 and 7 , the compaction tool  128  is divided into seven separate compaction blocks  128   1 ,  128   2 ,  128   3 ,  128   4 ,  128   5 ,  128   6 ,  128   7 . 
         [0067]    The compaction blocks  128   1 ,  128   2 ,  128   3 ,  128   4 ,  128   5 ,  128   6 ,  128   7  may also move down for compacting the preform  10   b  with different speeds and/or forces exerted by these compaction blocks on the preform which are different, whence pre-compaction levels or intermediate fiber volume levels resulting from this pre-compaction which are different among the compaction blocks  128   1 ,  128   2 ,  128   3 ,  128   4 ,  128   5 ,  128   6 ,  128   7 . 
         [0068]    In the illustrated examples, there are seven compaction blocks  128   1 ,  128   2 ,  128   3 ,  128   4 ,  128   5 ,  128   6  , 128   7  , but generally at least five of them may be provided, for example exactly five. 
         [0069]    A method for manufacturing a composite turbomachine blade, may comprise the following steps: 
         [0070]    a) a preform is made by weaving yarns  20   a,    20   b,    22  in three dimensions, said preform comprising at the same time the airfoil  12 , the foot  14  of the blade and between the airfoil  12  and the foot  14 , the root  13  of the blade, the yarns  20  comprising visually identifiable tracer yarns  22  positioned at least at the surface of the preform; 
         [0071]    b) said preform is cut out while leaving a series of tracer yarns  22  intact, located along a reference face  16  of the preform, whereby a cut-out preform  10   a  is provided, capable of assuming the shape and the dimensions of the constitutive portions of the blade; 
         [0072]    c) said cut-out preform  10   a  is pre-deformed, whereby a pre-deformed preform  10   b  is provided; 
         [0073]    d) pre-compaction of said pre-deformed preform  10   b  is achieved, whereby a pre-compacted preform  10   c  is provided; 
         [0074]    e) wetting of the pre-compacted preform  10   c  is performed and drying in an oven is performed, whereby a stiffened preform is provided; 
         [0075]    f) an injection mold  24  injection is provided, in which said stiffened preform is placed; 
         [0076]    g) a binder comprising a thermosetting resin is injected into said injection mold, in order to impregnate the whole stiffened pre-deformed preform and to maintain the relative arrangements between the yarns  20   a,    20   b,    22  of the stiffened preform; 
         [0077]    h) said injection mold is heated; and 
         [0078]    i) a composite molded part is extracted from the mold, substantially having the shape and the dimensions of said blade, 
         [0079]    During step c), said pre-deformation is carried out by placing the cut-out preform  10   a  in the housing  26  delimited by a shaping mold  24  and in that, during step d), said pre-compaction of said pre-deformed preform  10   b  is carried out by using a moveable compaction tool  128  and cooperating with the shaping mold  24  in order to form a compaction assembly defining the longitudinal direction and a vertical middle plane PM parallel to the longitudinal direction. 
         [0080]    Thus, during step d), the compaction tool  28  may preferably go down towards the shaping mold  24 . 
         [0081]    According to a preferred embodiment, said compaction tool  128 , is capable, during step d), of compacting at least the foot  12  of said pre-deformed preform  10   b  by starting with the middle and then advancing gradually until the edge of the pre-deformed preform  10   b.    
         [0082]    Thus, by means of this advantageous provision, fiber buckling is avoided in the foot area  12  and the root area  13  of the preform during the compaction step. 
         [0083]    In this method, during step d), said compaction tool  128  is capable of moving downwards towards the shaping mold  24  so that said compaction blocks move downwards one by one towards the shaping mold  24  in an order which compacts the whole width of said preform  10   b  by starting with its central portion passing through the middle plane PM and then each portion adjacent to the previous one, with gradually greater offsets from the middle plane PM. During step d), said compaction tool  128  may be capable of moving downwards towards the shaping mold  24  in a symmetrical way relatively to said middle plane PM. 
         [0084]    In the figures, the case of a foot  14  which remains rectilinear throughout the manufacturing method is illustrated. It is understood that without departing from the scope of the present invention, it is possible to envision the case of a foot which is twisted, or deformed according to any other action, when it is placed in the shaping mold  24 . 
         [0085]    Moreover, according to an alternative embodiment not shown, the compaction tool  128  not only covers the foot  14  and the root  13  of the airfoil, but also a portion of the airfoil  12  of the blade. 
         [0086]    Also, in the foregoing description, it was mentioned that the compaction tool  128  carried out a pre-compaction step, i.e. step d). However, it is also possible to use this compaction tool  128  alternatively as an element of the injection mold  24  and to only use it for steps f) and g). According to another alternative, it is possible to use this same compaction tool  128  both for the pre-compaction step d) and for steps f) and g). 
         [0087]    “Comprises/comprising” when used in this specification is taken to specify the presence of stated features but does not preclude the presence or addition of one or more other features. 
         [0088]    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 of the invention. Further, the various features of the embodiments or examples disclosed herein can be used alone or in varying combinations with each other, and are not intended to be limited to the specific combinations disclosed herein.