Patent Publication Number: US-2023142441-A1

Title: Composite turbomachine vane and method for manufacturing same

Description:
TECHNICAL FIELD OF THE INVENTION 
     The present invention relates to a composite turbomachine vane and its manufacturing method. 
     BACKGROUND 
     The technical background comprises in particular the documents US-A1-2015/110 636, U.S. Pat. No. 5,935,360, WO-A1-2015/057 369A1 and FR-A1-3 049 305. 
     The use of composite materials is particularly advantageous in the aeronautical industry because these materials are relatively light and have good mechanical properties. 
     A composite material typically used in aeronautic comprises a fibrous preform embedded in a polymeric resin. The preform may be a three-dimensional weaving or may be obtained by draping and superimposing several fabrics. 
     The resin can be injected into the preform or the preform can be pre-impregnated with the resin. 
     The shaping of the final part is usually carried out by means of a tooling comprising a mould. In the case where a resin is to be injected into a preform, the preform is arranged in the cavity of a mould and the mould is covered with a counter-mould. The tooling comprises a port for injecting resin into the mould cavity and a port for evacuating the cavity of the mould. 
     In the case where the preform is already impregnated with the resin, the preform is arranged in the cavity of a mould which can be covered with a flexible tarpaulin or a counter-mould. 
     The tooling also comprises a port for injecting resin into the cavity of the mould and a port for vacuuming the cavity of the mould. The counter-mould applies a pressure to the preform due to the vacuuming of the preform located between the counter-mould and the flexible tarpaulin or the mould. The use of a counter-mould allows to better control the thickness of the final part. 
     In the case of a vane, in particular for a fan, after the moulding operation described above, an operation to apply anti-wear strips to the root and the stilt of the vane must be carried out. 
     These strips are currently fitted and secured to the root and the stilt of the vane by gluing. Thus, the anti-wear strips are first impregnated with glue, usually phenolic, by hand. The operator then places the anti-wear strips on the root and the stilt of the vane, still manually. 
     The vane covered with the anti-wear strips is then placed back into the mould and the wear strips are vacuum glued using a silicone counter mould. 
     This operation of gluing the anti-wear strips is therefore very manual and generates many defects in the final part. In service, the anti-wear strips have been found to be detached, exposing the composite of the vane and making it unusable. 
     These detachments are mainly due to a poor gluing rate of the anti-wear strips. However, the correct gluing rate requires weighing the amount of glue to the nearest tenth of a gram and is virtually impossible to achieve when done manually. 
     In addition, the way in which the glue is distributed on the anti-wear strips has a direct influence on the quality of the gluing: even the smallest area that is poorly impregnated leads to a poor gluing. 
     The amount of glue also generates dimensional non-conformities: the amount of glue directly influences the final thickness of the anti-wear strips on the vane. 
     Thus, if the strips are over-impregnated or the glue is poorly distributed, the differences in flatness and the dimensions, in particular at the root of the vane, go out of tolerance and the vane becomes non-conforming. 
     The anti-wear strips are provided dry with variations in thickness that do not allow the quantity of glue to be standardised: a good gluing for a thinner anti-wear strip requires a smaller quantity of adhesive than for a thicker anti-wear strip. 
     Furthermore, as we have seen, the anti-wear strips are vacuum glued using a silicone counter-mould which, not fitting perfectly to certain geometries of the fan vane, generates accumulations of glue at certain points. 
     These glue accumulations in turn lead to thicknesses and dimensional non-conformities of the fan vane. 
     Another difficulty encountered with the current method for gluing the anti-wear strips to the vane is the difficulty of positioning the strips, to within several tens of millimetres, by hand on a left-hand form and the difficulty of maintaining this positioning of the strips during the operation of installing the vane coated with anti-wear strips in the mould and during the vacuum gluing operation. 
     In addition, once glued, the anti-wear strips serve as a dimensional reference for the vane. Thus, different gluing qualities can lead to problems in service or negatively impact the final geometry of the part. 
     The present invention relates to the aforementioned technology for manufacturing a composite vane on a surface of which at least one fabric anti-wear strip is to be secured, with a precise positioning and precise dimensions to be respected. 
     The present invention proposes an improvement to this technology, which is simple, effective and economical. 
     SUMMARY OF THE INVENTION 
     The invention relates to a turbomachine vane, this vane being made of composite material formed of fibres woven and embedded in a polymerised resin, this vane comprising a root connected by a stilt to a blade which comprises a pressure side and a suction side, at least one anti-wear strip of fabric being located on a surface of the root and/or the stilt, characterised in that the at least one anti-wear strip is secured to the surface of the root in a unitary manner by said resin. 
     In particular, the invention allows the anti-wear strip or the anti-wear strips to be precisely positioned on the vane. In addition, it allows the strip or the strips to be secured to the vane without the use of glue, as the resin used to manufacture the blade is used to carry out this securing. 
     The vane according to the invention may comprise one or more of the following characteristics, taken alone or in combination with each other:
         the vane comprises at least one, and preferably two, anti-wear strips on a first surface of the root and/or of the stilt located on the side of said pressure side, and at least one, and preferably two, anti-wear strips on a second surface of the root and/or of the stilt located on the side of said suction side;   the at least one anti-wear strip has an elongated shape and extends substantially from one end of the root located on the side of a leading edge of the blade, to an opposite end of the root located on the side of a trailing edge of the blade;   the at least one strip is formed by weaving PTFE and/or aramid fibres;   the at least one strip has a thickness that varies along its length.       

     The present invention also relates to a method for manufacturing a vane as described above, using a tooling comprising a mould defining a cavity configured to receive a woven fibre preform, said method comprising the following steps:
     a) positioning the at least one anti-wear strip on at least one wall of the mould opening into the cavity,   b) installing the preform in the cavity and on said wall, and   c) polymerising the resin present on the fibres of the preform or injected into the cavity, this resin being configured to solidify the vane and ensure the securing of the at least one anti-wear strip to this vane.   

     In step a), the at least one anti-wear strip is preferably positioned in a recess formed in said wall. 
     In step c), the resin is advantageously configured to soak the at least one anti-wear strip. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       Further characteristics and advantages will be apparent from the following description of a non-limiting embodiment of the invention with reference to the appended drawings in which: 
         FIG.  1    is a schematic perspective view of a composite vane according to the invention, 
         FIG.  2    is a larger scale schematic view of a portion of the vane of  FIG.  1   , and in particular its root and its stilt on which are located anti-wear strips, 
         FIG.  3    is a very schematic cross-sectional view of a tooling for manufacturing a vane according to the invention, and 
         FIG.  4    is a schematic perspective view of an embodiment of a mould of a tooling for manufacturing a vane according to the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Reference is made firstly to  FIGS.  1  and  2    which illustrate a composite material vane  10  for a turbomachine, this vane  10  being for example a fan vane. 
     The vane  10  comprises a blade  12  connected by a stilt  14  to a root  16  which has, for example, a dovetail shape and is shaped to be engaged in a complementarily shaped pocket of a rotor disc, in order to retain the vane on this disc. 
     The blade  12  comprises a leading edge  12   a  and a trailing edge  12   b  of the gases flowing through the turbomachine. The blade  12  has a curved or twisted aerodynamic profile and comprises a pressure side  18  and a suction side  20  extending between the leading  12   a  and trailing  12   b  edges. 
     Anti-wear strips  22  made of fabric are secured to the vane  10 . 
     In the example shown, the vane  10  comprises four anti-wear strips  22 , two on each side of the root  16  and two others on each side of the stilt  14 . 
     As the name suggests, the strips  22  are configured to limit the wear on the walls to which they are attached, by contact and/or friction. These strips  22  are located on the root  16  and the stilt  14  which are likely to come into contact with bearing surfaces of the aforementioned rotor disc. 
     Each strip  22  is generally elongate in shape and extends substantially from the leading edge  12   a  to the trailing edge  12   b  of the vane  12 . A strip  22  has for example a length of between 2 and 50 cm, and a width of between 2 and 7 cm. 
     An anti-wear strip  22  is carried out by weaving fibres such as aramid fibres and/or PTFE. 
     The vane  10  is made of composite material from a fibrous preform whose fibres, for example of carbon, are coated or impregnated with polymerisable and in particular cross-linkable resin (such as an epoxy resin). 
     The tooling used to manufacture the vane  10  comprises a mould and a counter-mould, the mould and the counter-mould defining between them a cavity configured to receive the fibrous preform 
     When manufacturing a vane, the tooling is opened and a fibrous preform is arranged into the cavity. This arrangement can be made with a three-dimensional woven preform or with fabrics that are draped and superimposed in the cavity. This step can be done manually or by means of a robot. The tooling is then closed by attaching in a sealing manner the counter-mould to the mould. 
     The preform is pre-impregnated with resin or the resin is injected into the mould to impregnate the preform. 
     The tooling is heated to raise the temperature of the resin and cause it to polymerized. 
     After the resin has polymerized and the vane has stiffened, the strips  22  are glued to the vane, for example with a phenolic adhesive, in the prior art. 
     This gluing operation is, at present, an entirely manual operation which comprises three steps, a step of coating the strips with the glue, a step of positioning the strips, and a step of holding the strips in position until the glue sets. 
     This manual operation is the source of many defects in the final part, as seen above. 
     The present invention proposes to eliminate the manual gluing operation and to carry out the assembly of the strips  22  at the same time as the polymerizing operation of the resin and the stiffening operation of the vane. 
     The manufacturing method of the vane according to the invention thus allows to do away with the manual gluing operation of the prior art, which allows to solve the problem of obtaining non-conforming parts and, moreover, to have a simpler method than that currently used 
     Indeed, the method of the invention comprises, as in the prior art method, the use of a tooling  24  comprising a mould  26  and a counter-mould  28 , the mould  26  and the counter-mould  28  defining between them a cavity  30  configured to receive the fibrous preform  32  of the vane ( FIG.  3   ). 
     However, in the method of the invention, before installing the fibrous preform  32  in the mould, the strip or the strips  22  of fabric are placed on at least one wall  26   a,    28   a  of the mould  26  or of the counter-mould  28 , which opens into the cavity  30 . 
     The fibrous preform  32  is then installed between the mould  26  and the counter-mould  28 . 
     As mentioned above, the preform is pre-impregnated with resin, or resin is injected through a port  33  in the mould to impregnate the preform. The injection of resin into the cavity of the tooling allows to exert a pressure on the preform and to prevent air bubbles and microporosities from appearing in the final part. The resin is then polymerized. 
     In the method of the invention, two types of resin are no longer used, the resin impregnating the fibres of the preform and a resin or glue for gluing the strips, but only the resin, for example epoxy. 
     The defects due to the wrong amount of glue, an extra thickness or a lack of glue between the strip  22  and the vane are therefore avoided. 
     In addition, a unitary part is obtained. 
     In order to achieve precision to within a few millimetres in the positioning and holding of the strips  22 , which was also a source of defects in the prior art method, the mould  26  advantageously comprises housings  34  provided to receive the strips  22 . 
     These housings  34  may be recesses or cut-outs formed in the wall  26   a ,  28   a  opening into the cavity  30 . They are advantageously calibrated to the nominal thickness of the strips  22 , which is for example between 0.1 and 1.5 mm. 
     The invention thus provides several advantages, including:
         the securing of the strips by means of the resin rather than dedicated glue, during the solidification of the vane, allows for a perfect geometry and a precise placement of the strips;   the variable thicknesses of the strips no longer have any impact since they are pressed against the walls of the tooling and received in calibrated housings in these walls;   the amount of resin is optimal at any point on the strips, driven by the injection pressure in the tooling and/or by the closing pressure of the mould; etc.