Patent Publication Number: US-2022235498-A1

Title: Method for manufacturing a ring sector

Description:
TECHNICAL FIELD OF THE INVENTION 
     The present invention relates to the manufacturing of a fibrous structure for the production of composite parts intended to be integrated, for example, in a turbomachine. 
     PRIOR ART 
     Composite parts, in particular ceramic matrix composite (CMC) parts, are increasingly used to replace metal parts in turbomachines. Indeed, CMC parts have particularly interesting mechanical properties at high temperatures, ideal for the design of, for example, turbine nozzles or stators. In these two examples, sectorised CMC parts are arranged and assembled on a metal housing and connected to each other by tight connections, in order to ensure the tightness of the vein despite the thermal expansions generated by the high operating temperatures. 
     In the aeronautical field, for the applications mentioned above, the CMC materials used are based on SiC fibres and a SIC matrix. 
     The SiC fibres are integrated into the CMC material in the form of fibrous structures, for example by three-dimensional weaving. This is multi-layer weaving using several layers of weft yarns and several layers of warp yarns, with warp yarns binding together different layers of weft yarns. Different types of 3D weaves can be used, e.g. interlock, multi-satin, multi-woven, multi-twill weaves. 
       FIG. 1  shows a stator sector  2  which is intended to be mounted radially opposite the tips of moving vanes. It comprises two radial flanges  4  axially spaced from each other and internally connected to an annular wall sector  6  which comprises a central portion  8  connecting the two flanges  4  and fairings  10  extending in opposite directions from the axial ends of the central portion  8 . The terms “radial” and “axial” are to be considered in relation to the axis A of the angular sector, this axis corresponding to the axis around which a plurality of sectors are intended to be arranged to surround a bladed wheel. 
     As can be seen in  FIG. 1 , the central portion  8 , also known as the bathtub, has a thickness e pc  greater than the thickness of the fairings e b . The thickness is measured in the radial direction. This is directly related to the manufacturing process of the fibrous structure  12 . 
     In order to produce the ring sector  2  of  FIG. 1 , a fibrous structure  12  as shown in  FIG. 2  is first produced. 
     This fibrous structure  12  comprises a central part  14  connected, at each of its ends, to a first  16  and a second  18  portion, untied between them. The central portion  14  of the fibrous structure  12  is intended to form the central part  8  of the ring sector  2  and the first  16  and second  18  portions are intended to form the fairings  10  and the flanges  4  of the ring sector  2 . 
     The central part  14  comprises x layers of woven warps, the first portions  16  each comprising z layers of woven warps and the second portions  18  each comprising y layers of woven warps. The warp layers are arranged in a thickness, indicated in the figure by the direction E. 
     The absence of a thickness connection between the first  16  and second  18  portions allows them to be structurally independent of each other and thus to be shaped in different directions in a mould. 
     Thus, once the fibrous structure  12  is obtained, it is shaped to have a similar shape to the desired part, i.e. “Pi” in the example considered, as shown in  FIG. 3 . The first portions  16 , on either side of the central part  14 , are thus deployed so as to obtain a fibrous preform with the “Pi” topology of the ring sector  2  shown in  FIG. 1 . 
     With today&#39;s weaving technique, the warp/weft ratio is the same at all points of the woven piece. Thus, the number of warp layers of the central part  14  depends on the number of warp layers of the first  16  and second  18  portions, and are related by the following formula x=y+Z. 
     The interdependence of the number of layers of warp and weft, with a constant warp/weft ratio, and therefore of their respective thicknesses, of the central part  14  and of the first  16  and second  18  portions, generates a thickness, functionally unnecessary, at the central part  14 . Indeed, the central part  8  functionally requires a minimum thickness e pc  equivalent to the thickness e b  of the fairings  10 . It is also possible to have a thickness e pc  of the central part  8  that is substantially greater than the thickness e b  of the fairings  10 . This excess thickness results in the use of a functionally unnecessary amount of fibrous material, which is an expensive element. 
     It is therefore necessary, for reasons of cost and also mass, to reduce the thickness of the central part  14  of the fibrous structure  12 , and thus to obtain a fibrous structure  12  of variable thickness. 
     A solution called “trimming” is used in the design of organic matrix composite (OMC) vanes. This method consists of removing warp and weft yarns from the fibrous structure by changing the weave. The exiting yarns are then cut, resulting in a fibrous structure with a thickness that evolves along the warp direction. 
     Such a method cannot be used for a CMC ceramic matrix composite part, in particular because of the fragility of the fibres used. The trimming method would then weaken the resulting fibrous structure, and consequently the preform. 
     In addition, the small dimensions of the above-mentioned parts mean that the preforms are small and it is difficult to produce warp yarns which would then be cut using the rimming process. 
     The invention aims to remedy such drawbacks in a simple, reliable and inexpensive way. 
     SUMMARY OF THE INVENTION 
     The present document firstly relates to a three-dimensionally woven multilayer fibrous structure having the same number of warp yarns woven at any level along the warp direction, the fibrous structure comprising, in the warp direction, a first part and a second part, the first part having a thickness measured in a direction perpendicular to the warp and weft directions, greater than the second part, characterised in that the spacing between two weft planes along the warp direction is greater in the second part than in the first part, and in that the number of weft yarns is lower in the second part than in the first part. 
     Thus, by varying the warp-weft ratio by adjusting two parameters, the spacing between two successive weft columns along the warp direction and the local insertion or disengagement of weft yarns, the thickness of the second part is no longer dependent on the thickness of the first part. The fibrous structure then obtained by three-dimensional weaving has a thickness of the first part greater than the thickness of the second part. 
     The number of weft yarns per weft plane of the second part may be less than the number of weft yarns per weft plane of the first part. 
     This method is therefore compatible with the production of fibrous structures for CMC parts, as it does not require the use of the trimming method to vary thickness. 
     The first part of the fibrous structure may comprise a first portion and a second portion, the first portion being arranged, in said perpendicular direction, over a second portion and being structurally independent of the second portion, said first portion and second portion of the first part being woven to the second part at a transition from the first part to the second part. 
     In particular, the first and second portions of the fibrous structure constitute the elements of the fibrous structure that will form the fairing and flange of the ring sector when shaped. A conformation in directions, preferably perpendicular, of the first and second portions is permitted by this structural independence. 
     The number of weft yarns may be greater than the number of warp yarns in either the first or second portion. 
     Another possibility to reduce the thickness of the second part is to vary the warp-weft ratio at the first part, i.e., at the first and second portions of the first part. This reduces the number of layers of warps to be woven in the second part. 
     In the second part, the number of weft yarns may be less than the number of warp yarns. 
     The non-insertion of certain weft yarns, present in the basic weave, is thus carried out in order to modify the warp/weft ratio, by modifying or not the spacing between the weft columns, within the limit of a 75/25 ratio, thus making it possible to reduce the thickness compared to the thickness of the first part. 
     The distance between two warp planes can be the same between the first part and the second part. In practice, this is simpler to achieve than variable spacing. 
     The spacing between two weft planes can be the same between the first and second part, and the spacing between two warp planes can be different. 
     In the particular case, not illustrated, of weaving parts at 90° to the orientation presented in this document, it is possible to play with the spacing between two successive warp planes and keep the spacing between two successive weft planes constant. 
     In practice, it is easier to change the weft parameters on the loom. This makes it easier to set the parameters related to the spacing between two successive layers of chains and the number of chains in the first and second parts. 
     The fibrous structure may comprise a third part identical to the first part and woven to the second part along the warp direction opposite the first part. 
     The first part of the fibrous structure may comprise a first portion and a second portion, the first portion being arranged, in said perpendicular direction, over a second portion and being structurally independent of the second portion, said first portion and second portion of the first part being woven to the second part at a transition from the first part to the second part. 
     The number of weft yarns per weft plane of the second part may be less than the number of weft yarns per weft plane of the first part. In this example, the fibrous structure has an axis of symmetry, similar to the ring sector shown above. The fibrous structure is therefore shaped into a “Pi” shape close to the desired ring sector. Thus, such a fibrous structure can form a preform with a thickness at the second part that may be less than or equal to the thickness of the first part and the third part. The second part, which forms the central part or bathtub in the fibre preform, then has a thickness that is suitable and sufficient for the thermal and mechanical requirements necessary for the use of this part. 
     The present document also relates to a method for manufacturing a fibrous structure as described above, wherein during the transition in the warp direction from the first part of the fibrous texture to the second part of the fibrous texture, the number of weft yarns is decreased and the spacing between two successive weft planes along the warp direction is increased. 
     The present document also relates to a method for manufacturing a fibrous structure as described above, wherein during the transition in the warp direction from the second part of the fibrous texture to the first part of the fibrous texture, the number of weft yarns is decreased and the spacing between two successive weft planes along the warp direction is increased. 
     The present document also relates to a method for manufacturing a composite material, comprising the following steps:
         a) Obtaining a fibrous structure by means of the method as described above;   b) Shaping the fibrous structure;   c) Obtaining a composite material by injecting a matrix into the fibrous structure.       

     The resulting composite material then contains a reduced amount of fibrous material, thereby reducing its production cost and mass. 
     The invention will be better understood and other details, characteristics and advantages of the invention will appear when reading the following description, which is given as a non-limiting example, with reference to the attached drawings 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  described above, is a perspective view of a ring sector according to the prior art; 
         FIG. 2  described above, is a schematic representation of a fibrous structure for the manufacture of the ring sector of  FIG. 1  obtained according to the prior art; 
         FIG. 3  described above, is a schematic representation of the 3D Pi conformation of the fibrous structure of a ring sector; 
         FIG. 4  is a schematic illustration of the fibrous structure according to the invention; 
         FIG. 5  is a diagram of a ring sector incorporating the fibrous structure of  FIG. 4 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In the embodiments detailed below, the fibrous structure woven from SiC fibres preferably has a target fibre content of between 25 and 50% by volume. 
       FIG. 5  is a diagram of a fibrous structure  20  according to the invention in which a warp direction C and a weft direction T and a direction E are shown, these directions being perpendicular to each other. This fibrous structure  20  has the same number of warp yarns woven at any level of the fibrous structure along the warp direction C. 
     The fibrous structure  20  comprises a first part  22 , a second part  24  and a third part  26  along the warp direction C, best seen in the schematic illustration of the fibrous structure  20  before shaping. The first  22 , second  24  and third  26  parts each have a thickness e 1 , e 2 , e 3  measured in a direction E perpendicular to the warp and weft directions. In this example, the fibrous structure  20  comprises a second part  24  whose thickness e 2  is lower than the thickness e 1 , e 2  of each of the first part  22  and the third part  26 . 
     The first  22  and third  26  parts each comprise a first portion  16  and a second portion  18 . Once the fibrous structure  20  has been formed into the shape of Pi as seen in  FIG. 5 , the first portions  16  of the first  22  and third  26  parts are arranged to form a non-zero angle, preferably between 0° and 45°, with the second portions  18  of the first  22  and third  26  parts respectively. Prior to this shaping of the fibrous structure  20 , i.e. at the end of the three-dimensional weaving, for each of the first  22  and third  26  parts, the first portion  16  is arranged above the second portion  18  along the E-direction, also called the thickness direction. The first  16  and second  18  portions, although woven simultaneously, are structurally independent, i.e. they are not woven to each other, which allows an arrangement of the first  16  portions at a non-zero angle to the second  18  portions and the second  24  part. The first  16  and second  18  portions of the first  22  and third  26  parts each have a thickness, in the E direction, of e p11 , e p12 , e p31  and e p32  respectively, such that e p11 +e p12 =e 1  et e p31 +e p32 =e 3 . 
     For the following, it will be assumed that the thicknesses of the first and second portions are identical for the first and third parts, i.e e p11 =e p31  et e p12 =e p32 . 
     Of course, it is possible that the thicknesses e 1  and e 3  are different, and also that the thicknesses e p11 , e p31 , e p12  et e p32  are different from each other in pairs. 
     The first portion  16  and the second portion  18  of the first part  22  are woven to the second part  24  at a transition from the first part  22  to the second part  24 . The first portion  16  and the second portion  18  of the first part  26  are woven to the second part  24  at a transition from the first part  26  to the second part  24 . These transitions, indicated by two boxes A and B, correspond to an intertwining of the wires from the first portion  16  and the second portion  18  of the first part  22 , to form the second part  24 . 
     The fibrous structure  20  is characterised by the spacing between two weft planes along the warp direction C being greater in the second part  24  than in the first part  22  and the third part  26 . In addition, the number of weft yarns is lower in the second part  24  than in the first part  22  and in the third part  26 . The number of weft yarns per weft plane of the second part may be less than the number of weft yarns per weft plane of the first part. The number of weft yarns per weft plane of the second part may be less than the number of weft yarns per weft plane of the first part. This allows the warp-weft ratio of the first  22  and third  26  parts to be influenced relative to that of the second part  24 , to limit the thickness of the second part  24 , without trimming. The second part  24  of the fibrous structure  20  thus has a thickness such that e 2 ≤e 1  et e 2 ≤e 3 . 
     Table 1 below illustrates an example of a fibrous structure  12  according to the prior art, comprising a first part and a second part comprising a first portion  16  and a second portion  18 , wherein the second part  14  has a thickness e 2 &gt;e p12  and in particular wherein e 1 =e 2 . 
     
       
         
           
               
               
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                   
                 1 st  part 
                   
               
            
           
           
               
               
               
               
            
               
                   
                   
                 2nd 
                   
               
               
                 Areas 
                 1st portion 
                 portion 
                 2nd part 
               
               
                   
               
            
           
           
               
               
               
               
            
               
                 Number of layers 
                 14 
                 7 
                 21 
               
               
                 Number of weft planes 
                 14 
                 7 
                 21 
               
               
                 Number of warp planes 
                 14 
                 7 
                 21 
               
               
                 Warp spacing (mm) 
                 1.25 
                 1.25 
                 1.25 
               
               
                 Weft spacing (mm) 
                 1.25 
                 1.25 
                 1.25 
               
               
                 WWR (warp/weft ratio) 
                 50/50 
                 50/50 
                 50/50 
               
               
                 Moulding thickness (mm) 
                 4 
                 2 
                 6 
               
               
                   
               
            
           
         
       
     
     This fibrous structure  12  made in the previous technique from 21 textile layers by a three-dimensional multi-layer weaving of the fibrous structure  12  has a warp-weft ratio of 50/50 invariant in the different parts of the fibrous structure  12 . 
     In this case, the number of layers, warp and weft planes in the second part  14  is equal to the sum of the number of layers, warp and weft planes in the first  16  and second  18  portions of the second part  14  (and the third part if applicable), respectively. 
     The fibrous structure  20  according to the invention makes it possible to limit the thickness e 2  of the second part  24 , intended to form the bathtub, so that its thickness e 2  is close to the thickness e p12  of the second portion  18  of the first part  22  (and the third part  26  if applicable). In other words, e 1 , e 2  and e 3  can thus be different and this without trimming. 
     Table 2 illustrates a fibrous structure  20  according to a first embodiment of the invention, comprising a first part  22  and a second part  24  comprising a first  16  and a second  18  portion: 
     
       
         
           
               
               
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                   
                 1 st  part 
                   
               
            
           
           
               
               
               
               
            
               
                   
                   
                 2nd 
                   
               
               
                 Areas 
                 1st portion 
                 portion 
                 2nd part 
               
               
                   
               
            
           
           
               
               
               
               
            
               
                 Number of layers 
                 14 
                 7 
                 21 
               
               
                 Number of weft planes 
                 14 
                 7 
                 9 
               
               
                 Number of warp planes 
                 14 
                 7 
                 21 
               
               
                 Warp spacing (mm) 
                 1.25 
                 1.25 
                 1.25 
               
               
                 Weft spacing (mm) 
                 1.25 
                 1.25 
                 1.5 
               
               
                 WWR (warp/weft ratio) 
                 50/50 
                 50/50 
                 74/26 
               
               
                 Moulding thickness (mm) 
                 4 
                 2 
                 4.1 
               
               
                   
               
            
           
         
       
     
     The thickness e 2  of the second part  24  of this fibrous structure  20 , once shaped, is reduced to 4.1 mm, with parameters for the first  16  and second  18  portions of the first part  22  unchanged from table 1 illustrating the prior art. For this purpose, the spacing between two weft planes along the warp direction is increased from 1.25 mm to 1.5 mm so that it is greater than the spacing between two consecutive weft planes in the first part  22 , in particular in the first  16  and second  18  portions of the first part  22 . Furthermore, the number of weft yarns of the second part  24  is lower than the sum of the numbers of weft yarns of the first part  22 , i.e. the sum of the weft yarns of the first  16  and second  18  portions of the first part  22 , by locally disengaging weft yarns at the transition A between the first  22  and second  24  parts, in order to achieve a warp-weft ratio close to the 75/25 limit. 
     Thus, the combination of increasing the spacing between two consecutive weft planes and not inserting weft yarns locally, so as to reduce the weft planes [, unbalances the warp-weft ratio, in the example shown at 74/26. This allows the thickness e 2  of the second part  24  of the fibrous structure  20  intended to form the bathtub of the ring sector to be reduced by 1.9 mm compared to the prior art fibrous structure  12  illustrated in table 2. 
     Thus, in the second part  24  of the fibrous structure  20 , the number of weft yarns is lower than the number of warp yarns, respectively  9  and  21 . For practical reasons, the imbalance in the warp-weft ratio is achieved by adjusting the spacing between two successive weft planes, not the spacing between two successive warp planes. As a result, the distance between two warp planes is identical between the first part  22  and the second part  24 . 
     In the particular case, not illustrated, of weaving parts at 90° to the orientation presented in this document, it is possible to play with the spacing between two successive warp planes and keep the spacing between two successive weft planes constant. 
     Although the example illustrated here describes the particular situation with a fibrous structure  20  having a first  22  and second  24  part, the fibrous structure  20  may comprise a third part  26  identical to the first part  22  and woven to the second part  24  along the warp direction opposite the first part  22 . 
     Table 3 illustrates a fibrous structure  20  according to a first embodiment of the invention, comprising a first part  22  and a second part  24  comprising a first  16  and a second  18  portion: 
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 3 
               
             
            
               
                   
                   
               
               
                   
                   
                 1 st  part 
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                   
                   
                 2nd 
                   
               
               
                   
                 Areas 
                 1st portion 
                 portion 
                 2nd part 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 Number of layers 
                 10 
                 6 
                 16 
               
               
                   
                 Number of weft planes 
                 15 
                 7 
                 16 
               
               
                   
                 Number of warp planes 
                 10 
                 6 
                 16 
               
               
                   
                 Warp spacing (mm) 
                 1.25 
                 1.25 
                 1.25 
               
               
                   
                 Weft spacing (mm) 
                 1 
                 1 
                 1.5 
               
               
                   
                 WWR (warp/weft ratio) 
                 35/65 
                 41/59 
                 55/45 
               
               
                   
                 Thickness obtained in  
                 4.1 
                 2.1 
                 4.2 
               
               
                   
                 moulding (mm) 
                   
                   
                   
               
               
                   
                   
               
            
           
         
       
     
     In this structure  20 , the warp-weft ratio is varied in the first  16  and second  18  portions of the first part  22 , in order to reduce the number of textile layers subsequently woven in the second part  24 . 
     Thus, in the second portion  18  of the first part  22 , the number of weft planes is greater than the number of warp planes. In the first portion  16  of the first part  22 , the number of weft planes is 1.5 times the number of warp planes. The spacing between two successive weft planes in the first  16  and second  18  portions is reduced to 1 mm. 
     The modification of these parameters, unbalancing the warp-weft ratio of the first  16  and second  18  portions to 41/59 and 35/65 respectively, combined with an increase in the spacing between two successive weft planes, thus makes it possible to obtain, for a thickness of 2.1 mm and 4.1 mm respectively for the first  16  and second  18  portions of the shaped fibrous structure  20 , a thickness e 2  of the second part  24  equal to 4.2 mm. 
     In this example of a fibrous structure  20 , the number of weft yarns is greater than the number of warp yarns in the first portion  16  and in the second portion  18  of the first part  22  of the fibrous structure  20 . 
     The invention also relates to a fibrous structure  22 , the thickness of which e 2  of the second portion  24  is lower than the thickness of the first portion  22 , i.e. the sum of the thicknesses of the first  16  and second  18  portions. Table 4 illustrates a third embodiment of the invention: 
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 4 
               
             
            
               
                   
                   
               
               
                   
                   
                 1 st  part 
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                   
                   
                 2nd 
                   
               
               
                   
                 Areas 
                 1st portion 
                 portion 
                 2nd part 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 Number of layers 
                 10 
                 6 
                 16 
               
               
                   
                 Number of weft planes 
                 15 
                 7 
                 7 
               
               
                   
                 Number of warp planes 
                 10 
                 6 
                 16 
               
               
                   
                 Warp spacing (mm) 
                 1.25 
                 1.25 
                 1.25 
               
               
                   
                 Weft spacing (mm) 
                 1 
                 1 
                 1.5 
               
               
                   
                 WWR (warp/weft ratio) 
                 35/65 
                 41/59 
                 73/27 
               
               
                   
                 Thickness obtained in  
                 4.1 
                 2.1 
                 3.1 
               
               
                   
                 moulding (mm) 
                   
                   
                   
               
               
                   
                   
               
            
           
         
       
     
     Keeping the parameters of the first  16  and second  18  portion of the first part  22  of the fibrous structure  20  of the example in table 3, the thickness of the second part  24  is further reduced, changing the warp-weft ratio to 73/27 by reducing the number of weft planes of the second part  24  of the fibrous structure  20  from 16 to 7. 
     A thickness of 3.1 mm is then obtained for this second part  24  compared to 4.2 mm for the structure described with reference to table 3. 
     Thus, the invention also relates to the method of making the fibrous structures  20  as described with reference to tables 2 to 4. 
     The method for manufacturing the weaving of a fibrous structure  20  according to the invention thus comprises a step consisting of decreasing the spacing between two successive weft planes along the warp direction and decreasing the number of weft yarns during a transition in the warp direction from a first part of the fibrous texture to a second part  24  of the fibrous texture  20  having a thickness greater than that of the first part  22 . 
     The manufacturing process also includes a step of increasing the number of weft yarns and decreasing the spacing between two successive weft planes along the warp direction, during the transition in the warp direction from the second part  24  of the fibrous texture  20  to the first part  22  of the fibrous texture  20 . 
     The resulting fibrous structures  20  can then be used to manufacture a composite part, for example a stator sector  12 , as described above. 
     Thus, the invention also relates to a method for manufacturing a composite material, comprising the following steps: 
     a) Obtaining a fibrous structure  20  by means of the method as presented above; 
     b) Shaping the fibrous structure  20 ; 
     c) Obtaining a composite material by injecting or densifying a matrix inside the fibrous structure. 
     Step b) consists in obtaining from the fibrous structure  20  a fibrous preform intended to form the fibrous reinforcement of the composite part. This fibrous preform has a shape similar to that of the composite part. Thus, in the example of a stator sector  12  as described above, the woven fibrous structure  20  is “Pi” shaped, that is, the first portions  16  of the first  22  and third  26  parts of the fibrous structure  20 , are arranged so as to form an angle with the second portions  18  of the first  22  and third  26  parts and with the second part  24  (the latter three being substantially aligned). This is done with the help of shaping tools, allowing the preform to be held in a shape close to that of the part to be manufactured. 
     The composite part is then obtained by densifying the fibrous preform, i.e. by injecting a matrix inside the shaped fibrous structure. The matrix may be a resin or, in the case of a thermostructural composite, a refractory material such as carbon or ceramic. 
     The matrix injection can be carried out for example by Chemical Vapour Infiltration (CVI), by the process known by the acronym PIP for Polymer Infiltration and Pyrolysis or any other process conventionally known for the design of CMC parts.