Abstract:
The present disclosure relates to a method for producing a composite skin forming a non-strippable rotationally-symmetrical collar. The method includes draping fabric plies over a mold, providing a separating line on the draped fabric plies, post-impregnating the draped plies with a resin, curing the resin, removing the resulting skin from the mold using a separating line, and, subsequently, splinting two edges of the skin defined by the separating line.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of International Application No. PCT/FR2013/050970, filed on May 2, 2013, which claims the benefit of FR 12/54258, filed on May 10, 2012. The disclosures of the above applications are incorporated herein by reference. 
     
    
     FIELD 
       [0002]    The present disclosure relates to the field of the manufacture of composite skins forming shrouds, that is to say having substantially a shape with rotational symmetry about an axis. 
       BACKGROUND 
       [0003]    The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. 
         [0004]    Such composite skins, obtained by arranging fabric plies over a tooling forming a shroud, impregnated by resin beforehand (called “pre-impregnated” plies) or afterwards (called “post-impregnated” or “infused” plies) upon their placing on the tooling, are used especially for air inlets of nacelles for turbojet engines of aircrafts, where they are then perforated and coupled with honeycomb cellular structures. 
         [0005]    In this manner, we obtain sandwich structures called “360°”, that is to say allowing to achieve an acoustic absorption function over the entire inner periphery of the air inlet: such structures are known for example from documents FR 2 847 304, FR 2 931 205 and WO 2005/090156. 
         [0006]    A constant problem involved in the manufacture of such sandwich structures is that the skin forming the shroud has generally convex zones which exclude the possibility of stripping this skin from a tooling in a single operation. 
         [0007]    We must therefore either carry out a complex tooling comprising several portions movable relatively to each other (called “keys”) or carry out the composite skin into a plurality of portions that will then be connected to each other. 
         [0008]    In either case, the operations are complex, and give rise to many aerodynamic accidents at the surface of the skin obtained at the end of the process, in the connection zone either between the different keys of the tooling, or between various portions forming the skin. 
       SUMMARY 
       [0009]    The present disclosure provides a method for manufacturing a composite skin forming a shroud comprising the successive steps:
       draping fabric plies, either pre-impregnated, or dry, on a mold, said mold forming a shroud and presenting a bulge preventing the stripping of the composite skin by axial sliding of said skin on said mold,   providing for a separation line defining two edges on the obtained draping,   post-impregnating this resin draping if the deposited fabric is dry,   baking this resin,   removing the obtained skin from the mold using the separation line,   splinting both edges of the skin.       
 
         [0016]    Therefore, to remove the baked skin from the mold forming a shroud, it is sufficient to space away the two edges of this skin located on either side of the separation line, by using the elasticity of this skin. 
         [0017]    The present disclosure thus allows greatly simplifying the manufacture of the composite skins forming non-strippable shrouds, and limit aerodynamic accidents on the surface of such skins. 
         [0018]    According to other features of the present disclosure:
       said separation line is carried out by means of a groove formed in said mold forming a shroud, in which a cutting tool is introduced before the finish of the resin;   a strip is placed in said groove prior to impregnation of the plies with the resin;   said separation line is carried out with at least a fixed strip integral with said mold forming a shroud, against which abut two edges of the plies draping;   a strip cover is placed on said strip prior to impregnation of the plies with the resin;   said separation line is carried out by a simple cutting of the plies draping by its thickness, with a cutting by full thickness followed by cuttings of a portion only of the draping thickness, allowing to obtain stepped edges;   said separation line is carried out by covering two edges of the draping;   a separator is placed between the two edges of the draping which are adjacent to the separation line prior to impregnation of the plies with the resin;   said separation line is carried out by covering a cavity formed on the mold forming the shroud;   said separation line is carried out by draping plies on a mold forming a shroud of dimensions greater than that of the final part, in order to obtain an open skin, and the two edges of this draping which are adjacent to the separation line are machined after baking of the resin;   said separation line is carried out according to a direction selected from the group comprising the longitudinal direction, the transverse direction, and any intermediate position between these two positions;   said resin draping is impregnated if the fabric is dry and used, in particular in the “infusion” version, using a bladder that is applied on this draping against the mold forming a shroud, and which is put under vacuum;   the splinting of both edges of the skin is carried out on or inside a key tooling;   a honeycomb cellular structure is brought on said splinted skin disposed on or inside said key tooling;   said composite skin is glued to the inside or to the outside of a set formed of a honeycomb cellular structure fixed to another composite skin, and the splinting of both edges of the skin is carried out on or inside this set.       
 
         [0033]    If necessary, the acoustic perforation of the skin can be done after polymerization of this skin, before implantation of the cellular structure. Alternatively, this skin can be perforated after implantation of the cellular structure. 
         [0034]    Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
     
    
     
       DRAWINGS 
         [0035]    In order that the disclosure may be well understood, there will now be described various forms thereof, given by way of example, reference being made to the accompanying drawings, in which: 
           [0036]      FIG. 1  is a top view of a mold forming a shroud on which are draped fabric plies intended to form a composite skin, corresponding to a first form of the method according to the present disclosure; 
           [0037]      FIG. 1   a  is a detailed view of Zone I of  FIG. 1 ; 
           [0038]      FIGS. 1   b  to  1   f  are views similar to those of  FIG. 1   a , highlighting the various steps of this first form of the method according to the present disclosure; 
           [0039]      FIGS. 1   g  and  1   h  are respectively similar to  FIGS. 1 and 1   a,  and relate to another form of the first form of the method according to the present disclosure; 
           [0040]      FIGS. 2 to 2   i  are respectively similar to  FIGS. 1   a  to  1   h , and relate to a second form of the method according to the present disclosure; 
           [0041]      FIGS. 3 to 3   e  relate to a third form of the method according to the present disclosure, being denoted that  FIG. 3   b  is a cross-sectional view of the separation zone of the draping disposed on the mold forming a shroud; 
           [0042]      FIGS. 4 to 4   e  are cross-sectional views of this separation zone, for a fourth form of the method according to the present disclosure; 
           [0043]      FIGS. 5 to 5   b  are cross-sectional views of this separation zone, for a fifth form of the method according to the present disclosure; 
           [0044]      FIGS. 6 to 6   a  are cross-sectional views of this separation zone, for a sixth form of the method according to the present disclosure; 
           [0045]      FIGS. 7 and 8  are views similar to those of  FIGS. 1 and 2 , in the case where the separation line on the draping is transverse; 
           [0046]      FIG. 8   a  is a detailed view of Zone VIII of  FIG. 8 ; 
           [0047]      FIG. 9  schematically shows an form of a composite skin on a mold forming a shroud, when this skin is disposed outside of this mold; 
           [0048]      FIG. 9   a  illustrates the splinting of the thus obtained composite skin, disposed outside a key tool; 
           [0049]      FIG. 9   b  illustrates the placing of a honeycomb cellular structure on the composite skin splinted at the end of step of  FIG. 9   a;    
           [0050]      FIGS. 10 to 10   b  illustrate steps similar to those of  FIGS. 9 to 9   b , when the composite skin is disposed inside a mold forming a shroud, then splinted and covered with a honeycomb cellular structure inside a key tool; 
           [0051]      FIGS. 11 to 11   c  are respectively similar to  FIGS. 9   a    9   b , and relate to the form of  FIG. 6  or  6   a , being denoted that  FIG. 11   b  is an enlargement of Zone XI of  FIG. 11   a;    
           [0052]      FIGS. 12 to 12   c  are respectively similar to  FIGS. 10 to 10   b , for an form similar to that of  FIGS. 6 to 6   a , being denoted that  FIG. 12   b  is an enlargement of Zone XII of  FIG. 12   a ; and 
           [0053]      FIGS. 13   a  and  13   b  are views of another form of the method according to the present disclosure. 
       
    
    
       [0054]    The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
       DETAILED DESCRIPTION 
       [0055]    The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features. 
         [0056]    In addition, note also that care was taken to represent for each of the figures a reference frame XYZ, each axis of which is collinear respectively to the longitudinal, transverse and vertical directions of an aircraft on which is mounted a nacelle incorporating at least one composite skin obtained by the method according to the present disclosure. 
         [0057]    Referring to  FIG. 1 , a mold forming a shroud  1  is shown, carried out for example of steel or other metal alloys. 
         [0058]    The mold  1  is intended to be covered with a fabric draping intended to form a composite part presenting a shape substantially with rotational symmetry. 
         [0059]    As seen in  FIG. 1 , the mold  1  presents a bulge  5  preventing the stripping of the composite skin by simple axial sliding of this skin on this mold. 
         [0060]    To enable this stripping, a longitudinal groove  7  formed in the thickness of the mold  1  is provided, and extending slightly beyond the area of the mold intended to be draped by the fabric plies  3 , as is seen in particular in  FIG. 1   b.    
         [0061]    To carry out the composite skin, we start with draping the fabric plies over the entire periphery of the mold  1 , including the groove  7 , as can be seen in  FIG. 1   b.    
         [0062]    Then, as seen in  FIG. 1   c,  by means of a manually or automatically operated cutting tool  9 , the plies draping is cut along the groove  7 . 
         [0063]    Next, as seen in  FIG. 1   d,  a strip  11  substantially presenting a T-section is brought to the inside of the groove  7 , so as to seal this groove along its entire length. 
         [0064]    And then the entire draping is covered, including the strip  11 , with a flexible bladder  14  that is put under vacuum, thus providing the sealed covering of the strip  11  and the draping  3  set. 
         [0065]    In case of infusion of resin, the polymerizable resin is introduced under pressure below the flexible bladder  14  (“post-impregnation” also called “infusion” of resin) so that this resin impregnates the entire draping. 
         [0066]    The temperature of the thus obtained set is raised, for example inside an autoclave, so as to cure the resin. 
         [0067]    Thereafter, the flexible bladder is removed, then the strip  11 , and the thus obtained composite skin is removed from the mold  1  using the separation line previously carried out along the groove  7 , and using the relative flexibility of this skin. 
         [0068]    Note that two substantially parallel grooves  7   a  and  7   b  can be provided, as shown in  FIG. 1   h , allowing to perform two cutting lines in the draping, for example when it is desired that the thus obtained composite skin presents a diameter more significant than the final need. 
         [0069]    Note that in this particular case, a strip similar to that of  FIG. 1   e  can be provided, but presenting two feet intended to insert respectively in the grooves  7   a  and  7   b.    
         [0070]    In the form of  FIG. 2 , a strip  11  fixedly mounted on the mold  1 , and extending longitudinally slightly beyond the two ends of the draping  3 , as can be seen in particular in  FIGS. 2 and 2   b.    
         [0071]    In this form, the draping  3  can be carried out so that one of its edges  13   a  abuts against the strip  11 , and that the other of its edges  13   b  slightly covers this strip  11 , being denoted that in the following step shown in  FIG. 2   c , the draping overlength is cut using a tool  9  so that both edges thereof abut properly on both sides of the strip  11 . 
         [0072]    In another form represented in  FIG. 2   d , both faces of the strip  11  can be used as faces of start and finish of the draping, the folding of the various plies forming this draping being carried out upon the abutment against the faces of this strip: in this case, no cutting tool is required. 
         [0073]    In either of these two forms, the strip  11  is then covered with a strip cover  15 , which is in fact a female part capable to receive this strip  11  while pressing the adjacent edges of the drape  3 . 
         [0074]    Step  2   f  is similar to step  1   f : this step consists indeed in covering the draping and the strip cover  15  of a bladder  14  which is put under vacuum, and then introducing the resin under pressure if the fabric is dry and used in the “infusion” version, the thus obtained set being placed in an autoclave to cure the resin. 
         [0075]    The stripping of the thus obtained composite skin is shown in  FIG. 2   g : as in the preceding form, the elasticity of this skin is used to space away the two adjacent edges of this skin of the strip  11  (arrows F 1 , F 2 ), to axially (arrows F 3  and F 4 ) get this skin out of the mold  1 . 
         [0076]    Note that alternatively, fabric plies pre-impregnated with resin can be used. This is also applicable to the forms which will be described hereinafter. 
         [0077]    In still another form as shown in  FIGS. 2   h  and  2   i , it is seen that two strips  11   a  and  11   b  can be provided, similarly to the two grooves  7   a  and  7   b  of the previous form, in which case a two-slot strip cover must be considered, suitable for fitting respectively on these two strips  11   a  and  11   b.    
         [0078]    In the form of  FIGS. 3   a ,  3   e , neither a groove nor a strip is provided at the surface of the mold  1 . 
         [0079]    As shown in  FIG. 3 , the draping  3  is simply cut at full skin using a cutting tool  9 , as indicated by the cutting line  17 . 
         [0080]    As shown in  FIG. 3 , a cutting  17  on a thickness of the draping  3  can be carried out, as well as a plurality of adjacent stepped cuttings  17   a,    17   b,    17   c,    17   d,  on the different thicknesses of the draping. 
         [0081]    After this cutting is carried out, as shown in  FIGS. 3   b  and  3   c , a sheet of a separator  19  is placed between the two edges  13   a  and  13   b  of the draping. 
         [0082]    This sheet  19 , which can be carried out for example of PTFE (polytetrafluoroethylene) is selected so that its outer face  19   a  is polymerizable with the resin, while its inner face  19   b  (that is to say its face located opposite to the mold  1 ) is not. 
         [0083]    This separator  19  allows, during the resin impregnation step (see  FIG. 3   d  similar to that of  FIGS. 1   f  and  2   f ) if the fabric is dry and used in the “infusion” version, to prevent the resin from slipping between the two edges  13   a  and  13   b  of the draping. 
         [0084]    Once the resin polymerization step is done, the two edges of the thus obtained composite skin can be spaced away, and removed from the mold  1 , as shown in  FIG. 3   e.    
         [0085]    The overflowing portion of the separator  19  can thereafter be suppressed, for example by cutting. 
         [0086]    The form of  FIGS. 4   a ,  4   e  differs from the previous one in the sense that it provides a cover between the edges  13   a  and  13   b  of the draping  3 . 
         [0087]    As in the previous form, the placing of a separator  19 , presenting the same characteristics of polymerization on its faces  19   a  and  19   b  as described in connection with  FIG. 3   b , is considered. 
         [0088]    In the variant shown in  FIG. 4 , this separator is glued under the edge  13   b  of the draping  3 , which edge is held away from the other edge  13   a  of this draping by a strip  21  of suitable shape. 
         [0089]    In another form shown in  FIG. 4   a , the separator  19  is glued to the edge  13   a  of the draping  3 , intended to be covered by the other edge  13   b  of this draping. 
         [0090]    In one case as in the other, once the edge  13   a  of the draping  3  is covered by the edge  13   b,  we come to the configuration of  FIG. 4   c , in which a mutual covering of these two edges can be observed, the separator  19  presenting a substantially bayonet section. 
         [0091]      FIG. 4   d  illustrates the positioning of the flexible bladder  14 , allowing the impregnation of the draping by the pressurized resin if the fabric is dry and used in the “infusion” version. 
         [0092]      FIG. 4   e  shows the result obtained after autoclaving: 
         [0093]    the separator  19  remains integral with the edge  13   b  of the draping, due to polymerization of the resin, but detaches easily from the other edge  13   a  of the draping, therefore allowing the spacing away of both edges of the thus obtained composite skin in view of its axial retraction from the mold  1 . 
         [0094]    In the form of  FIGS. 5   a ,  5   b , a longitudinal cavity  23  integral with the mold forming the shroud  1  is provided. 
         [0095]    The draping  3  is therefore disposed so that its edge  13   a  abuts between this cavity  23 , and its other edge  13   b  covers this cavity  23  almost entirely. 
         [0096]    Therefore, after disposition of the flexible bladder  14  ( FIG. 5   a ), the impregnation of the resin draping (if the fabric is dry and used in the “infusion” version) and autoclave baking, the two edges of the thus obtained composite skin can be moved, as seen in  FIG. 5   b , these two edges having a geometry appropriate for their subsequent covering, because of the bayonet shape conferred by the cavity  23  to the edge  13   b  of the composite skin, as seen in this  FIG. 5   b.    
         [0097]    The form of  FIGS. 6 and 6   a  shows that it is also possible to provide for a draping on a mold forming the shroud  1 , having dimensions greater than that desired for the final composite skin. 
         [0098]    In this case, the mold  1  is draped only over part of its periphery, so as to leave a circumferential distance d between the two edges  13   a  and  13   b  of this draping. 
         [0099]    The various plies of this draping can also be disposed so that they present a stepped configuration, as seen in  FIG. 6   a.    
         [0100]      FIG. 7  shows that the foregoing precepts can be applied to the carrying out of a transverse junction zone  25  between two halves  3   a  and  3   b  of the draping  3 . 
         [0101]    This transverse junction line  25  is then to the right of the bulge  5  of the mold forming the shroud  1 . 
         [0102]      FIGS. 8 and 8   a  illustrate the particular case where this junction line  25  is carried out in accordance with the precepts of the form of  FIGS. 5   a ,  5   b , that is to say with the carrying out of a cavity  23  on the entire circumference of the mold forming the shroud  1 . 
         [0103]    In the latter case, as in the form of  FIGS. 5   a ,  5   b , we thus end up with a composite skin comprising two edges  13   a  and  13   b  which cover one another, this covering being in this case circumferential. 
         [0104]      FIGS. 9   a ,  9   b , summarize the manufacturing of a composite skin according to any one of the forms of  FIGS. 1 to 5 , in the case where the draping is carried out on a mold forming the male shroud  1 . 
         [0105]    As seen in  FIG. 9 , thus we start by the draping  3  on the outer periphery of the mold  1 . 
         [0106]    After the steps of resin impregnation if the fabric is dry and used in the “infusion” and baking version, the obtained composite skin can be stripped from the mold  1  by elastic deformation of this skin, as indicated hereinbefore. 
         [0107]    This skin is then disposed on a key tooling  27 , that is to say on a tooling including a plurality of movable elements relative to one other, allowing removal of the composite skin, including when it became a single-piece, that is to say when these two opposite edges  13   a  and  13   b  have been joined to each other. 
         [0108]    On this key tool  27 , a splinting  29  of two edges  13   a,    13   b  of the composite skin is carried out. 
         [0109]    This splinting is typically carried out by provision and polymerization of an external composite element. 
         [0110]    Then, in the case where it is desired that the composite skin is covered with an acoustically absorbent structure, the outer periphery of this composite skin can be brought, by gluing, a honeycomb cellular structure  31 , which can be densified in the zone  33  that is opposite of the splinting  29 . 
         [0111]    Once all these operations are performed, the key tooling  27  can be dismounted so as to recover the thus obtained part. 
         [0112]    Note that the acoustic perforation in the skin can be carried out after polymerization of this skin, prior to implantation of the cellular structure. Alternatively, this skin can be perforated after implantation of the cellular structure. 
         [0113]      FIGS. 10   a  to  10   b  are similar to  FIGS. 9 and 9   b , and relate to another form in which the plies draping is carried out inside a mold  3 , then treated in conformity with the method according to the present disclosure. 
         [0114]    Specifically, once the composite skin obtained after the various steps described hereinbefore, this skin can be removed from inside the mold  1  by elastic approximations of these two edges  13   a,    13   b.    
         [0115]    The steps of skin splinting inside a key tooling  27  ( FIG. 10   a ), and then the provision of a honeycomb cellular structure  31  ( FIG. 10   b ), are then similar to those described regarding  FIGS. 9   a  and  9   b.    
         [0116]      FIGS. 11 to 11   c  are similar to  FIGS. 9 and 9   b , but relate to the form of the method according to the present disclosure described in  FIG. 6   a.    
         [0117]    As indicated hereinbefore, in this particular form, the plies draping  3  is carried out on a mold forming a shroud  1  presenting dimensions greater than those of the part desired to obtain in the end. 
         [0118]    The stepped draping can be seen in  FIG. 11 , corresponding to the one illustrated in  FIG. 3 . 
         [0119]      FIG. 11   b  shows that the splinting on a key tooling  27  in this case is performed by providing a plurality of external composite elements  29   a,    29   b.    
         [0120]    The form of  FIGS. 12 to 12   c  is similar to that of  FIGS. 11 to 11   c , but in the case where the plies draping  3  is carried out inside a mold forming a shroud  1 , and/or the splinting and provision of a cellular structure are carried out inside a key tooling  27 . 
         [0121]    As can be understood in the light of the foregoing, the method of the present disclosure allows carrying out composite skins in the form of shrouds, that is to say 360°, presenting minimal aerodynamic accidents, with extremely simple tooling. 
         [0122]    This method, according to which a separation line is carried out at a suitable location of the draping of fabric plies, and the composite skin obtained by elastic deformation relative to its mold is recovered, allowing to obtain composites skins having shapes substantially with rotational symmetry, which would be impossible to obtain without complex key tooling. 
         [0123]    Composite skins forming shrouds can in particular be obtained, presenting bulges and hollow zones excluding any translational stripping with respect to a traditional mold. 
         [0124]    Of course, the present disclosure is in no way limited to the described and represented forms, provided only as examples. 
         [0125]    This is how for example we can also consider placing a composite skin obtained by the method described hereinabove, inside or outside of a set  35  formed of a honeycomb cellular structure  31  fixed to another skin or composite shroud  37  already polymerized such as in RTM, and the splinting is carried out on both edges of the skin  13   a,    13   b  on or inside this set  35 , as shown in  FIGS. 13   a  and  13   b  appended hereinto. 
         [0126]    In this form, the set  35  constitutes a single-piece housing on which the composite skin obtained by the above method is brought by gluing.