Abstract:
A process for manufacturing a one-piece axisymmetric part includes: superposition, around a rotating cylindrical mandrel of at least respectively inner and outer metal-coated composite fibrous structures, wound in first and second crossed directions on the mandrel; arranging, between the crossed inner and outer fibrous structures, at least one layer of metallic wire; then placing a blank of the part, formed by the fibrous structures and the layer of metallic wire, in a tool to apply to the blank a hot isostatic pressing treatment, and to obtain the part.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a method for manufacturing an integral rotationally symmetrical metal part from composite fibrous structures in the form of fibers, fiber laps, fiber fabrics and similar, coated with metal. 
     2. Description of the Related Art 
     The importance of composite materials in the partial or total production of parts has emerged in recent years, in many technical fields, notably aeronautics, space, military, automobile, etc., because of the optimization of the resistance of such materials, for minimal weight and bulk. As a reminder, such a structure comprises metal composite fibers composed of a metal alloy matrix, by example titanium Ti alloy, within which extend fibers, for example ceramic fibers of silicon carbide SiC. Such fibers exhibit a tensile strength much greater than that of titanium (typically, 4000 MPa compared to 1000 MPa). It is therefore the fibers which take up the forces, the metal alloy matrix acting as a binder for the part, and providing protection and insulation for the fibers, which must not come into contact with one another. Furthermore, the ceramic fibers are resistant to erosion, but necessarily have to be reinforced with metal. 
     These composite materials can be used to produce annular, rotationally symmetrical gas turbine parts for aircraft or other industrial applications, such as rings, shafts, cylinder bodies, casings, spacers, monolithic part reinforcements such as blades, etc. 
     The known methods for manufacturing such integral rotationally symmetrical parts consist in superposing, around a rotary cylindrical mandrel, successive fibrous structures (fibers, fiber lap or fiber fabric) and then arranging the composite fibrous structures, wound and removed from the mandrel in a specific receiving outfit for them to be heat treated and to ultimately obtain the rotationally symmetrical part made of composite material. 
     For the rotationally symmetrical part to be particularly rigid and withstand forces in different directions, notably torsional forces, one of the superposed fibrous structures is oriented in a first winding direction relative to the longitudinal axis of the mandrel, then the other fibrous structure is wound on the preceding one in a second winding direction different from the first, so as to obtain two composite fibrous structures that have crossed winding directions. 
     However, it has been noted that crossing over the metal-coated ceramic composite fibers of the two fibrous structures superposed one on top of the other could create excessive local stresses which occur during the cooling of the part, after the creep of the thin metal cladding of the fibers of the structures. These excess stresses drastically reduce the mechanical characteristics of the part. 
     BRIEF SUMMARY OF THE INVENTION 
     The aim of the present invention is to remedy these drawbacks. 
     To this end, the method for manufacturing an integral rotationally symmetrical part by superposition, around a rotary cylindrical mandrel, of at least two metal-coated composite fibrous structures, respectively inner and outer, wound in first and second directions crossed on said mandrel, is noteworthy in that it consists:
         in arranging, around the inner fibrous structure constructed on the mandrel in the first winding direction, at least one layer of metal wire,   in winding, on said layer of metal wire, the outer fibrous structure in the second winding direction,   in placing the preform of said part, formed by the fibrous structures and the layer of metal wire, in a receiving outfit to apply to the preform a hot isostatic compaction or isothermal forging treatment, and   in extracting the treated preform from the outfit, and if appropriate, machining the treated preform to obtain said part.       

     Thus, by virtue of the invention, the layer of metal wire serves as interface between the superposed and crossed fibrous structures and increases the metal thickness between the structures, so that the excess stresses between the composite fibers of the structures no longer occur. 
     Advantageously, the metal wire is obtained, for example, by wire drawing and is of the same nature as the metal of the composite fibrous structures, so that there is obtained, after passage through the outfit, an intermediate and uniform metal layer that has an appropriate thickness between the fibers of the structures. However, the wire could be obtained other than by wire drawing. A “metal wire” should be understood to mean equally one and the same continuous wire and a plurality of wires placed end to end. The metal wire can also be individual or take the form of a lap or a band of a plurality of parallel or interlaced wires, a cable, a fabric of unidirectional wires, etc., without departing from the framework of the invention. 
     Preferably, the superposed winding layers of the metal wire and of the fibrous structures are made cold, at ambient temperature, which does not require any complex installation for the implementation of the relevant steps of the method. 
     Furthermore, the metal wire is wound substantially orthogonally to the longitudinal axis of the rotary cylindrical mandrel to form the layer of contiguous turns. 
     To insulate and protect the inner fibrous structure from the outside, at least one layer of metal wire, on which the inner fibrous structure is subsequently wound, can be arranged around said cylindrical mandrel, before the placement of the inner fibrous structure. 
     For the same purpose, at least one layer of metal wire can be arranged around the outer fibrous structure, so that the part obtained has, on the surface, a thickness of outer and inner metal layers. 
     According to an exemplary embodiment, the first winding direction of the inner fibrous structure is oriented at an angle relative to the longitudinal axis of the cylindrical mandrel, the second winding direction of the outer fibrous structure then being oriented symmetrically to the first relative to a radial direction of the mandrel, at right angles to its longitudinal axis. For the range of values, if the winding direction of the inner fibrous structure is between 30°-60° relative to the longitudinal axis of the mandrel, the winding direction of the outer structure will be between 30°-60°+π/2. 
     In this example, the inner and outer fibrous structures may be in the form of individual and parallel fibers wound in succession around the mandrel, or in the form of laps or strips of parallel fibers, or in the form of fabrics of parallel fibers, said structures being arranged crossed on the mandrel. 
     According to another exemplary embodiment, the first winding direction of the inner fibrous structure is parallel to the longitudinal axis of the cylindrical mandrel, the second winding direction of the outer fibrous structure then being oriented at an angle relative to the longitudinal axis of the mandrel. 
     In this example, the inner fibrous structure may be in the form of a fabric of mutually parallel fibers wound around the cylindrical mandrel parallel to its longitudinal axis, the outer fibrous structure being able to be any structure but, obviously, with the fibers oriented at an angle relative to those of the inner structure which are parallel to the mandrel. 
     Moreover, the metal wires used can have different diameters, and layers with a plurality of superposed windings of these wires may be provided in alternation with the superposed fibrous structures, the number of which can be greater than two. 
    
    
     
       The figures of the appended drawing will give a clear understanding as to how the invention can be produced. In these figures, identical references designate similar elements. 
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         FIGS. 1, 2, 3, 4A, 4B ,  4 C 1 ,  4 C 2 ,  5 ,  6 A,  6 B and  7  schematically show the main steps of the method according to the invention, for manufacturing an integral rotationally symmetrical part from composite fibrous structures,  FIGS. 4A, 4B ,  4 C 1  and  4 C 2  presenting various possible outer fibrous structures used after the method step illustrated in  FIG. 3 , while  FIGS. 6A and 6B  schematically represent perform treatment outfits for obtaining the part. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The aim of the method is to manufacture an annular integral rotationally symmetrical part  1 , illustrated in  FIG. 7 , solely from elongate elements in the form of wires, fibers or similar, as will be seen hereafter. 
     For this, the method consists in using a rotary cylindrical mandrel  2  of longitudinal axis X and in first of all winding, around the lateral surface  3  thereof, in a first step illustrated in  FIG. 1 , at least one metal wire  4 . Given the application of the part  1  to the aeronautical field, the metal wire  4  is produced notably in a titanium alloy of TA6V or 6242 type to provide thermo-mechanical resistance and lightness, and it is obtained in this non-limiting example by wire drawing so as to be able to be available in spool or reel form from which the wire is drawn. 
     Dimensionally, its diameter depends on the part to be obtained and can, for example, be of the order to a few tenths of a millimeter. 
     In the example illustrated in  FIG. 1 , the drawn metal wire  4  is taken from a spool which is not represented and is driven, substantially perpendicularly to the axis X, around the lateral surface  3  of the cylindrical mandrel  2  over a predetermined extent corresponding to the length that is to be obtained, after manufacture, for the rotationally symmetrical part  1 , by thus forming a plurality of contiguous turns  5 , and over a predetermined plurality of superposed layers  6 . 
       FIG. 2  shows the three layers  6  formed by the windings of contiguous turns  5  of the same metal wire  4  around the mandrel. It would also be possible to use a metal wire  4 ′ such as that shown in cross section in  FIG. 1 , with a different diameter, less in this case than the diameter of the metal wire  4 . This is to show that it is possible to wind metal wires that have distinct diameters. 
     The method continues with a second step shown in  FIG. 2  and consisting in arranging a composite fibrous structure  7  around the drawn metal wire  4 . 
     In this example, the composite fibrous structure  7  takes the form of a fabric  8  of fibers  9  joined together in parallel and made of ceramic (SiC) or of a similar material, coated with metal. The latter and the metal of the drawn wire are of identical nature (as an example, of titanium alloy of TA6V or 6242 type) to optimize the subsequent step of the method concerning the hot isostatic compaction or isothermal forging operation. The fabric  8  of the fibrous structure  7 , qualified as inner, since it is turned toward the mandrel, is wound around the metal wire  4  so that the fibers  9  are arranged parallel to the longitudinal axis X of the mandrel  2  (with a zero helix angle), thus defining a first direction D 1  of orientation of the fibers of the fabric  8 . 
     As  FIG. 2  shows, a single layer  10  of the fabric  8  is formed around the wire  4 . Obviously, a winding of a plurality of layers  10  could be provided from the same fabric, even from one or more other distinct fabrics wound concentrically. 
     Then, according to a third step of the method illustrated in light of  FIG. 3 , a drawn metal wire  11  which originates from a spool which is not represented and which is fed in substantially orthogonally to the longitudinal axis X of the rotary cylindrical mandrel  2 , is arranged around the fabric  8  of the inner composite fibrous structure  7 . 
     The metal wire  11  forms a single layer  12  of contiguous turns  13  around the fabric  8 . A winding of a plurality of layers is once again possible, dependent on the diameter of the wire used and on the separation to be provided between the inner composite fibrous structure  7  and a then outer composite fibrous structure  14  to be superposed as will be see hereinbelow. 
     The drawn metal wire  11  can be the same (diameter, nature) as that used to form the layers  6  on the mandrel  2  and originate from the same spool. However, it could also have a different diameter. 
     By virtue of the placement, as inner fibrous structure  7 , of a fabric  8  with ceramic fibers  9  parallel to the longitudinal axis X of the mandrel  2 , a number of possibilities can be envisaged with regard to the outer fibrous structure  14  to produce, at this stage, a preform E of the integral part to be obtained  1 , and these possibilities are shown in  FIGS. 4A, 4B ,  4 C 1  and  4 C 2 . 
     As  FIG. 4A  shows, the outer fibrous structure  14  is made up of ceramic composite fibers  15 , coated with metal, that may or may not be identical to the preceding fibers. These fibers  15  are wound in succession around the turns  13  of the layer  12  of intermediate metal wire  11 , which is located, according to the invention, between the two fibrous structures  7  and  14 . The fibers  15  are contiguous and oriented in a second direction D 2  relative to the axis X of the mandrel  2 , forming a helical angle A relative thereto. Thus, the wound fibers  15  and the fibers  9  of the fabric  8  have different respective directions of orientation D 1  and D 2  that are crossed to allow for the production of rigid, integral, composite rotationally symmetrical parts. Some of the fibers  15  are only partially represented. 
     The number of wound fibers  15  is variable and is a function of the helical angle A to be given, which is, for example, of the order of 30° to 60°, and of the diameter of the fibers. A single layer  16  of the fibers  15  is made around the metal wire  11 . However, a plurality of layers can be envisaged. 
     Thus, at this stage of the manufacturing method, the two inner  7  and outer  14  fibrous structures are not in direct contact with one another, being separated by the layer of winding of the intermediate drawn metal wire  11  serving as interface, in order to eliminate any excessive stress that might occur between them during the cooling of the preform E formed by the structures and the metal wires. 
     Instead of the individual composite fibers  15 , the outer fibrous structure  14  may be made up of a successive winding of laps or strips  17  each made up of parallel composite fibers  18  (six in this example), that is to say, having a core made of ceramic or of a similar material coated with metal, preferably identical to the drawn wire  11 . To keep the fibers  18  of a lap  17  mutually parallel, transversal metal weaving wires  19 , of identical nature to the drawn wire, are provided at regular intervals. Here again, the number of laps  17  to cover the layer  12  of intermediate metal wire  11  is dependent on the width of the lap and on the helical angle A thereof relative to the winding axis X of the rotary cylindrical mandrel  2 . The helical angle A of the laps defines the second direction D 2  of the outer fibrous structure  14 , crossing the direction D 1  of the inner fibrous structure  7 . It can be seen, in  FIG. 4B , that two successive identical laps  17  are used to form a single layer  20  of the outer fibrous structure  14 . More than one layer  20  could obviously be envisaged. And it goes without saying that the outer fibrous structure  14  covers all of the layer of metal wire  11 . 
     According to another design shown in FIGS.  4 C 1  and  4 C 2 , the outer fibrous structure  14  takes the form of a fabric  21  with metallic composite fibers  22 , assembled together in parallel. 
     In the example of FIG.  4 C 1 , the fibers  22  are oriented obliquely relative to the perpendicular sides  23 ,  24  of the fabric  21  in the form of a rectangular strip. In this way, when the fabric  21  is offered up by its corresponding side  23  (small side) parallel to the longitudinal axis X of the cylindrical mandrel  2 , it is wound, by the rotation of the latter, over the layer  12  of intermediate drawn wire  11  and these oblique parallel composite fibers  22  form the desired helical angle A defining the second direction D 2  of the outer fibrous structure  14 , crossed with the first direction D 1  of the inner fibrous structure  7 . The dimension of the fabric  21  is sufficient to cover all of the layer of drawn wire. A layer  25  (or a plurality of layers if necessary) of fabric  21  is thus wound on the intermediate drawn wire  11 . 
     In the example of FIG.  4 C 2 , the fibers  22  are parallel to the side  23  of the fabric  21  to be wound and are linked together by wires  27 . Also, to have a direction of orientation D 2  of the fibers that is different from that of D 1  of the inner structure, the fabric  21  itself is offered up obliquely by one of its corners  26  relative to the rotary cylindrical mandrel  2 , so as to form the desired helical angle A. Thus, the parallel fibers  22  of the fabric  21  are wound around the layer  12  of drawn metal wire  11  in the desired second direction D 2 , crossed with the first direction D 1  of the inner fibrous structure  7 , parallel to the axis X of the cylindrical mandrel  2 . The dimension of the fabric  21  is such that it makes it possible to cover all of the layer  12  of drawn wire by the winding of said fabric over one or more layers  25 . 
     Thus, whatever the solutions retained, the two fibrous structures  7  and  14  have directions D 1 , D 2  that are crossed and are separated from one another by at least one layer  12  of contiguous turns  13  of the metal wire  11  acting as interface, in accordance with the invention. As for the successive layers making up the two fibrous structures  7  and  14 , their fibers are always parallel from one layer to another with an orientation D 1  or D 2 . 
     At this stage, as  FIG. 5  shows, a subsequent step of the method consists in winding, on the outer fibrous structure  14 , at least one layer  28  of drawn metal wire  29  which can be taken from the same feed spool as previously. Thus, a winding with contiguous turns  30  of the wire  29 , performed substantially orthogonally to the axis X of the cylindrical mandrel  2 , is obtained (as a reminder, wire and/or fabric of metal wires). 
     Obviously, before this subsequent step, other superposed fibrous structures could be arranged by taking care to alternate between them according to the invention, intermediate layers of metal wire. 
     A preform E of the rotationally symmetrical part to be produced is obtained, which is constructed only from drawn metal wires  4 ,  11 ,  29  and inner and outer structures  7 ,  14  with composite fibers in individuals, lap, fabric or other form. 
     Then, as  FIG. 6  shows, the preform E is transferred to a compaction outfit  31 , schematically represented, where the hot isostatic compression step (CIC) is performed in an isothermal press or in an autoclave (the choice depending in particular on the number of parts to be produced). 
     However, before its transfer, there can be a step of linking or securing the windings of the metal wire to ensure the cohesion of all of the superposed layers of turns during the transfer to the compaction station. For this, a welding step can be performed, for example an electrical spot welding, on the windings of the visible inner and outer turns. Instead of the welding, foil or leaf, not represented, could be arranged to hold in place the windings of the preform E, welded or not. The latter, if made of a compatible material may they be involved in the manufacture of the part. 
     After the preform E has been transferred and placed in the vacuum press outfit  31 ,  FIG. 6A , more particularly in an open cylindrical receptacle  32  of the press, the reception volume of which, defined by its walls  33 , corresponds to that of the part to be obtained, the receptacle is closed by a cover  34  of a shape complementing the opening of the receptacle and the transversal face of the preform E facing it. 
     Under the action of the compression exerted by the plates of the press symbolized by the arrows F on the outfit, and at an appropriate high temperature, the identical metal of the drawn wires  4 ,  11 ,  29  and of the cladding of the composite fibers of the structures  7 ,  14  become pasty eliminating all the empty spaces between the compressed turns, and ultimately densifying the part being obtained by the displacement of the cover relative to the receptacle, without acting on the silicon carbide matrices of the fibers. 
     In the variant represented in  FIG. 6B  of the autoclave outfit  31 , the receptacle  32  and the cover  34  with the preform E inside are placed in a deformable pocket  36  made of mild steel which is then introduced into the autoclave of the outfit  31 . As an example, this autoclave is raised to an isostatic pressure of 1000 bar and a temperature of 940° C. (for TA6V), so that all of the pocket  36  is deformed, arrows F 1 , by shrinking through the evacuation of the air expelled through the hole  37  and is pressed against the receptacle  32  and the cover  34  which, in their turn, compress, under a uniform pressure, the windings of wires and fibers until the metal of which they are made (diffusion welding) creeps, as previously. 
     Thus, after the CIC treatment, cooling and removal from the receptacle have stopped, the composite integral rotationally symmetrical part  1  is obtained, represented in  FIG. 7 , which is made of titanium alloy of TA6V or 6242 type, with, at its core, the ceramic matrices (silicon carbide, for example) of the fibers  9 - 15  or  18  or  22  forming crossed reinforcing inserts, but separated by the metal layer derived from the intermediate wire, and the thickness of which is such that it avoids the appearance of stress between the crossed, superposed ceramic fibers. The part  1  can obviously be subjected machining operations after the CIC treatment. 
     Obviously, the direction of orientation of the fibers of the inner structure could be different from that described above (parallel to the axis of the mandrel), in the same way that the choice of a fabric as inner fibrous structure is in no way mandatory, any other choice being able to be envisaged. The same applies for the outer fibrous structure. It should also be specified that the steps of winding of the wires and of the fibrous structures are performed at ambient temperature without having to use a complex installation. 
     As examples, the coated composite fibers can be, in addition to SiC/Ti as described above, made of SiC/AI, SiC/SiC, SiC/B, etc. . . . 
     Dimensionally, the minimum radius of the mandrel is a function of the diameter of the metal wire and should be greater than the latter. The length of the part, for its part, can reach several meters if necessary.