FR2660673A1 - Process for producing preforms by means of a woven and wound texture for the manufacture of pieces of composite material - Google Patents

Abstract

The preform consists of a woven texture wound on a mandrel, the shape of which corresponds to that of the preform to be produced, weaving being carried out by drawing off the warp threads, coming from various feed bobbins, by means of a roller, the shape of which corresponds to the preform to be produced.

Description

PROCESS FOR PRODUCING PREFORMS USING A WOVEN TEXTURE
AND COIL, FOR THE MANUFACTURE OF PARTS OF COMPOSITE MATERIAL
The present invention relates to the production of parts made of composite material consisting of a fiber preform densified by a matrix.

 More particularly, the invention relates to the production of preforms by means of a woven and wound texture in order to manufacture revolution parts in composite material, in particular revolution parts of non-developable shape.

 One field of application of the invention is the manufacture of parts made of thermostructural composite materials such as, for example, diverging nozzles or parts of aircraft reactors.

 Thermostructural composite materials are characterized by mechanical properties making them suitable for the manufacture of structural elements and by the conservation of these properties at high temperatures. Well known thermostructural composite materials are carbon / carbon composites (C / C) and ceramic matrix composites (CMC). In the C / Cs, the constituent fibers of the preform are made of carbon, as is the matrix. In CMCs, the constituent fibers of the preform are made of a refractory material, in particular carbon or ceramic, and the matrix is made of ceramic material, for example silicon carbide.

 For the production of preforms of revolution, a well-known technique consists in winding a strip of two-dimensional fibrous texture on a mandrel whose profile corresponds to that of the preform to be produced. The fibrous texture is for example a fabric or a felt.

 When the preform is cylindrical, it is possible to use a strip of fibrous texture whose width corresponds to the axial dimension of the preform. The strip is wound in superimposed turns, possibly needled. It is, however, more possible when the preform is not cylindrical.

 When the preform is frustoconical, it can be produced by winding a spiral fabric. For more complex shapes, it has been proposed to use a ribbon of fibrous texture which is wound on a mandrel to form superimposed layers each consisting of contiguous turns or with slight mutual overlap. The ribbon is needled on the underlying structure, as soon as it is applied to it, which maintains the position of the wound ribbon and provides a connection between the layers of the preform. Such a process is described in document EP-A-0 147 297.

 The invention aims to provide a new technique for producing a fiber preform by means of a woven texture wound on a mandrel whose shape corresponds to that of the preform to be produced.

 This object is achieved, in accordance with the invention, thanks to a process according to which the texture is woven by calling the warp threads, coming from several supply reels, by means of a roller whose shape corresponds to that of the preform to be made.

 In accordance with a particular embodiment of the method, the take-up roller is constituted by the same mandrel on which the texture is wound as it is woven.

 The method according to the invention thus makes it possible to produce a preform of revolution by means of a woven and wound texture that can easily marry a complex, non-developable form of revolution.

The invention will be better understood on reading the description given below, by way of indication but not limitation, with reference to the appended drawings in which
- Figure 1 is a partial view of a part of revolution of non-developable shape;
- Figure 2 is a very schematic view of a weaving installation allowing the production of a fibrous preform intended for the manufacture of the part of Figure 1 in a composite material;
- Figures 3 and 4 are partial sectional views schematically illustrating preforms of diverging nozzles, which can be produced by the method according to the invention;
- Figure 5 is a schematic sectional view showing a preform of revolution closed at one end and achievable by the method according to the invention;
FIG. 6 is a view on an enlarged scale showing a detail of FIG. 5, and
- Figure 7 schematically illustrates a device for switching the preform during its manufacture.

 FIG. 2 illustrates by way of example an installation allowing the production of a substantially cylindro-conical and wavy preform of revolution. Such a preform 10, shown in FIG. 1, is intended for example for the production of a combustion chamber made of thermostructural composite material, for an afterburner channel of an aircraft reactor.

 The weaving installation illustrated in FIG. 2 is essentially distinguished from a traditional weaving machine by the fact that the drawing of the warp threads 12 is carried out by means of a take-up roller 20 whose cylindrical undulating profile conical corresponds to that of the preform 10 to be produced.

 The drawing of the warp threads 12 is carried out by rotation of the roller 20. For the same rotation angle of the take-up roller, the lengths of warp threads called are different due to the non-cylindrical shape of the roll. Also, the warp threads 12 are supplied by different supply coils 22 (only two of which are shown in FIG. 2).

 Conventionally, the weft threads 14 are introduced into the shed 16 formed by means of blades 24, and are driven out to be pressed against the fabric 18 previously formed. Due to the non-cylindrical shape of the take-up roller 20, the total width of the chain at the level of the shed 16 is greater than the width of the fabric 18, measured axially on the take-up roller 20.

 The tension exerted on the warp threads 12 causes the weft threads 14, in the fabric formed, to follow the profile of the take-up roller 20. If necessary, a counter-roller, of shape complementary to that of the roller 20 and recalled towards the latter can be used to force the fabric 18 to match the profile of the roller 20 while passing between the latter and the counter-roller.

 In the illustrated example, the take-up roller 20 has not only a profile corresponding to that of the preform to be produced, but also dimensions corresponding to those of the preform 10 and constitutes the very mandrel on which the fabric 18 is wound. constitute the preform 10.

 The mandrel 20 is then made of graphite. At the start of weaving, the ends of the warp threads 12 are glued to the surface of the mandrel 20 to allow the call by rotation of the mandrel. When the weaving has been carried out over a length corresponding to approximately a half-turn of the mandrel, that is to say before covering the glued ends of the warp threads, the fabric 18, already formed and wound on the mandrel 20, is glued in turn thereon and the end portions of the nonwoven warp threads are removed from the mandrel. The bonding of the fabric 18 to the mandrel is carried out for example by means of a fugitive resin, such as a PVA resin (polyvinyl alcohol), that is to say a resin which can be removed by heat treatment without leaving a solid residue. The elimination of the resin takes place automatically during the subsequent treatments to which the preform is subjected in order to obtain the composite part to be manufactured.

 Weaving is continued, with the fabric 18 being wound on the mandrel 20, until the desired thickness for the preform 10 is reached.

 At the end of winding, the end of the fabric strip is cut after being fixed on the preform 10, to prevent it from unwinding. This fixing can be carried out by gluing using a fugitive resin, or by sewing, or by implantation of wires. In the case of bonding with fugitive resin, additional means of fixing the end of the strip of fabric, in particular mechanical means, such as pliers or a bar, may be used in order to avoid any risk of unwinding of the fabric. when handling the preform.

 The preform 10, wound on the mandrel 20, is placed in a densification installation, for example a vapor infiltration installation, in order to deposit the material constituting the matrix. A first infiltration phase is carried out to consolidate the preform, that is to say until the fibers of the preform are bonded together sufficiently to allow manipulation of the preform.

 After consolidation, the graphite mandrel 20 is removed, by disassembly or machining. Densification is continued on the consolidated preform alone, as shown in FIG. 1, until the desired density is obtained.

 In the case envisaged for the manufacture of a part made of thermostructural composite material, the wires used for the production of the preform are made of fibers of refractory material, such as carbon or a ceramic material.

 When the refractory material in which the preform is to be produced has characteristics which make it unsuitable for textile operations, in particular needling, weaving and winding are produced from yarns formed of fibers into a precursor of the material the preform before needling. Thus, for example, in the case of carbon preforms, the weaving can be carried out on yarns of PAN fibers (polyacrylonitrile) preoxidized carbon precursor. Similarly, for a preform made of ceramic material, weaving can be carried out on threads formed of precursor fibers not yet ceramized.

A heat treatment must then be carried out on the preform 10, mounted on the mandrel 20, before densification.

 The material of the matrix is carbon or a ceramic. The techniques for infiltrating such materials in the vapor phase are well known. Reference may in particular be made to documents FR-A-2 189 207, FR-A-2 401 888 and EP-A-O 085 601.

 The weaving installation described above makes it possible to produce a fabric with a plain weave. Other types of armor may be used, for example a satin armor.

 If the wound preform has significant variations in diameter, certain weft threads may be placed over only part of the width of the shed, as is known per se for weaving spiral fabric in order to avoid deviations too high density of weft threads in the fabric.

 In the foregoing, the preform 10 is obtained by weaving and winding the fabric 18 directly on the mandrel acting as a take-up roller.

 It is of course conceivable to use a take-up roller having the profile of the preform to be produced, but not necessarily its dimensions, for example with a smaller diameter. The fabric shaped by passing over the take-up roller is then wound on a take-up roller, which preferably has a profile corresponding to that of the preform to be produced.

 The take-up roller can be constituted by the mandrel, intended to receive the preform, so that the preform is directly wound on its mandrel.

 The receiving roller can also constitute a storage roller from which the fabric is then unwound to be wound on a mandrel, in order to form the preform to be produced. In the case of developable preforms, it is then possible to store on the receiving roller a large length of fabric, obtained by continuous weaving, and making it possible to produce several similar preforms.

 The method according to the invention allows the production of preforms of revolution having very diverse non-developable shapes.

 FIG. 3 shows such a preform 30, mounted on a mandrel 35 which can constitute the take-up roller used for weaving the fabric constituting the preform. The preform 30 has an "egg cup" shape and is intended for the production of a nozzle divergent.

 Figure 4 shows another preform 40 achievable by the method according to the invention and intended for the production of a nozzle divergent with integrated neck.

 The preform 40 is formed on a mandrel 45 produced in two parts 451 '452 in order to allow the insertion of an annular preform 47 constituting the nozzle neck. The preform 47 is constituted by a three-dimensional fibrous texture, for example made of carbon, consolidated by impregnation with a fugitive resin or by chemical vapor infiltration by a carbon or ceramic matrix. The mandrel 45 with the integrated insert 47 can be used as a take-up roller for the winding of the preform 40, the latter at least partially covering the integrated insert 47. After winding, the assembly is densified to consolidate the preform 40.

During densification, the matrix co-infiltrated into the preform 40 and the insert 47 causes these two parts to bond or "stick" together. Densification is then continued until the final stage, the mandrel 45 having been removed.

 Of course, depending on the part to be produced, several inserts may be previously integrated in the mandrel used to form the preform of the part.

 FIG. 5 shows a preform 50 formed on a mandrel 55. The preform 50 has a shape of revolution with a section in a C-shaped axial plane, that is to say open at one axial end and closed at the second axial end. The mandrel 55 is therefore mounted cantilevered at the end of a shaft 57 for driving in rotation.

 The preform 50 is produced in two parts. A first part 501 of tubular shape is produced according to the method according to the invention, for example using the mandrel 55 as a take-up roller for weaving the texture constituting this part 501. A second part 502 in the form of a firm cap the first part 501 at the second axial end of the preform.

 The cap 502 is constituted by two-dimensional circular strata, for example in a fabric of the same kind as that constituting the part 501.

 As shown in Figure 6, the junction between the superimposed strata forming the cap 502 and the superimposed layers or turns forming the tubular part 501 is achieved by interposing the edges thereof with a slight overlap. The mandrel 55 may have a groove 59 at this junction to avoid the creation of an additional thickness on the outside of the preform 50.

 In a manner known per se, the preform obtained by the process according to the invention can be needled in order to make a connection between the layers of fabric wound on the mandrel.

 FIG. 7 schematically shows a weaving installation similar to that of FIG. 1, in which the take-up roller has been replaced by a mandrel 75 intended for the formation of a preform 70 similar to the preform 30 illustrated in FIG. 3 .

 The needling of the preform is carried out by means of a needle board 73 of shape corresponding to that of a generator of the preform 70. The needle board 73 is mounted in the vicinity of the mandrel 75, parallel to the latter, substantially at the level where the fabric constituting the texture coils.

 The needle board 73 is driven by an alternating movement directed radially relative to the mandrel in order to allow the needles 76 to penetrate into the preform.

 Needling can be performed after the end of the preform winding.

 To obtain a relatively homogeneous needling throughout the thickness of the preform, it is however preferable to carry out the needling as the fabric which constitutes it is wound.

 In all cases, the mandrel 75 is coated with a base 77 made of a material, such as a foam or a plastic felt, for example a polypropylene felt, into which the needles can penetrate without being damaged and without bringing back of particles or fibers within the preform. A film 79, made of a material which can easily be passed through by the needles, is bonded to the base 77 in order to prevent too much fiber coming from the preform from becoming encrusted in the base and complicating the separation between the preform and the 'base. The film 79 is, for example, made of polyvinyl chloride.

 Needling can be carried out with penetration of the needles into the preform to a constant depth, mutually separating the needle board and the axis of the mandrel, after each revolution of the mandrel, by a distance corresponding to the thickness of a layer of needled fabric. Such a needling principle is described in document FR-A-2 584 107, for the manufacture of cylindrical preforms.

 After winding, the preform, held in shape by the needling, is removed from the mandrel 75 and from the base 77, on which the film 79 remains bonded, without it being necessary to carry out a prior consolidation phase. It is therefore not useful in this case to use a mandrel made of a material, such as graphite, which can withstand the conditions of infiltration of the matrix.

 Of course, needling can be carried out whatever the profile of the preform, by adapting the shape of the needle board to this profile.

 It will also be noted that a connection between the layers of fabric wound on the mandrel can be carried out by implantation of threads rather than by needling. The method of implanting wires used is for example of the type described in patent application FR 2 565 262.

Claims (7)

1. Method for producing a fibrous preform of revolution for the manufacture of a part made of composite material, by means of a woven texture wound on a mandrel whose shape corresponds to that of the preform to be produced,  characterized in that the texture is woven by calling the warp threads, coming from different supply coils, by means of a roller whose shape corresponds to that of the preform to be produced. 2. Method according to claim 1, characterized in that the texture, as and when it is woven, is wound on the take-up roller constituting the mandrel on which the preform is formed.  3. Method according to claim 2, characterized in that the texture wound on the mandrel is needled. 4. Method according to claim 3, characterized in that the needling is carried out as the texture is wound. 5. Method according to any one of claims 1 st 2, characterized in that the layers of fabric formed by the wound texture are linked together by implantation of son. 6. Method according to any one of claims 1 to 5, characterized in that the mandrel comprises at least one integrated insert, constituted by a preform element. 7. Method according to any one of claims 1 to 6, characterized in that the wound preform is of substantially tubular shape and is closed at one end by strata of a fibrous texture whose edges are interspersed with those of the preform .