EP0657554A1 - Process for preparing a circular fiberreinforced metallic workpiece - Google Patents

Abstract

Process making it possible to produce by isothermal forging circular articles reinforced with fibres over chosen portions of their section, the other portions remaining available for performing the other functions of the article. The invention is noteworthy in that it consists chiefly in producing grooves (8) in a blank (3) of the article (1), in producing preforms (12) from reinforcing fibre and from added metal to the dimensions of the grooves (8), in closing these grooves (8) using plugs (14) and in forming the article (1) by isothermal forging. Application to high-performance rotors such as the rotors of turbine engines employed in aeronautics. <IMAGE>

Description

The invention relates to a method comprising isothermal forging and making it possible to obtain circular metal parts internally reinforced with fibers on one or more selected parts of their section. The invention also relates to obtaining the preforms of reinforcing fibers used in this process. These circular parts thus obtained are used in particular as blanks for the production of rotors with a high resistance / mass ratio such as the turbomachine rotors used in aeronautics.

Turbomachinery rotors have a general shape of revolution around a rotational axis and they comprise, at their periphery or laterally, a plurality of blades acting as compressor or turbine. These rotors generally rotate at high speed and are subjected to significant stresses mainly coming from centrifugal force, but also from machine vibrations and accidental ingestion of foreign bodies.

The design of these rotors is a compromise between aerodynamic or hydrodynamic performance, resistance and mass.

In order to improve the resistance / mass ratio, it is necessary to reinforce these rotors by rings or bandages made of more resistant materials and having a modulus of elasticity also called a higher Young's modulus.

Reinforcement rings are known for a rotor having a fibrous structure and more particularly fibers made of silicon carbide, boron carbide or other high-resistance material, these fibers being embedded in a matrix metallic. The patent FR 2 607 071 gives an exemplary embodiment thereof. In this patent, silicon carbide fibers (Sic) are assembled into a helical ribbon or preform, between the turns of which another ribbon produced in the matrix material is interposed. The assembly is pressed at high temperature, the pressure forces diffuse the matrix material between the fibers, which ensures the cohesion of the assembly.

In another embodiment, the preforms each consist of a single fiber wound in a flat spiral. This process allows a remarkable regularity of the radius of curvature of the fiber, for a better resistance of the ring.

The fiber can be held in position before pressing by bands or radiating threads passing alternately below and above the fibers to be held, like the threads of a fabric. This solution, which is difficult to implement, also has the drawback of causing the fibers to wave and thus reduce their ability to withstand a tensile force.

To avoid this drawback, patent EP 0 490 629 proposes to engrave a spiral groove in a strip of matrix material, to deposit the fiber in the groove and to maintain this fiber in position by projection of an organic binder or by plasma projection of matrix metal, which constitutes a preform containing both fiber and metal of the matrix. This solution no longer has the disadvantage of waving the fibers as previously, but it is costly and difficult to implement, because the grooves into which the fiber must be introduced have only a very small width. The ring is then produced by hot compression, with a temperature and a pressure sufficient for the metal to penetrate between the fibers and weld around them. If an organic binder is used it is destroyed by pyrolysis during the rise in temperature, this binder being chosen to leave only a minimum of carbonaceous residues after pyrolysis.

Reinforcement of rotors with such rings can be done by mechanical mounting of the ring on the rotor, this mounting inevitably having clearances. The ring therefore participates in the effort only when the rotor is sufficiently deformed for these clearances to be filled.

The rings can also be hooped on the rotors. This solution ensures excellent cohesion between the ring and the rotor, but has the drawback of putting the ring in prestress, which reduces its ability to hold the rotor. In addition, the geometry of the rotor must be arranged to receive the ring.

The reinforcement rings can also be slid over the periphery of the rotors or introduced into grooves machined in these rotors, then brazed or welded by any means to the rotor. This solution ensures excellent cohesion of the reinforcing ring with the rest of the rotor, but has the drawback of imposing on the fibers two thermal cycles, which increases their degradation. For example, the silicon carbide SiC often used to make reinforcing fibers can react at high temperature with the metal of the matrix. To reduce this phenomenon, the fibers can be covered with a layer of carbon, but this layer diffuses itself in the metal of the matrix and modifies its metallurgical structure. The reaction of the fiber material with the matrix is therefore only delayed.

We also know the advanced process of isothermal forging which consists, in a vacuum chamber or in a controlled atmosphere, heating the part to a temperature at which the metal can deform so superplastic, placing this part in a matrix heated to the same temperature and exerting continuous pressure on the part. This process allows a remarkable and very homogeneous metallurgical structure of the part. It also allows the blank to be produced in several parts which will be welded together during forging.

• réalisation d'une ébauche de la pièce,
• réalisation dans l'ébauche d'au moins une rainure annulaire ouverte au moins suivant la direction axiale,
• réalisation de préformes de fibres aux dimensions des rainures,
• introduction des préformes dans les rainures,
• pyrolyse du liant organique retenant les fibres,
• forgeage isotherme de l'ébauche avec les préformes, ce qui permet de réaliser en un seul cycle thermique la compression des préformes, le soudage des zones fibreuses au reste de la pièce et le formage par forgeage de cette pièce.

To solve this problem, the invention proposes to produce circular metal parts reinforced with fibers according to the following method:

• creation of a draft of the part,
• production in the blank of at least one annular groove open at least in the axial direction,
• production of fiber preforms with the dimensions of the grooves,
• introduction of the preforms into the grooves,
• pyrolysis of the organic binder retaining the fibers,
• isothermal forging of the blank with the preforms, which allows compression of the preforms, the welding of the fibrous zones to the rest of the part and the forming by forging of this part in a single thermal cycle.

In a preferred embodiment, the preforms comprise both fiber and filler metal, this filler metal having an isothermal forging temperature close to or slightly lower than that of the metal of the part and being weldable with the metal of the piece. The spaces left between the preforms and the walls of the grooves will advantageously be filled with powdered filler metal.

It is also advantageous to close the grooves with a cover which comes into contact with the preforms and protrudes from these grooves. The isothermal forging being carried out in the axial direction, this cover makes it possible to start the isothermal forging by the compression of the preforms. This cover will preferably in a material having an isothermal forging temperature close to or slightly higher than that of the material of the part, said material also being weldable to said material of the part.

The preforms will advantageously be a stack of fiber washers wound in monolayer spirals and of matrix metal strips.

Isothermal forging in an axial direction will advantageously be combined with radial isothermal forging in order to obtain a substantially isostatic compression, that is to say homogeneous in all directions, said isostatic compression improving the homogeneity of the welding of the fibrous zone with the rest of the room. Radial forging can be obtained by centrifugal pressure exerted from inside the part.

In a preferred embodiment, the isothermal forging die is annular with an L-shaped section, the opening of which is turned towards the outside. This matrix is surrounded by a belt made of a material with a low coefficient of thermal expansion and an expansion mandrel is arranged in its central part. An annular piston penetrates between the vertical wall of the L-shaped die and the belt, to allow the forging of the part.

• enrobage de la fibre par un liant organique,
• durcissement de l'enrobage,
• bobinage en spirale à spires jointives de la fibre sur un mandrin, en une seule couche plane et radiale.

The process for producing fiber preforms notably includes the following operations:

• coating the fiber with an organic binder,
• hardening of the coating,
• spiral winding with contiguous turns of the fiber on a mandrel, in a single flat and radial layer.

The hardening of the coating is just sufficient to prevent it from being crushed during winding. So the turns contiguous ones stick to each other during the winding under the effect of the tension of the fiber, which ensures the cohesion of the preform after its exit from the winding mandrel.

The fiber preforms can be economically produced using a device comprising in particular a fiber supply reel, a tank of binder solution, a device for drying the coated fiber such as a tube heated by an electrical resistance, as well as a mandrel comprising two planar and parallel flanges whose listening is equal to or slightly greater than the diameter of the coated fiber.

The process which is the subject of the present invention should not be confused with the processes for obtaining reinforcement rings such as that which is described in patent FR 2 607 071 already cited. This process which is the subject of the invention consists in fact in including fibrous reinforcing structures in parts while reserving material to ensure the functions of the part, and then in compressing these fibrous structures inside the part during forging said piece.

Patent FR 2 607 071 is, on the contrary, limited to obtaining entirely fibrous parts which must then be added to the parts to be reinforced.

Compared to the production of separate rings, as for example in the patent FR 2 607 071 already cited, the process which is the subject of the present invention thus has the advantage of achieving in a single thermal cycle the compression of the preforms and the intimate connection. , similar to welding, of the area reinforced by the fibers with the rest of the material of the part. The elimination of a thermal cycle protects the reinforcing fibers and allows more economical production of the parts.

The process also offers great latitude in the choice of areas to be reinforced. We can indeed have these areas different places in the section of the part, such as the center, the periphery or the sides. The material of the part will be distributed according to the functions to be performed. For example, in the case of a turbomachine rotor with axial circulation of the fluid, material will be provided at the periphery for machining the blades and on the flanks for machining the flanges connecting to the other stages of the machine , and also for example for the machining of sealing labyrinths or grooves for fixing balancing masses.

The process is also economical because it avoids a thermal cycle as well as precise machining of the reinforcing ring and the housing intended to receive it on the part. The production of the preforms is also particularly simple.

The invention will be better understood in view of an example of implementation of the method for obtaining a turbine engine vane rotor, given without limitation of the invention, as well as the appended figures.

Figure 1 shows a sectional view of the rotor blank and the preforms, all arranged in the isothermal forging die.

Figure 2 shows schematically the steps of coating the fiber and winding the preforms.

FIG. 3 represents a partial section of the mandrel for winding the preforms.

We will first refer to Figure 1.

The rotor is machined in the ring 1 which has a general shape of revolution around the geometric axis 2. The ring 1 is obtained by operations 1 to 7 below, and the rotor machined in operation 8.

1) Making a first blank 3 in the form of a ring along the geometric axis 2. This blank 3 is delimited axially by two sides 4 and 5 and radially by an inner surface of revolution 6 and an outer surface of revolution 7.

2) Production in one of the sides 4 or 5, or in the two sides 4 and 5 of the blank 3 of at least one annular groove 8 of axis 2.

In a preferred and more economical embodiment, a single annular groove 8 is produced in a sidewall 4.

The groove 8 has a U-shaped section open on the sidewall 4 in a direction parallel to the axis 2. The groove 8 has a circular bottom 9, planar and radial to the axis 2, said bottom 9 being adjacent to an interior wall 10 and an outer wall 11 cylindrical around the axis 2 and extending to the side 4 to form the opening of the groove 8. It is understood that the groove 8 defines inside the ring 1 the space annular in which will be arranged the reinforcing fibers. The groove 8 also provides access to this space for depositing the fibers and the filler metal therein.

Note that if we wanted to arrange the fibers at the periphery of the part, this groove would then take the form of an L open radially and axially.

3) Production of fiber and filler metal preforms 12. The preforms 12 are a sufficiently rigid shaping of the fiber and of the filler metal so that these two materials can be transported to the place of forging and placed in the grooves 8.

It is known to produce preforms 12 containing both fiber and filler metal. It is also known to produce preforms 2 of two different categories, either preforms 12A containing the fiber and separate preforms 12B containing the filler metal. The preforms 12A and 12B have the shape of a flat washer with the dimensions of the groove 8.

4) Introduction into the groove 8 of the preforms 12. In the case where the preforms 12 are different, the fiber preforms 12a and the filler metal preforms 12B will be introduced alternately, each metal preform 12B separating two fiber preforms 12A .

5) Introduction into the spaces 13 left between the preforms 12 and the walls 10 and 11 of the groove 8 of powder of filler metal in sufficient quantity to fill these spaces 13.

This will allow at the time of passage and isothermal forming to better fill these spaces 13, and thus to ensure better continuity between the material of the ring 1 in the fibrous zone and the material outside the fibrous zone.

6) Production and introduction into the groove 8 of a plug 14 for closing said groove 8. The plug 14 has a bottom 15 coming by gravity in contact with the preforms 12. In a preferred embodiment, the plug 14 emerges from the groove 8 in order to start the isothermal forging operation of the ring by a phase of compression of the fiber and filler metal preforms 12.

The plug 14 has the shape of a ring of axis 2 with a circular bottom 15, plane and radial to axis 2.

The bottom 15 is adjacent to an inner cylindrical wall 16 whose diameter is slightly greater than that of the wall 10 of the groove 8, and also adjacent to an outer cylindrical wall 17 whose diameter is a little less than that of the wall 11 of the groove 8, the plug 14 thus being able to penetrate the groove 8 with sufficient play. The plug 14 is also axially delimited by a surface 18 opposite the bottom 15. The surface 18 can be circular, planar and radial to the axis 2, but it can also be given a different shape depending on the profile of the ring 1 and the desired deformation of the metal during forging.

In a preferred embodiment, the part of the plug 14 external to the groove 8 has a protrusion 19 extending radially the plug 14. The protrusion 19 is delimited axially by the surface 18 of the plug 14 opposite the bottom 15, and by the surface 20 opposite the side 4 of the blank 3 and of shape complementary to said side 4, and surrounding the plug 14. The protuberance 19 is also delimited radially to the axis 2 by an internal cylindrical surface 21 in the extension of the surface 6 of the blank 3, and by an external cylindrical surface 22 in the extension of the surface 7.

This surface 18 will constitute after forging the second side of the ring 1 and opposite to the side 5.

When the plug 14 is simply placed on the preforms 12, the sidewall 4 and the surface 20 are separated to allow compression of the preforms 12.

The surface 13 of the projection also has a circular depression 23 extending to the surface 22. It will allow a radial creep of the metal during forging.

7) Isothermal heating and forging of the blank 3 with the preforms 12 in the groove 8 and the plug 14.

The blank 3 is placed on its side 5 in a machine 31 itself arranged on the lower plate 32 of a hydraulic press.

A piston 33 penetrates into the matrix and transmits on the surface 18 of the plug 14 the pressure 34 exerted parallel to the axis 2 by the upper plate of the press not shown in FIG. 1.

Initially, the bottom 15 of the plug 14 presses under the effect of the pressure 34 the preforms 12, causing the creep and the agglomeration of the filler metal between the fibers. As the filler metal fills the spaces between the fibers of the preforms 12, the total height of the preforms 12 decreases and the plug 14 enters the groove until the surface 20 of the protrusion 19 comes into contact with the sidewall 4 of the blank 3. The pressure 34 is then exerted axially on all the material of the ring 1 which gradually takes the shape imposed by the matrix 31 and the piston 33. In practice, the deformation of the cover 14 begins before the preforms 12 are fully compressed.

Under the effect of the pressure 34, the metal of the blank 3, the filler metal powder introduced into the spaces 13 and the filler metal of the preforms 12 completely fill the space between the fibers, arrive in mutual contact and weld together, thereby achieving compression of the fibers and metal during isothermal forging of the ring.

Preferably, a filler metal will be chosen having isothermal forging temperatures close to or slightly lower than that of the blank metal, so that the solder and the filler metal have greater plasticity which facilitates the penetration of the metal. between the fibers. This filler metal must obviously be weldable with that of the part. Advantageously, the metals of the part, the preforms and the powder may be identical, but this is not a necessity.

The metal of the plug 14 will preferably have an isothermal forging temperature close to or higher than the forging temperature of the metal of the blank 3 and the filler metal of the preforms 12, so that it is a little less plastic. than them in order to improve the pressing of the preforms 12 at the bottom of the groove 8, and in particular to start the compression of the preforms 12 before the isothermal forging proper of the ring 1.

In another embodiment, the metals of the blank 3 and of the plug 14, as well as the filler metal of the preforms 12 and of the powder are identical, which improves the homogeneity and the resistance of the ring 1 .

It is also advantageous to exert by a means 35 on the blank 3 a radial pressure 36 combined with the axial pressure 34, in order to generate inside the part an isostatic pressure, that is to say uniform in all the directions. This isostatic pressure improves the welding of the metal of the blank 3 and of the plug 14 around the preforms 12 and makes it possible to reduce the quantity of filler metal powder to be introduced into the spaces 13, which improves the homogeneity of the ring 1.

The piston 33 is supported on the plug 14 by its surface 37. This surface 37 includes an additional thickness 38 having the same shape as the depression 23, but the height of the additional thickness 38 is less than the depth of the depression 23. From this fact, there remains a space 39 between said excess thickness 38 and said depression 23, and this space 39 will be filled during isothermal forging by the displacement in a radial direction of the material of the plug 14 near the surface 18 in contact with the piston 33. This displacement of material gives the metal grains an elongated shape called fiberizing which increases their resistance.

Recall that the isothermal forging device of the ring 1 comprises a matrix 31 placed on the lower plate 32 of a press, a piston 33 on which the upper plate (not shown) of the press exerts an axial pressure 34, said piston 33 penetrating in said matrix 31, and a means 35 exerting a centrifugal pressure 36 on the matrix 31.

In a preferred embodiment, the matrix 31 has an annular shape around the axis 2 with an L-shaped section, the opening of which faces upwards and outwards.

The horizontal branch 41 of the L is at the bottom and forms by its upper surface the bottom 42 of the matrix 31.

The vertical branch 43 of the L faces the geometric axis 2 and constitutes the vertical wall 44 of the matrix 31.

Opposite this wall 44, the matrix 31 is delimited radially towards the axis 2 by a concave cylindrical surface 45 centered on the axis 2.

The means 35 for exerting centrifugal pressure 36 will advantageously be a radially expandable mandrel made of a material with a high coefficient of thermal expansion, the expansion being obtained by heating said mandrel 35. The mandrel 35 is delimited radially outwards by a cylindrical surface 46 and fits inside the cylindrical surface 45 of the vertical wall 44 with a reduced clearance between the surfaces 45 and 46.

It is understood that when the mandrel 35 expands under the effect of heat, the surface 46 of the mandrel 35 pushes the die 31 on its surface 45, thus causing centrifugal pressure 36.

The present device also includes a shaped belt 47 cylindrical centered on the axis 2 and resting by one of its sides 48 on the lower plate 32 of the press. The belt 47 has a cylindrical and concave inner wall 49 centered on the axis 2 which surrounds the matrix 31, which is opposite the vertical wall 44 and which delimits radially outwards the space in which the ring 1. The annular piston 33 also fits between the wall 44 of the matrix 31 and the wall 49 of the belt.

This belt 47 is made of a resistant material and having a low coefficient of thermal expansion, for example carbon fibers. This belt 47 prevents the radial expansion of the blank 3 and the plug 14 during isothermal forging, which improves the efficiency of the centrifugal pressure 36 while maintaining the fibers to prevent their stressing.

In this example, the rotor is made of TA6V titanium alloy and the reinforcing fibers of silicon carbide SiC covered with a carbon deposit. Isothermal forging takes place at 950 ° C under a pressure of 600 bars for 50 minutes.

8) Final machining of the rotor, starting from the ring 1 thus obtained. In the case of an axial rotor of a turbomachine, the blades not shown will be machined in the extra thickness of material 55 disposed between the preforms 12 and the external surface 7, while the flanges not shown for connection with the other stages of the turbomachine will be machined in the extra thicknesses of material 56A and 56B arranged between the preforms 12 and the sides 5 or 18.

We will now refer to Figure 2.

The reinforcing fiber 60 is taken from a supply reel 61. The fiber 60 plunges into a tank 62 containing a bath 63 of liquid organic binder, passes around a return pulley 64 immersed in the solution 63 and emerges from this solution 63 coated with a certain amount of binder solution.

The fiber 65 then passes through the drying hub 65, for example a tube heated with an electrical resistance, in order to harden the coating of organic binder while retaining sufficient ability to stick to neighboring fibers.

The fiber 66 thus coated then bypasses a deflection pulley 67 and is wound on the mandrel 68 to form the fiber preform 12A. With this process, the thickness of the coating is determined by the viscosity and therefore the concentration and the temperature of the solution 63, while its degree of drying and therefore its hardness are determined by the intensity of the heating in the heating tube. 65 and the duration of the passage of the fiber through this tube 65.

We will now refer to Figure 3.

The mandrel 68 rotates around the geometric axis of rotation 69. This mandrel 68 comprises two circular flanges 70 arranged on either side of a circular hub 71, as well as a means (not shown) for positioning and driving in rotation about the axis 69 of said flanges 70 and of said hub 71.

The two flanges 70 each have a flat and radial side face 72, said faces 72 facing one another to form an annular groove 73 open on the periphery 74 of the mandrel and delimited internally by the hub 71. The faces 72 are connected to the periphery 74 of the mandrel 68 by a radius 75, so as not to risk tearing off the coating 76 of the fibers 60.

The coated fiber 6 is wound in a spiral in the groove 73 to form the 12A fiber preform. The space formed between the turns being equal to twice the thickness of the coating 76 of the fiber 60.

The spacing of the faces 72 is equal to or slightly greater than the diameter of the coated fibers 66, and the diameter of the hub 71 is equal to the inside diameter of the fiber preform 12A to be produced.

In a preferred embodiment, one of the flanges 70 is removable to allow the preform 12A thus wound to be removed, and the hub 71 has the shape of a truncated cone whose small diameter is turned towards the side of the removable flange 70 , in order to facilitate the withdrawal of the preform 12A.

The drying of the coating 76 must be sufficient for this coating 76 to acquire a hardness allowing it not to deform significantly during winding, but not too much. As a result, the tension of the fiber 66 during winding on the mandrel 68 causes the adjacent turns of coated fiber 66 to stick together along the contact line 77 between these turns. This bonding ensures the cohesion of the preform during its withdrawal from the mandrel, during its transport, and during its introduction into the annular groove 8 of the blank 3 of the rotor.

The faces 72 and the periphery of the hub 71 are made of a hard, non-adhesive material such as Teflon.

The concentration and the temperature of the organic binder bath 63, the heating of the coated fiber 66 and the tension of said coated fiber 66 can be determined by current experiments for those skilled in the art. In the present embodiment, the binder bath 63 is a solution of polymethyl methacrylate of general chemical formula (CH₂C (CH₃) (CO₂CH₃) -) n (commonly called PMMA) in acetone. PMMA is pyrolyzable between 400 ° C and 600 ° C.

Therefore, during the heating of the rotor 1 before the isothermal forging operation, a plateau of one hour to 2 hours approximately is performed at around 500 ° to pyrolyze the binder and remove the gases resulting from this pyrolysis.

The stack of fiber preforms 12A and filler metal washers 12B is fairly compact. Therefore, and in order to facilitate the evacuation of the gases produced by the pyrolysis of the binder, it is preferable to perforate the washers 12B of filler metal separating the fiber preforms 12A. In order not to modify the respective proportions of fiber and metal, and also so as not to risk bringing the fibers of two neighboring preforms 12A into contact through the perforations of the washers 12B, these perforations will preferably be carried out without removing material , for example using a metal tip or a blade.

Claims (20)

Method for obtaining a circular metal part reinforced with fibers, said method comprising operations for shaping the fibers, compressing the fibers with a metal alloy and forming this part (1) by isothermal forging, characterized in what it involves the following operations: - making a blank (3) of the part (1), - Production of at least one groove (8) in the blank (3); said groove (8) being annular and open at least in the axial direction - production of fiber and filler metal preforms (12); - introduction into the groove (8) of preforms (12) of fiber and filler metal; - isothermal forging of the blank (3); said isothermal forging operation thus making it possible to simultaneously compress the preforms (12), the welding of the compressed preforms (12) with the rest of the part (1) as well as the isothermal forging of this part (1). Process for obtaining a circular metal part reinforced with fibers according to claim 1, characterized in that the spaces (13) remaining between the preforms (12) and the walls (10) and (11) of the groove ( 8) are filled with powder weldable to the metal of the part. Process for obtaining a circular metal part reinforced with fibers according to claim 1 or 2, characterized in that the powder and the filler metal of the preforms (12) have isothermal forging temperatures close to or lower than that of blank metal (3). Method for obtaining a circular metal part reinforced with fibers according to any one of Claims 1 to 3, characterized in that the groove (8) is closed by a plug (14). Process for obtaining a circular metal part reinforced with fibers according to claim 4, characterized in that the plug (14) comes into contact with the preforms (12) in the groove (8), and in that it is made of a metal having an isothermal forging temperature close to or higher than that of the filler metal of the preforms (12) so that the compression of said preforms (12) takes precedence over the isothermal forging of the part (1). Process for obtaining a circular metal part reinforced with fibers according to any one of Claims 1 to 5, characterized in that the isothermal forging operation is carried out with the press in a direction parallel to the geometric axis (2) of part (1). Process for obtaining a circular metal part reinforced with fibers according to claim 6, characterized in that a metal creep of the ring (1) in a radial direction is carried out on at least one side (18) of this part (1) during the isothermal forging operation, in order to further increase the resistance of this part (1). Method for obtaining a circular metal part reinforced with fibers according to any one of Claims 1 to 7, characterized in that the part (1) is subjected to centrifugal pressure (36) during isothermal forging. Method for obtaining a fiber-reinforced metal circular part according to claim 8, characterized in that the blank (3) is surrounded by a belt (47) having a low coefficient of thermal expansion, so as to preventing stressing of the fibers of the preforms (12) during isothermal forging. Process for obtaining a circular metal part reinforced with fibers, according to any one of Claims 1 to 9, characterized in that fiber preforms (12A) are produced which are separate from the filler metal preforms (12B), said fiber preforms (12A) and said metal preforms (12B) each having the shape of a flat washer hollowed out at its center, and in that the fiber preforms (12A) and the metal preforms ( 12B) are alternately stacked in the groove (8), so that each metal preform (12B) separates two fiber preforms (12A). Method for obtaining a circular metal part reinforced with fibers in accordance with claim 10, characterized in that the metal preforms 12B are perforated without loss of material. Process for obtaining a circular metal part reinforced with fibers according to claim 10 or 11, characterized in that the obtaining of the fiber preforms (12A) comprises in particular the following operations: - coating of the fiber (60) with a layer of binder, - winding of the fiber thus coated (66) on a mandrel (68). Method for obtaining a circular metal part reinforced with fibers according to claim 12, characterized in that the winding of the coated fiber (66) on the mandrel (68) is carried out in a single plane and radial layer. Method for obtaining a circular metal part reinforced with fibers according to claim 12 or 13 characterized in that the coating of the fiber (60) is carried out by soaking said fiber (60) in a solution (63) organic binder, followed by drying. Process for obtaining a circular metal part reinforced with fibers according to Claim 14, characterized in that the solution (63) is polymethylmetachrylate of chemical formula (CH₂C (CH₃) (CO₂CH₃) -n dissolved in acetone . Isothermal forging device designed for implementing the production process according to any one of claims 1 to 15, characterized in that it comprises: - an annular matrix (31) having an L-shaped section whose horizontal branch forms the bottom (42) of said matrix (31), and whose vertical branch (43) is towards the geometric axis (2) of the matrix ( 31) and constitutes its vertical wall (44), - a belt (47) surrounding the matrix (31) and made of material with a low coefficient of thermal expansion, - an annular piston (33) which is inserted between the vertical wall (44) of the matrix (31) and the belt (47), in order to transmit the axial pressing force (34), - A radially expandable mandrel (35) disposed inside the vertical wall (44) and exerting during isothermal forging the centrifugal pressure (36) on said vertical wall (44). Device designed for the implementation of the obtaining method according to any one of claims 1 to 16 characterized in that it comprises a reel (61) for supplying fiber (60), a tank (62) containing a binder bath (63), a drying means (65) and a mandrel (68) for winding the coated fiber (66). Device according to claim 17, characterized in that the mandrel (68) comprises a hub (71) flanked by two flanges (70) planes and radial to the geometric axis of rotation (69) of the mandrel (68), said flanges (69) being spaced apart by a distance equal to or slightly greater than the diameter of the coated fiber (66), at least one of said flanges (70) being removable to allow the preform (12A) obtained to be removed. Device according to claim 18, characterized in that the hub (71) of the mandrel (68) has the shape of a truncated cone whose small diameter is located on the side of the flange (70) which is removable, to facilitate the withdrawal of the preform (12A). Device according to any one of claims 18 or 19, characterized in that the surfaces (72) of the flanges (70) in contact with the coated fiber (66) are made of a hard, non-adhesive material such as Teflon.

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