EP2245205B1 - Process for manufacturing a metal part reinforced with ceramic fibres - Google Patents

Abstract

A process for manufacturing a metal part reinforced with ceramic fibers, in which: a housing for an insert is machined in a metal body having an upper face; an insert formed from a fiber bundle having a metal matrix is placed in the housing; a metal cover is placed on the metal body so as to cover the insert; the cover is welded onto the metal body; the assembly including the metal body with the cover undergoes a hot isostatic compression treatment; and the treated assembly is machined to obtain the part. The insert is a rectilinear insert and the housing forms a rectilinear groove that extends beyond the insert and is open at each end, the groove being filled by a tab when the cover is placed on the metal body.

Description

The present invention relates to the manufacture of metal parts comprising internal reinforcements formed of ceramic fibers, and comprising the incorporation of a composite material insert of the type consisting of ceramic fibers in a metal matrix.

In order to reduce the mass of the metal parts while providing greater strength, particularly in tension or compression, it is known to incorporate ceramic fibers in the mass. These are for example silicon carbide fibers, SiC, which have a tensile strength and compression much higher than that of a metal such as titanium.

The manufacture of these parts requires the prior formation of inserts from metal matrix ceramic son which comprise a ceramic fiber coated with metal. They are also called CMM fibers or coated wires. The metal provides the elasticity and flexibility to handle them.

A known method of manufacturing such parts with reinforcement comprises producing a coil of wire coated around a mandrel. The coil is then incorporated into a container or metal main body in which a groove forming the housing for the insert has been machined beforehand. The depth of the groove is greater than the height of the winding. A lid is placed on the container and welded to its periphery. The cover has a post complementary shape to that of the groove, and its height is adapted to that of the coil placed in the groove so as to fill the groove. A hot isostatic pressing step is then carried out during which the lid is deformed and the winding is compressed by the tenon.

The technique of hot isostatic compression consists in arranging the part in an enclosure where it is subjected to a high pressure of the order of 1000 bar and a temperature also high, of the order of 1000 ° C. for a few hours.

During this treatment the metallic sheaths of the coated wires are welded together and with the walls of the groove, by diffusion, to form a dense set composed of a metal alloy in which the ceramic fibers extend annularly. The resulting part is then machined to the desired shape.

The method allows the manufacture of axisymmetric aeronautical parts such as rotor discs or monobloc bladed disks as well as shafts, cylinder bodies, housings, etc.

The machining of the groove in the main body is difficult to achieve especially because of the small rays in the bottom of the groove. This small radius is necessary to allow the housing of the insert which has a rectangular section. Machining the corresponding post in the cover is not easy either because of the non-emerging angles.

The applicant has developed a method of manufacturing elongated parts incorporating an insert with straight portions contributing to the transmission of unidirectional tensile forces and / or compression. This process is described in the patent application FR07 / 05453 of July 26, 2007 . The Applicant has also developed a method of manufacturing a rectilinear insert. It consists in producing a coil-shaped insert blank, compacting it in a container by hot isostatic pressing and then machining the rectilinear inserts in the compacted container. Such a process is described in the patent application FR 07/05454 of 26 July 2007 .

However, when the parts to be made are not axisymmetrical but are long, with an oval shape or with rectilinear portions, a precise adjustment over long lengths is difficult to obtain. This is even more difficult for inserts formed of very rigid coated son, because of the ceramic fibers that force the realization of housing in which they fit perfectly and should not allow a fiber to escape.

Instead of making the insert separately and then transferring it into the groove of the main body, the patent FR 2886290 In the name of Snecma proposes to realize, according to a variant, the winding directly on the main body. Instead of a groove there are two shoulders in it. The first has a bearing surface for the direct winding of a coated wire. This surface is parallel to the winding direction. When the winding is complete, the groove is reconstituted by placing a piece on the main body which is of complementary shape to that of a second shoulder forming a step relative to the first shoulder. Then we have the cover with the pin on the insert that has just wound and compacts the whole. This solution only partially solves the manufacturing problem because the assembly remains complex.

Thus, current manufacturing techniques make it possible to create metal parts comprising one or more metal matrix composite reinforcements from coiled fiber winding and a container - body and lid. These structures are efficient but have a high manufacturing cost. In particular the machining of the main body of the container with its lid represents a significant fraction of the total cost of the parts.

The applicant has set itself the objective of improving the process for manufacturing elongated parts in the sense of simplifying the steps of the range and reducing costs.

• on usine, dans un corps métallique présentant une face supérieure, un logement pour un insert,
• on dispose un insert formé d'un faisceau de fibres à matrice métallique dans le logement,
• on place un couvercle métallique sur le corps de façon à recouvrir l'insert,
• on soude le couvercle sur le corps métallique,
• on traite l'ensemble du corps métallique avec couvercle par compression isostatique à chaud et
• on usine ledit ensemble traité pour obtenir ladite pièce,

caractérisé par le fait que l'insert est rectiligne, le logement forme une rainure rectiligne ouverte à chaque extrémité, ladite rainure étant comblée par une languette au moment de la fenneture par le couvercle.This object is achieved according to the invention with a method of manufacturing a metal piece reinforced with ceramic fibers, according to which:

• a housing for an insert is machined in a metal body having an upper face,
• an insert formed of a metal matrix fiber bundle is provided in the housing,
• a metal cover is placed on the body so as to cover the insert,
• we weld the lid on the metal body,
• the entire metal body with lid is treated by hot isostatic pressing and
• said treated assembly is machined to obtain said part,

characterized in that the insert is rectilinear, the housing forms a rectilinear groove open at each end, said groove being filled by a tongue at the time of closure by the lid.

The invention is based on the observation that the machining of a rectilinear groove passing through the entire body of the container is much easier to master than a non-through groove. The solution of the invention is of particular interest with the introduction of two inserts, of elongate shape, arranged in two parallel rectilinear branches or not. According to Prior art, to obtain two longitudinal internal reinforcements, is first carried out an annular insert with two rectilinear branches interconnected by two parts arcuate. Then the housing is machined according to the precise shape of the insert. Adjusting the shape of the housing to that of the insert has proved to be a very delicate and expensive operation. Thus by eliminating the rounding makes the machining and setting up more simple without sacrificing the strength of the piece in the end since the fibers work essentially in their longitudinal direction in the central section of the piece.

In practice the lid comprises a plate and one or more tabs secured to the plate. More particularly, the plate and the tongue or tabs are obtained by machining the same thick plate. According to one variant, the tongue or tabs and the plate form separate pieces.

Preferably, a chamfer is machined on the upper edge of the groove forming the housing of the insert. This chamfer allows the gradual settlement of the tongue on the insert and to obtain a gradual deformation, that is to say without discontinuity.

The invention is particularly advantageous when the insert is of polygonal cross section, in particular rectangular. It can be oval or circular. The insert is either formed of bundled metal-coated fibers or formed of ceramic fibers in a single metal matrix.

• La figure 1 montre les différentes étapes 1a, 1b, 1c, 1d de fabrication d'une pièce de forme allongée selon l'art antérieur connu du présent déposant ;
• La figure 2 montre un exemple de pièce obtenue après usinage d'un conteneur incorporant des inserts ;
• La figure 3 montre en perspective un corps métallique usiné conformément à l'invention ;
• La figure 4 montre en perspective des languettes associées à une plaque pour former le couvercle fermant le corps métallique de la figure 3 ;
• La figure 5 montre en perspective éclatée les différents composants avant leur assemblage.

The invention will now be described in more detail with reference to the accompanying drawings in which

• The figure 1 shows the different steps 1a, 1b, 1c, 1d of manufacturing an elongate piece according to the prior art known to the present applicant;
• The figure 2 shows an example of a part obtained after machining a container incorporating inserts;
• The figure 3 shows in perspective a metal body machined according to the invention;
• The figure 4 perspective watch tabs associated with a plate to form the lid closing the metal body of the figure 3 ;
• The figure 5 shows exploded perspective the different components before assembly.

On the figure 1 , extracted from the patent application FR 07/05453 , we see a container 1 with a main body 4 of elongate shape, for forming a connecting rod of a landing gear for example. A groove 41 has been machined on each of the two faces of the body 4. This groove makes it possible to hold an insert 3 which comprises two rectilinear portions parallel or not between them joined at the ends by a portion of an arc of a circle. The inserts are of the ceramic fiber type coated with metal such as titanium. The grooves and the inserts are complementary shapes so that the insert is fit without play in the groove. It is noted that the groove in the container and the pin on the cover must be perfectly assembled to prevent the fibers, which have a very small diameter, 0.25 mm can not escape during hot isostatic compaction. Two covers 5 are provided with a projecting portion forming a pin 51 and cover the faces of the body 4. The ten bears on the insert housed in the groove and closes the latter. The cover 5 is welded, for example by electron beam, to the body 4, providing a vacuum inside the container. The container is visible on the figure 1b ; it is partly torn off to show the inserts. The container is then placed in an enclosure to undergo hot isostatic compression treatment. The cross-section of the container of the figure 1c shows that the edges 42 of the groove 41 are chamfered so as to provide a clearance with the part of the cover 5 adjacent to the pin 51. During the hot isostatic pressing operation, the pressure is exerted in the direction perpendicular to the surface of the lid generating the collapse of the lids. The pressure and the heat, of the order of 1000 ° C. and 1000 bars, allow the metal of the matrix to occupy the voids between the coated wires constituting the insert. The volume of the insert decreases by about 23%. The tenon is thus moved down and the game on both sides of the tenon is absorbed. At the end of the process, the metal fused and the container compacted; the piece is thus reinforced by the wires imprisoned in the mass. The figure 1d represents the part blank obtained with two inserts visible in transparency. The blank is then machined so as to obtain the part 8 represented on the figure 2 . This part 8 has recesses 81 between the branches 82. The ceramic fibers are incorporated in the branches 82 which ensure the transmission of forces in traction and compression. The inserts used are ring-shaped but as described in the patent application FR 07/05454 they can be formed of rectilinear elements in bars. In the latter case the rectilinear elements are incorporated in the container after being compacted before.

The solution of the invention makes it possible to obtain such parts more economically.

Referring to Figures 3, 4 and 5 a metal body 10 of elongate shape with respect to the figure is shown an upper face 10A and a lower face 10B. Two rectilinear grooves 10A1, 10A2 and 10B1, 10B2 were machined on each of the two faces. The grooves pass through the body 10 in the direction of the length and open into the two end faces 10C and 10D. The length of the grooves is equal to that L of the body 10. They serve as housing for rectilinear inserts 11, formed of bundles of coated ceramic fibers and of length 1 less than L. The upper edge 10A1 ', 10A2', 10B1 'and 10B2 'of the groove portion forming the housing of the inserts is chamfered. A tongue 14 covers each insert 11 disposed in its housing. The tongue 14 of the same length L that the body 10 comprises a cutting height so as to form two end portions 14a and 14b and a central portion 14c of length 1. The plate 12 covers the upper face 10A respectively lower 10B of the body 10. The height of the tongue is equal to the depth of the groove which must be sufficient to contain the insert 11.

• On prépare un corps 10 métallique, en alliage de titane par exemple, avec une face plane supérieure et une face plane inférieure ;
• On usine deux rainures rectilignes ouvertes 10A1, 10A2 respectivement 10B1 10B2 sur chacune des deux faces, supérieure et inférieure. Les rainures débouchent sur les faces d'extrémité du corps. Cette opération est relativement simple car on n' à considérer que la profondeur et la largeur de la rainure.
• On usine deux zones centrales chanfreinées 10A1', 10A2' respectivement 10B1', 10B2' sur les faces libres des rainures, de longueur correspondant à celle des inserts.
• On met en place les inserts 11 dans les rainures au niveau des zones chanfreinées. Conformément à une première réalisation les inserts sont formés d'un faisceau assemblé de fibres rectilignes enduites. Conformément à un deuxième mode de réalisation préféré les inserts sont préfabriqués selon la méthode décrite dans la demande de brevet FR 07/05454 . Les inserts dans ce cas forment des barreaux avec des fibres céramiques dans une matrice métallique. Ce sont des éléments rectilignes déjà compactés par compression isostatique à chaud.
• On met en place les languettes 14 sur les inserts 11 avec la portion centrale 14c le long de l'insert et les portions d'extrémité 14a et 14b en bout de l'insert 11.
• On place les plaques et on les soude sous vide sur les faces du corps 10.
• On introduit les conteneurs ainsi préparés dans une enceinte à compression isostatique à chaud.
• On chauffe et on met en compression pour une compaction du conteneur.
• L'ébauche obtenue est prête pour être usinée.
• On obtient par exemple la pièce de la figure 2.

The manufacture of an exemplary part according to the invention with 4 inserts thus comprises the following steps:

• A metal body, of titanium alloy for example, is prepared with an upper planar face and a lower planar face;
• Two straight rectilinear grooves 10A1, 10A2 and 10B1 10B2 are machined on each of the two upper and lower faces. The grooves open on the end faces of the body. This operation is relatively simple because one only has to consider the depth and the width of the groove.
• Two chamfered central zones 10A1 ', 10A2' and 10B1 ', 10B2' are machined on the free faces of the grooves, of length corresponding to that of the inserts.
• The inserts 11 are placed in the grooves at the chamfered areas. According to a first embodiment the inserts are formed of an assembled bundle of coated rectilinear fibers. According to a second preferred embodiment, the inserts are prefabricated according to the method described in the patent application. FR 07/05454 . The inserts in this case form bars with fibers ceramics in a metal matrix. They are rectilinear elements already compacted by hot isostatic compression.
• The tabs 14 are placed on the inserts 11 with the central portion 14c along the insert and the end portions 14a and 14b at the end of the insert 11.
• The plates are placed and vacuum-welded on the faces of the body 10.
• The containers thus prepared are introduced into a hot isostatic compression chamber.
• It is heated and put into compression for compaction of the container.
• The blank obtained is ready to be machined.
• For example, the piece of the figure 2 .

Instead of separately reporting the tabs 14 and the plate 12, these two parts can be made in one piece by machining the tabs in a thick plate. The result obtained is the same a priori.

The method of the invention thus makes it possible to produce any elongate piece incorporating one or more rectilinear inserts.

Claims (9)

1. A process for manufacturing a metal part reinforced with ceramic fibers, in which:

   - at least one housing for an insert is machined in a metal body (10) having an upper face (10A, 10B);

   - at least one insert (11) formed from a bundle of fibers having a metal matrix is placed in the housing;

   - a metal cover (12) is positioned on the body so as to cover the insert (11);

   - the cover (12) is welded onto the metal body (10);

   - the assembly, namely the metal body with the cover, is treated by hot isostatic pressing; and

   - said treated assembly is machined in order to obtain said part,
   characterized in that the insert (11) is straight and the housing forms a straight slot (10A1, 10A2, 10B1, 10B2) which extends beyond the insert and is open at each end, said slot being filled by a tongue (14) at the moment of closure by the cover (12).
2. The process as claimed in the preceding claim, in which the tongue (14) is integral with a plate (12) forming the cover.
3. The process as claimed in the preceding claim, in which the tongue is integral with the plate and is obtained by machining a thick plate in order to form the cover.
4. The process as claimed in claim 1, the tongue (14) of which is separate from the plate (12) of the cover.
5. The process as claimed in one of the preceding claims, in which a bevel (10A1', 10A2', 10B1', 10B2') is machined on the upper edge of the slot (10A1, 10A2, 10B1, 10B2) forming the housing for the insert (11).
6. The process as claimed in one of the preceding claims, in which the insert has a polygonal, especially rectangular, oval or circular, cross section.
7. The process as claimed in one of the preceding claims, the insert of which is formed from metal-coated fibers assembled into a bundle.
8. The process as claimed in one of claims 1 to 6, in which the insert is formed from ceramic fibers in a metal matrix.
9. The process as claimed in one of the preceding claims, in which at least a second insert is placed in the metal body.

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