METHOD FOR MANUFACTURING AN INTEGRAL ROTATIONALLY
SYMMETRICAL METAL PART INCLUDING A REINFORCEMENT CONSISTING OF
CERAMIC FIBERS
Technical field of the invention .
The present invention relates to a method for manufacturing a single-piece, hollow metal part
of revolution, such as a torque transmission shaft, fi-om a composite fibrous structure in the
form of fibers, lap, fiber fabric, and other such materials, said fibers being coated with metal.
Prior art
In order to address the ongoing pressures to reduce specific consumption, efforts are being
made to replace certain forged parts in a turbomachine with lighter parts of simpler structure.
Such is the case with the power transmission shaft between the main shaft of a jet engine and'
its gearbox driving the accessory machines of the engine, referred to in the field by the
acronym AGB. This is a thin shaft that is relatively long, of the order of a meter, for
large-diameter engines and for which it is necessary to provide, in addition to the ends, an
intermediate bearing to ensure its support and the transfer of the specific vibratory frequency
modes.
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 fibrous structure made of composite material comprises a metal alloy
matrix, for example of 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 coated with metal.
These composite materials can be used to produce annular turbomachine parts of revolution
for aircraft or for other industrial applications, such as rings, shafts, cylinder bodies, casings,
spacers, monolithic part reinforcements such as blades, etc.
One known method for manufacturing hollow parts of revolution with a single-piece structure
consists in superposing, around a cylindrical mandrel, successive fibrous structures (fibers,
lap or fiber fabric) and then arranging the wound composite fibrous structures in a specific
receiving outfit to compact and bind the latter by diffusion welding and ultimately obtain the
part of revolution in composite material. A method for manufacturing a part of revolution by
lap lay-up is described in the Patent Application EP1726 678, in the name of the applicant.
Another known method consists in winding ceramic, but not coated, fibers around a mandrel
by inserting metal wires between the ceramic fibers. This method ha5 been patented by the
applicant under Patent FR 2.7 13.2 12.
Description of the invention
The applicant set out to develop a method that makes it possible to produce parts of revolution
with a diameter that can be very small, of the order of the diameter of the wires used, but also
very high, being limited only by the bulk of the outfit and with a length that depends on only
the means used.
Thus, the subject of the invention is a method for manufacturing a single-piece part of
revolution comprising the production of a preform of the part around a cylindrical mandrel,
the preform comprising at least one fibrous structure formed by metal-coated ceramic
composite fibers, followed by the difhsion welding treatment of the preform by hot isostatic
compaction, and the appropriate machining of the duly treated preform to obtain the part, and
the method is characterized in that the preform comprises at least one first layer of metal wire
between the maridrel and said composite fibrous structure and at least one second layer of
metal wire around said composite fibrous structure so as to embed the latter.
The method of the invention thus makes it possible to obtain a part that exhibits sufficient'
stiffness without increasing its density and, in the case of a torque transmission shaft such as
that mentioned above, to increase the ratio of Young's modulus to density, to raise the
specific vibratory frequency modes of the part and therefore, possibly, to produce a shaft with
no intermediate bearing.
Advantageously, the mandrel is in two tapered parts that can be separated from one another
and form a bobbin. This way, the preform after compaction can be stripped from the mold
without difficulty. The first layer of metal wire is preferably adapted so as to exhibit, after
compaction of the preform, a cylindrical portion forming, after machining, the inner wall of
the part. The layer of metal wire can be formed by winding one or more metal wires around
the mandrel.
The metal wire is, for example, obtained by wire drawing and is of the same type as that
which coats the composite fibers; in this way, after passage through the outfit, a uniform
metal layer of appropriate thickness is obtained on the fibers of the reinforcing structures.
The method of the invention also offers the advantage of being able to effect cold, at ambient
temperature, the superposed layers of metal wire and of the fibrous structure.
According to another feature of the method, the coated fibers of the fibrous structure are
arranged in one and the same direction, preferably the axial direction of the part.
More particularly, the composite fibrous structure is formed by winding metal composite laps
or fiber fabrics.
According to another feature, the layers are at least partly linked together by bonding, welding
or by means of foils.
According to another particular embodiment, transverse radial ribs are formed, notably at the
longitudinal ends bf the part, by winding metal wire. These transverse-ribs can be machined
and form the gear pinions for example. According to one production variant, a ceramic fiber
reinforcement is incorporated in said transverse ribs.
Moreover, the metal wires used can have different diameters, and layers with several
superposed windings of these wires can be provided in alternation with the superposed fibrous
structures, the number of which can be greater than two.
Brief description of the drawings
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.
Figure 1 schematically shows an example of a cylindrical part that can be obtained with the
method of the invention;
Figure 2 shows the step of formation of the first layer of metal wire of the part preform
according to one embodiment of the invention;
Figure 3 shows the step of formation of the layer of fibrous structure in coated ceramic fibers;
Figure 4 shows the step of formation of the second layer of metal wire;
Figure 5 schematically shows the step of hot isostatic compaction of the preform;
Figures 6 and 7 show a variant implementation of the method of the invention;
Figure 8 shows another variant implementation of the method of the invention for the
production of a part having a transverse radial rib.
Detailed description of the invention
The aim of the method is to manufacture an annular, single-piece part of revolution 1, only
from elongate elements in the form of wires, fibers or similar, as will be seen hereinbelow.
The invention targets more particularly the formation of parts with a long length compared to
their diameter. Figure 1 shows, in longitudinal cross section, the cylindrical hollow part with
metal wall 2, of axis XX, and incorporating reinforcing fibers 3, of ceramic material, in one or
more layers, preferably all the fibers of one and the same layer having one and the same
orientation, such as axial.
To obtain this type of part, a cylindrical mandrel 10 is used, of longitudinal axis X, around
which the part is formed. The mandrel is preferably in the form of a bobbin, in two tapered
parts 10a and lob which are fastened to one another by their apex, in a removable manner so
as to be able to separate them from one another. The half-angle alpha at the apex of the two
cones, exaggerated in the figure, is of the order of 6 to 7'. The aim of the bobbin shape is to
enable the part to be stripped from the mold after compaction of the wires and fibers as will
be seen hereinbelow. In a first step, a metal wire 4 is wound around the cylinder so as to form
a first layer of metal wire. Given the application of the part 1 to the aeronautical field, the
metal wire 4 is notably made of a titanium alloy of TiA6V or TI6242 type ensuring
thermomechanical resistance and lightness, and it is obtained notably by wire drawing so as to
be able to be available in bobbin or reel form from which the wire is drawn.
Means other than wire drawing can be envisaged.
Dimensionally, its diameter depends on the part to be obtained and can be of the order of a
few tenths of a millimeter to several millimeters.
In the example illustrated in figure 2, the drawn metal wire 4 is obtained from a reel which is
not represented and is driven, substantially perpendicularly to the axis X, around the
cylindrical mandrel 10 over a predetermined extent corresponding to the length that is to be
obtained, after manufacture, for the part of revolution 1, by thus forming a number of
contiguous turns, and over one or more superposed thicknesses so as to form the first layer of
metal wire 6. It would also be possible to use a plurality of metal wires or one or more metal
wires with a different diameter to the metal wire 4. Because of the taper of the cylinder 10, the .
first layer has a triangular longitudinal section. One of the functions of the layer 6 is to fill the
mold stripping part to the internal diameter of the finished part, after its machining.
The method continues with a second step shown in figure 3 and consisting in arranging a
composite fibrous structure 7 around the first layer 6 of metal wire 4.
The composite fibrous structure 7 may take the form of a fabric of mutually parallel
associated coated ceramic fibers 9 made of ceramic (Sic) or of a similar material coated with
metal. The latter and the metal of the drawn wire are preferably of identical type (of TiA6V or
of 6242 for example) to optimize the subsequent step of the method concerning the hot
isostatic compaction operation. The fabric of the fibrous structure 7 is wound around the
winding of the first layer 6 of metal wire 4 so that the fibers 9 are all arranged according to FL
the same orientation, for example and preferably parallel to the longitudinal axis X of the
mandrel 10.
A single layer of the fabric is formed around the first layer of wire 4. Obviously, a winding of
several layers could be provided from the same fabric, or even from one or more other distinct
fabrics wound concentrically. The fabrics may be of different species, of different coated wire
diameters. The length of the composite fibrous structure 7 is less than or equal to the length of
the outer surface of the first layer 6 of metal wire. It should be noted that the outer surface of
the latter may be domed to take account of the compaction of the layer 6 by hot isostatic
compression treatment. After this treatment, this surface should preferably be straight
cylindrical.
According to a third step of the method illustrated in light of figure 4, a metal wire 5, for
example wire drawn, from a reel not represented and which is fed in substantially
orthogonally to the longitudinal axis X of the rotary cylindrical mandrel 10, is arranged
around the fabric of the composite fibrous structure 7. The metal wire 5 forms a second layer
8 of contiguous turns around the fabric of the fibrous structure 7. The second layer 8 may
comprise a winding of several thicknesses. Also, as for the first layer, instead of winding one
metal wire, a plurality of metal wires or a sheet of metal wires can be put in place. When
using a plurality of wires, the latter may be of the same diameter or of different diameters.
The wires may also be metal wires preassembled in the form of cables. Layers of foi1,may
also be wound with the second layer. According to one feature of the method, the metal wire
or wires 5 is/are wound in such a way as to fully embed the composite fibers of the underlying
fibrous structure 7. As can be seen in figure 4, in particular, the second layer 8 covers the part
of the first layer 6 of metal wire which is not itself covered by the fibrous structure 7.
A preform E of the part of revolution to be produced is obtained, which is made only from
metal wires 4 and 5 and a structure 7 with composite fibers in individual form, in lap form, in
fabric form or similar.
Then, as figure 5 shows, the preform E is subjected to hot isostatic compression treatment
(CIC) in an isothermal press or in a bag in an autoclave (the choice depending notably on the
number of parts to be produced). A cover system of complementary shape is fitted over the
preform. Since the preform is cylindrical, the cover, in a plurality of parts, forms a cylindrical
jacket around the preform.
Under the compression exerted (as a result of a high pressure applied according to the arrow
F) at an appropriate high temperature, the metal of the metal wires and of the cladding of the
fibers of the structures becomes pasty and creeps, eliminating all the empty spaces between
the turns and layers, their diffusion welding then finally densifying the part.
In a variant, the assembly is placed in a deformable pocket of mild steel which is then
introduced into an autoclave. This autoclave is raised to an isostatic pressure of 1000 bar and
a temperature of 940°C (for TiA6V), so that all of the pocket is deformed by shrinking
through the evacuation of the air and is pressed against the mandrel and the cover which, in
their turn, compress, under a uniform pressure, the windings of wire and fiber until the metal
of which they are made creeps and is bound by diffusion welding. Advantageously, a number
of pockets can thus be introduced into the autoclave in order to simultaneously produce the
parts, reducing the manufacturing costs.
Thus, after the CIC treatment, cooling and mold-stripping have stopped, the preform is
machined to obtain the composite single-piece part of revolution 1, represented in figure 1,
which is made of metal with, at its core, the fibers forming reinforcing inserts.
The outfit formed by the cylindrical mandrel 10 and the cover system is preferably made of a
material which enables it to be used again for the manufacture of another part. It is, for
example, a superalloy which withstands the temperature and the pressure of the treatment
while retaining its integrity.
Obviously, the direction of orientation of the fibers could be different from that described
above (parallel to the axis of the mandrel), in the same way as the choice of a fabric as
internal fibrous structure is in no way mandatory, since any other choice can be envisaged. It
must also be stipulated that the steps of winding the wires and the fibrous structures are
performed at ambient temperature without using a complex installation.
As examples, the coated composite fibers may be, in addition to SiCITi as described above,
made of SiCIAI, SiCISiC, SiCB, etc.
Dimensionally, the minimum radius of the mandrel is a function of the diameter of the metal
wire and must be greater than the latter. As far as the length of the part is concerned, it can be
as long as several meters if necessary.
According to a variant implementation, represented in figures 6 and 7, flanges 13a and 14b
are added to the mandrel, on the side of the free ends of the half-mandrels 1OYa nd IO'b, so as
to complement the support of the second layer 8' of metal wire when the latter has a diameter
greater than that of the mandrel 1 O'a, 1 O'b. The thickness of the different layers applied takes
account of their expansion, with a view to the result that is desired after CIC treatment. The
cover system 12' as represented in figure 7 is adapted to the outer geometry of the preform.
According to another production variant, the method of the invention makes it possible to
manufacture parts in dumbbell form, that is to say with transverse radial ribs. To obtain them,
it is sufficient to adapt the geometry of the second layer so as to form these ribs. The thickness
of this second layer is increased for this purpose in the desired position. Thus, figure 8 shows
a detail of the preform produced in this way. The second layer 8" of metal wire is formed by
winding metal wire so as to exhibit a part forming a transverse rib 8"a, this rib after the CIC
treatment forming a transverse radial rib on the part. The function of this rib may be a
terminal fixing flange or a pinion after machining radial teeth.
In order to further reinforce the mechanical strength of this rib, ceramic fibers 8"b of a length
adapted to the width of the rib after CIC can be included. If the reinforcing fibers are oriented
transversely to the axis of the part, then they can be put in place by winding in the same way'
as are the metal wires. If the orientation chosen for the reinforcing fibers has to be axial, then
they will be put in place in the form of laps or fabric like the reinforcing layer 7.
It will be observed that the shape of the cover 12" is also adapted to that of the part preform
produced on the mandrel 10".

CLAIMS
1. A method for manufacturing a single-piece part (1) of revolution comprising the production
of a preform of the part around a cylindrical mandrel (lo), the preform comprising at least one
fibrous structure (7) formed by metal-coated ceramic composite fibers (9), followed by the
diffusion welding treatment of the preform by hot isostatic compaction, and the appropriate
machining of the duly treated preform to obtain the part (I), characterized in that the preform
comprises at least one first layer (6) of metal wire (4) between the mandrel (10) and said
composite fibrous strucke (7) and at least one second layer (8) of metal wire around said
composite fibrous structure (7) so as to embed the latter, the mandrel (10) comprising two
tapered parts (1 Oa, lob) that can be separated from one another. .J
2. The method as claimed in the preceding claim, whereby the first layer (6) of metal wire is
adapted so as to exhibit, after compaction of the preform, a cylindrical portion capable of
forming, after machining, the inner wall of the part.
3. The method as claimed in orie of the preceding claims, the first layer (6) of metal wire
being formed by winding one or more metal wires (4) arou~ndth e mandrel (10 ).
4. The method as claimed in one of the preceding claims, the metal wire (4) being of the type
obtained by wire drawing and of the same type as that which coats the composite fibers.
i L
5. The method as claimed in one of the preceding claims, in which the different layers (6, 7, ,..
8) are put in place cold, at ambient temperature.
6. The method as claimed in one of the preceding claims, whereby the coated fibers (9) of the
composite fibrous structure are arranged in one and the same direction, preferably the axial
direction of the part.
7. The method as,claimed in the preceding claim, whereby the composite fibrous structure (7)
is formed by winding one or more laps or fabrics of parallel metal composite fibers. or else of
individual and parallel fibers arranged in succession around the mandrel.
8. The method as claimed in one of the preceding claims, whereby the layers are at least partly
linked together by bonding, welding or by means of foils.
9. The method as claimed in one of the preceding claims, whereby transverse radial ribs (8"a)
are formed, notably at the longitudinal ends of the preform, by winding metal wire.
10. The method as claimed in the preceding claim, whereby a ceramic fiber
(8"b) is incorporated in said transverse ribs.
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Dated this 10.09.20 13 r
ATTORNEY FOR IT& mPLICANT[Sl