Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
SP 22930 AP
CA 02467846 2004-05-19
METHOD OF MANUFACTURING A HOLLOW BLADE FOR A TURBINE
ENGINE
TECHNICAL FIELD
The invention generally relates to the field of
methods of manufacturing blades for turbine engine,
such as hollow fan blades, or any other type of rotor
or stator blades for turbine engine.
STATE OF THE PRIOR ART
Usually, a hollow fan blade for turbine engine
comprises a relatively thick foot used to attach this
blade into a rotor disk, this foot being radially
extended towards the outside by a thin aerodynamic part,
called rotor blade.
From the prior art, it is known a method of
manufacturing such a hollow blade, principally based on
the use of the diffusion bonding technique, associated
with that of superplastic forming.
Indeed, in this method of the prior art, two or
three component parts of the blade are firstly defined,
then made separately before being stacked and assembled
to each other via the diffusion bonding technique, with
the purpose of obtaining a preform of the desired blade.
Subsequently, an airfoil profiling of the
previously fabricated preform is carried out, then
bulging via gas pressure and with superplastic forming
of this preform, in order to achieve a blade
substantially bearing its finished shape.
As was mentioned above, a production stage of the
blade preform requires the making of two external parts,
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and possibly a central part intended to be interposed
between these two external parts, with the purpose of
being used as a stringer later on.
The manufacturing of the external parts is
typically carried out through the machining of supply
elements that necessarily have relatively large initial
dimensions, as each of the two machined external parts
must have two radially facing sections of significantly
different thickness, these sections respectively being
used to define the foot part of the blade preform and
the rotor blade part of this said preform.
Thus, the manufacturing of the external parts
intended to constitute at least partially the blade
preform, for example obtained via lamination, generates
very high material costs and machining costs, and hence
this method of manufacturing the hollow blade is not
completely optimised.
To face up to this major inconvenience, it has
been proposed to produce the blade preform by means of
a single diffusion bonding stage implying a stacking of
at least five parts, of which some extend radially
along the entire length of the preform, and others only
along the foot part of the latter.
However, this method, which is notably disclosed
in the documents US-A-4 822 823 and EP-A-1 188 197, has
the inconvenience that major difficulties in the
implementing of the diffusion bonding technique appear
when the unit to be welded has extremely variable
thicknesses (foot/rotor blade), and a large number of
stacked parts.
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Furthermore, significant problems are also
encountered in ensuring good leak tightness around the
foot part of the stacked parts.
OBJECT OF THE INVENTION
The purpose of the invention is therefore to
propose a method of manufacturing a hollow blade for
turbine engine, resolving at least partially the
aforementioned inconveniences associated with the
method implemented in the prior art.
More precisely, the purpose of the invention is to
present a method of manufacturing a hollow blade whose
production stage of the blade preform engenders
significantly reduced manufacturing costs compared to
those encountered in the prior art.
To accomplish this, the object of the invention is
a method of manufacturing hollow blades for turbine
engine comprising a foot and a rotor blade, the method
comprising a production stage of the blade preform
bearing a rotor blade part and a foot part, the
production stage of the preform being performed in such
a way that it comprises a unit of at least two parts
stacked and diffusion bonded together. According to the
invention, the production stage of the blade preform
comprises the following operations:
- the making of the unit of at least two parts
stacked and diffusion bonded together, in such a way
that it solely forms the rotor blade part of the
preform;
- the making of an additional element intended
to wholly form the foot part of the preform; and
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- the assembling of the additional element onto
the unit so as to obtain the blade preform.
Advantageously, in the method of manufacturing
according to the invention, the unit of at least two
parts stacked and diffusion bonded together is not
intended to constitute the entire blade preform, but
only the rotor blade part of the latter.
Consequently, the making of this diffusion bonded
unit no longer integrates the rather costly production
of two external parts each intended to have two
sections of significantly different thickness and
respectively be used to define the foot part of the
rotor part of the blade preform. On the contrary, as
this welded unit does not constitute the foot part of
the preform, its two external parts can thus be wisely
defined so that each of them has a relatively even
thickness, thus naturally engendering a significant
reduction in the material costs and machining costs.
Furthermore, another advantage of the invention
resides in the non-integration of the foot part during
the diffusion bonding stage, which makes it possible to
avoid being confronted with the implementation
difficulties of this welding technique encountered when
the unit to be welded has extremely variable
thicknesses (foot/rotor blade), and a large number of
stacked parts. Indeed, the diffusion bonded unit being
envisaged to solely constitute the rotor blade part of
the preform, it can consequently be manufactured simply
thanks to the stacking of only two or three parts, each
having a substantially even thickness.
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Furthermore, the non-integration of the foot part
during the diffusion bonding stage makes it possible to
considerably facilitate the leak tightness between the
stacked parts intended to be welded, this leak
5 tightness being necessary for the implementing of the
diffusion bonding technique. Indeed, the leak tightness
at the foot part of the stacking is known to those
skilled in the art as being very difficult to produce,
so that not having to care for it constitutes a real
advantage.
Moreover, the separate making of the additional
element presents the possibility of carrying out all
sorts of intermediary machining operations on this
element, before it is assembled onto the diffusion
bonded unit obtained at the same time.
Moreover, the additional element not being
intended to enter into the constitution of the rotor
blade part of the blade preform but solely to wholly
form the foot part of the said preform, it is obvious
that the manufacturing costs can also be minimised,
notably due to their minor radial length.
The invention therefore envisages the making of
the blade preform using a plurality of previously made
parts prior to being assembled, notably via diffusion
bonding for some of them, none of these parts extending
along the entire radial length of the preform, which
thus makes it possible to easily overcome the
inconveniences directly linked to the extensive
variation of thickness of the blade preform along its
length.
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Preferably, the operation of assembling each
additional element to the unit is implemented using a
technique taken from among the group constituted of
linear friction welding and of friction stir welding,
these techniques being preferred in that they are
relatively easy to implement, reliable, inexpensive and
barely destructive metallurgically speaking.
Preferably, the manufacturing stage of the blade
preform is followed by the following stages:
- airfoil profiling of the preform; and
- bulging via gas pressure and superplastic
forming of the airfoil profiling preform.
It can be envisaged that the additional element
intended to wholly form the foot part of the preform is
made via extrusion, which constitutes a particularly
beneficial advantage in terms of manufacturing costs.
Indeed, this inexpensive technique to be implemented,
consists, from a material billet and through an
appropriate die, in making a profile of the additional
element bearing the desired geometry.
Other advantages and characteristics of the
invention will appear in the detailed non-restrictive
description below.
BRIEF DESCRIPTION OF THE DRAWINGS
This description will be made in relation to the
annexed drawings among which;
- figure 1 represents a perspective view of a
standard hollow blade far turbine engine;
- figure 2 represents a diagrammatic
perspective view of a blade preform obtained during the
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implementing of the manufacturing stage of the preform
of the method of manufacturing according to the
invention; and
- figures 3a to 3d diagrammatically illustrate
the embodiment stages of the method of manufacturing
according to the invention.
DETAILED PRESENTATION OF THE PREFERRED EMBODIMENTS
In reference to figure 1, we can notice a standard
hollow blade 1 for turbine engine (not represented),
for example made of titanium or one of its alloys.
This hollow blade 1, of fan rotor blade type with
large chord, comprises a foot 2 extended by a rotor
blade 4 in a radial direction.
The rotor blade 4, intended to be placed in the
circulation path of an airflow of the turbine engine,
has two external surfaces 6 and 8, respectively called
upper surface 6 and lower surface 8, connected by a
leading edge 10 and a trailing edge 12.
Figure 2 represents a blade preform 16, such as is
intended to be obtained during a manufacturing stage of
the blade preform of the manufacturing method according
to the invention.
This preform 14 comprises a foot part 16 of
variable and large thickness, which is extended in a
radial direction by a rotor blade part 18. As can be
seen in figure 2, the foot part 16 has an internal
radial section 20 of a high average thickness E, this
section 20 being radially extended externally by an
external radial section 22 of an average thickness a
inferior to the average thickness E. For information
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purposes it is noted that the internal radial section
20 is later intended to ensure the fixing of the blade
in the rotor disk of the turbine engine, notably thanks
to two projection parts 23a and 23b positioned on
either side of a central part 23c slotted into the
extension of the external radial section 22 of the foot
part 16.
Furthermore, the rotor blade part 18 of the
preform 14 has a radially internal end 24 of thickness
e' substantially equal to the average thickness e, and
a radially external end 26 of thickness a " inferior to
the thickness e'. However, the rotor blade part 18 of
the preform 14 has a substantially even thickness.
Furthermore, it is indicated that there is not
clear demarcation between the radially internal end 24
of the rotor blade part 18 and the external radial
section 22 of the foot part 16 of the preform 14, as
these elements are substantially aligned. Nevertheless,
a fictitious junction plan P diagrammatically
represented in figure 2 shows the commonly accepted
theoretical separation between the foot part 16 and the
rotor blade part 18 of the preform 14.
In a preferred embodiment of the method of
manufacturing according to the invention, a
manufacturing stage of the blade preform 14 is carried
out in the aforementioned manner, making reference to
figures 3a to 3c.
First of all a unit 28 is made of at least two
parts 30 and 32 stacked and diffusion bonded together,
the only two parts 30 and 32 visible in figure 3a
respectively constituting the upper and lower external
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parts of the unit 28. In this regard, it is indicated
that a third part (not represented) can also be
inserted between the external parts 30 and 32, so as to
constitute a stinger later on. Indeed, the unit 28,
being intended to solely and wholly form the rotor
blade part 18 of the preform 14, can therefore be
classically made using two identical external parts
with grooved internal surfaces, or even with three
parts of which the two identical external parts have
substantially smooth internal surfaces in contact with
the third intermediary part.
In this preferred embodiment of the invention, the
unit 28 solely forming the rotor blade part 18 of the
preform 14 has a substantially even thickness, the same
as the two identical external parts 30 and 32
constituting this unit 28. Thus, the technique to
obtain the parts 30 and 32 via lamination is therefore
particularly appropriate, and completely optimised in
terms of material costs and machining costs, as the
supply elements necessary for the manufacturing of the
parts 30 and 32 can easily have dimensions similar to
the final dimensions that these said parts 30 and 32
must have.
In the case when the unit 28 is solely constituted
of two identical external parts 30 and 32, once these
have been made as described above, they are then
diffusion bonded together, in a similar manner to that
encountered in the prior art in order to carry out the
assembling of the different component parts of the
preform. In this respect and in a continuous manner, it
is noted that the diffusion bonding operation is
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preceded by a depositing operation of fuel rod coating
according to a set pattern, the coatings being applied
to the internal surfaces 30a and 32a in contact with
the external parts 30 and 32.
5 At the same time as the manufacturing of the
hollow unit 28 solely and wholly forming the rotor
blade part 18 of the preform 14, a single additional
element 34 is made, intended to solely and wholly form
the foot part 16 of the said preform 14. Thus, it is
10 naturally specified that the unit 28 and the additional
element 34 each have a respective geometry
substantially identical to the geometry of the rotor
blade part 18 and of the foot part 16 of the preform 14
represented in figure 2.
As is shown in figure 3b, the additional element
34 therefore comprises a part 36 of considerable
thickness similar to the internal radial section 20
represented in figure 2, as well as a part 38 of
inferior thickness similar to the external radial
section 22 represented in the said figure 2. The
element 34 can consequently be easily made via
extrusion, this proven low cost technique consisting,
from a material billet and through an appropriate die,
in making a profile of the additional element 34
bearing the desired geometry. In this way, with such a
technique, it is possible to manufacture the additional
elements 34 one after the other, via single stripping.
Once the unit 28 and the additional element 34
have been simultaneously made, preferably in a titanium
alloy, they are then assembled in such a way so as to
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substantially obtain the geometry of the preform 14, as
illustrated in figure 3c.
This assembling can thus be performed via welding,
by putting an internal radial surface 40 of the unit 28
into contact with an external radial surface 42 of the
additional element 34. These surfaces 40 and 42 are
substantially flat and jointly define a flat contact
zone 44, approximately placed in a location identical
to that of the fictitious junction plane P represented
in figure 2, in comparison to the foot part 16 and
rotor blade part 18 of the preform 14.
By way of illustration, the assembling operation
of the additional element 34 to the unit 28 is
preferably done via linear friction welding, or by
friction stir welding. These known welding techniques
advantageously allow the welded zone to keep the
metallurgical characteristics compatible with the
diffusion bonding and superplastic forming techniques,
and ensure mechanical properties in compliance with the
specifications of the preform.
Of course, this welding operation is followed by a
machining operation of geometric reconditioning of the
welded zone.
Following the manufacturing stage of the blade
preform 14 which has just been described, standard
stages are then carried out first of all aiming at
airfoil profiling the preform 14, so that it has a
substantially twisted shape as illustrated in figure 3d.
Then, still in a continuous manner, bulging via gas
pressure and superplastic forming stage makes it
possible to obtain the blade 1 such as represented in
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figure 1, this stage being generally followed by a
final machining intended to strictly give the blade 1
the desired airfoil profile.
Of course, various modifications can be introduced
by those skilled in the art into the method of
manufacturing the hollow blade 1 which has just been
described, solely by way of non-restrictive
illustration.
