Tooling for machining a groove of a turbine engine casing
The invention relates to tooling for machining an annular groove
of a turbine engine casing in addition to a method of machining such a
5 groove.
A turbine engine conventionally comprises an intermediate
casing containing a shroud, known as an intermediate casing shroud,
designed to create an interface between the intermediate casing of the
turbine engine and the thrust reverser cowls of the nacelle.
10 An example of an intermediate casing shroud is described for
example in document FR 2 925 120.
The intermediate casing shroud comprises an annular groove
that is designed to receive an additional annular lip forming part of the
thrust reverser cowls. The lip rests radially and/or axially against the inner
15 faces of the groove.
During operation of the turbojet engine, the direction and
amplitude of the bearing forces vary according to the operating conditions
of the turbojet engine.
Thus, for example, when the turbojet engine is stationary, the
20 shroud supports the thrust reverser cowl and the lip therefore rests radially
downwards against the bottom of the groove.
Conversely, during thrust reversal, the lip rests axially in one
direction against a wall of the groove and radially against the bottom of the
groove.
25 Also, the turbojet engine produces vibrations that result in
relative motion between the lip and the groove.
All these stresses and vibrations cause wear of the walls of the
groove. This wear is distributed irregularly over the periphery of the groove.
When this wear exceeds a predetermined limit, on the order of a
30 few tenths of a millimetre, the groove needs to be repaired. Failing an
existing repair method, the shroud is replaced, which requires complete
dismantling of the engine, with an operation of this kind being long and
costly.
The invention proposes tooling allowing machining of the worn
areas with a view to their repair, directly under the wing of an aircraft, i.e.
5 without dismantling the engine.
For this purpose, the invention relates to tooling for machining an
annular groove of a turbine engine casing, wherein said tooling comprises a
machining tool, a baseplate, first means of positioning the machining tool in
relation to the baseplate along a first axis forming a radial axis, second
10 means of positioning the machining tool in relation to the baseplate along a
second axis perpendicular to the first axis, wherein said second axis
extends along the axis of the groove and of the annular casing and third
means of positioning capable of positioning the baseplate axially and
radially in relation to the groove of the casing.
15 Tooling of this kind allows precise positioning of the machining
tool in relation to the groove, via the various means of positioning,
subsequently allowing precise machining of each worn area, without any
need to dismantle the engine. Said machining can thus be performed area
by area under the wing of an aircraft. Complete dismantling of the engine is
20 avoided in this manner, in addition to complete replacement of the
intermediate casing shroud. After machining the various worn areas, an
anti-wear strip for example can subsequently be affixed to each machined
area, with an anti-wear strip of this kind being produced based on resin and
comprising fibres. Another solution involves for example applying a layer of
25 resin in addition to a solution for lubricating the repaired area.
Preferably, the first means of positioning comprise a micrometric
ring capable of adapting the position of the machining tool along the first
axis, by rotating the ring. A ring of this kind allows precise radial positioning
of the machining tool in relation to the groove.
30 Furthermore, the second means of positioning comprise a
micrometric table comprising a support that is mobile along the second axis
in relation to the baseplate, wherein the machining tool is mounted on the
mobile support. Use of the micrometric table allows precise axial positioning
of the machining tool in relation to the groove.
In this case, the machining tool can be mounted on the mobile
5 support via the first means of positioning.
Furthermore, the third means of positioning may comprise at
least one bearing area of the baseplate, capable of being engaged and/or
resting radially and axially in a form-fitting manner on annular sides, for
example radial sides, delimiting the groove of the turbine engine casing.
10 According to a characteristic of the invention, the machining tool
may be a milling tool.
The first means of positioning may be capable of positioning the
machining tool radially in relation to the baseplate with a tolerance of less
than 0.05 mm, preferably less than 0.025 mm, wherein the second means
15 of positioning may be capable of positioning the machining tool axially in
relation to the baseplate with a tolerance of less than 0.1 mm, preferably
less than 0.05 mm.
Furthermore, the tooling may comprise pressure means capable
of holding the baseplate against the casing. A characteristic of this kind
20 maintains the correct position of the baseplate and therefore of the
machining tool, in relation to the groove.
In this case, the pressure means may comprise at least one
roller and elastic return means intending to hold said roller on the casing,
opposite said groove and the baseplate.
25 The invention also comprises a process for machining an
annular groove of a turbine engine casing, for example of a turbine engine
intermediate casing, comprising the steps involving:
- identifying a worn area of said groove,
- installing tooling according to the invention on said casing
30 such that the baseplate is mounted on said groove via third means of
positioning, at the level of said worn area,
- machining at least part of said worn area of the groove by
moving the tooling along said worn area.
The invention thus proposes a simple machining method
allowing machining of only the worn areas of the groove, without
5 dismantling the engine and directly under the aircraft wing.
Preferably, the step of installing the tooling on the casing
comprises a step of radial and axial positioning of the machining tool in
relation to said groove, using the first, second and third means of
positioning.
10 Said positioning step may comprise a step of determining the
difference in size between the worn area and the sound area of the groove.
The invention will be better understood and other details,
characteristics, and advantages of the invention will appear on reading the
following description given by way of non-limiting example and with
15 reference to the accompanying drawings, in which:
- figure 1 diagrammatically illustrates a partial axial crosssection
of an aircraft turbojet engine,
- figure 2 is a larger-scale detailed view of the turbojet engine
illustrated in figure 1, showing the link between the casing revolution part
20 and the thrust reverser cowls,
- figure 3 is a perspective view of the tooling according to the
invention,
- figure 4 is a front view of the tooling,
- figure 5 is a perspective view of the tooling and of the
25 intermediate casing shroud, wherein the tooling is installed at the groove of
the shroud,
- figure 6 is a view illustrating a worn area of the groove that is
partially machined, wherein the baseplate of the tooling is installed on the
groove.
30 Figure 1 shows an aircraft turbojet engine 1 comprising a nacelle
2 and a fan casing 3, extended rearwards by an intermediate casing 4.
The intermediate casing 4 comprises a radially external shroud 5
located in the rearwards aerodynamic extension of the fan casing 3 and
crossways flanges 6 arranged radially inwards in relation to said external
shroud 5. The intermediate casing 4 furthermore comprises structural arms
5 7 distributed angularly and extending radially between the flanges 6 to the
external shroud 5 with which they come into contact.
The external shroud 5 of the intermediate casing 4 comprises, in
its downstream portion, a revolution part 8, the main purpose of which is to
establish a link between the external shroud 5 and the nacelle cowls
10 directly adjacent in the downstream direction.
The nacelle 2 forms a continuous aerodynamic external surface,
constituted by an air intake 9, fan cowls 10, thrust reverser cowls 11 and a
fixed rear casing 12, wherein these components are arranged adjacent to
each other from the front towards the rear.
15 The thrust reverser cowls 11, generally two in number and
hingedly connected to the rigid structure of the pylon, delimit in a known
fashion an annular channel of secondary flow 13, by means of annular
skins, external 14 and internal 15.
As can be seen in greater detail in figure 2, the link between the
20 revolution part 8 of the casing and the thrust reverser cowls 11 is
established by means of an annular groove 16 created in the revolution part
8 and an annular lip 17 which is mounted on a supporting structure 18
bearing the cowls 3 I , which is received in the groove 16.
This interaction between the annular lip 17 and the groove 16
25 provides the axial and radial hold of the reverser cowls 11 on the nacelle 2.
A annular seal 19 is arranged between the groove 16 and the lip
17 to prevent any air circulation at the junction between the revolution part
8 and the supporting structure 18.
The axial section of the groove 16 is globally U-shaped and the
30 groove 16 thus comprises a revolution front surface 20, a revolution rear
surface 21 opposite the front surface 20 and a cylindrical bottom surface 22
connecting the front and rear surfaces 20, 21 at their internal radial ends.
The annular lip 17 is received in the groove 16 and rests axially
andlor radially against the surfaces 20, 21, 22 of the groove 16.
5 During operation of the turbojet engine 1, the vibrations
generated by the moving parts cause movement of the lip 17 in the groove
16 and therefore gradual wear of the surfaces 20, 21, 22 of the groove 16.
In order to limit the overall weight of the turbojet engine, the
revolution part 8 is made of aluminium-based material, which wears out
10 quickly.
If wear of the surfaces 20, 21, 22 of the groove 16 is excessive,
a wide clearance develops beiween the lip 17 and the groove 16.
In order to be able to repair said surfaces 20, 21, 22, it is first of
all necessary to machine the worn areas 23 (figure 6) of these surfaces 20,
15 21, 22 before affixing an anti-wear strip for example on each machined
area, with an anti-wear strip of this kind being produced for example based
on resin and comprising fibres. Another solution involves for example
applying to each machined area a layer of resin in addition to a solution for
lubricating the repaired area.
20 In order to perform machining of the different areas used directly
under the wing of an aircraft, i.e. without removal andlor complete
dismantling of the engine 1, the invention proposes tooling 24 illustrated in
figures 3 to 6.
The latter comprises a machining tool 25 provided in the form of
25 a milling machine, the bur of which rotates around a radial axis Y,
perpendicular to the longitudinal axis X of the turbine engine 1. Said milling
machine 25 is for example of pneumatic type and is connected to a
compressed air supply line 26 (figure 5).
The radially internal end of the fixed part of said machining tool
30 25 is fixed to a ring-shaped plate 27, via a micrometric ring 28. The bur of
the machining tool 25 is therefore radially mobile, to a certain extent, in
relation to the plate 27. Pivoting of the ring 28 around the axis Y allows
adjustment of the position of the bur of the machining tool 25.
The radial position of the bur can be adjusted with a tolerance of
less than 0.05 mm, preferably less than 0.025 mm.
5 The plate 27 is fixed to a support 29 of a micrometric table 30.
The latter furthermore comprises a frame 31, with the support 29 being
mobile along the axis X in relation to the frame 31. Movement of the mobile
support 29 is actuated by a micrometric screw 32. The axial position of the
support 29 and therefore of the bur, can be adjusted with a tolerance of less
10 than 0.1 mm, preferably less than 0.05 mm.
The frame 31 is fixed to the radially external surface of a
baseplate 33. Said baseplate 33 furthermore comprises two grooves 34
(figures 5 and 6) extending circumferentially, i.e. perpendicularly to the axes
X and Y and emerging radially inwards. Said grooves 34 are of shapes that
15 match the sides 35 delimiting the groove 16 of the shroud 5 of the
intermediate casing 4 and mutually delimit a protruding portion 36 designed
to be engaged in the groove 16 of the shroud 5.
More particularly, the surfaces of said grooves 34 are designed
to rest on the surfaces 37 of the sides 35 opposite the surfaces 20, 21
20 delimiting the groove 16 and/or on the radially external ends 38 of the sides
35.
Said baseplate 33 is also equipped with a hollow handle 39,
serving to aspirate the chips generated during machining, connected to a
suction line not illustrated. The baseplate 33 is also equipped with blowing
25 means 40 (figure 3) arranged opposite the suction means 39, so as to
channel the chips towards said suction means 39. The blowing means 40
comprise a blowing nozzle connected in 41 to an auxiliary compressed air
supply line (not illustrated).
The tooling 24 furthermore comprises a base 42 exfending
30 radially, fixed to the baseplate 33, wherein a roller 43 is mounted on said
base 42, opposite the baseplate 33, wherein said roller 43 is mounted on a
yoke 44, fixed itself to the end of one or several mobile rods 45, wherein
said rods 45 and the roller 43 are returned radially outwards, i.e. in the
direction of the baseplate 33, via elastic return means comprising a helical
compression spring 46.
5 The procedure below is adopted to machine one or several worn
areas 23, i.e. one or several angular sectors of the groove 16 of the shroud
5 of the intermediate casing 4.
First of all, after opening the thrust reverser cowls 11 of the
nacelle 2, the operator mounts the tooling 24 on the shroud 5. In particular,
10 the protruding portion 36 of the baseplate 33 is engaged in the groove 16 of
the shroud 5 and the sides 35 are engaged in the grooves 34 of the
baseplate 33.
The roller 43 is applied, by means of the spring 46, to the radially
internal surface of the shroud 5, opposite the grooving 16. The radially
15 external ends 38 of the sides 35 are then able to rest on the bottoms of the
grooves 34 of the baseplate 33, thereby immobilising the latter radially in
relation to the shroud 5. Furthermore, the surfaces of the grooves 34 of the
baseplate 33 rest against the surfaces 37 of the sides 35, such that the
baseplate 33 is likewise immobilised axially in relation to the shroud.
20 Depending on the shape of the surfaces 37 (for example, fillet-shaped or
frustoconical), radial and axial positioning can be achieved merely by the
surfaces of the grooves 34 resting on the surfaces 37 of the shroud 5,
wherein the ends 38 of the sides 35 do not in this case bear against the
bottom of the grooves 34.
25 In order to precisely adjust the radial position of the bur in
relation to a non-worn and accessible reference of the shroud 5, for
example the area referenced 47 in figure 2, the operator rotates the
micrometric ring 28. Furthermore, in order to precisely adjust the axial
position of the bur in relation to said reference 47 of the shroud 5, the
30 operator turns the micrometric screw 32 of the micrometric table 30 so as to
move the support 29.
To this end, the operator can measure the wear of the worn part
using a comparator-type tool. For this purpose, if the groove is excessively
damaged, the latter is reconstructed, at least in part, using additional
metallic components and the thickness of a sound part of the groove is
5 subsequently used as a reference for the comparator. In other words, the
comparator is positioned, in order to be tared, on a sound part of the
groove. The comparator is subsequently mounted on a used portion of the
groove to determine the difference in thickness between the sound portion
and the worn portion of the groove. The position of the bur is then adapted
10 accordingly.
The milling tool 25 can subsequently be started and the tooling
24 can be moved circumferentially, using the handle 39, along the worn
area 23 of the groove 16 of the shroud 5, so that the bur is able to machine
the worn areas of the surfaces 20, 21, 22.
15 Figure 6 illustrates a worn area 23 of the groove that has been
partially machined. The part already machined is referenced 48 on this
figure.
The invention thus proposes tooling 24 and a machining method
allowing machining of only the worn areas 23 of the groove 16 of the
20 shroud 5, directly under the aircraft wing.

CLAIMS
1. Tooling (24) for machining an annular groove (16) of an
annular casing (4) of a turbine engine (I), wherein said tooling (24)
5 comprises a machining tool (25), a baseplate (33), first means of
positioning (28) the machining tool (25) in relation to the baseplate (33)
along a first axis (Y) forming a radial axis, second means of positioning (30)
the machining tool (25) in relation to the baseplate (33) along a second axis
(X) perpendicular to the first axis (Y), wherein said second axis (X) extends
10 along the axis of the groove (16) and of the annular casing and third means
of positioning (34) capable of positioning the baseplate (33) axially and
radially in relation to the groove (16, 37) of the casing (4), wherein said third
means of positioning comprise at least one bearing area (34) of the
baseplate (33) capable of being engaged andlor resting radially and axially
15 in a form-fitting manner on annular sides, for example radial sides (35)
delimiting the groove (16) of the casing (4) of the turbine engine (I),
wherein the tooling furthermore comprises pressure means (42, 43, 44, 45,
46) capable of holding the baseplate (33) against the casing (4).
2. Tooling (24) according to claim 1, characterised in that the
20 first means of positioning comprise a micrometric ring (28) capable of
adapting the position of the machining tool (25) along the first axis (Y), by
rotating the ring (28).
3. Tooling (24) according to claim 1 or 2, characterised in that
the second means of positioning comprise a micrometric table (30)
25 comprising a support (31) that is mobile along the second axis (X) in
relation to the baseplate (33), wherein the machining tool (25) is mounted
on the mobile support (31).
4. Tooling (24) according to claim 3, characterised in that the
machining tool (25) is mounted on the mobile support (37) via the first
30 means of positioning (28).
5. Tooling (24) according to any of claims 1 to 4,
characterised in that the machining tool (25) is a milling tool.
6. Tooling (24) according to any of claims 1 to 5,
characterised in that the first means of positioning (28) are capable of
5 positioning the machining tool (25) radially in relation to the baseplate (33)
with a tolerance of less than 0.05 mm, preferably less than 0.025 mm
andlor the second means of positioning (30) are capable of positioning the
machining tool (25) axially in relation to the baseplate (33) with a tolerance
of~lessth an 0.1 mm, preferably less than 0.05 mm.
10 7. Tooling (24) according to any of claims 1 to 6,
,
, characterised in that the pressure means comprise at least one roller (43)
and elastic return means (46) intending to hold said roller (43) on the casing
(4), opposite said groove (16) and the baseplate (33).
8. Method of machining an annular groove (16) of an annular
15 casing (4) of a turbine engine (I)fo,r example of an intermediate casing (4)
of a turbine engine (I), comprising the steps involving:
- identifying a worn area (23) of said groove (16),
- installing tooling (24) according to any of claims 1 to 7 on
said casing (4) such that the baseplate (33) is mounted on said groove (16)
20 via third means of positioning (34, 37), at the level of said worn area (23)
and such that the pressure means (42, 43, 44, 45, 46) hold the baseplate
(33) against the casing (4),
- machining at least part (48) of said worn area (23) of the
groove (16) by moving the tooling (24) along said worn area (23).
25 9. Method according to claim 8, characterised in that the step
of installing the tooling (24) on the casing (4) comprises a step of radial and
axial positioning of the machining tool (24) in relation to said groove (16),
using the first, second and third means of positioning.