System for mechanically stressing a blower cell

Abstract

The invention relates to an inspection system for a cavity (12) of a turbojet engine disk, this cavity (12) having a transverse contour arranged to receive a blade foot (33) to support this blade, this system comprising: – an extendable support (23) having a first end (26) and a second end (27) movable in translation relative to each other along a principal direction (D); – means for exerting a predetermined force tending to separate the first end (26) from the second end (27); – a template (31) having a blade foot (33) engaging in the cavity (12) and an external portion (34) protruding from the cavity (12); – a first securing element (29) of the first end (26) to the blade template (31); – a second securing element (32) of the second end (27) to the disc; – means for measuring the position and / or orientation of the external portion (34) of the template (31).Figure for the abbreviation: Figure 4.

Description

Title of the invention: System for mechanically stressing a blower cell technical field

[0001] The invention relates to the verification of the mechanical conformity of the cells of a blower disc, which receive the blades of this blower. STATE OF PRIOR ART

[0002] A turbofan engine of the double-flow type includes an inlet sleeve into which air is admitted which is sucked in by the blades of a fan before being divided into a central primary flow and a secondary flow which surrounds the primary flow.

[0003] The primary airflow then passes through a first compressor located after the blower while the secondary flow is propelled backwards to generate additional thrust by being blown around the primary flow.

[0004] The primary flow then passes through a second compression stage, before reaching a combustion chamber, after which it is expanded in a high-pressure turbine and then in a low-pressure turbine to rotate the compression stages and the blower, before being expelled rearward to generate thrust.

[0005] Each turbine comprises a succession of stages, each comprising a series of radially oriented blades regularly spaced around a central axis of the engine and carried by a disk of a central rotor of this engine.

[0006] The blower blades are carried by a disc of this central rotor and which has at its periphery a series of cells regularly distributed around this rotor and which extend parallel to each other along the direction of the axis of rotation or by forming a certain angle with respect to this axis.

[0007] Each cavity is a groove whose cross-sectional shape resembles a dovetail contour with rounded apexes. Each cavity delimits along its entire length a rectangular opening radiating outwards from the disk, and it terminates in the front and rear faces of this disk where it opens in the form of dovetail openings with rounded apexes.

[0008] Mounting a blade consists of engaging the foot of this blade in the cavity through a face of the disk into which it opens by axially moving this foot in the cavity to engage it.

[0009] The contour of each cell seen in cross-section, that is to say in a plane normal to its generatrices, is very rounded instead of having acute angles as in the case of a dovetail shape. As with all engine parts, the various characteristics of these discs are checked.

[0010] A manufacturing defect in these cavities, particularly with regard to geometric conformity, results in misalignment of the blades they receive. Metrological control of these cavities is therefore carried out during manufacturing to determine whether they conform or not, so that rework can be carried out if necessary, or even the disc can be scrapped if irreparable defects are identified.

[0011] This verification is ensured by measuring the shape of the alveolus contour in a transverse plane to determine whether or not it conforms to predetermined geometric criteria, as described in particular in French patent FR3032270.

[0012] However, direct metrological control of a cavity requires a small metrological sensor to allow its engagement in the cavity, and an analysis of the measurements which proves complex due to the particular shape of the contour to be measured, and its possible deformation in service.

[0013] It follows that the control of the alveoli as it is currently carried out is not entirely satisfactory.

[0014] The object of the invention is to propose a solution to remedy this drawback. Description of the invention

[0015] To this end, the invention relates to an inspection system for a cavity in a turbojet engine disk, this cavity having a transverse contour arranged to receive a blade root in order to support this blade, the system comprising:

[0016] - an extendable support comprising a first end and a second end mobiles in translation relative to each other along a principal direction;

[0017] - means for exerting a predetermined effort aimed at excluding the first end of the second end;

[0018] - a template comprising a blade foot engaging in the cavity and a portion external protruding from the alveolus;

[0019] - a first means of securing the first end of the support to the template dawn;

[0020] - a second means of securing the second end of the support to the disk;

[0021] - metrological means for measuring the position and / or orientation of the external portion of the template.

[0022] This system thus makes it possible to carry out reliable control of the cells since it is not necessary to make assumptions about their deformations in service, since the control can be carried out under a mechanical load corresponding to the operating conditions of the blade with regard to centrifugal forces.

[0023] The invention also relates to a system thus defined, in which the first fastening member comprises a first pivot joint with axis normal to the main direction.

[0024] The invention also relates to a system thus defined, in which the second securing member comprises a second pivot joint with an axis parallel to that of the first pivot joint.

[0025] The invention also relates to a system thus defined, in which the axis of the first pivot joint passes through a point of the blade template corresponding to the center of gravity of the blade to be carried by the cell.

[0026] The invention also relates to a system thus defined, in which the second securing member is arranged so that the axis of the second pivot joint coincides with the axis of rotation of the disk.

[0027] The invention also relates to a system thus defined, in which the means for exerting a force tending to separate the ends are carried by the support.

[0028] The invention also relates to a system thus defined, in which the support comprises a deformable parallelogram, the first end and the second end corresponding to two opposite vertices of this deformable parallelogram, with a spring tending to bring together the other two vertices of the deformable parallelogram.

[0029] The invention also relates to a system thus defined, in which the external portion of the template comprises calibrated surfaces. Brief description of the drawings

[0030] Fig. 1 is a schematic view of a turbofan engine in longitudinal section;

[0031] Fig. 2 is a schematic view of a reactor blower disk shown alone in perspective;

[0032] Fig. 3 is a schematic representation showing the outline of a cell in cross-section;

[0033] Fig. 4 is a schematic representation of the tool according to the invention installed on a disk;

[0034] Fig. 5 is a partial view showing the blade template installed in a cell to be controlled.

[0035] DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

[0036] In the turbojet 1 shown in [Fig. 1], outside air is admitted into an inlet sleeve 2 and then passes through a fan 3 comprising a series of blades rotating before splitting into a central primary flow and a secondary flow surrounding the primary flow.

[0037] The primary flow is then compressed in a first and second compression stage 4 and 6 before entering a combustion chamber 7, after which it expands as it passes through a set of turbines 8 before being discharged to the rear, generating thrust. The secondary flow, meanwhile, is propelled directly to the rear by the fan to generate additional thrust.

[0038] This motor comprises a rotor rotating around its axis of rotation AX, and including several discs each carrying on its outer periphery a series of blades or vanes, these discs corresponding to the blower, compressors and turbines.

[0039] As shown in [Fig. 2], a blower disk 11 has a general shape of revolution having on its outer periphery a series of cavities 12 regularly distributed around its axis of rotation AX and parallel to each other. These cavities 12, which are manufactured, for example, by broaching, are each intended to receive a blower blade, the blades extending radially with respect to the axis AX when mounted.

[0040] As can be seen in [Fig. 3], the contour C of a cell 12 in a plane normal to a generatrix of this cell, that is to say in cross-section, has a shape which generally corresponds to the contour of a dovetail shape with strongly rounded corners. This shape thus corresponds to that of a letter U having a base width greater than the distance separating the ends of its arms.

[0041] This contour C comprises a base 13, corresponding to the base of the letter U, with an orthoradial orientation with respect to the axis of rotation AX, and which is extended by two bearing surfaces 14, 16 inclined to converge towards each other and which correspond to the branches of the letter U. These bearing surfaces 14, 16 jointly form the socket of the alveolus 12, their ends corresponding to the lips or edges 17, 18 of the opening 19 of this alveolus in the radial direction.

[0042] The connecting portions of the bottom 13 with each span 14, 16 are rounded parts identified by 21 and 22, and the shape of the contour C has an axis of symmetry located halfway between the two lips 17 and 18 and passing through the center of the bottom 13.

[0043] The invention is based on the observation that the geometry of the cells changes when the engine is in operation due to the centrifugal forces exerted on the blades supported by these cells. It follows that a geometric inspection of the blades during manufacturing is ultimately not representative of the functional conformity of these cells.

[0044] The idea behind the invention is to subject a cavity to be inspected to a mechanical stress corresponding to the centrifugal forces it experiences when the The engine is in service to carry out a conformity check, in order to make such a check meaningful and consistent.

[0045] According to the invention, a gauge comprising a blade foot is engaged in the cavity to be inspected, and this gauge is supported by a support exerting on it a radial force corresponding to the centrifugal force experienced by a blade when the engine is in operation. The inspection of the cavity can then be carried out under a situation corresponding to the operating conditions in terms of mechanical stresses applied to the cavity.

[0046] In [Fig. 3], a support 23 comprises four bars 24 of the same length articulated to each other at their ends to form a deformable parallelogram. This deformable parallelogram constitutes a support having a first end 26 and a second end 27 corresponding to two of its opposite vertices.

[0047] These two ends are movable relative to each other in translation along a principal direction D, and a spring 28 extends between the two other opposite vertices of this parallelogram. The spring 28 works in tension (it tends continuously to retract) to bring the vertices of the parallelogram to which it is attached closer together, in order to continually tend to separate the first end 26 from the second end 27 of the support 23.

[0048] The first end 26 is equipped with a first fastening member 29 by which it is fastened to the blade template 31. Advantageously, this first fastening member 29 comprises, or forms with the template 31, a first pivot joint with axis normal to the main direction D.

[0049] The second end 27 is equipped with a second fastening member 32 allowing it to be fastened to a fixed element such as the disk 11 or a frame supporting this disk. Advantageously, this second fastening member 32 comprises, or forms with the fixed element, a second pivot joint with an axis parallel to that of the first pivot joint.

[0050] As can be seen in [Fig.5], the template 31 includes a blade foot 33 extended by an external portion 34 which extends radially out of the disk 11 when this foot 33 is engaged in the cavity 12. This external portion 34 corresponds substantially to the blade of a blade carried by a foot such as the foot 33, but its external faces 36 constitute or comprise metrological reference surfaces.

[0051] These reference surfaces are, for example, six in number to allow for the complete identification of the position and orientation of the blade template. These surfaces are oriented and positioned in a known and precise manner relative to the foot 33, these surfaces being advantageously flat so as to be accessible by a metrological means 37 which is here a metrological probe in the example of [Fig.5]. Thus, a metrological control of these reference surfaces makes it possible to deduce in a simple way the position and / or the precise orientation of the foot 33 with respect to a radial reference axis AR normal to the axis AX and passing through the alveolus.

[0052] The orientation of the foot (and therefore of the blade to be carried by such a foot) includes in particular its angle with respect to the radial axis AR measured in a plane normal to the axis AX (“circumferential tilt”), its angle with respect to the radial axis AR measured in a plane containing the axis AX (“perpendicularity”), and its inclination with respect to the axis AX around the radial axis AR (“inclination”).

[0053] Checking the recesses of the disk 11 thus consists of installing this disk on a test frame. The second end 27 of the support 23 is secured to this frame, at the axis of rotation AX of the disk 11, by means of the second securing member 32, and the foot 33 of the blade gauge 31 is then engaged in a recess 12, the spring 28 having, for example, one of its ends detached from the support. Once the foot 33 is in place in the recess 12, the spring is tensioned, for example by reattaching its temporarily released end to the corresponding top of the support.

[0054] Under these conditions, the foot 33 is supported on the bearing surfaces 14, 16 of the cavity, being held in support by the force exerted by the spring 28 which tends to move it away from the axis AX by exerting a force corresponding to the centrifugal force to which a blade is subjected when the motor is in operation.

[0055] At this stage, the blade template 31 is in place in the cavity 12 which is subjected to mechanical stresses identical or close to those it undergoes in operation, so that it deforms substantially to adopt the shape it has when the engine is in service.

[0056] A metrological probe can then be brought close to the reference surfaces of the outer portion 34 of the blade to measure, for example, six values, in order to identify the circumferential balance, perpendicularity, and inclination of the blade gauge. If these three parameters are within ranges of values ​​considered satisfactory, the cavity is considered valid; otherwise, it is decided that the cavity must be rectified before being put into service.

[0057] Once a cavity has been checked in this way, the tension of the spring 28 is released to extract the foot 33 from this cavity, and to place it in the neighboring cavity in order to proceed with its check in the same way.

[0058] In the example described, the connection of the first fastening member 29 with the template 31 is a pivot joint, and this fastening member 29 corresponds here to the mechanical axis connecting the two bars 24 of the deformable parallelogram at its first end 26, to articulate them to each other. This mechanical axis extends to fit into a corresponding bore formed in the blade template. 31, so that template 31 and the two bars 24 are linked to each other by the same pivot joint materialized by this axis.

[0059] In order for the forces exerted by the support 23 on the template 31 to correspond as closely as possible to the centrifugal forces suffered by a blade corresponding to this template 31, the first fastening member 29 constitutes a first connection with the template 31 whose center of connection is located in a central region of the template 31.

[0060] The connection center is more particularly located on a radial axis passing through the barycenter of the blade intended to be carried by the cell, and advantageously at the level of this barycenter.

[0061] This first connection, which is a pivot joint in the example described, can advantageously be a ball joint to generate an optimal distribution of forces. Conversely, this first connection could also be a fixed joint to simplify the system, in cases where the distribution of forces is not a relevant characteristic for controlling the cell.

[0062] As regards the second securing member 32, it includes a second connection with a fixed element of the control frame 38 or possibly with the disc 11 passing through a central part of the cavity and containing the axis of rotation AX of the disc 11. Advantageously, this second connection is located at the level of the axis AX, which avoids dismantling and reassembling the device for each cavity to be tested.

[0063] As in the case of the first fastening element, the second fastening element can be materialized by the mechanical axis linking the bars 24 of the deformable parallelogram at its second end.

[0064] In the example described, the second fastening element 32 has a connection with the disc 11 or the control frame which is a pivot joint, but this second connection could be of a different nature, such as a ball joint or a full joint. The nature of the second connection primarily affects the distribution of the forces exerted on the jig, so the choice of the type of connection is mainly determined by the impact of the force distribution on the control.

[0065] As will be understood, the second securing element 32 ensures, depending on the case, the securing of the support 23 with the disk 11 or with a control frame on which the disk 11 is installed to carry out its inspection.

[0066] In the description given, the support 23 is formed on the basis of a deformable parallelogram equipped with a spring, so as to be able to exert a force tending to move its two ends apart. Other arrangements are possible for the support 23; the spring 28 can be replaced by a jack, and the deformable parallelogram can be replaced by a rail carrying the two fastening members, one of which is movable relative to the other along this rail.

[0067] As regards the control frame, allowing the inspection of the cells, it includes means for receiving the disc by positioning it precisely, for receiving the support, and it is equipped with metrological means such as the probe 37 allowing to determine with precision the position and / or the orientation of the external portion of the blade template.

[0068] Furthermore, the invention has been described in the context of a blower disc cell, but it applies generally to the verification of the geometry of a turbine or compressor disc cell.

Claims

Demands

1. Inspection system for a cavity (12) of a disk (11) of a turbojet engine, this cavity (12) having a transverse contour (C) arranged to receive a foot (33) of a blade in order to support this blade, the system comprising: - an extendable support (23) comprising a first end (26) and a second end (27) movable in translation relative to each other along a principal direction (D); - means for exerting a predetermined force tending to separate the first end (26) from the second end (27); - a template (31) comprising a blade foot (33) engaging in the cavity (12) and an external portion (34) protruding from the cavity (12); - a first joining element (29) of the first end (26) of the support (23) to the blade template (31), comprising a first pivot joint with axis normal to the main direction (D);- a second securing element (32) of the second end (27) of the support (23) to the disc (11); - metrological means (37) for measuring the position and / or orientation of the external portion (34) of the template (31).

2. System according to claim 1, wherein the second fastening member (32) comprises a second pivot joint with an axis parallel to that of the first pivot joint.

3. System according to claim 1, wherein the axis of the first pivot joint passes through a point of the blade template (31) corresponding to the center of gravity of the blade to be carried by the cavity (12).

4. System according to claim 3, wherein the second securing member (32) is arranged so that the axis of the second pivot joint coincides with the axis of rotation (AX) of the disk (11).

5. System according to any one of the preceding claims, wherein the means for exerting a force tending to separate the ends are carried by the support (23).

6. A system according to any one of the preceding claims, wherein the support (23) comprises a deformable parallelogram, the first end (26) and the second end (27) corresponding to two opposite vertices of this deformable parallelogram, with 10 a spring (28) tending to bring together the other two vertices of the deformable parallelogram.

7. System according to any one of the preceding claims, wherein the external portion (34) of the template (31) comprises calibrated surfaces.

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