MULTI-DRILLING PROCESS BY ELECTROEROSION OF HOLES IN A ROOM WALL

Abstract

The invention relates to a method for multi-drilling holes (17) in a part (8) by electrical discharge machining (EDM) in a workpiece (8) comprising a wall (13) having an external surface (14) and an internal surface (15), an internal cavity (16) delimited by the internal surface (15), and an opposing wall (15a) located opposite the internal surface (15), comprising the following steps: (a) providing a multi-drilling EDM device (18), (d) moving the electrodes (20) of the device (18) to simultaneously drill the holes (17) in the wall (13), the method further comprises, between steps (a) and (d), the following steps: (b) fabricating a pattern (21) of the opposing wall (15a), (c) positioning each of the electrodes (20) opposite the guide (19) using the pattern (21) fabricated in step (b) so that a free end (20a) of each electrode (20) be positioned at the same predetermined distance (P) from the model (21). Abbreviated figure: Figure 5

Description

Title of the invention: METHOD FOR MULTI-DRILLING HOLES IN A WALL BY ELECTROEROSION PIECE Technical field of the invention

[0001] The invention relates to the field of multi-drilling processes by electro-erosion of holes in a wall of a part, in particular of a blade for an aircraft turbomachine.

[0002] The invention relates particularly to the field of multi-drilling processes by electrical discharge machining (EDM) employing a multi-drilling EDM device comprising a drilling guide and a plurality of electrodes movable as a single unit. Technical background

[0003] An aircraft turbomachine, such as a turbojet, typically comprises, from upstream to downstream in the direction of gas flow, a movable fan rotating about a longitudinal axis, a low-pressure compressor, a high-pressure compressor, a combustion chamber, a high-pressure turbine, a low-pressure turbine and a gas exhaust nozzle.

[0004] The blower allows the intake of an airflow that splits into a primary flow and a secondary flow. The primary flow passes through a primary channel of the turbomachine while the secondary flow is directed towards a secondary channel surrounding the primary channel.

[0005] The primary flow is compressed within the compressors. The compressed air is then mixed with a fuel and burned within the combustion chamber. The gases from the combustion pass through the turbines and then escape through the nozzle, the cross-section of which allows these gases to be accelerated to generate propulsion.

[0006] Turbines are typically equipped with blades regularly spaced around a rotating wheel about its longitudinal axis. A blade extends radially between a root and a tip. A blade also includes a blade connected to the root by a platform, for example. The blade has an aerodynamic shape and typically comprises an upper surface and an upper surface connected by a leading edge and a trailing edge.

[0007] Since high-pressure turbine blades are located downstream of the combustion chamber, they are subjected to high temperatures. Therefore, these blades are typically made of metallic or composite materials, particularly ceramic matrix composites (CMCs). These materials have the advantage of withstanding high temperatures. However, such blades may be subjected to temperatures exceeding those that metallic or ceramic matrix composites.

[0008] In this context, it has been proposed to equip the blades with a cooling system. The cooling system comprises a cooling circuit arranged inside the blades, allowing air from the compressors to pass through them. The cooling circuit includes internal cavities formed during the manufacturing of the blades. Each internal cavity is delimited by an internal surface of the blade. Furthermore, it has been proposed to drill holes in the blade, particularly on the upper or lower surface, opening into the internal cavities to create an air film around the blade. To increase the efficiency of this cooling system, it has been proposed to create at least one row of holes in the blade.

[0009] The holes are typically drilled by electrical discharge machining (EDM) after the blade has been manufactured, using an EDM device. Indeed, EDM processes are the only ones compatible with the complex geometries of blades and guarantee material integrity during drilling. In order to create these holes precisely and quickly, it has been proposed to use a multi-drill EDM device. Such a device allows for the simultaneous creation of a row of holes and offers a cost saving of 30% compared to a single-drill EDM device that only drills one hole at a time. Such a multi-drill EDM device comprises a drilling guide and a plurality of parallel electrodes mounted on the guide. The electrodes are aligned within the guide and are free to move in translation along a direction parallel to an axis of electrode elongation.The electrodes move simultaneously within the guide to perform the electro-erosion drilling of the blade.

[0010] The electrodes are typically either moved a predetermined distance or moved until a given condition is reached. Once this distance or condition is reached, the depth of the hole is considered to have been reached.

[0011] It is particularly important to predetermine this distance or condition precisely. Indeed, if these parameters are incorrect, there is a risk that the cavity wall opposite the wall containing the holes will be impacted by the electrodes and pierced. This can affect the blade cooling system and its mechanical strength.

[0012] The position of the internal cavity can vary from one blade to another. Also, the geometry of the internal cavity can vary within the blade and / or between two blades. Typically, the thickness of the internal cavity can vary along the length of the part. However, the electrodes are positioned in the guide assuming that this thickness is constant and identical for each of the blades. Thus, the position of the electrodes in the guide is not suitable for a series of blades in in which the position of the internal cavities varies. There is therefore a significant risk that during multi-drilling by electro-erosion with electrodes driven simultaneously, the internal cavity may be impacted by some of the electrodes.

[0013] In this context, there is a need to provide a multi-drilling process by electro-erosion of holes in a part comprising a wall having an external surface and an internal surface and an internal cavity delimited by the internal surface and an opposite wall, located opposite the internal surface, which makes it possible to guarantee drilling without impact of the part, i.e. without drilling of the opposite wall. Summary of the invention

[0014] To this end, the invention proposes a method for multi-drilling holes in a wall of a part by electro-erosion, the wall comprising an external surface and an internal surface, the part further comprising an internal cavity delimited by the internal surface and an opposite wall located opposite the internal surface, the method comprising the following steps:

[0015] (a) provide a multi-drilling electro-erosion device comprising a guide to drilling and a plurality of parallel electrodes carried by this guide, each electrode being configured to drill a hole in the wall by electro-erosion from the outer surface to the inner surface,

[0016] (d) move the electrodes in translation towards the wall of the part in a direction parallel to an axis of electrode extension to simultaneously drill holes in the wall.

[0017] The method according to the invention is remarkable in that it comprises between the steps (a) and (d), the following steps:

[0018] (b) fabricate a model of the opposite wall,

[0019] (c) position each of the electrodes vis-à-vis the guide using the model made at the step so that one free end of each electrode is positioned at the same predetermined distance from the model.

[0020] The part therefore comprises a wall having an external surface and an internal surface. The wall has holes that pass through both the external and internal surfaces. The part further comprises an internal cavity into which the holes open. The internal cavity is delimited by the internal surface of the wall and by an opposite wall, located opposite the internal surface and thus the holes.

[0021] According to the method of the invention, the model makes it possible to reproduce the actual opposite wall of the part that delimits the internal cavity of the part. Thus, the electrodes can be individually positioned in the guide so that the electrodes are at a predetermined distance from the model.

[0022] Once the electrodes are correctly positioned with respect to the model, their de- The placement will correspond to the shape of the internal cavity to be reached.

[0023] As the geometry of the opposite wall is correctly taken into account in step (c), once the hole detection has been carried out, the shape of the electrodes will respect the actual cavity and will prevent impacts in the part degrading the internal cavity.

[0024] Thanks to the invention, it is therefore possible to make holes without impacting the opposite wall, and thus to improve the quality of the cooling system of the part and its mechanical resistance.

[0025] The invention may comprise one or more of the following features, taken individually or in combination with each other:

[0026] - step (b) comprises the following substeps:

[0027] (bO) provide a virtual reconstruction of the internal cavity of the part, and

[0028] (bl) manufacture the model based on the virtual reconstruction obtained during the step (bO),

[0029] - substep (bO) is performed by imaging,

[0030] - step (bO) is carried out by tomography, advantageously by tomography at X-rays,

[0031] - the substep (bO) comprises the following substeps:

[0032] (bi) provide a series of virtual reconstructions of internal cavities of a series of parts,

[0033] (bii) perform an average virtual reconstruction of the internal cavity based on an average of the series of virtual reconstructions of step (bi),

[0034] - step (bl) is carried out by additive manufacturing,

[0035] - during step (c), the predetermined distance between the free end of each electrode and the model is zero so that the free end of each electrode is in contact with the model,

[0036] - the electrodes are mounted to slide in the guide and are individually adjustable dually positioned in the guide,

[0037] - the part is a blade comprising an intrados face and an extrados face connected by a leading edge and a trailing edge, the external surface being the intrados and / or the extrados surface,

[0038] - the part is made of metallic material or of ceramic matrix composite material. Brief description of the figures

[0039] Other features and advantages will become apparent from the following description of a non-limiting embodiment of the invention with reference to the accompanying drawings in which:

[0040] [Fig. 1] is a schematic longitudinal cross-sectional representation of half an aircraft turbomachine according to the invention,

[0041] [Fig.2] is a schematic representation of a blade drilled by the process according to the invention,

[0042] [Fig.3] is a schematic cross-sectional representation of the blade to be drilled by the process of the invention,

[0043] [Fig.4] is a schematic representation of a multi-drilling electro-erosion device implemented in the process of the invention,

[0044] [Fig. 5] is a schematic representation of the device in step (c) of the process,

[0045] [Fig. 5a] is a schematic representation of another example of the device in step (c) of the process,

[0046] [Fig. 6] is a schematic representation of the device in step (d) of the process,

[0047] [Fig.7] is a synoptic diagram of the process of the invention. Detailed description of the invention

[0048] An example of an aircraft turbomachine 1 according to the invention is shown in [Fig. 1]. The turbomachine 1 extends around and along a longitudinal axis X.

[0049] In the present application, the terms "upstream" and "downstream" are defined with respect to the direction of gas flow in the turbomachine 1 along the longitudinal axis X.

[0050] The terms "axial", "axially", "radial", "radially", "internal", "internal", "external", "externally", are defined with respect to the longitudinal axis X of the turbomachine 1.

[0051] The turbomachine 1 comprises, from upstream to downstream, a blower 2, at least one compressor such as a low-pressure compressor 3 and a high-pressure compressor 4, a combustion chamber 5, at least one turbine such as a high-pressure turbine 6 and a low-pressure turbine 7, and a nozzle (not shown).

[0052] The blower 2 allows the intake of an airflow F which divides into a primary flow Fl and a secondary flow F2. The primary flow Fl passes through the engine of the turbomachine 1 while the secondary flow F2 is directed towards a secondary channel.

[0053] The primary flow Fl is compressed within the low pressure compressor 3 and then the high pressure compressor 4. The compressed air is then mixed with a fuel and burned within the combustion chamber 5. The gases formed by the combustion pass through the high pressure turbine 6 and low pressure turbine 7. The gases finally escape through the nozzle whose cross-section allows the acceleration of these gases to generate propulsion.

[0054] The fan 2 is, for example, shrouded. It is surrounded by an annular casing 2b centered on the longitudinal axis X. The casing 2b is, for example, surrounded by a nacelle (not shown) of the turbomachine 1.

[0055] With reference to [Fig. 2], the high-pressure turbine 6 comprises blades 8 extending radially from a disk (not shown) that is either movable or fixed and rotates about the longitudinal axis X. Each blade 8 extends along a radial axis Y between a head 10 and a foot 12. Each blade 8 comprises a blade 9. The foot 12 is, for example, connected to the blade 9 by a platform 11. The foot 12 is mounted in the disk to retain the blade 8 on the disk. The blade 9 has an aerodynamic shape and comprises an upper surface 9i and an upper surface connected by a leading edge 9a and a trailing edge 9b.

[0056] With reference to [Fig.3], the blade 8 comprises a wall 13 including an external surface 14 formed by the intrados face 9i and / or the extrados face and an internal surface 15.

[0057] The blade 8 is made of an electrically conductive material. The material is, for example, a metallic material or a composite material. Advantageously, the composite material is a ceramic matrix composite (CMC). Such materials have the advantage of withstanding high temperatures and therefore allow these blades to be used in close proximity to the combustion chamber 5, in an environment subjected to high temperatures.

[0058] To further improve the temperature resistance of the blades 8, each blade 8 includes a cooling system. With reference to Figures 2 and 3, the cooling system includes at least one internal cavity 16 for the circulation of air, for example, drawn from the low-pressure compressor 4, inside the blade 8. The internal cavity 16 is delimited by the internal surface 15 and an opposing wall 15a located opposite the internal surface 15. The thickness of the internal cavity 16 is, for example, variable. It has, for example, a first thickness e1 and a second thickness e2 that is less than the first thickness e1. This is due, for example, to the variability of the geometry of the opposing wall 15a.

[0059] In order to further improve the temperature resistance of the blades 8, the cooling system further includes holes 17 drilled in the wall 13. The holes 17 extend from the external surface 14 to the internal surface 15. They thus open into the internal cavity 16. The holes 17 thus allow the passage of air from the internal cavity 16 to the external surface 14 in order to create an air film around the blade 8 to cool it.

[0060] The holes 17, for example, have a circular cross-section. They advantageously have a diameter on the order of a micrometer. The holes 17 are advantageously aligned and / or staggered. As shown in the example in [Fig. 2], the blade 8 may comprise a first series 17a of holes 17 aligned in a single row and a second series 17b of holes 17 staggered.

[0061] According to the invention, the holes 17 are made by electrical discharge machining (EDM). Indeed, such a process is compatible with the aerodynamic shape of the blade 8 and ensures material health during drilling of holes 17.

[0062] According to the invention, the holes 17 are made with a multi-drilling electrical discharge machining (EDM) device 18. Such a device 18 has the advantage of allowing the drilling of a plurality of holes 17 simultaneously. This results in an economic saving of at least 30% compared to a single-drilling EDM device with which only one hole can be made at a time.

[0063] With reference to [Fig.4], the device 18 comprises a drilling guide 19 and a plurality of electrodes 20 carried by the guide 19. The guide 19 comprises, for example, between four and thirty electrodes 20.

[0064] The electrodes 20 are arranged parallel to each other and each allows a hole 17 to be made by electrical discharge machining (EDM). Each electrode 20 has an elongated shape along an elongation axis Z. They extend along the elongation axis Z between a head (not shown) and a free end 20a. Each electrode 20 is configured to bore a hole 17 in the wall 13 by electrical discharge machining from the outer surface 14 to the inner surface 15.

[0065] According to the invention, each electrode 20 is mounted to slide in the guide 19 and is individually adjustable in position in the guide 19 so as to achieve the same predetermined distance D vis-à-vis the opposite wall 15a.

[0066] Each electrode 20 is free to move in translation along a direction T parallel to the elongation axis Z of the electrodes 20. The translational movement of the electrodes 20 allows them to be driven towards the wall 13 for drilling. The electrodes 20 are advantageously movable as a single unit.

[0067] A method for drilling multiple holes 17 will now be described with reference to Figures 4 to 7.

[0068] The drilling process according to the invention comprises the following steps carried out in chronological order:

[0069] (a) provide device 18,

[0070] (b) manufacture a model 21 of the opposite wall 15a,

[0071] (c) position each of the electrodes 20 opposite the guide 19 using the model 21 manufactured in step (b) so that the free end 20a of each electrode 20 is positioned at the same predetermined distance P from the model 21,

[0072] (d) move each electrode 20 in translation towards the wall 13 along a direction T parallel to the Z elongation axis of the electrodes 20 to simultaneously drill the holes 17 in the wall 13.

[0073] In step (a), the free ends 20a of each electrode 20 are, for example, aligned as shown in [Fig. 4]. The free ends 20a are aligned in a plane perpendicular to the elongation axis Z of the electrodes 20.

[0074] As can be seen in [Fig.5], model 21 makes it possible to reproduce the opposite wall 15a of the internal cavity 16.

[0075] Advantageously, step (b) comprises the following substeps:

[0076] (bO) provide a virtual reconstruction of the internal cavity 16, and

[0077] (bl) manufacture model 21 based on the virtual reconstruction obtained during the step (bO).

[0078] The substep (bO) is advantageously carried out by imaging and even more advantageously by tomography, for example by X-ray tomography. Indeed, tomography makes it possible to represent in three dimensions the blade 8 and therefore the internal cavity 16. On this basis, it is possible to manufacture the model 21.

[0079] According to one embodiment of the invention, substep (bO) comprises the following substeps:

[0080] (bi) provide a series of virtual reconstructions of internal cavities of a series of blades,

[0081] (bii) perform an average virtual reconstruction of the internal cavity 16 based on an average of the series of virtual reconstructions of step (bi).

[0082] This embodiment of the invention makes it possible to manufacture an average model corresponding to a series of blades. The model 21 can thus be used to adjust the position of the electrodes 20 for the entire series of blades 8.

[0083] Advantageously, the manufacturing step (bl) of model 21 is carried out by additive manufacturing.

[0084] According to an advantageous embodiment shown in [Fig. 5a], during step (c), the predetermined distance P between the free end 20a of each electrode 20 and the model 21 is zero so that the free end 20a of each electrode 20 rests on the model 21. According to this embodiment, step (c) comprises the following chronological substeps:

[0085] (cl) slide each electrode 20 in the guide 19 so that the free end 20a of each electrode 20 is in contact with the model 21,

[0086] (c2) lock each electrode 20 in position in the guide 19.

[0087] This facilitates the positioning of the electrodes 20 with respect to the guide 19.

[0088] Steps (b) and (c) thus make it possible to take into account the actual geometry of the internal cavity 16 and therefore the thickness of the wall 13 in order to carry out a drilling without impact of the opposite wall 15a located opposite the internal surface 15 of the internal cavity 16.

[0089] With reference to [Fig.6], at the end of step (c) of positioning the electrodes 20, each electrode is positioned at the same predetermined distance D from the opposite wall 15a.

[0090] During step (d), the electrodes 20 are moved as a block.

[0091] The stopping of the drilling of the holes 17 by the electrodes 20 can be achieved, for example, by detecting a given parameter. The parameter can be the current flowing through the electrodes 20. Indeed, the current intensity varies depending on the medium in which the electrodes 20 are located. When the electrodes 20 pass through the wall 13, a first intensity is measured, while when the electrodes 20 reach the internal cavity 16, a second intensity is measured, signaling the stopping of the drilling of the holes 17. Other means of stopping the drilling can be implemented.

[0092] Thanks to the invention, it is possible to correctly position the electrodes 20 according to the geometry of the internal cavity 16. Since the geometry of the opposite wall 15a is correctly taken into account in step (c), when the electrodes 20 are inserted into the internal cavity 16, the electrodes 20 will be correctly positioned to prevent the formation of holes in the opposite wall 15a located opposite the internal surface 15 of the cavity 16. The drilling can therefore be carried out without impact. The electrodes 20 can thus be moved as a single unit without risk of impact.

Claims

Demands

1. A method for multi-drilling holes (17) in a wall (13) of a part (8) by electrical discharge machining (EDM), the wall (13) comprising an external surface (14) and an internal surface (15), the part (8) further comprising an internal cavity (16) delimited by the internal surface (15) and an opposing wall (15a) located opposite the internal surface (15), the method comprising the following steps: (a) providing a multi-drilling EDM device (18) comprising a drilling guide (19) and a plurality of parallel electrodes (20) carried by this guide (19), each electrode (20) being configured to drill by EDM a hole (17) in the wall (13) from the external surface (14) to the internal surface (15), (d) moving the electrodes (20) in translation towards the wall (13) of the part (8) in a direction (T) parallel to an axis elongation (Z) of the electrodes (20) to simultaneously drill the holes (17) in the wall (13),characterized in that the method comprises, between steps (a) and (d), the following steps: (b) fabricating a model (21) of the opposite wall (15a), (c) positioning each of the electrodes (20) opposite the guide (19) using the model (21) fabricated in step (b) so that a free end (20a) of each electrode (20) is positioned at the same predetermined distance (P) from the model (21).

2. A method according to the preceding claim, characterized in that step (b) comprises the following substeps: (bO) providing a virtual reconstruction of the internal cavity (16) of the part (8), and (bl) manufacturing the model (21) on the basis of the virtual reconstruction obtained during step (bO).

3. Method according to the preceding claim, characterized in that the substep (bO) is carried out by imaging.

4. Method according to the preceding claim, characterized in that step (bO) is carried out by tomography, advantageously by X-ray tomography.

5. A method according to any one of claims 2 to 4, characterized in that substep (b0) comprises the following substeps: (bi) providing a series of virtual reconstructions of internal cavities from a series of parts, (bii) perform an average virtual reconstruction of the internal cavity (16) based on an average of the series of virtual reconstructions of step (bi).

6. A method according to any one of claims 2 to 5, characterized in that step (bl) is carried out by additive manufacturing.

7. A method according to any one of the preceding claims, characterized in that during step (c), the predetermined distance (P) between the free end (20a) of each electrode (20) and the pattern (21) is zero so that the free end (20a) of each electrode (20) is in contact with the pattern (21).

8. A method according to any one of the preceding claims, characterized in that the electrodes (20) are slidably mounted in the guide (19) and are individually adjustable in position in the guide (19).

9. A method according to any one of the preceding claims, characterized in that the part is a blade (8) comprising an intrados face (9i) and an extrados face connected by a leading edge (9a) and a trailing edge (9b), the external surface (14) being the intrados face (9i) and / or the extrados face.

10. A method according to any one of the preceding claims, characterized in that the part (8) is made of metallic material or of ceramic matrix composite material.

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