METHOD FOR MACHINING A SHAPED HOLE IN A PART

Abstract

The invention relates to a method for drilling a conduit (12) in a part (10), particularly for an aircraft turbomachine, the method comprising the steps of: - drilling (S10) by electrical discharge machining (EDM) of the conduit in the part, the conduit having at one end a hole (16) opening into a surface of the part, and - machining (S20; S30) of the hole to form a finished conduit in the part. Figure for the abstract: Figure 1

Description

Title of the invention: METHOD FOR MACHINING A SHAPED HOLE IN A PART Technical field

[0001] The present invention relates to a method of drilling a conduit in a part, in particular for an aircraft turbomachine blade. Prior art

[0002] The distributors of high-pressure turbomachinery turbines, and consequently the blades that constitute them, are components exposed to very high thermal stresses. They are located at the outlet of the combustion chamber and are therefore traversed by extremely hot gases, which subject them to very high thermal stresses. The distributors, and in particular the blades, therefore require cooling.

[0003] To ensure efficient cooling of a distributor vane, it is desirable to have a cooling device that is thermally efficient to dissipate a high thermal power by using a moderate airflow.

[0004] One of the most widespread solutions currently involves using one or more inserts / cores placed inside the blades. The inserts are multi-perforated metal sheets designed to cool the inner face of the blade by means of cooling air impacts.

[0005] Furthermore, the blades of a turbine distributor include, for example, drilled holes. The blade is hollow, and the holes pass through the blade wall to provide ventilation air passages between the internal cavity of the blade and the turbine runner, allowing the creation of a cold film around the blade.

[0006] In addition, the blades may include a thermal barrier reducing thermal effects and also ensuring corrosion resistance.

[0007] Hole drilling is generally carried out by electro-erosion or EDM drilling (acronym for the English "Electro Discharge Machining").

[0008] EDM drilling is a machining process that removes material from a workpiece using electrical discharges. It is also known as spark machining. This technique is characterized by its ability to machine all electroconductive (electrically conductive) materials, regardless of their hardness.

[0009] The machining process consists of passing a current from an electrode to the workpiece through a dielectric, in order to generate a "bubble" of vapor or vacuum which ionizes and is absorbed by implosion, resulting in the destruction of the workpiece material. This destruction (micro-implosion) causes the spark. The high-intensity current ionizes a channel through the dielectric. A disruptive discharge then occurs between the electrode and the workpiece, damaging the latter very locally (a few pm2).

[0010] This process allows holes to be drilled with very high precision and is suitable for very hard materials or in cases where the complexity of the part requires it, as is the case for parts of an aircraft turbomachine.

[0011] However, the resulting surface state is inhomogeneous and highly disturbed.

[0012] However, the surface condition of shaped holes, also called "Shaped Hole" in English, has an important impact on the flow of cold air protecting the thermal barrier.

[0013] The objective of the present invention is therefore to propose a drilling process that improves the surface condition of these holes in order to better control the flow through them. Summary of the invention

[0014] To this end, the invention relates to a method for drilling a conduit in a part, in particular for an aircraft turbomachine, the method comprising the steps of: - drilling the conduit in the part by electro-erosion, the conduit having at one end a hole opening into a surface of the part, and - machining of the hole to form a finished conduit in the part.

[0015] The method according to the invention makes it possible to improve the surface finish of the drilled shape while respecting the conventional constraints of drilling a part, such as a turbomachine turbine blade, namely: a small affected area, in particular less than 100 µm in depth, dimensional control, and the absence of machining impact in the cavities. "Dimensional control" means that the actual shape must be within a 0.5 mm thickness envelope relative to the theoretical shape.

[0016] To this end, the process according to the invention implements several processes consecutively in order to improve the surface condition of the shape of the bore in order to better control the air flow which protects the part, in particular for a turbine blade of a turbomachine.

[0017] The drilling method according to the invention may comprise one or more of the following features, taken individually or in combination with each other in all technically possible combinations: - the machining of the hole is carried out by electrochemical machining or by a femtosecond laser or by water jet cutting; - The hole is machined using a laser that creates a heat-affected zone on the workpiece surface around the hole, and the process includes a finishing step using a non-thermal process to shape the heat-affected zone. finished in the room; - the hole machining is done by a nanosecond laser; - the thermally affected area has a depth between 50 pm and 100 pm; - the finishing stage is carried out by mechanical machining or by electro-erosion or by electrochemical machining or by a femtosecond laser or by water jet cutting, preferably by a femtosecond laser; - the part is a turbomachine rotor blade having an aerodynamic profile and said duct is formed inside at least the aerodynamic profile. Brief description of the drawings

[0018] The present invention will be better understood and other details, features and advantages of the present invention will become more apparent upon reading the following description of a non-limiting example, with reference to the accompanying drawings in which: - [Fig.1] is a flowchart illustrating a first embodiment of a drilling process according to the invention; - [Fig.2] is a schematic cross-sectional view of a part after a drilling step according to the first embodiment of a drilling process according to the invention; - [Fig.3] is a schematic cross-sectional view of a part after a machining step according to the first embodiment of a drilling process according to the invention; - [Fig. 4] is a flowchart illustrating a second embodiment of a drilling process according to the invention; and - [Fig.5] is a schematic cross-sectional view of a part after a nanosecond laser machining step according to the second embodiment of a drilling process according to the invention.

[0019] Elements having the same functions in the different implementations have the same references in the figures. Description of the embodiments

[0020] The present invention relates to a method of drilling a conduit in a part, in particular for an aircraft turbomachine blade.

[0021] Fig. 1 illustrates a first embodiment of a drilling process according to the invention.

[0022] According to this first embodiment, the process includes a drilling step S10 by electro-erosion (EDM) of the conduit in the part.

[0023] Fig. 2 is a cross-sectional view of an example of part 10 with such a conduit 12 after the EDM drilling step.

[0024] The conduit 12 includes a cylindrical part 14, in particular produced during the EDM drilling. The cylindrical part 14 has an axis of revolution which is oblique to the surface of the part 10 in the example illustrated in [Fig.2].

[0025] The conduit 12 further includes at one end a hole 16 opening into a surface of the part.

[0026] Such an EDM drilling step S10 makes it possible to precisely produce the cylindrical part 14 of the conduit 12 and thus a clean and precise unblocking even in parts with complex geometry such as turbomachine blades having complex internal cavities.

[0027] Indeed, other known drilling methods have disadvantages.

[0028] For example, when drilling by mechanical machining with a tool such as a drill bit or milling cutter, the hole will only be successfully opened if the thickness of the workpiece is known. Consequently, this method generally requires prior tomography of the area in order to calibrate the theoretical model of the workpiece. Furthermore, such a method generates significant wear and breakage of the machining tools.

[0029] Furthermore, in the case of a turbomachine blade, laser drilling with a nanosecond source is not feasible because the dimensions of the blade cavities necessarily require the application of another material to protect the internal surface of the cavities during the unclogging of the hole. Given the complex shapes of the blade cavities, no easily removable material currently exists that would allow this step to be performed.

[0030] The use of a laser having a femtosecond source results in a very long machining time.

[0031] Finally, drilling by electrochemical machining or ECM (acronym for the English "ElectroChemical Machining") would require the handling of dangerous and toxic substances.

[0032] Such an EDM drilling step S10 nevertheless creates a slight bead 18 of material at the drilling entry, i.e. on the surface of the part 10 at the periphery of the hole 16.

[0033] In order to perfect the drilling of the conduit in the workpiece and, in particular, to improve the surface finish of the workpiece, the process according to the invention includes a step S20 of machining the hole to form a finished conduit in the workpiece and, in particular, the shape of the hole on the surface of the workpiece. This machining step S20 therefore follows the EDM drilling step S10.

[0034] This S20 hole machining step is carried out either by electrochemistry (ECM) or by a femtosecond laser or by water jet cutting and preferably by femtosecond laser in order to obtain a good surface finish of the final part.

[0035] Figure 3 is a cross-sectional view of part 10 of Figure 2 after the hole machining step, for example, by laser. The laser thus makes it possible to remove the bead of material 18 in contact with him.

[0036] The part thus drilled has a good surface finish, in particular a surface finish greatly improved compared to those obtained after a conventional drilling process.

[0037] A second embodiment of a drilling method according to the invention is illustrated in [Fig.4]. This second embodiment differs from the first in that the EDM drilling step S10 is followed by a hole machining step S30 performed by a laser, preferably a laser having a nanosecond source.

[0038] The nanosecond laser makes it possible to ablate the bulge of material 18 created by the S10 step of EDM drilling.

[0039] Laser machining of hole 16 forms a heat-affected zone 20 on the surface of part 10 around conduit 12, as shown in [Fig.5] which illustrates a cross-sectional view of part 10 with such conduit 12 after step S30 of nanosecond laser machining of hole.

[0040] By "heat-affected zone" is meant a zone of weakness in the material. Such a zone can degrade its resistance, which is detrimental to the part it forms.

[0041] The use of a laser having a nanosecond source creates a thermally affected area between 50 pm and 100 pm deep in the room.

[0042] To this end, part 10 is laser-machined during step S30 to obtain an intermediate shape of the bore enlarged by a dimension approximately equal to the depth of the heat-affected zone to ensure a suitable final shape. This shape is illustrated in [Fig. 5]. Thus, the intermediate shape of the bore corresponds to the desired / final bore shape plus the heat-affected zone.

[0043] In order to form the finished conduit in the part, the process includes, after the laser machining step S30, a finishing step S40 by an athermic process of the heat-affected zone 20.

[0044] This finishing step S40 is carried out by mechanical machining or by electro-erosion or by electrochemical machining or by a femtosecond laser or by water jet cutting, preferably by a femtosecond laser.

[0045] This S40 finishing step by an athermic process makes it possible to remove the thermally affected area created by the S30 machining step in order to obtain the final duct shape while having a good surface finish of the final part.

[0046] The drilling process according to the invention as described, regardless of the embodiment, makes it possible to improve the surface finish of the drilled shape while respecting the classic drilling constraints related to an application on a turbine blade, namely: a small affected area, dimensional control and absence of impact machining in the cavities.

Claims

Claims

1. A method of drilling a duct (12) in a part (10), in particular for an aircraft turbomachine, the method comprising the steps of: - drilling (S 10) by electroerosion of the duct in the part, the duct having at one end a hole (16) opening into a surface of the part, and - machining (S20; S30) the hole to form a finished duct in the part in which the machining (S30) of the hole is carried out by a nanosecond laser forming a heat-affected zone (20) on the surface of the part around the hole, and the method comprises a step of finishing (S40) by an athermal process of the heat-affected zone to form the finished duct in the part.

2. A drilling method according to claim 1, wherein the heat-affected zone (20) has a depth of between 50 pm and 100 pm.

3. A drilling method according to claim 1 or 2, wherein the finishing step (S40) is carried out by mechanical machining or by electroerosion or by electrochemical machining or by a femtosecond laser or by water jet cutting, preferably by a femtosecond laser.

4. A drilling method according to any one of the preceding claims, wherein the part is a turbomachine rotor blade having an aerodynamic profile and said duct is formed at least inside the aerodynamic profile.

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