Spark erosion process and spark erosion device

Abstract

A spark erosion process with: a step of fitting a root portion (8) of a blade (6) into a blade groove (10) of a blade holder (12) and attaching the blade (6) to a feed unit (4) of a spark erosion machine (2) via the blade holder (12); a step of selectively immersing only a portion (34) of the blade (6) in a spark erosion liquid (11) by moving the blade (6) through the feed unit (4) to the electrode (14) so ​​that a surface of a blade tip (36) of the blade (6) contained in the portion (34) of the blade (6) faces an electrode (14) immersed in the spark erosion liquid (11), and a step of applying spark erosion to the surface of the blade tip (36) by applying a voltage between the electrode (14) and the blade (6) in a state in which the portion (34) of the blade (6) is selectively immersed in the spark erosion liquid (11).

Description

TECHNICAL FIELD

[0001] The present disclosure relates to an electrical discharge machining method and an electrical discharge machining apparatus. TECHNICAL BACKGROUND

[0002] Typically, a grinder or polisher can be used to machine a workpiece, which is an object to be machined. For example, each outer end surface of blades used in rotating machinery such as gas turbines and compressors is usually machined by grinding a blade tip surface with an abrasive material such as sandpaper.

[0003] However, machining accuracy tends to be low when using a grinding jig and a polishing jig. Furthermore, it is necessary to cure parts other than the outer end surfaces of the blades to protect them from the separated powder generated by grinding, which requires a large amount of working time.

[0004] Patent Document 1 discloses a method for machining a blade shape of a turbine blade as a workpiece using an electric discharge machining apparatus rather than a grinder and polisher. In the machining method described in Patent Document 1, a pair of electrodes are fixed in an electric discharge machining liquid, and then the turbine blade is moved in a horizontal direction between the electrodes to perform electric discharge machining.

[0005] Patent Document 2 discloses that a multi-machining apparatus includes a mechanical electrode machining device for machining a fixed electrode material with a cutting tool connected to a spindle into an electrode having a predetermined configuration in such a manner that the electrode material is immersed in a machining solution; a parts exchange device for exchanging the cutting tool connected to the spindle after formation of the electrode with a workpiece to be machined; and a workpiece machining device for machining the workpiece with the electrode in the machining solution by electric discharge after the cutting tool is exchanged with the workpiece.

[0006] Patent Document 3 discloses a method and an apparatus for machining the front and back surfaces of a workpiece having thin-walled parts by means of electrode electric discharge, wherein the front and back surfaces of the workpiece are machined simultaneously by mounting the workpiece on an adapted movable table that supports two electrodes having surfaces corresponding to the surfaces to be machined from the workpiece so as to be opposed to the surfaces of the workpiece machined in such a manner and to be displaceable with respect to the surfaces of the workpiece being machined, and by controlling the two electrodes so that the two electrodes are brought closely to the workpiece in synchronization with each other at a substantially equal feed rate per unit time.

[0007] Patent Document 4 discloses methods for forming designed passages in an object, and more particularly, methods for forming passages having two or more regions, each of which requires a separate passage forming step.

[0008] Patent Document 5 discloses an electrode assembly for electrochemically machining an object such as a vane-shaped blade for a turbomachine.

[0009] Patent Document 6 discloses a method and an apparatus for drilling a mechanical part, particularly a blade of a compressor or a high-pressure turbine of a turbomachine. Citation listPatent literature Patent Document 1: JP 2010-274412 A Patent document 2: DE 40 12 878 A1 Patent document 3: DE 197 06 220 A1 Patent document 4: DE 695 00 808 T2 Patent Document 5: JP S55-48 539 A Patent document 6: FR 2 951 101 A1 SUMMARYProblems to be solved

[0010] In the machining method described in Patent Document 1, electrical discharge machining is performed in a state where the entire workpiece is immersed in the electrical discharge machining fluid. Thus, cleaning the workpiece after electrical discharge machining requires considerable time and expense.

[0011] At least one embodiment of the present invention has been made in view of the above typical problem, and an object is to provide an electric discharge machining method and an electric discharge machining apparatus capable of reducing time and cost required for the cleaning process of the workpiece after electric discharge machining. Solution to the problems

[0012] (1) An electrical discharge machining method according to at least one embodiment of the present invention comprises: a step of selectively immersing only a portion of the workpiece in an electric discharge machining liquid so that a machining object portion included in the portion of the workpiece faces an electrode immersed in the electric discharge machining liquid, and a step of applying electric discharge machining to the machining object portion by applying a voltage between the electrode and the workpiece in a state where the portion of the workpiece is selectively immersed in the electric discharge machining liquid, the portion including the machining object portion.

[0013] According to the electric discharge machining method described in (1) above, since the electric discharge machining is performed in a state where only the portion of the workpiece containing the machining object portion is selectively immersed in the electric discharge liquid, the time and cost required for the cleaning process of the workpiece after the electric discharge machining can be reduced. In (1) above, the term "selectively immersing only a portion of a workpiece containing a machining object portion in an electric discharge liquid" means immersing the portion of the workpiece containing the machining object portion in the electric discharge liquid, and not immersing portions other than the portion of the workpiece containing the machining object portion in the electric discharge liquid.

[0014] (2) In some embodiments of the electrical discharge machining method described in (1) above, the method further comprises a step of attaching the workpiece to a feed unit of an electrical discharge machining apparatus, in which, in the step of immersing in the electrical discharge machining liquid, the workpiece moves through the feed unit to the electrode while the electrode is held stationary.

[0015] According to the electrical discharge machining method described in (2) above, which differs from the typical electrical discharge machining method, the workpiece, instead of the electrode, is fixed to the feed unit of the electrical discharge machining system in such a way that the workpiece is capable of movement. Therefore, the electrical discharge machining system can be easily implemented in a state where only the portion of the workpiece is selectively immersed in the electrical discharge liquid. Accordingly, as described in (1) above, the time and cost required for the cleaning process of the workpiece after electrical discharge machining can be reduced.

[0016] (3) In some embodiments of the electric discharge machining method described in (1) or (2) above, in the step of plunging, the workpiece moves to the electrode from above the electrode by the supply unit to the electrode so that a lower surface of the machining object portion of the workpiece is opposed to an upper surface of the electrode.

[0017] According to the electrical discharge machining method described in (3) above, the machining target portion of the workpiece can simply face the electrode. Therefore, the electrical discharge machining system can be easily realized in a state where only the portion of the workpiece is selectively immersed in the electrical discharge liquid. Accordingly, as described in (1) above, the time and cost required for the cleaning process of the workpiece after electrical discharge machining can be reduced.

[0018] (4) In some embodiments of the electric discharge machining method described in any one of (1) to (3) above, electric discharge machining is performed on a blade end surface as a machining object portion of a blade as a workpiece in the step of applying electric discharge machining to the machining object portion.

[0019] For example, the outer end surfaces of blades used in rotating machinery such as gas turbines or compressors are typically finished by grinding the blade tip surface with an abrasive material such as sandpaper. At this time, it is necessary to post-treat a portion other than the outer end surfaces of the blades to protect the blades from the separated powder generated by grinding, which requires a large amount of working time.

[0020] According to the electric discharge machining method described in (4) above, applying electric discharge machining to the blade tip surface of the desired shape does not require the post-treatment process required for performing grinding, which is a typical machining process for the blade tip surface. Thus, the time and cost required for machining the blade tip surface can be reduced. Furthermore, as described in (1) above, since the portion immersed in the electric discharge machining fluid during electric discharge machining can be limited by performing electric discharge machining in a state where the portion of the blade including the blade tip surface is selectively immersed in the electric discharge machining fluid, the time and cost required for the cleaning process of the blade after electric discharge machining can be reduced.

[0021] (5) In some embodiments of the electric discharge machining method described in (4) above, in the step of immersing in the electric discharge liquid, only a portion of the blade on an outer end side relative to a root portion is immersed in the electric discharge liquid.

[0022] For example, according to the electric discharge machining method described in (5) above, when a coating is applied to a landing surface of the blade's root portion for the purpose of preventing seizure, the absence of immersion of the root portion in the electric discharge machining fluid eliminates the need for cleaning the root portion.

[0023] In one embodiment, when the workpiece is a gas turbine blade, the electrical discharge machining may be performed on the outer end surface of the gas turbine blade while only the outer end portion of the gas turbine blade is immersed in the electrical discharge machining fluid, so that the electrical discharge machining fluid is not prevented from entering a cooling hole provided on a blade profile or a platform of the gas turbine blades.

[0024] (6) In some embodiments, the blade is a rotor blade in a downstream stage of a compressor of a gas turbine.

[0025] According to the electrical discharge machining method described in (6) above, since the compressor rotor blade in the downstream stage, which is comparatively lightweight, is used as the machining object, the workpiece (blade) can be mounted on the supply unit of the electrical discharge machining system while satisfying the conditions caused by the electrical discharge machining specifications. Furthermore, the workpiece (blade) is mounted on the supply unit of the electrical discharge machining system, whereby electrical discharge machining can be easily realized in a state where only the portion of the workpiece is selectively immersed in the electrical discharge machining fluid.

[0026] (7) In some embodiments of the electric discharge machining method described in any one of (4) to (6) above, the method includes a step of fitting a root portion of the blade into a blade groove of a blade holder and attaching the blade to a supply unit of an electric discharge machining apparatus via the blade holder, wherein in the step of immersing in the electric discharge machining liquid, the blade moves through the supply unit to the electrode while keeping the electrode stationary.

[0027] According to the electrical discharge machining method described in (7) above, which differs from the typical electrical discharge machining method, the blade (the workpiece) is attached to the feed unit of the electrical discharge machining machine instead of the electrode, so that the blade is capable of moving. Therefore, electrical discharge machining can be easily realized in a state where only the portion of the blade is selectively immersed in the electrical discharge liquid. Accordingly, as described in (1) above, the time and cost required for the cleaning process of the blade after electrical discharge machining can be reduced.

[0028] (8) In some embodiments of the electric discharge machining method described in (7) above, the method further includes a step of pressing the blade by a reference member provided on the blade holder so that an abutment surface of the root portion contacts a wall surface of the blade groove.

[0029] According to the electric discharge machining method described in (8) above, the abutment surface of the root portion is brought into contact with the wall surface of the blade groove, after which the blade can be positioned relative to the blade holder with respect to at least the blade height direction. Accordingly, the accuracy of the electric discharge machining can be improved.

[0030] Furthermore, a typical blade abutment surface extends obliquely relative to the blade height direction. As described above, when the abutment surface of the root portion is brought into contact with the wall surface of the blade groove, the blade is positioned not only with respect to the blade height direction, but also with respect to a width direction of the blade root portion. Accordingly, the accuracy of electrical discharge machining can be improved.

[0031] (9) In some embodiments of the electric discharge machining method described in (7) or (8) above, the method further comprises a step of bringing an end surface of the root portion of the blade in an extension direction of the blade groove into contact with a reference block inserted into the blade groove.

[0032] According to the electric discharge machining method described in (9) above, one end surface of the root portion of the blade is brought into contact with the reference block, whereby the blade can be positioned with respect to the extension direction of the blade groove. Accordingly, the accuracy of the electric discharge machining can be improved.

[0033] (10) An electric discharge machining apparatus for a blade according to at least one embodiment of the present invention comprises: a supply unit, a blade holder attached to the supply unit and having a blade groove into which a root portion of the blade is fittable, an electrode immersed in an electric discharge machining liquid, and a power source for applying a voltage between the blade and the electrode.

[0034] According to the electric discharge machining apparatus described in (10) above, electric discharge machining can be performed in a state where only the tip side of the blade is immersed in the electric discharge liquid. Thus, the time and cost required for cleaning the blade after electric discharge machining can be reduced.

[0035] (11) In some embodiments of the electric discharge machining apparatus described in (10) above, the blade holder includes a reference member for pressing the blade toward a wall surface of the blade groove so that an abutment surface of the root portion is brought into contact with the wall surface.

[0036] According to the electric discharge machining apparatus described in (11) above, the abutment surface of the root portion is brought into contact with the wall surface of the blade groove, whereby the blade can be positioned relative to the blade holder in at least the blade height direction. Accordingly, the accuracy of the electric discharge machining can be improved.

[0037] Furthermore, a typical blade abutment surface extends obliquely relative to the blade height direction. As described above, when the abutment surface of the root portion is brought into contact with the wall surface of the blade groove, the blade is positioned not only with respect to the blade height direction but also with respect to a width direction of the blade groove portion. Accordingly, the accuracy of electrical discharge machining can be improved.

[0038] (12) In some embodiments of the electric discharge machining apparatus described in (10) or (11) above, the apparatus includes a reference block configured to be at least partially inserted into the blade groove of the blade holder so that an end surface of the root portion of the blade in an extension direction of the blade groove is brought into contact with the reference block.

[0039] According to the electric discharge machining apparatus described in (12) above, one end surface of the root portion of the blade is brought into contact with the reference block, whereby the blade can be positioned with respect to the extension direction of the blade groove. Accordingly, the accuracy of electric discharge machining can be improved.

[0040] (13) In the embodiments of the electric discharge machining apparatus described in any one of (10) to (12) above, an upper surface of the electrode includes a curved concave surface shape.

[0041] According to the electric discharge machining apparatus described in (13) above, the electric discharge machining on the surface of the blade tip is performed in a state where only the tip side of the blade is immersed in the electric discharge liquid, which facilitates machining in a curved convex shape and reduces the time and cost required for the cleaning process of the blade after the electric discharge machining. Beneficial effects

[0042] According to at least one embodiment of the present invention, an electrical discharge machining method and an electrical discharge machining apparatus are provided which are capable of reducing the time and cost required for the cleaning process of the workpiece after electrical discharge machining. BRIEF DESCRIPTION OF THE ILLUSTRATIONS Fig. 1 is a schematic view showing a schematic configuration of an electric discharge machining apparatus 2 according to an embodiment of the present invention. Fig. 2 is a perspective view illustrating a configuration of a blade 6. Fig. 3 is a view of a blade holder 12 in a state where a root portion 8 of the blade 6 is fitted into a blade groove 10, viewed from an outer end side of the blade 6 along a blade height direction. Fig. 4 is an AA cross-sectional view of Fig. 3. Fig. 5 is a flowchart of an example of an electrical discharge machining process. Fig. 6 is a diagram for describing a step of positioning the blade 6 in an extension direction of the blade groove. Fig. 7 is a diagram for describing a step of positioning the blade 6 in a blade height direction and a width direction. Fig. 8 is a diagram for describing a step of attaching a blade holder 12 to a supply unit. Fig. 9 is a diagram for describing a step of immersing a portion 34 of the blade 6, which includes a machining object portion 32, in an electric discharge machining liquid 11. Fig. 10 is a diagram for describing a step of applying a voltage between an electrode 14 and the blade 6. Fig. 11 is a diagram for describing a portion 34 of the blade 6 which is immersed in the electrical discharge machining liquid 11 when the blade 6 is a turbine blade. DETAILED DESCRIPTION

[0043] Embodiments of the present invention will now be described in detail with reference to the accompanying drawings. However, unless specifically stated, dimensions, materials, shapes, relative positions, and the like of components described in the embodiments are intended to be interpreted as illustrative only and are not intended to limit the scope of the present invention.

[0044] For example, expressions of a relative or absolute arrangement such as "in a direction", "along a direction", "parallel", "orthogonal", "central", "concentric" and "coaxial" are not intended to suggest that the arrangements be interpreted only in a strict literal sense, but are intended to include a condition in which the arrangement is relatively offset by a tolerance or by an angle or a distance, whereby the same function can be achieved.

[0045] For example, an expression of a same state such as "same", "equal", and "uniform" should not be construed to refer only to the state in which the characteristic is exactly the same, but should also include a state in which there is a tolerance or a difference that can still achieve the same function.

[0046] Furthermore, for example, an expression of a shape such as a rectangular or a cylindrical shape shall not only be construed as the geometrically accurate shape, but shall also include a shape having bumps or beveled corners within the range in which the same effect can be achieved.

[0047] On the other hand, an expression such as “comprise”, “include”, “have”, “contain” and “form” should not be exclusive of other components.

[0048] Fig. 1 is a schematic view showing a schematic configuration of an electric discharge machining apparatus 2 according to an embodiment of the present invention.

[0049] As in Fig. 1, the electrical discharge machining apparatus 2 comprises a feed unit 4, a blade holder 12 attached to the feed unit 4 and having a blade groove into which a root portion 8 of a blade 6 (workpiece) is fittable, a container 13 containing an electrical discharge liquid 11, an electrode 14 immersed in the electrical discharge liquid in the container 13, and a power source 16 for applying a voltage between the blade 6 and the electrode 14. The blade 6 is a blade attached to a rotor (not shown) of a rotary machine such as a gas turbine or a compressor.

[0050] The feed unit 4 is configured to move the blade holder 12 holding the blade 6 in three axial directions orthogonal to each other by a driving force of a motor, which is not shown.

[0051] The EDM fluid 11 is a dielectric fluid that fills a gap between the blade 6 and the electrode 14 in the EDM device 2. The EDM fluid 11 acts as an insulator, ionizes when a discharge occurs, and functions to maintain an electric field in which current flows. Furthermore, the EDM fluid 11 flowing through the gap serves to remove machining waste from the gap. For example, a fluid containing water with a resistivity set between 1 and 10 x 10,000 Ωcm or oil with an extremely high resistivity is preferably used as the main component for the EDM fluid 11.

[0052] A highly electrically conductive material such as graphite or copper is preferably used for the electrode 14. Furthermore, a pulsed energy source is preferably used as the energy source 16. The upper surface 44 of the electrode 14 includes a curved concave surface shape as an inverted shape of the target surface of the blade tip surface 36.

[0053] Next, the configuration of the blade 6 and the blade holder 12 as a workpiece with reference to the Fig. 2 to 4 are described. Fig. 2 is a perspective view showing the configuration of the blade 6. Fig. 3 is a view of the blade holder 12 in a state where the root portion 8 of the blade 6 is fitted into the blade groove 10, viewed from an outer end side of the blade 6 along a blade height direction. Fig. 4 is an AA cross-sectional view of Fig. 3.

[0054] In an embodiment such as in Fig. As shown in FIG. 2, the blade 6 includes a blade profile 28 having a blade-like cross-sectional shape, and the root portion 8 for mounting the rotor, which is not shown. The root portion 8 has a width greater than a blade thickness of the blade profile 28. Here, the "width" refers to a width in a direction orthogonal to each of the extension direction of the blade groove 10 and the blade height direction (hereinafter referred to as the width direction).

[0055] In an embodiment such as in Fig. 4, the blade holder 12 includes a bolt 22 as a reference part for pressing the blade 6 toward the wall surface 20 so that the abutment surface 18 of the root portion 8 of the blade 6 is brought into contact with the wall surface 20 of the blade groove 10. The abutment surface 18 is a surface that comes into contact with the rotor, which is not shown, when the blade 6 is attached to the rotor.

[0056] Furthermore, as for example in Fig. 4, the abutment surface 18 of the typical blade 6 is inclined with respect to the blade height direction. Thus, the blade 6 is positioned not only with respect to the blade height direction, but also with respect to the width direction of the root portion 8 of the blade 6 as described above when the abutment surface 18 of the root portion 8 is brought into contact with the wall surface 20 of the blade groove 10. Accordingly, the accuracy of the electrical discharge machining can be improved.

[0057] Furthermore, in the embodiment shown in the figures, a pair of abutment surfaces 18 are formed in the root portion 8. The pair of abutment surfaces 18 are inclined with respect to the blade height direction so that the interval between the pair of abutment surfaces 18 becomes narrower toward the blade tip side. Further, a pair of wall surfaces 20 in contact with the pair of abutment surfaces 18 are formed in the blade groove 10. The pair of wall surfaces 20 are inclined with respect to a depth direction of the blade groove 10 (blade height direction) so that the interval between the pair of wall surfaces 20 becomes narrower toward an opening side of the blade groove 10 (blade tip side).

[0058] In an embodiment as shown in the Fig. 3 and Fig. 4, the electrical discharge machining apparatus 2 further includes a reference block 26 configured to be at least partially inserted into the blade groove 10 of the blade holder 12 such that an end surface 24 of the root portion 8 of the blade 6 in the extension direction of the blade groove 10 is brought into contact with the reference block 26. In the illustrated embodiment, the reference block 26 is fixed to the blade holder 12 by a plurality of bolts 30.

[0059] With the above configuration, the one end surface 24 of the root portion 8 of the blade 6 is brought into contact with the reference block 26, after which the blade 6 can be positioned with respect to the extension direction of the blade groove 10. Accordingly, the accuracy of the electrical discharge machining can be improved.

[0060] Next, with reference to the Fig. 5 to 10, an example of an electric discharge machining method for machining the blade 6 as a workpiece described above by the electric discharge machining apparatus 2 will be described.

[0061] First, in step S1, as in Fig. 6, the root portion 8 of the blade 6 is inserted into the blade groove 10 of the blade holder 12, and an end surface 24 of the root portion 8 of the blade 6 in the extension direction of the blade groove 10 is brought into contact with the reference block 26. Thus, the blade 6 can be positioned relative to the blade holder 12 with respect to the extension direction of the blade groove 10.

[0062] Next, in step S2, as in Fig. As shown in Fig. 7, the blade 6 is pressed by the bolt 22 provided in the blade holder 12 so that the abutment surface 18 of the root portion 8 is brought into contact with the wall surface 20 of the blade groove 10. Thus, the blade 6 can be positioned relative to the blade holder 12 with respect to the blade height direction and the width direction.

[0063] Next, in step S3, as in Fig. 8, the blade 6 is attached to the feed unit 4 via the blade holder 12 by attaching the blade holder 12 to the feed unit 4 of the electrical discharge machining device 2.

[0064] Next, in step S4, as in Fig. 9, only the portion 34 of the blade 6 including the machining object portion 32 is selectively immersed in the electric discharge machining liquid 11 such that a lower surface 46 (surface of the blade tip 36 in the shown embodiment) of the machining object portion 32 of a blade 6 faces an upper surface 44 of the electrode 14 immersed in the electric discharge machining liquid 11. That is, in step S4, the supply unit 4 brings the blade 6 to approach the electrode 14 from above the electrode such that the lower surface 46 of the machining object portion 32 of the blade 6 faces the upper surface 44 of the electrode 14 while the electrode 14 is held stationary. In the illustrative example, only the portion 34 of the outer end side of the blade 6 relative to the root portion 8 is immersed in the electric discharge machining liquid.

[0065] Next, in step S5, as in Fig. 10, the electrical discharge machining is performed on the machining object portion 32 by applying the voltage between the electrode 14 and the blade 6 in a state where the portion 34 of the blade 6 described above is selectively immersed in the electrical discharge machining liquid 11. In the illustrative example, the electrical discharge machining is performed on the surface of the blade tip 36 as the machining object portion 32 of the blade 6. Accordingly, the surface of the blade tip 36 is machined into a curved convex shape as an inverted shape corresponding to a curved concave shape of the upper surface 44 of the electrode 14.

[0066] According to the above-described electric discharge machining method, electric discharge machining is carried out in a state where only the portion 34 of the blade 6 including the machining object portion 32 as a workpiece is selectively immersed in the electric discharge machining liquid 11, so that time and cost required for the cleaning process of the blade 6 after the electric discharge machining can be reduced.

[0067] Furthermore, the method differs from typical electrical discharge machining methods, in which, instead of the electrode, the blade 6 is attached to the feed unit 4 of the electrical discharge machining apparatus 2 so that the blade 6 is capable of moving. Therefore, electrical discharge machining can be easily realized in a state where only the above-described portion 34 of the blade 6 is selectively immersed in the electrical discharge liquid 11. Accordingly, the time and cost required for the cleaning process of the blade 6 after electrical discharge machining can be easily reduced.

[0068] Furthermore, performing electrical discharge machining on the blade tip surface 36 of the desired shape as the machining target portion 32 eliminates the above-described post-treatment process required for performing grinding, which is a typical machining method for the blade tip surface 36. Thus, the time and cost required for machining the blade tip surface 36 can be reduced.

[0069] Furthermore, when a coating is applied to the contact surface 18 of the root portion 8 of the blade 6 for the purpose of preventing seizure, by omitting the immersion of the root portion 8 in the spark erosion liquid 11, cleaning of the root portion 8 is not necessary.

[0070] In one embodiment, the blade 6 as a workpiece may be a rotor blade of a downstream stage of a compressor of a gas turbine, which is not shown.

[0071] In this case, since the downstream compressor rotor blade, which is comparatively lightweight, is used as the processing object, the blade 6 can be attached to the supply unit 4 of the electric discharge machining apparatus 2 while satisfying the conditions caused by the specifications of the electric discharge machining apparatus 2. Furthermore, the blade 6 is attached to the supply unit 4 of the electric discharge machining apparatus 2, so that electric discharge machining can be easily realized in a state where only the portion 34 of the blade 6 including the processing object portion 32 is selectively immersed in the electric discharge machining liquid 11.

[0072] In one embodiment, the blade 6 as a workpiece can be a turbine blade of a gas turbine. In this case, as in Fig.11, electrical discharge machining may be performed on the surface of the blade tip 36 while only the outer end portion of the blade 6 as the portion 34 including the machining object portion 32 is immersed in the electrical discharge machining liquid 11 such that the electrical discharge machining liquid 11 is not prevented from entering a cooling hole 42 provided on the blade profile 38 or the platform 40 of the blade 6.

[0073] The present invention is not limited to the embodiments described above, but includes embodiments formed by variations of the embodiments described above and embodiments formed by appropriate combinations of these embodiments.

[0074] For example, in the above-described electric discharge machining method, the present invention is applicable to a case of performing electric discharge machining on the machining object portion other than the surface of the blade tip, and is applicable to a case where electric discharge machining is performed on the workpiece other than the blade, although a case where electric discharge machining is performed on the surface of the blade tip 36 is described as an example.

[0075] Thus, in one embodiment, the method may include: a step of selectively immersing only the portion of the workpiece including the machining object portion in the electric discharge machining liquid so that the machining object portion of the workpiece faces the electrode immersed in the electric discharge machining liquid, and a step of applying the electric discharge machining to the machining object portion by applying the voltage between the electrode and the workpiece in a state where the portion of the workpiece including the machining object portion is selectively immersed in the electric discharge machining liquid.

[0076] In this way, the time and cost required for the cleaning process of the workpiece after the electrical discharge machining can be reduced because the electrical discharge machining is carried out in a state in which only the portion of the workpiece containing the machining object portion is selectively immersed in the electrical discharge machining liquid. List of reference symbols 2 spark erosion device 4 Feed unit 6 shovels 8 Foot section 10 Blade groove 11 Spark erosion fluid 12 shovel holders 13 containers 14 Electrode 16 Energy source 18 contact surface 20 wall surface 22 bolts 24 End face 26 Reference block 28 Blade profile 32 Editing object section Section 34 36 Surface of the blade tip 38 blade profile 40 Platform 42 Cooling hole 44 upper surface 46 lower surface

Claims

A spark erosion method comprising:a step of fitting a root portion (8) of a blade (6) into a blade groove (10) of a blade holder (12) and attaching the blade (6) to a feed unit (4) of a spark erosion machine (2) via the blade holder (12);a step of selectively immersing only a portion (34) of the blade (6) in an electrical discharge machining liquid (11) by moving the blade (6) to the electrode (14) by the supply unit (4) so ​​that a surface of a blade tip (36) of the blade (6) included in the portion (34) of the blade (6) faces an electrode (14) immersed in the electrical discharge machining liquid (11), and a step of applying electrical discharge machining to the surface of the blade tip (36) by applying a voltage between the electrode (14) and the blade (6) in a state where the portion (34) of the blade (6) is selectively immersed in the electrical discharge machining liquid (11); The spark erosion method according to claim 1, wherein in the step of immersing in the spark erosion liquid (11), the blade (6) is moved by the supply unit (4) to the electrode (14) while the electrode (14) is kept stationary. The spark erosion method according to claim 1 or 2, wherein in the step of immersing in the spark erosion liquid (11), the blade (6) is moved by the supply unit (4) from above the electrode (14) to the electrode (14) so ​​that the surface of the blade tip (36) of the blade (6) is opposite to an upper surface (44) of the electrode (14). The spark erosion method according to one of claims 1 to 3, wherein in the step of immersing in the spark erosion liquid (11), only a portion (34) of the blade (6) at an outer end side relative to a root portion (8) is immersed in the spark erosion liquid (11). The spark erosion method according to one of claims 1 to 4, wherein the blade (6) is a blade (6) in a downstream stage of a compressor of a gas turbine. The electrical discharge machining method according to one of claims 1 to 5, further comprising a step of pressing the blade (6) by a reference part provided on the blade holder (12) so that an abutment surface (18) of the root portion (8) contacts a wall surface (20) of the blade groove (10). The electrical discharge machining method according to one of claims 1 to 6, further comprising a step of bringing an end surface (24) of the root portion (8) of the blade (6) in an extension direction of the blade groove (10) into contact with a reference block (26) inserted into the blade groove (10). A spark erosion device (2) for a blade (6), comprising: a feed unit (4), a blade holder (12) attached to the feed unit (4) and having a blade groove (10) into which a root portion (8) of the blade (6) can be fitted, an electrode (14) immersed in a spark erosion liquid (11), and a power source (16) for applying a voltage between the blade (6) and the electrode (14), wherein the feed unit (4) is configured to move the blade (6) toward the electrode (14) such that a surface of a blade tip (36) of the blade (6) faces the electrode (14) immersed in the spark erosion liquid (11). The spark erosion device (2) according to claim 8, wherein the blade holder (12) comprises a reference part for pressing the blade (6) towards a wall surface (20) of the blade groove (10) so that an abutment surface (18) of the root portion (8) is brought into contact with the wall surface (20). The electrical discharge machining device (2) according to claim 8 or 9, further comprising a reference block (26) configured to be at least partially inserted into the blade groove (10) of the blade holder (12) such that an end surface (24) of the root portion (8) of the blade (6) is brought into contact with the reference block (26) in an extension direction of the blade groove (10). The spark erosion device (2) according to one of claims 8 to 10, wherein an upper surface (44) of the electrode (14) comprises a curved concave surface shape.

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