Wire cut electric discharge machining method

Abstract

To provide a wire cut electric discharge machining method which can improve work efficiency while preventing a core from falling down.SOLUTION: A wire cut electric discharge machining method cutting out a core 30 from a work-piece 20 comprises the steps of: forming a core holding part 22 holding the core 30 in the work-piece 20 to cut out the core 30 from the work-piece 20; removing the core 30 held by the core holding part 22; and cutting out the core holding part 22 from the work-piece 20. The core holding part 22 is formed in a shape protruding in an inner direction crossing an internal surface 21 from a part of the internal surface 21 of the work-piece 20 formed by cutting out the core 30, and the core holding part has at least one inclined plane 24 inclining in the inner direction as going toward a gravity direction.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a wire-cut electric discharge machining method. [Background technology]

[0002] In wire-cut electric discharge machining, a process of cutting out a core from a workpiece may be performed. The core is a scrap material that is cut out from the workpiece so that the workpiece can produce the required product part. In wire-cut electric discharge machining in which the core is cut out from the workpiece, the cut-out core may fall and damage the processing machine, so the core is often prevented from falling by being attracted to a magnet. However, when using a magnet to prevent the core from falling, it takes time to attach and remove the magnet, and there is a possibility that the core may pinch the wire electrode and break the wire electrode. Therefore, there is room for improvement in terms of improving work efficiency when using a magnet to prevent the core from falling.

[0003] One method for preventing the core from dropping without using a magnet is known, for example, in Patent Document 1. Patent Document 1 discloses a wire-cut electric discharge machining method in which a wire electrode and a workpiece are moved relatively to each other, the workpiece is machined into a continuous predetermined shape by the wire electrode, and the inside of the workpiece surrounded by the continuous electric discharge machining part is separated and dropped as scrap. The wire-cut electric discharge machining method disclosed in Patent Document 1 moves the wire electrode relatively from the electric discharge machining start part of the electric discharge machining part to perform electric discharge machining sequentially, and when the wire electrode reaches a position just before the end of the electric discharge machining, the wire electrode is moved back and forth relative to the inside of the workpiece and fed relative to the electric discharge machining start part a plurality of times to machine the escape part of the wire electrode while performing electric discharge machining up to the electric discharge machining start part. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 11-104918 Summary of the Invention [Problem to be solved by the invention]

[0005] The workpiece machined by the wire-cut electric discharge machining method disclosed in Patent Document 1 has a tapered surface inclined inwardly along the entire inner surface toward the direction of gravity. Therefore, when the inner surface of the workpiece that is originally required is a surface along the direction of gravity, the wire-cut electric discharge machining method disclosed in Patent Document 1 requires a process to cut out the unnecessary part having the tapered surface after removing the core from the workpiece. When cutting out the unnecessary part, the wire-cut electric discharge machining method disclosed in Patent Document 1 requires a very long time to perform the process because the unnecessary part is formed along the entire inner surface of the workpiece. Therefore, the wire-cut electric discharge machining method disclosed in Patent Document 1 has room for improvement in terms of improving work efficiency.

[0006] The present invention has been made in consideration of the above, and has an object to provide a wire-cut electric discharge machining method that can improve work efficiency while preventing the core from falling. [Means for solving the problem]

[0007] In order to solve the above problems, the wire-cut electric discharge machining method of the present invention is a wire-cut electric discharge machining method for cutting out a core from a workpiece, and includes the steps of forming a core holding portion in the workpiece to hold the core and cutting out the core from the workpiece, removing the core held in the core holding portion, and cutting out the core holding portion from the workpiece, wherein the core holding portion is formed in a shape that protrudes inwardly from a portion of the inner surface of the workpiece formed by cutting out the core, intersecting the inner surface, and has at least one inclined surface that inclines inwardly as it approaches the direction of gravity.

[0008] With this configuration, the core holding part can hold the cut-out core by having the inclined surface receive the cut-out core. That is, in the wire-cut electric discharge machining method of the present invention, the core holding part can hold the cut-out core by surface contact, so that it is possible to reliably prevent the core from falling.

[0009] Moreover, since the core holding portion is formed in a shape that protrudes inwardly from a part of the inner surface of the workpiece so as to intersect with the inner surface, it is not formed around the entire circumference of the inner surface of the workpiece. As a result, the wire-cut electric discharge machining method of the present invention does not require cutting out the core holding portion around the entire circumference of the inner surface of the workpiece, so the process of cutting out the core holding portion can be completed in a short time. Therefore, the wire-cut electric discharge machining method of the present invention can improve work efficiency while preventing the core from falling.

[0010] Furthermore, since the core holding portion is formed in a shape that protrudes inward from a part of the inner surface, in the step of cutting out the core holding portion, the core holding portion can be easily cut out by simply moving the wire electrode relatively in the circumferential direction along the inner surface to cut into the core holding portion. In other words, in the wire-cut electric discharge machining method of the present invention, the direction in which the wire electrode cuts into the core holding portion in the step of cutting out the core holding portion can be limited to the circumferential direction along the inner surface of the workpiece, and there is no need to relatively move the wire electrode in the outward direction toward the inner surface of the workpiece, which is the originally required product part. As a result, in the wire-cut electric discharge machining method of the present invention, the risk of the wire electrode cutting into the inner surface of the workpiece, which is the product part, can be reduced in the step of cutting out the core holding portion, so that the dimensions required for the workpiece can be easily guaranteed.

[0011] In a further preferred embodiment, the core holding portion includes a wedge portion extending in the direction of gravity and having the inclined surface, and a bridge portion protruding inward from a part of the inner surface of the workpiece and bridging between the inner surface and the wedge portion, wherein the wedge portion holds the core by receiving the cut-out core with the inclined surface, and the connection portion of the bridge portion with the inner surface of the workpiece is cut off in the process of cutting out the core holding portion.

[0012] That is, the core holding portion is clearly separated into a wedge portion, which is the portion responsible for holding the core, and a bridge portion, which is the portion connecting the wedge portion holding the core to the inner surface of the workpiece. With this aspect, in the wire-cut electric discharge machining method of the present invention, the portion cut in the step of cutting out the core holding portion can be limited to the bridge portion. Therefore, in the wire-cut electric discharge machining method of the present invention, the step of cutting out the core holding portion can be reliably completed in a short time. Therefore, the wire-cut electric discharge machining method of the present invention can reliably improve work efficiency while preventing the core from falling.

[0013] In a further preferred embodiment, the wedge portion is formed in the shape of a polygonal pyramid having a bottom surface facing the direction of gravity and an apex surface facing the opposite direction to the direction of gravity, and the inclined surface is a side surface.

[0014] This embodiment makes it possible to prevent the core from rotating in the circumferential direction, compared to when the wedge portion is formed in a cone shape. As a result, the wire-cut electric discharge machining method of the present invention can prevent the core from rotating and pinching the wire electrode 3 during the step of cutting out the core, which could lead to the wire electrode being broken. Therefore, the wire-cut electric discharge machining method of the present invention can further reliably improve work efficiency while preventing the core from falling.

[0015] In a further preferred embodiment, the bridge portion is formed in a plate shape extending in the direction of gravity and inward from a part of the inner surface of the workpiece.

[0016] According to this aspect, in the wire-cut electric discharge machining method of the present invention, in the step of cutting out the core holding portion, the connection portion of the bridge portion to the inner surface of the workpiece can be easily cut off by simply moving the wire electrode in the circumferential direction relative to the connection portion of the bridge portion to the inner surface of the workpiece. Therefore, in the wire-cut electric discharge machining method of the present invention, the step of cutting out the core holding portion can be easily completed in a short time. Therefore, the wire-cut electric discharge machining method of the present invention can further reliably improve work efficiency while preventing the core from falling.

[0017] Moreover, because the bridge portion has a plate shape as described above, the thickness of the bridge portion to be cut by the wire electrode hardly changes each time the wire electrode cuts into the bridge portion. As a result, the wire-cut electric discharge machining method of the present invention can generate stable electric discharge between the wire electrode and the bridge portion in the process of cutting out the core holding portion. Therefore, the wire-cut electric discharge machining method of the present invention can prevent the occurrence of abnormal electric discharge between the wire electrode and the bridge portion, and therefore can prevent breakage of the wire electrode due to the abnormal electric discharge. Therefore, the wire-cut electric discharge machining method of the present invention can further reliably improve work efficiency while preventing the core from falling.

[0018] In a further preferred embodiment, the core holding portion is formed as a plurality of core holding portions, and the plurality of core holding portions are equally spaced on the inner surface of the workpiece along a circumferential direction of the central axis of the workpiece that is aligned with the direction of gravity.

[0019] According to this aspect, the wire-cut electric discharge machining method of the present invention can hold the cut-out core in the core holder without tilting it with respect to the direction of gravity. Therefore, the wire-cut electric discharge machining method of the present invention can prevent the core from pinching the wire electrode and causing the wire electrode to break. Therefore, the wire-cut electric discharge machining method of the present invention can further reliably improve work efficiency while preventing the core from falling. Effect of the Invention

[0020] According to the present invention, it is possible to provide a wire-cut electric discharge machining method that can improve work efficiency while preventing the core from falling. [Brief description of the drawings]

[0021] [Figure 1] 1 is a diagram illustrating a wire-cut electric discharge machine for carrying out a wire-cut electric discharge machining method according to an embodiment of the present invention; [Diagram 2] 1A to 1C are diagrams for explaining an outline of a wire-cut electric discharge machining method according to an embodiment of the present invention. [Diagram 3] 2 is a diagram showing a workpiece and a core that have been electric discharge machined by the wire-cut electric discharge machining method of the present embodiment. FIG. [Figure 4] 3A to 3C are diagrams illustrating each step of the wire-cut electric discharge machining method according to the embodiment. [Diagram 5] 3A to 3C are diagrams illustrating each step of the wire-cut electric discharge machining method according to the embodiment. [Figure 6] 3A to 3C are diagrams illustrating each step of the wire-cut electric discharge machining method according to the embodiment. [Figure 7] 11A and 11B are diagrams showing other examples of a workpiece and a core machined by the wire-cut electric discharge machining method of the present embodiment. [Figure 8] 11A and 11B are diagrams showing other examples of a workpiece and a core machined by the wire-cut electric discharge machining method of the present embodiment. [Figure 9] 11A and 11B are diagrams showing other examples of a workpiece and a core machined by the wire-cut electric discharge machining method of the present embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] Hereinafter, embodiments of the present invention will be described with reference to the drawings. Components with the same reference numerals in each embodiment have the same functions in each embodiment unless otherwise specified, and description thereof will be omitted.

[0023] In this embodiment, the direction of gravity is referred to as the "downward direction," and the direction opposite to the direction of gravity is also referred to as the "upward direction." In this embodiment, the circumferential direction around the central axis A of the workpiece 20 fixed to the fixture 2 of the wire-cut electric discharge machine 1, which is aligned with the direction of gravity, is also simply referred to as the "circumferential direction." In this embodiment, the direction perpendicular to the direction of gravity and away from the central axis A is also referred to as the "outward direction," and the direction perpendicular to the direction of gravity and approaching the central axis A is also referred to as the "inward direction."

[0024] FIG. 1 is a diagram illustrating a wire-cut electric discharge machine 1 for carrying out a wire-cut electric discharge machining method according to the present embodiment.

[0025] The wire-cut electric discharge machine 1 supplies a discharge voltage from a power supply between a workpiece 20 fixed to a fixture 2 and a wire electrode 3, and performs electric discharge machining such as cutting out a core 30 from the workpiece 20 by moving the wire electrode 3 relative to the workpiece 20.

[0026] The wire-cut electric discharge machine 1 includes a supply unit 4 having a reel or the like around which the wire electrode 3 is wound and supplies the wire electrode 3, and rollers 5 and 6 that apply tension to the wire electrode 3 supplied from the supply unit 4 and guide it to an upper guide 7. The wire-cut electric discharge machine 1 further includes an upper guide 7 that supplies the wire electrode 3 guided by the rollers 5 and 6 to a machining space in which a workpiece 20 is disposed, and a lower guide 8 that draws the wire electrode 3 supplied to the machining space into a lower portion of the wire-cut electric discharge machine 1. The wire-cut electric discharge machine 1 further includes a roller 9 that guides the wire electrode 3 drawn by the lower guide 8 to a recovery unit 10, and a recovery unit 10 having a reel or the like around which the wire electrode 3 guided by the roller 9 is wound and that recovers the wire electrode 3.

[0027] The wire-cut electric discharge machine 1 further includes a moving mechanism 11 that moves the upper guide 7 in U-axis and V-axis directions that are perpendicular to each other on a plane (e.g., a horizontal plane) that intersects with the direction of gravity, and a support mechanism 12 that supports the upper guide 7 and the moving mechanism 11. The wire-cut electric discharge machine 1 further includes a moving mechanism (not shown) that moves the lower guide 8 in the U-axis and V-axis directions, and a support mechanism (not shown) that supports the lower guide 8 and the moving mechanism. The wire-cut electric discharge machine 1 may also include a moving mechanism that moves the workpiece 20 fixed to the fixture 2.

[0028] Fig. 2 is a diagram for explaining an outline of the wire-cut electric discharge machining method of the present embodiment. Fig. 3(a) is a top view showing the workpiece 20 and the core 30 machined by the wire-cut electric discharge machining method of the present embodiment. Fig. 3(b) is a bottom view showing the workpiece 20 and the core 30 machined by the wire-cut electric discharge machining method of the present embodiment.

[0029] The wire-cut electric discharge machining method of this embodiment includes the steps of forming a core holding portion 22 that holds a core 30 in the workpiece 20 and cutting out the core 30 from the workpiece 20, removing the core 30 held by the core holding portion 22, and cutting out the core holding portion 22 from the workpiece 20.

[0030] The workpiece 20 from which the core 30 and the core holding portion 22 have been removed is a product to be obtained by electrical discharge machining. The workpiece 20 from which the core 30 and the core holding portion 22 have been removed is also referred to as a "processed product." The workpiece 20 is, for example, a frame as shown in FIG. 3(a). The core 30 and the core holding portion 22 are unnecessary portions that are not originally required product portions. The core 30 is scrap material cut out from the workpiece 20 so that the originally required product portions can be obtained from the workpiece 20. The core holding portion 22 is scrap material formed in the workpiece 20 to hold the cut-out core 30, and is cut out after the cut-out core 30 is removed. The inner surface 21 of the workpiece 20 formed by cutting out the core 30 and the outer surface 31 of the core 30 formed by cutting out the core 30 correspond to each other.

[0031] The cut-out core 30 attempts to fall downward (in the direction of gravity) due to its own weight, but since it is held by the core holding part 22, it will not fall and collide with the lower guide 8. Furthermore, since there is always a machining groove K formed by electric discharge machining between the cut-out core 30 and the workpiece 20, and the core holding part 22 is formed during the process of cutting out the core 30, the cut-out core 30 will not pinch the wire electrode 3 between itself and the workpiece 20, causing the wire electrode 3 to break.

[0032] The core holding part 22 is formed in a shape that protrudes inwardly from a part of the inner surface 21 of the workpiece 20 formed by cutting out the core 30 and intersects with the inner surface 21 (orthogonal in this embodiment). The core holding part 22 has at least one inclined surface that inclines inwardly in the direction of gravity.

[0033] Core holding part 22 has an inclined surface 24, and therefore is able to hold core 30 by receiving the cut-out core 30 at inclined surface 24. That is, in the wire-cut electric discharge machining method of the present embodiment, core holding part 22 can hold cut-out core 30 in surface contact, and therefore it is possible to reliably prevent core 30 from falling.

[0034] Moreover, core holding portion 22 is formed in a shape that protrudes inwardly from a part of inner surface 21 of workpiece 20 so as to intersect with inner surface 21, and is therefore not formed over the entire circumference of inner surface 21 of workpiece 20. As a result, the wire-cut electric discharge machining method of this embodiment does not require processing to cut out core holding portion 22 over the entire circumference of inner surface 21 of workpiece 20, and the process of cutting out core holding portion 22 can be completed in a short time. Therefore, the wire-cut electric discharge machining method of this embodiment can improve work efficiency while preventing core 30 from falling.

[0035] Moreover, since the core holding portion 22 is formed in a shape that protrudes inward from a part of the inner surface 21, in the step of cutting out the core holding portion 22, the core holding portion 22 can be easily cut out by simply moving the wire electrode 3 relatively in the circumferential direction along the inner surface 21 to cut into the core holding portion 22. That is, in the wire-cut electric discharge machining method of this embodiment, the direction in which the wire electrode 3 cuts into the core holding portion 22 in the step of cutting out the core holding portion 22 can be limited to the circumferential direction along the inner surface 21, and there is no need to relatively move the wire electrode 3 in the outward direction toward the inner surface 21 of the workpiece 20, which is the originally required product part. As a result, in the wire-cut electric discharge machining method of this embodiment, the risk of the wire electrode 3 cutting into the inner surface 21 of the workpiece 20, which is the product part, can be reduced in the step of cutting out the core holding portion 22, so that the dimensions required for the workpiece 20 can be easily guaranteed.

[0036] In contrast, the workpiece machined by the wire-cut electric discharge machining method disclosed in Patent Document 1 has a tapered surface inclined inwardly along the direction of gravity all around the inner surface. Therefore, when the inner surface of the workpiece that is originally required is a surface along the direction of gravity, the wire-cut electric discharge machining method disclosed in Patent Document 1 requires that after removing the core from the workpiece, the unnecessary part having the tapered surface is cut off all around the inner surface of the workpiece. When cutting off the unnecessary part, the wire-cut electric discharge machining method disclosed in Patent Document 1 requires that the wire electrode is moved relatively outwardly toward the inner surface of the workpiece that is originally required, and then moved relatively in a direction along the inner surface of the workpiece. As a result, in the wire-cut electric discharge machining method disclosed in Patent Document 1, there is a high risk that the wire electrode will cut into the inner surface of the workpiece when cutting off the unnecessary part, making it difficult to guarantee the dimensions required for the workpiece. In particular, when the wire electrode is moved relatively outwardly toward the inner surface of the workpiece, the workpiece has the above-mentioned tapered surface, so that the machining allowance is smaller at the upper part of the inner surface than at the lower part of the inner surface. As a result, with the wire-cut electric discharge machining method disclosed in Patent Document 1, it is difficult to ensure the required dimensions, particularly at the upper part of the inner surface of the workpiece.

[0037] Furthermore, in the wire-cut electric discharge machining method of this embodiment, core holding part 22 includes a wedge part 23 that extends in the direction of gravity and has the above-mentioned inclined surface 24, and a bridge part 25 that protrudes inward from a part of the inner surface 21 of the workpiece 20 and bridges between the inner surface 21 and the wedge part 23. The wedge part 23 holds the core 30 by receiving the cut-out core 30 on the inclined surface 24. A connection part 26 of bridge part 25 with inner surface 21 of workpiece 20 is cut off in the process of cutting out core holding part 22.

[0038] That is, in core holding part 22, wedge portion 23, which is the portion responsible for holding core 30, and bridge portion 25, which is the portion that connects wedge portion 23 that holds core 30 to inner surface 21 of workpiece 20, are clearly separated. As a result, in the wire-cut electric discharge machining method of this embodiment, the portion that is cut in the step of cutting out core holding part 22 can be limited to bridge portion 25. Therefore, in the wire-cut electric discharge machining method of this embodiment, the step of cutting out core holding part 22 can be reliably completed in a short time. Therefore, the wire-cut electric discharge machining method of this embodiment can reliably improve work efficiency while preventing core 30 from falling.

[0039] The wedge portion 23 is formed in the shape of a polygonal pyramid (including a polygonal truncated pyramid) such as the quadrangular pyramid shown in Figures 3(a) and 3(b) and Figure 6(b) described later. This polygonal pyramid has a bottom surface on the side facing the direction of gravity, an apex (vertex or top surface) on the side facing the opposite direction to the direction of gravity, and the inclined surface 24 described above is a side surface.

[0040] As a result, the wedge portion 23 can prevent the core 30 from rotating in the circumferential direction, compared to when the wedge portion 23 is formed in a cone shape. As a result, the wire-cut electric discharge machining method of this embodiment can prevent the core 30 from rotating and pinching the wire electrode 3 in the step of cutting out the core 30, which could lead to breaking of the wire electrode 3. Therefore, the wire-cut electric discharge machining method of this embodiment can further reliably improve work efficiency while preventing the core 30 from falling.

[0041] Furthermore, in the wire-cut electric discharge machining method of this embodiment, the bridge portion 25 is formed in a plate shape extending in the direction of gravity and inward from a part of the inner surface 21 of the workpiece 20. Preferably, the bridge portion 25 is formed in a flat plate shape extending in the direction of gravity and inward from a part of the inner surface 21 of the workpiece 20 and having a substantially constant thickness. The thickness of the bridge portion 25 is the circumferential dimension of the bridge portion 25 and is equal to or smaller than the minimum circumferential dimension of the wedge portion 23. The circumferential dimension is the dimension in the direction in which the wire electrode 3 cuts into the bridge portion 25 in the step of cutting away the core holding portion 22.

[0042] As a result, in the wire-cut electric discharge machining method of this embodiment, in the step of cutting out the core holding portion 22, the connection portion 26 of the bridge portion 25 to the inner surface 21 of the workpiece 20 can be easily cut off by simply moving the wire electrode 3 in the circumferential direction relative to the connection portion 26 of the bridge portion 25. Therefore, in the wire-cut electric discharge machining method of this embodiment, the step of cutting out the core holding portion 22 can be easily completed in a short time. Therefore, the wire-cut electric discharge machining method of this embodiment can further reliably improve work efficiency while preventing the core 30 from falling.

[0043] Moreover, because the bridge portion 25 has the plate shape as described above, the thickness of the bridge portion 25 to be cut by the wire electrode 3 hardly changes each time the wire electrode 3 cuts into the bridge portion 25. As a result, the wire-cut electric discharge machining method of this embodiment can generate stable electric discharge between the wire electrode 3 and the bridge portion 25 in the process of cutting out the core holding portion 22. Therefore, the wire-cut electric discharge machining method of this embodiment can prevent abnormal electric discharge from occurring between the wire electrode 3 and the bridge portion 25, and can prevent breakage of the wire electrode 3 due to the abnormal electric discharge. Therefore, the wire-cut electric discharge machining method of this embodiment can further reliably improve work efficiency while preventing the core 30 from falling.

[0044] In contrast, the workpiece machined by the wire-cut electric discharge machining method disclosed in Patent Document 1 has a tapered surface inclined inwardly along the direction of gravity all around its inner surface. Therefore, when the inner surface of the workpiece that is required is a surface along the direction of gravity, the wire-cut electric discharge machining method disclosed in Patent Document 1 requires that after removing the core from the workpiece, the unnecessary portion having this tapered surface is cut off all around the inner surface of the workpiece. When cutting off the unnecessary portion, the wire-cut electric discharge machining method disclosed in Patent Document 1 requires that the thickness of the unnecessary portion to be cut off by the wire electrode changes significantly every time the wire electrode cuts into the unnecessary portion, which may cause the abnormal discharge described above and break the wire electrode.

[0045] 4 to 6 are diagrams for explaining each step of the wire-cut electric discharge machining method of this embodiment. FIG. 4(a) is a diagram showing the state of the workpiece 20 before electric discharge machining. FIG. 4(b) is a diagram showing the state of the workpiece 20 at the start of the step of cutting out the core 30. FIG. 5(a) is a diagram showing the state of the workpiece 20 during the step of cutting out the core 30. FIG. 5(b) is a diagram showing the state of the workpiece 20 and the core 30 at the end of the step of cutting out the core 30. FIG. 6(a) is a diagram showing the state of the workpiece 20 and the core 30 in the step of removing the core 30. FIG. 6(b) is a diagram showing the state of the workpiece 20 and the core holding part 22 in the step of cutting out the core holding part 22.

[0046] In the wire-cut electric discharge machining method of this embodiment, before electric discharge machining, as shown in Figure 4 (a), a machining start hole H is formed that passes through the center axis A of the workpiece 20 along the gravity direction and penetrates the workpiece 20, and the wire electrode 3 is inserted into the machining start hole H.

[0047] Next, in the wire-cut electric discharge machining method of this embodiment, a process of cutting out the core 30 is started. In this process, as shown in Fig. 4(b), the wire electrode 3 is moved relatively outward to the necessary contour of the workpiece 20 to perform electric discharge machining, and then the wire electrode 3 is moved relatively circumferentially along the necessary contour to perform electric discharge machining. As a result, a machining groove K is formed in the workpiece 20 according to a predetermined movement path of the wire electrode 3. The necessary contour of the workpiece 20 is the contour of the workpiece 20 that is originally required, and in this case corresponds to the contour of the inner surface 21 of the workpiece 20 that is originally required.

[0048] Next, in the wire-cut electric discharge machining method of this embodiment, as shown in Fig. 5(a), a core holding portion 22 is formed in the workpiece 20 during the process of cutting out the core 30. After forming the core holding portion 22, in the wire-cut electric discharge machining method of this embodiment, the wire electrode 3 is further moved relatively in the circumferential direction so that machining grooves K are formed on all necessary contours of the workpiece 20. This completes the process of cutting out the core 30, as shown in Fig. 5(b). The cut-out core 30 attempts to fall in the direction of gravity, but is received by the inclined surface 24 of the wedge portion 23 and is held in the core holding portion 22.

[0049] After the step of cutting out the core 30, the wire-cut electric discharge machining method of this embodiment carries out a step of removing the core 30 held by the core holding part 22, as shown in Fig. 6(a). In this step, the core 30 can be easily removed by lifting the core 30 using a predetermined crane mechanism or lift mechanism, or manually.

[0050] After the step of removing the core 30, the wire-cut electric discharge machining method of this embodiment carries out a step of cutting out the core holding portion 22 from the workpiece 20, as shown in Fig. 6(b). In this step, the wire electrode 3 is moved in the circumferential direction along the inner surface 21 relative to the connection portion 26 of the bridge portion 25 to the inner surface 21 of the workpiece 20. The wire electrode 3 cuts into the bridge portion 25, which has a substantially constant thickness, in the circumferential direction along the inner surface 21, reducing the risk of cutting into the inner surface 21, thereby preventing breakage of the wire electrode 3 due to abnormal electric discharge and reliably cutting out the core holding portion 22 in a short time.

[0051] In the wire-cut electric discharge machining method of this embodiment, after the step of cutting off the core holding portion 22, finish machining of the inner surface 21 of the workpiece 20 may be performed as necessary.

[0052] 7 to 9 are diagrams showing other examples of the workpiece 20 and the core 30 that have been electric discharge machined by the wire-cut electric discharge machining method of the present embodiment.

[0053] 7 shows an example in which the core 30 is a long rectangular parallelepiped in which one dimension in the U-axis direction or the V-axis direction is longer than the other. In this example, as shown in FIG. 7, the core holding portion 22 may be formed as two core holding portions 22. The two core holding portions 22 may be disposed on one inner surface 21 in the longitudinal direction and the other inner surface 21 in the longitudinal direction among the inner surfaces 21 of the workpiece 20. That is, the two core holding portions 22 may be disposed at equal intervals along the circumferential direction on the inner surface 21 of the workpiece 20. The wedge portion 23 of each core holding portion 22 may be formed in the shape of a polygonal pyramid having three inclined surfaces 24 facing one or the other in the circumferential direction or inward.

[0054] Fig. 8 shows an example in which the core 30 is a hollowed-out thin-walled cylinder. In this example, as shown in Fig. 8, the core holding portion 22 may be formed as four core holding portions 22. The four core holding portions 22 may be arranged at equal intervals along the circumferential direction on the inner surface 21 of the workpiece 20. Furthermore, the wedge portion 23 of each core holding portion 22 may be formed into a shape having one inclined surface 24 facing inward.

[0055] Fig. 9 shows an example in which the core 30 is a rectangular parallelepiped having a dimension in the gravity direction of, for example, 50 mm or more. In this example, as shown in Fig. 9, the core holding portion 22 may be formed as four core holding portions 22. The four core holding portions 22 may be arranged at equal intervals along the circumferential direction on the inner surface 21 of the workpiece 20. The wedge portion 23 of each core holding portion 22 may be formed into a shape having one inclined surface 24 facing inward. Furthermore, the wedge portion 23 and the bridge portion 25 of each core holding portion 22 may be formed integrally into a single flat plate shape.

[0056] 7 to 9, in the wire-cut electric discharge machining method of this embodiment, the core holding part 22 may be formed as a plurality of core holding parts 22. The plurality of core holding parts 22 may be arranged on the inner surface 21 of the workpiece 20 at equal intervals along the circumferential direction of the central axis A of the workpiece 20 aligned in the direction of gravity.

[0057] As a result, in the wire-cut electric discharge machining method of this embodiment, the cut-out core 30 can be held by the core holding part 22 without being tilted with respect to the direction of gravity. Therefore, in the wire-cut electric discharge machining method of this embodiment, it is possible to prevent the core 30 from pinching the wire electrode 3 and breaking the wire electrode 3. Therefore, the wire-cut electric discharge machining method of this embodiment can further reliably improve work efficiency while preventing the core 30 from falling.

[0058] Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the spirit of the present invention described in the claims. In the present invention, the configuration of one embodiment can be added to the configuration of another embodiment, the configuration of one embodiment can be replaced with the configuration of another embodiment, or a part of the configuration of one embodiment can be deleted. [Explanation of symbols]

[0059] 20...Workpiece, 21...Inner surface, 22...Core holding part, 23...Wedge part, 24...Inclined surface, 25...Bridge part, 26...Connection part, 30...Core, A...Central axis

Claims

1. A wire cut electric discharge machining method for cutting out a core from a workpiece, comprising the steps of: forming a core holding portion for holding the core in the workpiece and cutting out the core from the workpiece; removing the core held in the core holding portion; and cutting the core holder from the workpiece. The core holding portion is a shape that protrudes inwardly from a part of an inner surface of the workpiece formed by cutting out the core and intersects with the inner surface; The at least one inclined surface is inclined inwardly in the direction of gravity. A wire-cut electric discharge machining method comprising:

2. The core holding portion is a wedge portion extending in the gravity direction and having the inclined surface; a bridge portion protruding inward from a portion of the inner surface of the workpiece and bridging between the inner surface and the wedge portion, The wedge portion holds the cut-out core by receiving the cut-out core with the inclined surface, The bridge portion is cut off at a connection portion with the inner surface of the workpiece during the step of cutting off the core holding portion.

2. The wire-cut electric discharge machining method according to claim 1.

3. The wedge portion is formed in a polygonal pyramid shape, The polygonal pyramid has a bottom surface facing the direction of gravity, a top surface facing the opposite direction to the direction of gravity, and a side surface formed by the inclined surface.

3. The wire-cut electric discharge machining method according to claim 2.

4. The bridge portion is formed in a plate shape extending in the direction of gravity and inward from a part of the inner surface of the workpiece.

3. The wire-cut electric discharge machining method according to claim 2.

5. The core holder is formed as a plurality of core holders, The plurality of core holding portions are disposed on the inner surface of the workpiece at equal intervals along a circumferential direction of a central axis of the workpiece aligned along the direction of gravity.

2. The wire-cut electric discharge machining method according to claim 1.

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