Electrode wire for electrical discharge machining

Abstract

The present invention relates to an electrode wire for electrical discharge machining, which includes a core wire made of a first metal and an alloy layer formed on the outer periphery of the core wire by interdiffusion between the core wire and a second metal plated on the outer surface of the core wire, the alloy layer including a portion made of α phase + β' phase and β' phase grains, and cracks formed on the surface of the alloy layer. With the above configuration, it is possible to improve the machining speed and surface roughness of the workpiece, minimize the generation of fine debris from the electrode wire, and provide an electrode wire for electrical discharge machining with a uniform surface.

Description

Technical Field

[0001] The present invention relates to an electrode wire for electrical discharge machining. Specifically, by forming grains of a β' phase having cracks on the surface of the electrode wire and minimizing the generation of fine chips of the electrode wire, the discharge efficiency and machining speed can be improved, and the machining accuracy and surface roughness can be improved. The present invention relates to an electrode wire for electrical discharge machining.

Background Art

[0002] Wire electrical discharge machining is a method that has been conventionally practiced, in which a discharge is performed using a machining fluid such as water as a medium between a workpiece and an electrode wire for wire electrical discharge machining, and the electrode wire and the workpiece are relatively moved to cut the workpiece into a desired shape.

[0003] In this electrical discharge machining method, as the electrode wire, various types of electrode wires are used, including high-strength electrode wires containing molybdenum, tungsten, etc., and brass electrode wires, starting with pure copper electrode wires.

[0004] As such an electrode wire, U.S. Patent No. 4,686,153 discloses a prior art in which a zinc layer is coated on a copper-clad steel wire having a diameter of 0.49 mm, and then the zinc-coated copper-clad steel wire is drawn to a diameter of 0.2 mm and heated at about 300°C for 1 hour in a non-oxidizing nitrogen gas atmosphere to diffuse copper into the zinc layer and convert the zinc layer into a copper-zinc alloy layer. The copper-zinc alloy has a zinc concentration of about 45% and a concentration that gradually decreases with respect to the surface. The average concentration of zinc in the copper-zinc alloy layer is 50% or less and 10% or more. The β-phase copper-zinc alloy has a zinc concentration of 40 to 50%, and the surface layer includes a β-phase copper-zinc alloy layer on the outer surface. However, the above technique is required to improve the machining speed without deteriorating the accuracy of the surface obtained in the cutting process.

[0005] The inventor of the present invention proposed a porous electrode wire for electrical discharge machining disclosed in Korean Patent Registration No. 10-518727 and a method for manufacturing a porous electrode wire for electrical discharge machining disclosed in Korean Patent Registration No. 10-518731.

[0006] In the above technology, the core wire metal containing copper and the zinc plating layer form an alloy plating layer composed of fragments of γ-phase grains on the outer periphery of the core wire metal through an interdiffusion reaction, and cracks are formed on the surface of the electrode wire, thereby further improving the cooling effect of the electrode wire and making the machining speed significantly improved compared to the electrode wire proposed in U.S. Patent No. 4,686,153.

[0007] By the way, as a result of studying the γ-phase alloy plating layer formed on the brass core wire in the above technology, the inventor of the present invention was able to confirm the Brinell hardness of "HYPER Zn" containing 50% by weight or more of Zn in the Cu-Zn binary alloy through a state diagram and a hardness comparison graph based on the change of the Cu-Zn binary alloy phase, as shown in Figure 2, with the advice of the Korea Institute of Materials Science.

[0008] According to Figure 2 above, it was found that the γ-phase alloy plating layer has a Brinell hardness of 350 HB or more, which is very high and very brittle. The γ-phase alloy plating layer with such properties cannot withstand the drawing pressure during the drawing process, easily cracks, and fragments of cracks are generated. In addition, a large amount of fine chips adhere to the inside and outside of the cracks. When the above-mentioned crack fragments and a large amount of fine chips are used for electrical discharge machining, the secondary discharge caused by the crack fragments and fine chips becomes an inhibiting factor for improving the machining speed.

[0009] Therefore, the inventor proposed again a porous electrode wire for electrical discharge machining and a method for manufacturing the same disclosed in Korean Patent Registration No. 10-1284495.

[0010] Compared with the electrodes presented in Korean Patent Registration No. 10-518727 and Korean Patent Registration No. 10-518731, by forming grains (mainly α-phase and β-phase) that penetrate the cracks where the material forming the core wire is formed in the second alloy layer on the surface of the electrode wire for electrical discharge machining, the second alloy layer (mainly composed of γ-phase) with cracks is surrounded by relatively soft grains, and the second alloy layer can reduce the fine chips generated by cracking or breaking during the electrical discharge process, and the effect of further improving the electrical discharge machining speed and the surface roughness of the workpiece is obtained.

[0011] However, although the above technology can improve the machining speed of the workpiece and the surface roughness of the workpiece to a certain extent, there is a limit to minimizing the fine chips of the electrode wire generated by the cracking of the crack part (mainly the second alloy layer).

[0012] Also, in the electrode wire for electrical discharge machining and its manufacturing method of US Patent No. 5,945,010, similar to the above patent, it is a patent that introduces the concept of cracks into the wire electrode wire. To manufacture the wire electrode wire, zinc with a lower vaporization temperature than the core wire is first coated on the core wire by electroplating. In order for a sufficient diffusion reaction to occur between the zinc plating layer coated by electroplating and the core wire, a diffusion heat treatment process of 1 to 4 hours in the range of 150 °C to 400 °C is carried out until the zinc plating layer becomes an alloy layer of γ-phase (phase). As a result of such diffusion heat treatment, an electrode wire is manufactured in which a plurality of grain pieces (9) of γ-phase are formed on the surface as shown in Figure 3. The unlabeled symbol tf is the maximum thickness of the γ-phase brass alloy coating.

[0013] However, although the above technology also has the advantage of improving the machining speed by forming an electrode wire with an alloy plating layer composed of a plurality of grain pieces (9) of γ-phase, which is an alloy of zinc and copper, on the surface of the electrode wire, the alloy plating layer in which cracks are formed on the brass core wire (8) is mainly composed of γ-phase as shown in Figures 1 and 2. Therefore, it cannot withstand the drawing pressure during the drawing process, easily cracks, and a large number of crack fragments and fine chips are generated, and there is a limit to improving the machining speed and surface roughness.

Summary of the Invention

Problems to be Solved by the Invention

[0014] The present invention is for solving the above problems, and aims to provide an electrode wire for electrical discharge machining that can minimize the generation of fine debris of the electrode wire, improve the discharge efficiency and machining speed, while improving the machining accuracy and surface roughness.

[0015] Another object of the present invention is to form mainly β'-phase grains, cracks and pinholes in the outermost layer of the electrode wire, and form a fine space composed of ε-phase and γ-phase + ε-phase in the shape of a cave deeper than the crack in the core wire direction from the surface of the electrode wire, so that the cooling water provided at high pressure can penetrate to the core wire, maximizing the cooling effect and providing an electrode wire for electrical discharge machining that does not generate fine debris.

[0016] Another object of the present invention is to form β'-phase grains and cracks on the surface of the electrode wire rather than the conventional electrode wire on which γ-phase grains are formed on the surface of the electrode wire, and provide an electrode wire for electrical discharge machining with more uniform cracks than γ-phase cracks.

[0017] Another object of the present invention is to provide an electrode wire for electrical discharge machining that can coat a conductive polymer on the surface of the electrode wire, increase the electrical conductivity of the electrode wire surface, and further improve the machining speed.

[0018] Another object of the present invention is to coat a semiconductor or insulator polymer on the surface of the electrode wire, or form an oxide layer with semiconductor or insulating properties, provide an irregular discharge current evenly, reduce the generation of Micro Crack etc. on the surface of the workpiece, and provide an electrode wire for electrical discharge machining that improves the surface roughness and accuracy.

Means for Solving the Problems

[0019] To achieve the above object, the electrode wire for electrical discharge machining of the present invention includes a core wire made of a first metal, an alloy layer formed on the outer periphery of the core wire by interdiffusion between a second metal plated on the outer surface of the core wire and the core wire, the alloy layer including a portion composed of an α phase + β' phase and grains of the β' phase formed on the outer periphery of the portion composed of the α phase + β' phase, and cracks are formed on the surface of the alloy layer.

[0020] A recessed portion is formed at least partially on the outer periphery of the portion composed of the α phase + β' phase, and it is desirable that the grains of the β' phase are formed by being embedded in the recessed portion formed on the outer periphery of the portion composed of the α phase + β' phase.

[0021] It is desirable that the grains of the β' phase are formed by being embedded in the shape of a wedge in the outline of the portion composed of the α phase + β' phase.

[0022] It is desirable that the grains of the β' phase are formed discontinuously on the outline of the portion composed of the α phase + β' phase.

[0023] It is desirable that the alloy layer further includes grains of a β' phase + γ phase.

[0024] It is desirable that pinholes are further formed on the surface of the alloy layer.

[0025] It is desirable that the surface layer of the pinhole is composed of at least one of a γ phase + ε phase and an ε phase.

[0026] It is desirable that a fine space in the form of a cave dug deeper than the crack is further formed on the alloy layer from the surface toward the core wire side.

[0027] It is desirable that the surface layer of the portion having the fine space in the form of a cave is composed of at least one of a γ phase + ε phase and an ε phase.

[0028] It is desirable that cracks are formed in the grains of the β' phase.

[0029] It is desirable that at least a part of the core wire penetrates through the alloy layer and is exposed on the surface of the electrode wire.

[0030] It is desirable that at least one of an oxide layer, a conductive polymer, a semiconductive polymer, and an insulating polymer is applied to the surface of the alloy layer.

[0031] Note that the first metal is any one of copper, brass, and a metal containing copper, and the second metal preferably consists of any one of zinc, aluminum, tin, and their alloys.

Advantages of the Invention

[0032] The present invention can provide an electrode wire for electrical discharge machining that minimizes the generation of fine chips of the electrode wire, improves the discharge efficiency and machining speed, and at the same time improves the machining accuracy and surface roughness.

[0033] In the present invention, mainly grains of β'-phase, cracks, and pinholes are formed in the outermost layer of the electrode wire, and a fine space composed of ε-phase and γ-phase + ε-phase in the form of a cave deeper than the crack in the core wire direction is formed from the surface of the electrode wire, so that the cooling water provided at high pressure can penetrate to the core wire. Therefore, the cooling effect can be maximized, and an electrode wire for electrical discharge machining that does not generate fine chips can be provided.

[0034] The present invention can provide an electrode wire for electrical discharge machining that forms grains of β'-phase and cracks on the surface of the electrode wire, which is more uniform than γ-phase cracks, compared to a conventional electrode wire in which grains of γ-phase are formed on the surface of the electrode wire.

[0035] In the present invention, by applying a conductive polymer to the surface of the electrode wire and increasing the electrical conductivity of the electrode wire surface, the machining speed can be further improved.

[0036] The present invention provides an electrode wire for electrical discharge machining that improves surface roughness and accuracy by applying a semiconductor or insulator polymer to the surface of the electrode wire, forming a semiconductive or insulating oxide layer, providing a uniform irregular discharge current, and reducing the occurrence of Micro Crack or the like on the surface of the workpiece.

[0037] Since the present invention applies a conductive polymer, a semiconductor polymer, or an insulator polymer to the surface of the electrode wire, it is possible to prevent the detachment of fine chips, and thus an effect of preventing re-discharge or the like caused by the fine chips can be obtained.

Brief Description of the Drawings

[0038]

Figure 1

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Figure 4

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Figure 6

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Figure 8

Figure 9

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Figure 12

Embodiments for Carrying Out the Invention

[0039] The electrode wire for electrical discharge machining according to a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

[0040] The electrode wire for electrical discharge machining according to a preferred embodiment of the present invention includes a core wire and an alloy layer as shown in the cross-sectional enlarged photograph of FIG. 4.

[0041] The core wire is a wire made of a first metal located at the central portion of the electrode wire. As the first metal serving as the material of the wire, various types of metals can be used. For example, any one of copper, brass, and a metal containing copper can be used. Desirably, a brass core wire composed of 65 wt% copper: 35 wt% zinc, 63 wt% copper: 37 wt% zinc, or 60 wt% copper: 40 wt% zinc can be used. Here, although the core wire will be surrounded by the alloy layer described later on its outer periphery, depending on the manufacturing process, at least a part of the core wire may break through the alloy layer described later and be exposed on the surface of the electrode wire, and the components of the core wire can be detected as they are on the surface of the electrode wire.

[0042] The alloy layer is a layer formed on the outer periphery of the core wire by the mutual diffusion of the second metal plated on the outer surface of the core wire and the core wire. The second metal is composed of any one of zinc, aluminum, tin, and their alloys having a lower vaporization temperature than the core wire, and desirably zinc can be used.

[0043] The alloy layer includes a portion composed of the α-phase + β'-phase shown in the Cu-Zn binary phase diagram of FIG. 1, and the grains of the β'-phase formed on the outer periphery of the portion composed of the α-phase + β'-phase. Cracks are formed on the outer contour of the alloy layer, that is, the surface of the electrode wire, as shown in the enlarged cross-sectional photograph of FIG. 4. The cracks expand the surface area of the alloy layer formed on the outer contour of the electrode wire, increasing the contact area of the cooling water, thus maximizing the cooling effect and contributing to improving the processing speed.

[0044] The portion composed of the α-phase + β'-phase has the composition of the portion indicated by α + β' in the Cu-Zn binary phase diagram shown in FIG. 1, and is formed so as to surround the core wire on the outer contour of the core wire. Grains of the β'-phase, which will be described later, will be located on the outer contour of the portion composed of the α-phase + β'-phase. Here, the portion composed of the α-phase + β'-phase may be formed so as to partially break through the grains of the β'-phase, which will be described later, and reach the surface layer. In such a case, although it is a small part, the portion composed of the α-phase + β'-phase will partially form the outermost surface layer of the alloy layer.

[0045] As shown in the enlarged cross-sectional photograph of FIG. 4, the grains of the β'-phase are formed by being embedded in the outer contour of the portion composed of the α-phase + β'-phase such that a portion sunken into at least a part of the portion composed of the α-phase + β'-phase is generated. Depending on the position, the grains of the β'-phase may also be formed by being embedded in the outer contour of the portion composed of the α-phase + β'-phase in the shape of a wedge. Cracks are formed between the grains of the β'-phase and its surroundings.

[0046] Here, the grains of the β'-phase may be formed discontinuously on the outer contour of the portion composed of the α-phase + β'-phase, or may not be able to completely cover the outer periphery of the portion composed of the α-phase + β'-phase. When the grains of the β'-phase are formed discontinuously on the outer contour of the portion composed of the α-phase + β'-phase in this way, the portion composed of the α-phase + β'-phase will be partially directly exposed on the surface of the alloy layer.

[0047] The alloy layer may further include a portion forming grains of β' phase + γ phase shown in the Cu-Zn binary phase diagram illustrated in FIG. 1. In that case, the surface of the alloy layer may appear with a mixture of grains of β' phase, a portion composed of α phase + β' phase, and grains of β' phase + γ phase.

[0048] In addition to cracks, fine spaces in the form of pinholes or cavities can be further formed on the surface of the alloy layer as shown in the surface enlarged photograph of FIG. 6 and the cross-sectional enlarged photograph of FIG. 7.

[0049] The fine space in the form of a cavity is formed deeper than the crack in the core wire direction from the surface of the electrode wire as shown in the cross-sectional enlarged photograph of FIG. 7. The surface layer of the portion forming the fine space in the form of a cavity is partially vaporized and dezincification occurs during manufacturing processes such as diffusion heat treatment and drawing, so the zinc concentration increases and it may have a γ phase + ε phase or ε phase shown in FIGS. 1 and 2. Depending on the position, a portion where γ phase + ε phase and ε phase are mixed may also appear. FIG. 8 shows that the surface layer of the fine space in the form of a cavity is Cu 23.6%, Zn 76.37%, representing a γ phase + ε phase.

[0050] During electrical discharge machining, the cooling water provided at high pressure can penetrate to the core wire part (when the fine space in the form of a cavity extends to the vicinity of the core wire) for the fine space in the form of a cavity as described above. Thus, not only is the cooling effect significantly improved, but also the zinc components of the ε phase and γ phase + ε phase constituting the surface layer of the fine space in the form of a cavity easily vaporize and take away heat, further improving the cooling effect and significantly increasing the electrical discharge machining speed.

[0051] Also, many pinholes appearing on the surface of the alloy layer not only increase the surface area of the electrode wire and improve the cooling effect, but also due to the dezincification phenomenon occurring during diffusion heat treatment on the surface of the pinholes, a γ phase + ε phase and / or ε phase with a low vaporization temperature is formed, further improving the cooling effect during electrical discharge machining. FIG. 9 shows that the surface layer of the pinholes appearing on the surface of the alloy layer represents a phase with Cu 13.90% and Zn 86.10%.

[0052] As described above, together with the cracks, the cavity-shaped fine spaces and pinholes all serve to greatly increase the surface area of the electrode wire, maximize the cooling effect, and improve the machining speed.

[0053] As described above, the electric discharge machining electrode wire of the present invention includes a portion composed of an α phase + β' phase formed around the core wire and grains of the β' phase embedded in the outer contour of the portion composed of the α phase + β' phase, and cracks are formed in the grains of the β' phase and around them. Generally, when the surface layer of the electrode wire is formed of a γ phase as in the prior art, the alloy layer of the γ phase has a hardness of 350 HB or more as shown in FIG. 2, so it is a brittle alloy layer. During the drawing process, when it cannot withstand the drawing pressure and forms cracks while cracking, fine chips are generated and adhere to the surface of the cracks in a large amount. The fine chips adhering to the surface of the cracks become an inhibitory factor for improving the machining speed and surface roughness by secondary discharge or the like during electric discharge machining.

[0054] However, the grains of the β' phase of the present invention have a much lower hardness and a flexible property than the conventional γ-phase alloy layer in the surface layer of the electrode wire as shown in FIG. 2. Therefore, while not cracking in the drawing process, almost no fine chips adhere to the surface of the electrode wire. Thus, during electric discharge machining, not only can the secondary discharge caused by the fine chips be reduced to greatly improve the machining speed and surface roughness, but also clogging of the diamond guide dies through which the electrode wire passes can be prevented.

[0055] On the other hand, when comparing the vaporization temperature of the γ phase and the vaporization temperature of the β' phase, since the vaporization temperature of the γ phase is lower than the vaporization temperature of the β' phase, generally, it is known that the machining speed of the conventional electrode wire having a γ phase is faster than the machining speed of the electrode wire having a β' phase.

[0056] However, even if most of the surface of the alloy layer of the electrode wire of the present invention is formed of grains of the β' phase with a higher copper concentration and a lower zinc concentration than the γ phase, which is known to be the fastest in the prior art, there is almost no fine debris attached to the surface of the alloy layer of the present invention. Also, although many cracks and pinholes are formed mainly around the grains of the β' phase, the fine space in the shape of a cave formed of the γ phase + ε phase or ε phase extends to a deeper part than the cracks and pinholes, so that the cooling water provided at high pressure penetrates to the core wire and forms many elements that significantly improve the cooling effect. Therefore, it has been found that the processing speed is improved by at least 108% or more compared to the conventional electrode wire with cracks formed in the γ phase.

[0057] A method for manufacturing an electric discharge machining electrode wire for a desirable implementation of the present invention having the above structure will be described.

[0058] The method for manufacturing an electric discharge machining electrode wire according to the present invention relates to a method for manufacturing an electrode wire as described above. Specific embodiments are carried out through a core wire providing step, a plating step, a primary diffusion heat treatment step, a primary drawing step, a secondary diffusion heat treatment step, and a secondary drawing step.

[0059] (1) In the core wire providing step, a brass (65%: 35%) wire having a wire diameter of 2 mm (first diameter) is provided as the core wire of the first metal.

[0060] (2) In the plating step, zinc having a lower vaporization temperature than the core wire is used as the second metal, and electroplating is carried out to obtain a zinc-plated wire. While the core wire is being transferred by a roller, it is immersed in an electro-zinc plating bath and passed through at a predetermined speed to form a zinc plating layer (second metal) with a thickness of about 12 μm on the outer contour of the core wire.

[0061] (3) In the primary diffusion heat treatment step, the zinc-plated wire passes through the preheating section of an electric heating treatment machine, and while the temperature between the electrodes is heated to about 400 °C, it is passed through at a speed of about 200 m / min to carry out diffusion heat treatment and form an alloy layer on the outer contour of the intermediate wire.

[0062] (4) In the first drawing process step, the diffusion heat-treated intermediate wire rod is drawn at a wire diameter of 1.2 mm (second diameter) to form cracks on the surface of the intermediate wire rod. FIG. 10 shows that cracks have appeared on the surface of the intermediate wire rod.

[0063] (5) In the second diffusion heat treatment step, the first-drawn intermediate wire rod is heated up for about 2 hours, heated at 400 ° C. for 20 hours to perform diffusion heat treatment, opened after 6 hours, and the ratio of the copper (Cu) content diffused into the grain part where cracks are formed is increased to convert it into grains of the β' phase.

[0064] (6) In the second drawing process step, the second-diffusion heat-treated intermediate wire rod is processed with an automated facility capable of simultaneously performing the second drawing process and stress relieving heat treatment so as to have a wire diameter of 0.25 mm which is the standard of the electrode wire, and the electrode wire for electrical discharge machining of the present invention is manufactured. FIG. 5 is an enlarged photograph of the surface of the electrode wire finally manufactured according to the present invention, and the grains of the β' phase and the crack part are clearly shown in the photograph. When comparing the grains in the crack part shown in FIG. 5 with the grains in the intermediate wire rod crack part shown in FIG. 10, it can be seen that the area of the grains has become wider. It can be confirmed that the generation of fine chips in the crack part of FIG. 5 is significantly reduced as compared with the crack part of FIG. 10 due to the widening of the grains. Further, FIG. 4 is an enlarged photograph of the cross section of the electrode wire manufactured by the above method, and it can be seen from the photograph that the grains are embedded in the part where the alloy layer has sunken. FIG. 6 is an enlarged photograph of the surface of the electrode wire, and it can be confirmed that cracks, pinholes, and fine spaces in the shape of caves appear in the surface layer. FIG. 7 is an enlarged photograph of the cross section of the electrode wire, and it can be confirmed that cracks and fine spaces in the shape of caves appear.

[0065] The above manufacturing method can be selected and deformed in various forms for the diffusion heat treatment method, diffusion heat treatment temperature, time, plating method, and other processes according to the equipment owned by each company within the range not exceeding the basic concept of the present invention.

[0066] The results of the trial machining of the workpiece using the electrode wire with a wire diameter of 0.25 mm according to the present invention manufactured as described above and the electrode wires of Comparative Examples 1 and 2 are as shown in Table 1 below.

[0067]

Table 1

[0068] *The trial machining examples shown in Table 1 were carried out on a Charmilles Robofil 240SL for ST25A.Tec. The workpiece was an alloy tool steel of SKD-11 (1.5C-12Cr-1Mo-0.35V) with a Rockwell hardness of 58 - 65 and a height of 40 mm and a thickness of a square bar with a horizontal × vertical = 10 mm × 10 mm, and cutting was performed.

[0069] *Comparative Example 1 is an electrode wire with a wire diameter of 0.25 mm that forms cracks on the surface of the γ-phase alloy layer using ThermoJP2 of Thermocompact, France, and Comparative Example 2 is an electrode wire with a wire diameter of 0.25 mm that forms cracks on the surface of the γ-phase alloy layer using TopasPLUS H of Berkenhoff, Germany.

[0070] As can be seen from the above test results, when electric discharge machining was carried out up to secondary machining respectively under the Standard Parameter conditions generally used in the production site using the electrode wire of the present invention and Comparative Examples 1 and 2, it was confirmed that the electrode wire of the present invention had a machining speed improvement of at least 108% or more in at least the primary machining compared to Comparative Example 1, and the machining speed was improved up to 114% at most in the secondary machining.

[0071] On the other hand, in the example described above, it was described that the alloy layer of the electrode wire includes a portion composed of the α-phase + β'-phase and the grains of the β'-phase formed on the outer periphery of the portion composed of the α-phase + β'-phase. However, by partially changing the diffusion heat treatment conditions and the drawing process, etc., it is also possible to manufacture such that almost no grains of the β'-phase appear on the surface of the alloy layer, and a part of the grains of the γ-phase and the grains of the γ-phase + ε-phase are further mixed and appear.

[0072] As described above, the surface of the alloy layer of the electrode wire manufactured as such consists almost entirely of β'-phase grains, with a portion consisting of α-phase + β'-phase, and grains of γ-phase or grains of γ-phase + ε-phase appearing in a mixed state. On the other hand, for the electrode wire according to the present invention, an oxide layer can also be formed on the surface layer of the portion consisting of β'-phase grains and α-phase + β'-phase, which is exposed on the surface of the electrode wire and the portion forming fine spaces in the form of cracks, pinholes, and cavities. If an oxide layer is formed on the surface of the electrode wire and in the fine spaces in the form of cavities, the oxide layer promotes the absorption of cooling water, increases the conductivity, improves the discharge power, and thus the processing speed can be further improved.

[0073] Also, for the electrode wire according to the present invention, a conductive polymer can be applied to the surface of the electrode wire to increase the conductivity of the electrode wire surface, suppress the generation of fine chips, and improve the processing speed.

[0074] As can be seen from the electrical conductivity characteristic values in FIG. 11, the conductive polymer has an electrical conductivity of 10 0 s / cm or more and is very excellent, and doped PEDOT or doped polyaniline can be used. FIG. 12 shows an example of a corrosion prevention experiment on a metal using doped polyaniline. (A) in FIG. 12 shows the surface state of an iron plate, and (B) in FIG. 12 shows a photograph of the state after polyaniline is applied to the surface of the iron plate shown in (A) of FIG. 9 and a chlorine spray test is carried out to promote corrosion by spraying a 0.5M NaCl solution to test the corrosion resistance. In the photograph of (B) in FIG. 12, it can be confirmed that the portion coated with polyaniline is not corroded at all, and it can be confirmed that the uncoated portion has undergone considerable corrosion.

[0075] In addition, for the electrode wire according to the present invention, it is also possible to apply a semiconducting polymer or an insulating polymer to the surface of the alloy layer. The semiconducting polymer and the insulating polymer stabilize the amplitude of the discharge current in the normal state, so that the height, width, rise time, fall time, etc. of the discharge pulse are stabilized, further improving the surface roughness and accuracy of the workpiece.

[0076] In addition, at least one of an oxide layer, a conductive polymer, a semiconducting polymer, and an insulating polymer can be applied to the surface of the alloy layer, or two or more of these can be applied.

[0077] The technical configuration of the electrode wire for electrical discharge machining of the present invention described above is not limited to the content of the mode for carrying out the invention, and can be variously modified within the range not departing from the technical idea and object of the present invention.

Industrial Applicability

[0078] The present invention is used for an electrode wire for electrical discharge machining in which the generation of fine chips is minimized during electrical discharge machining, so that no re-discharge occurs, the machining speed is improved, and the surface roughness of the workpiece is greatly improved.

Claims

1. A core wire made of a first metal, including an alloy layer formed on the outer periphery of the core wire by mutual diffusion of a second metal plated on the outer surface of the core wire and the core wire, wherein the alloy layer comprises a portion consisting of an α phase + β' phase, and includes grains of the β' phase formed on the outer periphery of the portion consisting of the α phase + β' phase, cracks are formed on the surface of the alloy layer, pinholes are further formed on the surface of the alloy layer, and the surface layer of the pinholes consists of at least one of a γ phase + ε phase and an ε phase, characterized in that it is an electrode wire for electrical discharge machining.

2. A core wire made of a first metal, including an alloy layer formed on the outer periphery of the core wire by mutual diffusion of a second metal plated on the outer surface of the core wire and the core wire, wherein the alloy layer comprises a portion consisting of an α phase + β' phase, and includes grains of the β' phase formed on the outer periphery of the portion consisting of the α phase + β' phase, cracks are formed on the surface of the alloy layer, a fine space in the form of a cave dug deeper than the cracks from the surface toward the core wire side is further formed in the alloy layer, and the surface layer of the portion having the fine space in the form of the cave consists of at least one of a γ phase + ε phase and an ε phase, characterized in that it is an electrode wire for electrical discharge machining.

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