Electrode wire for wire electric discharge machining

Abstract

To provide an electrode wire for wire discharge machining where a coating layer containing zinc is provided around a core material, which can suppress reduction in machining speed even when a part of the coating layer disappears due to discharge during wire discharge machining.SOLUTION: An electrode wire 1 for wire discharge machining includes a core material 11 composed of brass having zinc (Zn) concentration of more than 40 mass%, and a coating layer 12 which is provided around the core material 11 and has zinc concentration higher than that of the core material 11.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an electrode wire for wire electric discharge machining. [Background technology]

[0002] Conventionally, there has been known a wire electric discharge machining electrode wire in which the outer periphery of a core material made of copper or a copper alloy is coated with a coating layer containing zinc (see, for example, Patent Document 1). Zinc is more likely to generate discharge than copper due to its larger work function. Therefore, in general, when a wire electric discharge machining electrode wire in which a coating layer containing zinc is provided around the core material is used, the machining speed of wire electric discharge machining is faster than when a wire electric discharge machining electrode wire made only of a core material is used. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2018-99773 Summary of the Invention [Problem to be solved by the invention]

[0004] In wire electric discharge machining, the electrode wire for wire electric discharge machining is worn away by discharge, so to prevent breakage, the electrode wire for wire electric discharge machining is always fed during machining so that discharge occurs from a new portion.

[0005] However, when the workpiece is thick, even if wire breakage can be prevented by feeding the wire-cutting electrode during machining, the zinc-containing coating layer may be lost due to electrical discharge during machining. In this case, part of the workpiece is machined by electrical discharge generated between the wire and the exposed core material, resulting in a decrease in the machining speed.

[0006] An object of the present invention is to provide an electrode wire for wire electrical discharge machining, which has a core material and a coating layer containing zinc provided around it, and which can suppress a decrease in machining speed even if part of the coating layer is lost due to discharge during wire electrical discharge machining. [Means for solving the problem]

[0007] In order to solve the above problems, the present invention provides a method for manufacturing a ceramic ceramic ceramic having a zinc (Zn) concentration of more than 40 mass %. <43% by mass or less The device comprises a core material made of brass and a coating layer provided around the core material and having a higher zinc concentration than the core material. An electrode wire , The electrode wire is subjected to a heat treatment at a temperature higher than 100°C and not higher than 170°C for not less than 1 hour after wiredrawing, so that the coating layer has a higher zinc concentration at the surface than at the interior, and is formed so that the zinc concentration at the surface is 80% by mass or more and the zinc concentration at the interior is 60% by mass or more. Provides an electrode wire for wire electric discharge machining. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide an electrode wire for wire electrical discharge machining, which has a coating layer containing zinc provided around a core material, and which can suppress a decrease in machining speed even if part of the coating layer is lost due to discharge during wire electrical discharge machining. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a cross-sectional view in the radial direction of an electrode wire for wire electric discharge machining according to an embodiment of the present invention. [Figure 2] Figure 2(a) is a schematic diagram showing how a flat workpiece is machined by wire electric discharge machining, and Figure 2(b) is a schematic diagram showing an enlarged view of the area around the machined part of the workpiece. [Figure 3] FIG. 3 is an SEM observation image of a cross section in the radial direction of the base material according to the example. [Figure 4] 4(a) and (b) are SEM observation images of the surface and the radial cross section of the wire electrode for wire electric discharge machining according to the example, respectively. [Figure 5] FIG. 5 is a perspective view of a rectangular parallelepiped sample piece cut out for the electrical discharge machining evaluation. DETAILED DESCRIPTION OF THE INVENTION

[0010] (Structure of electrode wire for wire electric discharge machining) 1 is a radial cross-sectional view of a wire electrical discharge machining electrode wire 1 according to an embodiment of the present invention. The wire electrical discharge machining electrode wire 1 includes a core material 11 made of brass having a zinc (Zn) concentration of more than 40 mass %, and a coating layer 12 provided around the core material 11 and having a higher zinc concentration than the core material 11.

[0011] Core material 11 is a metal wire made of brass with a zinc concentration of more than 40% by mass, i.e., an alloy containing more than 40% by mass of zinc with the remainder being copper, and has a higher zinc concentration than the core materials of conventional wire electric discharge machining electrode wires. Because zinc is more likely to generate electrical discharge than copper due to its larger work function, core material 11 is more likely to generate electrical discharge between itself and the workpiece during wire electric discharge machining than the core materials of conventional wire electric discharge machining electrode wires.

[0012] On the other hand, the higher the zinc concentration of the core material 11, the more difficult it is to maintain strength, making it more difficult to manufacture. For this reason, the zinc concentration of the core material 11 is set to, for example, 43% or less. The inventors of the present application have confirmed that when the zinc concentration of the core material 11 is set to 43% by mass, it is possible to manufacture a core material 11 with a wire diameter of 0.1 mm or more. Although it may be possible to manufacture a core material 11 with a wire diameter of less than 0.1 mm, it is believed that manufacturing would be more difficult due to the low strength resulting from the small wire diameter.

[0013] The coating layer 12 is a layer containing copper (Cu) and has a zinc film as its base material. The coating layer 12 is formed, for example, by plating the surface of the core material 11 with zinc, and copper diffuses from the core material 11 into the coating layer 12 during the manufacturing process of the wire electrical discharge machining electrode wire 1. When the coating layer 12 is formed by diffusing copper into a pure zinc layer in this way, the zinc concentration on the surface of the coating layer 12 is, for example, 80 mass % or more.

[0014] Furthermore, in the manufacturing process of the wire electric discharge machining electrode wire 1, when heat treatment is performed after wire drawing, the zinc concentration on the surface of the coating layer 12 becomes higher than the zinc concentration inside the coating layer 12. The zinc concentration inside the coating layer 12 is, for example, 60 mass % or more, and the zinc concentration on the surface of the coating layer 12 is, for example, 80 mass % or more. When the coating layer 12 has such a zinc concentration, it becomes easier to prevent a decrease in the machining speed.

[0015] Figure 2(a) is a schematic diagram showing how a flat workpiece 2 is machined by wire electric discharge machining. In wire electric discharge machining, as shown in Figure 2(a), a pulse voltage is applied from a machining power supply 3 between a wire electric discharge machining electrode wire 1 and a workpiece 2 made of a metal material such as SKD-11. With an electric discharge generated between the wire electric discharge machining electrode wire 1 and the workpiece 2 made of a metal material, the wire electric discharge machining electrode wire 1 is moved relative to the workpiece 2 like a jigsaw while being fed, and the workpiece 2 is two-dimensionally machined into a pre-programmed shape.

[0016] Fig. 2(b) is a schematic diagram showing an enlarged view of the periphery of the machined portion of the workpiece 2. When the thickness of the workpiece 2 is large, as shown in Fig. 2(b), part of the coating layer 12 may be lost due to discharge during machining of the workpiece 2. Here, the thickness of the workpiece 2 refers to the dimension of the workpiece 2 in the vertical direction in Figs. 2(a) and 2(b).

[0017] In the example shown in Figure 2(b), machining is performed while the wire electric discharge machining electrode wire 1 is fed downward, but the part of the coating layer 12 where the discharge begins disappears before passing through the bottom of the workpiece 2, so the lower part of the workpiece 2 is machined by the discharge that occurs between it and the exposed core material 11.

[0018] Because the zinc concentration in the core material 11 is lower than the zinc concentration in the coating layer 12, discharge is less likely to occur between the workpiece 2 and the core material 11 than between the workpiece 2 and the coating layer 12. However, as described above, because the core material 11 has a higher zinc concentration than usual, even if discharge occurs between the workpiece 2 and the exposed core material 11 after the coating layer 12 has disappeared, a decrease in the amount of discharge can be suppressed, and thereby a decrease in the processing speed of the workpiece 2 can be suppressed.

[0019] The wire diameter of the wire electric discharge machining electrode wire 1 is, for example, 0.1 mm to 0.4 mm, and the thickness of the coating layer 12 is, for example, 1.0 μm to 5.0 μm. The wire electric discharge machining electrode wire 1 also has a tensile strength (TS) of 750 MPa to 1500 MPa, an elongation (EL) of 0.4% to 5.0%, and an electrical conductivity of 20% to 30%.

[0020] Here, the tensile strength (TS) of the wire EDM electrode wire 1 is a value measured using a tension / compression testing machine SV-301-EL manufactured by Imada Manufacturing Co., Ltd. as the measuring device, according to the following procedure: (1) First, a wire EDM electrode wire 1 of a predetermined length is prepared as a sample. (2) Both ends of the sample are fixed to the measuring device to hold the sample in a straight line. (3) In this state, one end of the sample is pulled at a constant speed of 50 mm / min. (4) The maximum load when the sample breaks is measured (load range: 100 N). (5) The breaking load is divided by the cross-sectional area of ​​the sample to calculate the tensile strength.

[0021] The elongation (EL) of the wire electric discharge machining electrode wire 1 was measured using the same measuring device as that used for the tensile strength (TS) described above, and was performed using the same procedures as those described in (1) to (3). The length between the gauge points when the sample broke was measured, and the elongation was calculated using the formula "EL = 100 × (L - L0) / L0." Here, L is the length between the gauge points when the sample broke, and L0 is the length between the gauge points before the sample was stretched.

[0022] The electrical conductivity of the electrode wire 1 for wire electrical discharge machining is a value measured by a method conforming to JIS H 0505. Here, 8.89 was used as the specific gravity when calculating the electrical conductivity.

[0023] (Method of manufacturing electrode wire for wire electric discharge machining) As an example of a method for manufacturing the wire electric discharge machining electrode wire 1, an example of a method for manufacturing the wire electric discharge machining electrode wire 1 having a wire diameter of 0.3 mm will be described below.

[0024] First, a base material of the wire electric discharge machining electrode wire 1 before wire drawing is prepared, the base material having a wire diameter of 0.6 to 1.2 mm. The coating layer of the base material is, for example, a zinc film formed by zinc plating on the surface of the brass wire core. The base material is prepared in an amount appropriate for the purpose, for example, 50 kg.

[0025] Next, if the base material passes inspections such as property surveys and visual and cross-sectional observations, it is passed through a wire-drawing die attached to a wire-drawing machine and drawn at a speed of, for example, about 700 m / min until the wire diameter is 0.3 mm. This base material drawn into wire is called drawn wire material.

[0026] Next, the drawn wire is heat-treated using a furnace to obtain the wire electrical discharge machining electrode wire 1. This heat treatment is preferably carried out in order to suppress the generation of zinc dust from the coating layer 12 when the wire electrical discharge machining electrode wire 1 is used. Pure zinc is brittle and prone to generating zinc dust, so by performing the heat treatment to diffuse copper from the core material 11 into the coating layer 12, the generation of zinc dust from the coating layer 12 can be suppressed.

[0027] The heat treatment conditions are, for example, 150°C for 1.5 hours, but the temperature may be set lower to improve the straightness of the wire electric discharge machining electrode wire 1. Specifically, the heat treatment conditions can be set within the range of, for example, a temperature above 100°C and 170°C or less, and a time of 1 hour or more.

[0028] (Evaluation of electrode wires for wire electrical discharge machining) As an example of the electrode wire 1 for wire electric discharge machining according to the present invention, an electrode wire having a wire diameter of approximately 0.3 mm and having a coating layer 12 provided on the surface of a core material 11 made of brass (Cu:Zn=57:43) with a zinc concentration of 43 mass % was manufactured and evaluated.

[0029] First, a base material for the wire electric discharge machining electrode wire 1 according to the example was prepared and inspected. Here, the core material of the base material was a brass wire with a wire diameter of 0.9 mm made of brass with a zinc concentration of 43 mass %, and the coating layer was a zinc plating film with a thickness of 8±2 μm.

[0030] The appearance of the base material was observed using a microscope and SEM, and it was confirmed that there were no abnormal scratches or peeling of the zinc plating.

[0031] 3 is an SEM image of a radial cross section of the base material 100 according to the example. The cross section of the base material 100 has been subjected to an etching process to observe the metal structure. The convex portions 110a of the cross section of the core material 110 revealed by the etching process are the α phase of brass, and the concave portions 110b are the β phase of brass.

[0032] The results of elemental analysis by EDX on analysis areas A1 to A4 of the cross section shown in Figure 3 and on the surface of coating layer 120 (analysis area A0) are shown in Table 1. "CuK" and "ZnK" in Table 1 are the copper concentration and zinc concentration, respectively, analyzed using K rays as characteristic X-rays. Also, "mass%" and "at%" in Table 1 are mass% and atomic%, respectively.

[0033] [Table 1]

[0034] The results of elemental analysis of analysis areas A0 and A1 confirmed that the coating layer 120, which is a zinc plating film, was formed without any problems. The analysis results of analysis areas A3 and A4 indicate the element concentrations of the β and α phases of the core material 110, respectively.

[0035] 3, a layer 110c that is not separated into α-phase and β-phase can be seen on the surface of the core material 110. The composition of this layer 110c is unclear, but the results of elemental analysis by analysis section A2 indicate that it may be composed of β-phase. Furthermore, this layer 110c may be a layer that was formed during the wire drawing or zinc plating process of the core material 110.

[0036] Table 2 below shows the target values ​​and evaluation results of the mechanical properties of the base material 100 according to the example. The "wire diameter," "coating layer thickness," "tensile strength," "elongation," and "electrical conductivity" in Table 2 respectively represent the wire diameter of the base material 100, the thickness of the coating layer 120, the tensile strength (TS) of the base material 100, the elongation (EL) of the base material 100, and the electrical conductivity of the base material 100. The tensile strength, elongation, and electrical conductivity in Table 2 were measured by the methods described above. This evaluation of the mechanical properties was performed on three base materials 100.

[0037] [Table 2]

[0038] As shown in Table 2, it was confirmed that the tensile strength, elongation, and electrical conductivity of the base material 100 according to the example all satisfied the target values.

[0039] Next, the base material 100 was subjected to drawing, and the resulting drawn wire material having a wire diameter of 0.3 mm was subjected to heat treatment at 150° C. for 1.5 hours to produce an electrode wire 1 for wire electrical discharge machining.

[0040] 4(a) and (b) are SEM images of the surface and radial cross section of the wire electrical discharge machining electrode wire 1 according to the example, respectively. The image in Fig. 4(a) confirms that there are no cracks on the surface of the coating layer 12. It has been confirmed that cracks occur on the surface of the coating layer 12 when wiredrawing is performed after heat treatment, and it is believed that the heat treatment performed on the wire electrical discharge machining electrode wire 1 according to the example after wiredrawing prevented the occurrence of surface cracks.

[0041] The results of elemental analysis by EDX on the analyzed portion B1 on the surface of the coating layer 12 shown in Figure 4(a) and on the surface of the coating layer of the drawn wire material, which is the electrode wire 1 for wire electric discharge machining before heat treatment, are shown in Table 3. In Table 3, the element concentrations on the surface of the coating layer of the drawn wire material are represented as "before heat treatment."

[0042] [Table 3]

[0043] The results of the elemental analysis shown in Table 3 confirmed that copper had diffused into the coating layer 12 due to the heat treatment.

[0044] The results of elemental analysis by EDX on analyzed portions B2, B3, and B4 of the cross section of electrode wire 1 for wire electric discharge machining shown in FIG. 4(b) are shown in Table 4 below.

[0045] [Table 4]

[0046] The element concentration values ​​of analysis part B1 and analysis parts B2 and B3 confirmed that the zinc concentration was higher on the surface of coating layer 12 than inside coating layer 12. This is thought to be because the amount of diffused copper is greater inside coating layer 12, which is closer to core material 11. In addition, the element concentration values ​​of analysis parts B2 and B3 and analysis part B4 confirmed that the zinc concentration inside coating layer 12 was also sufficiently higher than the zinc concentration in core material 11.

[0047] Table 5 below shows the target values ​​and evaluation results of the mechanical properties of the wire electrical discharge machining electrode wire 1 according to the example. The "wire diameter," "tensile strength," "elongation," and "electrical conductivity" in Table 5 respectively represent the wire diameter of the wire electrical discharge machining electrode wire 1, the tensile strength (TS) of the wire electrical discharge machining electrode wire 1, the elongation (EL) of the wire electrical discharge machining electrode wire 1, and the electrical conductivity of the wire electrical discharge machining electrode wire 1. The tensile strength, elongation, and electrical conductivity in Table 5 were measured using the methods described above. This evaluation of the mechanical properties was performed on three wire electrical discharge machining electrode wires 1.

[0048] [Table 5]

[0049] As shown in Table 5, it was confirmed that the tensile strength, elongation, and electrical conductivity of the electrode wire 1 for wire electric discharge machining according to the example all satisfied the target values.

[0050] Next, an electric discharge machining evaluation was carried out using the electrode wire 1 for wire electric discharge machining according to the example (hereinafter referred to as the electrode wire according to the example).An electric discharge machining evaluation was also carried out using an HBZ-U(N) wire made by Hitachi Metals, Ltd., which is made of brass with a zinc concentration of 40 mass % (hereinafter referred to as the electrode wire according to the comparative example), as the electrode wire for wire electric discharge machining according to the comparative example.

[0051] In this electrical discharge machining evaluation, a ROBOCUT α-0iE manufactured by FANUC CORPORATION was used as the wire electrical discharge machine, and a 10 x 10 mm planar specimen 20 was cut out by electrical discharge machining from a flat plate material made of SKD-11 as the workpiece 2. Note that automatic connection of the electrode wire according to the example was able to be performed without any problems using the wire electrical discharge machine.

[0052] FIG. 5 is a perspective view of a rectangular parallelepiped sample piece 20 cut out for electrical discharge machining evaluation. The X direction shown in FIG. 5 is parallel to the planar direction of the workpiece 2, i.e., perpendicular to the wire feed direction, and the Y direction is parallel to the thickness direction of the workpiece 2, i.e., parallel to the wire feed direction. Here, the wire feed direction is the direction in which the electrode wire (wire) is fed by the wire electrical discharge machine in wire electrical discharge machining. The sample piece 20 shown in FIG. 5 was cut out from a workpiece 2 having a thickness of 20 mm. However, if it were cut out from a workpiece 2 having a thickness of 50 mm, its thickness, i.e., the dimension in the Y direction, would be 50 mm.

[0053] Table 6 below shows the machining speeds obtained in the electrical discharge machining using the electrode wires of the example and comparative example. The "plate thickness" in Table 6 refers to the thickness of the flat workpiece 2 used in the electrical discharge machining evaluation. "1st" in Table 6 indicates that only the first cut was performed, indicating that the number of machining passes was one. "3rd" in Table 6 indicates that the first, second, and third cuts were performed, indicating that the number of machining passes was three. The machining speed for "3rd" was calculated using the total machining time for the three passes. "Example" and "Comparative Example" in Table 6 indicate that the electrode wires used in the machining were the electrode wires of the example and the comparative example, respectively. The "ratio" in Table 6 refers to the ratio of the machining speed when the electrode wire of the example was used to the machining speed when the electrode wire of the comparative example was used.

[0054] [Table 6]

[0055] As shown in Table 6, it was confirmed that the machining speed when using the electrode wire of the Example was higher than the machining speed when using the electrode wire of the Comparative Example. Furthermore, the ratio of the machining speed to the Comparative Example was higher when the workpiece 2 was 50 mm thick than when the workpiece 2 was 20 mm thick. Based on these results, the electrode wire of the Comparative Example does not have a zinc-containing coating layer, and therefore does not experience a decrease in machining speed due to loss of the coating layer when the workpiece 2 is thick. Therefore, when using the electrode wire of the Example, it is believed that a high machining speed can be maintained even when the workpiece 2 is thick enough that part of the coating layer 12 is lost. Furthermore, the ratio of the machining speed to the Comparative Example was higher when the number of machining cycles was three than when the number of machining cycles was one.

[0056] Table 7 below shows the shape accuracy of the test piece 20 obtained by electrical discharge machining using the electrode wires of the example and comparative example. In Table 7, "Top" is the width in the X direction of the upper part of the test piece 20 in the Y direction, "Middle" is the width in the X direction of the central part of the test piece 20 in the Y direction, and "Bottom" is the width in the X direction of the lower part of the test piece 20 in the Y direction. Furthermore, "R" is the difference between the maximum and minimum values ​​of "Top," "Middle," and "Bottom," and can be used as an index of the variation in the width of the test piece 20 in the X direction.

[0057] [Table 7]

[0058] According to Table 7, the variation in width in the X direction of the test piece 20 when the electrode wire according to the example is used is almost the same as that when the electrode wire according to the comparative example is used, regardless of the processing conditions. From this result, it was confirmed that the shape accuracy of the test piece 20 when the electrode wire according to the example is used is the same as that when the electrode wire according to the comparative example is used.

[0059] (Effects of the embodiment) According to the above embodiment of the present invention, by using a wire electric discharge machining electrode wire 1 having a core material 11 made of brass with a zinc (Zn) concentration of more than 40 mass % and a coating layer 12 provided around the core material 11 and having a higher zinc concentration than the core material 11, it is possible to suppress a decrease in machining speed even if part of the coating layer 12 is lost due to discharge during wire electric discharge machining.

[0060] (Summary of the embodiment) Next, the technical ideas grasped from the above-described embodiments will be described by using the reference numerals and the like in the embodiments. However, the reference numerals and the like in the following description do not limit the components in the claims to the members and the like specifically shown in the embodiments.

[0061] [1] An electrode wire (1) for wire electrical discharge machining, comprising: a core material (11) made of brass having a zinc (Zn) concentration of greater than 40% by mass; and a coating layer (12) provided around the core material (11) and having a higher zinc concentration than the core material (11).

[0062] [2] The electrode wire (1) for wire electric discharge machining according to the above [1], wherein the zinc concentration of the core material (11) is 43 mass % or less.

[0063] [3] The electrode wire (1) for wire electric discharge machining according to the above [1] or [2], wherein the coating layer (12) has a higher zinc concentration on the surface than in the interior.

[0064] [4] The electrode wire (1) for wire electric discharge machining according to the above [1] or [2], wherein the coating layer (12) has a surface without cracks.

[0065] Although the embodiments of the present invention have been described above, the present invention is not limited to the above embodiments and various modifications can be made without departing from the spirit of the invention. Furthermore, the above embodiments do not limit the invention according to the claims. It should be noted that not all of the combinations of features described in the embodiments are necessarily essential to the means for solving the problems of the invention. [Explanation of symbols]

[0066] 1. Electrode wire for wire electric discharge machining 11 Core material 12 Covering layer 121 First Layer 122 Second Layer 2 Workpiece 20 sample pieces 3 Processing power supply

Claims

1. A core material made of brass having a zinc (Zn) concentration of more than 40% by mass and not more than 43% by mass; a coating layer provided around the core material and having a higher zinc concentration than the core material; An electrode wire comprising: The electrode wire is subjected to a heat treatment at a temperature higher than 100°C and not higher than 170°C for not less than 1 hour after wiredrawing, so that the coating layer has a higher zinc concentration at the surface than at the interior, and is formed so that the zinc concentration at the surface is 80% by mass or more and the zinc concentration at the interior is 60% by mass or more. Electrode wire for wire electrical discharge machining.

2. The coating layer has a crack-free surface formed after heat treatment. The electrode wire for wire electric discharge machining according to claim 1.

3. The thickness of the coating layer is 1.0 μm or more and 5.0 μm or less. The electrode wire for wire electric discharge machining according to claim 1 or 2.

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