Electrode wire for wire electric discharge machining

Abstract

To provide an electrode wire for wire electric discharge machining that can achieve both machining speed and surface accuracy of a workpiece in the wire electric discharge machining.SOLUTION: In one aspect of the invention, an electrode wire 1 for wire electric discharge machining comprises brass containing 43 mass% or less of zinc (Zn) and having an α-phase and a β-phase, where the component ratio of the α-phase in the brass is greater than 50 vol.% and less than or equal to 55 vol.%.SELECTED DRAWING: Figure 2

Description

[Technical Field]

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

[0002] Conventionally, an electrode wire for wire electrical discharge machining made of brass has been known (see Patent Document 1). The electrode wire for wire electrical discharge machining described in Patent Document 1 is made of brass containing 41 to 60 weight % Zn, and its composition is in a region where the β phase is the main component. This configuration is said to improve the properties of the brass wire, enabling improved strength, improved electrical discharge characteristics, and improved wiredrawability. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 9-11048 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the properties of brass electrode wires for wire EDM change depending on the Zn content, so it is necessary to optimize the Zn content and the ratio of the intermetallic compound phase, which changes accordingly, depending on the properties required for the desired machining.

[0005] An object of the present invention is to provide an electrode wire for wire electric discharge machining that can achieve both high machining speed and high surface precision of the workpiece in wire electric discharge machining. [Means for solving the problem]

[0006] The present invention aims to solve the above problems, 42% by mass or more, Provided is an electrode wire for wire electric discharge machining, which is made of brass containing less than 43 mass% zinc (Zn) and having α phase and β phase, and the component ratio of the α phase in the brass is greater than 50 volume% and not more than 55 volume%. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide an electrode wire for wire electric discharge machining that can achieve both high machining speed in wire electric discharge machining and high surface precision of the workpiece. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic diagram showing how a flat workpiece is machined by wire electric discharge machining. [Figure 2] 2(a) to 2(c) are images of the cross section of the electrode wire according to the example observed with a microscope. [Figure 3] 3(a) to 3(c) are images of the cross section of the electrode wire according to the comparative example observed with a microscope. [Figure 4] FIG. 4 is a perspective view of a rectangular parallelepiped sample piece cut out for the electrical discharge machining evaluation. DETAILED DESCRIPTION OF THE INVENTION

[0009] Figure 1 is a schematic diagram showing how a flat workpiece is machined by wire electric discharge machining. In wire electric discharge machining, as shown in Figure 1, a pulse voltage is applied between a wire electric discharge machining electrode wire 1 and a workpiece 2 made of a metal material by a machining power supply 3, and while an electric discharge is 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 wound up and moved like a jigsaw, and the workpiece 2 is two-dimensionally machined into a pre-programmed shape.

[0010] (Structure of electrode wire for wire electric discharge machining) The wire electric discharge machining electrode wire 1 according to the embodiment of the present invention is made of brass containing 43 mass % or less of zinc (Zn) and having α-phase and β-phase, and the α-phase component ratio in the brass is greater than 50 volume % and less than 55 volume %. Note that the components other than the α-phase of the brass constituting the wire electric discharge machining electrode wire 1 are almost entirely β-phase.

[0011] Brass is a copper alloy containing zinc, and the intermetallic compound phase changes depending on the zinc content. When the zinc content is low, the α phase is dominant, but when the zinc content exceeds 40% by mass, the α phase component ratio decreases rapidly, and at 45% by mass or more, the α phase almost disappears. Up to a zinc content of 45% by mass, the α phase and β phase coexist, and a wire EDM electrode wire 1 with a zinc content of 43% by mass or less contains both the α phase and the β phase. The zinc content of the wire EDM electrode wire 1 is set to 43% by mass or less to increase the α phase component ratio to more than 50% by volume.

[0012] The surface precision of the workpiece 2 is affected by the dimensional precision and surface smoothness of the wire electric discharge machining electrode wire 1, but also by the material. To facilitate the generation of discharge sparks between the workpiece 2 and the wire electric discharge machining electrode wire 1 and improve the surface precision of the workpiece 2, the zinc content of the wire electric discharge machining electrode wire 1 is preferably greater than 40% by mass, and more preferably 42% by mass or greater.

[0013] When the α-phase component ratio is greater than 50% by volume, the wire electric discharge machining electrode wire 1 is less likely to crack during wire drawing, resulting in less frequent wire breakage. Furthermore, when the α-phase component ratio is greater than 50% by volume but not greater than 55% by volume, the effect of reducing the directional variation in the surface roughness of the workpiece 2 is achieved. Therefore, the α-phase component ratio of the brass constituting the wire electric discharge machining electrode wire 1 is preferably greater than 50% by volume but not greater than 55% by volume. In particular, when the wire electric discharge machining electrode wire 1 has a zinc content of 42% by mass or more but not greater than 43% by mass and the α-phase component ratio of the brass constituting the wire electric discharge machining electrode wire 1 is greater than 50% by volume but not greater than 55% by volume, the wire electric discharge machining electrode wire 1 can achieve improved electrical discharge performance compared to a wire electric discharge machining electrode wire with a zinc content of 40% by mass or less. This improves both the surface precision and the machining speed when machining a workpiece 2 having a thickness of 20 mm to 100 mm.

[0014] Although the surface precision of the workpiece 2 can be improved by increasing the number of times of machining, the more the number of times of machining, the longer the machining time and the amount of wire EDM electrode wire 1 consumed, resulting in increased costs. The wire EDM electrode wire 1 can improve the surface precision of the workpiece 2 without increasing the number of times of machining. Also, the machined surface of the workpiece 2 is sometimes polished to obtain a mirror finish after EDM, but the use of the wire EDM electrode wire 1 can improve the surface precision of the workpiece 2, potentially shortening the working time for the additional polishing process.

[0015] The outer diameter of the wire electric discharge machining electrode wire 1 is, for example, 0.10 mm or more and 0.45 mm or less. The tensile strength (TS) of the wire electric discharge machining electrode wire 1 is 900 MPa or more and 1500 MPa or less, and the elongation (EL) is, for example, 0.4% or more and 10.0% or less when the outer diameter is within the above range.

[0016] The tensile strength (TS) of the wire EDM electrode wire 1 was measured using a universal material testing machine RTC-1150A manufactured by Orientec Co., Ltd. as the measuring device, according to the following procedure: (1) First, a wire EDM electrode wire 1 of a predetermined length was prepared as a sample. (2) Both ends of the sample were fixed to the measuring device, and the sample was held in a straight line. (3) In this state, one end of the sample was pulled at a constant speed of 50 mm / min. (4) The maximum load at which the sample broke was measured (load range: 100 N). (5) The breaking load was divided by the cross-sectional area of ​​the sample to calculate the tensile strength.

[0017] The elongation (EL) of the wire electric discharge machining electrode wire 1 was measured using the same measuring device as that used to measure the tensile strength (TS) and in the same procedures as those described above 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.

[0018] (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 an outer diameter of 0.25 mm will be described below.

[0019] First, a brass wire with an outer diameter of 0.90 mm before drawing is passed through a wire drawing die installed in a wire drawing machine and drawn at a predetermined speed (e.g., 1000 m / min or higher). At this time, the drawn brass wire is annealed using an annealer to remove strain accumulated in the brass wire due to the drawing process. The annealing to remove strain involves annealing the drawn brass wire under heating conditions (e.g., for a short time of a few seconds) that do not change the α-phase component ratio of the drawn brass wire. After drawing, the brass wire with an outer diameter of 0.25 mm is wound around a drum as the wire EDM electrode wire 1. The α-phase component ratio can be controlled by appropriately changing the manufacturing conditions (e.g., the cooling rate during casting) used to obtain the undrawn brass wire.

[0020] (Evaluation of electrode wires for wire electrical discharge machining) As an example of the wire electric discharge machining electrode wire 1 according to the present invention, an electrode wire made of brass with a zinc content of 42.2 mass% (copper content of 57.8 mass%) and an α-phase component ratio of 51 volume% was prepared by the above-described manufacturing method, and as a comparative example, an electrode wire made of brass with a zinc content of 42.44 mass% (copper content of 57.56 mass%) and an α-phase component ratio of 47 volume% was prepared and evaluated. The comparative example is HBZ-B wire manufactured by Hitachi Metals, Ltd., which has superior surface precision and machining accuracy compared to general-purpose wire electric discharge machining electrode wires.

[0021] The α-phase component ratios of the electrode wires according to the examples and comparative examples were determined by observing the entire cross section of the respective base materials, brass wires with an outer diameter of 0.90 mm. The α-phase component ratios and β-phase component ratios of the electrode wires of the present invention do not change due to annealing performed after wiredrawing of the brass wire, which is the base material of the electrode wire, or due to wiredrawing of the brass wire. Therefore, the α-phase component ratios of the electrode wires according to the examples and comparative examples can be said to be equal to the α-phase component ratios of the respective base materials, brass wires, which are 51% by volume and 47% by volume, respectively.

[0022] Figures 2(a) and 3(a) are microscope images of the cross sections of the brass wires that serve as the base material for the electrode wires of the example and comparative example, respectively. The entire cross sections of these brass wires were subjected to ion milling to observe the metal structure. Figures 2(b) and 3(b) are enlarged images of the areas enclosed by squares in Figures 2(a) and 3(a), including the centers of the electrode wires. Figures 2(c) and 3(c) are enlarged images of the areas enclosed by squares in Figures 2(b) and 3(b), respectively.

[0023] The darker areas in Figures 2(c) and 3(c) are the α phase, and the lighter areas are the β phase. The images of Figures 2(c) and 3(c) were binarized, and the area ratio of the α phase parts was automatically measured to calculate the α phase component ratio. It was confirmed that the α phase component ratios of the brass wire according to the example and the comparative example were 51 volume % and 47 volume %, respectively. By using this calculation method and observing the entire cross section of the brass wire shown in Figures 2(a) and 3(a), the α phase component ratio of the brass wire (i.e., the α phase component ratio of the electrode wire) was determined.

[0024] Next, an electric discharge machining evaluation was carried out using the electrode wires according to the example and the comparative example, each using an electrode wire with an outer diameter of 0.25 mm.

[0025] In this electrical discharge machining evaluation, a ROBOCUT α-0iE manufactured by FANUC CORPORATION was used as a wire electrical discharge machine, and a 10 x 10 mm planar sample piece 20 was cut by electrical discharge machining from a 20 mm thick flat plate material made of SKD-11 as the workpiece 2. The machining was performed three times, under standard conditions from the first cut to the third cut.

[0026] Figure 4 is a perspective view of a rectangular parallelepiped sample piece 20 cut out for electrical discharge machining evaluation. The X direction shown in Figure 4 is a direction parallel to the planar direction of the workpiece 2, i.e., a direction perpendicular to the wire feed direction, and the Y direction is a direction parallel to the thickness direction of the workpiece 2, i.e., a direction parallel to the wire feed direction. Here, the wire feed direction is the direction in which an electrode wire (wire) is fed by a wire electrical discharge machine in wire electrical discharge machining.

[0027] The surface roughness Ra (arithmetic mean roughness), Rmax (maximum height), and Rz (ten-point mean roughness) of the machined surface 21 of the sample piece 20 cut out using the electrode wires of the example and comparative example were measured. Here, the machined surface 21 of the sample piece 20 is a surface parallel to the thickness direction of the workpiece 2 along the Y direction.

[0028] The surface roughness Ra, Rmax, and Rz were measured using a surface roughness measuring instrument SE-3H manufactured by Kosaka Laboratory Co., Ltd., according to the following procedure: (1) Place the workpiece 2 on the surface roughness measuring instrument. (2) Lower the stylus so that it comes into contact with the workpiece 2. (3) Scan the stylus across the surface of the workpiece 2 three times in each of the X and Y directions. The scanning length of the stylus was set to 5 mm.

[0029] The average values ​​of the three Ra measurements, three Rmax measurements, and three Rz measurements obtained in the X direction were taken as the Ra, Rmax, and Rz values ​​in the X direction. Similarly, the average values ​​of the three Ra measurements, three Rmax measurements, and three Rz measurements obtained in the Y direction were taken as the Ra, Rmax, and Rz values ​​in the Y direction.

[0030] Table 1 below shows the machining speeds obtained in the electrical discharge machining evaluation using the electrode wires according to the examples and comparative examples, and the values ​​of Ra, Rmax, and Rz in the X and Y directions of the machined surface 21 of the sample piece 20.

[0031] [Table 1]

[0032] According to Table 1, the difference in Ra between the X and Y directions in the comparative example was 0.07 μm, while the difference in Ra between the X and Y directions in the example was 0.01 μm. Also, the difference in Rmax between the X and Y directions in the comparative example was 3.00 μm, while the difference in Rmax between the X and Y directions in the example was 0.46 μm. Also, the difference in Rz between the X and Y directions in the comparative example was 1.54 μm, while the difference in Rmax between the X and Y directions in the example was 0.13 μm.

[0033] As described above, the difference between the X- and Y-direction values ​​of Ra, Rmax, and Rz in the Example was smaller than that in the Comparative Example, confirming that the variation in surface roughness in each direction was reduced. This is thought to be due to the difference in the α-phase component ratio between the electrode wire of the Example and the electrode wire of the Comparative Example. That is, in the electrode wire of the Example, the α-phase component ratio is greater than 50 volume % and less than 55 volume %, and therefore the machined surface 21 of the test piece 20 is thought to be machined by fine discharge sparks.

[0034] As shown in Table 1, there was no significant difference in the machining speed between the Examples and the Comparative Examples. That is, it was confirmed that the electrode wire according to the Examples improved the surface precision of the workpiece while maintaining the machining speed, compared to the electrode wire according to the Comparative Examples, which had excellent surface precision and machining precision.

[0035] Furthermore, from the above results, when a workpiece 2 made of SKD-11 is machined using a wire electric discharge machining electrode wire 1 that contains more than 40 mass% and not more than 43 mass% zinc (Zn), is made of brass having α phase and β phase, and the α phase component ratio in the brass is more than 50 vol% and not more than 55 vol%, it can be expected that a surface precision with a difference in Ra between the X direction and the Y direction of 0.02 μm or less can be obtained.

[0036] Furthermore, when the elongation (EL) of the electrode wire according to the example and the electrode wire according to the comparative example was measured using the above method, the elongation (EL) of the electrode wire according to the example was 2.6%, and the elongation (EL) of the electrode wire according to the comparative example was 1.8%.

[0037] (Effects of the embodiment) According to the above embodiment of the present invention, by using a wire electric discharge machining electrode wire 1 made of brass containing 43 mass % or less of zinc (Zn) and having α phase and β phase, in which the α phase component ratio in the brass is greater than 50 volume % and less than 55 volume %, it is possible to achieve both machining speed in wire electric discharge machining and surface accuracy of the workpiece.

[0038] (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.

[0039] [1] An electrode wire (1) for wire electric discharge machining, which contains 43 mass% or less of zinc (Zn) and is made of brass having an α phase and a β phase, and the component ratio of the α phase in the brass is greater than 50 volume% and less than 55 volume%.

[0040] [2] The electrode wire (1) for wire electric discharge machining according to the above [1], which has an elongation (EL) of 2.0% or more when the outer diameter is 0.25 mm.

[0041] [3] The electrode wire (1) for wire electric discharge machining according to the above [1], wherein the zinc contained in the brass is 42 mass % or more.

[0042] 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]

[0043] 1. Electrode wire for wire electric discharge machining 2 Workpiece 3 Processing power supply

Claims

1. A brass containing 42% by mass or more and 43% by mass or less of zinc (Zn) and having α phase and β phase, The component ratio of the α phase in the brass is greater than 50% by volume and less than 55% by volume, Electrode wire for wire electric discharge machining.

2. The elongation (EL) when the outer diameter is 0.25 mm is 2.0% or more. The electrode wire for wire electric discharge machining according to claim 1.

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