Wire EDM electrode wire and method for manufacturing wire EDM electrode wire

Abstract

To provide an electrode wire for wire electric discharge machining having a coating layer made of brass with a high zinc concentration, the coating layer having a thickness suitable for high-speed machining, and a method for manufacturing the same.SOLUTION: An electrode wire 1 for wire electric discharge machining includes a core material 11 made of first brass having a zinc concentration larger than 40 mass%, and a coating layer 12 covering the core material 11. The coating layer 12 is made of a second brass having a zinc concentration larger than the zinc concentration of the first brass and equal to or larger than 44 mass% and equal to or smaller than 50 mass%, and a third brass having a zinc concentration larger than the zinc concentration of the second brass and exceeding 50 mass%, and a ratio of a thickness of the coating layer 12 to a diameter of the electrode wire 1 for wire electric discharge machining is equal to or larger than 2% and equal to or smaller than 20%.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an electrode wire for wire electrical discharge machining and a method for manufacturing an electrode wire for wire electrical discharge machining.

Background Art

[0002] Conventionally, an electrode wire for wire electrical discharge machining made of brass, which comprises a core material and a coating layer covering the periphery thereof and having a higher zinc concentration than the core material, is known (see Patent Document 1). Since zinc is more likely to generate discharge than copper due to the magnitude of its work function, by providing a coating layer with a high zinc concentration around the core material, the machining speed of wire electrical discharge machining can be increased as compared with the case where no coating layer is provided.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, the electrode wire for wire electrical discharge machining described in Patent Document 1 has a small ratio of the thickness of the coating layer to its diameter and a high consumption rate of the coating layer during machining, and thus is not suitable for high-speed machining.

[0005] An object of the present invention is to provide an electrode wire for wire electrical discharge machining provided with a coating layer made of brass having a high zinc concentration, the coating layer having a thickness suitable for high-speed machining, and a method for manufacturing the same.

Means for Solving the Problems

[0006] The present invention aims to solve the above problems and provides an electrode wire for wire electrical discharge machining comprising a core material made of a first brass having a zinc concentration greater than 40% by mass, and a coating layer covering the core material, wherein the coating layer consists of a second brass having a zinc concentration greater than that of the first brass and between 44% by mass and 50% by mass, and a third brass having a zinc concentration greater than that of the second brass and greater than 50% by mass, and the ratio of the thickness of the coating layer to the diameter of the electrode wire for wire electrical discharge machining is between 2% and 20%.

[0007] Furthermore, the present invention aims to solve the above problems and provides a method for manufacturing a wire electrical discharge machining electrode wire, comprising the steps of: heat-treating a linear material having a brass core and a zinc film or a brass film with a higher zinc concentration than the core to cover the core, thereby causing atomic diffusion between the core and the zinc film or the brass film to form a coating layer covering the core; and drawing the heat-treated linear material to process it into a wire electrical discharge machining electrode wire, wherein the core material is made of brass consisting of a first brass with a zinc concentration greater than 40% by mass, the coating layer is made of a second brass with a zinc concentration greater than that of the first brass and between 44% by mass and 50% by mass, and a third brass with a zinc concentration greater than that of the second brass and greater than 50% by mass, and the ratio of the thickness of the coating layer to the diameter of the wire electrical discharge machining electrode wire is between 2% and 20%. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a wire electrical discharge machining electrode wire having a coating layer made of brass with a high zinc concentration, wherein the coating layer has a thickness suitable for high-speed machining, and a method for manufacturing the same. [Brief explanation of the drawing]

[0009] [Figure 1]Figure 1 is a radial cross-sectional view of an electrode wire for wire electrical discharge machining according to an embodiment of the present invention. [Figure 2] Figure 2 is a schematic diagram showing how a flat workpiece is processed by wire electrical discharge machining. [Figure 3] Figures 3(a) and 3(b) show a microscope image of the radial cross-section of material A after heat treatment at 500°C for 1 hour, and a partially magnified image of the same. [Figure 4] Figures 4(a) and (b) show a microscope image of the radial cross-section of material B after heat treatment at 500°C for 1 hour, and a partially magnified image of the same. [Figure 5] Figures 5(a) and (b) show SEM images of the radial cross-section of material B after heat treatment at 400°C for 1 hour, and partially magnified images thereof. [Figure 6] Figures 6(a) and (b) show SEM images of the radial cross-section of material B after heat treatment at 500°C for 1 hour, and partially magnified images thereof. [Figure 7] Figures 7(a) and (b) show optical microscope images of the radial cross-section of a 0.3 mm diameter wire electrical discharge machining electrode wire obtained by drawing material A that has been heat-treated at 500°C for 1 hour, and partially magnified images thereof. [Figure 8] Figures 8(a) and (b) show optical microscope images of the radial cross-section of a 0.3 mm diameter wire electrical discharge machining electrode wire obtained by drawing material B, which has been heat-treated at 500°C for 1 hour, and partially magnified images thereof. [Modes for carrying out the invention]

[0010] (Configuration of electrode wires for wire electrical discharge machining) Figure 1 is a radial cross-sectional view of an electrode wire 1 for wire electrical discharge machining according to an embodiment of the present invention. The electrode wire 1 for wire electrical discharge machining comprises a core material 11 made of brass with a zinc (Zn) concentration greater than 40 mass%, and a coating layer 12 made of brass provided around the core material 11, having a zinc concentration higher than that of the core material 11 and between 44 mass% and 50 mass%.

[0011] Figure 2 is a schematic diagram showing the process of machining a flat workpiece 4 using wire electrical discharge machining. In wire electrical discharge machining, as shown in Figure 2, a pulse voltage is applied by a machining power supply 3 between the wire electrical discharge machining electrode wire 1 and the workpiece 4 made of a metal material such as SKD-11. While generating a discharge between the wire electrical discharge machining electrode wire 1 and the workpiece 4 made of a metal material, the wire electrical discharge machining electrode wire 1 is moved relative to the workpiece 4 like a hacksaw, thereby machining the workpiece 4 into a pre-programmed shape in two dimensions.

[0012] The electrode wire 1 for wire electrical discharge machining is an electrode wire for high-speed machining. In high-speed machining, a large current is passed through the electrode wire, so the rate of consumption of the coating layer is greater compared to normal machining. Therefore, in the electrode wire 1 for wire electrical discharge machining, the thickness of the coating layer 12 is made thicker than that of general-purpose electrode wires or electrode wires for high-precision machining in order to avoid the disappearance of the coating layer 12 during machining.

[0013] The diameter of the electrode wire 1 for wire electrical discharge machining is, for example, 0.1 mm or more and 0.3 mm or less. The ratio of the thickness of the coating layer 12 to the diameter of the electrode wire 1 is 2% or more and 20% or less. If the ratio of the thickness of the coating layer 12 to the diameter of the electrode wire 1 is 2% or more, the disappearance of the coating layer 12 during wire electrical discharge machining can be effectively suppressed, and a decrease in machining speed due to the disappearance of the coating layer 12 can be avoided. Furthermore, if the ratio of the thickness of the coating layer 12 to the diameter of the electrode wire 1 is 20% or less, the decrease in wire drawing processability due to an excessively large ratio can be suppressed, and wire breakage during wire drawing can be suppressed in the manufacturing of the electrode wire 1 for wire electrical discharge machining.

[0014] In order to more effectively suppress the disappearance of the coating layer 12 during wire electrical discharge machining, the ratio of the thickness of the coating layer 12 to the diameter of the electrode wire 1 for wire electrical discharge machining is preferably 4% or more and 20% or less. Further, in order to more effectively suppress the disappearance of the coating layer 12 during wire electrical discharge machining and more effectively suppress the decrease in wire drawing workability, the ratio of the thickness of the coating layer 12 to the diameter of the electrode wire 1 for wire electrical discharge machining is preferably 10% or more and 15% or less.

[0015] The zinc concentration of the core material 11 is, as described above, greater than 40% by mass and higher than the zinc concentration of the core material of a conventional general electrode wire for wire electrical discharge machining. This is for forming a thick coating layer 12 in a short time by atomic diffusion described later.

[0016] Also, the tensile strength (TS) of the electrode wire 1 for wire electrical discharge machining is, for example, 800 MPa or more and 1200 MPa or less, the elongation (EL) is, for example, 0.5% or more and 3% or less, and the conductivity is, for example, 20% IACS or more and 30% IACS or less.

[0017] Here, the tensile strength (TS) of the electrode wire 1 for wire electrical discharge machining is a value measured by the following procedure using a tensile-compression testing machine SV-301-E-L manufactured by Imada Co., Ltd. as a measuring device. (1) First, prepare a predetermined length of the electrode wire 1 for wire electrical discharge machining as a sample. (2) Fix both ends of the sample to the above measuring device and hold the sample in a straight line. (3) In that state, pull one end of the sample at a constant speed of 50 mm / min. (4) Measure the maximum load when the sample breaks (load range: 100 N). (5) Divide the breaking load by the cross-sectional area of the sample to calculate the tensile strength.

[0018] Furthermore, the elongation (EL) of the electrode wire 1 for wire electrical discharge machining was measured using the same measuring device as that used for the tensile strength (TS) described above, following the same procedure as (1) to (3) above. The length between gauge marks 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 gauge marks when the sample breaks, and L0 is the length between gauge marks before the sample is pulled.

[0019] Furthermore, the conductivity of electrode wire 1 for wire electrical discharge machining was measured according to the method conforming to JIS H 0505. Here, a specific gravity of 8.89 was used when calculating the conductivity.

[0020] (Method of manufacturing electrode wires for wire electrical discharge machining) As an example of a method for manufacturing an electrode wire 1 for wire electrical discharge machining, the method for manufacturing an electrode wire 1 with a wire diameter of 0.25 mm is shown below.

[0021] First, prepare a linear material, which is the material for the electrode wire 1 for wire electrical discharge machining, with a wire diameter of 1.2 mm. The linear material is, for example, a linear material in which a zinc film 8 μm thick is formed on the surface of a brass wire, which is the core material 11, and has a zinc concentration greater than 40 mass% (for example, 43 mass%). The zinc film is formed by a plating process or the like. Prepare the required amount of linear material, for example, 50 kg. Alternatively, a brass film with a higher zinc concentration than the core material 11 may be used instead of the zinc film.

[0022] Here, in order to make the ratio of the thickness of the coating layer 12 to the diameter of the electrode wire 1 for wire electrical discharge machining 2% or more and 20% or less, the ratio of the thickness of the zinc plating layer to the diameter of the linear material should be, for example, 0.5% or more and 0.9% or less. For example, if the diameter of the linear material is 1.2 mm, the thickness of the zinc plating layer should be 6.0 μm or more and 10.8 μm or less.

[0023] Next, after passing inspections such as characteristic surveys and visual and cross-sectional observations, the linear material is heat-treated using a furnace to induce atomic diffusion between the core material 11 and the zinc film, forming a coating layer 12 made of brass with a zinc concentration of 44% by mass or more and 50% by mass or less. The thickness of the coating layer 12 after heat treatment is greater than the thickness of the precursor zinc film, and the core material 11 becomes thinner than before heat treatment. The ratio T / D1, which is the ratio of the thickness T of the coating layer 12 to the diameter D1 of the linear material, is between 2% and 20%.

[0024] As described above, the coating layer 12 is formed thicker than the coating layers of general-purpose electrode wires and electrode wires for precision machining. Therefore, in forming the coating layer 12, atomic diffusion is promoted by heat treatment at a higher temperature than that used for forming the coating layers of these electrode wires, for example, between 300°C and 900°C. When the heat treatment temperature is 300°C or higher, a sufficient atomic diffusion rate can be obtained to form a thick coating layer 12. Also, when the heat treatment temperature is 900°C or lower, melting of the brass constituting the core material 11 and the coating layer 12 can be easily prevented by adjusting the heat treatment time, etc.

[0025] Furthermore, the heat treatment time for forming the coating layer 12 is, for example, 0.2 minutes or more and 120 minutes or less. When the heat treatment time is 0.2 minutes or more, atomic diffusion can be sufficiently advanced to form a thick coating layer 12. When the heat treatment time is 120 minutes or less, it is easier to prevent the thickness of the coating layer 12 from becoming too large (the ratio of the thickness of the coating layer 12 to the diameter of the electrode wire 1 for wire electrical discharge machining exceeding 20%).

[0026] Next, the wire material is passed through a wire drawing die installed in a wire drawing machine and drawn to obtain a wire electrode wire 1 for wire electrical discharge machining, with a wire diameter of 0.25 mm.

[0027] As described above, in the manufacture of the electrode wire 1 for wire electrical discharge machining, heat treatment is performed before drawing the wire. This is because the heat treatment to form the coating layer 12 is carried out at the high temperature mentioned above. Generally, applying heat treatment to the electrode wire at high temperatures such as 300 to 900°C reduces its hardness. Therefore, if heat treatment at a high temperature is performed after drawing the wire, the tensile strength of the final product, the electrode wire 1 for wire electrical discharge machining, will be reduced.

[0028] The electrode wire 1 for wire electrical discharge machining has high tensile strength, for example, 800 MPa or more, but such high tensile strength cannot be obtained by heat treatment after wire drawing. Furthermore, at low temperatures that do not affect the hardness of the electrode wire, for example, 100 to 170°C, the diffusion rate decreases significantly, making it impossible to form a thick coating layer 12 in a realistic amount of time.

[0029] Furthermore, in order to achieve high tensile strength in the wire EDM electrode wire 1, the elongation of the wire EDM electrode wire 1 must be small (for example, if the tensile strength is 800 MPa or more, the elongation must be 3% or less). In the method of applying heat treatment after wire drawing, if high temperature treatment is applied to obtain the coating layer 12, the tensile strength of the final product wire EDM electrode wire 1 decreases and the elongation increases, making it impossible to keep the elongation below 3%.

[0030] (Manufacturing test of electrode wires for wire electrical discharge machining) In order to derive the conditions for forming a thick coating layer 12 on the electrode wire 1 for wire electrical discharge machining according to an embodiment of the present invention, electrode wires were manufactured under various conditions and their structures were investigated.

[0031] First, a linear material 2 with a diameter of 1.2 mm (hereinafter referred to as material A) consisting of a core material 11 made of brass with a zinc concentration of 35% and a copper concentration of 65%, and a zinc plating film with a thickness of 10 μm covering it, and a linear material 2 with a diameter of 0.9 mm (hereinafter referred to as material B) consisting of a core material 11 made of brass with a zinc concentration of 43% and a copper concentration of 57%, and a zinc plating film with a thickness of 8 μm covering it, were heat-treated at 400-600°C for 1 hour in an N2 atmosphere to form a coating layer 12.

[0032] Figures 3(a) and 3(b) show a microscope image of the radial cross-section of material A, which has been heat-treated at 500°C for 1 hour, and a partially magnified image thereof. Figures 4(a) and 4(b) show a microscope image of the radial cross-section of material B, which has been heat-treated at 500°C for 1 hour, and a partially magnified image thereof.

[0033] As shown in Figures 3 and 4, the thickness of the coating layer 12 is greater for material B than for material A, even though the heat treatment temperature is the same. This is because material B has a higher zinc concentration in the core material 11 than material A.

[0034] Next, the radial cross-sections of the heat-treated linear materials 2 (materials A and B) were observed using a Scanning Electron Microscope (SEM). The zinc concentration, thickness, and thickness ratio (T / D1, which is the ratio of the thickness T of the coating layer 12 to the diameter D1 of the linear material 2) of the coating layer 12 in the linear materials 2 (materials A and B) obtained from the observed images are shown in Tables 1 and 2 below (all are average values ​​within the observed images).

[0035] [Table 1]

[0036] [Table 2]

[0037] As shown in Tables 1 and 2, the thickness ratio of the coating layer 12 is larger in material B than in material A, and the difference in the thickness ratio of the coating layer 12 between material A and material B increases as the heat treatment temperature increases. This is because material B has a higher zinc concentration in the core material 11 than material A. In material B, when heat treatment was performed at 600°C for 1 hour, the diffusion between the core material 11 and the coating layer 12 progressed excessively, causing the boundary between the core material 11 and the coating layer 12 to disappear. Therefore, in order to form an electrode wire 1 for wire electrical discharge machining with a coating layer 12 by performing heat treatment at 600°C, it is necessary to shorten the heat treatment time to the extent that diffusion does not progress excessively.

[0038] Figures 5(a) and 5(b) show SEM images of the radial cross-section of material B after heat treatment at 400°C for 1 hour, and partially magnified images thereof. Figures 6(a) and 6(b) show SEM images of the radial cross-section of material B after heat treatment at 500°C for 1 hour, and partially magnified images thereof.

[0039] The coating layer 12 is usually composed of β-phase brass, but as shown in Tables 2 and 3 and Figure 5, when the heat treatment temperature is relatively low at 400°C, the coating layer 12 is composed of an inner region 12a made of β-phase brass and an outer region 12b made of γ-phase brass. In this case, the coating layer 12 may also include a region 12b made of γ-phase brass. Note that the zinc concentration in the brass differs between the β-phase and γ-phase, and the boundary between the zinc concentrations of the β-phase and γ-phase is approximately 50% by mass.

[0040] In materials A and B, which have been heat-treated at 400°C for 1 hour, the average zinc concentration of the β and γ phases, calculated using the thickness and zinc concentration of the β and γ phases, is approximately 50%. In other words, the total zinc concentration of the coating layer 12 is approximately 50%.

[0041] The zinc concentrations in the core material 11 and coating layer 12 of the heat-treated linear material 2 are approximately equal to those in the core material 11 and coating layer 12 of the wire EDM electrode wire 1 after drawing. Therefore, in this test, the range of zinc concentration in the coating layer 12 of the wire EDM electrode wire 1 obtained by drawing material B is approximately 44% by mass or more and 50% by mass or less.

[0042] Next, materials A and B, which had been heat-treated at 500°C for 1 hour, were drawn by a drawing process to form wire electrical discharge machining electrode wires 1 with a diameter of 0.1 to 0.3 mm.

[0043] Then, the radial cross-section of the wire electrical discharge machining electrode wire 1 obtained by drawing materials A and B was observed using an optical microscope. The thickness ratio of the coating layer 12 in the wire electrical discharge machining electrode wire 1 (T / D2, which is the ratio of the thickness T of the coating layer 12 to the diameter D2 of the wire electrical discharge machining electrode wire 1) obtained from the observed image is shown in Table 3.

[0044] [Table 3]

[0045] As can be seen from Tables 1, 2, and 3, the thickness ratio of the coating layer 12 in the linear material 2 (material A or material B) heat-treated at 500°C for 1 hour and the wire EDM electrode wire 1 with a diameter of 0.1 to 0.3 mm obtained by drawing the linear material 2 are the same. Thus, the thickness ratio of the linear material 2 and the wire EDM electrode wire 1 obtained by drawing it are approximately equal.

[0046] Figures 7(a) and 7(b) show optical microscope images of the radial cross-section of a 0.3 mm diameter wire EDM electrode wire 1 obtained by drawing material A that has been heat-treated at 500°C for 1 hour, and partially magnified images thereof. Figures 8(a) and 8(b) also show optical microscope images of the radial cross-section of a 0.3 mm diameter wire EDM electrode wire 1 obtained by drawing material B that has been heat-treated at 500°C for 1 hour, and partially magnified images thereof.

[0047] As shown in Table 3, Figures 7 and 8, the wire electrical discharge machining electrode wire 1 obtained by drawing material B has a larger ratio of coating layer thickness 12 than the wire electrical discharge machining electrode wire 1 obtained by drawing material A. This is because material B has a higher zinc concentration in the core material 11 than material A, resulting in a larger thickness of the coating layer 12 formed by heat treatment.

[0048] (Effects of the embodiment) According to the above embodiment of the present invention, it is possible to provide a wire electrical discharge machining electrode wire having a coating layer made of brass with a high zinc concentration, wherein the coating layer has a thickness suitable for high-speed machining, and a method for manufacturing the same.

[0049] (Summary of the embodiments) Next, the technical concept understood from the embodiments described above will be described using the reference numerals and other symbols from the embodiments. However, the reference numerals and other symbols in the following description are not limited to the components in the claims that are specifically shown in the embodiments.

[0050] [1] A wire electrical discharge machining electrode wire (1) comprising a core material (11) made of a first brass having a zinc concentration greater than 40 mass%, and a coating layer (12) covering the core material (11), wherein the coating layer (12) consists of a second brass having a zinc concentration greater than that of the first brass and between 44 mass% and 50 mass%, and a third brass having a zinc concentration greater than that of the second brass and greater than 50 mass%, and the ratio of the thickness of the coating layer (12) to the diameter of the wire electrical discharge machining electrode wire (1) is between 2% and 20%.

[0051] [2] The electrode wire (1) for wire electrical discharge machining described in [1] above, having a tensile strength of 800 MPa or more.

[0052] [3] The process includes the steps of: heat-treating a linear material (2) having a core material (11) made of brass and a zinc film or a brass film with a higher zinc concentration than the core material that covers the core material (11), thereby causing atomic diffusion between the core material (11) and the zinc film or the brass film to form a coating layer (12) that covers the core material (11); and drawing the heat-treated linear material (2) to process it into an electrode wire (1) for wire electrical discharge machining, wherein the electrode wire (1) has a core material (1 1) is made of brass consisting of a first brass having a zinc concentration greater than 40% by mass, the coating layer (12) is made of a second brass having a zinc concentration greater than that of the first brass and between 44% by mass and 50% by mass, and a third brass having a zinc concentration greater than that of the second brass and greater than 50% by mass, and the ratio of the thickness of the coating layer (12) to the diameter of the wire electrical discharge machining electrode wire (1) is between 2% and 20%. A method for manufacturing a wire electrical discharge machining electrode wire (1).

[0053] [4] The method for manufacturing an electrode wire (1) for wire electrical discharge machining as described in [3] above, wherein the temperature of the heat treatment is 300°C or higher and 900°C or lower.

[0054] Although 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 as defined in the claims. It should also be noted that not all combinations of features described in the embodiments are necessarily essential for solving the problem of the invention. [Explanation of Symbols]

[0055] 1. Electrode wire for wire electrical discharge machining 2. Linear materials 11 Core material 12 Covering layer

Claims

1. A core material made of first brass with a zinc concentration greater than 40% by mass, In an electrode wire for wire electrical discharge machining, comprising a covering layer that covers the core material, The aforementioned coating layer is A second brass having a zinc concentration greater than that of the first brass, and with a zinc concentration of 44% by mass or more and 50% by mass or less, It consists of a third brass having a zinc concentration greater than that of the second brass, exceeding 50% by mass, The ratio of the thickness of the coating layer to the diameter of the electrode wire for wire electrical discharge machining is 2% or more and 20% or less. Electrode wire for wire electrical discharge machining.

2. The tensile strength is 800 MPa or more. The electrode wire for wire electrical discharge machining according to claim 1.

3. A linear material comprising a brass core and a zinc film or a brass film with a higher zinc concentration than the core, is subjected to heat treatment to induce atomic diffusion between the core and the zinc film or brass film, thereby forming a coating layer that covers the core. A step of drawing the heat-treated linear material to process it into an electrode wire for wire electrical discharge machining, Includes, In the aforementioned electrode wire for wire electrical discharge machining, the core material is made of brass consisting of a first brass having a zinc concentration greater than 40% by mass. The aforementioned coating layer is A second brass having a zinc concentration greater than that of the first brass, and with a zinc concentration of 44% by mass or more and 50% by mass or less, It consists of a third brass having a zinc concentration greater than that of the second brass, exceeding 50% by mass, The ratio of the thickness of the coating layer to the diameter of the electrode wire for wire electrical discharge machining is 2% or more and 20% or less. A method for manufacturing electrode wires for wire electrical discharge machining.

4. The temperature of the heat treatment is 300°C or higher and 900°C or lower. A method for manufacturing an electrode wire for wire electrical discharge machining according to claim 3.

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