Electrode wire for wire electric discharge machining and method for manufacturing the same

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 electric discharge machining and a method for manufacturing the electrode wire for wire electric discharge machining. [Background technology]

[0002] Conventionally, there has been known a wire electrode wire for wire electrical discharge machining made of brass, which comprises a core material and a coating layer surrounding the core material, the coating layer having a higher zinc concentration than the core material (see Patent Document 1).Since zinc generates discharge more easily than copper due to its larger work function, providing a coating layer with a high zinc concentration around the core material can increase the machining speed of wire electrical discharge machining compared to when no coating layer is provided. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2024-39167 Summary of the Invention [Problem to be solved by the invention]

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

[0005] An object of the present invention is to provide a wire electric discharge machining electrode wire 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. [Means for solving the problem]

[0006] In order to solve the above-mentioned problems, the present invention provides a wire electric discharge machining electrode wire having 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 is made of a second brass having a zinc concentration greater than that of the first brass and between 44% and 50% by mass, and a third brass having a zinc concentration greater than that of the second brass and exceeding 50% by mass, and wherein the ratio of the thickness of the coating layer to the diameter of the wire electric discharge machining electrode wire is between 2% and 20%.

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

[0008] According to the present invention, it is possible to provide a wire electric discharge machining electrode wire 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. [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] FIG. 2 is a schematic diagram showing how a flat workpiece is machined by wire electric discharge machining. [Figure 3] Figures 3(a) and (b) show a microscope image of a radial cross section of material A that was heat treated at 500°C for 1 hour, and a partially enlarged image of the same. [Figure 4] Figures 4(a) and (b) show a microscope image of a radial cross section of material B that was heat-treated at 500°C for 1 hour, and a partially enlarged image of the same. [Figure 5] Figures 5(a) and (b) show SEM images of the radial cross section of material B that was heat-treated at 400°C for 1 hour, and a partially enlarged image of the same. [Figure 6] Figures 6(a) and (b) show SEM images of the radial cross section of material B that was heat-treated at 500°C for 1 hour, and a partially enlarged image of the same. [Figure 7] Figures 7(a) and (b) show optical microscope images of the radial cross section of a 0.3 mm diameter wire EDM electrode obtained by drawing material A that had been heat-treated at 500°C for 1 hour, and a partially enlarged image of the same. [Figure 8] Figures 8(a) and (b) show optical microscope images of the radial cross section of a 0.3 mm diameter wire EDM electrode obtained by drawing material B, which had been heat-treated at 500°C for 1 hour, and a partially enlarged image of the same. 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 electric discharge machining electrode wire 1 according to an embodiment of the present invention. The wire electric discharge machining electrode wire 1 includes 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 made of brass with a higher zinc concentration than that of the core material 11, and with a zinc concentration of 44 mass % or more and 50 mass % or less.

[0011] Figure 2 is a schematic diagram showing how a flat workpiece 4 is machined by wire electric discharge machining. In wire electric discharge machining, as shown in Figure 2, a pulse voltage is applied from a machining power supply 3 between a wire electric discharge machining electrode wire 1 and a workpiece 4 made of a metal material such as SKD-11, and while an electric discharge is generated between the wire electric discharge machining electrode wire 1 and the workpiece 4 made of a metal material, the wire electric discharge machining electrode wire 1 is fed and moved relative to the workpiece 4 like a jigsaw, and the workpiece 4 is two-dimensionally machined into a pre-programmed shape.

[0012] The wire electric discharge machining electrode wire 1 is an electrode wire for high-speed machining. In high-speed machining, a large current is passed through the electrode wire, and therefore the coating layer is consumed at a faster rate than in normal machining. Therefore, in order to prevent the coating layer 12 from being lost during machining, the thickness of the coating layer 12 of the wire electric discharge machining electrode wire 1 is made thicker than that of a general-purpose electrode wire or an electrode wire for high-precision machining.

[0013] The diameter of the wire electric discharge machining electrode wire 1 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 wire electric discharge machining 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 wire electric discharge machining electrode wire 1 is 2% or more, it is possible to effectively prevent loss of the coating layer 12 during wire electric discharge machining and avoid a decrease in machining speed due to loss of the coating layer 12. Furthermore, if the ratio of the thickness of the coating layer 12 to the diameter of the wire electric discharge machining electrode wire 1 is 20% or less, it is possible to prevent a decrease in wire drawability caused by an excessively large ratio and prevent wire breakage during wire drawing in the manufacture of the wire electric discharge machining electrode wire 1.

[0014] Furthermore, in order to more effectively prevent the loss of coating layer 12 during wire electrical discharge machining, the ratio of the thickness of coating layer 12 to the diameter of wire electrical discharge machining electrode wire 1 is preferably 4% or more and 20% or less. Furthermore, in order to more effectively prevent the loss of coating layer 12 during wire electrical discharge machining and to more effectively prevent a decrease in wire drawability, the ratio of the thickness of coating layer 12 to the diameter of wire electrical discharge machining electrode wire 1 is preferably 10% or more and 15% or less.

[0015] As described above, the zinc concentration of core material 11 is greater than 40 mass %, which is higher than the zinc concentration of the core material of a conventional electrode wire for wire electric discharge machining. This is because a thick coating layer 12 is formed in a short time by atomic diffusion, which will be described later.

[0016] The tensile strength (TS) of the wire electric discharge machining electrode wire 1 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 using a tension and compression testing machine SV-301-EL manufactured by Imada Manufacturing Co., Ltd. as a measuring device in the following procedure. (1) First, a wire electric discharge machining electrode wire 1 having a predetermined length is prepared as a sample. (2) Fix both ends of the sample to the measuring device and 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) Measure the maximum load when the sample breaks (load range: 100 N). (5) The breaking load is divided by the cross-sectional area of ​​the sample to calculate the tensile strength.

[0018] 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.

[0019] 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.

[0020] (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 0.25 mm will be described below.

[0021] First, a wire material having a wire diameter of 1.2 mm is prepared as the material for the wire electric discharge machining electrode wire 1. The wire material is, for example, a wire material in which a zinc film having a thickness of 8 μm is formed on the surface of a brass wire having a zinc concentration of more than 40 mass % (for example, 43 mass %) as the core material 11. The zinc film is formed by a plating process or the like. An amount of the wire material, for example, 50 kg, is prepared as needed. Note that a brass film having a higher zinc concentration than the core material 11 may be used instead of the zinc film.

[0022] In order to set the ratio of the thickness of the coating layer 12 to the diameter of the wire electric discharge machining electrode wire 1 to be 2% or more and 20% or less, the ratio of the thickness of the zinc plating layer to the diameter of the linear material is set to 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 is set to be 6.0 μm or more and 10.8 μm or less.

[0023] Next, if the linear material passes inspections such as property surveys and visual and cross-sectional observations, it is heat-treated in a furnace to cause 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 that of the zinc film, which is its precursor, and the core material 11 is 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 2% or more and 20% or less.

[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, when forming the coating layer 12, atomic diffusion is promoted by heat treatment at a temperature higher than that used in the heat treatment for forming the coating layers of these electrode wires, for example, at a temperature between 300°C and 900°C. When the heat treatment temperature is 300°C or higher, a sufficient atomic diffusion rate is obtained to form a thick coating layer 12. Furthermore, when the heat treatment temperature is 900°C or lower, melting of the brass that constitutes the core material 11 and the coating layer 12 can be easily prevented by adjusting the heat treatment time, for example.

[0025] 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 easy 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 wire electric discharge machining electrode wire 1 exceeds 20%).

[0026] Next, the wire material is passed through a wire drawing die provided in a wire drawing machine to be drawn to a wire diameter of 0.25 mm, thereby obtaining an electrode wire 1 for wire electric discharge machining.

[0027] As described above, in the manufacture of the wire electric discharge machining electrode wire 1, heat treatment is performed before wire drawing. This is because the heat treatment for forming the coating layer 12 is performed at the above-mentioned high temperature. Generally, when an electrode wire is heat treated at a high temperature, such as 300 to 900°C, its hardness decreases. Therefore, if heat treatment is performed at a high temperature after wire drawing, the tensile strength of the wire electric discharge machining electrode wire 1 as a final product decreases.

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

[0029] Furthermore, in order for the wire electric discharge machining electrode wire 1 to exhibit high tensile strength, the elongation of the wire electric discharge machining 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 performing heat treatment after wire drawing, if high-temperature treatment is performed to obtain the coating layer 12, the tensile strength of the wire electric discharge machining electrode wire 1 as a final product decreases and the elongation increases, making it impossible to achieve an elongation of 3% or less.

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

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

[0032] Figures 3(a) and (b) are microscopic images of the radial cross section of material A that was heat treated at 500°C for 1 hour, and a partially enlarged image of the same. Figures 4(a) and (b) are microscopic images of the radial cross section of material B that was heat treated at 500°C for 1 hour, and a partially enlarged image of the same.

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

[0034] Next, the radial cross sections of the heat-treated linear materials 2 (materials A and B) were observed using a SEM (Scanning Electron Microscope). 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 linear materials 2 (materials A and B) obtained from the observation images are shown in Tables 1 and 2 below (all are average values ​​within the observation images).

[0035] [Table 1]

[0036] [Table 2]

[0037] As shown in Tables 1 and 2, the thickness ratio of the coating layer 12 is greater in Material B than in Material A, and the difference in thickness ratio of the coating layer 12 between Material A and Material B increases as the heat treatment temperature increases. This is because the zinc concentration in the core material 11 is higher in Material B than in Material A. Note that when Material B was heat treated at 600°C for 1 hour, diffusion between the core material 11 and the coating layer 12 proceeded excessively, resulting in the disappearance of the boundary between the core material 11 and the coating layer 12. Therefore, in order to form a wire electrical discharge machining electrode wire 1 having a coating layer 12 by heat treatment at 600°C, it is necessary to shorten the heat treatment time to a degree that prevents excessive diffusion.

[0038] Figures 5(a) and 5(b) are SEM images of a radial cross section of Material B heat-treated at 400°C for 1 hour, and a partially enlarged image of the same. Figures 6(a) and 6(b) are SEM images of a radial cross section of Material B heat-treated at 500°C for 1 hour, and a partially enlarged image of the same.

[0039] The coating layer 12 is usually made 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 made of an inner region 12a made of β-phase brass and an outer region 12b made of γ-phase brass. As in this case, the coating layer 12 may also include region 12b made of γ-phase brass. Note that the zinc concentrations in the β-phase and γ-phase brass differ, with the boundary between the zinc concentrations in the β-phase and γ-phase being approximately 50% by mass.

[0040] For materials A and B that were heat-treated at 400°C for 1 hour, the average zinc concentration of the β and γ phases was calculated using the thickness and zinc concentration of the β and γ phases, resulting in a value of approximately 50%. In other words, the zinc concentration of the entire coating layer 12 was approximately 50%.

[0041] The zinc concentration in the core material 11 and the coating layer 12 in the heat-treated linear material 2 is approximately equal to the zinc concentration in the core material 11 and the coating layer 12 in the drawn wire electrical discharge machining electrode wire 1. Therefore, in this test, the zinc concentration in the coating layer 12 in the wire electrical discharge machining electrode wire 1 obtained by drawing material B ranges from approximately 44 mass% to 50 mass%.

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

[0043] Then, the radial cross sections of the wire electrical discharge machining electrode wire 1 obtained by drawing material A and material B were observed using an optical microscope. The thickness ratio of the coating layer 12 in the wire electrical discharge machining electrode wire 1 obtained from the observation image (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) is shown in Table 3 below.

[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 electrical discharge machining electrode wire 1 having a diameter of 0.1 to 0.3 mm obtained by drawing the linear material 2 are the same. In this way, the thickness ratio of the linear material 2 and the wire electrical discharge machining electrode wire 1 obtained by drawing the linear material 2 are approximately the same.

[0046] 7(a) and 7(b) are optical microscope images of the radial cross section of a 0.3 mm diameter wire EDM electrode wire 1 obtained by wiredrawing material A that had been heat treated at 500°C for 1 hour, and a partially enlarged image of the same. Also, Figures 8(a) and 8(b) are optical microscope images of the radial cross section of a 0.3 mm diameter wire EDM electrode wire 1 obtained by wiredrawing material B that had been heat treated at 500°C for 1 hour, and a partially enlarged image of the same.

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

[0048] (Effects of the embodiment) According to the above-described embodiment of the present invention, it is possible to provide a wire electric discharge machining electrode wire 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.

[0049] (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.

[0050] [1] A wire electric discharge machining electrode wire (1) comprising a core material (11) made of a first brass having a zinc concentration greater than 40% by mass, and a coating layer (12) covering the core material (11), wherein the coating layer (12) is made of a second brass having a zinc concentration greater than that of the first brass and not less than 44% by mass and not more than 50% by mass, and a third brass having a zinc concentration greater than that of the second brass and exceeding 50% by mass, and wherein the ratio of the thickness of the coating layer (12) to the diameter of the wire electric discharge machining electrode wire (1) is not less than 2% and not more than 20%.

[0051] [2] The electrode wire (1) for wire electric discharge machining according to [1] above, which has a tensile strength of 800 MPa or more.

[0052] [3] The method includes a step of heat-treating a linear material (2) having a core material (11) made of brass and a zinc film or a brass film having a higher zinc concentration than the core material that covers the periphery of the core material (11) to cause atomic diffusion between the core material (11) and the zinc film or the brass film to form a coating layer (12) that covers the periphery of the core material (11), and a step of wire-drawing the linear material (2) that has been subjected to the heat treatment into a wire electric discharge machining electrode wire (1), wherein in the wire electric discharge machining electrode wire (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 not less than 44% by mass and not more than 50% by mass, and a third brass having a zinc concentration greater than that of the second brass and exceeding 50% by mass, and the ratio of the thickness of the coating layer (12) to the diameter of the wire electric discharge machining electrode wire (1) is not less than 2% and not more than 20%.

[0053] [4] The method for producing the electrode wire (1) for wire electric discharge machining according to [3] above, wherein the temperature of the heat treatment is 300°C or higher and 900°C or lower.

[0054] 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 scope of the invention as defined by the claims. Furthermore, 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]

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

Claims

1. A core material made of first brass having a zinc concentration greater than 40% by mass; a coating layer covering the core material, The coating layer is A second brass having a zinc concentration greater than that of the first brass and having a zinc concentration of 44% by mass or more and 50% by mass or less; A third brass having a zinc concentration greater than that of the second brass and exceeding 50% by mass; a ratio of the thickness of the coating layer to the diameter of the wire electric discharge machining electrode wire 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 electric discharge machining according to claim 1.

3. a step of subjecting a linear material having a core material made of brass and a zinc film or a brass film having a higher zinc concentration than the core material to heat treatment to cause atomic diffusion between the core material and the zinc film or the brass film, thereby forming a coating layer that covers the core material; a step of drawing the heat-treated linear material into an electrode wire for wire electric discharge machining; Including, In the wire electric discharge machining electrode wire, the core material is made of brass made of first brass having a zinc concentration of more than 40 mass %, The coating layer is A second brass having a zinc concentration greater than that of the first brass and having a zinc concentration of 44% by mass or more and 50% by mass or less; A third brass having a zinc concentration greater than that of the second brass and exceeding 50% by mass; a ratio of the thickness of the coating layer to the diameter of the wire electric discharge machining electrode wire is 2% or more and 20% or less; A method for manufacturing an electrode wire for wire electric discharge machining.

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

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