Electrode wire for electro-discharge machining and method for manufacturing the same

Abstract

An electrode wire for electro-discharge machining includes a core wire including a first metal including copper and having one of phases , +, and , a first alloy layer formed at a boundary region between the core wire and a second metal plated on an outer surface of the core wire due to mutual diffusion between the core wire and the second metal and having a phase , and a second alloy layer formed due to diffusion of the first metal to the second metal and having a phase and/a phase . A core wire material is erupted onto a surface of the electrode wire for electro-discharge machining, which includes the core wire, the first alloy layer, and the second alloy layer, along cracks appearing on the second alloy layer, so that a plurality of grains are formed on the surface of the electrode wire.

Claims

1. An electrode wire for electro-discharge machining, the electrode wire comprising: a core wire including a first metal comprising brass having a mixture of copper and zinc and having one of phases , +, and ; a first alloy layer of a first alloy material formed at a boundary region between the core wire and a second metal, the second metal being plated and diffused on an entire outer circumferential surface of the core wire, and said first alloy layer having a phase ; and a second alloy layer of a second alloy material formed at an entire outer surface of the first alloy layer due to the diffusion of the first metal to the second metal and having a phase and a phase , wherein the second metal includes one selected from the group consisting of zinc, aluminum, tin, and an alloy thereof, wherein the second alloy layer has a higher hardness and lower tensile strength than the first alloy layer, wherein the second alloy layer is provided with a plurality of cracks, wherein the core wire is distributed onto a surface of the second alloy layer, wherein the core wire directly contacts the first alloy layer and the second alloy layer, wherein the first alloy layer directly contacts both the core wire and the second alloy layer, wherein the core wire, the first alloy layer and the second alloy layer are exposed onto the outer circumferential surface of the electrode wire for electro-discharge machining, wherein , +, , and are crystalline structures, and wherein said core wire projects through the first alloy layer and through the cracks of the second alloy layer to the outer circumferential surface of the electrode wire.

2. The electrode wire of claim 1, wherein the core wire is arranged in a direction substantially perpendicular to a longitudinal direction of the electrode wire for electro-discharge machining, and has a length in a circumferential direction of the core wire two times to ten times greater than a width a direction perpendicular to the longitudinal direction.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The patent or application file contains at least one color drawing. Copies of this patent or patent application publication with color drawing will be provided by the USPTO upon request and payment of the necessary fee.

(2) The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description when taken in conjunction with the accompanying drawings, in which:

(3) FIG. 1 is a schematic view showing the technical configuration and the principle of an electro-discharge machine according to the related art;

(4) FIG. 2 is a view showing a method for manufacturing an electrode wire for electro-discharge machining according to the present invention;

(5) FIG. 3 is a photograph showing a product of the electrode wire for the electro-discharge machining according to a first embodiment of the present invention;

(6) FIG. 4 is a photograph showing a product of an electrode wire for electro-discharge machining according to a second embodiment of the present invention;

(7) FIG. 5 is a photograph showing a product of an electrode wire for electro-discharge machining according to a third embodiment of the present invention;

(8) FIG. 6 is a photograph showing a product of an electrode wire for electro-discharge machining according to a fourth embodiment of the present invention;

(9) FIG. 7 is a photograph showing cracks appearing when stress is applied to an intermediate wire rod throughout the whole steps of an elongation process according to the second embodiment of the present invention;

(10) FIG. 8 is a photograph showing cracks appearing when stress is applied to an intermediate wire rod throughout the whole steps of an elongation process according to the fourth embodiment of the present invention;

(11) FIG. 9 is a sectional view schematically showing the product according to the first and third embodiments of the present invention; and

(12) FIG. 10 is a sectional view schematically showing the product according to the second and fourth embodiments of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

(13) Hereinafter, the structure of an electrode wire for electro-discharge machining according to the present invention, the technical configuration in a method for manufacturing the electrode wire according to the present invention, and effects of the present invention will be described in detail with reference to FIGS. 2 to 10.

(14) Referring to FIG. 2, a core wire 12 including brass including about 65 weight % of copper and about 35 weight % of zinc and having one of phases , +, and is provided with a diameter in the range of about 0.9 nm to about 1.2 nm.

(15) The core wire 12 is dipped into a plating bath 10 containing melted zinc having a vaporization temperature lower than that of brass for a predetermined time and passed through the plating bath 10, so that the melted zinc is plated on an outer portion of the core wire 12.

(16) In particular, the entrance temperature of the plating bath 10 is adjusted to the range of about 550 C. to about 700 C., and the exit temperature of the plating bath 10 is adjusted to the range of about 420 C. to about 500 C. In addition, the core wire 12 is dipped into the plating bath 10 and passed through the plating bath 10 within time of about 1 second to about 10 seconds, thereby adjusting the tensile strength of the core wire 12 to the tensile strength of 500 N/mm.sup.2 or less and adjusting the elongation percentage of about 5 or more.

(17) In this case, the core wire 12 is provided on the interfacial surface thereof with an alloy layer representing higher hardness and the lower elongation percentage due to the diffusion reaction between zinc, which is melted in the plating bath 10, and brass when comparing with a core wire including only brass.

(18) The core wire 12 plated with the alloy layer while being passed through the plating bath 10 under the above conditions is drawn by a drawing unit 14, so that the core wire 12 obtains a proper diameter, for example, the diameter of about 0.07 mm to about 0.35 mm.

(19) The core wire 12 including brass, which is plated with zinc at a thickness of about 3 m to about 10 m through an electroplating scheme or a chemical plating scheme other than the scheme of passing the core wire 12 through the plating bath 10, may be subject to a heat treatment process at a speed of about 100 m/min to about 600 m/min under the voltage of about 10V to about 60V, so that the zinc plated core wire 12 including brass can represent the tensile strength of about 500 N/mm.sup.2 or less and the elongation percentage of about 5 or more.

(20) A copper component of the core wire 12 is diffused to the zinc plated layer to form a second alloy layer having a phase and/or a phase at an outer portion of a first alloy layer which is interposed between the core wire 12 and the zinc plated layer and has a phase . Since the second alloy layer represents the highest hardness and the lowest tensile strength, a great amount of cracks appear on the second alloy layer due to the difference in the hardness and the elongation percentage between the second alloy layer and other layers when the second alloy layer is drawn. Accordingly, softer brass constituting the core wire 12 is erupted onto the surface of the second alloy layer as if lava and distributed onto the surface of the second alloy layer.

(21) The mechanical properties of the fine wire can be more stabilized through the heat treatment process.

(22) FIGS. 3 and 5 are photographs showing the surface of the drawn electrode wire for electro-discharge machining, and FIG. 9 is a sectional view schematically showing the electrode wire for electro-discharge machining of FIGS. 3 and 5.

(23) Referring to FIG. 9, a core wire material of brass and the alloy material are significantly distributed onto the surface of the electrode wire for the electro-discharge machining. The core wire material and the alloy material are erupted upward as if lava along cracks, so that the core wire material and alloy material are distributed on the surface of the electrode wire together with grains of the alloy layer or the alloy material is surrounded by the core wire material.

(24) A twist unit 33 is additionally provided between a roller 16 and the drawing unit 14 to make the intermediate wire rod curved in at least one of up, down, left, and right directions, or make the intermediate wire rod twisted when drawing the core wire 12 in order to finely form the core wire 12 having the first and second alloy layers, thereby more causing cracks on the intermediate wire rod, so that softer brass is erupted onto the surface of the zinc plated layer through the cracks to form grains in a circumferential direction of the intermediate wire rod.

(25) If stress is applied to the intermediate wire rod constituting the core wire 12 before a fine wire process is performed, grains having a long length may be arranged on the surface of the intermediate wire rod in the circumferential direction of the intermediate wire rod. The length of each grain is about twice to ten times greater than the width of the grain.

(26) FIGS. 4 and 6 are photographs showing the surface of the electrode wire for electro-discharge machining which is finely drawn after stress such as curving is applied to the intermediate wire rod for the electrode wire before the fine wire process is formed. FIG. 10 is a sectional view schematically showing the electrode wire for electro-discharge machining of FIGS. 4 and 6.

(27) Referring to FIG. 10, a core wire material of brass is significantly distributed on the surface of the electrode wire for the electro-discharge machining, and brass grains are arranged on the surface of the electrode wire in the circumferential direction while forming a predetermined pattern.

(28) The grains including the core wire material are greatly distributed on the surface of the electrode wire. This is because conditions of the heat treatment process for the material constituting the core wire 12 are properly adjusted, so that the tensile strength becomes about 500 N/mm or less, and the elongation percentage becomes about 5% or more through the plating process/heat treatment process, and the intermediate wire rod is curved in a predetermined direction or stressed due to twist by the twist unit 33 before the fine wire process (elongation process) is performed.

(29) The electrode wire for electro-discharge machining according to the present invention includes the core wire 12 including brass, the first alloy layer 22 formed at the boundary region of the core wire 12 by mutually diffusing zinc and a material of the core wire to each other, and a second alloy layer 23 formed at an outer portion of the first alloy layer 22 by diffusing the material constituting the core wire to the zinc layer.

(30) The material constituting the core wire 12 may include metal including copper, for example, brass. The core wire 12 made of the material satisfies the conditions of the electrical conductivity and the mechanical strength required as an electrode wire. The second alloy layer 23 includes a material, such as zinc, representing a lower melting point and a lower vaporization temperature as compared with those of a material constituting the core wire 12 to protect the core wire 12 and to improve the machining speed when the electro-discharge machining is performed.

(31) In addition, since the second alloy layer 23 has a greater amount of cracks and grains, the second alloy layer 23 can obtain a cooling speed superior to that of the conventional electrode wire. The properties of materials used in a plating process must desirably represent a lower melting point and a lower vaporization temperature as compared with those of the second alloy layer 23. The materials must be metal which is dip-plated on the metal of the core wire 12 including copper or brass and forms an alloy layer representing higher hardness through the diffusion reaction with copper in the dip-plating process. The metal includes zinc, aluminum, and tin.

(32) Therefore, when the zinc-alloy intermediate wire rod is finely drawn to form the electrode wire for electro-discharge machining, the alloy layer may be easily cracked due to the difference in the elongation percentage between the core wire 12 and the alloy layer.

(33) As shown in FIGS. 3 and 6, since the softer material constituting the core wire 12 softly surrounds the alloy layer representing a greater strength between the cracks, the probability of generating machining particles from the core wire and the alloy layer constituting the electrode wire is reduced in the electro-discharge machining process, In addition, by-products such as fragments of the workpiece may be absorbed and removed through the cracks between boundary regions of the grains. Accordingly, the detergency effect can be more increased when comparing with the conventional electrode wire for electro-discharge machining.

Embodiment 1

(34) A core wire (including the first metal) having a diameter of about 0.9 mm, which is a brass wire (i.e., core wire including the first metal) having a compositional ratio of about 65 weight % of copper and about 35 weight % of zinc and having one of phases , +, and , is prepared as an intermediate wire rod.

(35) A zinc dip-plating process is performed with respect to the core wire by using zinc which is the second metal.

(36) The core wire used in the zinc dip-plating process is passed through an alkaline degreasing bath so that the core wire is cleaned. Then, after the core wire is subject to an acidic washing process, the core wire is cleaned again and passed through an ammonium chloride flux bath.

(37) When the wire including the first metal that has been subject to the flux treatment is dipped into an zinc dip-plating bath of the second metal and passed through the plating bath so that the wire is plated with zinc, the intermediate wire rod for the core wire 12 is dipped into the plating bath for one second to ten seconds and passed through the plating bath in a state that the temperature of a bath entrance is maintained in the range of about 550 C. to about 750 C. which is higher than the temperature of a bath exit, and the temperature of the bath exit is maintained in the range of about 420 C. to about 500 C. which is lower than the temperature of the bath entrance, so that the intermediate wire rod is plated with zinc.

(38) The intermediate wire rod for the core wire 12 is plated with zinc at the high temperature so that the intermediate wire rod can represent the tensile strength of about 500 N/mm.sup.2 and the elongation percentage of about 5% or more.

(39) In order to make the conditions for a soft wire, if the zinc dip-plating process is performed by dipping the core wire into the plating bath at a high temperature and passing the core wire through the plating bath, the core wire is formed on the boundary surface thereof with the first alloy layer 22 including the copper-zinc alloy and having a phase due to the mutual diffusion reaction with zinc when the core wire is dipped into the melted zinc and passed through the melted zinc, and the second alloy layer 23 including the zinc-copper alloy and having a phase and/or a phase is formed on the outer portion of the first alloy layer 22 while forming a soft core wire.

(40) The second alloy layer 23 including the zinc-copper alloy represents the highest hardness and represents the elongation percentage significantly lower than that of the soft core wire.

(41) Through the zinc dip-plating process and the mutual diffusion reaction, the first alloy layer 22 including the copper-zinc alloy is formed at the thickness of about 1 m to about 3 m on the boundary surface of the core wire 12, and the second alloy layer 23 including the zinc-copper alloy is formed at the thickness of about 3 m to about 10 m on the outermost layer.

(42) The first alloy layer 22 is formed due to the mutual diffusion reaction between the solid-phase core wire 12 and the liquid-phase melted zinc, and the second alloy layer 23 including zinc and copper is formed by bonding the liquid-phase melted zinc with the material of the core wire 12 including the solid-phase first metal through the mutual diffusion reaction therebetween, so that the bonding strength with the core wire can be increased.

(43) The second alloy layer is significantly cracked when the intermediate wire rod including the first alloy layer 22, the second alloy layer 23, and the soft core wire 12 is subject to a fine wire (elongation) process, and the softer metal constituting the core wire is erupted onto the surface of the second alloy layer 23, which is provided at the outermost layer, through the gap between the cracks as if lava and distributed on the surface of the second alloy layer 23.

(44) The intermediate wire rod including the alloy layers is drawn, so that the intermediate wire rod is formed as a fine wire having a diameter of about 0.07 mm to about 0.35 mm.

(45) Since the second alloy layer 23 of the drawn fine wire represents higher hardness and lower elongation percentage as compared with the core wire 12, cracks significantly appear on the surface of the outermost layer corresponding to the second alloy layer 23 when the fine wire is formed through the drawing process, and the second alloy layer 23 forms an interfacial surface together with the first metal constituting the core wire 12 while interposing the first alloy layer 22 between the second alloy layer 23 and the first metal of the core wire 12.

(46) Grains having the compositional ratio of three components of the first metal of the core wire, the metallic component of the first alloy layer including the copper-zinc alloy layer, and the metallic component of the second alloy layer including the zinc-copper alloy layer are formed on the surface of the electrode wire for electro-discharge machining that has been manufactured through the above method as shown in FIGS. 3 and 9.

(47) The electrode wire for electro-discharge machining that has been manufactured through the fine wire process is additionally subject to a heat treatment process within 0.05 second to three seconds at the temperature of about 300 C. to about 600 C., so that the mechanical property of the core wire can be stabilized.

Embodiment 2

(48) A core wire (including the first metal) having a diameter of about 0.9 mm, which is a brass wire (i.e., core wire including the first metal) having a compositional ratio of about 65 weight % of copper and about 35 weight % of zinc and having one of phases , +, and , is prepared as an intermediate wire rod.

(49) A zinc dip-plating process is performed with respect to the core wire by using zinc which is the second metal.

(50) The core wire used in the zinc dip-plating process is passed through an alkaline degreasing bath so that the core wire is cleaned. Then, after the core wire is subject to an acidic washing process, the core wire is cleaned again and passes through an ammonium chloride flux bath.

(51) When the wire including the first metal that has been subject to the flux treatment is dipped into an zinc dip-plating bath of the second metal and passed through the plating bath so that the wire is plated with zinc, the intermediate wire rod for the core wire is dipped into the plating bath for one second to ten seconds and passed through the plating bath in a state that the temperature of a bath entrance is maintained in the range of about 550 C. to about 750 C. which is higher than the temperature of a bath exit, and the temperature of the bath exit is maintained in the range of about 420 C. to about 500 C. which is lower than the temperature of the bath entrance, so that the intermediate wire rod is plated with zinc.

(52) The intermediate wire rod for the core wire 12 is plated with melted zinc at the high temperature so that the intermediate wire rod can represent the tensile strength of about 500 N/mm.sup.2 and the elongation percentage of about 5% or more.

(53) In order to make the conditions for a soft wire, if the zinc dip-plating process is performed by dipping the core wire into the plating bath at a high temperature and passing the core wire through the plating bath, the core wire is formed on the boundary surface thereof with the first alloy layer 22 including the copper-zinc alloy and having a phase due to the mutual diffusion reaction with zinc when the core wire is dipped into the melted zinc and passed through the melted zinc, and the second alloy layer 23 including the zinc-copper alloy and having a phase and/or a phase is formed on the outer portion of the first alloy layer 22 while forming a soft core wire.

(54) The second alloy layer 23 including the zinc-copper alloy represents the highest hardness and represents the elongation percentage significantly lower than that of the soft core wire.

(55) Through the zinc dip-plating process and the mutual diffusion reaction, the first alloy layer 22 including the copper-zinc alloy is formed at the thickness of about 1 m to about 3 m on the boundary surface of the core wire 12, and the second alloy layer 23 including the zinc-copper alloy is formed at the thickness of about 3 m to about 1 m on the outermost layer.

(56) The first alloy layer 22 is formed due to the mutual diffusion reaction between the solid-phase core wire 12 and the liquid-phase melted zinc, and the second alloy layer 23 including zinc and copper is formed by bonding the liquid-phase melted zinc with the material of the core wire 12 including the solid-phase first metal through the mutual diffusion reaction therebetween, so that the bonding strength with the core wire 12 can be increased.

(57) The intermediate wire rod including the first alloy layer, the second alloy layer, and the soft core wire is passed through the twist unit 33 between the roller 16 of FIG. 2 and the drawing unit 14 before the intermediate wire rod is subject to a fine wire process (elongation process), so that the intermediate wire rod is curved in a zigzag pattern.

(58) After the intermediate wire rod has been passed through the twist unit 33 of curving the intermediate wire rod in a zigzag pattern as described above before the intermediate wire rod is formed as the fine wire, the intermediate wire rod is formed as a fine wire having a diameter of about 0.07 mm to about 0.35 mm through a drawing process.

(59) In particular, according to the present embodiment, stress is applied to the intermediate wire rod so that the intermediate wire rod is curved in a predetermined direction before the intermediate wire rod is drawn as the fine wire. Accordingly, as shown in FIG. 7, cracks appear on the second alloy layer in a direction perpendicular to a longitudinal direction of the intermediate wire rod, and core wire metal made of soft brass is erupted onto the surface of the second alloy layer along the cracks as if lava, so that a plurality of grain groups are formed on the surface of the second alloy layer.

(60) Core wire materials including brass are significantly distributed onto the surface of the electrode wire for electro-discharge machining through the stress process of curving the intermediate wire rod, and brass grains are arranged on the surface of the electrode wire in the circumferential direction while forming a predetermined pattern. The length of the brass grain is twice to ten times greater than the width of the brass grain.

(61) Grain fragments having the compositional ratio of three components of the first metal of the core wire, the metallic component of the first alloy layer including the copper-zinc alloy layer, and the metallic component of the second alloy layer including the zinc-copper alloy layer are formed on the surface of the electrode wire for electro-discharge machining that has been manufactured through the above method as shown in FIGS. 4 and 10.

(62) The electrode wire for electro-discharge machining that has been manufactured through the fine wire process is additionally subject to a heat treatment process within 0.05 second to three seconds at the temperature of about 300 C. to about 600 C., so that the mechanical property of the core wire can be stabilized.

Embodiment 3

(63) A core wire (including the first metal) having a diameter of about 0.9 mm, which is a brass wire (i.e., core wire including the first metal) having a compositional ratio of about 65 weight % of copper and about 35 weight % of zinc and having one of phases , +, and , is prepared as an intermediate wire rod.

(64) A zinc-electroplating process is performed with respect to the core wire by using zinc which is the second metal.

(65) After the core wire used in the zinc-electroplating process has been passed through the alkaline cleaning bath, the core wire is subject to cleaning and acidic washing processes. Then, after the core wire is subject to the cleaning process again, the core wire is passed through a zinc-electroplating bath.

(66) The intermediate wire rod, which has been subject to the zinc-electroplating process, is put into heat treatment machine and subject to a heat treatment process at the speed of about 155 m/min under the voltage in the range of about 50V to about 60V. Accordingly, the core wire is formed with the tensile strength of about 500 N/mm.sup.2 or less and the elongation percentage of about 5% or more.

(67) If the heat treatment process is performed after the electroplating process in order to fabricate an intermediate wire rod having the core wire satisfying the above conditions, the first alloy layer 22 including copper-zinc and having a phase is formed on the boundary surface between the core wire (including the first metal) and the second metal, which is plated through the zinc-electroplating process, due to the mutual diffusion reaction between the core wire and the second metal, and the second alloy layer 23 including zinc-copper and having a phase and/a phase is formed at the outer portion of the first alloy layer 22.

(68) The second alloy layer including zinc-copper represents the highest hardness and represents the elongation percentage lower than that of the soft core wire.

(69) Through the zinc-electroplating process and the mutual diffusion reaction, a first alloy layer including copper-zinc is formed at the thickness of about 1 m to about 3 m on the boundary surface of the core wire, and the second alloy layer including zinc-copper is formed at the thickness of about 3 m to about 1 m on the outer portion of the first alloy layer 23.

(70) The first alloy layer is formed due to the mutual diffusion reaction between the first metal of the core wire and zinc (i.e., the second metal) plated in the electroplating process, and the second alloy layer is formed by diffusing the first metallic component constituting the core wire to the second metal plated in the zinc-electroplating process, so that the core wire becomes in a soft wire state representing the tensile strength of about 500 N/mm.sup.2 or less and the elongation percentage of about 5% or more.

(71) In the intermediate wire rod, which is obtained by forming the first and second alloy layers on the core wire, cracks significantly appear on the second alloy layer representing the highest hardness, and the softer metal constituting the core wire is erupted onto the surface of the second alloy layer corresponding to the outermost layer along the gap between cracks as if lava and distributed onto the surface of the second alloy layer.

(72) The intermediate wire rod having the alloy layers is formed as a fine wire having a diameter of about 0.07 mm to about 0.35 mm through a drawing process.

(73) Since the second alloy layer of the drawn fine wire represents the higher hardness and the lower elongation percentage, a great amount of cracks appear on the surface of the outmost layer corresponding to the second alloy layer when the fine wire is formed through the drawing process. The second alloy layer forms an interfacial surface together with the first metal while interposing the first alloy layer between the second alloy layer and the first metal.

(74) Grain fragments having the compositional ratio of three components of the first metal of the core wire, the metallic component of the first alloy layer including the copper-zinc alloy layer, and the metallic component of the second alloy layer including the zinc-copper alloy layer are formed on the surface of the electrode wire for electro-discharge machining that has been manufactured through the above method as shown in FIGS. 5 and 9.

(75) The electrode wire for electro-discharge machining that has been manufactured through the fine wire process is additionally subject to a heat treatment process within 0.05 second to three seconds at the temperature of about 300 C. to about 600 C., so that the mechanical property of the core wire can be stabilized.

Embodiment 4

(76) A core wire (including the first metal) having a diameter of about 0.9 mm, which is a brass wire (i.e., core wire including the first metal) having a compositional ratio of about 65 weight % of copper and about 35 weight % of zinc and having one of phases , +, and , is prepared as an intermediate wire rod.

(77) A zinc-electroplating process is performed with respect to the core wire by using zinc which is the second metal.

(78) After the core wire used in the zinc-electroplating process has been passed through the alkaline cleaning bath, the core wire is subject to cleaning and acidic washing processes. Then, after the core wire is subject to the cleaning process again, the core wire is passed through a zinc-electroplating bath.

(79) The intermediate wire rod, which has been subject to the zinc-electroplating process, is put into heat treatment machine and subject to a heat treatment process at the speed of about 155 m/min under the voltage in the range of about 50V to about 60V. Accordingly, the core wire is formed with the tensile strength of about 500 N/mm2 or less and the elongation percentage of about 5% or more.

(80) If the heat treatment process is performed after the electroplating process in order to fabricate an intermediate wire rod satisfying the above conditions, the first alloy layer 22 including copper-zinc and having a phase is formed on the boundary surface between the core wire (including the first metal) and the second metal, which is plated through the zinc-electroplating process, due to the mutual diffusion reaction between the core wire and the second metal, and the second alloy layer 23 including zinc-copper and having a phase and/or a phase is formed at the outer portion of the first alloy layer 22.

(81) The first alloy layer is formed due to the mutual diffusion reaction between the first metal of the core wire and zinc (i.e., the second metal) plated in the electroplating process, and the second alloy layer is formed by diffusing the first metallic component of the core wire to the second metal used in the zinc-electroplating process, so that the core wire becomes in a soft wire state representing the tensile strength of about 500 N/mm.sup.2 or less and the elongation percentage of about 5% or more.

(82) The second alloy layer including zinc-copper represents the highest hardness and represents the elongation percentage lower than that of the soft core wire.

(83) Through the heat treatment process after the electroplating process, the first alloy layer including the alloy of copper-zinc is formed at the thickness of about 1 m to about 3 m on the boundary surface of the core wire, and the second alloy layer including the zinc-copper alloy is formed at the thickness of about 3 m to about 1 m on the outermost layer.

(84) The intermediate wire rod including the first alloy layer, the second alloy layer, and the soft core wire is passed through the twist unit 33 between the roller 16 of FIG. 2 and the drawing unit 14 before the intermediate wire rod is subject to a fine wire process (elongation process), so that the intermediate wire rod is curved in a zigzag pattern.

(85) After the intermediate wire rod has been passed through the twist unit 33 of curving the intermediate wire rod in a zigzag pattern before the intermediate wire rod is formed as a fine wire, the intermediate wire rod is formed as a fine wire having a diameter of about 0.07 mm to about 0.35 mm through a drawing process.

(86) In particular, according to the present embodiment, stress is applied to the intermediate wire rod so that the intermediate wire rod is curved in a predetermined direction before the intermediate wire rod is drawn as the fine wire. Accordingly, as shown in FIG. 8, cracks additionally appear on the second alloy layer in a direction perpendicular to a longitudinal direction of the intermediate wire rod, and core wire metal made of soft brass is erupted onto the surface of the second alloy layer through the cracks as if lava, so that a plurality of grain groups are formed on the surface of the second alloy layer.

(87) Core wire materials including brass are significantly distributed onto the surface of the electrode wire for electro-discharge machining due to the stress process of curving the intermediate wire rod, and brass grains are arranged on the surface of the electrode wire in the circumferential direction while forming a predetermined pattern. The length of the brass grain is twice to ten times greater than the width of the brass grain.

(88) Grain having the compositional ratio of three components of the first metal of the core wire, the metallic component of the first alloy layer including the copper-zinc alloy layer, and the metallic component of the second alloy layer including the zinc-copper alloy layer are formed on the surface of the electrode wire for electro-discharge machining that has been manufactured through the above method as shown in FIGS. 6 and 10.

(89) The electrode wire for electro-discharge machining that has been manufactured through the fine wire process is additionally subject to a heat treatment process within 0.05 second to three seconds at the temperature of about 300 C. to about 600 C., so that the mechanical property of the core wire can be stabilized.

(90) As described above, according to the embodiments, since grains, which surround the second alloy layer, are formed by erupting the softer core wire upward onto the surface of the electrode wire through the cracks and exposing the core wire onto the surface of the electrode wire, a small amount of machining particles are derived from the electrode wire. In addition, since the second alloy layer having a vaporization temperature lower than that of the first metal increases instantaneous vaporization power of thermal energy in discharging, the manufacturing speed is increased, and the surface roughness of the workpiece and the manufacturing speed are maximized in the electro-discharging process.

(91) The embodiments have been described in terms of the electroplating process and the dip-plating process. However, even if a heat treatment process may be performed after a chemical plating scheme has been performed, the same effects can be made.

(92) The first metal may include copper or the alloy of copper other than brass, and the second metal may include zinc, aluminum, tin, or the alloy thereof.

(93) Although a preferred embodiment of the present invention has been described for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.