RU2449865C2 - Electrode wire for electric erosion processing, method of its production and system to produce base wire there for - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: invention relates to electrode wire for electric erosion processing. Electrode wire comprises brass strand, layer of pure zinc formed by strand hot galvanising and zinc-coated base wire with thermodiffusion layer formed by thermal diffusion of said pure zinc layer and cold drawing strand. Pure zinc layer features thickness making 1.2% to 3.2% of electrode wire OD while thermodiffusion layer from copper-zinc alloy with zinc concentration varying from 50 wt % to 100 wt % features thickness making 0.36% to 1.08% of said OD. Note here that pure zinc layer is formed with thickness of said range and exceeding thermodiffusion layer. Note also that there no cracks on electrode wire surface.

EFFECT: higher stability of arc discharge, higher processing rate, better roughness of processed part surface.

4 cl, 10 dwg, 3 tbl

Description

FIELD OF TECHNOLOGY

[0001] The present invention relates to an improved electrode wire for wire EDM, a method for its manufacture and a system for manufacturing a base wire for an electrode wire.

BACKGROUND OF THE INVENTION

[0002] Wire EDM is a technology for cutting a workpiece using heat energy generated by an electric discharge between an electrode wire and a workpiece, and is particularly suitable for metal working to produce metal molds or other complex shapes.

This type of EDM must meet several requirements, including: a. Fast processing speed; b. Reduced amount of metal powder formed during prolonged passage of electrode wire; from. Good surface finish and dimensional accuracy of the workpiece, and d. Good positioning when determining the position of the electrode wire relative to the workpiece.

[0003] The traditional electrode wire, which has been widely used for this type of processing, is a non-layered solid brass wire with a zinc concentration of 35-40 wt.%.

This brass electrode wire has a speed limit due to the impossibility of increasing the zinc content.

Various studies have been conducted to achieve a higher EDM rate than that of a brass electrode wire. It is well known that a higher zinc content in the electrode wire provides a higher processing speed.

In order to increase the processing speed, these studies are broadly classified into two approaches: increasing the concentration of zinc in the composition of the brass of the electrode wire to 40 wt.% Or more; and providing a layer of copper-zinc alloy with a zinc concentration of at least 40 wt.% or a layer of pure zinc on the surface of the electrode wire.

[0004] JP3303296B2 discloses a first approach, i.e. increasing the concentration of zinc in the composition of the brass electrode wire to 40 wt.% or more. However, this copper-zinc alloy has a problem in that a thin wire is made from it. As shown in the phase diagram of the double alloy in FIG. 10, this alloy includes α, β, γ, ε, and η solid solutions, among which only the α phase having a maximum solubility of zinc in the solid solution of approximately 39 wt.% Can subjected to cold drawing in case of practical use, and β- and other phases are fragile and break when cold drawn.

To solve this problem in that invention, zirconium or another metal is added to the β-phase fragment, thereby increasing ductility, which leads to a multicomponent alloy containing copper, zinc or another metal, and increases the manufacturing cost.

[0005] JP3718617B2 discloses a porous electrode wire on the surface of which there is a layer of copper-zinc alloy with a zinc concentration of at least 40 wt.% Or a layer of pure zinc.

This porous electrode wire has a layer of copper-zinc alloy or a zinc layer formed by hot-dip galvanizing a copper-containing core and extended to deliberately crack its surface, as a result of which the surface area of the electrode wire brought into contact with the working fluid during electric discharge machining increases and the electrode the wire cools faster, which increases the processing speed.

[0006] However, cracks on the surface of the electrode wire pose the following problems:

a. Since wire EDM is a hacksaw-type treatment and leads to thermal cutting of the workpiece using an electric discharge between the electrode wire and the workpiece, a crack on the surface of the electrode wire destabilizes the electric discharge and gives a poor surface finish for the workpiece;

b. Such a brittle surface, such as a surface with cracks during cold drawing, generates a significant amount of metal powder due to friction or abrasion on the guides and pulleys in the mechanism during the continuous passage of the electrode wire during processing and affects the workability;

from. The cracked surface of the electrode wire reduces the positioning accuracy, since the EDM machine cannot accurately determine the position of the electrode wire relative to the workpiece due to unstable continuity between them; and

d. Cracked surface reduces the reliability of the electrode wire, since the wire tends to break when handling or processing.

[0007] JP3602402B2 discloses a wire electrode for electrical discharge machining, having on its surface a layer of copper-zinc alloy with a zinc concentration of at least 40 wt.% And a layer of zinc.

This wire electrode has a conductive core, which basically takes on tension, and a coating that includes two layers and wears out during erosion. The inner layer has a thickness of at least 2.5 μm and is made of an almost homogeneous alloy containing 40-48 wt.% Zinc, for high-speed cutting. The outer layer has a thickness of 0.5-5 μm and contains 80-100 wt.% Zinc for precision cutting. The thickness of the outer layer is within one fifth of the thickness of the inner layer.

[0008] However, this electrode wire would crack upon cold drawing and cause problems similar to those described with respect to the above-described JP3718617B2, since its outer layer containing a maximum of 100 wt.% Zinc is extremely thin compared to the brittle layer of copper-zinc alloy containing 40-48 wt.% zinc.

[0009] JP3405069B2 discloses a method for manufacturing an electrode wire with two layers of a copper-zinc alloy, i.e. including the inner layer of the β-phase and the outer layer of the α-phase, to prevent the appearance of cracks on the surface during cold drawing.

However, this method increases the manufacturing cost due to complicated processes, since before cold drawing of the wire, a suspension containing mainly zinc powder is first applied, dried and heat treated, then another suspension containing zinc powder with a lower concentration of zinc is applied, dried and subjected to heat treatment.

SUMMARY OF THE INVENTION

[0010] As described above, conventional electrode wires for high speed wire EDM can actually increase the speed of processing, but they degrade other EDM characteristics (JP3718617B2 and JP3602402B2) or increase the manufacturing cost (JP3303296B2 and JP3405069B2).

The present invention aims to solve these problems by proposing an electrode wire for electrical discharge machining, which can be made without complicating the processes and without cracks on its surface.

Another objective of the present invention is to propose an electrode wire for EDM, which provides a higher processing speed, improves the surface roughness of the workpiece, reduces the amount of metal powder generated during continuous passage of the electrode wire, provides good positioning to determine the position of the electrode wire relative to the workpiece and Does not collapse when handling it or during processing.

Another objective of the present invention is to provide a method and system for the manufacture of the above electrode wire for EDM.

[0011] In the embodiment of claim 1, the electrode wire for electrical discharge machining includes a core made of copper or a copper alloy, a pure zinc layer formed by hot-dip galvanizing the core, and a copper-zinc alloy layer formed by mutual thermal diffusion across the interface between a layer of pure zinc and residential. The pure zinc layer is thicker than the copper-zinc alloy layer, and there are no cracks on the surface of the electrode wire.

In the embodiment according to claim 2 of this application, the electrode wire for EDM is made of a base wire having a sufficiently thick layer of pure zinc to prevent cracking during cold drawing and has no cracks on its surface.

In the embodiment of claim 3 of the present application, the pure zinc layer is at least 1.2% of the diameter of the electrode wire of claim 1 or 2.

In an embodiment according to claim 4 of this application, the core is made of brass, instead of copper or a copper alloy according to any one of claims 1-3.

[0012] In the embodiment of claim 5 of this application, a brass wire made by melting, casting and drawing processes is used as a core in a method for manufacturing an electrode wire for EDM wire. Such a core is subjected to surface washing and then passed through a galvanizing bath containing pure zinc at a given temperature for a predetermined immersion time to form a pure zinc layer exceeding a predetermined thickness, then cooled to form a layer of copper-zinc alloy by mutual thermal diffusion across the boundary section between the brass wire and a layer of pure zinc, getting a galvanized base wire, and then subjected to cold drawing into the electrode wire for electrical discharge machining and wire.

In the embodiment of claim 6, the immersion time is adjusted so that the immersion time does not exceed 1.2 seconds to ensure that the pure zinc layer is at least 1.2% of the diameter of the wire electrode.

In the embodiment of claim 7 of this application, the temperature of the galvanizing bath is limited to 500 ° C. or less, so that the pure zinc layer becomes thicker than the thermal diffusion layer.

In an embodiment according to claim 8 of this application, a zinc purification process is carried out by blowing non-oxidizing gas onto the surface of the bath through which the vein emerges from the bath.

In an embodiment according to claim 9 of the present application, a blowing process is carried out by passing around a layer of pure zinc a non-oxidizing gas heated to a temperature higher than that of molten zinc.

[0013] In an embodiment according to claim 10 of the present application, there is provided a system for manufacturing a base wire for an electrode wire for wire EDM. This system forms a layer of pure zinc by hot-dip galvanizing a pre-heated core made of copper or a copper alloy. The system contains a jet gas blower with a jet tip facing the surface of the bath through which the vein emerges from the bath, for blowing through the jet tip of non-oxidizing gas to remove a layer of impurities, including oxide films and flux reaction products, and to maintain the exposed surface of the pure zinc bath.

In the embodiment of claim 11 of the present application, the pure zinc layer is controlled by the pressure of the non-oxidizing gas supplied to the blow pipe, so that the gas flows around the galvanized core in the direction opposite to that in which the galvanized core is taken out, making the thickness of the pure zinc layer uniform and preventing decentration.

In an embodiment according to claim 12 of the present application, a system for manufacturing a base wire for an electrode wire for electric discharge machining includes a blow pipe having a heater for heating the non-oxidizing gas to a temperature higher than the melting point of zinc, a jet blower located below the blow pipe and having a bottom facing the surface of the zinc bath, a first gas supply means for supplying non-oxidizing gas from above the blow pipe to its internal cavity, and a second gas supply medium GUSTs for feeding warmed non-oxidizing gas to the jet blower.

[0014] In the embodiments of paragraphs 1-4, the electrode wire can be made without complicating the processes and without cracks on its surface. This provides a higher rate of EDM and extremely improved surface roughness of the workpiece.

Moreover, the amount of metal powder generated during continuous passage of the electrode wire is reduced, so that the electrode wire can be accurately positioned relative to the workpiece and can withstand tearing during handling or processing with increased reliability.

If the core is made of brass, then the discharge characteristics are improved, and therefore, the manufacturing cost can be reduced.

[0015] In embodiments according to claims 5-9, a thick layer of pure zinc can be formed, and therefore, electrode wire can be made without cracks on its surface.

Simple process control to limit immersion times within 1.2 seconds or to limit the temperature of a galvanizing bath to below 500 ° C makes it easier to fabricate a base wire having a sufficiently thick layer of pure zinc to prevent cracking during cold wire drawing.

By blowing non-oxidizing gas onto the surface of the bath through which the vein emerges from the hot dip galvanizing bath, a layer of impurities, including oxide films or reaction products with flux, can be removed, and the surface of the pure zinc bath can be maintained so that a pure zinc layer can be formed on the core .

As a result of the blowing process, the occurrence of smudges and uneven thickness of the pure zinc layer can be avoided, and cracks on the surface of the electrode wire during its cold drawing can also be avoided.

[0016] In the embodiments of claims 10-12, it is easy to form a layer of pure zinc on the base wire and electrode wire for EDM by arranging a jet blower with a jet tip facing the surface of the hot dip galvanizing bath through which the core emerges from the bath, and blowing non-oxidizing gas through the jet tip onto the surface of the bath in order to remove a layer of impurities, including oxide films and fluxed reaction products, and to maintain a clean qi bath surface nka nude.

By forcing non-oxidizing gas to flow at high pressure around the core in the direction opposite to the direction in which the core is taken out, the layer obtained by galvanizing can be adjusted to make the thickness of this layer obtained by galvanizing uniform and preventing the core from being decentered.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] FIG. 1 is a sectional view showing an electrode wire of the present invention;

FIG.2 shows the concentration of zinc in the radial direction of the electrode wire;

3 shows a hot dip galvanizing device;

FIGURE 4 is an enlarged view of the surface cleaning device of the zinc bath and blowing;

FIGURE 5 is an optical micrograph at a 1000-fold increase in the cross section of a galvanized brass core according to example No. 2;

FIG.6 is an optical micrograph at a 1000-fold increase in the cross section of the electrode wire according to example No. 2;

FIG.7 is a micrograph in a scanning electron microscope (SEM) with a 350-fold increase in the surface of the electrode wire according to example No. 2;

FIG. 8 is an optical micrograph at a 1000-fold increase in the cross section of the electrode wire according to comparative example No. 1;

FIGURE 9 is a micrograph in a scanning electron microscope (SEM) with a 350-fold increase in the surface of the electrode wire according to comparative example No. 1; and

10 shows a state diagram of a binary copper-zinc alloy.

BEST MODE FOR CARRYING OUT THE INVENTION IN PRACTICE

[0018] The electrode wire of the present invention includes a core 1 made of copper or a copper alloy, a thermal diffusion layer 2, and a pure zinc layer 3, as shown in FIG. 1.

The method for manufacturing the electrode wire of the present invention provides an electrode wire having a zinc concentration gradient in the radial direction of the electrode wire, as shown in FIG. 2, provided that the composition of the copper or copper alloy of the core 6, its outer diameter, the temperature of the galvanizing bath and the immersion time properly selected.

In this case, a non-oxidizing process is carried out by blowing non-oxidizing gas onto the surface of the galvanizing bath to maintain the surface of the pure zinc bath naked, forming a layer of high-purity zinc on the core, then a blowing process is carried out on the galvanized layer to prevent oxidation of the surface of the galvanized layer, smudges and uneven thickness obtained by galvanizing layer, getting a galvanized base wire, and then carry out cold wire drawing.

[0019] According to the present invention, an electrode wire is obtained on which, after cold drawing, there are no cracks or microcracks, since the outermost layer is coated with a relatively thick layer of pure zinc having better deformability than the diffusion copper-zinc layer.

Such an electrode wire, with a non-cracked outermost layer of pure zinc, contributes to electric discharge and, thus, improves discharge stability, and, with its underlying layer of copper-zinc alloy formed by thermal diffusion, improves processing speed and reduces the formation of metal powder, improves roughness surface of the workpiece and provides better positioning.

[0020] Further, the present invention will be more specifically described with reference to examples.

Electrode wire for EDM

First group of examples

Examples No. 1-4

65/35 brass wire (65 wt.% Copper and 35 wt.% Zinc) with a diameter of 1.2 mm, made by melting, casting and drawing, was used as core 6. The surface of core 6 was washed in etching bath 4 and washing the flux forming part of the hot dip galvanizing apparatus of FIG. 3. The core 6 was then passed through a dip galvanizing bath 5 containing pure zinc at 460 ° C, vertically stretched in a galvanizing bath 5 and subjected to a blowing process to form a layer of copper-zinc alloy by mutual thermal diffusion through the interface between the brass wire and zinc. To find the immersion time range at which a pure zinc layer is formed on the core 6, four types of galvanized base wires 7 were made for the electrode wire by varying the immersion time: 0.5 second, 0.7 second, 1.0 second and 1.2 seconds.

Regarding the blowing process, the non-oxidizing process and the blowing process were carried out to remove oxides on the surface of the bath and to prevent smudges and uneven thickness of the galvanized layer using the device 8 for cleaning the surface of the zinc bath and the blow located above the hot-dip galvanizing bath 5, as shown on an enlarged view in FIG. 4. In a non-oxidizing process, non-oxidizing gas, such as nitrogen gas and argon gas, was blown onto the surface of the galvanizing bath to remove oxides on the surface of the bath. Details of this will be described below.

Then the galvanized base wires 7 were subjected to cold drawing to obtain electrode wires with a diameter of 0.25 mm

In all examples, including the comparative examples described below and the comparative examples described below, pure electrolytic zinc obtained by electrolysis was used in a hot dip galvanizing bath.

[0021] The second group of examples

Examples No. 5 and 6

Electrode wires with a diameter of 0.25 mm were obtained under the same conditions as in the first group of examples described above, except that the temperature of the hot dip galvanizing bath was set to 440 ° C and the immersion time was set to 0.5 seconds and 1 second.

[0022] The third group of examples

Examples No. 7 and 8

Electrode wires with a diameter of 0.25 mm were obtained under the same conditions as in the first group of the examples described above, except that the temperature of the hot dip galvanizing vessel was set to 500 ° C and the immersion time was set to 0.5 seconds and 1 second respectively.

[0023] The first group of comparative examples

Comparative Examples No. 1-7

The base wires were obtained by galvanizing in a hot dip galvanizing bath at the same temperatures as in the above examples, Nos. 1-7, for longer immersion times specified by slowing down the winding speeds compared to the above examples, followed by the blowing process . The base wires were cold drawn to produce 0.25 mm diameter electrode wires.

[0024] The second group of comparative examples

Reference Example No. 8

The base wire was obtained by galvanizing in a hot dip galvanizing bath set to 520 ° C for an immersion time of 1 second, followed by a blowing process. The base wire was cold drawn to produce a 0.25 mm diameter electrode wire.

[0025] The electrode wires obtained in examples No. 1-8 and in comparative examples No. 1-8 were evaluated on the following points:

a. Characteristics of electric discharge machining (processing speed, amount of metal powder formed, surface roughness of the workpiece and positioning accuracy);

b. The thickness of the layer of copper-zinc alloy formed by thermal diffusion across the interface between the core and molten zinc, and the thickness of the layer of pure zinc; and

c. The presence of cracks on the surface.

The EDM performance was evaluated using an SX10 wire EDM machine from Mitsubishi Electric under the processing conditions shown in Table 1 and the methods shown in Table 2.

The evaluation results are shown in Table 3.

[0026] Table 1 PARAGRAPH CALIBRATION SETUP NOTES VOLTAGE SELECTION 12 Selection of interelectrode voltage in an unloaded state MANUFACTURING INSTALLATIONS eleven Selection of maximum current between electrodes SIMPLE EQUIPMENT one Selection of the time interval from the end of the discharge to the repeated application of voltage WIRING SPEED 12
(12 m / min) Selection of electrode wire feed speed for wire EDM TENSION OF WIRE eleven
(16 N) Selection of electrode wire tension for wire EDM SPECIFIC RESISTANCE OF THE WORKING LIQUID 9
(5.8 × 10 ⁴ Ohm · cm) The choice of resistivity of the working fluid PROCESSED PART MATERIAL SKD-11 THICKNESS 60 mm

[0027] table 2 CHARACTERISTIC LIST ASSESSMENT METHOD MACHINE SPEED The cross-sectional area processed per unit time (processing speed multiplied by the thickness of the workpiece) under the processing conditions presented in Table 1 is determined and expressed as the ratio to the processing speed (set to 1.00) of an electrode wire made of traditional brass wire 65/35. NUMBER OF FORMED METAL POWDER When passing an electrode wire for EDM wire without performing EDM processing, the electrode wire is scratched on the guides on the wire path and forms a metal powder. This metal powder gradually accumulates on a diamond die, which limits the oscillation of the wire during processing, and the wire as a result cannot pass and eventually breaks. An estimate of the amount of metal powder formed is alternatively expressed as the time to wire break. POSITIONING ACCURACY Positioning is an operation performed by applying voltage to find the point at which continuity occurs when moving the electrode wire for EDM wire 1 μm at a time between the electrode wire and the workpiece. The point at which the continuity arises is taken as the reference point. Reference points were measured 50 times under the processing conditions shown in Table 1, and the positioning accuracy is expressed as the standard deviation (St. Off) of the measured values. ROUGHNESS OF THE SURFACE OF THE PROCESSED PART The surface roughness of a part treated under the processing conditions shown in Table 1 was measured using a surface roughness measuring instrument and expressed as the average of ten roughness points (Rz) specified in JIS B0601 (1994).

[0029] FIG. 1 is a sectional view of an electrode wire in an embodiment of the present invention; FIG.2 illustrates the concentration of zinc in the radial direction of the electrode wire.

As shown in FIGS. 1 and 2, the surface of the electrode wires in Examples No. 1-8 consisted of the outermost layer of pure zinc containing 100% zinc, an underlying layer of a copper-zinc alloy with a zinc concentration of from 50 wt.% To 100 wt. % (exclusively) formed by thermal diffusion.

[0030] As shown in detail in Table 3, the outermost pure zinc layer has an average layer thickness of 3.0-8.0 μm, comprising 1.2-3.2% of the outer diameter of the electrode wire.

This share significantly exceeds the share of 0.08-1.04%, characteristic of comparative examples No. 1-8.

[0031] The thermal diffusion layer includes an inner layer A of a copper-zinc alloy with a zinc concentration of 50-80 wt.%, Formed by thermal diffusion of zinc into the core material 6, and an outer layer B of a copper-zinc alloy formed by thermal diffusion of copper from the core material 6 into molten zinc. The inner layer A of the copper-zinc alloy has an average layer thickness of 0.4-1.5 μm, while the outer layer B of the copper-zinc alloy has an average layer thickness of 0.5-1.2 μm.

The entire A + B thermal diffusion layer has an average layer thickness of 0.9-2.7 μm, which is 0.36-1.08% of the outer diameter of the electrode wire of 0.25 mm.

[0032] On the other hand, the A + B thermal diffusion layer of a copper-zinc alloy with a zinc concentration of from 50 wt.% To 100 wt.% (Exclusively) in comparative examples No. 1-8 has an average layer thickness of 1.4-3, 0 μm, which is slightly thicker than the layer in the examples, amounting to 0.56-1.20% of the outer diameter of the electrode wire of 0.25 mm

These A + B thermodiffusion layers have zinc concentration gradients that gradually increase towards the surface of the electrode wire, i.e. from the core to the galvanized layer, without a sharp change in the zinc concentration that occurs at the interface between the galvanized layer and the core.

[0033] FIGURE 5 is an optical micrograph with a 1000-fold increase in the cross section of a galvanized base wire obtained by hot-dip galvanizing a brass core in example No. 2; FIG.6 is an optical micrograph at a 1000-fold increase in the cross section of the electrode wire after cold drawing; and FIG. 7 is a scanning electron microscope (SEM) image of the surface of an electrode wire after cold drawing.

As can be seen from these images, in example No. 2, the inner brittle layer of the copper-zinc alloy formed by thermal diffusion was surrounded by a layer of pure zinc with high ductility, so that there were no cracks or microcracks on the surface of the electrode wire after cold drawing.

[0034] As can be seen from Table 3, the electrode wires in examples No. 1-4, which meet the conditions of the present invention, have led to an increase in processing speed by approximately 20% compared to traditional brass electrode wire 65/35.

Regarding the surface roughness of the workpiece (average roughness measured at ten points), the electrode wire of the present invention is also improved, providing a roughness of 16.2-16.3 microns, while the traditional brass electrode wire 65/35 provided 18.4 microns. This is due to the fact that the electrode wire of the present invention has a thick layer of pure zinc, which contributes to electric discharge and, thus, improves the stability of the discharge.

Regarding the amount of metal powder formed and positioning accuracy, the electrode wire of the present invention is similar to the traditional 65/35 brass electrode wire.

[0035] As can be seen from Table 3, similarly to the first group of examples No. 1-4, in examples No. 5-6, in which the temperature of the hot dip galvanizing bath was set to 440 ° C, which was 20 ° C lower than the temperature of the first groups of examples No. 1-4, and immersion times were set equal to 1 second and 0.5 seconds, respectively, layers A + B of a copper-zinc alloy formed by thermal diffusion through the interface between the brass core and molten zinc have an average layer thickness, approximately 0.4% of the outer diameter of the electrode wire Oka and pure zinc layers on the thermal diffusion of these layers have an average layer thickness constituting 1.8-3.2% of the outer diameter of the electrode wire, the surface of the electrode wire after cold drawing are no cracks or microcracks.

The characteristics of EDM were the same as the characteristics of the first group of examples; the processing speed was increased by approximately 20% compared to the traditional 65/35 electrode wire, and the surface roughness of the treated sample was improved from 18.4 μm to 16.3 μm.

[0036] As can be seen from Table 3, similarly to the first group of examples, in examples No. 7-8, in which the temperature of the molten zinc was set equal to 500 ° C, which was 40 ° C higher than the temperature from the first group of examples, and the immersion times were set equal to 1 second and 0.5 second, respectively, layers of a copper-zinc alloy formed by thermal diffusion across the interface between a brass core and molten zinc have an average layer thickness of approximately 0.72-1.08% of the outer diameter of the electrode wire , and the layers are pure of zinc on these thermal diffusion layers have an average layer thickness constituting 1,20-2,84% of the outer diameter of the electrode wire, the surface of the electrode wire after cold drawing no cracks and microcracks.

The characteristics of EDM were the same as the characteristics of the first group of examples; processing speed was increased by approximately 20% compared to traditional 65/35 brass electrode wire; and the surface roughness of the workpiece was improved from 18.4 microns to 16.2-16.3 microns.

[0037] The electrode wire obtained in comparative example 1 was also evaluated in the same manner as for the electrode wires in the examples. The evaluation results are shown in Table 3.

As can be seen from Table 3, in comparative examples No. 1-6, in which the immersion time was 1.4-6.0 seconds, which was longer than the immersion time from the examples with the same temperatures of the hot dip galvanizing bath, the layers of copper-zinc The alloys formed by thermal diffusion were thicker, and the layers of pure zinc were thinner.

In particular, in comparative example No. 1, in which the immersion time was set to 1.4 seconds, in contrast to 1.2 seconds in example No. 1, while the temperature of the hot dip galvanizing bath was the same as in example No. 1, the thickness of the pure zinc layer changed dramatically, and cracks and microcracks arose.

[0038] FIG.8 is an optical morphology with a 1000-fold increase in the cross section of the electrode wire in comparative example No. 1; FIG.9 is an image obtained in a scanning electron microscope (SEM) with a 350-fold increase in the surface of the electrode wire in comparative example No. 1.

As can be seen from these images, a pure zinc layer with good ductility of the electrode wire in comparative example No. 1 is thin, with cracks and microcracks on the surface of the electrode wire after cold drawing.

[0039] Further, the characteristics of the EDM of the electrode wires in the examples of the present invention will be compared with the characteristics of the comparative examples. Processing speed increased by approximately 20% compared to traditional 65/35 brass electrode wire. A pure zinc layer with good ductility is thicker than the thermal diffusion layer, and there are no cracks or microcracks on the surface of the electrode wire. The amount of metal powder formed is accordingly improved from 20-45 minutes to 10 hours or more, positioning accuracy increases from 1.6 microns to 0.8 microns, and the surface roughness of the workpiece improves from 17.8-18.1 microns to 16.2 -16.3 microns.

[0040] Moreover, the electrode wires obtained in the second group of comparative examples were evaluated and compared with the electrode wires in the examples. The evaluation results are shown in Table 3.

As can be seen from Table 3, in comparative example No. 7, in which the temperature of the hot dip galvanizing bath was set to 500 ° C, and the immersion time was set to 2 seconds, which is significantly higher than 1.2 seconds, and in comparative example No. 8, where the temperature of the hot dip galvanizing bath was higher than 520 ° C, the pure zinc layers with good ductility were thinner, the brittle alloy layers were thick, and cracks and microcracks were present on the surface of the electrode wire after cold drawing, unlike examples Nos. 2, 5 and 7 in The temperatures of the hot dip galvanizing bath were set to 500 ° C or less, and unlike the examples in which the dipping time was set to 1 second.

The characteristics of electrical discharge machining in comparative examples No. 7, 8 are similar to those in comparative examples No. 1-6, due to the presence of cracks and microcracks present on the surface of the electrode wires. Compared to the examples, the amount of metal powder formed, the positioning accuracy, and the surface roughness of the workpiece are extremely poor.

Although the brass electrode wire 65/35 is used as the traditional electrode wire in the above examples, a galvanized electrode wire can be used instead. The galvanized electrode wire has only a zinc layer, without a thermal diffusion layer, in which the zinc concentration gradually increases from the core to the layer obtained by galvanizing, so that the zinc concentration changes sharply at the interface between the galvanized layer and the core. Therefore, this provides good discharge stability and thus a good surface roughness, but does not allow to achieve the first objective of the present invention, i.e. increase the speed of EDM, since zinc is quickly consumed due to its low melting point.

Compared to hot dip galvanizing (i.e. dipping), galvanizing is slow at the speed of galvanizing, so that it is not possible to form a thick layer obtained by galvanizing in one galvanizing cycle, and it requires several galvanizing cycles, which leads to an increased cost manufacture.

[0041] Manufacturing Method

As can be seen from the results of these examples and comparative examples, it is possible to change the thickness of the layer of copper-zinc alloy formed by thermal diffusion, and the thickness of the layer of pure zinc by adjusting the temperature of the hot dip galvanizing bath and the immersion time. They are interconnected as follows:

(1) Thermal diffusion layer (copper-zinc alloy layer)

- The thermal diffusion layer of the alloy becomes thinner when the immersion time is shorter, provided that the temperature remains the same.

- The thermal diffusion layer of the alloy becomes thinner when the temperature is lower, provided that the immersion time remains the same.

(2) Layer of pure zinc

- The pure zinc layer becomes thicker when the dipping time is shorter, provided that the temperature remains the same.

- The pure zinc layer becomes thicker when the temperature is lower, provided that the immersion time remains the same.

[0042] A method for manufacturing an electrode wire of the present invention has been formulated based on the above findings. Using this method, the electrode wire for electrical discharge machining can be made with the thickness of its thermal diffusion layer, the gradient of zinc concentration and the thickness of the outermost layer of pure zinc, adjusted as desired, without complicating the processes, simply by appropriate selection of the temperature of the hot dip galvanizing bath and the time of immersion. The resulting electrode wire has no cracks or microcracks on its surface and provides excellent electrical discharge machining characteristics.

[0043] As described above, the inventors also found, based on the results of these examples and comparative examples, that a thicker layer of pure zinc and a thicker layer of pure zinc than the thermal diffusion layer are effective factors to prevent cracking or microcracking on the surface of the electrode wire .

Therefore, the basic principles of the manufacturing method of the present invention are to form a thicker layer of pure zinc by limiting the time the core is immersed in the hot dip galvanizing bath within a predetermined time and to form a thinner thermal diffusion layer by limiting the temperature of the hot dip galvanizing bath to a predetermined temperature.

[0044] Production System

An embodiment of the manufacturing system of the present invention will be described with reference to FIGS. 3 and 4.

Referring to FIG. 3, a device 8 for cleaning the surface of a zinc bath and a blower (not shown), including a blower pipe 9 and a jet blast device 10 (shown in an enlarged image in FIG. 4), are located above the rear of the hot dip galvanizing bath 5 where the vein is taken out of the bath.

[0045] The device 8 for cleaning the surface of the zinc bath and blowing has two features: firstly, achieving a 100% concentration of zinc in the galvanized layer formed on the surface of the core, and secondly, preventing smudges and uneven thickness of the formed clean layer zinc.

[0046] The first feature is realized by arranging the jet gas blower 10 with its jet tip facing the surface of the bath through which the core emerges from the hot dip galvanizing bath, and by blowing non-oxidizing gas through this jet tip to remove a layer of impurities, including oxide film and products reaction with flux, and maintaining the exposed surface of the bath of pure zinc.

The second feature is realized due to the impact of non-oxidizing gas at high speed on the core in the jet gas blower 10 of the device 8 for cleaning the surface of the zinc bath and blowing and due to the passage of non-oxidizing gas at high speed around the core in the hollow blow pipe 9 in the opposite direction to the direction of the core.

[0047] The blowing portion includes a hollow blow pipe 9 with a length of 100 mm and an inner diameter of 18 mm, a heater heated to 600 ° C, and a gas supply device supplying non-oxidizing gas such as nitrogen gas and argon gas from the top of the blow pipe 9. When passing through the blow pipe 9, the non-oxidizing gas is heated by the heater, so that the temperature at point A reaches or exceeds the melting point of zinc, for example, 420 ° C.

The blow pipe 9 at its bottom is connected to a jet gas blower 10 containing a zinc purification section. The jet gas blower 10 is a pipe with a length of 15 mm and an inner diameter of 9.6 mm. A plurality of gas supply pipes 11 are connected in a radial direction to a pipe wall through which non-oxidizing gas is heated, heated to the aforementioned temperature.

[0048] Non-oxidizing gas flowing through the gas supply pipes 11 to the center of the jet gas blower 10 is met with a plentiful stream of non-oxidizing gas flowing downward into the blower pipe 9, redirected to and blown onto the surface of the bath, through which the core emerges from the hot dip galvanizing bath 5, removing under the influence of pressure, zinc oxides and flux films formed on the surface of the bath, and keeping the surface of the bath of pure zinc exposed, thus preserving the surface of the bath.

With this action, this device makes a layer of pure zinc formed on the surface of the electrode wire 100% pure.

In the device in this embodiment, to expose the surface of pure zinc at the outlet of the jet gas blower 10, a gas flow rate of 20 ml or more is provided.

[0049] Inside the jet gas blower 10, the gas stream supplied by the aforementioned gas supply device, heated by a heater and flowing downward into the blower pipe 9, and the gas stream flowing through the aforementioned gas supply pipes 11 to the center, make the thickness of the galvanized layer on the surface of the core uniform. hot dip galvanized from the bath 5, preventing smudges and uneven thicknesses.

[0050] Above the blow pipe 9, a widely used forced cooling section (not shown) is located so as to immediately cool the galvanized base wire with non-oxidizing gas or air, so that the galvanized base wire is not damaged during the subsequent winding process.

[0051] Using the aforementioned processes, an electrode wire base wire for electric discharge machining can be made with a thicker outermost layer of pure zinc than the underlying thermal diffusion layer and without cracks or microcracks.

This base wire is cold drawn into the article. In this cold drawing process, the base wire is reduced in diameter while maintaining the same layered structure and the same ratio of layer thicknesses.

Therefore, the electrode wire for electrical discharge machining can be easily obtained without cracks or microcracks on its surface, provided that the layered structure and the ratio of the thicknesses of the layers are strictly controlled in the manufacture of the base wire.

For this reason, it is possible to achieve similar quality with an electrode wire of any external diameter, such as 0.1-0.3 mm, although an electrode wire with an external diameter of 0.25 mm is shown as a finished product in the above examples and comparative examples.

Claims (4)

1. The electrode wire for electrical discharge wire machining, wherein the electrode wire includes a brass core, a pure zinc layer formed by hot-dip galvanizing the core, and a galvanized base wire with a thermal diffusion layer formed by mutual thermal diffusion through the interface between the pure zinc layer and said core, for cold drawing with the manufacture of electrode wire, wherein the pure zinc layer of the electrode wire has a thickness of 1.2% to 3 , 2% of the outer diameter of the electrode wire, and said thermal diffusion layer of a copper-zinc alloy with a zinc concentration of from 50 wt.% To 100 wt.% Exclusively has a thickness of 0.36% to 1.08% of said outer diameter, wherein said pure zinc layer is formed within said thickness range and is thicker than said thermal diffusion layer within said thickness range, and there is no cracking on the surface of the electrode wire. 2. A method of manufacturing an electrode wire for wire erosion treatment, which includes the steps of: providing a core of brass wire made by melting, casting and drawing, washing the surface and pre-heating the core, passing the core through a hot dip galvanized bath of pure zinc to form on the core obtained by hot-dip galvanizing a layer of pure zinc, the formation of a thermal diffusion layer by mutual thermal diffusion through the interface between the said layer of the zinc and said core to produce a galvanized base wire for the electrode wire and cold drawing the galvanized base wire to the electrode wire, while reducing the temperature and / or immersion time of said hot dip galvanizing bath within the range from 440 ° C to 500 ° C and / or from 0.5 to 1.2 s, the thickness of said zinc layer is made thicker, and the thickness of said thermal diffusion layer of a copper-zinc alloy with a zinc concentration of from 50 wt.% to 100 wt.% exclusively is made thinner, increasing said rate the thickness and / or the said immersion time within the said ranges are made thinner and the thickness of the said thermal diffusion layer is thicker, the galvanized base wire is obtained by immersing the core in the hot dip galvanizing bath at a controlled temperature and / or immersion time, and during cold drawing of a galvanized base wire, I control the thickness of the pure zinc layer of the aforementioned electrode wire for EDM wire within the range from 1.2% to 3.2% of the outer diameter of said electrode wire for wire EDM, and the thickness of said thermal diffusion layer is controlled within the range of 0.36% to 1.08% of said outer diameter, forming said layer pure zinc is thicker than the mentioned thermal diffusion layer, while also preventing cracking on the surface of the electrode wire. 3. The method according to claim 2, characterized in that non-oxidizing gas is blown onto the surface of the zinc melt of the hot-dip galvanized bath, flowing downward inside the pipe around the core, drawn in an upward direction, a layer of impurities such as an oxide film is removed under pressure from the pressure and the reaction product with flux formed on the surface of the molten zinc bath, exposing the surface of pure zinc, the surface of the bath in the stretching region of the core on said surface of the zinc melt is supported from pure zinc, and clean the layer of pure zinc on the surface layer of said core. 4. A system for manufacturing a base wire for electrode wire for electrical discharge wire by forming a layer of pure zinc obtained by hot-dip galvanizing on a pre-heated brass core made of brass by immersing the core in a hot-dip galvanizing bath open from above, including a zinc bath surface cleaning and blowing device made with a blowing section formed by blowing a pipe through which the core with zinc passes on the surface, and a gas supply device that delivers the supply gas to the upper part of the blowing pipe, and the zinc cleaning section formed by the blowing gas blower, which is connected to the bottom of the blowing pipe, has a tubular wall on which a plurality of non-oxidizing gas supply pipes are radially mounted, and has a blowing tip located facing the surface of the bath through which the vein emerges from said hot dip galvanizing bath open from above, wherein said device for cleaning the surface of the zinc bath and blowing by blowing a non-oxidizing g a base gas supplied to said blow pipe in said gas supply device and a non-oxidizing gas supplied from said non-oxidizing gas supply pipes to the surface of the zinc bath of said open top hot dip galvanizing bath from the blow tip of said blow gas blower and removing a layer of impurities such as zinc oxide and the reaction product with flux formed on the surface of the bath of molten zinc, under the influence of pressure head with exposure of the surface of pure zinc, supports the surface of the van s, through which the core appears, from pure zinc without the mentioned impurities and makes the pure zinc layer formed on the surface of the base wire clean, and also makes the thickness of the hot-dip galvanized layer on the surface of the core drawn from the hot dip galvanized to prevent smudges and uneven thickness.

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