Electric heating – Metal heating – Cutting or disintegrating
Reexamination Certificate
2000-06-28
2001-10-09
Elve, M. Alexandra (Department: 1725)
Electric heating
Metal heating
Cutting or disintegrating
C219S069110, C219S069150
Reexamination Certificate
active
06300587
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a wire electrode which is employed for wire electro-discharge machining, and to a method of manufacturing method thereof.
2. Description of the Background Art
Wire electro-discharge machining is a method of causing intermittent discharge between a linear working electrode called a wire electrode for electro-discharge machining and a workpiece through a working fluid such as water or oil. The workpiece is moved relative to the wire electrode for electro-discharge machining, thereby melting and cutting the workpiece into a desired configuration. This method is utilized for manufacturing various types of metal molds and the like. In such wire electro-discharge machining, required are processing characteristics such as excellent finishing, high working accuracy, good finished surface state of the workpiece, no adhesion of the wire electrode material to the workpiece, and a short electro-discharge machining time. A wire electrode employed for such wire electro-discharge machining is generally prepared from a brass wire, which has good drawability and high strength required for a wire electrode.
As working power sources have been improved/advanced, it is desirable to provide a wire electrode which can improve processing speed. A wire electrode for improved processing speed is particularly desired for applications employing a power source of a wire electro-discharge machining which repeatedly applies a high and short-time pulse voltage.
However, wire electrodes for electro-discharge machining typically prepared from a brass wire are incapable of attaining a sufficiently high processing speed. Further, brass wires are problematic in that electrode material adheres to the workpiece. As a result, the cut surface of the workpiece is roughened and the wire electrode is easily broken when electro-discharge machining is performed at a high processing speed.
A wire electrode for wire electro-discharge machining prepared by covering a core formed of Cu (copper) or a Cu alloy with Zn (zinc), or prepared by covering the core with Zn, heat treating to generate a Cu—Zn alloy at a surface layer by diffusion and having an oxide film on the outermost surface has been used in some applications. The Zn coated Cu or Cu alloy wire electrode results in improved cut surface of the workpiece; however, it cannot provide a sufficiently high processing speed. The diffusion alloy coated wire electrode improves to some extent the processing speed; however, the property of the cut surface of the workpiece is not sufficiently improved and it is difficult to position the wire electrode before starting electro-discharge machining. As compared with the brass wire, the conventional wire electrode for wire electro-discharge machining having a core and a coating layer formed on an outer periphery of the core has improved electro-discharge machining characteristics. However, the wire electrode itself, a wire contact (a roller or die for feeding electricity), a guide die and the like suffer wear and undergo considerable damage, thereby shortening their lifetime and significantly increasing the cost of electro-discharge machining.
DETAILED DESCRIPTION OF THE INVENTION
An object of the present invention is to provide a wire electrode for wire electro-discharge machining which allows reduction in electro-discharging machining time, suppresses adhesion of electrode material to the workpiece and provides a smoothly cut workpiece surface, at a low cost. Another object of the present invention is to provide a wire electrode for wire electro-discharge machining which allows easy positioning, does not reduce the lifetime of the wire contact and the guide die and, hence, generally reduces the cost of electro-discharge machining.
After extensive investigation and experimentation, it was found that the formation of a thick coating layer at extremely high speed by exposing the core to a prescribed vapor to cause reaction between copper contained in the surface layer of the core with an element of the vapor, provides a wire electrode for wire electro-discharge machining having superior electro-discharge machining characteristics (high processing speed, no adhesion at the cut surface of the workpiece and a smoothly cut surface).
In the method of manufacturing a wire electrode for wire electro-discharge machining according to one aspect of the present invention, a core, at least a surface layer of which contains copper, is exposed to a vapor containing at least one element selected from the group consisting of Zn, Cs (cesium), Se (selenium), Te (tellurium) and Mg (magnesium), which element of the vapor reacts with copper contained in the surface layer of the core, thereby forming a coating layer on the outer periphery of the core.
In the inventive manufacturing method, the core is only exposed to the vapor and, therefore, the manufacturing process is simplified as compared with conventional methods including electroplating followed by diffusion. Accordingly, the manufacturing cost is reduced and inexpensive wire electrodes for wire electro-discharge machining are provided.
According to the inventive method of manufacturing, the core can be exposed several times to the same or different vapor without encountering any problem as in conventional methodology. A wire electrode for wire electro-discharge machining prepared through diffusion unavoidably suffers from the problem of oxidation or tarnishing of the surface. However, in the inventive manufacturing method utilizing vapor, the surface is neither oxidized nor tarnished, and the electrode wire has a smooth and satisfactory surface.
In the inventive method of manufacturing utilizing vapor, it is preferred that after formation of the coating layer, the wire is subjected to plastic working to effect an area reduction rate (reduction rate in the cross sectional area) of about 40% to about 99%. Plastic deformation includes drawing, roll working or the like, for example. When the area reduction rate of plastic working is smaller than 40%, sufficient strength of the wire electrode is not ensured. When the area reduction rate exceeds 99%, strength at high temperature is lost, resulting in frequent breaking of the wire electrode during electro-discharge machining. The area reduction rate is defined by the following equation:
Area reduction rate (%)={(d
1
2
−d
2
2
)/d
1
2
}×100; wherein
d
1
: is the wire diameter before processing; and
d
2
: is the wire diameter after processing.
It was found that the electro-discharge machining characteristics can be further improved when the coating layer is formed with a copper content of about 50.5 wt % to about 75 wt %. When the copper content is less than about 50.5 wt %, the processing speed is not satisfactory; and when copper content exceeds about 75 wt %, the processing speed, reduction of adhesion of electrode material to the cut surface and surface properties are not satisfactory. Further, when the copper content in the coating layer is smaller than about 50.5 wt %, plastic working, such as drawing, is difficult, thereby increasing cost.
In a preferred embodiment of the inventive method, the coating layer is formed by exposing the core to the vapor at a temperature of about 300° C. to about 1050° C. When the temperature is lower than about 300° C., it becomes necessary to expose the core to the vapor for a long period of time to form the coating layer, which leads to increased cost; and when the temperature exceeds about 1050° C., the surface properties of the wire electrode are deteriorated, thereby adversely affecting electro-discharge machining characteristics.
Preferably, the inventive wire electrode for wire electro-discharge machining is formed by rapid cooling after forming the coating layer by vapor exposure. Rapid cooling provides surface hardening of the wire electrode, thereby improving electro-discharge machining characteristics. A suitable cooling rate to achieve a suitable degree of hardening is about 10° C./sec. to abou
Ezaki Shigeo
Inazawa Shinji
Kume Toshihiro
Miyazaki Kenji
Nakai Yoshihiro
Elve M. Alexandra
McDermott & Will & Emery
Sumitomo Electric Industries Ltd.
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