Electric heating – Metal heating – Cutting or disintegrating
Reexamination Certificate
2004-02-18
2004-09-28
Evans, Geoffrey S. (Department: 1725)
Electric heating
Metal heating
Cutting or disintegrating
Reexamination Certificate
active
06797911
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
This invention relates to an electric discharge machining electrode suitable as an electrode used for an electric discharge machine such as an engraving electric discharge machine, a wire electric discharge machine, a micro electric discharge machine, a generating electric discharge machine, and the like. These machines are adapted to subject an article to an electric discharge machining process by generating electric discharge pulses between the article and an electrode disposed at a distance from the article. This invention also relates to an electric discharge machining apparatus, and more particularly to an electric discharge machining electrode capable of improving the quality of a finished surface of an article and/or increasing the machining speed. Optimization of the machining speed may be performed by improving the electric discharge generation rate &eegr;, even in a fine machining process, and even when the conditions including a time width and a voltage of the electric discharge pulses applied to the electric discharge machining electrode are the same. Optimization of the machining speed may also be performed by rendering it possible to maintain the electric discharge generation rate &eegr;, even when a time width and an applied voltage of each pulse are reduced. This invention also relates to an electric discharge machine. The present invention is preferably used for a micro electric discharge machining process.
2. Description of Related Art
In an electric discharge machining process, when a time width of pulses (which will hereinafter be referred to simply as a pulse width) of a voltage (which will hereinafter be referred to as a gap voltage) applied to a position between an article and an electric discharge machining electrode is large, the quality of the finished surface of the article lowers. Therefore, the pulse width is set to a small value in accordance with the level of required quality of the finished product.
However, when the pulse width is set to a small value, failure in the generation of the electric discharge may occur frequently, even when a voltage pulse is applied between the article and the electrode. Especially, when the area of the article that is directly opposite to the electrode is small, and when the gap voltage is low, failure occurs very noticeably.
The causes of such a failure in the generation of an electric discharge reside in the fact that a long time is needed to electrolytically dissociate any interelectrode substance existing between an article and an electric discharge electrode, i.e., for instance, processing liquid, such as pure water or oil.
The electric discharge generation rate &eegr; will be defined as follows.
Electric Discharge Generation Rate &eegr;={(Number of Generations of Electric Discharges)/(Number of Applied Pulses)}×100 [%]
In the above equation, the <Number of Applied Pulses> is the number of applied pulses of a gap voltage, and the <Number of Generations of Electric Discharges> is the number of electric discharge pulses generated when the voltage pulses are applied between an article and an electrode. Accordingly, in a case where electric discharge pulses occur at all times when the pulses of a gap voltage are applied between an article and an electrode, the electric discharge generation rate &eegr; in the above equation becomes 100%.
For instance, when a gap voltage and a pulse width of the applied voltage are 100V and 10 nano-seconds respectively, an electric discharge generation rate &eegr; is only about 1% at the highest. However, when the pulse width is 10 micro-seconds with the gap voltage at the same level, the electric discharge generation rate &eegr; becomes very close to 100%. It is true that, when the pulse width is 10 nano-seconds, a treated surface close to a specular surface may be obtained but, when the pulse width is 10 micro-seconds, the treated surface may become extremely rough.
It has been ascertained that, even when the pulse width is set to a small value, the electric discharge generation rate &eegr; can be improved when the gap voltage is increased. However, when the gap voltage is increased, the quality of the treated surface lowers.
When an article has a larger size, the area opposite the electric discharge machining electrode becomes wide, so the electric discharge generation rate &eegr; increases as compared with a case where an article has a small area opposite the electric discharge machining electrode. It is generally said that, when the area of an article which is opposite such an electrode is up to 0.2 mm×50 mm, the electric discharge generation rate &eegr; is improved in exponential proportion to the area. Such relation between the electric discharge generation rate &eegr; and the area of the article opposite the electric discharge machining electrode is called the “area effect.”
However, since the fine electric discharge machining of an article of a small area of 5 &mgr;m×5 &mgr;m to 25 &mgr;m×100 &mgr;m is also much in demand, it is necessary that the electric discharge generation rate &eegr; for an article with a small area does not decrease either.
In view of the above, when a finely machined finished product of high quality having a sub-specular surface is demanded, it is unavoidable that the electric discharge generation rate &eegr; decreases. This necessarily causes the machining rate to decrease.
SUMMARY OF THE INVENTION
The present invention has been made in view of the above-described problems and to address the problems encountered in techniques of this kind, and aims at providing an electric discharge machining electrode capable of improving the quality of a finished surface of an article and/or increasing the machining speed. The present invention also improves the electric discharge generation rate &eegr;, even in a fine machining process, and even when the conditions including a time width and a voltage of the electric discharge pulses applied to the electric discharge machining electrode are the same, and by rendering it possible to maintain the electric discharge generation rate &eegr; substantially constant even when a time width and an applied voltage of each pulse are reduced. The present invention is also directed to an electric discharge machining apparatus.
The present invention solves these problems by providing an electric discharge machining electrode, used as an electrode for the machining of a surface of an article carried out by generating electric discharge pulses between the article and the electrode, which is located at a distance from the article, wherein a radioactive metal is contained at least in or near the portion of the electrode in which the electric discharge occurs.
In this electric discharge machining electrode, the above-mentioned problems are addressed by forming the electrode out of a superhard material obtained by sintering a mixture containing at least a fine powder of tungsten and cobalt, turning the superhard material into a radioactive metal, as mentioned above, by irradiating the superhard material with neutrons and thereby substituting radioactive cobalt atoms for the above-mentioned cobalt atoms, and using the radioactive metal as a negative pole. The electric discharge machining electrode according to the present invention is different from a conventional electric discharge machining electrode with a superhard material in the fact that the electrode in this invention is radioactive. Also, the mechanical characteristics, such as rigidity, as well as the electrical characteristics of the electrode according to the present invention can be set identical to the mechanical and electrical characteristics of a conventional electrode, which exhibits proven results in an electric discharge machining process. Therefore, the reliability of the electrode according to the present invention during its use as an electric discharge machining of an article can be ensured.
Also, the above-mentioned problems may be addressed by prov
Hara Sotomitsu
Yanaka Shinichirou
Evans Geoffrey S.
Mitutoyo Corporation
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