Abrading – Machine – Combined
Reexamination Certificate
1999-08-19
2001-06-12
Hail, III, Joseph J. (Department: 3723)
Abrading
Machine
Combined
C451S056000, C451S060000, C451S443000, C451S444000
Reexamination Certificate
active
06244939
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a micro-discharge truing device for truing a very fine or thin electrically conductive grindstone and a fine machining method using the device.
2. Description of the Related Art
Recently, for development of a micro-machine and the like, there have been demands for a machining technique to machine constituting fine components with high precision. As a machining method suitable particularly for making holes or channels in such fine components, an electrolytic in-process dressing grinding method (hereinafter referred to as ELID grinding method) has been noted.
In the electrolytic in-process dressing grinding method (ELID grinding method), a very fine electrically conductive grindstone using fine diamond grains, or a very thin electrically conductive grindstone is used, and the grindstone is electrolytically dressed to machine an article to be machined (workpiece). The method is characterized in that machining precision is high, high-quality surface roughness is obtained, and hard three-dimensional shaped components are relatively easily machined.
Even a very fine/thin grindstone to be applied to fine machining surely has an offset or a deflection during processing. Therefore, such offset or deflection needs to be removed by truing prior to application to a precision machining like ELID grinding machining.
However, in a metal bond grindstone for use in the ELID grinding machining, a bond material is very hard. Therefore in a conventional truing method, a correction efficiency is low, a correction precision is limited, and the application is difficult. Specifically, since the grindstone to be applied to the fine machining is very fine or thin (e.g., a diameter of 1 mm or less, thickness of 1 mm or less), by contact with a tool for mechanical truing, the grindstone itself is deformed, which causes a problem that a high-precision truing cannot be realized.
On the other hand, as a machining method of machining a workpiece with no contact therewith, electric discharge machining is known. In the machining method, the workpiece and a machining electrode are opposed to each other with a gap therebetween in an insulating machining liquid, and a short-time pulse arc discharge is repeated, to perform removal machining.
In the machining method, however, there are problems that (1) a shape of the electrode needs to be conformed beforehand to a desired machining shape, (2) precise position control is necessary to keep a constant interval between the electrode and the workpiece, (3) a large current pulse needs to be supplied between the electrode and the workpiece, and a large complicated power equipment is necessary, and (4) since the electrode shape is changed by consumption of the electrode, the electrode needs to be frequently replaced.
SUMMARY OF THE INVENTION
The present invention has been developed to solve the above-mentioned various problems. Specifically, an object of the present invention is to provide a micro-discharge truing device and a fine machining method using the device in which an offset or a deflection of a very fine/thin grindstone can efficiently be removed, a high-precision truing can be performed without deforming the grindstone itself, a power equipment with small size and output is sufficient, neither complicated control circuit nor control apparatus is necessary and electrodes and other consumables are easily manufactured/reprocessed.
Inventors of the present invention have noticed that when a disc-shaped electrode is rotated to generate fine sparks (micro-discharge) between an outer peripheral edge of the electrode and a grindstone, not only a non-contact efficient high-precision truing but also reduction of a power equipment in size and output can be realized, and that a shape change by consumption of the electrode can remarkably be reduced. In other words, when an electric conductivity of a metal bond grindstone for use in ELID grinding machining is used, by a micro-discharge phenomenon in a fine gap between the grindstone and the electrode, a metal bonded portion is molten/removed with no contact therewith and with high precision, so that a grindstone surface can be corrected to a desired shape. The present invention is based on such inventive finding.
Specifically, according to the present invention, there is provided a micro-discharge truing device, comprising: an electrically conductive grindstone (
12
) for machining a workpiece (
1
); a disc-shaped discharge electrode (
14
) having an outer peripheral edge (
14
a
) which can be disposed in the vicinity of a machining surface (
12
a
) of the electrically conductive grindstone; an electrode rotating unit (
16
) for rotating the discharge electrode around an axial center Z; a position controller (
18
) for controlling a relative position of the outer peripheral edge of the electrode and the grindstone; a voltage applying unit (
20
) for applying a predetermined voltage between the grindstone and the electrode in a pulse manner; and a machining liquid supply unit (
22
) for supplying an alkaline liquid between the grindstone and the electrode.
According to the above-mentioned constitution of the present invention, by stably generating the sparks (micro-discharge) by the voltage applying unit (
20
) between the outer peripheral edge of the rotating disc-shaped discharge electrode (
14
) and the machining surface (
12
a
) of the electrically conductive grindstone (
12
) whose position is controlled by the position controller (
18
), the metal bonded portion of the electrically conductive grindstone is molten/removed with no contact therewith and with high efficiency and precision, and the grindstone surface can be corrected to the desired shape.
Moreover, since the discharge electrode (
14
) is rotated around the axial center Z by the electrode rotating unit (
16
), even the electrode worn by the micro-discharge can maintain roundness, and can be used continuously for a long time.
Furthermore, since the alkaline liquid is supplied between the grindstone and the electrode by the machining liquid supply unit (
22
), as compared with a dry state or a case where an insulating liquid is supplied, a lower voltage, higher current micro-discharge can stably be generated, and the power equipment can be reduced in size and output.
According to a preferable embodiment of the present invention, the voltage applying unit (
20
) comprises a direct-current power supply (
24
) for generating a predetermined direct-current voltage; a pulse discharge circuit (
25
) having a capacitor C, a resistance R, and a pair of output terminals to charge the capacitor when the terminals are open therebetween and to discharge electricity from the capacitor when a resistance between the terminals is reduced; and a current supply line (
26
) for connecting a plus side of the output terminal to the grindstone and connecting a minus side to the electrode.
In the constitution, the capacitor C is charged via the resistance R with a direct-current power, and the voltage is raised to a constant voltage between capacitor poles (between the output terminals). Additionally, when the electrode and the grindstone come close to each other to reduce the resistance therebetween, there arises dielectric breakdown of medium (alkaline liquid) between the electrode and the grindstone, and a discharge state is brought about. When discharge starts, energy in the capacitor is discharged, insulation properties of the medium are restored, and a charge state is returned. When the frequency of such cycle is increased, an excellent micro-discharge truing can be realized. Therefore, by the constitution, as compared with the conventional discharge machining, the power equipment can largely be reduced in size and output, thereby obviating the necessity of a complicated control circuit or control apparatus.
Moreover, according to the present invention, there is provided a fine machining method, comprising: (A) a micro-discharge truing process provided with a disc-shaped discharge electrode
Ohmori Hitoshi
Yamagata Yutaka
Griffin & Szipl, P.C.
Hail III Joseph J.
McDonald Shantese
Riken
LandOfFree
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