Electric arc discharge device and method

Electric heating – Metal heating – Cutting or disintegrating

Reexamination Certificate

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Details

C219S069150, C219S069170

Reexamination Certificate

active

06180908

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention generally relates to an electric discharge device and a method of using the electric discharge device. More specifically, the present invention relates to an apparatus and method of performing a hole forming process on a workpiece by utilizing an electric discharge device.
2. Background Information
An electric arc discharge process is often used to cut or form holes in a metal workpiece. Specifically, an arc voltage charging device is connected between an electrode and a workpiece. Current flows from the arc voltage charging device to the electrode. When the electrode is located adjacent the workpiece, an arc is formed between the electrode and the workpiece such that current passes from the electrode through the workpiece and back to the arc voltage charging device. The arc from the electrode then causes material of the workpiece to be eroded away. The workpiece is often processed under an insulating liquid, with intermittent electric arcs occurring between the electrode and the workpiece under the insulating liquid. The conventional electric discharge methods used to form a hole in a workpiece have many advantages over conventional mechanical methods of forming a hole. For example, prior art electric discharge processes typically do not create burrs during the formation of holes. Moreover, these prior art electric discharge processes can typically form diagonal holes without any difficulty. These prior art electric discharge processes can also be used to process workpieces made of very hard rigid material.
An example of a conventional electric arc discharge process is diagrammatically illustrated in
FIGS. 1 and 2
. As seen in
FIG. 2
, a hole is formed in a workpiece
1
using a long cylindrical discharging electrode
2
. The diameter of the electrode
2
is sized to correspond to the diameter of the hole to be formed. This discharging electrode
2
is cylindrical and has an internal pathway
2
a
through which processing liquid flows. The hole is formed in the workpiece as the discharging electrode
2
is moved downwardly towards the workpiece with the processing liquid being supplied through the pathway
2
a.
When a hole forming process is performed with a processing liquid being supplied to the above-described discharging electrode
2
, a sludge or process powder is formed. The sludge or process powder from the workpiece is disposed of by the processing liquid, which flows upwardly around the discharging electrode
2
. This disposal of the sludge or process powder occurs until the hole formed in the workpiece
1
by the discharging electrode
2
passes through the workpiece
1
.
However, as shown in
FIG. 2
, when the discharging electrode
2
passes through the workpiece
1
, the processing liquid starts to flow out of the hole, which decreases the pressure of the processing liquid. Also, the sludge or process powder builds up around the electrode since it is no longer being properly disposed of by the processing liquid. Furthermore, the electric discharge between the electrode
2
and the workpiece
1
becomes unstable because the arc or electric discharge is occurring in the air instead of under the processing liquid. The discharging electrode
2
is moved downward by a servo-actuated control. When electric discharge or arcs becomes unstable, the discharging electrode
2
goes down less smoothly. As a result, just prior to completion of the hole forming process, the discharging electrode
2
keeps moving up and down, which lengthens the time to complete the hole forming process.
To solve such problems, prior art electric arc discharging devices blow compressed air from beneath the processing hole to keep the processing liquid from escaping out of the bottom of the processing hole. Although this method prevents arcs or electric discharges from occurring in the absence of the processing liquid, it still does not stabilize the pressure of the processing liquid. Therefore it is difficult for electric discharges or arcs to take place under the most desirable conditions.
In view of the above, there exists a need for electric discharge device which overcomes the above mentioned problems in the prior art. This invention addresses this need in the prior art as well as other needs, which will become apparent to those skilled in the art from this disclosure.
SUMMARY OF THE INVENTION
One purpose of the present invention is to provide a method of forming a hole with an electrode submersed in a processing liquid such that the pressure of the processing liquid is maintained after the hole passes through the workpiece to stabilize the electric discharge.
An electric discharge device performs a hole forming process on a workpiece, using electric discharge in accordance with the present invention. The electric discharge device basically comprises a discharge electrode, an arc voltage charging device, a control mechanism, a supply of processing liquid and means for maintaining the pressure of the processing liquid when the through hole is formed in the workpiece. The discharging electrode has a free end that is positioned adjacent the workpiece. The arc voltage charging device is operatively coupled to the discharging electrode to supply a discharged voltage for applying discharged voltage between the discharging electrode and the workpiece. The control mechanism is coupled to the discharging electrode to move the discharging electrode towards and away from the workpiece. The supply of processing liquid is arranged to supply a processing liquid under pressure to the free end of the discharging electrode.
This electric discharge device forms a hole on a workpiece by moving the discharging electrode while letting electric discharge take place between the workpiece and the discharging electrode. Simultaneously, processing liquid is disposed of together with sludge to outside the hole on the workpiece through a space between the discharging electrode and the workpiece. In this way, the electric discharge process is kept stable until the hole passes through the workpiece.
Furthermore, when the process reaches the point where the hole passes through the workpiece, the pressure of the processing liquid is maintained by a pressure maintenance means. In this way, the electric discharge is kept under the liquid, and the electric discharge process remains stable. Also, the pressure of the processing liquid is maintained even after the workpiece hole extends all the way through the workpiece. Therefore, the processing speed can be kept stable all the way through the end of the process.
The means of maintaining the pressure of processing liquid is a jig that has concave portions or recesses corresponding to the discharging electrode. The jig is coupled to the workpiece. In this device, the jig is coupled in a space on a rear surface side of the workpiece. The concave portions or recesses are formed on portions of the jig corresponding to the discharging electrode. When the hole goes through the workpiece, the processing liquid flowing out of the hole collides against the concave portion and is directed upwardly between the workpiece and the electrode. The sludge is also carried by the processing liquid through a space between the hole of the workpiece and the discharging electrode.
In this case, since the concave portions or recesses are formed on the jig with sufficient depths, the jig will not be processed, even after the discharging electrode passes through the workpiece. Therefore, a plurality of workpieces can be processed with one jig, which is very important in mass production.
In a preferred embodiment, the workpiece is a gear member that has teeth portions on the outer peripheral portion, and a space on an inner peripheral side of the teeth portions. Holes are formed on the bottom of the teeth portions by the electric discharge device. The jig is inserted into the space of the gear member to be coupled therewith.
Processing liquid can be supplied to a workpiece through an internal passageway of the cylindrical dischargin

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