JP2962600B2 - Electric discharge machining method and apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric discharge machining method and apparatus for generating an electric discharge in a machining gap between a machining electrode and a workpiece through a machining fluid, thereby machining the workpiece into a desired shape. .

[0002]

2. Description of the Related Art In electric discharge machining, a machining pulse is applied to a machining gap between a machining electrode and a workpiece in a liquid (machining fluid) having a high electrical insulation property, and a spark discharge is generated by dielectric breakdown. The workpiece is processed by a thermal action. Therefore, in electric discharge machining, it is important that a good spark discharge state is maintained during the electric discharge duration.

[0003] However, if the energy of the applied machining pulse is small, it is difficult to maintain the spark discharge state until the end of the pulse application, so that a sufficiently large energy is usually supplied. For this reason, in the case of machining conditions in which the machining pulse width is relatively long, the discharge state generally tends to easily change from spark discharge to arc discharge. In order to prevent such a tendency, Japanese Patent Publication No. 3-29529 discloses that when water is used as a working fluid, a gas such as air is forcibly contained in the working fluid in advance, and the working electrode and the working electrode are processed. There has been proposed an electric discharge machining method in which the electric discharge machining is supplied to a machining gap when the electric discharge machining is performed with an object.
The electric discharge machining is performed with the machining electrode and the workpiece to be accommodated in a pressurized container. Part of the energy of the applied machining pulse evaporates the gas dissolved in the machining fluid under high pressure. As a result, the arc discharge caused by excessive energy as in the prior art is prevented, the spark discharge state is maintained until the end of pulse application, and a good processing speed and processing quality can be obtained. Things.

[0004]

However, according to this proposal, it is necessary to perform the electric discharge machining in a pressurized container, and there are disadvantages that the apparatus becomes complicated and large-scale and the operation becomes complicated. The present invention solves the problems of the prior art, and the electric discharge machining itself can be performed under normal open normal pressure, and furthermore, the electric discharge machining method and the electric discharge machining method capable of achieving the improvement of machining speed, electric discharge stability and machining surface roughness. It is an object to provide a device for performing this.

[0005]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides an electric discharge machining method for performing electric discharge machining by interposing a machining fluid in a machining gap between a machining electrode and a workpiece. After the gas is dissolved and contained in the liquid, the processing liquid is flowed and agitated under normal pressure to release the gas dissolved in the processing liquid in an unstable state, and the processing is performed so as to remove a gas portion which is easily bubbled. It is characterized in that a fluid is prepared, the prepared machining fluid is supplied to the machining gap, and electric discharge machining is performed under normal pressure. Another aspect of the present invention is an electric discharge machining apparatus for performing electric discharge machining by interposing a machining fluid in a machining gap between a machining electrode and a workpiece, a tank, gas introducing means for introducing a pressurized gas into the tank, and a tank. A working fluid introducing means for introducing a working fluid to a predetermined level, a stirring means for flowing and stirring the working fluid inside the tank, and a pressurized gas introduced into the tank to dissolve and contain the pressurized gas in the working fluid. After that, the gas introducing means was opened to make the inside of the tank normal pressure, and the working fluid was flown and stirred using the stirring means to release gas which was dissolved in the working fluid in an unstable state. A structural feature comprising: a working fluid preparation means comprising control means for automatically preparing a desired working fluid; and a working fluid supply means for supplying the prepared working fluid to the working gap. I do.

[0006]

[Action] By dissolving a sufficient amount of gas in the working fluid under pressure, followed by flow and stirring under normal pressure, some gas contained in the working fluid in an unstable state is positively released. Is done. Therefore, the gas remaining in the working fluid after preparation is
It is firmly held in the space between the molecules of the liquid. Accordingly, gas is no longer released from this working fluid even if it is given a mechanical stimulus even under normal pressure.

On the other hand, a place where a gas is present has a property that discharge is more likely to occur than a place where no gas is present. Here, since a large number of gases are evenly dissolved in the working fluid, the immediately preceding discharge and the next discharge are likely to occur in different places. As a result, even if the pulse time is reduced, a stable discharge state is maintained without shifting to the concentrated discharge,
Electric discharge machining efficiency is improved. Excessive bubbles cause unstable discharge, but unstable discharge does not occur in the working fluid after the preparation.

Hereinafter, based on a preferred embodiment shown in the drawings,
The present invention will be described in more detail.

[0009]

FIG. 1 is a structural view of a main part of an electric discharge machining apparatus for carrying out the present invention. The inside of the processing tank 1 under normal pressure is filled with a processing liquid 16 prepared in advance as described later. The workpiece mounting base 2 is installed therein, and the workpiece 3 is mounted by a predetermined mounting tool (not shown). An electrode mounting plate 5 is mounted on the electrode head 4 located above the workpiece 3, and a processing electrode 6 is mounted on the electrode mounting plate 5. The workpiece mounting base 2 and the electrode head 4 are mounted on a frame (not shown) so as to be relatively movable in three axial directions of X, Y, and Z, and the relative positions of the workpiece 3 and the processing electrode 6 being processed. Is configured to be determined. In addition,
Since these driving structures are not the essence of the present invention, the details will be omitted.

The machining electrode 6 is provided with a suitable number of machining fluid passages 7 extending vertically through the protruding end portion thereof, and the electrode mounting plate 5 is provided with a flow passage 8 communicating therewith. . At the time of electric discharge machining, the machining fluid 16 is pumped up from the machining tank 1 by a pump 14, introduced into the flow passage 8 through a pipe 15, and subjected to electric discharge machining through a machining fluid passage 7 from the tip of the machining electrode. The cycle ejected into the processing gap G between the object 3 and the processing electrode 6 is circulated and repeated.

A feature of the present invention is that a pipe 17 and a pipe 17 are provided to the machining tank 1 separately from the circulation path of the machining fluid at the time of electric discharge machining.
The processing fluid preparation means 9 is connected via the
The pressurized gas supplied from 2 is dissolved in the liquid in the tank 20 to prepare and prepare in advance a working liquid which is saturated.
The purpose of the present invention is to introduce the prepared working fluid into the working tank 1 and use it at the time of electric discharge machining.

FIG. 3 shows details of an example of the structure of the working fluid preparation means 9. According to this, a gas introduction port 21 is provided on a top wall of a tank 20 which forms a main part of the apparatus, and is connected to the pressurized gas source 12 via a three-way valve 23, and one outlet of the three-way valve 23 is provided. Is open to the atmosphere.
The tank 20 is provided with an upper level sensor 24 for specifying the highest liquid level of the processing liquid contained therein and a lower level sensor 25 for specifying the lowest liquid level.

Two liquid inlets 26 and 27 are provided on the bottom wall. One of the liquid inlets 26 rises inside the tank 20 and has an outlet at a position higher than the maximum liquid level, and the other liquid inlet 26 has the other outlet. The liquid inlet 27 has an outlet on the bottom surface. A pipe 17 communicating with the processing tank 1 reaches the liquid inlet 27 via a pump 29 and an on-off valve 28. Another pump 30 is connected to the outlet side of the on-off valve 28, and further reaches the liquid inlet 26 via a three-way valve 31. One outlet of the three-way valve 31 is connected to the pipe 18 and communicates with the processing tank 1.

Preparation of a working fluid by this apparatus is performed in the following procedure. First, the three-way valve 31 is operated to shut off the outlet on the pipe 18 side. Then, after opening only the atmosphere side of the three-way valve 23 to make the inside of the tank 20 equal to the atmospheric pressure, the on-off valve 28 is opened to form a passage to the liquid inlet 27, and the pump 29 is operated to process through the pipe 17. Pump the processing fluid in the tank 1. As a result, the working fluid is introduced into the tank 20, and the air in the tank is gradually released to the atmosphere via the three-way valve 23. When the liquid level reaches the highest level, the upper level sensor 24 operates to close the on-off valve 28 and at the same time stop the pump 29. In this state, a space where the liquid does not reach remains at the upper part of the tank 20.

Next, the three-way valve 23 is operated to shut off the outlet to the atmosphere, and pressurized gas is introduced into the tank 20 from the pressurized gas source 12. Thereby, the internal pressure of the tank 20 increases. When the pressure sensor 32 detects that the internal pressure has increased to a predetermined value, the supply of the pressurized gas is stopped while operating the three-way valve 23 to prevent communication with the atmosphere. In this state, the three-way valve 31 is operated to open only the outlet on the liquid inlet 26 side, and the pump 30 is operated. Thus, the processing liquid in the tank 20 circulates through the path including the pump 30 and the three-way valve 31 through the two liquid introduction ports 26 and 27. At this time, the pressurized gas in the upper part of the tank 20 is mixed and stirred in the working fluid and dissolved therein, so that the internal pressure of the tank 20 decreases. Therefore, the pump 30 is stopped, and the gas from the pressurized gas source 12 is again introduced into the tank 20 to increase the internal pressure, and the above-described mixing and stirring operation is performed. By repeating the introduction of the pressurized gas and the mixing and stirring operation in this manner, the dissolution of the gas in the working fluid becomes saturated when the internal pressure is no longer substantially reduced by the mixing and stirring operation. Operation is stopped.

Thereafter, the atmosphere side of the three-way valve 23 is opened to release an excessive internal pressure into the atmosphere, and the inside of the tank 20 is returned to normal pressure.
In this state, the above-described mixing and stirring operation by the pump 30 is performed again. Part of the gas dissolved in the working fluid in a supersaturated state due to the return of the pressure in the container to the normal pressure is separated from the fluid by this mixing and stirring operation, and is released to the atmosphere. However, after a lapse of a predetermined time, the release of gas no longer converges even if stirring is continued. At this point, the mixing and stirring operation is stopped, and the operation of preparing the working fluid is completed. The working fluid thus prepared is supplied to the pump 30 and the three-way valve 3 if necessary.
1 flows into the machining tank 1 through the pipe 18 and is used for electric discharge machining. This series of working fluid preparation cycles is executed with good timing by the control unit 33 connected to each pump, valve, pressure sensor, level sensor, and the like.

Under normal pressure, the gas dissolved in the unstable state is completely removed by repeating mechanical mixing and stirring operations in the preparation process, and the remaining gas is It is held in a stable state in the space between the molecules. Discharge machining has a property that discharge is more likely to occur in a place where a gas is present than in a place where no gas is present. Here, since a large amount of gas is evenly dissolved in the working fluid, the probability that the immediately preceding discharge and the next discharge occur in different places is increased. As a result, even if the pulse time is shortened, it does not shift to the concentrated discharge,
A stable electric discharge state is maintained, and electric discharge machining efficiency is improved.
Although excessive bubbles cause unstable discharge, the working fluid after the preparation does not cause unstable discharge.

Examples of the working fluid used in the present invention include fluids having excellent electrical insulation properties, such as pure water and white kerosene. As the gas to be dissolved therein, air, oxygen and the like are preferable. FIG. 2 shows another embodiment of the present invention. In this case, the machining fluid prepared by the machining fluid preparation means 9 is supplied through a separately provided nozzle 13 without providing the machining fluid passage 7 in the machining electrode 6. It is sprayed from the side into the processing gap G between the processing electrode 6 and the workpiece 3.

By using such a nozzle 13, the present invention can be applied not only to the illustrated die-sinking electric discharge machining but also to the wire electric discharge machining. Table 1 shows that when the electric discharge machining apparatus shown in FIG. 1 was used, electric discharge machining was performed on a mold material with a graphite machining electrode in an area of 9.7 × 9.7 cm ² , and the discharge current was gradually reduced. 4 is a table of experimental results obtained by examining a lower limit at which electric discharge machining becomes impossible.
Conductivity of 0.5 μs / cm by ion exchange
In the case of the present invention, a working fluid prepared by dissolving oxygen as a gas by the above-described method of the present invention was used in the case of the present invention. On the other hand, as a comparative example, a case where a working fluid without gas dissolution was used was listed.

[0020]

[Table 1]

As is apparent from the above description, in the case of the present invention, even when the average current value was reduced to 3 ampere or less, good spark discharge was maintained and a beautiful machined surface was obtained. In contrast,
In the case of the prior art, the discharge was already unstable at 6.5 amps, and stopped below 5 amps. As a result, when the processing speed is compared, in the case of the present invention, several tens of
Processing speeds up to several times can be obtained.

[0022]

According to the present invention, a working fluid prepared by dissolving a gas sufficiently in a working fluid under high pressure in advance and flowing and stirring under normal pressure to release an unstable gas is used. Since the electric discharge machining is performed at normal pressure, the structure of the apparatus is simplified and the operation becomes easier as compared with the electric discharge machining in a high-pressure vessel in the related art.

In spite of machining at normal pressure, a stable spark discharge can be obtained even in a low current range, and the machining speed is improved and the quality of the machined surface is improved.

[Brief description of the drawings]

FIG. 1 is a main part configuration diagram of an embodiment of an electric discharge machine for carrying out the present invention.

FIG. 2 is a main part configuration diagram of a second embodiment of the electric discharge machining apparatus to which the present invention is applied.

FIG. 3 is a structural diagram of a means for preparing a working fluid used in the method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Processing tank 3 ... Workpiece 6 ... Processing electrode G ... Processing gap 9 ... Processing liquid preparation means 12 ... Pressurized gas source 14 ... Pump 16 ... Processing liquid 20 ... Pressurized container 21 ... Gas introduction port 23, 31 ... Three-way valve 24, 25 Level sensor 26, 27 Liquid inlet 28 On-off valve 29, 30 Pump 32 Pressure sensor 33 Control means

Claims (2)

(57) [Claims] In an electric discharge machining method for performing electric discharge machining by interposing a machining fluid in a machining gap between a machining electrode and a workpiece, a gas is dissolved and contained in a machining fluid under pressure and then under normal pressure.
The working fluid flow and stirred to working fluid to release the gas member which has been dissolved in an unstable state and a prone gas portion was aerated removed
A working fluid is prepared such that the prepared working fluid is
An electric discharge machining method characterized in that electric discharge machining is performed under normal pressure by supplying the electric discharge machining to a machining gap . 2. An electric discharge machining apparatus for performing electric discharge machining with a machining fluid interposed in a machining gap between a machining electrode and a workpiece, comprising: a tank; and a gas introducing means for introducing a pressurized gas into the tank. stage and the working fluid introducing means for introducing a working fluid to a predetermined level in the tank, and agitating means for flow and stir the inside of the working fluid in the tank, pressurizing the working fluid by introducing a pressurized gas into tank <br/> After the gas is dissolved and contained, the gas introduction means is opened.
Te internal tank to atmospheric pressure, the desired processing solution to release <br/> air body that was dissolved in an unstable state in a fluidized-stirred to machining liquid processing fluid using said stirring means a working fluid preparation means comprising at a control means for automatically preparing, machining fluid supplying the prepared working fluid to the machining gap
Discharge machining apparatus characterized by comprising a supply means.