JPH0323288B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for electrically processing defective conductors such as ceramics.

In electrical discharge machining, a machining power source is connected to the workpiece electrode and the tool electrode, and electrical energy is supplied in pulses.
Machining is performed by generating electrical discharge.

Therefore, the first condition for a workpiece that can be subjected to electrical discharge machining is that it be a good electrical conductor. Therefore, poor electrical conductors cannot be machined with conventional electric discharge machines. Ceramics, which are now being used in all sorts of fields, are molded, dried, and finally fired, but they often require secondary processing. However, this ceramic is hard enough to cut molybdenum high-speed steel at will, but it also has the disadvantage of being extremely brittle, so it cannot be cut with ordinary knives. Therefore, even if you try to process it by electric discharge machining, which can process regardless of hardness etc.,
Since many of these types of ceramics are poor conductors of electricity at room temperature, they cannot be processed using conventional electrical discharge machining methods. Furthermore, Japanese Patent Publication No. 44-28639 discloses an electric discharge machining method in which grooves are formed in a diamond by causing a spark discharge at the tip of a counter electrode in contact with the surface of the diamond in oil. When ceramics were used instead of diamond, the entire ceramic workpiece was destroyed by the discharge impact, making it impossible to machine the desired shape.

The present invention was made for the purpose of processing ceramics and the like that are electrically poor conductors at room temperature, but whose electrical resistance decreases as the temperature rises. Therefore, taking aluminum oxide ceramics as an example of processing, this aluminum oxide ceramics can be used in crucibles and the like that are used at high temperatures of 1600℃, and can withstand long-term use.
In terms of crystal chemistry, it belongs to ionic crystals and is an excellent electrical insulator, so it is widely used as an electrical insulating material. The raw material for aluminum oxide ceramics is pure aluminum oxide, which is molded, dried, and finally fired. The aluminum oxide ceramics formed in this way have many of the advantages mentioned above.
Despite their wide range of uses, they also have drawbacks. For example, ceramics have the common flaw of being brittle, meaning they cannot withstand strong mechanical shocks and will break if dropped on a cement floor. Furthermore, although this aluminum oxide ceramic has sufficient pressure resistance, its ability to withstand tension is ten times smaller than its ability to withstand pressure. Moreover, it is susceptible to rapid temperature changes and has poor resistance to temperature shocks such as rapid heating and cooling. Therefore, it is understood that this ceramic cannot be processed by conventional cutting or electrical discharge machining. Therefore, when we further investigated the properties of this ceramic, we found that the valence electrons of the ions that make up the oxidized ceramic are usually bound to each ion by the strong attraction of the atomic nucleus, and even if an electric field is applied from the outside, these atoms will not be able to move. Since valence electrons cannot move freely, oxide ceramics such as aluminum oxide, silicon oxide, potassium oxide, and sodium oxide are generally electrical insulators at room temperature. It was then discovered that heating the ion would be sufficient to release the binding of the outer shell electrons of the ion. As the outer shell electrons gain energy through heating, they overcome the attraction of the atomic nucleus and become free electrons, so as the temperature rises, the electrical resistance of oxide ceramics decreases, and they exhibit certain electronic conductivity characteristics. The electrical resistance of aluminum oxide ceramics is only 10 ⁶ Ωcm at 1000°C, which is 1/100 millionth of that at room temperature.
Furthermore, the resistance of stable zirconium oxide ceramics is even lower, 1 to 10 Ωcm. Therefore, we focused on this poor temperature shock resistance and electrical conductivity at high temperatures, and completed a processing method. In this method, the tips of a pair of electrodes are placed close to the surface of a workpiece such as ceramics, which is an electrically poor conductor at room temperature but whose electrical resistance decreases as the temperature rises, and the tips of each electrode face each other across a desired discharge gap. In addition, a heat-resistant insulator is provided in the discharge gap close to the surface of the workpiece to limit and narrow the cross-sectional shape and dimensions of the discharge gap. Then, a conductive liquid such as an electrolytic solution is applied to the machining surface portion of the workpiece, which is opposed to each other, corresponding to the discharge gap, and intermittent voltage pulses are applied between the pair of electrodes. Intermittent discharge accompanied by current flow is generated between each tip of the electrode through the conductive liquid, increasing the current density in the discharge gap and restricting heat radiation, thereby reducing the heat-resistant insulation in the discharge gap. Electrophysical effects such as heat and shock generated as a result of electrical discharge on the surface of the workpiece brought close to the surface, and chemical and electrochemical effects that generate heat due to conductive liquid and electrical discharge that accompanies energization. By applying an action, the ceramic surface of the workpiece is decomposed, melted, melted, or deteriorated, such as becoming brittle, and a part of it is melted and scattered, thereby making it possible to remove any heat-resistant material that is an electrically poor conductor. materials, nitrides,
DESCRIPTION OF THE PREFERRED EMBODIMENTS The processing method of the present invention for processing workpieces such as ceramics made of carbides, silicides, borides, oxides, etc. will be explained based on diagrams illustrating examples.

In FIG. 1, a workpiece 1 made of ceramics or the like is fixed to a table 2. As shown in FIG. 2 is slidably supported on this table by a saddle 3, and a screw 4 and an X-axis servo motor 5 that rotates the screw 4 (Fig. 2)
As a result, the robot moves in the X direction perpendicular to the plane of the paper in FIG. The saddle 3 is slidably supported by the bed 6 and is moved in the Y direction perpendicular to the X direction by a screw 7 and a Y-axis servo motor 8 that rotates the screw 7. The X-axis servo motor 5 and Y-axis servo motor 8 are controlled by a numerical control device (not shown), and move the workpiece 1 to an arbitrary position on a horizontal plane. Columns 9 and 10 are provided on the sides of the bed 6, and horizontal beams 11 and 12 are fixed to the columns 9 and 10. This beam 11,
A pair of movable bases 13 and 14 are slidably supported on 12, and screws 15 and 16 that are screwed together with the movable bases 13 and 14 are pivoted by brackets 17 provided on the beams 11 and 12 and columns 9 and 10. It is supported and rotated by servo motors 18 and 19. The servo motors 18 and 19 are driven by a numerical control device or a manual switch (not shown), and the movable bases 13 and 1
4 are individually moved and positioned on the beams 11 and 12, respectively.

In FIG. 2, a shaft 20 pivotally supported on a movable table 14 is indexed in the rotational direction and positioned at the indexed position by a servo motor 21. A bracket 22 is fixed to one end of this shaft 20. This axis 2
0. A servo motor 21 is similarly provided on the movable table 13, and a bracket 23 is provided at one end thereof. The brackets 22 and 23 include a holder 24,
It supports 25. And this pivot holder 2
Reference numerals 4 and 25 indicate pinions provided on shafts (not shown) of servo motors 26 and 27 attached to brackets 22 and 23, and holders 24 and 24 that mesh with the pinions, respectively.
The holders 24 and 25 are moved in the axial direction (in the direction of the arrow A-B in the figure) by means of a rack (not shown) provided on the holder 25. The servo motors 26 and 27 are driven by a numerical control device or manual switch (not shown). This holder 2
Rod-shaped electrodes 28 and 29 held at 4 and 25 are connected to a high voltage DC power supply 30, a discharge capacitor 31, a resistor 32, and a switch 33 of a well-known electric discharge machining apparatus. In place of the electrodes 28 and 29, a disk-shaped electrode 44 may be used as shown in FIG. When this disk-shaped electrode 44 is used, when the electrode is worn out,
Not only can the axial positions of the holders 24 and 25 be corrected by simply rotating them by a predetermined angle, but also
By rotating at a predetermined speed, it is possible to apply a scratching force to the machined part on the surface of the workpiece 1 or its vicinity, or to remove or renew generated processing waste, gas, conductive liquid, etc., thereby contributing to the promotion of the processing action. . A heat-resistant insulating plate 34 is inserted into the gap between the surfaces of the workpiece where the tips of the electrodes 28 and 29 face each other so as to be close to the workpiece surface. This insulating plate 34 is intended to limit the discharge path that accompanies current flow between the electrodes 28 and 29.
It is pivotally supported by bars 35 and 36 supported by columns 9 and 10, and is threadedly engaged with a screw 37 also supported by columns 9 and 10. This screw 37 is rotated by a servo motor 38. This insulating plate 34
is not only used for insulation, but can be used as follows, although not shown. That is,
A nozzle hole is provided here and can be used for both spraying and dropping the conductive liquid 41, which is the machining liquid. Furthermore, it is also possible to have a structure in which the abrasive material is injected together with the machining fluid.

Normally, a conductive liquid 41 is discharged from a nozzle 39 onto the surface of the workpiece 1 to form a thin film of the conductive liquid 41 on the surface of the workpiece 1, thereby forming a gap between the pair of electrodes 28 and 29. A conductive path is formed in the opposing gap. The conductive liquid 41 flowing from the surface of the workpiece 1 and collecting in the liquid tank 40 is circulated and used while being purified by a circulation device (not shown).
This conductive liquid 41 includes the following.

(a) Water.

(b) Acid or alkali dissolved in water.

(c) Strong acid aqueous solutions such as hydrochloric acid, sulfuric acid or nitric acid.

(d) Aqueous solutions of strong bases such as caustic soda or caustic potash.

(e) Aqueous solutions for electroplating or electroless plating containing metal ions.

It is preferable to cover the entire device with a cover 42 and provide a device for purifying the gas generated therein by suctioning it with a suction device 43.

The present invention fixes a workpiece 1 to a table 2,
This table 2 is moved to any position on a horizontal plane by an X-axis servo motor 5 and a Y-axis servo motor 8, which are controlled by a numerical control device (not shown). Electrodes 28 and 29 on the workpiece 1 are moved to arbitrary positions along the beams 11 and 12, respectively, by servo motors 18 and 19 controlled by a numerical control device (not shown). The inclination angles of the electrodes 28 and 29 can be arbitrarily selected by the servo motor 21 controlled by a numerical control device (not shown). In this way, the horizontal position and inclination angle of the electrodes 28 and 29 are controlled and moved, and the servo motor 26,
At step 27, the electrodes 28 and 29 are moved in the axial direction to control and define the gap with the workpiece 1. Electrode 2
The insulator 34 provided between the electrodes 28 and 29 is moved to the processing position of the workpiece 1 by a servo motor 38 controlled by a numerical controller or a manual switch (not shown), and is moved between the electrodes 28 and 29. This prevents direct discharge and allows the discharge current to flow through the conductive liquid 4 on the surface 1 of the workpiece.
This acts to ensure that the fluid flows through the thin film of No. 1.

All of the above movements are performed by a numerical control device, but manual operation using a switch is also possible.

Once the mechanical positional relationship is determined in this way, the conductive liquid 41 is ejected from the nozzle 39 to form a film on the surface of the workpiece 1, and the electrodes 28, 29 are
When intermittent voltage pulses are applied between the electrodes 28 and 29, an electrolytic current flows between the electrodes 28 and 29 through the thin film of conductive liquid, i.e. an electrochemical effect occurs during the initial period at the beginning of each voltage pulse. , then the electrolytic current increases rapidly, accompanied by Joule heating, reaches a high temperature, and finally transitions to discharge, but the discharge in a state accompanied by electrolysis and Joule heating is shorter than the duration of the applied voltage pulse. The new conductive liquid is supplied to the surface of the workpiece during the voltage pulse pause period until the next voltage pulse application starts.
The discharge gap is cooled, washed away, and the liquid replaced, and in preparation for the application of the next voltage pulse, the above-described operations of electrolysis, heating, discharge, and pause are repeated. To apply energy such as electric discharge to the surface of the workpiece, the position can be changed by applying one to a predetermined number of voltage pulses or by continuously driving the servo motors 5 and 8 at a predetermined speed. I can do it. The surface portion of the workpiece that is exposed to the electrolysis, heating, and discharge in the presence of a conductive liquid may be kept at room temperature, depending on the combination of the conductive liquid and the ceramics of the workpiece, their properties, etc. Even with ceramics that are not susceptible to the chemical effects of contact conductive liquids or the electrochemical effects caused by electricity, when the above effects are carried out at high temperatures such as heating, they may react, dissolve, or dissolve due to one or both of the above effects. Melting or altered parts are generated, and discharge shock pressure is also generated along with heat due to discharge.Furthermore, the electrical resistance of the corresponding part of the surface of the workpiece decreases due to the increase in temperature, and a portion of the current due to electrolysis, discharge, etc. Coupled with the above-mentioned discharge impact pressure, decomposition, melting, and impact scattering of the molten material will occur at the part of the workpiece surface where the part flows. This phenomenon causes voltage pulses to be applied to the electrodes 28 and 29 intermittently.
The application is repeated each time the supply is applied, and the workpiece is sequentially machined from the surface.

The present invention has been made in order to efficiently carry out the processing, etc. for each voltage pulse application as described above, while concentrating and limiting it to a desired local area. At the same time, discharge electrodes 28 are arranged at intervals along the surface.
29, a heat-resistant insulator is placed in the discharge gap close to the surface of the workpiece in order to limit the discharge gap formed therebetween. In other words, the discharge gap between the discharge electrodes becomes a thin film-like part filled with a conductive liquid between the surface of the workpiece and the heat-resistant insulator, and a voltage pulse that can be supplied to this discharge gap and control the application conditions, etc. , from where the electrolytic current, the thermoelectric heating current, and the discharge current are supplied, the generating action states such as electrolysis, heat, and impact pressure are concentrated and efficiently performed, and
It is easy to change the control of the action area, and it is possible to process the ceramic workpiece as desired. The present invention can be implemented by adding various changes to the method and apparatus illustrated and described above.

Although not shown here, it is also possible to irradiate the conductive liquid supplied to the processing portion of the workpiece 1 with a laser to heat the processing liquid and increase its conductivity. or,
Plasma discharge in water heats up ceramics,
At the same time, it can be used as an intermediate electrode. A high-temperature plasma is generated by irradiating a laser into water at the same time to generate a discharge, and ceramics are used as an electrode.Also, a high-speed liquid (H ₂ O) or a high-pressure liquid containing abrasive grains is supplied from another external source, or a gaseous body is supplied. Supply and process. The most efficient way to supply this gas is to supply halogen gas, Cl ₂ . and,
If the processing section of the workpiece 1 or the entire apparatus is evacuated and a gas (halogen) is supplied into the vacuum, processing is performed by dry ion etching. Electric discharge machining can be performed by coating C (carbon) of C _n H _o with a laser using oil and using this as an electrode.

Experimental examples of the present invention will be explained below.

S ₁₃ N ₄ was used as the workpiece ceramic, and S ₁ C was used as the heat-resistant insulator. The no-load voltage of the voltage pulse to be applied is approximately 90 V, and the supply amount of the conductive liquid is approximately 20 c.c./min to 100 c.c./min, depending on the discharge conditions, etc.
As electrodes, graphite with a horizontal cross section of approximately 8 mm x 15 mm is placed in parallel on the surface of the workpiece at an interval of approximately 7 mm, and in the 7 mm gap, a 25 mm L S _i C plate with a thickness of approximately 5 mm is placed.
Insert ×20mmH. In addition, the tip of this S _i C board,
10mmL x 0.5mm for the part facing the surface of the workpiece
An H-shaped recess is formed, and this recess serves as a current conduction and discharge path between the graphite electrodes.

With the above configuration, the electrode and the S _i C plate are fixed together, and the surface of the workpiece is moved at a speed of about 10 mm/min. Of course, it may be used while being fixed at one location.

Experimental example 1 A conductive liquid of 10% NaOH and the balance water is supplied at 30c.c./min, and the voltage pulse is set at the duration of the voltage pulse.
Current output with 50μS and pause time between voltage pulses of 50μS
When 10 A was used, an average current of about 5 A flowed, and intermittent discharge occurred between the graphite electrodes through the gap between the surface of the workpiece and the tip of the S _i C plate. When the same point was discharged for about 3 minutes, the surface part of the workpiece corresponding to the above-mentioned recess at the tip of the S _i C plate between the electrodes had become brittle to the extent that it could be easily ground with a grindstone to a depth of about 5 mm. I was able to scrape with a knife to a depth of 2mm.

Experimental Example 2 Using 8% HNO ₃ and the balance water as the conductive liquid, and using the same method as Experimental Example 1, the conductive liquid became brittle to a depth of about 3 mm, and the surface was about 0.1 mm thick due to thermal melting. It had been removed.

Experimental example 3 The gap between the graphite electrodes was set to approximately 12 mm, and a vitrified S _i C grinding wheel of 150 mmφ and thickness was used instead of the S _i C plate.
10mm, rotate at 3000RPM, make a gap of about 0.1mm between the grinding wheel and the surface of the workpiece, and increase this gap to about 200mm.
Hz, repeating about 4 mm separation and restoration approach,
The same conductive liquid as in Experimental Example 1 was used, and the applied voltage pulse conditions were 50 μS continuous, 50 μS pause, and current output Ip:
Using a 15A machine and an average machining current of about 7.5A, machining could be continued at a moving speed of about 15mm/min with a depth of cut of about 0.5mm.

As described above, the method of the present invention has the excellent effect of enabling secondary processing of defective conductors such as ceramics, which was previously considered impossible.

[Brief explanation of drawings]

FIG. 1 is a front view of an apparatus for carrying out the method of the present invention, FIG. 2 is a partially sectional side view of FIG. 1, and FIG. 3 is a view of another embodiment of the electrode. 1...Workpiece, 2...Table, 3...Saddle, 5...X-axis servo motor, 6...Bed, 8
... Y-axis servo motor, 9, 10 ... Column, 1
1, 12... Beam, 13, 14... Moving platform, 1
8, 19, 21... Servo motor, 22, 23...
...Bracket, 24, 25...Holder, 26, 2
7... Servo motor, 28, 29... Electrode, 34
...Insulating board.

Claims (1)

[Scope of Claims] 1. Each tip is provided with a desired discharge gap in a desired machining area of a workpiece such as ceramics, which is a poor conductor at room temperature but whose electrical resistance decreases as the temperature rises, so that each tip faces each other. A conductive liquid such as an electrolyte that is attached to or interposed on the surface of the machined part corresponding to the discharge gap between at least the pair of electrodes of the workpiece, and has a conductive liquid such as an electrolyte that is interposed between the pair of electrodes. In a device for processing ceramics, etc., which applies a voltage pulse to generate a discharge through the conductive liquid between each tip of the electrode, a heat-resistant insulator is placed close to the workpiece between the pair of electrodes. A method for processing ceramics or the like, characterized in that a discharge is generated based on the intermittent application of voltage pulses through a gap between the heat-resistant insulator and the workpiece, in which the conductive liquid is interposed. 2. The method for processing ceramics or the like according to claim 1, wherein each of the pair of electrodes is a rod-shaped electrode. 3. The method for processing ceramics or the like according to claim 1, wherein the pair of electrodes are disk-shaped electrodes that rotate as required. 4. Claims 1 to 3, wherein the distance between the pair of electrodes on the rear end side opposite to the surface side of the machined part of the workpiece is arranged and configured to be sufficiently larger than the discharge gap on the tip side. A method for processing the ceramics, etc. described in any one of the above. 5. Ceramics, etc. according to any one of claims 1 to 4, wherein the pair of electrodes is configured to be able to move close to or be fed out for close proximity to the surface of the processed part of the workpiece. Processing method. 6. A workpiece facing the pair of electrodes is controlled to move relative to the pair of electrodes at substantially right angles to the opposing direction, and desired processing parts are sequentially processed. A method for processing ceramics, etc., according to any one of items 1 to 5. 7 Claim 1, wherein the conductive liquid is water
A method for processing ceramics, etc., according to any one of items 6 to 6. 8. Claims 1 to 6, wherein the conductive liquid is a processing liquid in which acid or alkali is dissolved in water.
A method for processing ceramics, etc. described in any one of the items. 9. The method for processing ceramics, etc. according to any one of claims 1 to 6, wherein the conductive liquid is a processing liquid consisting of an aqueous solution of a strong acid such as hydrochloric acid, sulfuric acid, or nitric acid. 10. The method for processing ceramics, etc., according to any one of claims 1 to 6, wherein the conductive liquid is a processing liquid consisting of an aqueous solution of a strong base such as caustic soda or caustic potash. 11. The method for processing ceramics or the like according to any one of claims 1 to 6, wherein the conductive liquid is an aqueous plating solution for electroplating or electroless plating containing desired metal ions.