JP2003181725A - Electric discharge machining apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric discharge machining apparatus having both high machining accuracy and high machining speed and suitable for micromachining. <P>SOLUTION: The electric discharge machining apparatus machines a workpiece 6 by applying voltage to a gap defined between an electrode 6 and a workpiece 5 from a machining power source 1 to generate electric discharge and by relatively moving the electrode 6 and the workpiece 5. The apparatus comprises an interelectrode voltage dividing means 8 arranged in parallel to the gap of the electrodes of the electrode 6 and workpiece 5 for dividing the voltage between the discharge electrodes and a discharging state detecting means 10 comprising a comparator means 11 for outputting a logic signal by comparing a voltage proportional to potential difference generated at the gap of the electrodes detected from the interelectrode voltage dividing means 8 and a reference voltage, a pulse width extending means 12 for retaining a logic value for a given period of time triggered by either rise or decay of the logic signal, an OR means 13 for taking OR from the input and the output of the pulse width extending means 12, and a smoothing means 14 for smoothing the logic signal output of the OR means 13 to convert it into analogue voltage is provided. <P>COPYRIGHT: (C)2003,JPO

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 apparatus for machining a work piece by electric discharge machining, and in particular, electric discharge machining for machining a fine axis of 50 micrometers or less by wire machining with high machining accuracy in a short time. Regarding the device.

[0002]

2. Description of the Related Art Electric discharge machining has many characteristics such as high precision and easy machining of fine shapes using an electric discharge phenomenon as a medium, and is non-contact machining. For this reason, it is necessary to always maintain the distance between the electrode and the workpiece at a distance suitable for generating an electric discharge. In die-sinking EDM, it is necessary to constantly push the gap between electrodes by the amount by which the electrode and the work piece are removed as the machining progresses.However, machining scraps between the electrodes, gas generation, changes in the shape of the discharge surface, etc. Correspondingly, it is necessary to maintain the discharge electrode spacing.

Further, in wire electric discharge grinding as disclosed in Japanese Patent Laid-Open No. 1-103234, an outer edge of a wire slowly traveling on a wire guide is used for a portion corresponding to a grindstone for ordinary grinding, and a rotating workpiece is machined. It is a method of machining an object like cylindrical grinding, but when making a notch, it is necessary to always push in the polar interval by the amount that the electrode and the workpiece are removed as the machining progresses Similarly to the above, it is necessary to maintain the discharge electrode interval.
In wire electric discharge machining, the discharge area also changes when the plate thickness of the work piece changes, so the amount of electric discharge also changes, and the groove width changes significantly when feeding at constant electrical conditions and constant speed. However, the processing accuracy is significantly reduced. That is, since the discharge electrode interval changes with the change in the processing area, it is necessary to maintain the discharge electrode interval corresponding to the change in the plate thickness.

In order to solve such a problem, generally, there is a method of comparing the inter-electrode average voltage of the discharge interval with a certain reference voltage and changing the feed rate so that the inter-electrode average voltage becomes constant. It is taken. Furthermore, there is also a method that outputs not only the feed rate but also the optimum electrical conditions using a computer (Precision Engineering Society New Edition Precision Machinery Handbook, Corona P46).
5, P494 <1992>). A short circuit between the electrode and the workpiece can be detected by detecting the average voltage between the electrodes.

In Japanese Patent Laid-Open No. 59-7523, in addition to the method of controlling the feed rate so that the average voltage between electrodes is constant, the average machining current is further detected to determine the relative between the workpiece and the wire electrode. We provide a wire-cut electric discharge machine that detects sheet thickness from speed and desired machining groove width and switches electrical processing conditions.

In Japanese Patent Laid-Open No. 10-235521, the number of electric discharges per unit time is counted in the wire electric discharge grinding, and the counted value is compared with a predetermined value to determine the feed rate and the distance between the electrode and the workpiece. Provided is an electric discharge machining apparatus that controls electric discharge machining conditions. This utilizes the property that the number of discharges increases as the spacing between the discharge electrodes becomes narrower. For example, if the workpiece has undulations, the amount of electrical discharge machining to be removed increases at the ridges, so the number of electrical discharges increases, so it is possible to supply the desired amount of electrical discharge machining by slowing the feed rate. A short circuit can be prevented and the discharge interval can be made constant. On the contrary, since the electric discharge machining amount to be removed is small in the valley portion, the number of electric discharges is reduced, and the machining speed can be increased by increasing the feeding speed.

[0007]

However, in such a conventional electric discharge machine, a method of controlling the electric discharge machining conditions by detecting the average voltage between the electrodes and the average machining current is a constant cycle and a constant width. It is very effective for a circuit that uses a switching element that supplies a pulse voltage between the electrodes, but the voltage supply between the electrodes is irregular, and the discharge energy supply period is ignored compared to the non-supply period. In a circuit that uses the charging and discharging of a capacitor and a resistor that supply a pulse that is as steep as possible, there is almost no difference between the average voltage between contacts and the average machining current when there is no discharge, so there is the problem that control is difficult. . In addition, since the inter-electrode average voltage and inter-electrode average current are the results output by combining the discharge energy and the discharge frequency, when changing the discharge energy between rough machining and finishing machining, the peak value, pulse width, etc. However, there is a problem that the reference point cannot be determined by a simple calculation such as a proportional expression because the parameter of must be taken into consideration.

In this respect, in Japanese Patent Laid-Open No. 10-235521, the value of the number of discharges is used for control, so that it is also effective in a circuit using charge and discharge of a resistor and a capacitor. However, at least a certain time is required for counting, which is disadvantageous in terms of responsiveness, and a short-circuit detecting means is additionally required, so that the number of parts is increased and there is a problem in cost. Further, when fine machining such as machining a fine shaft of 50 micrometers or less is required, the discharge interval becomes short, and the insulating liquid that has a function of suppressing discharge does not easily enter. May occur, and discharge pulses may be counted several times in one discharge, and there is a risk of miscounting the number of discharges that is more than twice the actual number of discharges.

The present invention is intended to solve the above problems, and an object of the present invention is to provide an electric discharge machining apparatus having both high machining accuracy and high speed, which is particularly suitable for fine machining.

[0010]

In order to achieve the above object, the invention according to claim 1 applies a voltage from a machining power source to a gap formed by an electrode and a workpiece. In an electric discharge machine for generating an electric discharge and for moving the electrode and the workpiece relative to each other to machine the workpiece, a discharge electrode provided in parallel with a polar interval between the electrode and the workpiece. A voltage dividing means for dividing the voltage between the discharging electrodes is provided, and a voltage proportional to the potential difference generated in the pole interval detected from the voltage dividing means between the discharging electrodes is compared with a reference voltage to output a logical signal. And a comparator means, a pulse width extending means for holding a logical value for a certain period of time by using one of the rising edge and the falling edge of the logic signal as a trigger, and the input and output of the pulse width extending means. Provided a logical OR means taking the sum, the smooth discharge state detection means comprising a smoothing means into an analog voltage by a logic signal output of the logical sum means. According to the present invention, the discharge frequency that changes according to the discharge electrode interval can be converted into an analog voltage with a fast response without miscounting, and short-circuit detection can also be provided. Further, it is easy to recognize the difference in discharge frequency even when using a processing power source that uses charging and discharging of a resistor and a capacitor. Furthermore, since only the discharge frequency is detected, it is easy to obtain a reference point for control, and thus it is possible to detect the pole interval for realizing highly accurate machining.

According to a second aspect of the present invention, the electrode and the workpiece are identified from the analog voltage data output from the discharge state detecting means and the set value data of the processing power source recorded in the storage means. Discharge electrode interval calculation means for calculating the estimated discharge electrode distance, and axial movement control means for correcting the relative movement condition of the electrode and the workpiece recorded in the storage means from the calculation result of the discharge electrode distance calculation means. And an axial movement drive means that is driven by the axial movement control means so as to relatively move the electrode and the workpiece based on the corrected relative movement condition. According to the present invention, the discharge electrode interval can be estimated from the output of the discharge state detecting means, and mechanical control can be performed to keep the discharge electrode interval constant, and high-precision machining can be performed in a short time.

According to a third aspect of the present invention, there is provided a machining power supply control means for correcting the electrical condition of the machining power supply recorded in the storage means from the calculation result of the discharge electrode interval calculation means. . According to the present invention, it is possible to estimate the discharge electrode interval from the output of the discharge state detection means and perform electrical control so as to keep the discharge electrode interval constant, thereby enabling highly accurate machining.

According to a fourth aspect of the present invention, in the electric discharge machining apparatus in which the machining power source includes a DC power source, a resistor, and a capacitor, the voltage dividing means between the discharge electrodes is arranged in parallel with both electrodes of the DC power source. In addition to providing a DC power supply voltage dividing means having a voltage division ratio to be a voltage lower than the divided voltage at the time of no discharge detected by, the output voltage of the DC power supply voltage dividing means and the reference voltage of the comparator section. Configured to be. According to the present invention, the threshold value of the comparator unit can be automatically corrected even when the applied voltage supplied from the DC power source changes, so that the condition setting for high-precision machining becomes simple.

According to a fifth aspect of the present invention, in the electric discharge machining device wherein the electrode is a wire electrode and the workpiece is a fine shaft rotated by a rotating means, the wire electrode and the shaft of the fine shaft are provided. It was equipped with a wire guide for traveling orthogonal to the direction. According to the present invention, it is possible to process a fine axis of 50 micrometers or less with high accuracy.

According to a sixth aspect of the present invention, the electrode is a tool electrode pre-machined into a desired three-dimensional shape, and the three-dimensional shape of the tool electrode is transferred to the workpiece. According to the present invention, high-precision machining is possible even in a die-sinking electric discharge machine.

According to a seventh aspect of the present invention, in an electric discharge machine in which the electrode is a wire electrode and the work piece is a plate-shaped conductor, the wire electrode and the plane direction of the plate-shaped conductor are set. It is arranged to be orthogonal to each other and to be provided with at least two or more axis moving means for changing the relative position of the wire electrode and the plate conductor. According to the invention,
High-precision machining is possible even with a wire-cut electric discharge machine.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 shows a first configuration example of an electric discharge machine according to the present invention. The processing power supply 1 includes a DC power supply 2, a resistor 3, and a capacitor 4. DC power supply 2
Of the DC power source 2 is connected to the electrode 6. The space between the workpiece 5 and the electrode 6 is filled with water, discharge oil or the like. Further, the workpiece 5 is connected to an axial movement drive unit 7 that moves vertically and horizontally. When the DC power supply 2 applies a DC voltage, the capacitor 4
Is charged, and the voltage across the terminals of the capacitor 4 gradually rises. When the voltage between the terminals of the capacitor 4 exceeds the discharge start voltage in the interval between the work piece 5 and the electrode 6, a discharge is generated between the work piece 6 and the electrode 6. The change in the potential difference between the workpiece 5 and the electrode 6 in this process is detected by the inter-discharge voltage dividing means 8. Voltage dividing means 8 between discharge electrodes
Is realized by voltage division with a sufficiently high resistance value, for example, by connecting a resistance of 8.2 megohm and a resistance of 1 megohm in series and detecting the potential difference across both ends of the resistance of 1 megohm.

Further, the potential difference between the two electrodes of the DC power supply 2 is detected by the DC power supply voltage dividing means 9. The DC power supply voltage dividing means 9 is also realized by voltage division with a sufficiently high resistance value, but the voltage dividing ratio is set to be slightly larger than the voltage dividing ratio of the inter-electrode voltage dividing means 8 so as to discharge when there is no discharge. The voltage detected by the DC power supply voltage dividing means 9 is always lower than the voltage detected by the inter-electrode voltage dividing means 8. For example, the voltage dividing means 8 between the discharge electrodes has a resistance of 8.2 megohm and a
When it is configured with a resistance of mega ohm, the DC power supply voltage dividing means 9 is configured with a resistance of 10 mega ohm and a resistance of 1 mega ohm. At this time, when the applied voltage of the DC power supply 2 is set to 100 V, the voltage across the 1 megohm resistor of the inter-discharge electrode voltage dividing means 8 when the capacitor 4 is sufficiently charged becomes 10.86 V. Therefore, the voltage across the 1 megohm resistor of the DC power supply voltage dividing means 9 is 9.0.
It will be 6 volts. When the applied voltage of DC voltage 2 is changed,
In response to this, the output of the voltage dividing means 8 between the discharge electrodes and the DC power supply voltage dividing means 9 change while the ratio between them is always kept constant. That is, when the capacitor 4 is sufficiently charged, the DC power supply voltage dividing means 9 always has a smaller value than the discharge electrode interval voltage dividing means 8. It should be noted that the voltage division ratio between the discharge electrode voltage dividing means 8 and the DC power supply voltage dividing means 9 are set to the same value, and the output of the DC power supply voltage dividing means 9 is set to an arbitrary voltage value using an operational amplifier or the like. Alternatively, the DC power supply voltage dividing means 9 may have a smaller value than the inter-discharge electrode voltage dividing means 8 when the capacitor 4 is sufficiently charged.

The output voltage of the DC power supply voltage dividing means 9 is input to the reference voltage of the comparator means 11 in the discharge state detecting means 9, and the output voltage of the inter-electrode voltage dividing means 8 is input to the comparator means 11. To do. Furthermore, via the pulse width expansion means 12, the logical sum means 13, and the smoothing means 14,
An analog signal proportional to the discharge frequency is output to the discharge electrode interval calculation device 15. The discharge electrode interval calculation device 15 estimates the discharge electrode interval, and based on the estimated value, the axis movement control means 1
6, a speed change command, a temporary reverse motion command of the feed motion, and the like are issued to operate the axis movement drive means so that the discharge electrode interval becomes constant.

FIG. 2 shows the waveform of each part of the discharge state detecting means according to the present invention. The waveform of the output 19 from the discharge electrode voltage dividing means 8 is as shown in 25. When discharge is generated at the gap between the workpiece 5 and the electrode 6, the potential difference between the electrodes sharply decreases and the charge is recharged. Be started. When descending, vibration may be seen depending on the conditions, such as when discharge oil is slowly entering the pole interval.

On the other hand, the waveform of the output 20 from the DC power supply voltage dividing means 9 is as shown by 26, and if the applied voltage of the DC power supply 2 is constant, it is constant regardless of whether or not there is discharge, and its value is The value is lower than the output of the voltage dividing means between discharge electrodes when the capacitor 2 is sufficiently charged, and the difference is the threshold value at which the output 21 of the comparator means 11 is inverted. That is, the output voltage of the DC power supply voltage dividing means 9 is inputted as the reference voltage of the comparator means 11 in the discharge state detecting means 9, and the output voltage of the inter-electrode voltage dividing means 8 is inputted to the comparator means 11. At this time, when the capacitor 2 is sufficiently charged, the output of the inter-discharge electrode voltage dividing means 8 is higher than the reference voltage, and at this time, the output of the comparator means 11 is set to LOW. Then, when the discharge is started and the output of the voltage dividing means 8 between the discharge electrodes becomes lower than the reference voltage, the output of the comparator means 11 becomes HIGH, as shown by the waveform 27.

When the discharge electrode gap between the work piece 5 and the electrode 6 is narrow due to finishing work or the like, and water or discharge oil is difficult to enter, the voltage may oscillate, so that once. There is a possibility that several pulses will be generated in the output waveform 27 of the comparator means during discharge by the discharge. The discharging comparator means output 21 is branched into two, one is inputted to the pulse width extending means 12 and the other is inputted to the logical sum means 13. In addition,
It is desirable to insert a delay circuit for adjusting timing in a path that does not pass through the latter pulse width expansion means 12. The pulse width expansion means 12 uses, for example, a monostable multivibrator, outputs a pulse having an arbitrarily set time width by using an input pulse as a trigger, and ignores the rising edge of the pulse input within the time width. As a result, the output waveform 27 of the comparator means during discharging is 1
Even if a plurality of pulses are generated by one discharge, the pulse width expansion means output waveform 28 during discharge is such that one pulse is output and a pulse having a constant time width is output.

Since the discharge cycle is random and the voltage pulse width output from the inter-discharge electrode voltage dividing means 8 is very short with respect to the discharge cycle, the output of the inter-discharge electrode voltage dividing means 8 is changed. Even if it is directly smoothed, the change width of the smoothed signal due to the change of the discharge frequency is small, but the pulse width expansion means 12 lengthens the pulse width of one discharge to increase the change width of the smoothed signal depending on the discharge frequency. It becomes possible. That is, the pulse width due to the discharge is constant, but the smoothing signal largely changes depending on the discharge frequency because the discharge cycle is random. The discharge pulse width expansion means output 22 is input to the logical sum means 13 and is logically summed with one of the signals branched by the comparator means output 21. At the time of discharge, the pulse width expansion means output waveform 27
Waveform becomes the output waveform 29 of the logical sum means as it is, is inputted to the smoothing means 14, and becomes the analog signal waveform 30 which changes according to the discharge frequency.

The above is the case where the discharge is normally generated between the workpiece 5 and the electrode 6, but when the short circuit accident occurs, the smoothing means output 24 becomes constant at the maximum voltage, and the short circuit can be detected.

FIG. 3 shows the waveform of each part of the discharge detection circuit when a short circuit according to the present invention is detected. When a short circuit occurs, the output of the voltage dividing means 8 between discharge electrodes becomes 0 volt or a value close to 0 volt. Therefore, due to the short circuit, the output 19 of the comparator means 11 continues to be in the HIGH state from the time of occurrence of the short circuit to the cancellation of the short circuit as indicated by the waveform 33. At this time, the pulse width expansion means 12 outputs a pulse having a constant width when a short circuit occurs, and thereafter remains LOW until the short circuit is resolved.

On the other hand, with respect to the output 19 of the comparator means 11, since the HIGH state is continued after the short circuit, the output 23 of the logical sum means 13 is HIG after the short circuit as shown by the waveform 35.
The H state is continued. Therefore, the output 24 of the smoothing means 14 becomes constant at the maximum voltage as shown by the waveform 36, and a short circuit can be detected by monitoring this. Also, FIG.
As the discharge frequency increases, the smoothing means output waveform 30 at the time of discharge becomes high-value analog data, and a short circuit occurs as a result of excessive discharge frequency, and the waveform 3 in FIG.
Since the maximum voltage is obtained as shown in 6, the control logic is consistent and easy to control.

FIG. 4 shows a second configuration example of the electric discharge machine according to the present invention. On the basis of the estimated discharge electrode interval, the inter-discharge electrode calculation means 14 compares the set value of the processing power supply 1 recorded in the storage means 17, and the processing power supply control means 18 controls the processing power supply with respect to the processing power supply. , The applied voltage change command, etc., are operated so that the discharge electrode interval becomes constant.

In the above embodiments, the wire electric discharge grinding was mainly described as an example, but the present invention is not limited to this and may be applied to die-sinking electric discharge machining or wire cut electric discharge machining.

[Brief description of drawings]

FIG. 1 is a diagram showing a first configuration example of an electric discharge machine according to an embodiment of the present invention.

FIG. 2 is a diagram showing a waveform of each part of the discharge state detecting means according to the embodiment of the present invention.

FIG. 3 is a diagram showing a waveform of each part of the discharge detection circuit when a short circuit according to an embodiment of the present invention is detected.

FIG. 4 is a diagram showing a second configuration example of an electric discharge machine according to the present invention.

[Explanation of symbols]

1 ... Machining power supply, 2 ... DC power supply, 3 ... Resistance, 4 ... Capacitor, 5 ... Workpiece, 6 ... Electrode, 7 ... Shaft movement drive means,
8 ... Discharge electrode voltage dividing means, 9 ... DC power supply voltage dividing means, 10 ... Discharge state detecting means, 11 ... Comparator means, 12 ... Pulse width extending means, 13 ... Logical sum means, 14
... smoothing means, 15 ... discharge electrode calculation unit, 16 ... axis movement control unit, 17 ... storage unit, 18 ... machining power supply control unit, 19 ... discharge electrode voltage dividing means voltage dividing voltage, 20 ... DC power supply voltage Voltage dividing means divided voltage, 21 ... Comparator section output, 22 ... Pulse width expansion means output, 23 ... Logical sum means output, 24 ... Smoothing means output, 25 ... Discharging inter-electrode voltage dividing means divided voltage waveform, 26 Discharge DC power supply voltage dividing means Divided voltage waveform 27 Discharge comparator output waveform 28 Discharge pulse width expansion means output waveform 29 Discharge logical sum output waveform 30 Discharge smoothing means output Waveform 31 ... Voltage waveform between voltage dividing means between discharge electrodes at short circuit, 32 ... Voltage waveform of DC power source voltage dividing means at short circuit, voltage waveform 33 ... Comparator output waveform at short circuit, 34 ... Pulse width expansion means output waveform at short circuit, 35 ... Output of OR means at short circuit Form, 36 ... short-circuit smoothing means output waveform

Claims (7)

[Claims] 1. A machining power source applies a voltage to a gap formed by an electrode and a workpiece to generate a discharge, and the electrode and the workpiece are moved relative to each other to process the workpiece. In the electric discharge machining device for performing, an inter-discharge electrode voltage dividing means is provided in parallel with a polar interval between the electrode and the workpiece to divide a voltage between the discharge electrodes, and the inter-discharge electrode voltage dividing means is provided. The comparator means for comparing the voltage proportional to the potential difference generated in the pole interval detected from the reference voltage with the reference voltage and outputting the logic signal, and the logical value for a certain period of time triggered by either one of the rising edge and the falling edge of the logical signal. Pulse width extending means for holding
Discharge state detecting means is provided which comprises a logical sum means for taking a logical sum of the input and output of the pulse width expanding means, and a smoothing means for smoothing the logical signal output of the logical sum means to convert it into an analog voltage. Electric discharge machine characterized by. 2. An estimated discharge electrode distance between the electrode and the workpiece is calculated from analog voltage data output from the discharge state detection means and setting value data of the processing power source recorded in the storage means. The discharge electrode interval calculation means, the axis movement control means for correcting the relative movement condition of the electrode and the workpiece recorded in the storage means from the calculation result of the discharge electrode distance calculation means, and the axis movement control means. The electric discharge machining apparatus according to claim 1, further comprising: an axial movement driving unit that drives the electrode and the workpiece to move relative to each other based on the controlled relative movement condition that has been corrected. 3. A machining power supply control means for correcting the electrical condition of the machining power supply recorded in the storage means from the calculation result of the discharge electrode interval calculation means. The electric discharge machine described. 4. The processing power source is a direct current power source, a resistor,
In an electric discharge machine comprising a capacitor, a DC power supply voltage having a voltage division ratio such that the voltage is lower than the voltage division voltage at the time of no discharge detected by the voltage dividing means between the discharge electrodes in parallel with both electrodes of the DC power supply. 4. The electric discharge machine according to claim 1, wherein the voltage dividing means is provided and the output voltage of the DC power supply voltage dividing means is configured to be a reference voltage of the comparator section. 5. In the electric discharge machining apparatus, wherein the electrode is a wire electrode and the workpiece is a fine shaft rotated by a rotating means, the wire electrode and the fine shaft run in a direction orthogonal to each other. An electric discharge machine according to any one of claims 1 to 4, further comprising a wire guide. 6. The tool electrode according to claim 1, wherein the electrode is a tool electrode pre-machined into a desired three-dimensional shape, and the three-dimensional shape of the tool electrode is transferred to the workpiece. Electric discharge machine. 7. An electric discharge machine in which the electrode is a wire electrode and the workpiece is a plate-shaped conductor, and the wire electrode and the plate-shaped conductor are made to intersect at right angles with each other, and 5. The electric discharge machine according to claim 1, further comprising at least two or more axis moving means for changing the relative position of the plate-shaped conductor.