JPH07132417A - Electric discharge machine - Google Patents

Abstract

PURPOSE:To get stable discharge delay time and prevent the unevenness in machining property by equipping a voltage control circuit where capacitors are connected in parallel between poles, and applying voltage based on the charge voltage to the capacitor of pulsated voltage between the poles, and raising the voltage between poles slowly. CONSTITUTION:An electric discharge machine machines a work by applying voltage being made by pulsating the power source voltage with a switching element 32 between the poles between a machining electrode 1 and a work 2 so as to generate intermittent discharge between the poles. In this case, this is equipped with a voltage control circuit 4 where the series circuit composed of a switching element 45 and a resistor 44, and a capacitor are connected in parallel between the poles, respectively, through a diode 42. The voltage based on the charge voltage at charge of the capacitor 43 by the pulsated voltage is applied between the poles, and the voltage between poles is raised slowly by the time constant at the time of the capacitor 43 being charged. Moreover, by the series circuits 44 and 45, the discharge is performed by the time constant at the time of discharging the charge accumulated in the capacitor 43 with a resistor 44.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric discharge machine,
Particularly, the present invention relates to an electric discharge machine power supply suitable for a die-sinking electric discharge machine.

[0002]

2. Description of the Related Art In an electric discharge machine of a die-sinking electric discharge machine, an electric current is intermittently supplied between a workpiece and an electrode to generate an electric discharge between the electrodes to perform electric discharge machining. There is. Conventionally, as a method of applying a voltage between the electrodes,
A method is known in which a power supply voltage is pulsed by a switching element and the pulse voltage is applied between electrodes. In the voltage application by the pulse voltage, the voltage between contacts rises immediately to the power supply voltage when the voltage application is started, and the voltage is maintained until the discharge is started.

FIG. 8 is a block diagram of a machining power supply circuit of a conventional electric discharge machine, and FIG. 9 is a diagram showing a voltage state of a machining power supply circuit of a conventional electric discharge machine. In FIG. 8, a machining power source circuit 3 including a series circuit of a DC power source 31, a switching element 32, and a current limiting resistance resistor 2 is connected in series to the machining electrode 1 and the workpiece 2, and the DC power source is connected by the switching element 32. The voltage of 31 is pulsed, and the voltage is applied between the machining electrode 1 and the workpiece 2. When the switching element 32 is controlled as shown in FIG. 9A, the power supply voltage is applied between the electrodes as shown in FIG. 9B at the rising timing of the switching element 32, and the discharge is performed after the discharge delay time. Is started. During discharge, an arc voltage lower than the power supply voltage is applied between the electrodes.

[0004]

However, in the above-mentioned conventional electric discharge machining apparatus, by applying a pulse voltage between the electrodes, the power supply voltage is immediately raised from the start of voltage application,
When the voltage is maintained until the start of discharge, the discharge conditions change due to minute changes in the distance between the electrodes and the concentration of the sludge between the electrodes,
The discharge delay time from the start of voltage application to the start of discharge is
There is a problem in that it fluctuates significantly (see the broken line in FIG. 9B). This variation in the discharge delay time causes, for example, the discharge to be locally concentrated when the discharge delay time is short, resulting in a roughened surface.

Further, in the conventional electric discharge machine, the control of the inter-electrode voltage is performed by, for example, integrating the inter-electrode voltage, averaging the results and comparing it with the reference voltage, and lowering the inter-electrode voltage when it is larger than the reference voltage. On the contrary, when the voltage is smaller than the reference voltage, servo control is performed such that the voltage between contacts is increased. In such control of the inter-electrode voltage, if the fluctuation of the discharge delay time is large, servo control becomes difficult, which causes instability of the inter-electrode voltage.

As a method of solving the above-mentioned problems of the electric discharge machine by applying the pulse voltage, for example, FIG.
As shown in (c) of FIG. 9, the switching element of the machining power supply circuit is controlled to gradually shift from the cutoff region to the saturation region, and the inter-electrode voltage is gradually increased as shown in (d) of FIG. It is conceivable that the discharge delay time is stabilized by increasing the temperature to a higher level. However, in the inter-electrode voltage control according to the solution, when discharge is started before the switching element reaches the saturation region, the voltage applied between the electrodes during the discharge fluctuates and the current flowing between the electrodes becomes unstable, This causes a variation in processing characteristics.

Therefore, an object of the present invention is to solve the above-mentioned problems in the conventional electric discharge machining apparatus and to provide an electric discharge machining apparatus which can obtain a stable electric discharge delay time.

[0008]

DISCLOSURE OF THE INVENTION According to the present invention, a pulsed voltage is applied to a gap between a machining electrode and a workpiece, and an intermittent discharge is generated between the gaps to perform machining. The processing device is provided with a voltage control circuit in which capacitors are connected in parallel between the electrodes, and the voltage control circuit is
A pulsed voltage is applied between the electrodes, which voltage is determined by charging the capacitor by charging the capacitor.
The above object is achieved by gradually increasing the inter-electrode voltage according to the time constant when the capacitor is charged.

Further, the present invention provides an electric discharge machining apparatus for applying a pulsed voltage to a gap between a machining electrode and a workpiece to generate intermittent electric discharge between the gaps for machining. It is equipped with a series circuit of a switching element and a resistor, and a voltage control circuit in which a capacitor is connected in parallel between the poles via a diode. The voltage control circuit is based on charging of a capacitor by a pulsed voltage. A voltage determined based on the charging voltage of the capacitor is applied between the poles, the voltage between the poles is gradually increased by the time constant when the capacitor is charged, and it is stored in the capacitor by the series circuit of the switching element and the resistor. The object is achieved by discharging the electric charge with a time constant when the electric charges are discharged by the resistor.

The switching element of the present invention is turned on after the start of the discharge rest period and is turned off before the end of the discharge rest period.

[0011]

According to the present invention, in an electric discharge machining apparatus, a pulsed voltage is applied between the electrodes between the machining electrode and the workpiece, and intermittent electric discharge is generated between the electrodes for machining. .
Then, the voltage applied between the poles is a voltage determined by the voltage control circuit configured by the capacitors connected in parallel between the poles based on the charging voltage of the capacitor when the pulsed voltage charges the capacitor, The voltage between contacts gradually rises due to the time constant when the capacitor is charged.

Further, according to the present invention, in an electric discharge machining apparatus, a pulsed voltage is applied between the machining electrodes and the workpiece to generate an intermittent electric discharge between the machining poles for machining. I do. Then, the voltage applied between the poles is charged by the pulsed voltage by the voltage control circuit configured by the series circuit of the switching element and the resistor connected in parallel via the diode between the poles and the capacitor. The voltage is determined based on the charging voltage of the capacitor, and the time constant when the capacitor is charged gradually increases the voltage between contacts, and the series circuit of the switching element and the resistor suspends the switching element from discharging. The capacitor is controlled to be turned on after the start of the period and turned off before the end of the discharge pause period, and the capacitor is discharged within the discharge pause period with a time constant when the capacitor is discharged by the resistor.

[0013]

Embodiments of the present invention will now be described in detail with reference to the drawings, but the present invention is not limited to the embodiments.

(Configuration of First Embodiment) FIG. 1 is a schematic block diagram of a power supply circuit according to a first embodiment which is an embodiment of the present invention.

In FIG. 1, 1 is a machining electrode, 2 is a workpiece, and a machining power supply circuit 3 and an inter-electrode voltage control circuit 4 are connected in parallel to a series circuit of the machining electrode 1 and the workpiece 2. There is. The processing power supply circuit 3 is configured by connecting a DC power supply 31, a switching element 32, and a current limiting resistor 33 in series,
The machining element 1 and the workpiece 2 are formed by the switching element 32.
The voltage applied between the electrodes is controlled. The current limiting resistor 33 is a resistor that limits the upper limit of the value of the current flowing between the electrodes.

Further, the inter-electrode voltage control circuit 4 includes a charging circuit 4A composed of a charging resistor 41, a diode 42 and a capacitor 43 connected in parallel between the electrodes, a discharging resistor 44 connected in parallel with the capacitor 43 and a switching circuit. The discharge circuit 4B is composed of the element 45. In FIG. 1, the machining power supply circuit 3 is shown by a broken line, and the inter-electrode voltage control circuit 4 is shown by a dashed line. In addition, the switching element 3
2. The switching element 45 can be composed of, for example, a FET, and ON / OFF drive control is performed by a control signal from a control circuit (not shown).

(Operation Example 1 of Embodiment 1) Next, a time chart of the first operation example of the embodiment 1 of the present invention in FIG. 3 and FIG. 4 will be described with reference to the flowchart of the first operation example of the embodiment of the present invention.

In the voltage between contacts shown in FIG. 2A, the voltage is applied to the workpiece 2 by repeating a time T1 which is the sum of the on time Ton and the off time Toff of the switching element 32 as one cycle. Done. As the voltage applied between the electrodes, the voltage V1 is applied at the rising timing of the switching element 32 shown in FIG. 2C, and gradually rises to the power supply voltage during the discharge delay time T4, and the discharge is generated. The voltage suddenly drops to the arc voltage at the timing, and the electric discharge machining is performed during the electric discharge time T2. This discharge time T2 is
It is a time preset according to the conditions of the electric discharge machining, and after this discharge time T2, the voltage applied between the electrodes is stopped during the preset discharge pause time T3. After that, the same voltage is applied again. Here, the value of the voltage V1 applied between the electrodes when the switching element 32 is turned on is the resistance value R33 of the current limiting resistor 33.
And the voltage division ratio of the resistance value R41 of the charging resistor 41.

In the electric discharge machining apparatus of the present invention, the inter-electrode voltage during the electric discharge delay time T4 has a characteristic of gradually increasing with time, and this characteristic is determined by the charging circuit 4A. This rise in the voltage between contacts is caused by the processing power supply circuit 3
The resistance value R33 of the current limiting resistor 33 and the resistance value R41 of the charging resistor 41 of the charging circuit 4A of the inter-electrode voltage control circuit 4,
The time constant Ta (=
(R33 + R41) · C). The discharge delay time T4 is tentatively determined by the time constant Ta as described above. For example, as shown in FIG. 2A, the discharge delay time T4 is not constant but varies depending on the discharge state. By increasing the inter-electrode voltage, the discharge delay time T4 is stabilized as compared with the case of the pulsed applied voltage.

When discharge occurs and the voltage between the electrodes drops to the arc voltage, the capacitor 43 in the charging circuit 4A becomes
The diode 42 separates the gap from the gap, and the gap is supplied with the machining current from the machining power supply circuit 3 during the charging time T2.

During the discharge rest time T3, since the switching element 32 is off and the switching element 45 is on, the electric charge stored in the capacitor 43 is discharged.
The discharge is performed with a time constant Tb (= 1 / R44 · C) determined by the resistance value R44 and the capacitance C of the capacitor 43.

Therefore, in the first embodiment, a voltage is applied between the electrodes with a time constant Ta determined by the capacitances of the charging resistor 33, the charging resistor 41, and the capacitor 43.

Next, the control for applying the voltage between contacts will be described with reference to the flow chart of the first operation example of FIG.
In addition, in the flowchart of the figure, the description will be given using the reference numeral of step S.

Step S1: A control device (not shown) outputs a control signal to the switching element 32 to turn on the switching element 32. This switching element 32
When the switch is turned on, the voltage V1 is applied between the electrodes, and the time constant T determined by the capacitor C, the resistance value R33, and the resistance value R41.
The applied voltage increases according to a. This state is maintained until discharge occurs. The time from the application of voltage to the start of discharge is the discharge delay time T4. The switching element 45 is turned off before the switching element 32 is turned on.

Step S2: It is judged whether or not a discharge is generated between the electrodes, and the time counting of the discharge time is started from the time when the discharge is generated. The determination of the occurrence of discharge between these poles is
It is performed by monitoring the voltage between contacts and detecting that the voltage between contacts becomes equal to or lower than a preset voltage. This determination detects a voltage drop between the electrodes due to discharge, and the voltage during discharge is an arc voltage of, for example, about 20 to 30V. Therefore, the set voltage for determination is, for example, a power supply voltage of 200V. Then set to 60V.

Step S3: When the electric discharge is started in the step S2, the time T from that time is counted, and the elapse of the electric discharge time T2 preset according to the machining conditions is judged. By this step, discharging for the discharging time T2 is performed.

Step S4: At the step S3, a control signal is transmitted to the switching element 32 at the end of the discharge time T2 to turn off the switching element 32. Further, the time counting started at the start of the discharge is continued, and the discharge pause time T3
Monitor the progress of.

Step S5: The switching element 32
The switching element 45 is turned on after a lapse of a minute time Δt after turning off. This minute time Δt is set so that at least the switching element 45 does not turn on before the switching element 32, and the power source and the switching element 45 are turned on.
This is because the timing is set so that no short circuit occurs, and can be set arbitrarily.

Step S6: The time T measured is compared with the time (T2 + T3-Δt) obtained by subtracting the minute time Δt from the time obtained by adding the discharge time T2 and the discharge rest time T3, and the time (T2 + T3-Δt) After elapse, the process proceeds to the next step S7. Through this step, the fall timing when the switching element 45 is turned off is obtained. The minute time Δt is equal to the switching element 45 and the switching element 32.
This is for preventing a short circuit of the power source except that both are turned on, and can be set arbitrarily.

Step S7: The switching element 45 is turned off at the timing of the step S6.

Step S8: The time T measured is the time (T2) obtained by adding the discharge time T2 and the discharge rest time T3.
Compared with + T3), as time (T2 + T3) elapses,
One cycle of electrical discharge machining is completed.

Step S9: It is judged whether or not the electric discharge machining is finished, and if the electric discharge machining is to be continued, the step S9 is executed again.
Returning to 1, the above process is repeated. When the electric discharge machining is completed, the process is completed.

Next, the setting of the values of the resistance and the capacitor in the first working example of the first embodiment of the electric discharge machining apparatus of the present invention will be described with reference to the flowchart shown in FIG. It should be noted that FIG. 4 will be described using step T.

Step T1: In the first embodiment, R33 is set according to the actually used machining current. Generally, the larger the peak value of the machining current, the faster the machining speed but the worse the surface roughness.Therefore, the peak value of the machining current is determined according to the machining speed and the surface roughness of the electric discharge machining. R33 is set so as to have a peak value.

Step T2: The discharge time T2 and the discharge rest time T3 are set in advance. Generally, if the discharge time is long, the machining speed increases but the surface roughness deteriorates. The discharge time T2 and the peak value of the machining current are set according to the machining speed of the electric discharge machining and the accuracy of the processing surface. To be done. Further, the discharge pause time T3 is also set according to the machining conditions.

Step T3: While performing the test processing,
By determining the time constant Ta according to the discharge delay time, C and R41
To set. The number of time points Ta is the resistance value R33 of the current limiting resistor 33, the resistance value R41 of the charging resistor, and the capacitor 4
During the capacity C of 3, Ta = (R33 + R41).
Since there is a relationship of C, capacitance C and resistance R33, R41
It can be set from.

Step T4: The time constant Tb is set within the discharge pause time T3, and the electric charge accumulated in the capacitor 43 at the end of the discharge pause time influences the waveform of the next voltage application between the electrodes. In other words, it is determined that the capacitance of the capacitor 43 is discharged within the discharge pause time. Then, the time constant Tb is calculated by the following equation in the circuit shown in FIG.
Since it is represented by R44 · C, the resistance value R44 is determined from the set time constant Tb and the capacitance C set in step T3.

(Second Operation Example of First Embodiment) Next, regarding the second operation example of the first embodiment having the above-mentioned structure, a time chart of the second operation example of one embodiment of the present invention in FIG. 6 and 7, and a flowchart of a second operation example of the embodiment of the present invention will be described.

At the inter-electrode voltage shown in FIG. 5A, the voltage application to the workpiece 2 is the same as in the first operation example.
On time Ton and off time To of the switching element 32
The time T1 consisting of ff is repeatedly performed as one cycle, and in the second operation example, the time T1 is set to a preset constant time interval.

The operation during the discharge delay time T4 and the discharge time T2 from the rise of the switching element 32 is the same as that of the first operation example, and the switching element 32
The voltage of V1 is applied at the rising timing of the voltage, gradually rises to the power supply voltage during the discharge delay time T4, sharply drops to the arc voltage at the timing when the discharge occurs, and the electric discharge machining is performed during the discharge time T2. Be seen. This discharge time T2
Is set in advance according to the conditions of electric discharge machining.
On the other hand, the time interval of the discharge rest time T3 is determined by the end time of the discharge time T2 and the end time of the time T1.
The value obtained by subtracting the discharge delay time T4 and the discharge time T2 from (T
1-T4-T2), which varies according to the discharge delay time T4. Therefore, the time interval of the discharge rest time T3 is
The minimum required value is set based on the processing conditions, and normally, the discharge pause time is set to be the minimum time or longer. Also,
Since the time constant Tb of the discharge circuit 4B needs to be a value such that the discharge is completed within this discharge pause time T3, it is set by the minimum value of the discharge pause time T3.

The charging circuit 4 in the second operation example
The inter-electrode voltage value of A and the time constant Ta are set in the same manner as in the first action example, and the operation during the charging time T2 after the occurrence of discharge is also the same as in the first action example.

During the discharge rest time T3, discharge is performed with a time constant Tb (= R44 · C) determined by the resistance value R44 of the discharge resistor 44 and the capacitance C of the capacitor 43, and the discharge state is maintained until the time T1 elapses. Therefore, the discharge rest time T3 changes according to the discharge delay time T4.

Next, the control for applying the voltage between contacts will be described with reference to the flow chart of the second operation example of FIG.
It should be noted that in the flowchart of the drawing, description will be given using the reference numeral of step P.

The steps P1 to P5 are the same as the steps S1 to S5 of the first operation example.
Therefore, the description is omitted here. In step P1, a timer (not shown) starts counting when the switching element 32 rises, and the elapsed time To within one cycle is counted.

Step P6: The elapsed time To from the rising of the switching element 32 is measured, and the elapsed time To is compared with the time (T1-Δt) obtained by subtracting the minute time Δt from the time T1 of one cycle. After a lapse of time (T1−Δt) from the time when the switching element 32 rises, the process proceeds to the next step S7. Through this step, the fall timing when the switching element 45 is turned off is obtained. The minute time Δt is for preventing the short circuit of the power supply except that both the switching element 45 and the switching element 32 are in the ON state, and can be set arbitrarily.

Step P7: The switching element 45 is turned off at the timing of the step P6.

Step P8: The elapsed time To from the rising of the switching element 32 is compared with the time T1 of one cycle, and one cycle of the electric discharge machining is completed when the time T1 has elapsed.

Step P9: It is judged whether or not the electric discharge machining is completed, and if the electric discharge machining is to be continued, the step P9 is carried out again.
Returning to 1, the above process is repeated. When the electric discharge machining is completed, the process is completed.

Next, setting of the values of the resistors and the capacitors in the second working example of the first embodiment of the electric discharge machining apparatus of the present invention will be described with reference to the flowchart shown in FIG. Note that FIG. 7 will be described using step Q.

Step Q1: R33 is set according to the actually used machining current. Similar to the step T1, the peak value of the machining current is determined according to the machining speed and surface roughness of the electric discharge machining, and R33 is set to be the peak value.

Step Q2: 1 of the switching element 32
A pulse interval T1 in units of on and off is set in advance as the time of one cycle of electrical discharge machining,
This pulse interval T1 is read.

Step Q3: The discharge time T2 and the minimum discharge pause time T3 are set in advance. The discharge time T2 is set according to the machining speed of the electric discharge machining and the accuracy of the processing surface, and the discharge pause time T3 set by the machining conditions is set as the minimum discharge pause time T3.

Step Q4: Next, the discharge delay time T4 is calculated. The discharge delay time T4 is the pulse interval time T1.
It is obtained by subtracting the discharge time T2 and the discharge rest time T3 from.

Step Q5: The time constant Ta corresponding to the discharge delay time T4 is set, and the capacitance C and the resistance value R41 are set. The time constant Ta is the resistance value R33 of the current limiting resistor 33,
Resistance value R41 of charging resistor and capacitance C of capacitor 43
And Ta = (R33 + R41) · C, the capacitance can be set from the capacitance C and the resistances R33 and R41.

Step Q6: The time constant Tb is set within the discharge pause time T3, and the charge accumulated in the capacitor 43 at the end of the discharge pause time influences the waveform of the next voltage application between the electrodes. So that the electric charge of the capacitor 43 is discharged within the discharge rest time. Then, the time constant Tb is calculated by the following equation in the circuit shown in FIG.
Since it is represented by R44 · C, the resistance value R44 is determined from the set time constant Tb and the capacitance C set in step Q5.

(Structure of Second Embodiment) FIG. 10 is a schematic block diagram of a power supply circuit according to a second embodiment which is an embodiment of the present invention.

The power supply circuit of the second embodiment has a structure in which the charging resistor 41 is not provided in the charging circuit 4A of the inter-electrode voltage control circuit 4 of the first embodiment, and other structures are the same as those of the first embodiment. Since it is the same as, the detailed description will be omitted.

The capacitor 43 according to the second embodiment is charged with a time constant determined by the resistance value R33 of the current limiting resistor 33 and the capacitance C of the capacitor 43, and when the switching element 32 is turned on. The inter-voltage V1 becomes the voltage Vc applied to the capacitor 43.

The operation of the second embodiment is the same as the operation of the first embodiment, and the description thereof is omitted here.

(Effects of Embodiments) According to the embodiments of the present invention, the voltage between contacts which gradually rises is controlled by a simple circuit configuration of the charging / discharging circuit without controlling the rising characteristics of the switching elements. You can Further, during the discharge period, the peak value of the discharge current and the discharge time can be determined only by controlling the machining power supply circuit by disconnecting the inter-electrode voltage control circuit with a diode.

[0061]

As described above, according to the present invention,
In the electric discharge machine, a stable electric discharge delay time can be obtained.

[Brief description of drawings]

FIG. 1 is a schematic block diagram of a power supply circuit according to a first embodiment which is an embodiment of the present invention.

FIG. 2 is a time chart of the first operation example of the embodiment of the present invention.

FIG. 3 is a flowchart of a first operation example of an embodiment of the present invention.

FIG. 4 is a flowchart for setting a circuit constant of a first operation example of the embodiment of the present invention.

FIG. 5 is a time chart of a second operation example of the embodiment of the present invention.

FIG. 6 is a flowchart of a second operation example of the embodiment of the present invention.

FIG. 7 is a flow chart for setting a circuit constant of a second operation example of the embodiment of the present invention.

FIG. 8 is a block diagram of a machining power supply circuit of a conventional electric discharge machine.

FIG. 9 is a diagram showing a voltage state of a machining power supply circuit of a conventional electric discharge machining apparatus.

FIG. 10 is a schematic block diagram of a power supply circuit according to a second embodiment which is an embodiment of the present invention.

[Explanation of symbols]

 1 Machining Electrode 2 Workpiece 3 Machining Power Supply Circuit 4 Inter-electrode Voltage Control Circuit 31 DC Power Supply 32, 45 Switching Element 33 Current Limiting Resistance 41 Charging Resistance 42 Diode 43 Capacitor 44 Discharging Resistance 4A Charging Circuit 4B Discharging Circuit

Claims (3)

[Claims] 1. An electric discharge machining apparatus for applying a pulsed voltage to a pole between a machining electrode and a workpiece to generate intermittent electric discharge between the poles for machining. A voltage control circuit in which capacitors are connected in parallel, the voltage control circuit applying a voltage based on a charging voltage of the pulsed voltage to the capacitors between the electrodes, and gradually increasing the voltage between the electrodes; Characteristic electric discharge machine. 2. A switching element and a resistor in an electric discharge machining apparatus for applying a pulsed voltage to a pole between a machining electrode and a workpiece to generate intermittent electric discharge between the poles for machining. And a voltage control circuit in which a capacitor is connected in parallel between the poles via a diode, and a voltage based on a charging voltage of the pulsed voltage to the capacitor is applied between the poles. An electric discharge machining apparatus, characterized in that a voltage between electrodes is gently increased and the capacitor is discharged by a series circuit of the switching element and a resistor. 3. The electric discharge machining apparatus according to claim 2, wherein the switching element is turned on after the start of the discharge rest period and is turned off before the end of the discharge rest period.