JP3574503B2 - Electric discharge machining method and apparatus - Google Patents

Description

[0001]
[Industrial applications]
The present invention relates to an electric discharge machining method and an electric discharge machine, and more particularly, to electric discharge machining in which an intermittent electric discharge is generated between an electrode formed between a machining electrode and a workpiece to remove the workpiece. The present invention relates to a method and an apparatus therefor. More particularly, the present invention relates to an electric discharge machining method and an apparatus for preventing electrolytic corrosion when using a water-soluble machining fluid.
[0002]
[Prior art]
In electric discharge machining, electrolytic action is known as a cause of reducing machining accuracy. Generally, in electric discharge machining, a minute gap is provided between a machining electrode and a workpiece to be opposed to each other, and a machining fluid is interposed in the gap. In some cases, a water-soluble processing liquid having an electrolytic property such as water is used as the processing liquid.
[0003]
In such electric discharge machining, there is a problem that when a voltage is applied between the electrodes, the machining surface is deteriorated by an electrolytic action. While the discharge inducing voltage is applied to the machining gap, the higher the discharge inducing voltage, the larger the electrolytic current. This electrolytic current ionizes and elutes the workpiece, deteriorating the quality of the machined surface. The elution amount is, for example, from several μm to several tens of μm, which is a serious problem in processing requiring high accuracy of several μm. In addition, when the workpiece is an alloy, the elution rate differs for each alloy component, which causes a problem such as a loss of a specific metal. For example, when the workpiece is an iron-based material, the conductivity of the working fluid becomes partially non-uniform, thereby lowering the processing accuracy and easily generating rust. Further, in the case of a superhard containing cobalt as a binder, there is a problem that cobalt is ionized and eluted to cause material defects.
[0004]
As a technique for preventing such a deterioration of a processed surface of a workpiece due to an electrolytic action, the following methods are conventionally known.
(1) In the first method, a voltage having a polarity opposite to that of the discharge inducing voltage is applied between the poles during a rest period after the end of the discharge, and the voltage between the poles is reduced so that the average voltage between the poles becomes zero. This is a method of eliminating bias.
(2) A second method is to apply a discharge inducing voltage having a polarity opposite to that of the main discharge power supply to reduce the bias of the interelectrode voltage as disclosed in, for example, JP-A-60-146624. It is.
(3) The third method is a method of inducing a discharge by applying a high-frequency AC voltage as shown in, for example, Japanese Patent Application Laid-Open No. 56-82127.
[0005]
[Problems to be solved by the invention]
The conventional methods for preventing the surface deterioration of a workpiece have the following problems.
(1) In the first method in which a voltage having a polarity opposite to that of the discharge induction voltage is applied during the idle period, the idle period is substantially extended, the cycle of electric discharge contributing to machining becomes longer, and the machining speed decreases. There is a problem that.
(2) In the second method in which a discharge inducing voltage having a polarity opposite to that of the main discharge power supply is applied, the machining speed does not decrease, but it is difficult to reduce the average voltage between the electrodes to 0 V, and the There is a problem that the bias of the voltage remains and the electrolytic action cannot be sufficiently suppressed. This is because the gap is in a discharge state during the main discharge current application period and is maintained at about the arc voltage, and this voltage is generally lower than the discharge inducing voltage. In addition, the duration of application of the main discharge current is usually shorter than the duration of application of the discharge inducing voltage, and as a result, the average voltage between the electrodes is considerably biased on the polarity side of the discharge inducing voltage.
[0006]
(3) The third method of applying a high-frequency AC voltage requires a high-frequency oscillator, which complicates the circuit and increases the cost. In addition, in order to apply a stable voltage between the poles, it is necessary to connect a resonant circuit that tunes to the frequency of the discharge-inducing power supply between the poles. There is a problem that the applied voltage changes.
[0007]
In order to solve such a conventional problem, there is a method in which the polarity of the discharge inducing voltage is alternately switched at every discharge or at a period such that the forward and reverse voltages have the same ratio (see, for example, Japanese Patent Application No. Hei. 107455). In this method, the ratio of the positive polarity discharge inducing voltage to the reverse polarity discharge inducing voltage is made equal to set the average voltage to 0V.
However, even in this method, the gap voltage (arc voltage) while the main discharge current is flowing is not taken into consideration, and the gap voltage is actually biased.
[0008]
Furthermore, when the discharge inducing voltage is applied in the opposite polarity, the current of the opposite polarity flows for a short time of several hundred ns from the start of the discharge to the flow of the main machining current. There is also a problem that the consumption of the electrodes increases when the temperature rises.
[0009]
In addition, when the voltage application is started, the voltage of a constant polarity is continuously applied until the discharge is induced. Therefore, there is a problem that the electrolytic corrosion occurs locally, particularly when the discharge interval such as the cut portion becomes long.
[0010]
SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-described conventional problems and to provide an electric discharge machining method and an electric discharge machining method capable of reliably preventing the surface of a workpiece from deteriorating due to an electrolytic action. In addition, according to the degree of electrolytic corrosion of the workpiece, processing to completely prevent the deterioration of the processing surface and processing to suppress electrode wear are performed, and optimal processing according to the material of the workpiece is performed. It is an object of the present invention to provide an electric discharge machining method and an electric discharge machining method in which a machined surface is not deteriorated even if the interval is widened.
[0011]
[Means for Solving the Problems]
Further, according to the present invention, a discharge inducing voltage is applied between the electrodes formed between the machining electrode and the workpiece, and the discharge inducing voltage causes the insulation between the electrodes to be broken and the discharge to be induced. In the electric discharge machining method, the application of the voltage for inducing discharge is stopped, the current pulse for machining is applied to the gap at the same time to remove the workpiece, and the machining is repeated after a predetermined pause time. The average voltage ofThe reference voltage is made variable and set to a desired value, an average voltage between the electrodes is detected, and the average voltage matches the set reference voltage.The above object is achieved by switching the polarity of the discharge inducing voltage with respect to the gap..
[0012]
Also, after the application of the discharge inducing voltage is started, the discharge is induced within a predetermined time.NotIn this case, the application of the discharge inducing voltage can be stopped, and after a short rest time different from the rest time in the normal machining, the next application of the discharge inducing voltage can be started.
[0013]
In the electric discharge machining of the present invention, the electric discharge inducing voltage is applied between the electrodes between the machining electrode and the workpiece, and is a voltage that induces electric discharge by breaking insulation between the electrodes. The polarity of the discharge inducing voltage between the poles can be, for example, a positive polarity when the processing electrode is negative, and a reverse polarity when the polarity is negative with respect to the workpiece.
An electric discharge machining apparatus according to the present invention is an electric discharge machining apparatus that generates an electric discharge intermittently between a pole formed between a machining electrode and a workpiece and removes the workpiece by flowing a machining current. A discharge inducing circuit for applying a positive and negative voltage for inducing a discharge between the electrodes, a main discharge circuit for supplying a machining current pulse between the electrodes after the start of discharge, Detecting means for detecting an average value;Variable reference voltage set to desired value by setting meansCompare hand to compareDan,The above object is achieved by providing a control means for outputting a signal for switching the output polarity of the discharge inducing circuit according to the output of the comparing means.
In the electric discharge machine of the present invention, SystemThe control means includes a first time counting means that operates only during the application of a voltage to the gap, a second time counting means that defines a machining pause time during normal machining, and a second timing means that defines a pause time different from the machining pause time. And 3 timing means,PreviousThe operation command to the discharge inducing circuit is stopped by the output of the first time measuring means, the third time measuring means is operated, and the application of the next discharge inducing voltage is started by the output of the third time measuring means.
[0014]
[Action]
According to the above-described electric discharge machining of the present invention, first, a discharge inducing voltage is applied in a certain polarity direction from a discharge inducing circuit to a gap formed between a machining electrode and a workpiece. Between the electrodes to which the discharge inducing voltage is applied, after a lapse of a certain period of time, the discharge inducing voltage causes dielectric breakdown to start discharging. From the start of the discharge, a main discharge current is supplied from the main discharge power supply to the gap, and the discharge is continued for a predetermined time. The voltage between the electrodes at the time of discharge has a value sufficiently smaller than the voltage for inducing discharge. The electric discharge machining of the workpiece is performed by this electric discharge. After a lapse of a predetermined time, the discharge between the poles is stopped by cutting off the supply of the main discharge current. After the discharge is stopped, the insulating state between the electrodes is restored by taking a rest time, and one discharge is completed.
Further, the polarity of the discharge inducing voltage applied between the poles from the discharge inducing circuit can be set to the opposite polarity to induce the discharge between the poles. The discharge inducing voltage of the opposite polarity has the same effect as that of the discharge inversion, except that the polarity is reversed. To start. Then, the subsequent electric discharge machining is performed similarly. Therefore, only the polarity of the discharge inducing voltage before the discharge with respect to the gap is different, and the operation at the time of discharge is the same.
[0015]
In the electric discharge machining of the present invention, the switching of the polarity of the discharge inducing voltage with respect to the gap is performed by detecting the voltage between the gaps and based on the gap voltage, and is performed between the machining electrode and the workpiece. By integrating the voltage between the electrodes, the average voltage between the electrodes related to the value of the voltage between the electrodes and the application time is obtained.Desired reference voltageIt can be performed so that
The time from the application of the discharge inducing voltage to the start of the discharge depends on the state of the gap, and there is a difference in the application time of the discharge inducing voltage when comparing individual discharges. By integrating the voltage between the electrodes and the workpiece to obtain a value related to the voltage between the electrodes and the application time, the average voltage between the electrodes is calculated asReference voltage set to any desired valueAnd the deterioration of the workpiece surface caused by the electrolytic action caused by the application of the discharge inducing voltage can be prevented..
[0016]
If the discharge is not induced within a predetermined time after the application of the discharge induction voltage, the application of the voltage is stopped, and after a pause shorter than the pause during normal machining, the next voltage application is started.
[0017]
The switching of the polarity of the discharge inducing voltage of the present invention is performed by driving the switching circuit by a control circuit that outputs a control signal based on the occurrence of discharge. By controlling the opening and closing of switch means provided between the electrodes, the connection state of the discharge inducing power supply is changed or a discharge inducing power supply having a different polarity is selected. By controlling the discharge inducing power supply, the polarity of application of the voltage for inducing a discharge between the electrodes is switched, and the average voltage of the voltage for inducing a discharge between the electrodes is changed.Reference voltage set to any desired valueThe effect of the electrolytic action generated by the application of the discharge inducing voltage is substantially stopped, and the surface of the workpiece is prevented from deteriorating.
[0018]
【Example】
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
The electric discharge machine for performing the electric discharge machining of the present invention is almost the same as a normal electric discharge machine, and has a method for applying a voltage between the machining electrode and a pole between the workpiece and the apparatus. ing. Therefore, in the following embodiments of the present invention, a configuration in which a voltage is applied between the poles will be mainly described, and a description of a known electric discharge machine will be omitted.
[0019]
[Example 1 of the present invention]
First, the configuration and operation of the first embodiment of the present invention will be described with reference to FIGS.
(Configuration of Embodiment 1 of the Present Invention)
FIG. 1 is a configuration diagram of a power supply unit of an electric discharge machine for explaining electric discharge machining according to a first embodiment of the present invention. In FIG. 1, reference numeral 1 denotes a machining electrode, and 2 denotes a workpiece. The processing electrode 1 is provided with a gap between the workpiece 2 and the gap. Has formed. An electric discharge machining is performed on the workpiece 2 by generating an intermittent discharge via a machining fluid between the grounded workpiece 2 and the electrode formed between the machining electrode 1. .
The power supply unit of the electric discharge machine according to the present invention includes two power supply units, a main discharge circuit 3 and a discharge induction circuit 4. The discharge inducing circuit 4 is a circuit for inducing a discharge between the electrodes, and the main discharge circuit 3 is a circuit for supplying a main discharge current for performing electric discharge machining. After that, the main discharge current for machining is superimposed on the current for inducing discharge. The driving of the main discharge circuit 3 and the discharge inducing circuit 4 is performed based on a control signal from the control circuit 5.
[0020]
The main discharge circuit 3 has a main discharge power supply 31 for supplying a main discharge current between the poles, and forms a closed circuit of the main discharge current via a switch element 32 and a switch element 33 connected in series. In the main discharge circuit, for example, a diode 34 is connected in a direction from one electrode terminal of the main discharge power supply 31 to a ground terminal of the workpiece 2, and a direction from the processing electrode 1 to the other electrode terminal of the main discharge power supply 31. And a diode 35 is connected to the power supply to form a cross-type power supply. The opening and closing of the switch elements 32 and 33 are performed by a control signal s3 from the control circuit 5.
The discharge inducing circuit 4 has a discharge inducing power supply 41 for applying a discharge inducing voltage between the poles, and forms a closed circuit for applying the discharge inducing voltage via a diode 42 and a current limiting resistor 43 connected in series. are doing. In the discharge inducing circuit 4, a circuit configuration for switching the polarity of application of the discharge inducing voltage to the machining electrode 1 includes switch elements (44 to 47). In the first embodiment, the switching circuit including the switch elements 44 to 47 connects the switch element 44 between one electrode of the discharge induction power supply 41 and the machining electrode 1, and connects the switch element 45 to the other of the discharge induction power supply 41. The switch element 46 is connected between one electrode of the discharge inducing power supply 41 and the ground side of the workpiece 2, and the switch element 47 is connected between the electrode and the ground side of the workpiece 2. It is configured by connecting between the other electrode 41 and the processing electrode 1.
[0021]
Then, the same control signal is input to the switch elements 44 and 45 to perform opening and closing control at the same time, and a control signal different from the switch elements 44 and 45 is input to the switch elements 46 and 47. Open / close control at the same time.
[0022]
In the embodiment of the present invention, the polarity of the main discharge power supply is positive. However, the polarity is not limited to this, and may be reversed depending on the processing.
[0023]
The control circuit 5 detects a discharge by inputting a gap voltage between the machining electrode 1 and the workpiece 2 and outputs a control signal s3 to the main discharge circuit 3 based on the discharge detection signal, The control signal s4 is output to the discharge inducing circuit 4.
Further, the switching circuit is a circuit that receives the gap voltage and the control signal s4 from the control circuit 5 and controls the opening and closing of the switch element of the discharge inducing circuit 4. In the first embodiment, the switching circuit detects the gap voltage. Dynamic amplifier 57, a reference voltage 58, an adder 59 that outputs the sum of the inter-electrode voltage from differential amplifier 57 and reference voltage 58, an integrator 56 that integrates the output of adder 59, and an integrator 56. 55, a latch circuit 54 that receives the output of the comparator 55 and the control signal s4 from the control circuit 5 as input signals, and the logic of the output of the latch circuit 54 and the control signal s4. An AND gate 51 that outputs the AND output to the switch elements 44 and 45 and a logical product of the inverted output of the latch circuit 54 and the control signal s4, and outputs the AND output to the switch element 46 and And an AND gate 52 which outputs to the switch element 47. Note that the inverted output of the latch circuit 54 can be obtained by inverting the output of the latch circuit 54 by the inverter 53.
In addition, the first time counting means 60 starts operation by the control signal s4 from the control circuit 5, and outputs a signal which becomes high after the time-up to the control circuit 5. The first time measuring means 60 is a time measuring means that operates only during the application of a voltage between the electrodes, and is used to stop the voltage application when the discharge is not induced within a predetermined time after the voltage application is started. is there. The second timing means 61 starts operation by the control signal s5, and outputs a signal which becomes high after the time-up to the control circuit 5. The second timing means 61 defines a machining pause time during normal machining. The third timer 62 starts operation by the control signal s 6, and outputs a signal that goes high after the time-up to the control circuit 5. The third clocking means 62 defines a pause time shorter than the processing pause time during normal processing defined by the second clocking means 61.
[0024]
In FIG. 1, the main discharge circuit 3 and the discharge inducing circuit 4 are indicated by broken lines.
[0025]
(Operation of Embodiment 1 of the Present Invention)
Next, the operation of the first embodiment of the present invention will be described with reference to the time charts of FIGS. 2 and 3 and the circuit diagrams of FIGS. In the following description, the description will be given according to the signs of time a to time w in the time charts of FIGS.
In the time chart shown in FIG. 2, during a period from time a to time k and from time p to time r, a discharge inducing voltage having a positive polarity (a voltage polarity of a negative polarity with respect to the workpiece with respect to the workpiece) is used. In this case, a voltage for inducing discharge having a reverse polarity (a voltage polarity of which the machining electrode is positive with respect to the workpiece) is applied during a period from time k to time p and from time r to time w. Shows the case.
The time charts in FIGS. 2 and 3 show the state of four discharges during continuous electric discharge machining. The gap voltage Vg is detected by the differential amplifier 57. The output of the differential amplifier 57 is input to the control circuit 5, added to a reference voltage 58 by an adder 59, and then input to an integrator 56 for integration.
[0026]
It is assumed that the output Vg (INT) of the integrator 56 is positive, the output of the comparator 55 is high, and the latch circuit 54 is also latched high by the electric discharge machining before time a. In the illustrated example, it is assumed that the reference voltage 58 is set to a positive voltage so that the average voltage between the electrodes maintains a positive value.
[0027]
Time a: The control circuit 5 sends out a high control signal s4. At this time, since the output Vg (INT.) Of the integrator 56 is in a plus state, the output of the comparator 55 is in a high state. In this time chart, since the output of the latch circuit 54 is higher than before this time, the output of the latch circuit 54 does not change and maintains the high output.
[0028]
The output of the latch circuit 54 is ANDed with the signal s4 by the AND gate 51, and inverted by the inverter 53 to be ANDed by the signal s4 and the AND gate 52. At this time, since the output of the latch circuit 54 is high, the output of the AND gate 51 is high. This output is input to the discharge inducing circuit 4, turns on the switch elements 44 and 45, and applies a positive discharge inducing voltage between the electrodes.(See Fig. 4).
[0029]
Further, the first time counting means 60 starts the time counting operation by the control signal s4, and monitors whether or not a discharge is induced within a predetermined time.
[0030]
Note that, in the time chart of FIG. 2, the polarity voltage Vg has a positive polarity at the fall and a reverse polarity at the rise.
[0031]
FIG. 3 shows a circuit connection state of the power supply unit of the electric discharge machine when the switch elements 44 and 45 are on, the switch elements 46 and 47 are off, and the switch elements 32 and 33 are off. Is connected to the workpiece 2 to apply a positive voltage to the workpiece 2, and the negative electrode of the discharge induction power source 41 is connected to the machining electrode 12 to apply a negative voltage to the machining electrode 1. are doing. By this voltage application, a discharge inducing voltage is applied between the poles.
When a positive discharge inducing voltage is applied to the processing electrode 1, the state in which the positive polarity voltage Vg is applied continues until insulation is broken between the electrodes and discharge starts. In the time chart of FIG. 2, a period from when the discharge inducing voltage is applied to the machining electrode 1 to when the discharge starts is represented by a period T1.
[0032]
Time b: When the insulation between the electrodes is broken and a discharge occurs, the voltage Vg between the electrodes decreases (in the time chart of FIG. 2, this is represented by an upward change). As a result, the output of the differential amplifier 57 decreases, and the control circuit 5 detects discharge based on this voltage drop.
[0033]
Time c: The control circuit 5 that has detected the discharge sets the control signal s3 to high to turn on the switch elements 32 and 33 of the main discharge circuit 3, and sets the signal s4 to low to turn off the switch elements 44 and 45. When the switch elements 32 and 33 are turned on, the main discharge power supply 31 is applied between the electrode 1 and the workpiece 2, and the main discharge current Ig flows in the direction of the arrow. At this time, a slight voltage Vg is applied between the electrodes, and the integrator 56 further continues the integration to output an integrated value Vg (INT.).
Although the integrated value Vg (INT.) Of the integrator 56 decreases during the interval T1, the value is still positive, so the output of the comparator 55 is high, and the output of the latch circuit 54 is maintained at high. . Although the output of the latch circuit 54 is maintained at a high level, the control signal s4 of the control circuit 5 is at a low level, so that the logical product output of the AND gates 51 and 52 is at a low level and the switch elements 44, 45, 46, 47 is turned off.
[0034]
Therefore, the switching elements 44, 45, 46, and 47 are all turned off, and the application of the discharge inducing voltage to the gap is stopped. Figure5Shows the circuit connection state of the power supply unit of the electric discharge machine when the switch elements 44, 45, 46, 47 are off and the switch elements 32, 33 are on. Not connected to the workpiece 2, the positive electrode of the main discharge power supply 31 is connected to the workpiece 2, the negative electrode of the main discharge power supply 31 is connected to the machining electrode 1, and the main The discharge voltage is applied, and the main discharge current Ig flows.
Also, the first time counting means 60 was in the timing operation by the rise of the control signal s4, but before the predetermined time was counted, the control signal s4 fell and became low. The output remains low.
[0035]
Since there is a delay time from the detection of the decrease in the voltage Vg between the electrodes to the turning on of the switching elements 32 and 33, there is a time delay of t1 from the start of the discharge to the turning on of the switching elements 32 and 33. This time delay is typically several hundred ns.
In order to maintain the discharge during this delay time, the switching elements 44 and 45 are kept on until the switching elements 32 and 33 are turned on.
In order to ensure that the discharge leads to the main discharge current, it is also possible to control so that the ON of the switch elements 44 and 45 and the ON of the switch elements 32 and 33 overlap.
[0036]
Time d: The control circuit 5 sets the control signal s3 to low after a predetermined time t2, turns off the switch elements 32 and 33 of the main discharge circuit 3 and sets the signal s5 to high. Of the processing stop time t3 is started.
[0037]
When the switch elements 32 and 33 are turned off, the application of voltage to the machining electrode 1 and the workpiece 2 of the main discharge power supply 31 is stopped, but the electromagnetic energy accumulated in the inductance component of the main discharge circuit passes through the diodes 34 and 35. Therefore, the main discharge current Ig continues to flow even after the switch elements 32 and 33 are turned off.
Time e: When the main discharge current Ig stops, the inter-electrode voltage Vg becomes 0 V, and only the reference voltage 58 is integrated by the integrator 56.
[0038]
In this case, the output Vg (INT.) Of the integrator 56 remains positive because the sum of the time from the application of the voltage until the discharge and the discharge time between the time a and the time e is short. As long as Vg (INT.) Is positive, a positive polarity discharge inducing voltage is applied.
Time f: When the second clocking means 61 times the machining pause time t3 during normal machining, it outputs a time-out signal to the control circuit 5, and the control circuit 5 sets the control signal s4 to high in accordance with the time-out signal. During this pause time, the discharge inducing voltage and the main discharge voltage are not applied between the electrodes, and during this time, the insulation between the electrodes is restored.
By the process from the time point a to the time point f, the electric discharge machining in the case of applying the discharge inducing voltage of the positive polarity (the voltage polarity of the negative polarity of the machining electrode with respect to the workpiece) between the electrodes is performed. Complete.
[0039]
Time f to time k: At time f, a high control signal s4 is transmitted. At this time, since the output of the comparator 55 is high as in the case of the time a, a positive discharge inducing voltage is applied between the electrodes. Thereafter, substantially the same operation as the above-described time a to time f is performed, and the electric discharge machining when a positive discharge inducing voltage is applied between the electrodes at the time k is completed.
At this time, when the inter-electrode voltage Vg is integrated by the integrator 56, the integrated value passes from positive to zero and becomes negative from time f to time g or from time f to time j. In the time chart of FIG. 2, the integral value is inverted from positive to negative between time f and time g. This change in the polarity of Vg (INT.) Is detected by the comparator 55 whose reference value is set to 0 V, and the output of the comparator 55 is set to low.
Time k: When the control signal s4 goes high, the voltage of the comparator 55 is latched by the latch circuit 54 at the rise of the control signal s4, and the output of the latch circuit 54 goes low. The output of the latch circuit 54 turns off the switch elements 44 and 45 by setting the logical product of the AND gate 51 to low, and the output of the latch circuit 54 is inverted by the inverter 53 to be high, and the logical product output of the AND gate 52 is high. It becomes. This high output turns on the switch elements 46 and 47 of the discharge inducing circuit 4 to apply a voltage for inducing a reverse polarity between the electrodes.
[0040]
Figure6Indicates the circuit connection state of the power supply unit of the electric discharge machine when the switch elements 44 and 45 are off, the switch elements 46 and 47 are on, and the switch elements 32 and 33 are off. Is connected to the workpiece 2, the positive electrode of the discharge inducing power supply 41 is connected to the machining electrode 1, and the discharge inducing voltage of the polarity opposite to that shown in the time a and FIG. Is applied.
When a voltage for inducing a discharge of a reverse polarity is applied to the processing electrode 1, the state where the voltage Vg of the reverse polarity is applied continues until insulation is broken between the electrodes and discharge starts. . In the time chart of FIG. 2, a period from when the discharge inducing voltage is applied to the machining electrode 1 to when the discharge starts is represented by a period T2.
From this time k, since the polarity applied between the poles is reversed, the direction of integration in the integrator 56 increases in the positive direction in the integral value Vg (INT.), Contrary to the above-described discharge process. I do.
[0041]
Time 1: When the insulation between the electrodes is broken and discharge occurs, the absolute value of the voltage Vg between the electrodes decreases (in the time chart of FIG. 2, this is represented by a falling change). The current Ig flows by the discharge between the poles. The direction of the current Ig is opposite to the direction at times b and g. The control circuit 5 detects the discharge by the change of the voltage Vg between the electrodes via the output of the differential amplifier 57.
Time m: The control circuit 5 that has detected the discharge sets the control signal s3 to high, turns on the switching elements 32 and 33 of the main discharge circuit, and applies the main discharge power supply 31 between the electrodes 1 and the workpiece 2. The main discharge current Ig flows. The direction of the main discharge current Ig is the same direction as the arrow shown in FIG. On the other hand, since the control signal s4 is low, the AND output of the AND gate 52 is low, and the switch elements 46 and 47 are turned off.
Further, the output of the AND gate 51 remains low, and the switch elements 44 and 45 maintain the off state.
[0042]
Therefore, the switching elements 44, 45, 46, and 47 are all turned off, and the application of the discharge inducing voltage to the gap is stopped. This circuit state is shown in the figure5The main discharge voltage Ig is applied between the poles, and the main discharge current Ig flows.
Since there is a delay time from when the absolute value of the voltage Vg decreases to when the switch elements 32 and 33 are turned on, the time t1 is between the time when the discharge is started and the time when the switch elements 32 and 33 are turned on. There is a delay.
Then, in order to maintain the discharge during this delay time, the switch elements 46 and 47 are kept on until the switch elements 32 and 33 are turned on.
In order to ensure that the discharge is connected to the main discharge current, it is also possible to control so that the ON of the switch elements 46 and 47 and the ON of the switch elements 32 and 33 overlap.
[0043]
Times n and o: After a predetermined time t2, the control circuit 5 sets the control signal s3 to low, turns off the switch elements 32 and 33 of the main discharge circuit 3, and suspends machining during normal machining by the second timing means 61. The timing of time t3 is started.
[0044]
When the switch elements 32 and 33 are turned off, the application of voltage to the machining electrode 1 and the workpiece 2 of the main discharge power supply 31 is stopped, but the electromagnetic energy accumulated in the inductance component of the main discharge circuit passes through the diodes 34 and 35. Therefore, the main discharge current Ig continues to flow even after the switch elements 32 and 33 are turned off.
Time p: When the second timing means 61 counts the machining pause time t3 during normal machining, it outputs a timing end signal to the control circuit 5, and the control circuit 5 sets the control signal s4 to high according to the timing end signal.
[0045]
Since the output Vg (INT.) Of the integrator 56 is in a positive state, a positive voltage is applied between the electrodes. At the same time, the first timing means 60 starts operating.
[0046]
During the rest time from the time o to the time p, the discharge inducing voltage is not applied with the main discharge voltage between the electrodes, and during this time, the insulation state between the electrodes is restored.
In the process from time k to time p described above, the discharge when the discharge inducing voltage of the opposite polarity (the voltage polarity of the polarity that the working electrode is positive with respect to the workpiece) is applied between the electrodes. Processing is completed.
[0047]
Time q: When the time counting by the first time counting means 60 is completed before the discharge starts between the gaps, the first time counting means 60 outputs a time counting signal to the control circuit 5. The control circuit 5 changes the control signal s4 to low in response to the timing signal, and stops applying the voltage to the gap.
[0048]
At the same time, the control signal s6 is set to high, and the third timer 62 starts timing. The third time measuring means 62 is set to a shorter time than the second time measuring means 61 for defining the downtime during normal processing.
[0049]
In this case, since the insulation between the poles is maintained, the main discharge current does not flow, and the idle time starts.
[0050]
Time r: When the third timer 62 finishes counting the pause time, the control circuit 5 sets the control signal s4 to high in response to the end of the counting, and restarts the voltage application to the gap.
From time p to time q, the sign of the output Vg (INT.) Of the integrator 56 changes from positive to negative, and as a result, a discharge induced voltage of the opposite polarity is applied between the poles. .
[0051]
Time r to time w: Same as the operation from time k to time p, and the description is omitted here.
[0052]
At this time, when the inter-electrode voltage Vg is integrated by the integrator 56, the integrated value passes from negative to zero and becomes positive from time k to time 1 or from time k to time m. In the time chart of FIG. 2, the integral value is inverted from negative to positive between time k and time l. This change in the polarity of Vg (INT.) Is detected by the comparator 55 whose reference value is 0 V, and the output of the comparator 55 is set to high.
Then, the discharge process by the positive polarity discharge inducing voltage from time a to time f (time f to time k) and the discharge process by the reverse polarity discharge inducing voltage from time k to time p are repeated. Thus, the electric discharge machining of the workpiece is performed. Here, a section of the discharge process using the positive polarity discharge inducing voltage from time a to time e and a time f to time j, and a section of the discharge process using the opposite polarity discharge inducing voltage from time k to time m. Compare with In these two sections, an integral value corresponding to a value obtained by multiplying the voltage of the sum of the applied voltage and the reference voltage by the applied time is controlled by the integrator 56 to be “0” when the average is taken. The polarity of the voltage applied to is changed.
Therefore, the average voltage between the poles is controlled so that the polarity is opposite to the reference voltage 58 and the absolute value is equal, so that optimum machining can be realized depending on the material of the workpiece.
[0053]
In this embodiment, when the output of the latch circuit 54 is inverted, a pulse signal may appear at the output of the AND gate. The AND gate 51 takes the logical product of the output of the latch circuit 54 and the control signal s4, and the AND gate 52 takes the logical product of the signal obtained by inverting the output of the latch circuit 54 by the inverter 53 and the control signal s4. The latch circuit 54 is configured to latch at the rising edge of the control signal s4, which causes an operation delay of the latch circuit 54. For example, at time k in the time chart of FIG. 2, a pulse is generated at the output of the AND gate 51.
In FIG. 1, a delay circuit is inserted between the control circuit 5 and the input terminals of the AND gates 51 and 52, and the control signal s4 is delayed by this delay circuit until the output of the latch circuit 54 is determined. Generation of this pulse signal can be prevented.
[0054]
[Example 2 of the present invention]
Next, the configuration and operation of the second embodiment of the present invention will be described with reference to FIG. (Configuration of Embodiment 2 of the Present Invention)
FIG. 7 is a configuration diagram of a power supply unit of an electric discharge machine for explaining electric discharge machining according to a second embodiment of the present invention. The configuration of the second embodiment of the present invention shown in FIG. 7 is almost the same as the configuration of the first embodiment of the present invention, and includes a machining electrode 1, a workpiece 2, a main discharge circuit 3, a discharge induction circuit 8, and a control circuit. Circuit 5 is included. The difference between the second embodiment and the first embodiment in the configuration of the discharge inducing circuit 8. Therefore, hereinafter, only the configuration of the discharge inducing circuit 8 will be described, and description of the other processing electrodes 1, the workpiece 2, the main discharge circuit 3, and the control circuit 5 will be omitted.
The discharge inducing circuit 8 according to the second embodiment of the present invention uses two power supplies, a power supply for a positive polarity voltage and a power supply for a reverse polarity voltage. The polarity of the voltage is switched. In FIG. 6, a series circuit of a discharge induction power supply 81 for positive polarity voltage, a diode 82 and a switch element 83 and a series circuit of a discharge induction power supply 84 for reverse polarity voltage, a diode 85 and a switch element 86 are connected in parallel. Are connected to the processing electrode 1 and the workpiece 2 via the current limiting resistor 87. The polarities of the discharge inducing power supply 81 and the discharge inducing power supply 84 with respect to the machining electrode 1 or the workpiece 2 are opposite to each other.
The connection between the electrodes of each discharge inducing power supply is performed by a switch element provided in each of the electrodes, and the switch elements are switched by signals from AND gates 51 and 52.
[0055]
(Operation of Embodiment 2 of the Present Invention)
Next, the operation of the second embodiment of the present invention will be described. The operation of the second embodiment of the present invention is substantially the same as the operation of the first embodiment, and differs only in the switching of the power supply of the discharge inducing circuit 8. Therefore, only the switching of the power supply of the discharge inducing circuit 8 will be described below.
The power supply for the positive polarity voltage and the power supply for the reverse polarity voltage of the discharge inducing circuit 8 are connected to the gap by opening and closing the switch element 83 and the switch element 86. The switch element 83 and the switch element 86 are connected to the AND gate 51. , 52, and only one of them is connected as shown in the first embodiment.
According to the configuration of the second embodiment, although two DC power supplies are required, the number of switch elements can be reduced, and there is no need to consider a shift in operation timing of the switch elements. is there.
[0056]
【The invention's effect】
As described above, according to the present invention, the average voltage between the electrodes is made closer to the reference voltage, and the deterioration of the surface of the workpiece caused by the electrolytic action and the consumption of the electrodes are coordinated, and the material is adjusted to the material of the workpiece. It is possible to provide an electric discharge machining method and an apparatus therefor that can perform optimal machining.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a power supply unit of an electric discharge machine according to a first embodiment of the electric discharge machining of the present invention.
FIG. 2 is a time chart of Example 1 of the electric discharge machining according to the present invention.
FIG. 3 is a time chart of Example 1 of the electric discharge machining according to the present invention.
FIG. 4 is a circuit connection state diagram of a power supply unit according to the first embodiment of the present invention.
FIG. 5 is a circuit connection state diagram of a power supply unit according to the first embodiment of the present invention.
FIG. 6 is a circuit connection state diagram of the power supply unit according to the first embodiment of the present invention.
FIG. 7 is a configuration diagram of a power supply unit of an electric discharge machine for explaining electric discharge machining according to a second embodiment of the present invention.
[Explanation of symbols]
1 Processing electrode
2 Workpiece
3 Main discharge circuit
4,8 Discharge induction circuit
5 Control circuit
31 Main discharge power supply
32, 33, 44 to 47, 83, 86 switch element
34, 35, 42, 82, 85 Diode
41, 81, 84 Discharge induced power supply
43,87 Current limiting resistor
51,52 AND gate
53 inverter
54 Latch Circuit
55 comparator
56 integrator
57 Differential Amplifier
58 Reference voltage
59 Adder
60 First timekeeping means
61 Second timing means
62 Third timing means

Claims (4)

A discharge-inducing voltage is applied between the electrodes formed between the machining electrode and the workpiece, and the discharge-inducing voltage is detected by detecting that the insulation between the electrodes has been broken and the discharge has been induced by the discharge-inducing voltage. In the electric discharge machining method in which the application of the application voltage is stopped, the machining current pulse is simultaneously passed between the poles to remove the workpiece, and the machining is repeated after a predetermined pause time.
The reference voltage variable and is set to a desired value, by detecting the average voltage of the machining gap, characterized in that switching the polarity for between poles of the electric discharge inducing voltage to said average voltage matches the set reference voltage Electrical discharge machining method. After the application of the discharge inducing voltage is started, if the discharge is not induced within a predetermined time, the application of the discharge inducing voltage is stopped, and after a short rest time different from the rest time during normal machining, the next time. discharge machining method according to claim 1 Symbol mounting, characterized in that to start the application of the electric discharge inducing voltage. In an electric discharge machining apparatus that performs intermittent discharge between the poles formed between the machining electrode and the workpiece and removes the workpiece by passing a machining current,
A discharge inducing circuit for applying a positive and negative voltage for inducing a discharge between the poles,
After the start of discharge, a main discharge circuit that supplies a current pulse for machining between the poles,
Detecting means for detecting an average value of the voltage between contacts;
Comparing means for comparing the detected value with a variable reference voltage set to a desired value by setting means ;
Control means for outputting a signal for switching the output polarity of the discharge inducing circuit according to the output of the comparing means. The control means,
First time counting means that operates only during voltage application between the electrodes,
A second timing means for defining a machining pause during normal machining,
Third timing means for defining a pause time different from the machining pause time;
Stopping the operation command to the discharge inducing circuit by the output of the first time measuring means, activating the third time measuring means, and starting the application of the next discharge inducing voltage by the output of the third time measuring means. The electrical discharge machining device according to claim 3, wherein:

Images