JPS59330B2 - Houden Kakoseigiyohouhou Oyobi Sonosouchi - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides electrical discharge machining in which machining is performed by applying a pulse voltage to generate electric discharge between a workpiece and an electrode facing each other, and the pulse width of the pulse is extremely narrow. The present invention relates to a method and apparatus for controlling a machining gap so that machining in a region is stably performed.

The pulse generation circuit (discharge circuit) applied between the poles is, for example, as shown in FIG.
A pulsed current controlled by Flows into the machining gap formed between the electrode 4 and the workpiece 5.

The switching frequency of the switching element 2 can be varied in accordance with signals from the control circuit 6.
On the other hand, the machining gap length is normally controlled to be constant by a servo mechanism including a hydraulic cylinder 7, a servo pulp 8 that controls the amount of oil in the hydraulic cylinder 7, and the like. The method is to use a control voltage e corresponding to the average voltage between poles (voltage between 4 and 5) E, and a reference voltage E. This is a method of comparing and controlling the difference so that it becomes zero. 9 and 10 are resistors for dividing the voltage between the electrodes, 11 is a smoothing capacitor provided to average the voltage between the electrodes, and 12 is a variable resistor for adjusting the servo sensitivity.

Now, the inter-electrode voltage waveform in the case shown in Fig. 1 is generally:
The result will be as shown in Figure 2.

That is, the pulse voltage application time τ, the time τd from when the pulse voltage is applied between the electrodes until the discharge starts, the time for discharging (τ, -τd), and the time required to recover the insulation between the electrodes. It is composed of the pause time τ, .

Of these, τ and τ are constant, but τd is usually not constant. However, by controlling the average voltage between the poles to be constant using the servo mechanism shown in FIG. 1, the average value of τd becomes constant. That is, when the relationship between the average voltage E between the electrodes and τd (171) is determined, E is E based on the specification values shown in FIG.

Assuming that control is performed to maintain a constant value, the average value τ of τd is expressed as follows. (3) In formula τ,, τ1,
The voltage VB of the DC power supply 1 shown in Fig. 1 is kept constant, and the discharge voltage VG also varies slightly depending on the combination of the electrode and the workpiece, but since it shows a constant value, teeth,
It can be seen that it remains constant.

Now, let's consider the size of τd.

The fact that there is a ring force breakdown means that the time from when a pulse voltage is applied between the electrodes until the discharge occurs is long, so it is difficult for discharge to occur, that is, the gap between the electrodes is wide7. A small value indicates that the gap between the poles is narrow. By the way, since the maximum value of τ is τp as seen from FIG. 2, the maximum value of the pole gap is determined by τ. In the machining region where p, that is, τ, is extremely small, P
)
) The gap between the poles becomes extremely narrow, causing frequent short-circuits between the poles and problems in removing machining powder, making it impossible to expect stable machining.

If you want to widen the gap between the poles so that stable machining can be achieved, it would be ideal if the pulse voltage application time τ was lengthened so that the delay time τd was increased so that the pulse waveform became as shown in Figure 3 Ap. In reality, τ varies considerably, resulting in a pulse waveform as shown in Figure 3b, so the machining characteristics,
In particular, it is inevitable that the roughness of the machined surface will worsen, which is extremely problematic.

In order to solve this problem, as shown in FIG. 4a, the discharge time τ is adjusted regardless of the value of τd. It is known that there is a control method that maintains a constant value. With this control method, the above-mentioned problems are improved and the discharge time τ is reduced to 4. Even in the case of machining where the distance is extremely small, the gap between the poles does not become too narrow, and moreover, the roughness of the machined surface is kept uniform. However, with this control method, as shown in Figure 4b, when the rest time changes, the discharge delay time τ also changes despite the same average interelectrode voltage, and as a result, the interelectrode gap cannot be kept constant. Therefore, it is inconvenient for the purpose of processing without changing the gap between the poles. The present invention solves the above-mentioned problems by controlling the gap to a desired value to perform safe machining, and also to prevent the roughness of the machined surface from worsening by keeping the discharge time below a certain value. This paper proposes a method for

Examples will be described in detail below. FIG. 5a shows a voltage pulse waveform applied between electrodes according to the present invention, and FIG. 5b shows a discharge current waveform.

Furthermore, FIG. 4c shows a control signal for controlling the pole gap length. This pulse is composed of a plurality of pulses, each having an equal time width, and starting from the time when the pulse voltage is applied between the poles, P,, P2, P3, P, respectively.
4, P5, P6, . . ., P8, which are distinguished by the minimum pause time Δτ. Now, P that appears between the poles,, P2, P3, P4, P5, P6...P
For example, the relationship between the number of N pulse voltages at which discharge occurs and the control signal V can be determined as follows. Note that the control signals during the pause time τ are the previously determined control signals Vl, V2, and V3.
If it is determined in this way, when discharge occurs at Pl and P2, the gap between the electrodes will be reduced because the discharge occurs with almost no delay after voltage application Since it can be determined that the length is narrow or the impedance between the poles is decreasing, control is performed to widen the gap between the poles.(Raising operation) Next, P
3. If a discharge occurs with any of the pulses up to P4, P, and P6, it is assumed that the discharge occurs with a delay time that corresponds to the appropriate pole gap, and this state must be maintained. Control. (Stationary operation) Next, if a discharge occurs with a pulse after P7, or if it does not occur at all, it can be determined that the gap between the poles is too wide, so the control is performed to narrow the gap between the poles.

(Lowering operation) Furthermore, regarding the pulses after P7, as shown in Figure 6 A, b, and c, by adding weight to the high voltage, even if the gap between the electrodes is wide to some extent, the high voltage will force the The discharge efficiency can be increased by discharging the battery. As described above, the gap between the poles is actively controlled so that the discharge occurs with one of the pulses P3, P4, P, and P6, and the width of the discharge current pulse is larger than the width of one pulse. Therefore, it is possible to prevent deterioration of machined surface roughness due to uneven current pulse widths, which is a drawback of the conventional method as shown in Fig. 3b above, and also to improve the method shown in Fig. 3. Like the methods in Figure 4 A and b,
The gap length between the poles does not change by changing the pause time. That is, Fig. 5 A, b, c
As shown in Figure 2, the state of the gap between the poles is detected based on the number of pulses after the voltage pulse is applied between the poles, and the state of the control signal (increase Since the control signal V is determined on the basis of the idea that the position ( , stationary, lowering) is maintained, the pole gap does not change depending on the rest time. Moreover, since the gap between the poles can be arbitrarily set to ensure safe machining, extremely stable machining is possible. Next, examples of the method of the present invention will be described.

FIG. 7 shows an apparatus for generating the voltage pulses shown in FIG. 5a. 13 is a time setting circuit that sets the pulse application time or rest time τ, and the minimum rest time Δτ, and when a pulse voltage is applied between the electrodes and no discharge occurs, the minimum rest time is set. When Δτ is set and discharge occurs, a predetermined pause time τ is set.

The discharge detection circuit 14 determines whether or not discharge has occurred.
detected by.

Discharge is detected by detecting changes in inter-electrode voltage and inter-electrode current, and in this embodiment, the inter-electrode current is detected using a CT (current transformer) or a shunt resistor. 15 is a counting circuit that counts the number of pulses that have not been discharged. It is initialized before the start of counting, that is, at the end of τ, and then counts the pulses to calculate P,, P2, P3.
, P4, etc. are numbered.

The maximum count value of this counting circuit only needs to be up to the number of pulses that define the lowering operation. That is, P in Figure 5a
If it does not discharge at 7, the lowering operation will be forced, so P
There is no need to count the number of non-discharge pulses after 7. 16
is a decoder that determines which pulse is currently being applied between the poles based on the counting result of the counting circuit 15, and the decode outputs are P1 to 2, (P1 and P
2 is applied between the poles) P3 (P3 is applied between the poles), P3 to 6 (P3, P4, P5,
Either P6 is applied between the poles), P7 (P7
The following pulses are applied between the poles).

Reference numeral 17 denotes a control signal generating circuit for determining the control signal V for the pole gap, and the detailed circuit is shown in FIG.

SO is a discharge detection signal, and its logic level is "1" while current is flowing between the electrodes.

18, 19, 20, 21 are AND logic elements, 22 is a negative logic element, 23 is a differential circuit that outputs a signal when the logic value changes from "0" to "F", and 24 is 0R logic. These elements constitute a judgment circuit for controlling the pole gap depending on the number of pulse discharges.

If discharge occurs at either P,, P2, then AN
The output S1 of the D logic element 18 becomes 1, and the R. SFllp
FlOp25 is set and Q1=1, P3, P4
, P5, P6, the output of the AND logic element 19 becomes S2-1, and the R. SFllpFl
Op is set and Q2=1.

Furthermore, if no discharge occurs at P3, the output R6 of the AND logic element 20 becomes 1, and FLIP and FLOP 25 and 26 are reset, resulting in Q1-0 and Q2-0. The states of Ql and Q2 are temporarily held, and the state of J-KFl is maintained at timing T.
It is transmitted to lpFlOp27,28. Timing T is the discharge detection signal S. The trailing edge of , that is, the point of end of discharge,
This is constituted by the case where no discharge has occurred at P7, and the pole spacing control signal is determined at the end of discharge. Also, when there is no discharge even at P7, the lowering operation is forced because it is Q1-0, Q2-0 at P3, and the lowering operation is performed as long as there is no discharge. There is. 29,
30 is a NAND logic element, 31 is an AND logic element J-
A logical operation is performed based on the states of KFlipFlOps 27 and 28, and the output thereof is applied to transistors 35, 36 and 37 through resistors 32, 33 and 34, thereby performing switching.

Since two or more of these transistors are not in the 0N state at the same time and only one is always in the 0N state (the other two are 0FF), the control signal V will be one of the values of V, , 2, and V3. ing. The values of Vl, V2, and 3 in the embodiment are relatively low because they are below the voltage value of the logic circuit element, V1-1.
It was set to 2V, V2-6V, and V3-0V. In this case, the reference voltage (corresponding to that in Figure 1) is P
Since the main purpose is to control the discharge to occur between 3 and P6, it is set to around 6. FIG. 9 is a time chart showing the state of each signal in the circuit 17 in FIG. 8, and shows the voltage waveform between poles and the timing relationship of each signal. Although the control signal V changes stepwise in Figure 5c or Figure 9, this signal is passed through a filter circuit using a resistor and a capacitor as shown in Figure 1 to make the waveform continuous. The operation is similar to that used in ordinary control circuits. FIG. 10 shows a circuit for obtaining a pulse voltage as shown in FIG. 6, where 1a and 1b are voltage 1 (
v), DC power supply with V2(v), 2a, 2b and 3a,
3b is a transistor and a resistor that have the same function as those shown in FIG. 1, and D is a diode to prevent current from flowing backward and damaging the transistor. Further, 6a and 6b are amplifiers for driving the transistors 2a and 2b.
First, the transistor 2a is made conductive, and if it is not discharged until the sixth pulse, the transistor 2b is made conductive from the seventh pulse.

By controlling in this manner, a voltage waveform as shown in FIG. 6a can be applied between the poles. What actually contributes to processing is the current flowing from the DC power supply 1a through the transistor 2a, which is 1
The purpose of the DC power source b is to simply apply a high voltage between the electrodes when no discharge is occurring between the electrodes, so the current should be smaller than the above current. Therefore, the value of resistor 3b is set larger than that of resistor 3a, and when a discharge occurs between the electrodes and a relatively large current flows through transistor 29, the potential at point PO becomes V1 (v), which contributes to machining. The current is
It is uniquely determined by the voltage V, (v) of this power supply 19 and the value of the resistor 3a. That is, first, due to the conduction of the transistor 2a, the voltage V1 of the power supply 19 is maintained until the pulses P1 to P6.
(v) is applied between the electrodes, and if a discharge occurs up to P6, the transistor 2b is not made conductive; however, if no discharge occurs, the transistor 2b is made conductive and a high voltage is applied between the electrodes, causing a discharge. This increases the discharge efficiency by making it easier to generate. Furthermore, as described above, since the transistors 2a and 2b are rendered non-conductive by the pulse at which the discharge occurs, the width of the discharge pulse does not exceed the width of one pulse, and the surface roughness does not deteriorate. Although the present invention has been described in detail above, the lifting operation, stationary operation, etc. as in this embodiment,
The number of pulses, which is the standard for determining whether to perform a lowering operation, should not be fixed, but should be able to be changed in various ways depending on the width of one pulse, as well as the number of pulses. It is also possible to perform control by dividing the time.

In other words, the time interval for the raising operation is 2 to 5μ.
Sec, 30μSec as the time interval for performing the lowering operation
c or more, and determine the number of pulses. In addition, the polarity of the voltage pulse train applied between the poles is not necessarily
It is not limited to positive or negative, but may also be a cage pressure pulse whose polarity changes alternately between positive and negative.For example, using a sine wave AC voltage has the advantage that there is no need to specially set an extremely short pause time Δτ. .

The present invention described above realizes stable machining in a region where the pulse width is extremely narrow and improves surface area, and is extremely effective for high-frequency electrical discharge application.

[Brief explanation of drawings]

Fig. 1 is a principle diagram of a conventional electrical discharge machining device that performs machining by applying controlled pulses between machining holes, Fig. 2 is a waveform diagram for explaining the voltage waveform between machining holes in the conventional method, and Fig. 3 A , b are waveform diagrams showing examples of inter-electrode voltage waveforms according to the conventional method, FIGS. c, FIGS. 6A, b, and c are waveform diagrams showing an example of the inter-electrode voltage waveform, current waveform, and inter-electrode gap control voltage according to the method of the present invention, and FIGS. 7 and 8 are waveform diagrams showing an example of the inter-electrode gap control voltage according to the method of the present invention. FIG. 9 is a timing chart showing the operation timing of each signal in the configuration shown in FIGS. 7 and 8, and FIG. 10 is a timing chart showing the operation timing of each signal in the configuration shown in FIGS. FIG. 2 is a configuration diagram showing an embodiment for generating inter-electrode voltage and current waveforms according to the method of the invention. In the figure, 1 is a DC power supply, 2 is a switching element, 5 is a workpiece, 4 is an electrode, 6 is a control circuit, 7 is a hydraulic cylinder, 1
3 is a time setting circuit, 15 is a counting circuit, 16 is a decoder,
17 is a control signal generation circuit, 18 to 21, 31 are AND logic elements, 22 is a negative logic element, 23 is a differentiation circuit, 24 is an 0R logic element, 25 and 26 are R. SFllpFIOpl
27,28 is J-KFllpFlOpl29,3O is N
AND logic elements, 32 to 34 are resistors, and 35 to 37 are transistors.

Claims (1)

[Scope of Claims] 1 In electrical discharge machining, in which machining is performed by applying a voltage pulse train between opposing poles of an electrode and a workpiece to cause a discharge, a pulse voltage is applied between the poles and a discharge occurs. If the discharge does not occur, apply the next pulse voltage after a minimum pause time, or if discharge occurs, apply the next pulse voltage at a predetermined pause time, and apply an intervening pulse between one discharge pulse and the next discharge pulse. A method for controlling electrical discharge machining, comprising: counting the number of pulses in which no electrical discharge occurs, and controlling the pole gap based on the counted value. 2 In electrical discharge machining, in which machining is performed by applying a voltage pulse train between the electrodes and the workpiece to cause an electric discharge, if a pulse voltage is applied between the electrodes and no discharge occurs, an extremely small After a rest period, or if a discharge occurs, after a predetermined rest period, apply the next pulse voltage to ensure that no intervening discharge occurs between one discharge pulse and the next discharge pulse. Count the number of pulses,
Furthermore, the counted value is divided into three categories, and if discharge occurs up to the number of pulses corresponding to the first predetermined division, it is determined that the gap between the poles is in a narrow state, and the gap is widened. The electrode feed is controlled, and if a discharge occurs within the number of pulses corresponding to the predetermined second division, it is determined that the electrode gap is in an appropriate state, and the electrode feed is controlled to maintain this state as much as possible. control, and if discharge occurs or does not occur at the number of pulses corresponding to the final predetermined third division, it is determined that the gap between the poles is wide, and the gap is narrowed. A method for controlling electric discharge machining, characterized in that the speed of an electrode is controlled in a direction. 3. Machining is performed by applying a voltage pulse train between the electrodes and the workpiece to cause an electric discharge. In electrical discharge machining, a pulse voltage is applied between the electrodes, and if no discharge occurs, there is a very small pause. After a period of time, or if a discharge occurs, after a predetermined rest time, apply the next pulse voltage, and apply the pulse that does not cause a discharge between one discharged pulse and the next discharged pulse. The number of pulses is counted, and the counted value is further divided into three categories. If discharge occurs up to the number of pulses corresponding to the first predetermined division, it is determined that the gap between the poles is narrow and the condition is determined. The feeding of the electrodes is controlled in the direction of widening the gap, and if discharge occurs within the number of pulses corresponding to the predetermined second division, it is determined that the electrode gap is in an appropriate state, and this state is maintained as much as possible. The electrode feeding is controlled so that the electrode gap is wide, and if discharge occurs or does not occur at the number of pulses corresponding to the final predetermined third division, it is determined that the electrode gap is wide. , the electrode feeding is controlled in the direction of narrowing the gap, and a predetermined voltage V_1 higher than the arc voltage is applied to the pulses corresponding to the first and second sections, and from the pulse corresponding to the third section, the above voltage is applied. An electric discharge machining control method in which a voltage V_2 higher than V_1 is applied between the machining electrodes to increase electric discharge efficiency. 4 In electrical discharge machining, in which machining is performed by applying a voltage pulse train between opposing electrodes and causing electrical discharge, if a pulse voltage is applied between the electrodes and no electrical discharge occurs, it is extremely small. After a pause period of The number of pulses that do not occur is counted, and the counted value is divided into three categories. If discharge occurs up to the number of pulses corresponding to the first predetermined division, it is determined that the gap between the poles is narrow. Then, if discharge occurs within the number of pulses corresponding to the predetermined second division, it is determined that the electrode gap is in an appropriate state, and this state is The electrode feed is controlled to be maintained as much as possible, and if discharge occurs or does not occur at the number of pulses corresponding to the final predetermined third division, it is determined that the electrode gap is in a wide state. Then, the electrode feeding is controlled in the direction of narrowing the gap, and from the trailing edge of the pulse where the discharge occurs to the first pulse of the third segment, regardless of the pause time or the pulse application time, the electrode feeding is controlled in the direction of narrowing the gap. An electrical discharge machining control method in which an electrode feed control operation of widening, maintaining, or narrowing a selected electrode gap is maintained. 5 Pulse voltage application means for applying a pulse voltage between the electrodes and the workpiece facing each other; a discharge state detection circuit that detects the presence or absence of discharge between the electrodes; based on the output signal from the discharge state detection circuit, a set time circuit that sends out a timing signal for the rest time or a predetermined rest time; a control circuit that controls the timing of the output pulse train of the pulse voltage application means based on the timing signal from the set time circuit; the number of pulses that are not discharged; A counting circuit that measures the count value of the counting circuit; a decoder that divides the count value of the counting circuit into three categories and determines which category it is currently in; receives signals from the decoder and the discharge state detection circuit, and sends out a control signal according to the category. An electrical discharge machining control device comprising: a control signal generation circuit; a servo mechanism that controls an electrode feeding mechanism based on a control signal from the control signal generation circuit. 6 Pulse voltage application means that applies a pulse voltage between the electrodes and the workpiece facing each other; a discharge state detection circuit that detects the presence or absence of discharge between the electrodes; based on the output signal from the discharge state detection circuit, a set time circuit that sends out a timing signal for the rest time or a predetermined rest time; a control circuit that controls the timing of the output pulse train of the pulse voltage application means based on the timing signal from the set time circuit; the number of pulses that are not discharged; a counting circuit that measures the count value of the counting circuit; a decoder that divides the count value of the counting circuit into three categories and determines which category it is currently in; a signal from the decoder and a discharge state detection circuit is given; on the other hand, two sets of memory circuits are provided; The first memory circuit memorizes the state of discharge occurrence in the first section and the second section, and the second memory circuit stores the state of discharge occurrence in the first section and the second section, and the second memory circuit stores the state of discharge occurrence in the first section and the second section, and the second memory circuit stores the state of discharge occurrence in the first section and the second section. By storing the memory contents of the first memory circuit using a signal generated at a timing signal as a timing signal and retaining the memory contents until the arrival of the next timing signal, regardless of the pause time or the pulse application time, the It is characterized by comprising a control signal generation circuit that sends out a control signal to maintain the selectively stored state of the electrode gap; and a servo mechanism that controls the electrode feeding mechanism based on the control signal from the control signal generation circuit. Electrical discharge machining control device.