JPS6057970B2 - Electric discharge machining equipment - Google Patents

Description

Detailed Description of the Invention The present invention is applicable to electric discharge machining (including electrolytic erosion machining) in which a machining gap between an electrode and a workpiece is repeatedly discharged by machining pulses. The purpose of this invention is to accurately detect and judge changes in the machining gap state, whether they are good or bad, and to control the machining state in the best way possible.

In electric discharge machining, machining pulses are controlled according to the gap state (discharge state), flow rate of machining fluid, control of electrical conductivity, electrode vibration when machining debris accumulates, cleaning work by pulling up the electrode, and machining of gap length. It is necessary to perform servo control etc. optimally to follow the

Conventionally, to determine the state of the machining gap and the discharge state, it was necessary to apply pulses to the machining gap to determine whether a discharge occurred or not, and to determine whether the generated discharge was an arc discharge, a short circuit, a normal discharge, etc. based on the discharge pressure. However, accurate detection and discrimination were not possible, and optimal control was not possible.

The present invention detects and discriminates a high frequency component (vibration component) contained in the discharge in the machining gap or a signal containing this.

The high frequency component has an amplitude ΔV of the high frequency AC voltage component at the discharge sustaining voltage of each pulse discharge, as shown in the voltage waveform in Figure 1.
takes the form of superimposed VG is the machining gap voltage (average value) during pulse discharge. The superimposed high frequency component usually has a frequency of about 1 MHz to 30 MHz, and once the arc state is established, this high frequency component disappears. Of course, this will not occur even if there is a short circuit. Therefore, the presence or absence of this high frequency component is detected and determined, and if the high frequency component is present, it is determined that the discharge is good, and if there is no high frequency component, it is determined that it is a bad discharge, and the machining state can be controlled based on this. can be done. However, according to subsequent research, there is a dependence on the type and change of the machining fluid, and the generation of high frequency components,
The magnitude of high frequency components changes. That is, in pure water with a small molecular weight (molecular weight 18), the voltage ΔV of the high frequency component is extremely small, in kerosene (molecular weight 200 to 300), Δv is large, and in spindle oil (molecular weight ~700), an even larger ΔV occurs. Figure 2 is a graph of the gap voltage (discharge pressure) depending on the molecular weight of the working fluid.The gap voltage is the sum of the anode drop voltage Va and the cathode drop voltage Vc, the DC component of 1+VC, and the amplitude of the high-frequency AC voltage component. ΔV is added. That is, the machining gap voltage (peak value) Vm is V.
．． =■1+VO+ΔV, the high frequency component Δ■ is DC biased and the machining gap voltage V. ．． form.

As mentioned above, the high frequency AC component Δ■ seems to increase depending on (in proportion to) the molecular weight of the processing fluid. Pure water with a small molecular weight (molecular weight 18 to 36) has a very small discharge even during normal discharge, but spindle oil with a large molecular weight (molecular weight 300 to 36)
700), ΔV≠10V. Moreover, this high frequency alternating current component disappears as soon as the discharge becomes an arc. This is because if the medium (processing fluid) has a high molecular weight, the emitted electrons will be absorbed and the discharge will easily become pulsed, generating a high-frequency AC component, but if the medium has a low molecular weight, it will be difficult for the electrons to be absorbed. Therefore, if the number of electrons becomes too large, the discharge will continue and arc will easily occur, so it is thought that the high frequency alternating current component will no longer be generated. Furthermore, it can be seen that even if a high molecular weight medium is used, if the medium is cracked and the molecular weight is reduced during processing, the high frequency component will gradually decrease by 5 and finally reach the arc. This is because the amplitude Δ■ of the high frequency AC voltage component shown in FIG. 1 gradually decreases as time passes after the start of discharge. That is, discharge pressure,
The temperature changes over time, and the molecular weight changes due to temperature-induced decomposition of the medium. In this way, the amplitude (peak value) of the high-frequency alternating current component that occurs during one pulse discharge reaches its maximum at the start of discharge, and then decreases depending on the state of the machining fluid. In this case, it is desirable to perform machining in a discharge state in which the amplitude does not decrease as much as possible during discharge.

Therefore, it is not possible to accurately detect the quality of the discharge state even if the presence or absence and magnitude of the high-frequency alternating current component at a certain point after the start of discharge (startup) is detected and determined. Therefore, the present invention detects and discriminates the average rate of change in the amplitude of the high-frequency AC component, which decreases with the passage of time as shown in FIG. As shown in Fig. 3, the setting time is T immediately after the start of discharge. , the middle time is TO, the end time is Te, and the amplitude (peak value) of the high frequency AC voltage component at each time is ΔVO.
, ΔVx, ΔVe, since ΔVe is extremely small, the average rate of change is detected and determined from ΔVO to ΔVx at the time of TO-Tx. That is? The discharge state is determined by detecting and determining T.
x-TO Umono desu.

Of course, if it is possible to accurately detect ΔVe, then 514 or ? It is also possible to detect and determine Te-TOte-ζ.

The present invention will be explained below with reference to one embodiment.

In FIG. 4, reference numeral 1 denotes a machining gap in which the electrode and the workpiece face each other, and 2 denotes a machining pulse power source, which repeatedly generates pulsed discharge in the machining gap. This discharge voltage (or current) is detected by the detection circuit 3. As mentioned above, the discharge voltage (or current) detected by the detection circuit 3 contains a high frequency component (vibration component), and it has already been explained that this component depends on the molecular weight of the medium. Also, this is during discharge,
It was also explained that the molecular weight decreases as the molecular weight of the medium decreases due to cracking, etc. (Figure 3). Only the high frequency component of the detection signal is extracted by the high pass filter 4, and then converted by the next DC conversion amplifier 5 into a DC signal having a magnitude corresponding to a high frequency voltage. On the other hand, the discharge start (start of discharge) is detected by the discrimination circuit 6, and a predetermined time T is elapsed from the start of discharge. (FIG. 3) The delay timer 7 operates, and when the time is completed, the check pulse generating circuit 8 outputs T. The hour check pulse is output. Further, the timer 9 is activated by the output signal of the timer 7, and when the Tx-TO time is completed, the check pulse generation circuit 10 generates a check pulse at the time of Tx. The check pulse of the circuit 8 is applied to the latch circuit 11 to memorize and hold the amplifier 5 output ΔVO at the time of TO, and the check pulse of the circuit 10 is applied to the latch circuit 12 to store the amplifier 5 output ΔVO at the time of Tx.
The output ΔVx is memorized and held. 13 is a clock pulse oscillator, and this clock pulse replaces the latch signal and counts.

14 is a counter that counts the latch signal ΔVO; 15
is a counter that counts the latch signal ΔVx, and 16 is a comparator that compares the outputs of both counters 14 and 15.
The compared difference output Δ■o−ΔVx is output.

The output signal is again replaced by a clock pulse and the counter 17
is counted. 18 is the operating time T8 of the timer 9
The outputs of both counters 17 and 18 are compared and divided by the next divider 19, in which -TO is replaced by a clock pulse and counted.

The output signal is 6V-6V. That is, this is the average rate of change in the amplitude of the high Tx-TO frequency AC component that we are looking for, and this signal is also replaced by a clock pulse and sent to the counter 2.
It is counted as 0.

Reference numeral 21 denotes a comparator that compares and discriminates the output of the counter 20, that is, the average rate of change in the amplitude of the high frequency AC component 2 Htx-TO, with a reference value.The reference value is preset by the preset circuit 22.

The preset corresponds to the type and molecular weight of the machining fluid, and is optimal according to the pulse width of the machining pulse, pause width, peak value (1,), polarity, electrode material, workpiece material, combination thereof, and other machining conditions. It is set in the machining range. For example, 4ゝ14゜ is V
It is expressed as lpS and is usually Tx-TO which is about 0.
06-0. A value of about 0.1 to 0.0 is considered to be normal, and a value of about 0.1 to 0.0 is considered bad.

The discrimination output is, for example, a 0K signal if the condition is good by comparing it with the set value, and a DAME if the condition is bad.
or output the 0K signal only when the condition is good, or output the 0K signal only when the condition is bad. There may also be a device that outputs an AME signal. Reference numeral 23 denotes a display circuit for the discrimination signal, a logic circuit combining counters, etc., and a control circuit for controlling the machining pulse power source, servo device, machining fluid supply device, etc. by collective signals.

Each pulse discharge repeated in the machining gap 1 is discriminated by the circuit device described above, and of course, if it is an arc or a short circuit, the detection signal is blocked and discriminated by the filter 4, but even if it is a discharge accompanied by a high frequency component. , the average rate of change in the amplitude of the high-frequency AC component? Check the second h Tx-
If the TO output is determined and the discharge is not compatible, it is discriminated from the compatible good discharge, so the discharge state can be detected accurately.

For example, in Figure 3, if ΔVO is large but ΔVO is small and the average rate of change is large and the high-frequency AC component decreases rapidly after the start of discharge, the high-frequency AC component will decrease until the end of one-pulse discharge. The generation does not continue, and therefore the amount of machining due to this is extremely small.In other words, the amount of machining and machining speed tend to increase in proportion to the generation of high frequency, and discharges where the high frequency component is small or disappears quickly are Since the machining is small, it is possible to accurately determine whether the discharge state is good or bad by detecting the average rate of change in the amplitude of the high frequency alternating current component. Note that the discharge in the machining gap is not limited to the machining pulse; discharge is performed before the discharge of the machining pulse or by adding an inspection pulse to the discharge pulse train, and this discharge is detected and determined, and the high-frequency components during the discharge, Alternatively, signals such as discharge voltage and current containing high frequency components can be detected and discriminated, and the circuit may be configured in such a manner.

In addition, the circuit diagram of the above-mentioned embodiment is for digital detection and discrimination of signals.
Although an example in which logical operation processing is performed has been described, analog detection and discrimination may of course be used, and the circuit configuration can be arbitrarily designed.

In this way, by detecting and determining the average rate of change of the high-frequency AC component present or included in the discharge, it is possible to accurately and accurately detect the discharge state. Process control is also very accurate. For example, based on the detected and determined signal, the molecular weight of the machining fluid may be controlled, for example, the addition of a high molecular weight solution to the base fluid and the amount of addition may be controlled, and the jet speed and flow rate of the machining fluid may be controlled. Optimal results can also be obtained by controlling the vibration of the electrode, controlling the frequency and width of the electrode, controlling the reciprocating motion of the electrode, and controlling the servo.

In addition, the pulse width, pause width, and peak value of the processing pulse, etc.
Combination control can be performed, and both types of control have high detection accuracy for machining status and discharge status, and optimal control is always possible.

[Brief explanation of the drawing]

Fig. 1 is a graph of the discharge pressure waveform, Fig. 2 is a graph of the gap voltage (discharge pressure) against the molecular weight of the machining fluid, Fig. 3 is an explanatory diagram of the waveform of the high frequency component changing over time, and Fig. 4 is a diagram of the waveform of the present invention. A circuit configuration diagram of one embodiment is shown. 1 is a machining gap, 2 is a machining pulse power source, 3 is a detection circuit, 4
5 is an amplifier, 6 is a discharge start detection circuit, and 7 is a T.

Claims (1)

[Claims] 1. In an electric discharge machining device that performs machining by repeating pulse discharge in a machining gap between a machining electrode and a workpiece disposed facing each other, high-frequency alternating current contained in the discharge voltage and discharge current during the pulse discharge is used. a circuit that detects the amplitude at a set period after starting discharge of the component; and a circuit that detects the amplitude at another period after a period of several cycles or more of the high-frequency AC component has elapsed from the one period. , a circuit that calculates an average rate of change in the amplitude of the high frequency AC component during the period by dividing the difference between the two detected amplitude values by the period, and compares the average rate of change with a set reference value. What is claimed is: 1. An electric discharge machining apparatus characterized in that a circuit for determining whether a discharge state is good or bad is provided, and the machining state is displayed or controlled based on the determination result.