JPS6130335A - Electric discharge machining equipment - Google Patents

Abstract

PURPOSE:To protect an electrode and a workpiece from damage, by stopping the application of voltage pulses between the electrode and the workpiece when the duration or magnitude of a discharge current based on the voltage pulses has been different from a set value for a prescribed time. CONSTITUTION:When a discharge current flows between an electrode 1 and a workpiece 2, an output pulse from a circuit 10 is applied to an element 9 to operate a timer 8. When an element 6 is reset by the timer 8, a timer 7 is operated to repeat discharge. The output pulse from the circuit 10 is also applied to a circuit 12. Output pulses from a generator 13 are counted through the circuit 12. The counted value is compared with a reference number by a comparator 15. If the difference between the compared values is over an allowable range, a pulse is sent to a circuit 24. A shaped pulse signal is applied to a circuit 19 to detect the peak value of the signal. A comparator 21 compares the amplitude of the discharge current with a reference value. If the difference between the compared quantities is over an allowable range, a pulse is sent to the circuit 24. When the number of the pulses from the comparators 15, 21 is larger than a prescribed value, the circuit 24 turns off a transistor 5 and makes a notification.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an electric discharge machining apparatus, and particularly to an improvement of a control circuit for controlling a power supply for the electric discharge machining apparatus.

[Conventional technology]

Unlike normal machining, which performs machining by applying mechanical force directly to the workpiece, electrical discharge machining equipment applies voltage pulses to the gap between the workpiece and electrode, where the machining fluid is present, and generates electrical discharge. This is a non-contact processing that utilizes this phenomenon.

Therefore, when performing electrical discharge machining, the material of the electrode should be selected taking into account the material of the workpiece, the purpose and conditions of machining, etc., and the machining conditions and conditions should be selected to suit the shape of the workpiece and the purpose of the product. In other words, the power supply voltage, the duration of the voltage pulse or discharge current pulse, the rest time, the amplitude of the discharge current, and the method of supply intervention such as the hydraulic pressure of the machining fluid, the required machined surface roughness, and the electrode wear. Machining is performed by selecting and setting the ratio and machining speed.

Among the above machining conditions, the duration of the voltage pulse or discharge current (TON>) and the amplitude of the discharge current ('I'p) are major factors that affect discharge machining, and are set to predetermined values before starting machining. However, it varies depending on the electrode of the machining discharge section, the shape and dimensions of the workpiece, the area of the machining gap, the amount and properties of the machining fluid present in the machining gap, the length of the machining gap or the gap length of the machining discharge section, etc. be.

Therefore, the duration of the voltage pulse or discharge current (τON) and the amplitude of the discharge current (Ip) set before the start of the machining
If machining is no longer performed, the machining speed usually decreases, machining performance such as electrode wear and machined surface roughness changes, and machining is not performed smoothly. This will result in damage to the workpiece.

In the above case, if the duration of the voltage pulse is selected as τON, it is inevitable that the duration of the discharge current will vary for each discharge, so in such a case, for example, 5 pulses, etc. If the statistics of the discharge current duration during the application period of 10 voltage pulses is within a predetermined value or a predetermined percentage range, for example, 50 to 75% of the total duration of the voltage pulses of that period, On the other hand, when the duration of the discharge current is selected and set as τON, the average rate of change in one or more discharge pulses is , 2 to 3% to at least 5%, it is detected that the duration of the discharge current has changed from a predetermined value.

[Problems to be solved by the present invention]

The present invention has been made from a paper perspective, and its purpose is to determine the duration of the discharge current or the discharge current duration ( τON) or discharge current value (Ip
) is different from the preset value and continues for a certain period of time, the supply of voltage pulses between the workpiece and the electrode will be stopped, and the electrode and workpiece will be damaged due to abnormal discharge, etc. It is an object of the present invention to provide an electrical discharge machining device that can prevent damage.

In the above case, control of machining gap length by servo feed, etc.
Control of machining fluid by so-called electrode jump, machining fluid jet, etc.
Alternatively, if the machining state can be recovered by controlling one or more voltage pulses or the pause time between discharge pulses, it goes without saying that such control may be used to measure the recovery.

(Means for solving the problem) A discharge current amplitude comparison circuit that generates a signal when a difference greater than an allowable range is detected between the two, and a discharge current amplitude comparison circuit that compares the two with a preset reference value, and A discharge duration comparison circuit that compares the duration of discharge with a preset reference value and generates a signal when a difference exceeding an allowable range is detected between the two, and the discharge current amplitude comparison circuit or discharge duration. An output signal is generated when the signal from the time comparison circuit is emitted continuously for a certain period of time, or when the signal is emitted for a predetermined ratio of discharge pulses, such as 50% or more, to a predetermined number of discharge pulses. This is achieved by adding an output circuit that emits the .

[For production]

As mentioned above, if the discharge current amplitude or discharge duration of each discharge pulse including a voltage pulse differs from a preset value and continues for a certain period of time or reaches a certain percentage of the voltage or discharge pulse, Since the output circuit performs control such as stopping the power supply circuit and corrective control operations, it is possible to prevent expensive electrodes or workpieces from being damaged by abnormal discharge or the like.

(Example〕 Hereinafter, the details of the present invention will be specifically explained with reference to the drawings.

FIG. 1 is a drawing and an explanatory diagram showing an embodiment of an electric discharge machining apparatus according to the present invention.

In the figure, 1 is a processing electrode, 2 is a workpiece, 3 is a DC power supply,
4 is a resistor, 5 is a switching transistor, 6 is an RS bistable element, and 7 is a discharge stop time (τcrr
) is set, 8 is a timer to which discharge duration (τON) is set, 9 is a monostable element, 1
0 is a Schmitt trigger circuit, 11 is a discharge duration comparison circuit, 12 is an AND circuit, 13 is a clock pulse generator, 14 is a counter, 15 is a comparator, 16 is a memory, 17 is a discharge current amplitude comparison circuit, 18 is a low-pass filter, 19 is a sampling circuit, 20 is a buffer resistor, 21 is a comparator, 22 is a memory, 24 is an output circuit, 24 is an OR circuit, 25 is a preset counter, 26
27 is an inhibitor/node circuit, 29 is a start switch, and 29 is an alarm. .

The machining electrode 1 and the workpiece 2 are opposed to each other with a substantially constant machining interval maintained in a machining liquid (not shown), are given an appropriate machining feed, and a switching transistor is connected between them. 5, a voltage pulse of a predetermined value is supplied to perform electrical discharge machining.

Timer 7 is connected to the S input of RS bistable element 6.
is connected to the timer 7, and a discharge voltage rest time (τ0FF) is set in the timer 7. On the other hand, a discharge duration (τ0I()) is set in the timer 8 connected to the R input of the RS bistable element 6.

Therefore, at the start of machining, the RS bistable element 6
is in the cent state, and the output of the inhibit circuit 27 is in the state 0.

When the start switch is turned on, the set output of the RS bistable element 6 passes through the inhibit circuit 27, operates the switching transistor 5, and applies the voltage of the DC power supply 3 between the processing electrode 1 and the workpiece 2. be done. When discharge starts between the machining voltage 1 and the workpiece 2 and a discharge current begins to flow, the simulator throat 1 trigger circuit 10 is triggered, and its output pulse is input to the monostable element 9. , the output pulse of the monostable element 9 operates the timer 8.

The timer 8 defines the discharge duration (τON>) and generates an output pulse when the duration (τON') elapses to reset the RS bistable element 6.

When the RS high stable element 6 is reset by the timer 8, the timer 7, on the other hand, operates. The above-mentioned timer 7 regulates the discharge body stop time (T"), and when the discharge body stop time (τ0FF) elapses, it generates an output pulse and reverses the RS bistable element 6 to the cent state again. Processing electrode 1 and workpiece 2
A voltage pulse is applied in between.

Thereafter, similar cycles are repeated, voltage pulses are supplied between the machining electrode 1 and the workpiece 2, and discharge is repeated. On the other hand, the output of the above-mentioned circuit 10 is:
It is also input to the AND circuit 12. The pulse from the clock pulse generator 13 is constantly input to the AND circuit 12, and while the input from the Schmitt trigger circuit 10 is in state 1, the AND circuit 12 receives the pulse output from the clock pulse generator 13 while the input from the Schmitt trigger circuit 10 is in state 1. passes through the AND circuit 12 and is counted by the counter 14, and the counted value is compared with the reference number of pulses emitted within the discharge time recorded in the memory 16 by the comparator 15 when the RS bistable element 6 is reset. , when a difference exceeding a predetermined tolerance is detected, the comparator 15 generates a pulse and inputs it to the OR circuit U.

Furthermore, the low-pass filter 18 removes high frequency components from the detection signal pulse and shapes the waveform when a discharge current flows through the machining gap, and the waveform-shaped pulse signal is sent to the sampling circuit 19. The sampling circuit 19 detects the peak value at one or several locations during the duration of each input pulse, and inputs the data to the comparator 21 via the buffer resistor 20.

Then, the comparator 21c;j compares this data, that is, the discharge current amplitude (ip) with the reference current value (1) recorded in the memory 22, and determines that an error exceeding the allowable error range is found in both. When this occurs, an output pulse is generated and input to the OR circuit 24.

When a pulse is generated from the comparator 15 or 21, the OR circuit 24 generates an output pulse and inputs it to the preset counter 25. The preset counter 25 counts the pulse signals transmitted from the OR circuit 24, and the number is counted by the clock pulse generator 26.
If the number of pulses transmitted from
At the same time as stopping the supply of voltage pulses between
It operates to notify you of abnormal discharge.

31. Sometimes during machining, the discharge duration (τON) and discharge current amplitude (Ip) are detected during lightning. If the discharge duration (τON) or discharge current amplitude (, Ip) set before machining deviates from the allowable range due to the condition of the machining gap or an unexpected accident, the machining electrode l and the workpiece may In addition to carrying out control or correction control operations such as stopping the supply of voltage pulses between the two, the system also sends a *report, thereby preventing damage to the expensive machining electrode 1 and the workpiece 2 due to abnormal discharge. This can be prevented.

〔Effect of the invention〕

Since the present invention is configured as shown on paper, when the present invention is applied, the discharge duration or the discharge current amplitude of the voltage pulse supplied between the machining electrode and the workpiece deviates significantly from a preset value. , If this continues for a certain period of time or reaches a certain percentage of the voltage or discharge pulse, control such as stopping the supply of voltage pulses between the machining electrode 1 and the workpiece 2 is performed. Alternatively, since an alarm is used to notify the user of any abnormality, it is possible to prevent expensive electrodes, workpieces, etc. from being damaged by abnormal discharge or the like.

Note that the present invention is not limited to the embodiments on paper. That is, in this embodiment, for example, if the discharge duration or discharge current amplitude of the voltage pulse supplied between the machining electrode and the workpiece deviates from a preset value, and this continues for a certain period of time, However, if the voltage or discharge pulse exceeds a certain percentage, the power supply circuit is controlled to be stopped, and an alarm is issued. It is also recommended to ensure that the discharge occurs smoothly. Furthermore, it is of course possible to use a switching element such as a SIRISK instead of a switching transistor, and for example, an AND circuit may be used instead of an OR circuit, or the output of timer 8 and a Schmitt trigger circuit li! The present invention can be freely modified within the scope of its purpose, such as by comparing the outputs of 810 to detect changes in discharge duration, and the present invention encompasses all of them. It is.

[Brief explanation of drawings]

The drawings show 3. of the electric discharge machining apparatus according to the present invention. It is an explanatory diagram showing one example.

Claims (1)

[Scope of Claims] An electric discharge machining device that supplies machining fluid between a workpiece and an electrode, and applies a voltage pulse of a predetermined value between the two from a power supply circuit to generate electric discharge, thereby performing machining. In this case, the discharge current comparison circuit compares the discharge current value with a preset reference value and generates a signal when a difference exceeding an allowable range is detected between the two, and the discharge duration time is set in advance. A discharge time comparison circuit that generates a signal when a difference exceeding a permissible range is detected between the two compared with a reference value, and a signal from the discharge current comparison circuit or discharge time comparison circuit that is continuously emitted for a certain period of time. The electric discharge machining apparatus described above is further provided with an output circuit that transmits an output signal when the electric discharge machining device is activated.