JPS6044224A - Electric discharge machine - Google Patents

Abstract

PURPOSE:To prevent discharge concentration and suppress occurrence of abnormal arc discharge, by decreasing the rate of increase in the interelectrode voltage per unit time and slowing down the rising of the applied voltage when it is judged from impulse waves produced by the discharging that the conditions between the electrodes are such that an abnormal arc will imminently occur. CONSTITUTION:When an ultrasonic wave produced and transmitted to an ultrasonic wave sensor 35 is detected thereby as an electric signal, the output portion of the sensor 35 generates a signal Sp. A peak hold circuit 42 then stores the value which was the highest of the signal Sp. Then, a comparator 47 makes judgment whether the impulse signal Sp is normal or not and allows a normal signal to be input to a counter 49 as a reset signal. If the conditions indicating imminent occurrence of abnormal discharge last, the counts in the counter 49 are increased, and when the counts reach a predetermined value, a light emitting diode 52 is turned on and a signal S of a switch 51 is turned to ''1'' level and output to the outside. The voltage responding to the output of the counter 49 is then inverted through an inversion amplifier, whereby the voltage rising rate dv/dt is made smaller and the rising of the applied voltage is slowed down in proportion as the conditions between the electrodes are worse to make the discharge difficult to occur and prevent discharge concentration.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to an electric discharge machining apparatus, in particular, an electric discharge machining apparatus in which an electrode and a workpiece are opposed to each other with an insulating machining liquid interposed therebetween, and an electric discharge is generated in the gap between the electrodes. The present invention relates to an electric discharge machining apparatus for machining the workpiece described above.

[Prior art]

FIG. 1 shows a schematic configuration diagram of a conventional electric discharge machining apparatus. In FIG. 1, an electrode 10 faces a workpiece 14 placed in a processing tank 12 with an insulating processing liquid 6 interposed therebetween. A processing power source 18 is connected between the electrode 10 and the workpiece 14. This processing power source 18 includes a DC power source 18a,
Switching element 18b for intermittent machining current
, a current limiting resistor 18c, and the switching element 18
The machining current is intermittently supplied to the gap 20 between the electrode 10 and the workpiece 14.

The above machining current 1 is - (E is the voltage value of the DC power source 18a, R is the resistance value of the current limiting resistor 18c,
v9 is the interelectrode voltage value). Electrode voltage value v
9 is 20 to 30V during arc discharge, Ov1 during short circuit and EV during no discharge, and 0■ when switching element 18b is in the off state.

Therefore, if this inter-electrode voltage value v9 is detected and averaged by the smoothing circuit 22, the inter-electrode gap can be controlled using this value. That is, when the inter-electrode gap 20 is wide, discharge is difficult to occur and the average voltage value Vs is high. When the inter-electrode gap 20 is narrow, short circuits or discharges occur easily, resulting in a decrease in the average voltage value Vs. Therefore, if this average voltage value Vs is compared with the reference voltage value Vt, and this difference is amplified by the amplifier 24 and inputted to the hydraulic servo coil 26, the oil/pressure generating pump 28 and the hydraulic cylinder 30 are configured. A hydraulic servo mechanism can control and shift the electrode 0 so that the interpolar gap 20 is approximately constant.

When determining whether the machining condition is good or bad with a conventional electrical discharge machining device, the most common method is to use the average voltage value Vs of the machining voltage value v9 mentioned above.
It is to *Jl 1rrll. In other words, when the average voltage value Vs is low, the impedance between the electrodes is low, resulting in a short circuit and continuous arc discharge, and the gap between the electrodes is 20.
Possible causes include accumulation of processed powder and sludge. However, the most dangerous abnormal arc discharge in electric discharge machining is - When it occurs, carbon is generated due to thermal decomposition of the machining fluid, resulting in an electric discharge between the carbon and the workpiece, resulting in a state where the impedance between the electrodes becomes high. become. Therefore, the average voltage value Vs is tq has the disadvantage that it is impossible to detect deterioration of the inter-electrode gap condition due to abnormal arc discharge.

[Summary of the invention]

The present invention has been made in view of the above-mentioned conventional problems, and its purpose is to detect the shock wave at the time of discharge occurrence, determine the state of the gap between the poles, and detect the gap between the poles when it is determined that the state is a precursor to the occurrence of an abnormal arc. The rate of increase dν/dt of the inter-electrode voltage per hour is changed so that the state becomes normal, and as the condition becomes abnormal, the rate of increase is decreased (as the rise of the north-north voltage) becomes more gradual, and the discharge is reduced. The object of the present invention is to provide an electric discharge machining apparatus which prevents the occurrence of abnormal arc discharge by preventing concentration of electric discharge.

In order to achieve the second object, the present invention makes an electrode and a workpiece face each other with an insulating machining liquid interposed therebetween, and generates an electric discharge in the gap between the electrodes to machine the workpiece. In electrical discharge machining equipment, abnormal electrical discharge is detected by a detector installed in the machining fluid that generates waves such as ultrasonic waves when electrical discharge occurs in the gap between the electrode and the workpiece, and detects the arc precursor phenomenon caused by concentrated electrical discharge. a detecting means, a gap state determining means for determining that the gap condition is in a bad state by analyzing the waveform of the shock wave and outputting No. 48; and a pulse for applying a pulse to the gap based on the output. The present invention is characterized by comprising means for controlling the slope of the rise time of the voltage.

[Embodiments of the invention]

Hereinafter, preferred embodiments of the present invention will be described based on the drawings. FIG. 2 is a schematic diagram showing the configuration of an embodiment of the present invention, in which the same parts as in FIG. 1 are denoted by the same reference numerals. The relationship with the ultrasonic pressure waveform detected by the sonic sensor 35 is shown in FIG. In the upper diagram of FIG. 3, a discharge current (2) flows at each time from L1 to t4, and the machining fluid near the discharge point rapidly vaporizes and explodes due to the high temperature of approximately 6000 degrees, producing bubbles (A). As a result, the nearby machining fluid undergoes a rapid pressure change, which propagates as an ultrasonic shock wave into the narrow gap between the poles, is transmitted to the ultrasonic sensor 35 via the electrode, and is detected as an electrical signal. During normal discharge, the shock waves mentioned above are detected periodically depending on the magnitude of the current, but when the discharge becomes concentrated at one point, the shock waves are detected at an accelerated rate. , The ion concentration at point B increases as it approaches the non-insulating state due to an increase in the amount of carbon due to thermal decomposition of the processed powder and processing fluid. In such a case, the discharge point (usually 0.1 to 2 m5) will eliminate the bubbles.
Since the discharge is performed again before the discharge (necessary as much as ec) occurs, the rate of change in volume is not as large as in the case of normal discharge, unlike discharge in a liquid, and therefore the generated ultrasonic impact force is also reduced. 40 in Fig. 2 detects normal discharge and abnormal discharge based on the above operating principle, and detects the ultrasonic pressure L5 due to the discharge flow generated at t5 as shown in Fig. 3. An abnormal discharge is determined when a certain number of consecutive occurrences occur in which the discharge voltage is smaller than that during normal discharge.

FIG. 4 is a detailed diagram of the device 40, in which the output of the ultrasonic sensor 35 is amplified by an amplifier 41 and the signal S
generate l. 42 is a peak hold circuit,
The highest value of the signal S is stored. That is,
To the integral quantity #I43, only a voltage higher than the highest output of the integral quantity g843 is charged to the capacitor C of the integrating circuit via the analog isator 44 and the comparator 45 through the resistor R. Therefore, the output of the voltage dividing resistor 46 is the voltage divided version of the highest output during normal operation.
This is used to distinguish between normality and abnormality.

This is because the explosion pressure changes depending on the discharge energy and energy application time, and in machining such as electrical discharge machining, which has many types of energy landscapes from rough machining to fine finishing machining, it is uniformly applied. ,normal! 1!7%! It is difficult to standardize the force, and it is necessary to use a peak hold circuit 42 like the device 40 to compare it with the most normal impact force.

The comparator 47 determines whether the 'tj attack wave signal SD is correct or not, and inputs it to the counter 49 as a reset pulse. Current detection pulse SI is Karen 1, transformer CT
As a result, current is detected and input as an up-count signal to the counter 49 via the amplification and shaping circuit 50. Therefore, in this circuit, each time a current flows through the gap between the poles, +1. r! The counter contents do not increase because the current is counted and immediately after that, a normal discharge occurs. If an abnormal discharge occurs and the conditions like t4 and t5 in FIG. The input of the driver 53 becomes "1" level, 52 lights up, and the output signal S of 51 becomes "1 level" and is output to the outside. This is to prevent the counter from increasing any further. By detecting and processing the contents of this counter, various situations associated with the discharge occurring in the gap between the electrodes can be easily determined. In other words, if the contents of the counter are large, If there is, the gap condition between the machining poles will worsen and the discharge will be concentrated, which may indicate some kind of problem, such as sludge accumulating in the machining gap due to the retention of machining powder, or thermal decomposition of the machining fluid due to an abnormal arc. Is carbon being generated?
It can be detected that a part of the electrode is damaged and its fragments are present in the gap between the electrodes.

Now, based on the output obtained by the above-mentioned detection circuit, by varying the slope dV/dt of the voltage applied between the electrodes per time, if the electrode gap condition is poor, the voltage can be raised slowly. It is possible to make it difficult to generate electric discharge, prevent concentration of electric discharge, and when the condition is good, to quickly rise and stop the electric discharge, thereby improving machining efficiency. An embodiment for this purpose will be described with reference to FIG. 5, and an explanation of the operation using time chart 1 of FIG. 6. Reference numeral 100 in FIG. 5 is an inverting amplifier, and an analog voltage V corresponding to the output of the counter 49.

This is a circuit for inverting the analog voltage Vo (obtained by connecting the digital output of the counter 49 to the I/A converter 40) and applying it to the base of the PNP transistor 101.

Now, the voltage v9 applied to the gap between the electrodes has the following value.

Vg=IcXt/C---(11) where Ic is the collector current of the transistor 101, t is the elapsed time after the pulse voltage is applied, and C is the capacity of the capacitor 102.

Next, Ic is approximately equal to the current flowing through the emitter follower load resistor 103 of the transistor 101 (approximately 99).If the value of the resistor 103 is Ri, Ic can be expressed as follows.

Note that vE is the emitter voltage of the transistor 101, and VB is the base voltage. Therefore, the voltage applied between electrodes v9 is obtained from equation +11 and equation (2).

Otsu and Te, R=5Ω, C=0.01μF, V,=O
~IOV, voltage slope c/V/dtl;t, 0~
It will change in the range of 200V///S. still,
The inverting amplifier 100 is designed so that when the input is 0V (7), the output is 10V, and when the human power is 10V, the output is OV.
The larger o is, the worse the electrode gap condition is, the lower the slope dV/dt of the applied voltage is. Also, resistance 1
04, when discharging the charge accumulated in the capacitor 102,
The die 4-de 105 is for discharging so as not to affect machining, and prevents the current from the machining switching transistor 18b from flowing back into the capacitor 102.

Further, the transistor 18b is turned on for a predetermined period of time after discharge occurs in the gap between the electrodes. The internal gate of the inverting amplifier 100 receives the control signal S of the pulse width pause width control circuit 18d.
J is also controlled to prevent voltage from being applied to the interelectrode gap during the rest period. The time chart in FIG. 6 provides a concrete explanation of the above explanation, and shows the relationship between the detection voltage Vo and the capacitor charge m I c, and the logic level when the mutual on-t state of the transistors is 1.0. It is shown in

According to this embodiment, when discharge is concentrated or an arc precursor state occurs, the content of the counter 49 of the detection circuit increases, the output of the inverting amplifier decreases, and the slope of the applied voltage becomes slower, making it difficult to discharge and preventing discharge. I no longer concentrate, and my state of extremes is restored.

In the above embodiment, the slope of the applied voltage is controlled continuously according to the contents of the counter 49 of the detection circuit, but it does not necessarily have to be continuous, and may be controlled linearly, in several steps, or in a series. Even if it is changed, it still meets the purpose of implementing the present invention.

〔Effect of the invention〕

As described above, in the present invention, an abnormality in the contact gap state is determined by the detection method described above, and the slope of the voltage applied between the contacts is changed in order to recover the contact gap state based on the determination result. to control the ease with which discharge occurs, concentrating the discharge on one point,
The object is to provide an unprecedented electrical discharge machining apparatus that prevents continuous application of high voltage without deionization and restores the gap state.

[Brief explanation of the drawing]

Fig. 1 is a principle diagram of a conventional electric discharge machining device, Fig. 2 is a principle diagram of a device according to the present invention, Fig. 3 is a time chart for explaining the detection device according to the present invention, and Fig. 4 is a diagram showing the principle of a conventional electric discharge machining device. FIG. 5 is a detailed explanatory diagram of the present invention, and FIG. 6 is a time chart showing the operating state of the device shown in FIG. 5. In the figure, 10 is an electrode, 14 is a workpiece, 16 is a processing liquid, and 49
is a discharge concentration detection counter. Note that the same reference numerals in the figures indicate the same or equivalent parts. Agent Masuo Ohatsu

Claims (1)

[Claims] In electrical discharge machining equipment, an electrode and a workpiece are opposed to each other with an insulating machining fluid interposed between them, and a pulse voltage is applied to the gap between the electrodes to generate force or electricity to machine the workpiece. A detector installed in the machining fluid detects shock waves such as ultrasonic waves generated in the gap between the poles of the workpiece, and an abnormal discharge detection means detects the arc precursor phenomenon caused by concentrated discharge. The present invention is characterized by comprising: a gap condition determining means for determining that the gap condition is in a bad condition and outputting a signal; and a control means for controlling the rate of rise of the pulse voltage per time based on the output. electrical discharge machining equipment.