JPS5924921A - Electric discharge machine - Google Patents

Abstract

PURPOSE:To prevent generation of abnormal arc discharge by detecting the shock wave generated between a working gap during electric discharge and discriminating the working state according to the magnitude of the shock wave and varying and controlling the value of the pulse voltage applied to the gap. CONSTITUTION:When a workpiece 14 is electric-discharge-worked by an electrode 10, shock waves are generated at the moment when electric discharge is generated in a working gap 20, and the magnitude of the shock wave is large in normal electric discharge and is small in abnormal arc discharge. The detection signal for the shock wave by a sensor 35 and the detection signal for the discharge current by a current detector CT are inputted into a discriminating apparatus 40, and the electric discharge state such as normal electric discharge, abnormal arc discharge etc. are discriminated. The number of abnormal arc discharge in continuation is counted, and the pulse voltage value 18a of a power source 18 is controlled in accordance with said counted value. As the number of abnormal arc discharge in continuation is larger, the pulse voltage value is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electric discharge machine, in particular, an electric discharge machine, in which an electrode and a workpiece are opposed to each other with an insulating machining liquid interposed between them, and an electrical discharge is generated in the gap between the electrodes to treat the workpiece. The present invention relates to an electrical discharge machining device for machining.

FIG. 1 shows a schematic configuration diagram of a conventional electric discharge machining apparatus. In FIG. 1, an electrode 10 faces a workpiece 4 placed in a processing tank 12 with an insulating processing fluid 16 in between. 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 18 for intermittent machining current σ)
b, the current limiting resistor 18c, and the switching element 1
The machining current is intermittently supplied to the pole 11ft gap 20ζ between the electrode 10 and the workpiece 14.

The above machining current I is expressed by the following formula: Hail to you.

The period voltage value v9 is 20 to 30V during arc discharge, 11ζV during Ov1 non-discharge during short circuit, and 0■ when the switching element 18b is in the blank state.

Therefore, if this inter-electrode voltage value v9 is detected and averaged by the smoothing circuit 22, the inter-electrode gap control can be performed using the value B. In other words, 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 amplification N 24 and a force is applied to the hydraulic servo coil 26, the hydraulic pressure generating pump 2 and the hydraulic cylinder 30 are configured. The electrode 1o can be controlled by the hydraulic servo mechanism so that the gap 20 between the electrodes is approximately constant.

When determining whether the machining state is good or bad with conventional electric discharge machining equipment, the most common method is the average voltage value Vs of the above-mentioned machining voltage value V9.
It is to [measure]. In other words, when the average voltage value Vs is low, the impedance between the electrodes is low, and short circuits and
Continuous arc discharge occurs, and machining powder and sludge may remain in the gap 20 between the electrodes. However, the most dangerous abnormal arc discharge in electric discharge machining is that once 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. For this reason, observation of the average voltage value V++ has the disadvantage that it is impossible to detect aiirrIJ or deterioration of the a-gap condition due to abnormal arc discharge.

The present invention has been developed 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 gap state between the poles, and when it is determined that the 011 drive state with abnormal arc occurrence occurs, the machining power supply It is an object of the present invention to provide an electric discharge machining apparatus which prevents the concentration of electric discharge and the occurrence of abnormal arc discharge by lowering the applied voltage to make the electric discharge 9i.

In order to achieve the above object, the present invention provides an electric discharge method for machining the workpiece by arranging an electrode and a workpiece to face each other with an insulating machining liquid interposed therebetween, and generating an electric discharge in the gap between the electrodes. In the machining device, abnormal discharge detection means detects shock waves such as ultrasonic waves generated in the gap between the electrode and the workpiece by a detection means installed in the machining fluid, and detects an arc precursor phenomenon due to concentrated discharge; An inter-electrode gap condition determining means for determining an inter-electrode gap condition based on the magnitude of the shock wave and outputting a signal;
The present invention is characterized by comprising means for changing and controlling the applied value of the Panotos voltage based on the output.

Hereinafter, a preferred embodiment of the present invention will be described based on Drawing 1ζ. 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 the third
As shown in the figure. In the upper diagram of Figure 3, a discharge current I flows at each time from t1 to t4, and the machining fluid near the point of discharge is approximately 6,000 yen.
Due to the high temperature close to 100°F, a rapid vaporization explosion occurs and bubbles are generated. As a result, the nearby machining fluid undergoes a rapid pressure change, which propagates into the narrow gap between the poles as an ultrasonic shock wave, and is transmitted to the ultrasonic sensor 35 via the electrode.
It is detected by electric signal and ().During normal discharge,
The above-mentioned shock waves are detected at irregular intervals fiυ depending on the magnitude of the current, but if the discharge occurs concentratedly at one point, the ionic concentration at that point will increase at an accelerating rate. Due to the increase in carbon density due to thermal decomposition of processing powder and processing fluid, II, which approaches a non-insulating state, increases. In such cases, at the discharge point, the bubbles disappear due to discharge (usually 0.1~
Since the discharge is performed again before the discharge (about 2 m5ee is required), 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 impact force of the generated ultrasonic wave 1ti is also reduced. 40 in Fig. 2 detects normal discharge and abnormal discharge based on the above Re 161 operating principle, and as shown in Fig. 3, the ultrasonic pressure due to the discharge stream generated at t5 is detected at t5.
When a situation in which this value is -C smaller than that during normal discharge occurs a certain number of times in a row (this is determined as abnormal discharge).

FIG. 4 is a detailed diagram of the device 40 described in "2", in which the output of the ultrasonic sensor 35 is amplified by an amplifier 41, and a signal S
. will occur. A peak hold circuit 42 stores the highest value of the signal S. That is, in the integrating circuit 43, only a voltage higher than the highest output of the integrating circuit 430 is charged to the capacitor C of the integrating circuit through the resistor R via the analog switch 44 and the comparator 45. Therefore, the output of the voltage dividing resistor 46 is
This is a partial pressure of the highest output during normal conditions, and is used to distinguish between normal and abnormal conditions.

This is because the explosion pressure changes depending on the discharge energy and energy application time, and in machining that requires many types of energy, from rough machining to fine finishing machining, such as electric discharge machining, it is uniformly Since it is difficult to standardize the normal tFi impact force, it is necessary to compare it with the most normal impact force using a peak hold circuit 42 like the 111 device 40.

A comparator 47 generates a circular wave signal S. is determined to be correct or not, and inputted to the counter 49 as a reset pulse. The current detection pulse S process detects the current using a current transformer CT and increases lll1i! The signal is input to the counter 49 via the shaping circuit 50 as an up-count signal. In this lever circuit, each time a current flows through the gap between the poles, +1t! The counter is counted, and immediately after that, it is reset 2ζ when it is a normal discharge, so the counter contents do not increase. If an abnormal discharge occurs and the conditions like t4 and t5 in Fig. 3 continue, the counter 49 will not be reset, so the internal field will increase more and more, and when it reaches the amount set in switch 5], it will start emitting light. The input of the driver 53 of the diode 52 becomes II II II level, 52 lights up, and the output signal SA of 51 becomes 1°° level and is output to the outside. This is to prevent it from increasing further when the amount increases.

The embodiment shown in FIG. 5 is an example in which the voltage applied to the gap between the electrodes is changed based on the above output signal, and if the discharge starting voltage is lowered, it becomes difficult to cause a discharge, and the discharge at the same gap between the electrodes becomes more difficult. It can prevent concentration. Also, if there is no discharge concentration,
By increasing the voltage applied to the gap between the electrodes, it is possible to increase the speed of discharge in the same discharge gear V-tube.

Reference numeral 100 in FIG. 5 is an amplifier for amplifying and applying an analog voltage corresponding to the output of the control circuit 11540 to the base ζ of the transistor 51. Note that the analog pressure is the output Q of the Karin-49.

By connecting the digital-to-analog converter 102 to Q, , Q, , Q4, and Q5, 111 seconds can be calculated. Now, the voltage v9 applied to the gap between the electrodes is expressed as follows.

v9=-1CR1,... (1) Also, Ic is the emitter follower load R of the transistor 51
It is approximately equal to the current flowing through 2+ζ (approximately 992), and is expressed as Ic of Otsu. Therefore, v9 is v from equations (1) and (2).
9 ” --ELl/Is ---=!31
R.

becomes. Here, R, = 30KQ, R, = i K Q
, E = 300V, the voltage changes from 0 to 300V by 1' due to a change from 0 to IOV.

As a result, discharge concentration occurs and the contents of the counter 49 increase, the output of the reverse increase [PJllol decreases, and the interelectrode gap voltage v9 decreases and is released? It disappears during lim.

In addition, in the above embodiment, the voltage applied between the electrodes is continuously changed according to the contents of the discharge concentration detection surface @40, but the counter contents and the voltage do not necessarily have a proportional relationship. Changing the ratio is more effective in preventing arc discharge transfer.

As described above, according to the present invention, the concentration of discharge can be reduced to the discharge F71.
It is possible to provide an electric discharge machining apparatus that is unique and unprecedented in that it discriminates the wave size based on the size of the wave and controls the voltage applied to the gap between the poles to improve discharge dispersion.

[Brief explanation of drawings]

1st is a principle diagram of the conventional 11i electric machining device, 2nd is a principle diagram of the device according to the present invention, 3rd is a time chart 1 for explaining the detection device according to the present invention, and 4th figure is is a diagram of the detection device and abnormal discharge discrimination device, 5th v! ! Jl yo pole 11611
11 is an explanatory diagram of a control circuit for applying a voltage lrI in the gap. In the figure, 1011i1ii, 14 is the workpiece, 16 is the machining liquid, 35 is the detector, 40 is the control circuit, 49 is /js (detection counter during electric result), and 51 is the applied voltage control transistor. Note that the same reference numerals are used in the figure. indicates the same or a corresponding portion. Agent Nobu 8 No.

Claims (1)

[Claims] In an electric discharge machining device that processes the above-mentioned workpiece by placing an electrode and a workpiece facing each other with an insulating machining fluid interposed therebetween, and applying a pulse voltage to the gap during the period to generate an electric discharge,
Impact % when electric discharge occurs in the gap between the electrode and the workpiece! ! A detection means for detecting waves, and a wave detected by the detection means [
The apparatus is equipped with an inter-electrode gap condition determining means for determining the inter-electrode gap condition based on the magnitude of the shock wave and outputting a signal (No. 4), and a means for changing and controlling the applied value of the pulse voltage based on the output of this determining means. An electrical discharge machining device characterized by: