JPS6034222A - Electric discharge machine - Google Patents

Abstract

PURPOSE:To improve the working efficiency by controlling the rising time of pulse voltage to be applied across an inter-pole gap on the basis of the output from an inter-pole state decision means between an electrode and work. CONSTITUTION:When applying proper pulse voltage across an electrode 10 and a work 14, the output from a counter 67 is provided through D/A converter 40 to an inverter amplifier 100 to be controlled by a pulse width pause width control circuit 18d thus to control a transistor Tr101. Here, the voltage to be applied across the poles is such that Vg=VBXt/REXC, where, the emitter voltage of Tr101 is VE, base voltage is VB, elasped time after application of pulse voltage is t and the capacitance of capacitor 102 is C. The gradient of inter-pole applying voltage per unit time dV/dt is varied on the basis of the output from an abnormal state detection/decision circuit such that under bad inter-pole state, it is rised slowly to suppress discharge thus to prevent concentrated discharge while under good state, it is rised quickly to promote discharge resulting in improvement of working efficiency.

Description

DETAILED DESCRIPTION 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 (1) between the machining electrodes to machine the workpiece. This invention relates to electrical discharge machining equipment for machining objects.

FIG. 1 shows a schematic configuration diagram of a conventional electric discharge machining apparatus. In FIG. 1, the electric current 5i10 faces the workpiece 14 placed in the processing tank 12 with an insulating processing fluid J6 interposed therebetween. A processing power source 18 is connected between the electrode 10 and the workpiece 14. The machining power supply 18 of B includes a DC power supply 18a and a switching element 18 for intermittent machining current.
b, the current limiting resistor 18c, and the switching element 1
8b, and an oscillator 18d for controlling the on/off of the machining current fIi10 and the workpiece 1.
4 and the gap 20 between the poles.

The above machining current ■ is, ■=-L−yL (E is the DC type source 1
8a voltage value, R is the resistance value of current limiting resistor 18c, V9
is the voltage between electrodes). The interelectrode voltage value v9 is 20 to 30v1 during arc discharge, OV1 during short circuit, EV during no discharge, and Ov 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 (2) 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, this average voltage value Vs is set as the reference voltage value V
t, and if this difference is amplified by the amplifier 24 and inputted to the hydraulic servo coil 26, the hydraulic servo mechanism composed of the hydraulic pressure generation pump 2B and the hydraulic cylinder 30 generates
The electrodes 10 can be controlled 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 measure IewA. That is, the average voltage value Vs
When is low, the inter-electrode impedance is low, and short circuits, continuous arc discharge, etc. may occur, and machining powder and sludge may remain in the inter-electrome gap 20. 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 (3), and the impedance between the electrodes becomes high. It becomes a state. Therefore, observation of the average voltage value Vs has the disadvantage that it is impossible to detect deterioration of the inter-electrode gap condition due to abnormal arc discharge.

The present invention has been made in view of the above-mentioned conventional problems, and its purpose is to analyze the frequency spectrum of the discharge voltage waveform of the gap between poles when a discharge occurs, to distinguish between normal discharge and abnormal discharge, and to determine the gap between poles. The rate of rise dV/dt of the voltage applied between the electrodes per hour is changed so that the condition becomes normal, and as the condition becomes abnormal, the rate of rise is decreased to make the rise of the applied voltage gradual, making it difficult to generate a discharge. The company provides electric discharge machining equipment that prevents the concentration of

In order to achieve the above object, the present invention provides an electric discharge machining apparatus that machines the workpiece by arranging an electrode and a workpiece to face each other with an insulating machining liquid interposed therebetween, and generating electric discharge in the opposing gap. , an abnormal discharge detection means that analyzes the frequency spectrum of the discharge voltage waveform between the electrode and the workpiece and identifies whether it is an abnormal discharge state or a normal discharge state; an interpolation state determining means for outputting a signal;
The present invention is characterized by comprising a control means for controlling the slope of the rise time of the pulse voltage applied to the gap between the electrodes based on the output of the discrimination means.

Hereinafter, preferred embodiments of the present invention will be described based on the drawings. Figure 2 shows a discharge voltage waveform and its frequency spectrum to explain the detection principle in the present invention. It can be expressed relatively easily, and the spectrum when the amplitude is E2, the period is T, and the pulse intensity is τ can be expressed as follows. (However, in the case of a discharge waveform, it is at random and is difficult to formulate.) However, the spectrum diagram in FIG. 2 for ω=−81 is described using the case of T=21 as an example. The following items can be determined from this spectral distribution and discharge state.

(1) Regardless of the state of the spectrum, the surrounding gll
Frequency f is the reciprocal of T(5). shows high output. However, in the case of normal discharge, the peak value is low compared to others.

(2) In the case of discharges such as those related to arcs, high frequency fi
(Approximately 2M1 (above z) hardly exists, and in the case of normal discharge, high frequency components are generated up to around 200MH without attenuation.

(If the output at 31fo is low and the output at fl is sufficient, it can be considered that normal discharge is occurring.

From the above results, it can be seen that if it can be determined that the state described in item (3) is present, abnormality in the discharge state can be identified.

FIG. 3 is a schematic diagram showing this embodiment, which basically has the same configuration as a frequency spectrum analyzer.

The voltage signal F(t) of the gap between the poles is mixed with the output signal Ht) of the FM modulation filter 51 by a mixer, and by heterodyne detection, an intermediate frequency j ( Only the frequency of t) is extracted and a difference is also produced, but
This is the intermediate frequency amplification N5 that is removed by the filter.
(6) The amplitude component is detected by the waveform 54 and amplified by the low frequency amplifier 55. The above-mentioned FM modulation signal 51 is frequency modulated by an analog voltage ^v, so by changing this analog voltage ^v in proportion to time, the relationship between time and frequency becomes linear, and F( It is possible to extract as the output of the low frequency amplifier 55 the amplitude of the frequency spectrum that is larger than the frequency of J(t) in t). Therefore, the time when the analog voltage ^ becomes a voltage corresponding to the aforementioned foSf can be determined by the accurate oscillator 56 and the counter 57 that counts the output.

581 is a classifier for etto, and 59 is a classifier for export.

The content of the counter 57 becomes an analog voltage ν by D/A conversion @1i60, which modulates the FM conversion @51. The level comparison @H61 responds to the timing signal from the fo discriminator or f discriminator and determines whether the amplitude amplified at a lower frequency, that is, the frequency spectrum, is larger or smaller than a predetermined reference value at that timing, Based on this result, an output S^ is output when an abnormal discharge occurs. For example, assume that fo is 3KIhfl is 5MH. Also, intermediate frequency 10
．． If it is 7MH2, f (t) is 10.693MH
z17) Time fH is 5,700 MH, 17) Time fH vector can be detected. If the FM converter 51 is of wide band type, 5 MH2 when the input voltage is Ov, 10 MH2 when the input voltage is IOV, and the D/A conversion is of 16 bit type, it is necessary to use a spectrum analyzer with a resolution of about ±80 H. Become. Further, since fo is always changed every time machining conditions are selected, it is necessary to perform calculation control of fo - up and down (however, the period T is the sum of on-time and off-time).

Now, regarding the above output SA, the level comparator 6 in FIG.
This will be explained in more detail using detailed explanatory diagram No. 1. Low frequency amplification f! The outputs of 55 are outputted by analog switches 62 and 63, respectively, to the comparator 6 in addition to the timing of fo discrimination and f discrimination.
4.65 is no longer connected. Do it N
At the 'b discrimination timing, the spectral amplitude pigeon is vl
If it is larger, the output of the comparator 64 will be “IN”, and the output of the comparator 64 will be “IN”,
Counter 67 is counted up via D gate 66. Further, at the fH determination timing, if the above vo is (8) larger than vl, the output of the comparator 65 becomes "1", and the AND
Since the counter 67 is reset via the gate 68,
This counter 67 is f. When the spectrum amplitude is large at the timing, the content increases, and when vo is large at the fl timing, the counter content immediately becomes zero. Therefore, if there is a high frequency component, the value becomes zero, and if the 'O acid component is large, the state increases.
It is also possible to determine whether the inter-electrode gap condition is good or bad by observing the analog voltage v6 using 0. In other words, if vo is large, it means that an abnormal discharge is approaching, and for example, sludge has accumulated in the gap between the poles due to the retention of machining powder, or carbon is generated due to thermal decomposition of the machining fluid 16 due to an abnormal arc. Problems such as a part of the electrode being damaged and its fragments being present in the interelectrode gap 20 can be easily detected.

However, in a very short period of time, the state of the gap between the poles is constantly changing, and even if the above-mentioned vo exists for a short time, it cannot necessarily be determined that the state of the gap between the poles is bad. So digital 1sp
It is necessary to determine whether the state of the gap between the poles is good or not by detecting that there is a time line in which the output vo of the converter @40 has a predetermined (9) value or more.

A voltage comparison N148 in FIG. 5 determines whether the output of the digital-to-analog converter 40 is larger or smaller than a predetermined jump. When V, > V, the output of the voltage comparator N148 becomes negative, turning off the switching transistor 152 via the pace resistor 150. Therefore, the time measuring capacitor 154 is charged via the resistor 156, and the voltage across the capacitor 154 is expressed by the following equation: VJI = V41 (1-e, zp r2C/), where r2 is the resistance The resistance value C of the capacitor 156 is compared with the voltage 3- across the capacitor 1540 by the reference voltage V and the voltage comparison signal 158. %, >V2. During the period , the output of the voltage comparison N158 does not become negative, so the light emitting diode 160 does not light up. Mote V.

(10) 〉When the condition of the tow continues for a predetermined period of time and reaches "Jl>V21," the output of the voltage comparison w158 becomes negative, and the light emitting diode 160 is turned on via the resistor 162 to indicate the occurrence of an abnormality in the gap between the electrodes. It is something to do.

The switch 164 is a switch for switching between determining the pole gap state only as a function of time or as a function of the product of the magnitude of the output V of the digital-to-analog converter 40 and time. That is, simply time t! In machining where it is difficult to determine abnormalities in the gap between poles, for example, when cracking due to arcing or chipping of tungsten occurs instantaneously, such as when machining cemented carbide, the product of the voltage difference and time can be used to detect cracks. The occurrence of an abnormality can be immediately known as a function of In other words, if the difference is large even for a short time, the charging current of capacitor C increases, and the capacitor voltage v3 immediately increases.
This is because the value reaches v2.

In addition, by observing the difference voltage V directly with a voltmeter,
It is clear that the difference between the optimum value and the current value can be directly measured in g and can be used as a monitor of the interpolar gap condition.

(11) Now, by changing the slope dV/dt per time of the voltage applied between the electrodes based on the output obtained by the above detection circuit, if the electrode gap condition is bad, it can be made to rise slowly. It is possible to improve machining efficiency by preventing discharge from concentrating, and by making it easier to start up the discharge when the condition is good.An example of this is shown in Fig. 6-1. The operation will be explained using the time chart of FIG. 7. Reference numeral 100 in FIG.
can be obtained by connecting the digital output of the D/A converter 40 to the D/A converter 40. ) is inverted and PNP) is added to the pace ξζ of the transistor 101. Now, the voltage v9 applied to the gap between the electrodes has the following value.

Vg=1cXt/C--11) Note that IC is the collector current of the transistor 101, t is the elapsed time after the pulse voltage is applied, and C is the capacitance of the capacitor 102. Next, Ic is approximately equal to the current flowing through the emitter follower load resistor 103 of the transistor (12) 101 (about 99X), and this Ic is
If the value of is RI:, it is expressed as follows.

Note that vE is the emitter voltage of the transistor 101, and v8 is the base voltage. Therefore, if the voltage applied between electrodes is V91, the voltage slope is dV/dtl! ,0~200v/p
It will change within the range of. In addition, since the inverting amplifier N100 is designed so that when the input is Ov, the output is 10V, and when the human power is 10V, it is Ov, so the larger Vo is, that is, the worse the gap condition is, the slope of the applied voltage is dV/d.
t decreases. The resistor 104 is for discharging the electric charge accumulated in the capacitor 02 so as not to affect machining, and the die 105 is for switching transistor 18 for machining.
This prevents the current from flowing backward 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.
, which prevents voltage from being applied to the gap between the electrodes during the rest period. The time chart in FIG. 7 specifically explains the above, and shows the relationship between the detection voltage Vo and the capacitor charging current 1c, and the on/off states of the transistors at a logic level of 1.0. .

According to this embodiment, when discharge is concentrated or an arc precursor state occurs, the content of the counter 67 of the detection circuit increases, the output of the inverting amplifier decreases, and the slope of the applied voltage becomes blunt, making it difficult to discharge and concentrating the discharge. This will no longer be the case, and the state of extremes will be restored.

In the above embodiment, the gradient of the applied voltage is controlled continuously according to the contents of the counter 67 of the detection circuit (14), but it does not necessarily have to be continuous; Even if it is changed in a series, it still meets the purpose of implementing the present 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 state based on the determination result. This is an unprecedented electrical discharge machining method that controls the ease with which electrical discharge occurs, prevents electrical discharge from concentrating on one point, prevents high voltage from being continuously applied without being deionized, and restores the gap state. The company provides equipment.

[Brief explanation of drawings]

Fig. 1 is a principle diagram showing a conventional electrical discharge machining device, Fig. 2 is an explanatory diagram of the principle according to the present invention, Fig. 3 is an explanatory diagram of a frequency spectrum analysis circuit, and Fig. 4 is an abnormal state detection/discrimination circuit diagram. FIG. 5 is a display circuit diagram thereof, FIG. 6 is a detailed explanatory diagram of the present invention, and FIG. 7 is a time chart showing the operating state of the device shown in FIG. 6. In the figure, 10 is an electrode, 14 is a workpiece, 18 is a processing power source, and 67 is an abnormality detection counter. )

Claims (1)

[Claims] In an electric discharge machining device, an electrode and a workpiece are opposed to each other with an insulating machining liquid interposed therebetween, and a pulse voltage is applied in the gap between the electrodes to generate an electric discharge to machine the workpiece. Detection means for detecting the distribution of frequency components in an electrical signal in the gap between the poles when a discharge occurs in the gap between the poles of the object;
a comparison means for comparing the distribution of frequency components detected by the detection means with a preset distribution of frequency components; and an interpolar gap for determining the interpolar gap state based on the output signal of the comparison means and outputting a signal. An electrical discharge machining apparatus comprising: a state determining means; and a control means for controlling the rate of rise of the pulse voltage per time based on the output of the determining means.