JPS6034220A - Electric discharge machine - Google Patents

Abstract

PURPOSE:To improve the working efficiency by controlling the ejection pressure or the suction pressure of working liquid to remove contamination from the inter-pole gap on the basis of the output from means for deciding the inter- pole state between the electrode and a work. CONSTITUTION:Working liquid sucked through a feed pump 100 from a working liquid tank 99 is fed through a solenoid valve 101 and manual value 102 to an ejection path 104 provided in an electrode 10. Upon exceed over predetermined pressure level, signal SB is fed back from a liquid pressure meter relay 105 to a controller 106 for said valve 101 to maintain specific pressure level of working liquid. Upon accumulation of chips in the inter-pole gap, signal SA is fed from an abnormal discharge detecting means for analyzing the frequency spectrum of discharge voltage waveform across the electrode 10 and a work 14 and for deciding whether it is abnormal discharge or normal discharge to a valve controller 106 thus to open the solenoid valve 101. Consequently, chips accumulated in the inter-pole gap are removed quickly by the ejected pressure to recover the inter-pole state.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electric discharge machining apparatus, in particular, an electrode and a workpiece (1) are faced to each other with an insulating machining liquid interposed therebetween, and an electric discharge is generated in the gap between the 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, an electrode 10 faces a workpiece 14 placed in a processing tank 12 with an insulating processing fluid 16 in between. A processing power source 18 is connected between the cutting edge 10 and the workpiece 14. This machining power source 18 includes a DC power source 18&, a switching element 18b for switching on and off the machining current, a current limiting resistor 18c, and the switching element 18b.
The machining current is intermittently supplied to the gap 20 between the electrode 10 and the workpiece 14.

The above machining current I is 1 = once turned - (E is the voltage value of the DC power supply scale 18a, R is the resistance value of the current limiting resistor 18c, ν
9 is the voltage between electrodes). Electrode voltage value v9
is 20 to 30v1 during arc discharge.When short-circuited, OV1 becomes EV1 during no discharge, and when the switching element 18b is in the off state, becomes Ov.

(2) Then, if this inter-electrode voltage value vg is detected and averaged by the smoothing circuit 22, the inter-electrode gap ¥Kll! Be able to do +. Also in Zunao), when the gap 20 between the electrodes 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, so the average voltage value Vs
decreases. Therefore, if this average voltage value Vs is compared with the reference voltage value Vt, and the difference between them is amplified by the amplifier 24 and inputted to the hydraulic servo coil 26, the hydraulic pressure generated by the hydraulic pressure generating pump 28 and the hydraulic cylinder 30 is The servomechanism allows the electrodes 10 to 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.
13131. That is, the average voltage value V
When s is low, the impedance between poles is low,
Short circuits and continuous arc discharge may occur, and machining powder and sludge may remain in the gap 20 between the poles. However, the most dangerous abnormal arc discharge in electric discharge machining is that once it occurs, carbon is generated due to the thermal decomposition of the machining fluid (3), resulting in an electric discharge between the carbon and the workpiece, and the impedance between the electrodes increases. 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 electrodes when a discharge occurs, to distinguish between normal discharge and abnormal discharge, and to determine the state of the gap between electrodes. By increasing the pressure of the machining fluid that is ejected or sucked into the gap between the poles so that the process becomes normal, substances that can cause abnormal arc generation such as machining powder, carbon, and sludge that have accumulated in the gap between the poles are discharged. It is an object of the present invention to provide an electrical discharge machining device which prevents discharge concentration by removing the discharge.

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 (4) and identifies whether it is an abnormal discharge state or a normal discharge state; and a control means for controlling the jetting pressure and striking of the machining fluid so as to eliminate contamination in the gap between the machining fluids based on the output of the discriminating means. Features.

Hereinafter, preferred embodiments of the present invention will be described based on the drawings. Figure 2 shows the discharge voltage waveform and its frequency spectrum to explain the detection principle in the present invention, and shows the voltage pulse that is simply applied without discharging as in the case of no discharge. In this case, the spectrum can be expressed relatively easily, and the spectrum when the amplitude is E2, the period is T, and the pulse width is τ can be expressed as follows. (However, the discharge waveform is at random and difficult to formulate.) However, ω= , ? The spectrum diagram in FIG. 2 has been described using the case of T=2τ as an example. The following items can be learned from this spectral distribution and discharge state (5).

The spectrum in either state shows a high output at a frequency f, which is the reciprocal of the period T. 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
-1 (approximately 2 MHz or more) hardly exists, and in the case of normal discharge, high frequency components occur up to around 200 MHz without attenuation.

(If the output at 31fO is low and the output at EH is sufficient, it can be considered that the discharge is normal.

From the above results, it can be seen that if it is possible to determine that the state is as in item 31, it is possible to identify an abnormality in the discharge state.

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

The voltage signal F(t) at the gap between the poles is FM variable l! 11M51
The output signal f (t) of is mixed by the mixed sugar, and by heterodyne detection, only the frequency of intermediate frequency 3 (tl) is extracted from the sum of frequencies of F (t) and f (t) (6) and a difference is also generated. However, this is amplified by the intermediate frequency amplifier 53 which is removed by a filter, and the amplitude component is detected by the detection M54 and amplified by the low frequency amplifier 55. Therefore, this analog voltage AV
By changing proportional to time, the relationship between time and frequency becomes linear, and ``(t) of FTt) changes at each time.
) can be extracted as the output of the low frequency amplifier 55. Therefore, the time at which the analog voltage ^ν reaches the voltage corresponding to the fo, fH mentioned above is accurate! ! ! ! 58 and a counter 57 that counts this output.

58 is a discriminator for f6, and 59 is a discriminator for fI. The contents of the counter 57 are converted into an analog voltage ^v by the D/A converter 60, which modulates the FM modulator 51. Level comparison @s61 is f. In response to the timing (No. 8) from the discriminator or the f1 discrimination booklet, determine whether the amplitude of the lower frequency amplification, that is, the frequency spectrum, is larger or smaller than the predetermined reference value at that timing (7). Based on the result, output SA is output when there is an abnormal discharge.For example, f is 3KH2, 11, 1 is 5M 11
Set it to 2. Also, if the intermediate frequency is 10.7M+(2),
f when f(t) is 10.693MH. is 5.70
At 0 MH, each spectrum of f can be detected. FM
If the variable W4JIN51 is of wide band type, 5MH when the input voltage is OV, and 10MH when the input voltage is IOV, and the D/A conversion is of the 16-bit type, the spectrum analyzer has a resolution of about ±80H. Also, regarding ■, f is always changed every time the machining conditions are selected. - It is necessary to perform some (however, period T is the sum of on-time and off-time) arithmetic control.

Now, regarding the above output SA, level comparison 11 of thickness 4 diagram
This will be explained in more detail using a detailed explanatory diagram of i61. The output of the low frequency amplifier 55 is prevented from being connected to the comparators 64, 65 by analog switches 62, 63 except at the timings of f, discrimination and f11 discrimination, respectively. Then, at the 10th discrimination timing, the spectrum amplitude V. is larger than vl, the output of the comparator 64 is 1'', and A
The counter 67 is counted up through the ND gate 66 (81).
1 determination timing, if the above-mentioned ■ is larger than vl, the output of the comparator 65 becomes "1", and the AND gate 6
Since the counter 67 is reset via f. When the spectral amplitude at the timing is large, the content increases, and when f) vo is large at the I timing, the counter content immediately becomes zero. Therefore, if there is a high frequency component, it will be zero, and if the fO acid component is large, it will increase. It is possible to determine whether the condition is good or bad.In other words, if VQ is large, it means that abnormal discharge is approaching, and for example, sludge has accumulated in the gap between the machining plates due to the retention of machining powder.
Problems such as thermal decomposition of the machining fluid 16 due to an abnormal arc and generation of carbon, or a part of the electrode being damaged and its fragments being present in the inter-electrode gap 2o can be easily detected.

However, for a very short time, the state of the gap between the poles is constantly changing, so even if the above-mentioned η exists for a short time, it cannot always be determined that the state of the gap between the poles is bad. So digital analog conversion @! It is necessary to determine whether the inter-electrode gap condition is good or bad by detecting that there is a time line in which the output vo of j40 is equal to or greater than the FLt value.

A voltage comparator 148 in FIG. 5 determines whether the output V of the digital-to-analog converter 40 is larger or smaller than a predetermined value 'vlI. When Vo>V, , voltage comparator 1
The output of 48 becomes negative, turning off switching transistor 152 via 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 formula: The resistance value C is the capacitance t of the capacitor 154, and the voltage V across the capacitor 154 is the reference voltage.
The light emitting diode 4-160 does not light up. Mote V.

When the state of 〉VII continues for a predetermined time and becomes V, > V, μ, the output of the voltage comparator 158 becomes negative, and the light emitting diode 160 is turned on via the resistor 162 to prevent the abnormal occurrence of the gap between the poles. It is to be displayed.

The switch 164 is a switch for switching whether to judge the state of the gap between poles only as a function of time or as a function of the product of the magnitude of the output (2) 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 That is, if the difference is large even for a short time, the charging current of the capacitor C will increase, and the capacitor voltage v3 will reach vz at f-.

Furthermore, by directly observing the voltage difference with a voltmeter, it is possible to directly observe the difference between the most advanced value and the current value, and it is clear that it can be used as a monitor of the gap between poles.

Therefore, by changing the machining fluid jetting pressure to the machining gap according to the presence or absence of the detection signal SA, the machining gap state can be restored. In FIG. 6, the machining fluid sucked up from the machining fluid tank 99 by the machining fluid supply pump 100 is
Pipe 1 via electromagnetic valve 101 and manual valve 102
03 and is connected to a jetting passage 104 provided in the electrode 10, and the machining fluid pressure is monitored by a fluid pressure meter relay 105, and when a predetermined pressure is exceeded, a feedback signal SR is output and the electromagnetic valve 101 controller 10
6 to maintain an appropriate predetermined pressure.

Further, the manual valve 102 is for maintaining the minimum pressure when the electromagnetic valve 101 is not operating. When the machining condition worsens and machining powder accumulates in the gap between the machining poles, the detection signal SA
is output and input to the valve controller 106, so the electromagnetic valve is opened and remains open until a signal is fed back from the hydraulic pressure meter relay 105. This-
f\19) Due to the strong jetting pressure, the machining powder present in the gap between the electrodes is quickly removed, and the condition between the electrodes is restored. When the pressure is recovered, the detection signal S is no longer output, and the electromagnetic valve 101 closes to return to the weak pressure set only by the manual valve. In addition, to explain why two types of pressure are necessary, generally speaking,
When the pressure is about 0.05 kg/cd, the impedance between the electrodes is most appropriate (the more dirty the electrode is, the easier it is to discharge and the stability of machining is better), and there is less wear on the electrode. Also,
When it is above 0.5 kg/aJ9, the electrode surface temperature decreases,
The generation of pyrographic material that protects the electrode surface can no longer be expected, resulting in increased electrode wear.Alternatively, the impedance of the gap between the electrodes becomes too high, making the gap length for discharge too narrow, making short circuits more likely to occur. Normally it is 0.05k due to problems such as unstable processing.
It is preferable to process at less than g/csf, and a high-pressure liquid flow is required only when the gap between the poles is too dirty or processing sludge accumulates in a part. According to experiments,
For copper electrode and iron combination, low pressure 0.05kg/cd
and high voltage 1 kg cj 1 copper tungsten (13) :;'H' Zene electrode and tungsten carbide, low voltage 0.2
kg/cd High pressure such as 4kg/cd has not been found to be effective.

As described above, according to the present invention, since the machining fluid jetting pressure is controlled in response to the quality of the machining gap condition, machining powder generated in the machining gap can be efficiently discharged, and machining Efficiency can be significantly improved. In other words, when machining powder is present in the gap between the machining electrodes, sparks from the discharge are generated along the path between electrode - machining powder -> workpiece, so a considerable proportion of the discharge energy is spent on thermal decomposition of the machining powder and machining fluid, resulting in machining. This has the effect of being able to prevent the phenomenon of speed reduction and preventing arc discharge due to processing powder and carbon caused by thermal decomposition. As described above, abnormalities in electrical discharge are determined by the detection method described above, and based on the detection results, machining fluid pressure is changed to remove machining powder and carbon particles in the gap between the machining holes in order to recover the machining gap condition. The purpose is to provide an unprecedented electric discharge machining apparatus that eliminates this and restores a good state.

Although this embodiment has been explained using examples of jetting and jetting (14), it is clear that the same effect can be obtained in machining using suction.

[Brief explanation of the drawing]

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, and FIG. 6 is a detailed explanatory diagram of the present invention. In the figure, 10 is an electrode, 14 is a workpiece, 18 is a processing power source, and 67 is an abnormality detection counter. Note that the same reference numerals in the figures indicate the same or equivalent parts. Agent Masuo Ookimi (15)

Claims (1)

[Claims] The electrode and the workpiece are opposed to each other with an insulating machining fluid interposed between them, and the machining fluid is pressurized and ejected from the gap between the machining poles, generating an electric discharge in the gap between the machining poles, thereby machining the workpiece. In an electrical discharge machining apparatus, a detection means detects the distribution of frequency components in an electric signal in the gap between the electrodes and the workpiece when electric discharge occurs in the gap between the electrodes and the workpiece, and a distribution of the frequency components detected by the detection means. a comparison means for comparing the distribution of frequency components set in advance; a pole gap state determining means for determining the state of the gap between the poles based on the output signal of the comparing means and outputting a signal; An electrical discharge machining apparatus characterized by comprising a control means for controlling the pressure of the machining fluid based on the