JPS59205236A - Electric discharge machining device - Google Patents

Abstract

PURPOSE:To remove sludge etc. forcedly by sensing the time distribution condition from voltage impression till generation of electric discharge, judging whether it is normal or abnormal discharge, and then controlling the pressure of machining liquid so as to restitute to normal condition. CONSTITUTION:Time distribution condition in the gap between electrode 10 and a work to be machined 14 from impression of voltage till generation of electric discharge is sensed to be compared with the reference distribution condition, and the result is used to judge the condition of the interpolar gap, and if the state of the gap is considered to have worsened, a sensing signal SA is emitted. In accordance with the sensing signal SA, a controller 106 opens a solenoid valve 101 to allow a pump 100 to supply the machining liquid to a jet path 104, and there the liquid pressure is boosted above the pressure liquid obtained with a manual valve 102, and if a certain specified pressure value is exceeded, a feedback signal from a liquid pressure meter relay 105 maintains the pressure at a proper set value. Thus splash etc. produced in the interpolar gap can be exhasuted effectively to ensure a well improved machining 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 electrical discharge is generated between the opposing electrodes to machine the workpiece. This invention relates to electrical discharge machining equipment.

FIG. 1 shows a schematic configuration diagram of a conventional electric discharge machining apparatus. In FIG. 1, the electrode head faces a workpiece α4 placed in a processing tank with an insulating processing liquid θG interposed therebetween. A processing power source (to) is connected between the electrode αO and the workpiece 041. This processing power source (2) is a DC power source (18a
) and a switching element (
is'b), a current limiting resistor (18C), and an oscillator (18d) for controlling the switching element (181)), and the machining current is intermittently connected to the electrode 00 and the workpiece α4. Supply to the gap between the poles.

Processing military engineering is T = E vg (E is DC power supply (1
8a) is a positive value, R is the resistance value of the current limiting resistor (180), and Vg is the voltage between electrodes. The interelectrode voltage value Vg is 20 to 80■ during arc discharge, Ov during short circuit,
During no discharge, it becomes EV, and when the switching element (18b) is in the off state, it becomes 0■.

Therefore, if this inter-electrode voltage Vg is detected and averaged by the smoothing circuit (a), it is possible to perform gap control using this chain.In other words, when the inter-electrode gap is wide, discharge is less likely to occur.
<The average pressure value Vs is high. When the gap between the electrodes is narrow, short circuits or discharges occur easily, so the average voltage IVs decreases. Therefore, if this average voltage value Vs is compared with the reference electric current 'Vr, and this difference is amplified by an amplifier and inputted to the hydraulic servo coil wire, the hydraulic pressure generated by the hydraulic pressure generating pump wire and the hydraulic cylinder ω is The servo mechanism ensures that the gap between the trees is almost constant. r can be controlled.

When determining whether the machining state is good or bad using a conventional electrical discharge machining apparatus, the most common method is to observe the average voltage value Vs of the machining voltage value Vg. That is, when the average voltage value VS is low, the inter-electrode impedance is low, resulting in short circuits and continuous arc discharge, and it is possible that machining powder and swamp particles remain in the inter-electrome gap. 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 a discharge between the carbon and the workpiece, and the impedance between C and fM increases. The situation will be as follows. For this reason, observation of the average voltage value Vs has the drawback that it is impossible to detect the deterioration of the original state from time to time due to abnormal arc discharge.

The present invention was made in view of the above-mentioned conventional problems, and detects the time distribution state from voltage application to the occurrence of discharge, and distinguishes between normal discharge and abnormal discharge based on the detection result. By fully controlling the pressure of the machining fluid supplied to the gap between the rods and forcibly removing the sludge and machining powder that has accumulated in the gap between the rods, so that the gap between the rods returns to its normal state. It is an object of the present invention to provide an electrical discharge machining device which prevents the concentration of electrical discharge and prevents the occurrence of abnormal arc discharge.

In order to achieve the above object, the present invention provides an electrical discharge machining apparatus that machines the workpiece by arranging an electrode, a workpiece, and a completely insulating machining fluid to face each other, and generating electric discharge in the gap between the electrodes. In this step, the distribution state of the time from the voltage application to the occurrence of electric discharge in the gap between the electrode and the workpiece is detected, and the detection result is compared with a typical distribution state indicating the quality of the bar gap condition to determine the bar gap condition. A means for determining that the gap between the poles is in a bad state based on the above detection result and outputting a signal, and a means for outputting a signal based on the output to determine whether the original gap between the poles is in a good state! The present invention is characterized by comprising a control means for controlling to recover IIC.

Preferred embodiments of the present invention will be fully explained below based on the drawings.

Fig. 2 shows the discharge pressure waveform for clarifying the detection +g-con of -fQ in the present invention, and the distribution state of the no-discharge time in that waveform until the immediate pressure application discharge starts. , l:9 is the result obtained. Note that the discharge start point is determined by the time point at which the voltage falls.
A signal is also output when the pulse is on and off. The following has been found from the relationship between this distribution state and the interpolar state.

(6) Except for the open state between the electrodes (the state where the electrode and workpiece are completely separated and are not being processed), 5 μm after voltage application.
The rate of initiation of discharge within seconds is high.

(G) In the pre-arc state, the rate of complete discharge initiation within the above 5 μsec exceeds 70%.

(Q: If the safety level of the servo system is poor and a hunting state occurs, no discharge and short circuit will occur repeatedly, and there will be no discharge distribution after 5 μs.

(Odor) During normal discharge, the distribution up to 5 μs after voltage application is 3
The distribution is approximately 0% and then gradually decreases.

(g) The distribution when the arc state is reached is as shown in (8) above and (
(g)) are repeated alternately at intervals of several seconds.

This is probably because the abnormal arc discharge caused a discharge between two carbon atoms, and the mode of the discharge was different from the usual combination of electrode and workpiece in electric discharge machining.

(g) When the gap between the poles is made extremely narrow, it becomes similar to the arc precursor state described in ◎ above, but even then, the distribution between 5 μsec and 80 μsec is more than 10%.

0 If the inter-electrode servo is performed so that the inter-electrode gap is widened, 10~
20% discharges within 5 microseconds and then gradually decreases.

Based on the above results, it can be determined that the unipolar gap condition is not abnormal if the following conditions exist.

(1) There are 10% or more pulses that start discharging in 5 μ to 30 μ seconds.

(2) The ratio of pulses that discharge within 5 μs does not exceed 50%.

(3) Even at τp, the ratio of no discharge does not exceed 50%.

FIG. 3 is a schematic diagram including this embodiment, in which a switching transistor (18b) that applies a voltage to the gap between poles and causes a discharge current to flow is driven by a switching amplifier 7' (18e), and an amplifier (18e). ) is generated by a pulse pause generation circuit (18f). This (18f) basic clock pulse is generated by a clock pulse generator (18g). Since the frequency of the clock pulse is also used for sampling the time until the discharge of the voltage applied between the electrodes, a total frequency of 1 or more is required. TON is a circuit that detects the fall of the voltage between electrodes, and is divided by resistors rl and r2, and is connected to a comparator (50a).
), the signal at the point when it is lower than the reference voltage Vr is connected to the resistor r3
, falling differential IEI composed of r4 capacitor CI
It is taken out as a signal S2 by the l path. ψ1) is a discharge state determination port 1, and the operation content 'fr: will be explained below using FIGS. 4 and 5. A voltage is applied to the gap between the two plates, the ring counter 6 operates, and the QR gate wt:
mu, the gate becomes open every time. For example, OR
The output of the gate so is 1' for 0 to 5 microseconds.When discharge occurs during this period and the direct voltage fall signal S2 is input, the output is output through the AND gate 6 (4). counter 6
91 (joi (61)), the number of pulses along the discharge section for each section in a predetermined period is counted.The predetermined time is 10 to BOm, considering the speed of the original state deterioration from time to time.
Seconds are considered appropriate based on experimental results. The contents of these counters are determined by a digital comparator, and it becomes clear how many or fewer pulses are discharged in a given time and with what distribution of no-load voltage application time. As mentioned above, the distribution status is classified into distributions that are determined to be abnormal and distributions that are determined to be normal, and if the distribution is determined to be abnormal, the distribution is further counted by the counter.

In addition, in the case of a distribution that is judged to be normal, the counter @all resets, so when it is judged as an abnormal state, that is, the rate of discharge within 5 μs after voltage application is 50% or more. The content of b increases when the rate of non-discharge at the end of the pulse is 50% or more, and the counter 6η is immediately reset when there are 10% or more of the pulses that discharge in 5 to 30 μsec. Therefore, if it is normal, it will be zero, and if it is abnormal, the counter content will increase. Therefore, the counter content can be changed very easily by observing the analog voltage 0 using the DigiCure Analog Converter (A). It is possible to determine whether the gap condition is good or bad. In other words, if the analog voltage VO is large, it is close to an abnormal discharge.For example, slough may have accumulated in the gaps between the bars due to the accumulation of workpiece powder, or the machining fluid OG may have been thermally decomposed due to an abnormal arc. It is easy to detect problems such as carbon being generated in the electrode, or a part of the electrode being damaged and its fragments being present in the gap between the electrodes.

However, for a very short period of time, the pole-to-bar gap condition is constantly becoming poorer, and even if there is a short-time analog voltage Vo, it cannot necessarily be determined that the bar-to-bar gap condition is bad. Therefore, it is necessary to determine whether the gap between the rods is good or not by detecting that the output Vo of the digital-to-analog converter continues to be at or above a predetermined value for a certain period of time.

Voltage comparison in Figure 6! (148) is a digital-analog poor converter (41 that determines whether the output Vo is larger or smaller than a predetermined value V11. ■○) When it becomes V++, the output of the voltage comparator (148) becomes negative, and the base Resistance (150
) 'r: Intermediate, te switching transistor (15
2) is turned off. Therefore, the time measurement capacitor (154) is a resistor (156)'! i: is charged through the capacitor (154), and the voltage across the capacitor (154) is developed as follows.

rZ Supervisor C V31-■4I (1-eXp) However, rZ1 is the resistance value of the resistor (156) C is the capacitance t of the capacitor (154) is the time m pressure across this capacitor (154) V31 times the base voltage VH and the voltage A comparator (158) compares them. V31<V
During period 21, the output of the voltage comparator (158) does not become negative, so the light emitting diode (160) does not light up.

Then, the state of Vo') Vu continues for a predetermined time ■31>
■2! When this occurs, the output of the voltage comparator (158) 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 state.

The switch (164) is a switch for switching whether to judge 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 ((0) and time. In other words, by simply detecting time, l''j: In machining where it is difficult to determine abnormalities in the gap between poles, for example, when machining cemented carbide, arc cracking or tungsten chipping occurs instantaneously. , when the switch (164) is turned on to the contact (164a) side as shown in the example, the output of the digital-to-analog converter (to) ■0
As a function of the product of and time, the occurrence of an abnormality in the polar gap state can be quickly detected. If the above output 'Vo is large, the charging current of the capacitor (154) increases, and the voltage V31 across the capacitor (154) immediately changes to the reference voltage V.
This is because it reaches 21.

Furthermore, it is clear that by directly observing the output VO with a voltmeter, it can be used as a monitor for the state of the gap between the rods.

Therefore, by changing the machining fluid jetting pressure to the machining gap depending on the presence or absence of the detection signal SA, the machining gap state can be restored. In figure ig7, the machining fluid sucked up from the machining fluid tank by the machining fluid supply pump 0 (a) is supplied to the electromagnetic valve (101) and the manual valve (1 (+2)'
i through the pipe (103) all the way through this pipe (10
B) is connected to the jetting passage (104) provided in 1jO, and the machining fluid pressure is monitored by a fluid pressure meter relay (105), and when the pressure exceeds a predetermined value, a feedback signal ``SE'' is output and the A feed pack is applied to the controller (106) of the valve (101) to maintain an appropriate set pressure 'f'. Note that the hand valve (102) is for maintaining the minimum pressure when the electromagnetic valve (101) is not operating. When the machining condition deteriorates and machining powder accumulates in the spaces between the condyles, a detection signal SA is output, and this signal S
Since A is input to the valve controller (106),
The electromagnetic valve (101) is opened and remains open until signal feedback is received from the hydraulic pressure meter relay (105). Due to this strong ejection pressure, the machining powder present in the gap between the machining plates is quickly removed, and the condition between the machining plates is restored.

Once recovered, the detection signal S7 is no longer output, the electromagnetic valve (101) closes, and the pressure returns to the weakening pressure set only by the manual valve (1, 02). In addition, to explain why two types of pressure are necessary, in general, the impedance between electrodes is most appropriate when the pressure is about 0.05 k, 7 d (moderately dirty is easier to discharge, Good processing stability.)
, the wear of the electrode αO is also small. In addition, if it exceeds 0.5 kg/d, the surface temperature of the electrode 01 will decrease, and the generation of pyrographic material that protects the electrode 000 surface cannot be expected, and the wear of the electrode 01 will increase. is too high, the gap length for discharge becomes too narrow, short circuits are likely to occur, and machining becomes unstable, so it is usually 0. o5kg/ai
It is preferable that the machining process be carried out below, and a high-pressure liquid flow is required only when the machining gap is too dirty or machining sludge accumulates in some areas. According to experiments, the combination of copper electrode and iron has a low pressure of 0.05 kg/d and a high pressure of 1
Next/Cd, low pressure 0.2 kg/c for copper tungsten electrode and tungsten carbide! High pressure 4 kg/
d etc. have been found to be effective.

As described above, according to the present invention, since the machining fluid ejection pressure is controlled in response to the quality of the gap between the machining plates, the machining powder generated in the gap between the machining plates is efficiently discharged, and the machining powder is efficiently discharged. Efficiency can be significantly improved.

In other words, when machining powder is present in the gap between the machining plates, sparks from the discharge are generated along the path of electrode → machining powder → workpiece, so a considerable proportion of the discharge energy is spent on thermal decomposition of machining powder and machining fluid. It is possible to prevent the phenomenon of slowing down the processing speed, and to reduce arcing caused by processing powder and carbon caused by thermal decomposition.
i) It has the effect of being able to prevent it from happening. In addition to the above, in order to determine the discharge abnormality using the detection method described above, and to recover the gap state based on the detection result, the machining fluid pressure is changed and the machining powder in the gap is determined. The purpose is to provide an unprecedented electric discharge machining apparatus that eliminates the power and force and restores the machine to a good state.

In addition, although this example has been explained using examples of ejection and injection,
It is clear that the same effect can be obtained when processing by suction.

[Brief explanation of drawings]

Fig. 1 is an original diagram showing a conventional electric discharge machining device, Fig. 2 is an explanatory diagram of the principle of the present invention, Fig. 3 is a schematic diagram of the detection circuit of the present invention, and Fig. 4 is a diagram of the detection circuit. 5 is a time chart for explaining the circuit of FIG. 4, FIG. 6 is a detailed diagram of the circuit for discriminating the original state of the gap between poles, and FIG. FIG. 4 is a diagram showing an embodiment of the present invention of a control means for controlling. In the figure, 00 is an electrode, 0 brown is a workpiece, (c) is a machining failure source, and (2) is an abnormality detection counter. Note that the same reference numerals in the figures indicate the same or equivalent parts. Agent Masuo Oiwa 2nd figure late 114s
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2-- Ring Sa1, Indication of the case Japanese Patent Application No. 58-78719 29 Name of the invention Electric discharge machining device 3, person making the amendment Relationship to the case Patent applicant address 2-3 Sara-chome, Marunouchi, Chiyoda-ku, Tokyo Name (601) Mitsubishi Electric Co., Ltd. Representative Hitoshi Katayama 4, Agent 6, Date of amendment order August 8, 1980 (shipment date) 6, Subject of amendment (1) Full text of specification 7, Amendment Contents (1) Engrave the entire specification as shown in the attached sheet. , (No change in content) 8. List of attached documents (1) At least 1 statement

Claims (1)

[Claims] The electrode and the workpiece are placed facing each other with an insulating processing fluid interposed between them.
The electric discharge machining device generates an electric discharge between the electrodes and processes the entire workpiece, and detects the entire state of distribution of time after voltage application when electric discharge occurs between the electrodes and the workpiece. and a distribution state of the time from voltage application to discharge occurrence detected by the detection means is compared with a distribution state indicating the quality of the interpupillary gap state set in advance, and a signal is output after determining the entire interpupillary gap state. An electrical discharge machining apparatus comprising: a machining gap state determining means; and a control means for changing and controlling the pressure of the machining fluid supplied to the machining fluid gap based on the output of the discriminating means.