JPS61125723A - Electric discharge machine - Google Patents

Abstract

PURPOSE:To prevent wear damage of electrode and improve efficiency in normal time by providing quiescent time in applied voltage pulse of interpole with an abnormality discriminating signal from an interpole condition discriminating means regardless of presence of electric discharge and applying voltage continuously in normal time and eliminating discharge concentration. CONSTITUTION:When interpole machining condition is normal, pulse voltage is applied to interpole until electric discharge is generated without providing futile quiescent time so as not to make a switching element 15b OFF, and when machining condition of interpole is deteriorated to perform complete deionization, and concentration of electric discharge is eliminate and wear and damage of electrode are prevented. That is, when output Q of flip-flop 101 is 1, a switching element 15b is turned OFF via an amplifier 15d and when ON time setting output tau 9 of a counter 103 becomes 1, an AND gate 102 resets the flip-flop 101, then Q becomes zero (Q=0) and OFF time is obtained. And OFF condition is kept on until an OFF time setting terminal taur becomes 1, and taur becomes a predetermined OFF time of 0-1.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an electrical discharge machining apparatus that generates electrical discharge between an electrode and a workpiece, and uses the discharge energy to completely cut the workpiece.

[Conventional technology]

Conventionally, this type of electrical discharge machining equipment has two types of electrical discharge machining equipment: one that drills a hole in a workpiece using a rod-shaped electrode, and the other that drills a hole in the workpiece with a drill or the like and then passes the wire electrode through it. There is one that cuts the workpiece by moving the two relative to each other.

The outline of this electric discharge machining apparatus will be explained below by taking as an example the electric discharge machining apparatus using a wire electrode shown in FIG.

In Fig. 7, 1 is the workpiece, and at the start of processing, the spinning hole 1
An insulating liquid 3t is interposed between the wire electrode 2 passed through a and the wire electrode 2.

The above-mentioned insulating liquid 3 will be hereinafter referred to as a processing liquid. The processing fluid is
From the tank 4 to the bonder 5, the workpiece 1 and the wire electrode 20
The nozzle 6 sprays the liquid into the gap (gap between the poles).

The relative movement between the workpiece 1 and the wire electrode 2 is performed by moving the table 11 on which the workpiece 1 is placed.

Table 11Vi, Y-axis drive motor 13 and X-axis top-41
2. With the above configuration, the relative movement between the workpiece 1 and the electrode 2 becomes a movement in a 2tK plane within the aforementioned XXYl[Il plane.

The wire electrode 2 is supplied to a wire supply reel 7,
The wire passes through the lower wire guide 8A and the workpiece 1, reaches the upper guide 8B, and is wound up by the wire winding/tension roller IOK via the electric energy feeding section 9. As the control device 14 that drives and controls the drive motors 12 and 13 of the XSY axes, a numerical control device (tNc control device), a copying device, or a control device using computer sound is used. The processing power supply 18 that supplies electrical energy is composed of, for example, a DC current switching element 15a%, a current limiting resistor 15c, and a control circuit 15d&C controlling the switching element 15bl.

The operation of the conventional device will be briefly explained. A high-frequency pulse voltage is applied between the workpiece 1 and the wire electrode 2 from the machining power supply 15, and the workpiece @
Part of 1? : Melting and splattering vomiting.

In this case, since the gap between the electrodes is gasified and ionized due to the high temperature, a certain rest period is required before the next full pulse voltage is applied, and if this pause time is too short, the gap between the electrodes is insufficient. Before the insulation has been recovered, the discharge concentrates again at the same location, causing the wire electrode 2 to completely melt.

Therefore, with a normal machining power source, depending on the type of workpiece, plate thickness, etc., it is normal to process the electrical conditions such as the down time of the machining power source 15 with enough margin to prevent the wire electrode cutting metal from becoming active. It is. Therefore, the machining speed has to be considerably lower than the theoretical limit value, and furthermore, if the wire electrode 2 is not uniform and changes in thickness, or if there is a protrusion or scratch on a part of the wire and the discharge is concentrated. In this case, melting of the wire electrode 2 is unavoidable.

[Problem to be solved by invention]

As described above, in the conventional wire-cut electric discharge machining apparatus, in order to prevent the wire electrode 2 from discharging, the output energy of the machining power source 15 is reduced, so that if the concentration of electric discharge does not occur on the wire electrode 2. The problem was that the processing speed was extremely low because it was designed to prevent the wires from breaking even if they were concentrated at one point.

Conventionally, safety measures have been taken to determine whether the machining condition is good or bad or whether the electrode is about to be damaged, and based on this determination result, automatically restore the normal machining condition or completely avoid damage to the electrode, thereby increasing the machining speed. Efforts are being made to prevent a total decline.

In this case, the most common means for determining whether the machining condition is good or not, or whether the wire electrode is about to break, is to observe the average value of the voltage between the electrodes. In other words, when the average voltage value is low, the impedance between the electrodes is low, and insulation breakdown due to discharge is more likely to occur due to short circuits or accumulation of sludge or machining powder, resulting in discharge concentration (the main cause of wire breakage). ) is occurring.

However, when machining with narrow gaps (essential for high-precision machining), short circuits occur even under normal machining conditions, so if all short circuits were detected and safety measures were taken, machining efficiency would be significantly reduced. There was a problem with the decline.

This invention was made to solve this problem, and is an electric discharge machining device that can accurately determine whether the machining condition is good or bad without reducing the machining speed, and can prevent electrode damage accidents. The goal is to earn money.

[Means for solving problems]

The electrical discharge machining device according to this invention is! Detection means for detecting leakage current until a discharge occurs between opposing electrodes when a full pulse voltage is applied between the electrode and the workpiece, and a electrode for determining the state between the electrodes based on the ejection output. and control means for controlling whether to continue applying the pulse voltage until a discharge occurs between all poles or to repeatedly turn it on and off, based on the determination result. .

[Effect]

When the control means in this invention receives an abnormality determination signal from the inter-electrode state determination means, the control means sets a pause time for the bottom pressure pulse applied between the electrodes regardless of the presence or absence of discharge, and provides a deionization effect. Eliminates discharge concentration and prevents wear and tear on the electrodes. When receiving a determination signal indicating that the electrode spacing is good, voltage is continuously applied until discharge starts.
The machining efficiency is increased by increasing the discharge frequency.

〔Example〕

FIG. 1 is a schematic diagram showing an embodiment of the present invention, and numerals 1 to 15 are the same as those in the conventional device described above. 16
1 is a current detector for detecting the pulsed electricity i supplied between the machining power sources 15, and 17 is a control command signal generator, which has all inputs of the detected current from the current detector 16 and the voltage Vg between the machining holes. , a control device 14, a machining power source 15, etc., to supply control command signals.

FIG. 2 is a time chart showing the current waveform obtained from the current detector 16 in the circuit shown in FIG. signal (also shaping signal S1, electrode voltage signal Vg
t-threshold voltage■.

, the signal SvJ? was determined to be in a fully loaded state or during discharging.
j and the following two signals Sυ, s obtained from the above compensation code S, Sv
It is shown in D'. That is, a signal S in which current is flowing but not discharging. is written as the logical formula 5U-8v SI, which shows that leakage current exists during pulse application. Moreover, the signal SD is a logical formula S.

= Sv-SI, which indicates that there is no current at all during pulse application.

Figure 3 shows the signal group S described in the time chart of Figure 2.
□、Leakage current detection means 1 for obtaining 5v1 SUXSD
8 is an example of a circuit configuration. The signal waveform shaping circuit 19 of the current detector 16 generates a shaped signal SI, which is a signal indicating the presence or absence of current.

The electrode-to-electrode voltage vg is divided by a voltage dividing circuit r3,
Reference threshold voltage with level comparator 20
A comparison is made to see if it is larger or smaller, and it is determined whether it is a discharge state or a no-load state.

A signal S indicating the presence of leakage current. is outputted by the AND gate 21 in the form of the above-mentioned logical formula sU=sv-SI, and the no-load signal SD is outputted by the AND gate 22 in the form of the logical formula S
D: Output in the form of 5v-8I.

According to experiments, it has been found that when the signal S = 1, that is, when the leakage current is flowing in a no-load state, an interpole state occurs as described below.

(1) When @ n t l flows, the concentration of sludge, metal ions, etc. becomes abnormally high at one point in the gap between the electrodes, and the resistance becomes less than several hundred Ω.

(2) Signal SU continuously for several microseconds to 1 milliseconds! 1
In this case, if some countermeasure for deionization is taken, the state between the electrodes can be recovered, but if the condition continues for several tens of milliseconds or more, recovery is impossible and even wire breakage occurs.

(3) If there is a protrusion or a hole on the wire electrode, the electric field strength at that one point will become stronger inside the gap between the electrodes.
And the signal Sυ=1, and the concentration of discharge is 1.
Occurs after the point is dragged.

(4) When there is no leakage current and the signal SD = 1, the ion concentration is low and the condition between the electrodes is good, resulting in concentrated discharge,
No abnormal arc discharge occurred. However, the signal 5D-1 may sometimes occur even in an abnormal state. In this case, it does not persist (SD=1 does not continue for several milliseconds).

As described above, the gap state can be detected based on the signal SU and the signal SD. That is, (2) above,
As shown in (4), if the continuous amount of the signal SU and the signal SD or the way in which they occur can be analyzed, the interpole state can be detected.

Figure 4 shows the above signals S, , S, i and gate 23.2.
41, the number of input signals 5U1SD is counted by a reversible counter 25. Therefore, Shinji! If the ISU occurs more frequently than the signal S, the counter 25t: is multiplied and its contents gradually become larger.

When the integrated value of the counter 25 exceeds a predetermined value, for example 100, the digital converter 26 outputs a gap defect determination signal (hereinafter referred to as SA) at full output (SA=1). This signal SA is also applied to the negative input terminal of the AND gate 23 to eliminate the output from the AND gate, thereby preventing the contents of the counter 25 from increasing any further and overflowing or overscaling.

Further, the signal SA is supplied to a control means to be described later and is used for pole spacing recovery control.

When the state between the poles becomes normal and the signal sD=g i continues, the counter 25 starts subtracting, and finally, the content becomes Σ=O, so the output signal SB of the digital comparator 27 is changed to prevent further subtraction. ``f: Applied to the negative input terminal of the AND gate 24 to eliminate the output from the AND gate.

Therefore, what is the content of the counter 25? If the signal is converted into an analog quantity by the 1 digital to analog converter 28 and measured, the state between the 11C electrodes can be continuously monitored using the output signal St- of the converter 28.

FIG. 5 shows each signal S of the gap state discriminating circuit shown in FIG.
U% SD% SM I SM is analog output),
It is a time chart of SA and an inter-electrode current signal I and an inter-electrode voltage signal g indicating an inter-electrode state.

Hereinafter, an example of the control means 30 that controls whether to continuously or intermittently apply a pulse voltage to the gap between electrodes based on the abnormal discharge signal SA will be described with reference to FIG. 6.

When the machining condition between the machining holes is normal, the switching element 1 remains closed until a pulse voltage is applied to the machining gap and discharge occurs.
If the machining condition between the machining holes deteriorates, a stopping time is provided to completely eliminate the iodine/l-, even if no discharge occurs. The entire operation is to eliminate one factor in concentration: money.

In Figure 6, 101 is the R-S flip 170 knob,
When the output is Q-1, the switching element 15bi is turned on via the amplifier 15di. When Q=1, the AND gate 102 outputs the on-time setting output τ of the counter 103,
The output power is 10. until it reaches 41%. However, τP′
When it becomes 1, the free lag flop 101t is reset, so it becomes Q-0 and it is off time.

At this time, the output of the AND gate 102 is simultaneously reset to the oscillator (O3C) 110 and the counter 103 via the OR gate (OR gate) 104t, so that counting is performed from the beginning.

On the other hand, when Q-0 becomes Q-1, this off state is maintained until the input of one gate of the AND gate 105, that is, the off-time setting terminal τ, becomes 1, and until τ becomes 1 from 0. The predetermined period of time will be off time.

In the circuit shown in FIG. 6, the input gate 106 of the counter 103 passes the output of the oscillator O8C as it is, and makes a complete decision as to whether or not to perform the above-mentioned on/off control.
The input of input gate 106 is controlled by NAND gate 107. That is, when the abnormal discharge signal SA from the counter 25 is 1, that is, when the machining condition has deteriorated or when the inter-electrode voltage 2 is low due to short circuit, discharge, suspension, etc., the output of the oscillator O8C is counted by the counter 103. Ru.

In addition, R1-Rt is a voltage divider circuit for voltage divider circuit R7, 108 is a voltage comparator, and a reference voltage V+t'' is set from power supply 109 and volume VRK. , is higher than the reference voltage V1, the output becomes 1, and if the signal SA is O, the output of the NAND gate 107 becomes 0 and does not count.

Therefore, when the voltage between electrodes Vg is high, it is not counted, and short circuits and
Count the times of discharge, pause, and deterioration of the machining condition (, t, turn on/off of the switching element 15b f: repeat.

Incidentally, in the above description, the present invention is applied to a wire-cut electric discharge machining apparatus using wire electrodes, but it goes without saying that it can also be applied to an electric discharge machining apparatus using rod-shaped electrodes.

〔Effect of the invention〕

As described above, according to the present invention, after the full pulse voltage is applied between the workpiece and the electrode, the leakage [flow] is detected until the discharge occurs, and based on this detection result, it is determined that the discharge is normal. Since abnormal discharge is determined, it is possible to accurately determine whether the machining condition is good or bad without reducing the machining speed.

Based on the determined result, the pulse voltage is fully controlled as to whether it is applied continuously or intermittently, so when an abnormal condition is detected, a rest period is set for the pulse voltage applied between the poles, regardless of whether or not there is a discharge. , Group 1 by giving it a deionization effect! This has the effect of eliminating the concentration 11 to prevent damage to the electrodes, and if the gap between the electrodes is good, the pulse voltage is continuously applied until the discharge starts, increasing the discharge by a similar amount and improving the machining ability.

[Brief explanation of drawings]

FIG. 1 is a principle explanatory diagram showing an embodiment of the present invention, FIG. 2 is a time chart for explaining its operation, and FIG. 3 is a leakage current detection circuit diagram for detecting the gap state. II! Fig. 4 is a circuit diagram for determining the gap state, Fig. 5 is a time chart for explaining its operation, Fig. 6 is a block diagram showing the circuit configuration of the control means, and Fig. 7 is a conventional wire-cut electrical discharge machining device fi1'.
It is a principle diagram showing t-. 1... Workpiece, 2... Electrode (wire electrode),
18... Leakage fi current detection means, 29... Inter-electrode state determination means, 3o... Control means〇The same reference numerals in the drawings indicate the same or equivalent parts.

Claims (1)

[Claims] An electrode and a workpiece are placed opposite to each other with an insulating machining fluid interposed therebetween, and a pulse voltage is applied between the two electrodes to generate an electric discharge between the two electrodes, and the discharge energy is used to cause the workpiece to be machined. In an electric discharge machining device for machining an object, a detection means for detecting a leakage current in the period from application of the pulse voltage between the electrode and the workpiece until discharge occurs, and a detection means based on the detection output of the detection means. and an inter-electrode condition determining means for discriminating the inter-electrode condition and outputting a signal, and determining whether to continue applying the pulse voltage until it is discharged or to repeatedly turn it on and off based on the output of the inter-electrode condition discriminating means. An electric discharge machining apparatus characterized by comprising a control means for controlling the electric discharge machining apparatus.