JPS61111813A - Spark erosion apparatus - Google Patents

Abstract

PURPOSE:To prevent the electrodes from being damaged without reducing the working speed by judging the between-electrode state on the basis of the arc voltage level and changing the application state of the pulse voltage applied between a workpiece and an electrode according to the result of the above- described judgment. CONSTITUTION:The pulse current supplied into between electrodes from a working power source 15 is detected by a current detector 16, and the output is input into a control instruction signal generator 17. Said control instruction signal generating apparatus 17 judges the between-electrode state on the basis of the comparison between the arc voltage level and a set standard value, and supplies the control instruction signal into a controller 14 and the working power source 15. Therefore, the operation is controlled to continue the application of the pulse voltage between a workpiece 1 and an electrode 2 until electric discharge or to the repetition of the ON/OFF operation.

Description

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

[Conventional technology]

Conventionally, this electric discharge machining apparatus for rice has two types: one machine drills a hole in the workpiece with a rod-shaped electrode, and the other machine drills a hole in the workpiece with a drill or the like, and a wire electrode completely passes through the spindle hole drilled in advance in the workpiece. 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, taking as an example the electric discharge machining apparatus using a wire electrode shown in FIG.

In FIG. 7, reference numeral 1 denotes a workpiece, and an insulating liquid 3 is interposed between it and a wire electrode 2 passed through seven spinning holes 1a.

The above-mentioned insulating liquid 3 will be hereinafter referred to as a processing liquid. The processing fluid is
From tank 4 to pump 5, workpiece 1 and 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.

The table 11 is driven by a Y-axis drive motor 13 and an X-axis motor 12.
Driven by. With the above configuration, the relative motion between the workpiece 1 and the electrode 2 becomes a two-dimensional subplane motion within the aforementioned XXY-axis plane.

The wire electrode 2 is supplied by a wire supply reel 7,
The lower wire guide 8A passes through the workpiece 1 and reaches the upper guide 8B via the electric energy feed section 9, where it is wound up by the wire winding/tension roller lOK.

The control device 14 that drives and controls the drive motors 12 and 13 for the X and Y axes is a numerical control device (NC control device), a copying device, or a control device using a computer.

The processing power supply 15 that supplies electrical energy is composed of, for example, a DC power supply 15a, a switching element 15b1', a current limiting resistor 15c, and a control circuit 15d that controls the switching element 15b.

Next, the operation of the conventional device will be explained. A high-frequency pulse voltage is applied between the workpiece 1 and the wire electrode 2 from the machining power supply 15, and a part of the workpiece 1 is melted and scattered by a discharge explosion due to one pulse.

In this case, the gap between the electrodes is gasified and ionized by the high temperature, so a certain pause time is required before applying the next pulse voltage, and if this pause time is too short, the insulation between the electrodes will not recover sufficiently. Before this occurs, the discharge concentrates again at the same location, causing the wire electrode 2 to melt.

Therefore, with a normal machining power source, depending on the type of workpiece, plate thickness, etc., it is normal to set the electrical conditions such as the down time of the machining power source 15 with enough margin to prevent the wire electrode from breaking. be. Therefore, the machining speed must be considerably lower than the theoretical limit value. Furthermore, if the wire electrode 2 is not uniform and its thickness changes, or if a portion of the wire electrode has protrusions or scratches and discharge is concentrated, fusing of the wire electrode 2 is unavoidable.

[Problem to be solved by the invention 3 As described above, in the conventional wire-cut electric discharge machining apparatus, in order to prevent the wire electrode 2 from breaking, the output energy of the machining power source 15 is reduced, etc. Since the wire was prevented from breaking even if the electric discharge was concentrated at one point on the wire electrode 2, the machining speed was significantly reduced. ``There was a problem that it was low.

Therefore, conventional methods have been used to determine whether the machining condition is good or not, or whether the electrode is damaged or not.
The previous state is determined, and based on the result of this determination, safety measures are taken to automatically return to the normal machining state, or to avoid damage to the electrode, so as not to reduce the machining speed. There is.

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 inter-electrode impedance is low, and insulation breakdown due to discharge is likely to occur due to short circuits or accumulation of sludge or machining powder, and discharge concentration (the biggest cause of wire breakage) is likely to occur. Indicates that something is occurring.

[7 or [-1] In machining with a narrow gap (essential for high-precision machining), short circuits occur frequently even under normal machining conditions, so it seems likely that safety measures were taken to detect these short circuits. There was a problem that processing efficiency was significantly reduced.

The present invention has been made in order to solve these problems.It provides an electrical discharge machining device that can accurately determine whether the machining condition is good or bad without reducing the t1 machining rate, and can prevent electrode damage accidents. The purpose is to obtain.

[Means for solving problems]

The electrical discharge machining apparatus according to the present invention includes a detection means for detecting the level of arc discharge voltage in multiple stages during the energization period when a discharge occurs between an electrode and a workpiece, and an arc voltage level detected by the detection means and a set reference value. Provide an inter-mole gap condition determining means for determining the inter-electrode condition based on the comparison result between the electrodes, and continue applying the pulse voltage between the workpiece and the electrodes until discharge based on the output of this determining means. It is equipped with a control means for controlling whether to repeat on/off.

[Function] In the present invention, the detection result of the detection means that detects the arc discharge voltage level in multiple stages during the energization period is compared with a preset reference value by the comparison means [-1] Based on the comparison result, the The gap state determining means determines the state of the gap between the electrodes, and when the control means receives an abnormality determination signal from the determining means, the control means sets a pause time in the voltage pulse applied between the electrodes, regardless of the presence or absence of discharge, to achieve a deionization effect. This eliminates discharge concentration and prevents electrode damage.
Voltage is continuously applied until the start of discharge, and the frequency of discharge is increased to improve machining efficiency.

〔Example〕

FIG. 1 is a schematic diagram showing an embodiment of the present invention, and numerals 1 to 15 are the same as those of the conventional device described above. 16
17 is a control command signal generator for detecting the pulse current supplied between the machining power source 15, and 17 is a control command signal generator, which includes means for receiving detected current from the current detector 16, means for detecting voltage between machining electrodes, and detection means. It has a comparison means for comparing the voltage with a reference value, a gap state determination means for determining the state of the gap based on the output of the comparison means, and supplies a control command signal to the control device 14, the machining power source 15, etc. It is configured as follows.

FIG. 2 shows the current signal obtained from the current detector 16.
From this, the shaped signal S■ detects the presence or absence of current, the inter-electrode voltage signal Vg, and the inter-electrode signal SD k sampled when current was flowing, that is, when S = 1 among the inter-electrode voltage signals Vg. Classified into three levels: arc discharge voltage V1 or higher (25 V or higher) when machining conditions are normal, level V lower than this (about +IOV), and level V if higher than this (approximately +IOV).
, lower level, high level V, and lower level, respectively, and form a signal group of Vt<, V+ to vt, vt>.

FIG. 3 shows an example of a configuration for obtaining the signal group shown in FIG. 2.The current signal of the current detector 16 is converted into a shaped signal S□ by the waveform shaping circuit 18, and the signal of the analog switch 19 is switched. The interelectrode voltage signal Vg is divided by a voltage dividing circuit rI r rl serving as the voltage detection means. The midpoint P of this voltage dividing circuit is connected to the analog switch 19,
Only when the current is flowing, that is, when the current is 5I-1, it is taken out as the electrode gap signal SD and supplied to the voltage comparators 20 and 21.

The voltage comparator 20 outputs 1 when the input signal SD is greater than Vt, and the voltage comparator 21 outputs Vt.
If it is smaller, the output is 1.

The AND gate 22 is for extracting a signal that is larger than Vt and smaller than (2).

According to experiments, when the arc discharge voltage is greater than VI, that is, approximately 25 V or more, the discharge itself causes the generation of an arc column in the liquid and the generation of high heat (50 V).
00 to 7,000° C.) and the pinch effect was smoothly generated, indicating that sufficient energy was distributed to the workpiece.

Also, when the arc discharge voltage is above IOV and below 25V, spark discharge does exist between the electrodes, but it does not exist directly between the electrode and the workpiece, but from the electrode → sludge → workpiece etc. It has been found that even if a discharge occurs from electrode-1 metal ions to the workpiece, the energy is not sufficiently distributed to the workpiece and the discharge state simply damages the wire.

Therefore, such a discharge state must be removed immediately (-
Damage and disconnection of the wire electrode will occur.

In the case of a short circuit, which is generally considered to be a malfunction,
In other words, it has been found that if V is smaller, the wire electrode is damaged, and there is no need to install it separately, and it is sufficient to simply enlarge the machining gap.

Therefore, if the machining state is controlled depending on whether vI< or (1) to vt, damage and disconnection of the wire electrode can be prevented. FIG. 4 shows an example of the configuration of the discriminating means 23 for discriminating the state of the gap between the poles based on the outputs of the voltage comparators 20 and 21. , are counted by the counter 25.

Further, the normal discharge signal v, < resets the counter 25 so that it does not continue counting unless abnormal discharge continues.

Therefore, it can be said that the contents of the counter 25 directly indicate the state between the poles. This is because when the discharge is normal, the thermal counter 25 is °°0'', but when normal and abnormal discharges are repeated, the average value of the counter 25 becomes larger as it becomes abnormal, and decreases as it becomes normal. Become.

If there is a series of abnormal discharges immediately before the wire electrode 2 breaks, the digital comparator 26 outputs a danger signal, and based on this signal, control can be performed to improve the condition. .

t*, the analog output SM from the D/A converter 27 is used for analog display, or the above-mentioned danger (US) is supplied to the monitor circuit 28. This monitor circuit 2B includes a negative AND gate 29, a light emitting diode (ILED) 30, and a resistor. r
It is configured as 0.

FIG. 5 is a time chart of abnormal discharge detection described above, showing the analog value of the contents of the counter 25, S M% danger signal S
It shows the relationship between the current signal 11 and the voltage signal Vg between electrodes.

Hereinafter, based on the danger signal SA, the control means 31 controls whether to apply the pulse voltage continuously or intermittently to the gap between the electrodes.
An example will be explained using 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.
5b is not turned off to avoid unnecessary downtime, and if the machining condition between the machining holes deteriorates, even if no discharge occurs, a stoppage time will be provided to ensure complete deionization and discharge. It performs an action that eliminates one factor of concentration.

In FIG. 6, 101 is an R-8 flip-flop;
When this output is Q=1, the switching element 15b'i is turned on via the amplifier 15d. When this Q=1, AND
The output of the gate 102 is 10'' until the on-time setting output τ1 of the counter 103 becomes 1'';
When it becomes "1", the flip-flop 101 is reset, so Q=0 and it is off time.

At this time, the outputs of the A and ND gates 102 are O
R game) 104” i-interface oscillator (OS C) 110
Since the counter 103 is reset, counting is performed from the beginning.

When 10,000, Q=0, Q=1, so the input of the 10,000 gate of the AND gate 105, that is, the off-time setting terminal τ, becomes 1. This off state is maintained, and τ changes from 0 to 1. It will be off time for a predetermined period of 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 determines 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 signal SA from the color/reel 25 is 1, that is, when the machining condition deteriorates or when the inter-electrode voltage Vg is low due to short circuit, discharge, suspension, etc., the output of the oscillator O8C is counted by the counter 103. .

Note that R1, R, is a voltage divider circuit for the voltage between electrodes Vg, 108 is a voltage comparator, and a reference voltage vI is set by a power supply 109 and a volume VR. , is higher than the reference voltage VI, the output becomes 1, and if the signal SA is 0, 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
The switching element 15b is repeatedly turned on and off by counting the times of discharge, suspension, and deterioration of the machining condition.

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

〔Effect of the invention〕

As described above, according to the present invention, the level of arc discharge voltage during the energization period when discharge occurs between the workpiece and the electrode is detected in multiple stages, and based on the detection results, normal discharge and abnormal discharge are detected. Therefore, it is possible to accurately determine whether the machining condition is good or bad without reducing the machining speed. Then, based on the determined result, it controls whether to apply the voltage pulse continuously or intermittently.
When an abnormal condition is detected, regardless of the presence or absence of discharge,
By setting a pause time in the voltage pulse applied between the electrodes and giving it a deionization effect, discharge concentration is eliminated and damage to the electrodes is prevented.If the electrode gap condition is good, the voltage is continuously applied until the discharge starts. This has the effect of increasing the discharge frequency and improving machining efficiency.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing an embodiment of the present invention, FIG. 2 is a time chart showing the operation of this embodiment, FIG. 3 is a circuit diagram showing an example of an arc discharge voltage level detection means, and FIG. 4 5 is a circuit diagram showing an example of a means for determining the gap state between poles, FIG. 5 is a time chart showing its operation, FIG. 6 is a circuit diagram showing an example of a control means, and FIG. 7 is a conventional wire-cut electrical discharge machining device. FIG. 1... Workpiece, 2... Wire electrode, '1 m
'*... Arc discharge voltage detection means (minute 11E circuit), 20.21... Comparison means 1 [, ■ comparator), 23
. . . Interpolar gap state determination means; 31. . . control means. Note that the same reference numerals in the figures indicate the same or equivalent parts.

Claims (1)

[Claims] An electrode and a workpiece are placed facing each other with an insulating machining fluid interposed between them, and a pulse voltage is applied between the electrode and the workpiece to generate an electric discharge between the two, and the workpiece is machined using the discharge energy. The electrical discharge machining apparatus includes a detection means for detecting the level of arc discharge voltage in multiple stages during a current-carrying period when discharge occurs between the electrode and the workpiece, and an arc voltage level detected by the detection means is set in advance. a comparison means for comparing with a reference value; an electrode gap state determining means for determining the state of the gap based on the output signal of the comparing means and outputting a signal; and discharging the pulse voltage based on the output of the determining means. An electric discharge machining apparatus characterized in that it is equipped with a control means for controlling whether to continue applying voltage until it is applied or to repeatedly turn it on and off.