JPS62287919A - Electric discharge machine - Google Patents

Abstract

PURPOSE:To prevent accidents due to damage of an electrode without lowering the rate of machining, by detecting the degree of insulation of an insulative machining fluid existing in the gap between the electrode and a workpiece and by comparing thus detected value with a reference value to control the tension of a wire electrode. CONSTITUTION:A control instruction signal generating device 17 superposes high frequency alternate voltage from an electrical sources 18 during a deionizing period or the quiescent time of pulse voltage applied between a wire electrode 2 and a workpiece 1 from the machining power source 15, and a current detector 6 detects interpole leakage current running due to the lowering of insulation of the machining fluid 3 which is caused by machined chips, so that thus detected current is compared with a preset reference value to discriminate the interpole condition. With the result of the discrimination a control instruction signal is fed to a control device 14 and the machining power source 15, and if there would be any risk that the degree of insulation of insulative machining fluid 3 is lowered so that abnormal electric discharge occurs, the tension of the wire electrode 2 applied by a wire feed and tension roller 10 is reduced so that the wire electrode whose proof-tension is weakened due to wire- consumption is prevented from being broken. Thus, it is possible to prevent breakage of the wire electrode without the machining rate being lowered.

Description

Detailed Description of the Invention 3. Detailed Description of the Invention [Field of Industrial Application] This invention relates to electric discharge machining, which generates electrical discharge between an electrode and a workpiece, and uses this discharge energy to cut the workpiece. It is related to the device.

[Conventional technology]

Conventionally, this type of electrical discharge machining equipment involves drilling a hole in a workpiece using a rod-shaped electrode, and drilling a hole in the workpiece with a drill or the like and passing a wire electrode through it. There is a method in which a workpiece is cut by relatively moving a wire electrode.

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, (1) is the workpiece, and its cut hole (1a
) and an insulating liquid (3) between the wire electrode (2) passed through the
).

The above-mentioned insulating liquid (3) will be hereinafter referred to as a processing liquid. The machining fluid is pumped from the tank (4) to the workpiece (1) by the pump (5).
It is sprayed by a nozzle (6-inch) into the gap between the seven wire electrodes (2).

The relative movement between the workpiece (1) and the wire electrode (2) is performed by moving the table 01) on which the workpiece (1) is placed. Table 01) is driven by Y-axis drive motor Q3
．． ! : Driven by X-axis mork α2. With the following configuration, the workpiece (1), l! :The relative motion of the fa pole (2) is a two-dimensional plane motion within the aforementioned X and Y axis planes.

The wire electrode (2) is supplied from the wire supply reel (7), and is connected to the lower wire, the wire guide (8A), and the workpiece (1).
), the wire reaches the upper guide (8B), and is wound up by the wire winding/tension roller 0G via the electric energy feeder (9).

The drive motor Q2 for the X and Y axes mentioned above. The control device for driving and controlling Q3 uses a numerical control device (NC control device), a copying device, or an fco control device using a computer.

The processing power source 05 that supplies electrical energy includes, for example, a DC power source (158), a switching element (15b), a current limiting resistor (15), and the switching element (158).
The control circuit (15d) controls the control circuit 51.

Next, the operation of the conventional device will be explained. A high-frequency pulse voltage is applied from the machining power source a5 to the workpiece (1) and the wire electrode (
2) A part of the workpiece (1) is melted and scattered by a discharge explosion caused by one pulse applied during the process, in this case,
Because the space between the poles is gasified and ionized by the high temperature,
A certain pause time is required before the next pulse voltage is applied, and if this pause time is too short, the insulation between the guns will not be fully recovered; This causes the electrode (2) to melt.

Therefore, with normal machining power supplies, the type of workpiece.

Depending on the thickness of the plate, etc., the electrical conditions such as the downtime of the processing power source α9 are normally set to a sufficient margin to prevent wire electrode breakage. 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 there are protrusions or scratches on a part of the wire electrode, the discharge will be concentrated.1 In this case, fusing of the wire electrode (2) is inevitable. .

[Problem that the invention seeks to solve]

As mentioned above, in the conventional wire force discharge machining equipment, in order to prevent the wire electrode (2) from breaking, the output energy of the machining power supply α9 is reduced, etc. Since the wire electrode (2) is prevented from breaking even if it is concentrated at one point, there is a problem in that the processing speed is extremely low.

Therefore, 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 the determination results, automatically return to the normal machining condition or avoid damage to the electrode, thereby increasing the machining speed. Efforts are being made to prevent this from decreasing.

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 dielectric breakdown due to discharge is likely to occur due to short circuit or retention of sludge or machining powder, resulting in discharge concentration (wire cutting). Indicates the severity of the occurrence of the biggest factor.

However, when machining with narrow gears (not suitable for high-precision machining), short circuits occur frequently even under normal machining conditions, so safety measures are taken to detect these short circuits. However, there was still a problem in that the processing efficiency was significantly reduced.

In order to solve these problems, this invention 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 purpose is to obtain.

[Means for solving problems]

The electrical discharge machining apparatus according to the present invention is characterized by the degree of insulation of the machining fluid in the gap between the machining electrodes, based on the "rest time" of the pulse voltage applied between the electrode and the workpiece (the value during on-time that does not contribute to machining). Detection means for detecting, and insulation degree of the gap between the poles and the workpiece detected by the detection means;
An inter-electrode gap state discriminating means is provided for discriminating the inter-electrode gap state based on the relative softness result of the preset moe value of 7. Based on the output of this discriminating means, the wire tension is This protects the wire whose tension resistance has weakened from being cut.The wire is equipped with a control means to gradually increase the tension.

[Effect]

In the present invention, during the rest time of pulse voltage application)
By applying a high-frequency alternating current voltage, it is possible to detect the pure insulation degree independent of the ion concentration. In other words, when a high-frequency AC voltage is applied between the electrode and the workpiece where processed powder (sura zino) or electrolytic ions coexist, the mobility of the electrolytic ions is resistant to high frequencies, so the insulation by the processed powder is In general, the cause of accidents during machining is the concentration of discharge points, which causes wire breakage.The concentration of discharge points is caused by poor removal of machining powder, machining powder This occurs due to a decrease in impedance between the poles, but in the conventional detection method, a unipolar voltage was applied, so
Deterioration in insulation due to electrolytic metal ions was also detected without distinction. As a result, although the concentration of electrolytic metal ions is not a factor in the discharge concentration, the inter-electrode condition is unnecessarily aggravated and the recovery means is operated frequently, reducing machining efficiency. However, the true discharge concentration factor is detected by the detection means of the present invention, and the detection result of this detection means is compared with a preset reference value ♂ comparison means, and the inter-electrode gap condition is determined based on this detection result. The determining means determines the inter-electrode gap state, and the control means receives an abnormality determination signal from the discriminating means and controls the inter-electrode gap state so as to restore the inter-electrode gap state.

This is to avoid reducing the machining speed.

[Embodiments of the invention]

FIG. 1 is a schematic diagram showing an embodiment of the present invention, and reference numerals (1) to 09 are the same as those of the conventional device described above.

αG is a current detector for detecting the interpole leakage current (r, - current flowing through the insulation caused by processing powder) drawn by the high-frequency AC power supply α, and 0 is a control command signal generator; means for receiving a detected current from the detector αG, means for detecting voltage between electrodes, and comparing means for comparing the detected voltage with a reference value;
The control device 041. has an inter-electrode gap condition determining means for determining the inter-electrode condition based on the output of the comparison means. It is configured to supply control command signals to the processing power source 09 and the like.

High frequency AC power supply 0υ is 10~25V 1 cycle e number l M
Hz (100K-H7~20 AiFl, z available)
It consists of an alternating current generator (18aJ) and a current limiting impedance element (18b) connected in series, and when the processing power source 09 generates a pulse voltage, the impedance element (18aJ)
8h), when the switching element (151) J of the machining power source 09 is off, without giving any shadow vi to the machining gap, f
That is, an alternating current voltage is applied between the poles only during the rest time.

FIG. 2 shows the interelectrode voltage V according to the configuration shown in FIG.
The waveform of g (during the pause time), the current signal obtained from the above-mentioned current detector QQ, and the processing power source 0.
Take out the signal SP when the pulse voltage of 9 is on, and the current signal only during the rest time with this SP, 1coSD, further; Detect the wave and set the level in 3 levels. The impedance between the electrodes is low and a large amount of leakage current is flowing.■1
or higher (equivalent to 200Ω or lower), lower level V2
(corresponding to about Ω to 1,5), and is divided into levels lower than level Vl and ■2 or less (determined by the specific resistance of the liquid when not processed), 'f: fL tre V + <,
V + −V 2 , V 2〉) Signal fg is active.

Fig. 3 is an example of a circuit for obtaining the signal group shown in Fig. 2. The current signal of the current detector OG is amplified by the amplifier circuit (117) and input to the analog switch (118) as the signal ■. Become. The opening/closing of analog switch J (118J) is controlled by Sp, which is the pause side signal of the pulse signal of processing power supply 09, and in this example, the signal 16 is activated only during the pause time; ing.

The output SE of (119) is supplied to a voltage comparator m, 21). When the input signal SD is larger than ■1, the output of the voltage comparator is 1, and the voltage comparator Qυ
■If smaller than 2, the output is 1. ! :Become. The AND gate (A) is for outputting seven signals that are greater than vl and smaller than vl.

According to experiments, the impedance between poles is 500-700Ω
In the above cases, the discharge itself generates an arc column in the liquid and generates high heat (5000 to 700
0°C) and the pinch effect hail is arranged smoothly, indicating that sufficient energy is distributed to the workpiece side.

In addition, when the resistance is 200Ω or less, spark discharge does exist between the electrodes, but it does not exist directly between the electrode and the workpiece, but rather between the electrodes and the workpiece. It has been found that even when the metal ions and the workpiece are discharged together, the energy is not sufficiently distributed to the workpiece, resulting in a discharge state that simply damages the wire. Therefore,
If such a discharge state is not removed immediately, the wire electrode will be damaged and disconnected.

Therefore, if the machining state is controlled depending on whether it is (1) or (1) to (V2), damage and disconnection of the wire electrode can be prevented. FIG. 4 shows an example of the configuration of the discriminating means (A) for discriminating the state of the gap between the electrodes based on the output of the voltage comparator (2) and the slope. (to) is counted by counter 4. Further, the normal insulation degree signal (vI to V2) is arranged so that the counter (to) does not continue counting unless abnormal discharge continues.

Therefore, it can be said that the contents of the r-counter (5) directly indicate the state between poles. This is because if the discharge is normal, the thermal counter (c) is 10', but if the royal discharge and abnormal discharge are repeated. If there is, the average of the contents of the counter (the more it becomes abnormal, the larger it becomes, and the more it becomes normal, the less it becomes).

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

Mac 1, analog output S by D/A converter (5)
, M for analog display, or the danger multiplier signal S
A is supplied to the example monitor circuit. This monitor circuit is composed of a negative AND gate, one light emitting diode (LED), and a resistor ro.

FIG. 5 is a time chart of the abnormal discharge detection described above, and shows the analog content (+uS, v) of the counter (to).

This figure shows the relationship among the danger signal SA, the current signal, and the interelectrode voltage signal Vg. Hereinafter, a specific method for activating the gap state recovery means based on the contents of the counter □□□ to eliminate the problem leading to wire breakage will be described in detail below.

Now, a method of changing the tension of the wire electrode based on the above output will be explained with reference to FIG.

The wire feeding mechanism includes a supply reel (to
The wire coming out from a) is connected to a tension motor (9) that generates wire tension, a tension reel (lot), and an auxiliary reel (
The capstan (103J) is pulled out through a machining gap with a predetermined tension by a capstan (102), a capstan roller (104), and a capstan (105J), and is wound up by a take-up reel (10I).

Now, when the inter-electrode condition deteriorates and a precursor state of discharge concentration or wire breakage is detected, a voltage is output from the detection circuit (a), and this voltage is amplified by the amplifier (106) and the control transistor <LO7) is output. Output as base voltage. Emi・
The resistance (108) is R, and the current flowing through the motor is 1.
Then, ■-V Vs-Vng, Vs 1 is also -IL it Note that VS is the motor control 11 voltage due to @, VBE is a weak constant of about 0.6V, and can be ignored, and the motor current is dependent on Vs. However, VS decreases, the motor current decreases, and the wire tension decreases, making it possible to protect the wire whose tension resistance has weakened due to wire wear (abnormal wear due to discharge concentration) from being cut. Also, it got better 1
Gradually increase the tension.

The stronger the wire tension, the higher the electrode rigidity, the fewer short circuits, and the faster the processing speed; however, in this method, the purpose of this method is to constantly control the wire tension up to the tension limit. Matoko,
Another effect is to reduce the tension to cause a short circuit, prevent wire breakage, and perform a short circuit burr.
This makes it possible to escape from abnormal machining more reliably than other discharge concentration prevention measures (current reduction, unloading by barring motion).

As described above, the present invention provides an unprecedented wire force release processing machine that changes the wire tension in response to the machining gap condition.

[Brief explanation of drawings]

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 means for detecting the degree of insulation between electrodes, and FIG. The figure is a circuit diagram showing an example of the inter-electrode gap condition determination means, FIG. 5 is a time tsade showing its operation, FIG. 6 is a circuit configuration diagram showing an example of the control means, and FIG. 7 is a conventional wire force/torque discharge. It is a principle diagram showing a processing device. In the figure, (1) is the workpiece to be cut, (2) is the wire electrode, α9
0e is a processing power supply, 0e is a current detector, α force is a control command signal generator, 08) is a high frequency AC chamber υ, and @ is a discrimination means for discriminating the state of the gap between poles. 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. In the electric discharge machining apparatus, a means for superimposing a high frequency AC voltage during a rest time of the pulse voltage applied between the electrode and the workpiece, and a means for superimposing a high frequency AC voltage on the insulation existing in the gap between the electrode and the workpiece by the high frequency AC voltage. a detection means for detecting the degree of insulation of the processing fluid; a comparison means for comparing the insulation degree of the gap between the electrode and the workpiece detected by the detection means with a preset reference value; and an output of the comparison means. Electrical discharge machining characterized by comprising a gap state determining means for determining the state of the gap based on a signal and outputting a signal, and a control means for controlling the tension of the wire electrode based on the output of the determining means. Device.