JPS61111812A - 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 controlling the servo-gain in the case when the servo for the gap length between an electrode and a workpiece is carried-out, on the basis of the result of the above-described judgment. CONSTITUTION:The pulse current supplied into between electrodes from a working poser 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. The servo-gain in the case when the servo for the gap length between an electrode 2 and a workpiece 1 is carried-out is controlled, and the electrode 2 can be prevented from being damaged.

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 type of electrical discharge machining equipment involves drilling a hole in a workpiece with a rod-shaped electrode, and one in which a wire electrode is passed through a hole pre-drilled in the workpiece with a drill, and the wire electrode is connected to 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, 1 is a workpiece, and an insulating liquid 3 is interposed between it and a wire electrode 2 passed through a cut hole 1g.

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
It is sprayed by the nozzle 6 into the gap (gap between the poles).

The relative motion between the workpiece 1 and the wire electrode 2 is:

This is done 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. With the above configuration, the relative movement between the workpiece 1 and the electrode 2 is a two-dimensional plane movement within the aforementioned X and Y axis planes.

The wire electrode 2 is supplied by 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 10 via the electric energy feed section 9.

The control device 14 that drives and controls the X%Y-axis drive motors 12 and 13 is a numerical control device (NC control device).
A control device using a computer, a copying device, or a computer is used.

The processing power supply 15 that supplies electrical energy includes, for example, a DC power supply 15a, a switching element 15b1, a permissive current limiting resistor 1
5c 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 caused by 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 that the invention seeks to solve]

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 supply 15 is reduced, etc., so that the electric discharge concentrates on one point on the wire electrode 2. The problem was that the processing speed was extremely low because it was designed to prevent wire breakage even if the wires were concentrated.

Therefore, in the past, safety measures were taken to determine whether the machining condition was good or not, or whether the electrode was about to be damaged, and based on the results of this determination, 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 impedance between the electrodes is low, and due to short circuit or accumulation of sludge or machining powder, dielectric breakdown in the discharge reservoir is likely to occur, resulting in discharge concentration (
This indicates that the main cause of wire breakage) has occurred.

However, when machining with a narrow gap (unnecessary for high-precision machining), short circuits occur frequently even under normal machining conditions, so it is difficult to detect short circuits and take safety measures. There was a problem in that efficiency was significantly reduced.

This invention was developed to solve these problems, 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 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. control for controlling the servo gain when performing gap length servo between the electrode and the workpiece based on the output of the discrimination means; It is equipped with the means.

[Effect]

In this 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, and based on the comparison result, the electrode gap state determination means The control means increases the servo gain of the gap length servo that receives the abnormality determination signal from the discrimination means to increase the opening speed and approach speed of the gap, thereby quickly adjusting the gap. The condition is normalized to prevent damage to the electrode, and when a normality determination signal is received, the above servo gain is lowered, and the gap length is controlled not to change in order to maintain the normal condition, improving machining speed. We aim to

〔Example〕

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

FIG. 2 shows the current signal I obtained from the current detector 16.
And from this, the presence or absence of current is detected from the shaped signal 81b, the inter-electrode voltage signal g1, of the inter-electrode voltage signal Vg, the inter-electrode signal 8D sampled when the current was flowing, that is, when sl"l, is divided into three levels. Arc discharge voltage is 71 or higher (25■ or higher) when the machining conditions are normal, and a lower level ■.

(10Vi degree), dogs are divided into level V, lower level and level V, lower level, respectively, Vl<,V
, ~V, , V, > signal group.

FIG. 3 shows a configuration example for obtaining the signal group shown in FIG. 2, in which the current signal of the current detector 16 is converted into a shaped signal SI by the waveform shaping circuit 18, and the signal of the analog switch □19 is switched. The electrode-to-electrode voltage Vg is divided by a voltage dividing circuit rI+rl serving as the voltage detecting means. The midpoint P of this voltage divider circuit is connected to the analog switch 19, and only when a current is flowing, that is, when Sr = 1, it is taken out as a gap signal 8D and supplied to voltage comparators 20 and 21.

The voltage comparator 20 outputs 1 when the input signal 8D is 1 and 1, and the voltage comparator 21 outputs 1 when the input signal 8D is V and 1 and 1, respectively. The AND gate 22 is for extracting a signal that is larger than p and smaller than ■.

According to experiments, when the arc discharge pressure is greater than ■1, that is, approximately 25 V or more, the discharge itself causes the generation of an arc column in the liquid and the accompanying generation of high heat (5000 ~ 7,000° C.) and the pinch effect hail was occurring smoothly, indicating that sufficient energy was distributed to the workpiece side.

In addition, if the arc discharge voltage is above IOV and below 25V, spark discharge does exist between the electrodes, but it is dangerous if it exists directly between the electrode and the workpiece, and the spark discharge occurs between the electrode → sludge → workpiece. It has been found that even if a discharge occurs from the electrode to the metal ion to the workpiece, the energy is not sufficiently distributed to the workpiece and the discharge simply damages the wire.

Therefore, if such a discharge state is not removed immediately, the wire electrode will be damaged and disconnected.

On the other hand, in the case of a short circuit, which is generally considered to be a malfunction,
It was also found that in the case of small wire electrodes, there is no need to install a separate wire electrode, and the machining gap should simply be expanded.

Therefore, if the processing state is controlled depending on whether ■, <, or ■, ~■, it is possible to prevent damage and disconnection of the wire electrode. FIG. 4 shows an example of the configuration of the discriminating means 23 for discriminating the state of the gap between the electrodes based on the outputs of the voltage comparators 20 and 21, in which the abnormal discharge signals ■1 to ■ are transmitted via the gates 24. , are counted by the counter 25.

In addition, the signal 1 < for normal discharges resets the counter 25 so that it does not continue counting unless abnormal discharges continue.

Therefore, it can be said that the contents of the counter 25 directly indicate the extremely open state. This is because when the discharge is normal, the thermal counter 25 is %Ol, but when normal discharge and abnormal discharge 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 is disconnected, the digital comparator 26 outputs a danger signal 8A, and based on this signal, control can be performed to improve the condition.

Further, the analog output SM from the D/A converter 27 is used for analog display, or the danger signal SA is supplied to the monitor circuit 28. This monitor circuit 28 includes a negative AND gate 29, a light emitting diode (LED) 30, and a resistor r.
Consists of 0.

FIG. 5 is a time chart of abnormal discharge detection described above, in which the analog value of the contents of the counter 25 is 8M.

This figure shows the relationship between the danger signal 8A%m flow signal (■) and the electrode-to-electrode voltage signal Vg.

(Below 1υ, based on the contents of the counter 25, the servo gain, that is, the sensitivity, of the means for controlling the interpole gap can be changed to prevent a short circuit or an open state.

Alternatively, the state immediately before the wire electrode is disconnected can be recovered.

In other words, in the case of a bad gap condition as described above, by increasing the servo gain and increasing the speed of opening and closing the gap, it is possible to quickly avoid the bad mechanical condition. It is possible to recover the temporary state.

An example of the control means 3101 that performs the above control will be explained in detail using FIG. 6. Reference numeral 100 denotes a multiplication type digital-to-analog converter, which is an element capable of outputting a result of multiplying the speed command voltage F according to the output of the counter 25, and AD7520 manufactured by Analog Devices, Inc., USA, etc. is well known. In other words, it can be thought of as having a volume function on the input signal. The value of this volume changes according to the output (digital value) of the counter 25.

Therefore, according to this example, the servo gain is increased by the multiplier type digital-to-analog converter 100 as the gap condition deteriorates, and the speed command voltage Fx is The input terminal of the motor drive amplifier 105 in the control device 14, which had been directly inputted, is connected to the amplifier 101.
By connecting to the output end of the table feed motor Mx, the speed of the table feed motor Mx is changed.

Note that in this example, the servo gain is increased almost linearly in proportion to the poorness of the inter-electrode condition, but it does not necessarily have to be changed linearly, and may be changed in a quadratic function or in a polygonal manner. When performing two-step control using the detection signal of the counter 25, it is easy and inexpensive.

Also, according to experiments, when the gap condition deteriorates, if the speed is not at least 20 m/min, the wire will break, and if a large amount of machining powder stays in the gap, the speed will exceed 20 m/min.
It has been found that speeds of the order of m/min are required. In addition, it has been confirmed that during stable machining, machining efficiency is high at a speed of 5 to 10 w/7 min in finishing machining with a surface roughness of 15 μRmax or less, and speed settings are generally required in these areas. It is considered that.

Incidentally, 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 the present invention can also be applied to an electric discharge machining apparatus using a rod-shaped electrode.

〔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. When an abnormality in the pole gap condition is determined, the sensitivity of the pole gap servo means is changed to control the servo motor in order to recover the pole gap condition based on the determination result. By controlling the speed and quickly opening and closing the gap between the electrodes, it is possible to reliably prevent damage to the electrodes and improve the machining speed.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing one 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 a level detection means for arc discharge 1ttt pressure, and FIG. Figure 4 is a circuit diagram showing an example of the means for determining the gap state between poles;
FIG. 6 is a time chart showing its operation, FIG. 6 is a circuit configuration diagram showing an example of a control means, and FIG. 7 is a principle diagram showing a conventional wire-cut electric discharge machining apparatus. 1 is the workpiece, 2 is the wire electrode%, rlsrf is the arc discharge voltage detection means (voltage dividing circuit), 20.21 is the comparison means (voltage comparator), 123 is the electrode gap state determination means, 3
1 is a control means.

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; a gap state determination means for determining the state of the gap based on the output signal of the comparison means and outputting a signal; An electrical discharge machining apparatus characterized by comprising a control means for controlling a servo gain when servoing the gap length of an object.