JPS5820732B2 - Houden Kakoseigiyohouhou - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to electric discharge machining by generating a special shape pulse current other than a rectangular pulse current, such as a triangular pulse current, using a switching element such as a transistor. A small discharge is caused from the point at which signs of discharge appear depending on the condition of the gap between the electrodes.
The present invention relates to an electric discharge machining control method characterized in that optimum machining is performed by passing a large current after a certain period of time has passed.

In general, in electric discharge machining, there is a high probability that a short circuit will occur between the electrode and the workpiece due to build-up of discharge scars, machining debris, etc. during machining.

Figure 1 shows the voltage and current waveforms between the poles during actual machining.
Figure a shows the interelectrode voltage waveform, and the same figure shows the discharge current waveform.

Here, Vl p V2 is the inter-electrode voltage waveform during stable machining, ll, 12 is its discharge current waveform, and ■3 is the voltage waveform when short-circuited, and the resistance of the electrode and workpiece itself,
A slight voltage is generated due to contact resistance, etc.

i3 is the current waveform, and the current peak value is higher than that of the current waveforms il and i2.

When machining is performed with a high current peak value, such as during rough machining, or when this short circuit occurs in a region where the machining pulse frequency is high, the average machining current increases due to the short circuit, and the Joule heat causes the electrode and Frequently, the workpiece was damaged and the transistor was damaged due to an increase in the average processing current.

In this case, the operator generally changes the average machining current depending on the state of the machining gap, but it is difficult to appropriately select this average machining current, and the operator is also required to have considerable skill.

In order to solve this problem, the devices shown in FIGS. 2 to 5 have been proposed.

That is, FIG. 2 shows an example of a conventional electrical discharge machining apparatus, in which switching transistors la, 1 b p 1 c p
....

The control circuit 2 causes a base current to flow through the base of each of the 1n transistors at different times in order, and turns each switching transistor 0N-OFF at different times in order.
Switching transistors 1a, 1by from DC power supply 3
1cy......, In and collector resistance of each switching transistor 4at4by4cy...
, 4n, a specially shaped pulsed current is passed between the tool electrode 5 and the other electrode 6, which is the workpiece, to perform machining.

Figure 3 shows an example of the voltage and current waveforms applied to the machining gap by the device shown in Figure 2. In Figure 3, 7 is the pulse voltage application time, 8 is the rest time, and 9 is the no-load voltage. The application time, 10 is the discharge duration time, 11 is the no-load voltage, 12 is the discharge voltage, 13 is the discharge current, and 14 is the average machining current.

When the machining is performed stably here, the no-load voltage is 11
There is a very high probability that the average no-load voltage application time 9 will eventually be controlled to a certain value.

This is because the servo mechanism controls the average machining voltage between the machining poles to be constant.

This control is performed stably when the condition between the poles is good.

However, if the condition between the machining holes worsens due to the accumulation of machining powder between the machining holes, the no-load voltage application time becomes shorter or disappears, as shown in Figure 4a, and the discharge converges to a single point. There is a danger that they will concentrate and create relatively large depressions.

The current waveform in this case is as shown in Figure 4.
Compared to the figure, the average machining current naturally increases.

If this state continues for a certain period of time, since deionization is not performed, the discharge will concentrate on one point, and the state between the electrodes will deteriorate, and there is a possibility that the state will increasingly shift to the state shown in FIG. 4a.

In order to escape from this state, it is necessary to reduce the average machining current in order to restore the condition between the machining edges well.

By the way, as a method to reduce the average machining current, a method has been considered in which the state of the machining gap is detected on an average basis and the oscillation frequency is changed based on the detection result. The disadvantage is that the effect on the state of

In view of the above-mentioned drawbacks, the present invention provides that when the condition between the electrodes deteriorates and the no-load voltage application time almost disappears, each pulse is adjusted according to the length of the no-load voltage application time in each pulse. In this method, a minute discharge is generated from the point at which a sign of discharge appears, and the time from that point until a large current is generated is controlled, thereby controlling the average machining current.

It has a very quick response, and even if the condition between the poles deteriorates, it can quickly recover and perform stable machining again.

FIG. 5 shows the principle of an embodiment of the present invention.

The voltage waveform shown in Figure 5a is the voltage waveform between the electrodes, where a certain time τS is set, and when the no-load voltage application time 9 is greater than τS, processing is performed with the current waveform as initially set as shown at 15. 16 when the no-load voltage application time 9 is less than τS.
As shown in , a micro discharge current 17 with a low current value that does not contribute to machining is initially applied, and the average machining current is lowered by changing the micro discharge duration 18 according to the length of the no-load voltage application time 9. It's a method.

FIG. 6a shows the voltage waveform between machining points in actual machining using this method, and FIG. 6 shows the current waveform.

In the case of the inter-electrome voltage waveform 19.22, the no-load voltage application time is greater than τS, so machining is performed using a current larger than the point at which the discharge occurs.In the case of 20°21, the no-load voltage application time is less than τS. Therefore, a minute discharge is generated from the moment the discharge occurs, and machining is performed with a large current after a certain period of time.

Next, an embodiment of the above method is shown in FIG. 7, and will be described. Reference numeral 27 represents a gap state detection device, and 28 represents an evaluation circuit.

When the no-load voltage application time is measured by the inter-electrode state detection device 27, the evaluation circuit 29 compares the no-load voltage application time with a predetermined time τS, and determines that the no-load voltage application time is less than or equal to τS. , first switching transistor groups 1a, 1b, 1c,...
・”.

A signal that makes one or a part of 1n conductive is sent to the control circuit 2.

On the other hand, from the time when a discharge occurs, a portion of the control circuit 2 that generates a special shaped pulse is driven, but the signal is not sent to each pace of the transistor group.

After a certain delay time corresponding to the length of the no-load voltage application time, the evaluation circuit 28 sends a signal to open the gates of the transistor group and the portion of the control circuit that has been driven from the time of discharge occurrence that has generated the special shaped pulse. It flows into control circuit 2.

The signal output from the control circuit 2 is sent to the switching transistor group 1 az 1 b t I Cy..., 1n
flows into the bases of each of the switching transistors and makes the switching transistors conductive.

As a result, the switching transistor groups 1 a , 1 b , 1 c , . . . from the DC power supply 3 are transmitted.

1n and collector resistance groups 4a, 4b, 4c,...
・.

4n, the pulsed current is applied to the tool electrode 5 and the workpiece 6.
It flows between the poles made up of.

In the embodiments described above, a triangular wave whose current peak is at the rear is described, but the present invention can also be applied to a triangular wave whose current peak is at the front or other special shaped pulses.

As explained above, according to the method of the present invention, when the no-load voltage application time from the time a voltage is applied to the machining gap until the occurrence of electric discharge is longer than a predetermined time, the workpiece is machined using a set pulse current. However, when the no-load voltage application time does not reach the predetermined time, the controlled pulse current is caused to flow into the machining gap by a controlled desired time delay from the time when the electric discharge occurs; During the above delay time, a minute discharge current that does not substantially contribute to machining was applied, so the length of the no-load voltage application time in each pulse was adjusted so that signs of discharge were observed for each pulse. It is possible to generate a minute discharge from a certain point and control the time from that point to the generation of a large current, thereby controlling the average machining current. Therefore, it is rich in quick response, and even if there is a situation between the poles, it is possible to control the average machining current. Even if the condition worsens, it will recover quickly and stable machining can be performed again.

[Brief explanation of drawings]

Figure 1 is a diagram showing the actual voltage waveform and current waveform between the machining points in the conventional electrical discharge machining method, Figure 2 is a diagram explaining the principle of the conventional device, and Figures 3 and 4 are the voltage waveforms between the machining points in the conventional method. and its current waveform, FIG. 5 is an explanatory diagram of the principle of the present invention, FIG. 6 is a diagram showing the inter-electrode voltage waveform and current waveform according to the method of the present invention, and FIG. 7 is a diagram of an example of an apparatus for implementing the method of the present invention. It is. Note that the same reference numerals in the figures indicate the same or equivalent parts. 1at 1bt 1ct...yln...
・Switching transistor, 2...control device, 3...DC power supply, 5...tool electrode,
6...Electrode to be processed, 27...
Interpolar condition detection device, 28...Evaluation circuit.

Claims (1)

[Claims] 1 In an electric discharge machining method in which machining is performed by intermittently passing a pulse current through a machining gap where an electrode and a workpiece face each other, no-load voltage is applied from the time when voltage is applied to the machining gap until the occurrence of electric discharge. When the time is longer than the predetermined time, the workpiece is machined with the set pulse current, and when the no-load voltage application time does not reach the predetermined time, the desired time is controlled from the point at which discharge occurs. The electric discharge machining control is characterized in that a controlled pulse current is caused to flow through the machining gap with a delay of .times., and a minute discharge current that does not substantially contribute to machining is caused to flow during the delay time. Method.