JPH0440126B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in an electrical discharge machining apparatus for machining a workpiece using a wire electrode, a rod-shaped electrode, a plate-shaped electrode, a full-shaped electrode, or the like.

For example, in a wire-cut electrical discharge machining device, a wire electrode is unwound from one reel and wound onto the other reel while applying a predetermined tension, and the workpiece is placed almost perpendicularly to the moving wire to create a machining gap. A machining liquid such as water or oil is supplied to this gap, and a machining pulse is supplied to generate a pulse discharge. By repeating this discharge, the workpiece is cut along the movement of the wire. At this time, if the moving direction of the wire is Z according to the progress of machining of the electrode or workpiece, various shapes can be cut, extracted, etc. by feeding in the X and Y directions perpendicular to this direction. At this time, although the wire electrode is moving, the moving speed is usually about 3 m/min at the most, and the processing is performed at a repetition rate of several tens to several hundred KHz. Compared to the period of the pulse, the movement is slow, almost stationary, and the portion of the wire from the point where the wire energizing device is provided to the point facing the workpiece is heated by the energizing current. On the other hand, wire electrodes are usually 0.05 to 0.1 mmφ, at most 0.2 to 0.3
A thin wire or thin strip-shaped electrode of about mmφ is used, and tension is applied to it to the extent that it does not bend. Because it is rolled up and moved, it is heated to a high temperature by the above-mentioned Joule thermal heating and conduction of discharge heat from the discharge part. This makes it difficult to perform high-speed machining with a high average machining current, since wire breakage is likely to occur due to heating.

For this reason, conventionally, for example, as described in Japanese Patent Application Laid-open No. 50-22393, the unwinding side of the wire electrode, which is the front side facing the workpiece, and the winding side, which has moved past the part facing the workpiece, By providing an energizing device for each of the energizing devices, and providing a switch element between each energizing device and the DC power source, and controlling both switch elements alternately on and off, the wire is less An invention has been proposed that aims to improve the machining speed by making it possible to increase the average machining current without causing the electrode to overheat and break. However, in such inventions, there is no off time (discharge rest time) in the discharge part, which tends to result in continuous arc discharge or concentrated discharge instead of intermittent spark discharge, and it is difficult to perform machining in a stable and good discharge state. It is difficult to do so.

In view of the above points, it is an object of the present invention to provide an electric discharge machining device that can increase the average machining current and perform high-speed machining in a stable electric discharge state. In an electrical discharge machining device that performs machining by applying voltage pulses from a machining power source to a machining gap, current-carrying terminals connected to the machining power source are provided at two or more locations on the electrode, and each current-carrying terminal is connected to the machining power source. An energization changeover switch is provided between the two, and a control circuit is provided for switching the changeover switch each time a plurality of voltage pulses are applied to one of the energization terminals.

The present invention will be explained below with reference to an embodiment of the drawings.

In FIG. 1, a wire electrode 1 in the form of a thin wire or strip is supplied from a reel 2, moves between guides 4 on the way, and is wound onto a reel 3. Although not shown, the wire electrode 1 runs under tension while maintaining a predetermined tension between the processing section guides 4 by means of a tensile force from a capstan and braking control from a brake. 5 is a workpiece facing the inter-guide wire electrode 1, and 6 is a workpiece fixing table. Although this table 6 is not shown, scheduled shape machining feeds in the X-axis and Y-axis directions are given by signals from an NC device or copying device, and the required shape cutting process is performed. Reference numeral 7 denotes a processing power supply for supplying processing pulses, and the other is provided to supply electricity to the wire electrode 1 through current-carrying rollers 8 and 9, and from the table 6 to the workpiece 5. Reference numerals 10 and 11 denote transistor switches inserted into the connection circuit between the power supply 7 and the current-carrying roller 8, and between the power supply 7 and the current-carrying roller 9. Configure. Reference numeral 13 denotes a switching control circuit that outputs switching signals for on-pulses and off-pulses of at least two cycles of the machining pulses of the machining power source 7.

In the above, a machining pulse is supplied from the machining power supply 7 to the gap between the wire electrode 1 moving between the rollers 4 and the workpiece 5, and the workpiece 5 is given a machining feed of the desired shape by an NC signal or the like. In particular, the workpiece is subjected to electrical discharge machining according to the feed shape. Processing pulses from power supply 7 are sent to switches 10 and 1.
1, the power supply 7-switch 10-
It flows through the roller 8 - electrode 1 - workpiece 5 - table 6 - power supply 7, and also flows through the closed circuit of power supply 7 - switch 11 - roller - electrode 1 - workpiece 5 - table 6 - power supply 7.

In this way, by switching the energizing rollers 8 and 9 by switching the switches 10 and 11 and energizing alternately from both sides of the wire electrode 1 between the guide 4, a large current can be energized without causing the wire electrode 1 to generate heat. This can prevent breakage due to heat generation.

In addition, when a pulse discharge occurs once, machining debris is generated and a discharge is likely to occur in that area. Therefore, by applying multiple machining pulses in the same energized state from the same energized position, the pulse can be efficiently processed. Electric discharge can be generated. However, if pulse discharge continues to be generated for too long in the same part, machining debris will be generated excessively, and the area between machining will become dirty, making it easier to shift from concentrated discharge to steady arc discharge, but it is necessary to switch the energization position every few pulses. By doing so, it is possible to change the state of the electric field and magnetic field, move the discharge generation site, and prevent concentrated discharge and the like.

Further, in the present invention, since the energization position is switched every plural pulses, the off time of the machining pulse can be used as the discharge rest time, and the discharge generation site can be changed by switching the energization position. As a result, the time width during which multiple machining pulses are applied can be used as a discharge pause time for the part where electric discharge has occurred up to that point, and there is sufficient cleaning time between machining. Even if the off time is made shorter than before, it is possible to generate a good pulse discharge in a stable state, and the average machining current can be increased to perform high-speed machining.

Moreover, the switches 10 and 11 are switched according to the time pulses generated by the control circuit 13, and the circuits are switched every time a plurality of processing pulses are supplied from the processing power source 7. The off time of the machining pulse to be processed can be used as the discharge rest time in the discharge part,
Machining can be performed under stable and good electrical discharge conditions. Further, it is possible to cause a change in the electric discharge between the wire electrode 1 and the workpiece 5 for each plurality of electric discharges,
Concentrated discharge etc. can be prevented. In other words, the current value, waveform, etc. may be changed by changing the resistance, impedance, etc. of the circuit depending on whether the wire electrode 1 is energized from the energizing roller 8 or the wire electrode 1 is energized from the energizing roller 9. It is possible to apply electricity from a power source to change the voltage, current, waveform, etc. Also, the direction of the electric field and magnetic field when the processing pulse flows through the wire electrode 1 between the roller 8 and the workpiece 5, and the direction of the electric field and magnetic field when the processing pulse flows between the roller 9 and the wire electrode 1. By changing and acting, it is possible to cause a change in the pulse discharge in the gap, promoting the movement of the discharge generation site, preventing concentrated discharge, etc., eliminating wire breakage, and performing stable machining. .

In addition, when a pulse discharge occurs once, machining debris is generated and discharge is likely to occur in that area, so applying multiple machining pulses in the energized state from the same energized position improves efficiency. Pulse discharge can be generated. However, if pulse discharge continues to be generated in the same part for too long, machining debris will be generated excessively and the machining gap will become dirty, making it easy to shift from concentrated discharge to steady arc discharge. Due to the electric field,
Concentrated discharge and the like can be prevented by changing the state of the magnetic field and moving the discharge generation site.

Further, in the present invention, since the energization position is switched every plural pulses, the off time of the machining pulse can be used as the discharge rest time, and the discharge generation site can be changed by switching the energization position. As a result, the time width during which multiple machining pulses are applied can be used as a discharge pause time for the area where electric discharge has occurred up to that point, and the machining gap can be sufficiently cleaned, so the machining pulses can be turned off. Even if the time is shorter than before, it is possible to generate a good pulse discharge in a stable state, and the average machining current can be increased to perform high-speed machining.

Note that the signal pulses for switch switching control generated by the control circuit 13 are not limited to the above-mentioned time signals;
A signal pulse may be generated every time a plurality of output machining pulses are calculated using a counter or the like, or the signal pulse may be output depending on the discharge state of the gap between the electrode 1 and the workpiece 5. It is also effective to vary the switching time, number of continuous pulses, etc. depending on the current direction.

In this way, by changing the energization position and direction of the machining pulse to the wire electrode 1 for each plurality of pulses, it is possible to increase the average machining current and to perform machining in a stable discharge state.
In addition, since concentrated discharge is less likely to occur, the machining power source 7
It is possible to increase the discharge repetition frequency due to this, and therefore, the machining speed can be improved. In addition, the wire electrode can be prevented from breaking and the processing speed can be increased, so that wire cutting can be performed stably and with extremely high efficiency.

There is also a switch 1 that switches the energizing terminal (roller).
Since 0 and 11 are switching control for every plurality of processing pulses generated by the processing power source 7, even if the repetition frequency of the processing pulse is high, it can be easily controlled. Of course, the switches 10 and 11 can also be used as machining pulse generation switches for the machining power source 7, and in that case, switching control may be performed using an AND combination signal of the machining pulse generation signal and the switching signal. FIG. 2 shows the case of the embodiment shown in FIG. 1, in which electricity was applied alternately from both the upper and lower sides of the wire electrode every multiple pulses, and the case of conventional processing, in which electricity was applied from either the upper or lower sides of the wire electrode.
It is an experimental graph showing the average machining current with respect to the plate thickness of the workpiece. The wire electrode used was a thin wire made of brass with a diameter of 0.2 mm and was run at a speed of 1 m/min. Compared to conventional machining, according to the present invention, even if the average machining current was increased, the wire electrode did not break, concentrated discharge was prevented, and the machining speed was improved by about 1.5 times on average.

FIG. 3 shows an example in which a plate-shaped electrode 14 is used as the processing electrode. Electrode plate 14 facing workpiece 15
Current-carrying terminals 16a, 16b, 16 are provided in each divided portion of
c, 16d, 16e, and 16f are provided, and the processing power source 1
Switches 18a, 18b, 18c, 18d, 18e, 18 are connected to each energized circuit to which 7 is connected.
f is inserted and switched by the one shot ring counter 19. Reference numeral 20 denotes a circuit that determines the discharge state of the gap, and each time a discharge state that may cause concentrated discharge or steady arc discharge is detected, the ring counter 19 is driven to perform switching control step by step. do.

In FIG. 4, energizing terminals 22a, 22b, and 22c are provided at each part of the full-form electrode 21, and the machining pulses of the machining power source are switched to energize these terminals.

Even with such electrodes other than wire electrodes, it is possible to change the discharge in the machining gap by distributing current-carrying terminals evenly over the entire electrode according to the shape, and by switching the machining pulses and energizing them. , concentrated discharge, arc discharge, etc. can be prevented and stable machining can be performed.

The machining power source is a switching type using a transistor, a type based on charging and discharging a capacitor,
Any combination of switching pulses and charging/discharging of a capacitor can be used, and separate machining power sources can be connected to a plurality of energizing terminals provided on the electrodes so that they can be energized independently.

As described above, according to the present invention, by switching the energized part for each plurality of pulses,
It is possible to generate pulsed discharge efficiently and to take sufficient time to clean the machining gap.
In addition, since the electric field and magnetic field conditions are changed to prevent concentrated discharge and arc discharge, stable machining is possible even if the machining pulse off time is shorter than before, and the discharge repetition frequency is increased and the average Efficient high-speed machining can be performed by increasing the machining current.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram of an embodiment of the present invention, Fig. 2 is a graph of a comparative experiment between the present invention and conventional processing in which electricity is applied from either the upper or lower side of the wire electrode, and Figs. It is another Example figure of invention. DESCRIPTION OF SYMBOLS 1... Wire electrode, 4... Guide, 5... Workpiece, 7... Processing power supply, 8, 9... Current-carrying roller (terminal), 10, 11... Changeover switch, 12...
Schmitt circuit, 13... switching control circuit.

Claims (1)

[Scope of Claims] 1. In an electrical discharge machining device that processes an electrode and a workpiece by applying a voltage pulse from a machining power source between facing machining spaces, a current-carrying terminal connected to the machining power source is connected to the electrode. An energization changeover switch is provided between each energization terminal and the processing power source, and each time a plurality of voltage pulses are energized by the changeover switch to the energization terminal connected to the processing power source, An electric discharge machining device equipped with a control circuit that switches a changeover switch to another energizing terminal. 2. The electric discharge machining apparatus according to claim 1, wherein the control circuit of the changeover switch uses a detection signal of a discharge state during machining as a control signal.