JPS60146624A - Method of electric discharge machining and device therefor - Google Patents

Abstract

PURPOSE:To prevent the surface of a workpiece from being deteriorated under electrolytic reaction, by superposing a working current in the direction reverse to that of a current which is fed between a machining electrode and the workpiece, just after dielectric breakdown of the working gap. CONSTITUTION:When an output having a waveform C is delivered from a pulse control circuit 27 to a swtiching element control circuit 20, a switch element 18 is turned on so that a voltage ES from a d.c. current source 17 is applied across the working gap. At this time, since the polarity of a workpiece is negative, and therefore no electrolysis comes about. When spark discharge is initiated, the voltage drops are indicated by a waveform (a), and a current as indicated by a waveform (b) runs, which is detected by a current detector 28 whose an output signal is delivered to the pulse control circuit 27. Accordingly, a switching element 22 is turned on at the tming as indicated by a waver form (d) so that a current as indicated by the waveform (b) runs across the working gap. In this stage even after deenergization of the element 22 electromagnetic energy is discharged through a diode 24 due to the inductance of electrical energization system wire, so that a current runs across the working gap. Thus, without lowering the electric discharge machining speed, the surface of the workpiece may be prevented from being deteriorated due to electrolytic reaction.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a method for discharging power 11 and an apparatus therefor, and more particularly) J] 1 work - 7 JU work in which a pole and a workpiece are opposed to each other. The present invention relates to an electric discharge machining method and apparatus for machining by generating intermittent electric discharge in a gap.

[Behind the invention]

In recent years, the speed and machining accuracy of wire free-cut machining machines have been greatly improved, but when the JJD speed change speed is increased, the JJu machining accuracy tends to decrease. In particular, it has been revealed that the recently developed high-speed loe gel source has a relatively large electrolytic action, which is one of the causes of lower loe sheath degree. The present invention has been made to solve this problem.

FIG. 1 shows the overall configuration of a conventional wire electrical discharge machining device, in which 1 indicates a wire electrode, which is guided by a roller 2.3 and faces a workpiece 4. The relative position of the electrode 1 and the workpiece 4 is controlled by motors 5, 6 of a positioning device operated by commands from a numerical control device. The machining gap Q formed between the electrode 1 and the workpiece 2 is supplied with ion '9S replacement water, which is a 7JO working fluid, from the machining fluid supply nozzle 7.8, and the electrode 1 is supplied with ion '9S replacement water from the current-carrying terminal 9.10. Powered. Noyarusu Electric's 11, which supplies power, is a DC power source 12. It is composed of a switching element 13, its control circuit 14, a current reducing resistor 15, and a discharging capacitor. The voltage and current waveforms in the machining gap of this type of pulse power supply are as shown in FIG. , When an electric discharge occurs in the machining gap, an oscillating current flows as shown in Fig. 2 (phantom).

This oscillating current waveform is determined by the inductance and resistance value of the current-carrying thread from the discharge capacitor to the machining gap, and the capacity of the discharge capacitor, and is generally an oscillating current waveform as shown in FIG. 2(a).

Furthermore, a power supply circuit in which the discharging capacitor 16 shown in FIG. 1 is removed has also been used in the past, and its waveform is as shown in FIG. 2 (b). In either case, the polarity of the applied pulse at the time of dielectric breakdown is such that the workpiece is the anode. This polarity was chosen as the polarity that increases the machining speed of the workpiece, and experiments have confirmed that it is better to flow current from the workpiece to the electrode in order to increase the machining speed.

However, since water is used in the machining fluid, an electrolytic reaction occurs when a voltage is applied to the machining gap, making the machined surface of the workpiece soft and deteriorating the quality of the loe surface. Since this amount ranges from several micrometers to more than ten micrometers, it has been a major obstacle to high-precision machining to achieve dimensional accuracy of several micrometers.

To solve this problem, there is a method of applying a bipolar, slightly pulsed voltage so that the average voltage between the poles is 0, but this method lowers the frequency of the machining pulses that contribute to machining. The problem remained that the machining speed decreased.

[Objective of the Invention J The object of the present invention has been made in view of the problems of the prior art described above, and is to provide an electrical discharge that eliminates the soft layer on the machining surface caused by the electrolytic reaction in the machining gap without deteriorating the electrical discharge machining performance. The purpose of the present invention is to provide a processing method and an apparatus therefor.

[Summary of the invention]

One feature of the present invention is to generate intermittent discharge in the 7JO machining gap between the jJO machining electrode and the workpiece to
In the discharge power Roe method for performing zero-axis, immediately after the machining gap has dielectric breakdown, a machining current is superimposed in the direction opposite to the direction of the current output between the machining electrode and the workpiece in 11. be.

Another feature of the present invention is that the electrical discharge 7JII machining equipment generates intermittent discharge in the machining gap between the machining electrode and the workpiece to machine the workpiece.
After connecting the cathode of the DC power source constituting the r1l path and the anode of the DC power source constituting the main discharge circuit to the workpiece, and turning off the switching element inserted in the dielectric breakdown circuit, the main discharge circuit is turned off. A pulse control circuit is installed to turn on the switching element inserted in the machine, and the intermittent discharge voltage of the workpiece at the time of dielectric breakdown is used as a cathode, completely preventing deterioration of the workpiece's surface due to electrolytic reaction without reducing the discharge machining speed. The point is that it is configured like this.

[Embodiments of the invention]

The present invention will be described in detail below with reference to FIGS. 3 to 6. Third
The figure shows one embodiment of the present invention, and those having the same reference numerals as those in FIG. 1 have the same functions. In the figure, the power supply circuit is mainly shown to simplify the explanation. In Figure 3, i#! DC power supply 17 is used for the three edge destruction/mother loop circuits.

Switching element 18. A switching control circuit that controls the current reducing resistor 19 and the switching element 18 or a diode 29 is configured. In addition, the main discharge 'a current circuit is DC current #, 21. Switching element 22 and its control circuit. Sub-DC by diode? It consists of an iE source. Additionally, a current detector for detecting the start of discharge is connected between the machining gap and the dielectric breakdown pulse circuit.

Also shown is a pulse control circuit, which processes the output signal from the current detector and outputs a pulse signal to the switching element and control circuit 23.

Next, the operation of the circuit shown in FIG. 3 will be explained using FIG. 4.

First, the output of the waveform (e) in FIG. 4 from the i4 pulse control circuit 27 is input to the switching element control circuit, and the switching element 18 is turned on. At this time, the switching element 22 is off. A power supply voltage E of the DC type #t17 is applied to the machining gap. At this time, since the polarity of the workpiece is cathode, the workpiece is not electrolyzed. When the discharge starts, the voltage decreases as shown in the waveform (a) in Figure 4, and then (
b) A current flows out like a waveform, the current is detected by the current detector path, the signal is input to the noise suppression circuit, and the signal to control the switching element U is sent to the switching element control circuit. Output. As a result, the switching element 22 is turned on at the timing of the waveform (d) in FIG. 4, and the current flowing through the machining gap at that time is (
It will look like bJrHL type. The reason why current continues to flow even after switching element 4 is turned off in the waveform (b) of FIG. 4 is that electromagnetic energy accumulated in the inductance of the wiring in the current-carrying system is released through the diome.

As shown in FIG. 4, there is a delay of time t3 from the start of discharge until the switching element 22 turns on.
This is because the signal processing time from when the current detector detects the start of discharge until the switching element is turned on takes 200 to 500 na at the shortest due to the signal processing time of the element used, and the time t3 is 2()0 to 500 na. ns or more. Also time 1. and t2 are usually controlled to be constant.

Next, another embodiment of the present invention will be described with reference to FIG. This embodiment uses a discharging capacitor in the dielectric breakdown/loss circuit, and differs from the circuit shown in FIG. 3 in that a discharging capacitor is added. inductance 31
The resistor 32 is the resistance of the current conduction path 0'''r from the discharge core 7'7''j0 to the machining gap, and is set so that the discharge current becomes 111, which sufficiently satisfies the vibration condition. The operation of the circuit shown in FIG. 5 will be explained with reference to FIG.

The waveform (a) in Figure 6 shows the voltage in the Loe gap, the waveform (b) shows the current in the machining gap, and the waveforms (c) and fd) show the on and off signal states of switching element 18 and switching element B. .

When the switching element 18 is turned on as shown in the waveform (C) of FIG. 6, the discharge capacitor I is charged from the DC type @17 through the resistor 19. When the discharge starts, a discharge current flows from the discharge capacitor into the machining gap Q, which is detected by the current detector path and output to the Noculus control circuit n. Then, the pulse control circuit outputs a signal to turn off the switching element 18, and the time from the start of discharge until the switching element U is turned on becomes t'3, as shown in waveform (d) in FIG. like,
The pulse control circuit 27 outputs a timing signal to the switching element U via the switching element control circuit O. The discharge current at that time has a waveform as shown in Figure 6 (b), which is the second waveform of the discharge current output from the discharge capacitor.
A large current from the DC power supply 21 is superimposed on the half wave.

In addition, time t'3 may be set to time t4>t'3. In that case, time t'3 is longer than the signal transmission time at 1 when the switching element operates from the start of discharge, as shown in time t3 in Fig. 4. It has to be bigger.

In the above description of the two embodiments of the present invention, a current detector was used to detect the start of discharge, but the same effect can be obtained by measuring the voltage in the machining gap and detecting the voltage drop at the time of dielectric breakdown. It will be done.

゛Although the above embodiment was explained using a wire electrical discharge machining device using a wire-shaped electrode, the same effect can be obtained in a die-sinking dielectric machining device when a water-based machining fluid is used. Needless to say, it can be done.

〔Effect of the invention〕

As is clear from the above embodiments, the present invention has the advantage and effect of preventing deterioration of the machined surface of the workpiece caused by the electrolytic reaction without reducing the discharge force Roe speed.

[Brief explanation of the drawing]

Fig. 1 is an overall configuration diagram of a conventional radiator machining device, Fig. 2 (a) and (b) voltage and current waveform diagrams in Fig. 1, and Fig. 3 shows an embodiment of the present invention. FIG. 4 is a pulse waveform diagram explaining the operation of FIG. 3, FIG. 5 is a turtle circuit diagram of the electrical discharge machining device showing another embodiment of the present invention, and FIG. 6 is a power supply circuit diagram of the electrical discharge machining device. 6 is a pulse waveform diagram illustrating the operation of FIG. 5. FIG. DESCRIPTION OF SYMBOLS 1... Electrode for processing, 4... Workpiece, 17... DC electrolytic erosion of the pulse circuit for dielectric breakdown, 18.22... Switching element, 20... Switching element side of the pulse circuit for dielectric breakdown Sub-circuit, 21... 1st current current of the main discharge circuit, B... switching element restraint circuit of the main discharge circuit, 5... rigid DC power supply of the main discharge circuit, 27. ...Pulse control rI circuit, ah...current detector, 30...discharging capacitor. Agent Patent Attorney Tadashi Akimoto No. t FBI No. 21.” (.) (b) Item 3 Figure 4 Figure 5 Figure 6 t4

Claims (1)

[Claims] 1. In an electric discharge machining method in which a workpiece is machined by generating intermittent discharge in a machining gap between a machining electrode and a workpiece, the machining process is performed immediately after dielectric breakdown occurs in the machining gap. An electric discharge machining method characterized in that a machining current is superimposed in the direction opposite to the direction of the current output between the machining electrode and the workpiece. The electric discharge machining apparatus according to claim 1, wherein the operation of superimposing the machining current in the direction opposite to the direction of the current output between the electrode and the workpiece is performed at every intermittent and master pass. □ i,'nu Electrical discharge machining equipment that processes a workpiece by generating intermittent discharge in the machining gap between the industrial electric qt and the workpiece. In addition to connecting the anode of the DC power source constituting the main discharge circuit to the workpiece, there is also a power supply control circuit that controls the insulation value and the switching element inserted in the destructive pulse circuit. Electrical discharge machining equipment featuring: