JPH01257513A - Electric discharge machine - Google Patents

Abstract

PURPOSE:To prevent lowering of surface coarseness and to prevent the occurrence of impossible machining due to the generation of electrolysis by a method wherein polarity of a voltage pulse is changed at intervals of the given number of pulses. CONSTITUTION:When a gate signal G1 is turned ON, a transistor T1 is turned ON, a bath voltage is generated at an interpole 10 only during an ON-period of the signal G1, and a discharge current 11 flows. Thereafter, by the generation of a gate signal G2 by means of a control circuit 20, a transistor T2 is turned ON, and a voltage in a reverse direction is applied at the interpole 10 and a discharge current 12 flows in a reverse direction to the direction of the current 11. Since the gate signals G1 and G2 are alternately generated, a voltage alternately different in polarity is generated at the interpole 10, and a discharge current also alternately different in a direction flows. Thereby, discharge by a floating capacity present in parallel to the interpole 10 is not generated, and thus since a discharge current by a charge charged by a floating capacity does flow between poles, a discharge current can be controlled by limit resistors R1 and R2.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to an electric discharge machine.

[Prior Art] As shown in FIG. 3, a conventional wire-cut electrical discharge machine includes a transistor T for controlling voltage application and a limiting resistor for limiting the discharge current between the power source B and the gap 11. R are connected in series. Trumpafusta T has the following figure 4 (1).
) is applied, and the voltage of power source B is intermittently applied to the gap 11.

[Problem to be solved by the invention] l: In the conventional example described above, the gate signal G is connected to the transistor T.
, the same voltage waveform as the gate signal G is applied to the gap 11.
However, the situation changes slightly due to the stray capacitance IiC applied in parallel with the electrode gap 11.6 In other words, if no discharge occurs in the electrode gap 11 even if a voltage is applied to the electrode gap 11, the As shown in Figure 4 (2), the gate signal G
Even if it disappears, a voltage remains between the electrodes 11 due to the charge charged in the stray capacitance C. Then, when a discharge is caused in the gap 11 by the next gate signal G, a discharge current flows in the gap 11.

As shown in FIG. 4 (3), this discharge current includes not only the current IB flowing from the battery B via the limiting resistor R, but also the discharge current IC caused by the charge that was being charged in the floating capacitor 1c. can be controlled by adjusting the value of the limiting resistor R, but even if the limiting resistor R is adjusted, the current IC1 cannot be controlled. For this reason, there is a problem in that the electric discharge machining energy cannot be reduced and the surface roughness decreases.

Further, if discharge is repeated at the same potential, there is a problem that electrolysis occurs, a degraded layer is generated, and machining may become impossible.

SUMMARY OF THE INVENTION An object of the present invention is to provide an electric discharge machine that does not reduce surface roughness and can prevent machining from occurring due to electrolysis.

[Means for Solving the Problems] In the present invention, firstly, the polarity of the voltage pulse is changed every predetermined number of voltage pulses.

[Function] Since the present invention changes the polarity of the voltage pulse every predetermined number of voltage pulses, the surface roughness does not decrease and it is possible to prevent processing failure due to electrolysis.

[Example〕 FIG. 1 is a block diagram showing one embodiment of the present invention.

This embodiment has a pole spacing 10 and two power supplies B1, B2.2.
two transistors T1, T2 and two limiting resistors I(1
, R2, and a control circuit 20.

The transistor T1 has a voltage [Bli,': Therefore, the electrode gap 10
The transistor T2 controls the supply of current in a predetermined direction from the power source B2 to the electrode gap 10 in the opposite direction.

Next, the operation of the above embodiment will be explained.

FIGS. 2(1) to 2(4) are diagrams ν1 of the operation of the above embodiment.

The control circuit 20 receives a gate signal G1 that controls the transistor T1 and a gate signal G2 that controls the transistor T2.
The pulse of the gate signal G1 and the gate signal G2 are generated.
The phase of the pulse is not different from that of the pulse.

First, when the gate signal G1 shown in Fig. 2 (1) turns on, the transistor Tff turns on, and a voltage between the electrodes (Fig. 2 (3)) is generated between the electrodes during the ON period of the gate signal Gl. However, the discharge current shown in FIG. 2 (4) is applied between the electrodes 10.
flows. Thereafter, the control circuit 20 generates the gate signal G2 shown in FIG. 2(2), so that the transistor T2 is turned on, and a voltage in the opposite direction is applied to the electrode gap 1o for only this period, thereby causing a discharge current l2 (in the opposite direction to Ij) flows. 17 as above, the gate signals G1 and G
2 are generated alternately, so voltages with alternately different polarities are generated between the electrodes 10, and the discharge 'i! Electric lights also have current flowing in different directions alternately.

In this way, since a voltage with a different polarity is applied to the electrode gap 10 each time, there is no discharge due to stray capacitance existing in parallel with the electrode gap 10. For example, when the transistor T1 is turned on, the electrode gap 10 is applied to the electrode gap 10. Even if the stray capacitance existing in parallel with 10 is charged, when the transistor T2 is turned on at the next timing, the charge charged in the stray capacitance does not pass through the electrode gap 10 and is transferred to the transistor T2.
2. It is discharged via the limiting resistor R2 and the power source B2. 1
．． Therefore, the discharge due to the charge stored in the stray capacitance 'f
L flow does not flow to the gap 10 between poles.

In this way, since the discharge current due to the electric charge charged in the stray capacitance does not flow into the gap 10, the discharge current can be controlled by the limiting resistors R1 and R2, and the electric discharge machining energy can be reduced. The machined surface roughness can be improved.

Further, since electric discharges of opposite polarity are alternately repeated in the gap 10, no oxide film is formed in the gap 10, which is advantageous for electric discharge machining of aluminum, ceramics, etc.

Note that since the polarity between the poles is always reversed, the state is such that electric discharge is likely to occur, and electric discharge is reliably generated for almost all pulses, increasing the machining speed. In other words, in the conventional device,
In order to allow sufficient insulation recovery time, the time from one discharge to the next is made long. Therefore, in the conventional device, the number of discharges per unit time is small, but in the above embodiment, the recovery time of the insulation does not need to be so long, so the number of discharges per unit time can be increased. Processing can be made faster.

Furthermore, since the voltage across the machining gap 10 is apparently higher, the waiting time can be reduced, and the number of repetitions of electric discharge per unit time can be increased, so that the machining speed can be increased.

In the above embodiment, one voltage pulse of opposite polarity is generated for one voltage pulse of a certain direction, and pulses of mutually different polarities are generated alternately. In contrast, pulses of the opposite polarity may be continuously applied to the plurality of electrode gaps 10.

In the above case, the number of consecutive voltage pulses with a polarity negative on the electrode side and positive on the workpiece side is equal to the number of consecutive voltage pulses with a polarity positive on the electrode side and negative on the workpiece side. The number may be greater than the number applied to the electrode gap 10. Since machining is faster when the polarity voltage pulse is negative on the 'frL pole side and positive on the workpiece side, the overall machining speed is improved by doing the above.

Furthermore, the value of the discharge current in a voltage pulse of a predetermined polarity and the value of the discharge current in a voltage pulse of a polarity opposite to the predetermined polarity may be made different by adjusting the limiting resistors R1 and R2. By doing so, the machining speed can also be improved.

Note that the on time and off time of the gate signal G1 or G2 can be changed depending on the decoration.

In addition, power source B1. , B2 may be set to be different from each other, and other switching elements may be used in place of the transistors T1 and T2, and the present invention may be applied to both wire-cut electric discharge machines and die-sinker electric discharge machines. It can be applied.

[Effects of the Invention] According to the present invention, there is an effect that the surface roughness does not decrease (and the inability to process due to electrolysis can be prevented).

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing one embodiment of the present invention. FIGS. 2(1) to 2(4) are explanatory diagrams of the operation of the above embodiment. FIG. 3 is a discharge circuit diagram of a conventional device. FIGS. 4(1) to 4(3) are explanatory diagrams of the above-mentioned conventional device. B1. B2...power supply, R1, R2...limiting resistance, 10...between poles. Patent applicant Sodick Co., Ltd. Agent Arata Yokubo - rt rt Figure 3 (1) Gate anxiety G (2) Electromagnetic tile [゛''Re, I (:.

Claims (5)

[Claims] (1) An electrical discharge machine that applies a rectangular-wave voltage pulse between machining electrodes, characterized in that the polarity of the voltage pulse is changed every predetermined number of voltage pulses. (2) According to claim (1), electrical discharge machining characterized in that for each voltage pulse of a predetermined polarity, at least one of the voltage pulses of a polarity opposite to the predetermined polarity is applied between the poles. Machine. (3) The electrical discharge machine according to claim (1), wherein the voltage pulse of a predetermined polarity and the voltage pulse of a polarity opposite to the predetermined polarity are alternately applied between the poles. (4) In claim (1), the number of consecutive voltage pulses applied between the electrodes with the polarity negative on the electrode side and positive on the workpiece side is defined as the number of voltage pulses with the polarity negative on the electrode side and positive on the workpiece side. The electric discharge machine is characterized in that the number of the voltage pulses is set to be greater than the number of voltage pulses that are continuously applied between the electrodes. (5) The electric discharge machine according to claim (1), wherein the value of the discharge current in the voltage pulse of a predetermined polarity is different from the value of the discharge current in the voltage pulse of the opposite polarity to the predetermined polarity.