JPS614620A - Electric discharge machining power supply device - Google Patents

Abstract

PURPOSE:To prevent a decrease of accuracy on a machining surface and eliminate its electrolytic corrosion or the like by an electrolytic current, by applying a voltage pulse of both positive and negative polarities across a machining gap between a electrode and a work to be machine and setting average voltage across the machining gap to zero. CONSTITUTION:Resistance values R11, R12 of current limiting resistors 16, 17 are selected to a sufficiently large level as compared with a resistance value R2 of a resistor 19. A peak current value, fed from the second DC power supply 7 by turning on a semiconductor switching element 18, is in sufficiently high level as compared with a peak current value fed from the first DC power supply 3 through switching elements 12-15, causing the switching element 18 to supply an electric current, contributing to electric discharge machining, across electrodes. An average value in a waveform of voltage between the electrodes is set to zero, but the current flowing between the electrodes never generates an average value of zero, and a device allows the currents to flow from a work 2 to be machined to the electrode 1, accurately machining the work.

Description

[Detailed description of the invention] [Invention Q5 technical field] The present invention relates to a power supply device for electrical discharge machining.

[Prior art]

Figure 7 shows the circuit configuration of a conventional electric discharge machining power supply device.
In the figure, (1) is an electrode for electrical discharge machining, (2) is a workpiece, (6) is a DC power source of lightning E El, and (41 is an electrode (1) and a first DC power source (3). Resistance value R4 between
The power MO8 connected through the current limiting resistor (5)
, a first semiconductor switching element such as an FET, (61
is a first drive circuit for driving the first semiconductor switching element (4). (7) is an electric IEE with a high voltage El of the first DC power supply (3)! (81 is a second semiconductor switching element connected between the electrode (1) and the second DC power source (71) via a resistor (9). The resistance value is much smaller than the resistance value R1 of the current limiting resistor (5). 6 (10) is a second drive circuit for driving the second semiconductor switching element (8) + ( 11X:J
Between the electrode (11) and the workpiece (21 (hereinafter referred to as the gap)
Each semiconductor switching element +4 is connected to the first drive circuit (6) and the second drive circuit (1o) according to the state of
1. (This is a control circuit that provides on/off signals of 81.

The operation of the conventional device configured as L5 above will be explained based on the flowchart shown in FIG. 8 and the voltage and current waveforms shown in FIG. (4) is turned on, the second semiconductor switching element (8) is turned off, and the first DC power supply (3) of 8EE is applied between the electrodes (based on the circuit shown in FIG. 9). Hiroshi 801
),.

At the end of the cycle, the current peak value is in a low state as shown in FIG. 9 fbl. This state continues until the insulation state in the minute gap between the electrodes breaks down and a discharge current flows, and as soon as the discharge occurs between the electrodes, the first semiconductor switching element (4
) and the second semiconductor switching element (8) are both turned on, and the discharge current Ip is supplied (state 803). After this state continues for a certain period of time Tp (state 804), the first
and a second semiconductor switching element +41. +81 is turned off and enters a so-called hibernation state (state 805). After this hibernation state continues as TOFF for a certain period of time (state 806), the first semiconductor switching element (4) is turned on again, and the second semiconductor switching element (8 ) returns to the off state.

The above-described first semiconductor switching element (4) and the second semiconductor switching element (4)
The semiconductor switching element (8) is repeatedly turned on and off by the control circuit (11). That is, the first DC power supply (3), the semiconductor switching element (4),
Current limiting resistor [5], electrode (1) and workpiece (2)
) The first switching circuit formed by the type 0] ignition circuit until a discharge occurs between the poles.

Current peak value is low. On the other hand, the second DC power supply (7).

Semiconductor switching element (81, resistor f91. electrode (
1) and the workpiece (2), the second switching circuit is for supplying current after the discharge occurs, and the current peak value Ip is % compared to the first switching circuit.
It is configured to be much higher.

Since the conventional electric discharge machining power supply device is configured as shown in step 5 above, the average value of the voltage between the machining electrodes has a polarity. An electrolytic current of 5 flows in one direction, as shown by the diagonal line in Fig. 9 fbl. This electrolytic action causes problems such as metal ions adhering to the surface of the workpiece and further causing electrolytic corrosion of the conductive parts of the workpiece or the workpiece joist gradually starting from the surface. In addition, when the surface area of the workpiece is large or when the workpiece is subjected to overlapping machining, the electrolytic current increases and a large-capacity power source is required. There was also the problem that the discharge power could not be achieved unless it was increased.

[Summary of the invention]

This invention was made with the aim of improving this problem, and by applying voltage pulses of both positive and negative polarities to the machining gap between the electrode and the workpiece, the average voltage in the machining gap is brought to zero and the electrolytic action is suppressed. It is an object of the present invention to provide a power supply device for electric discharge machining that is not affected by the influence and can flow machining current in one direction.

[Embodiments of the invention]

FIG. 1 is a diagram showing a circuit configuration of an embodiment of the present invention, in which numerals (12) to (15) are semiconductor switching elements, and the semiconductor switching element (12) is a first
DC power supply + 310) Resistance value R1 between the anode and electrode (1)
The semiconductor switching element (15) is connected between the cathode of the first DC power supply [3] and the workpiece (2). Further, the semiconductor switching element (13) is connected between the cathode surface electrode (1) of the first DC power supply (31), and the semiconductor switching element (
14)i! The anode of the first DC power supply (3) and the workpiece (2)
) between the current limiting resistor (i7) with a resistance value of R'12)
Even if the electrode (18) is connected through the electrode (11) and the workpiece (
2), a second DC power supply with a voltage E2 (power, resistance value R
2 resistor (19), current backflow prevention diode (2)
0) is a semiconductor switching element connected in series with 0). Here, as in the conventional device, the voltage E of the second DC power supply (7)
2 is the voltage IEE1 of the first DC power supply (3), and the resistance value R2 of the resistor (19) is the current limiting resistor (16).
This is a much smaller value than the resistance value of (17) "'11 * R42. (21) to (25) are the drive circuits that drive each semiconductor switching element (12) to (15) 418)v% (26) are these drive circuits (21) depending on the state between the poles.
This is each semiconductor switch control circuit.

What is the operation of the embodiment configured in X) above? The flowchart shown in FIG. 2 and the voltages shown in FIG.

The explanation will be based on the current waveform.

First, start operation (state 201), electrode 11)
And the semiconductor switching elements (12) to (15) connected to the bridge to be processed, the semiconductor switching elements (12), (15) ' on the diagonal line, and the semiconductor switching elements on the other diagonal line Motoko (13)
, (14) and the semiconductor switching element (18) connected to the second DC power supply (7) are turned off (state 201).
As shown in FIG. 6 (al), a voltage of 1 is applied between the two electrodes. After a period of time T1 has elapsed in this state (state 202), regardless of whether or not a discharge occurs between the electrodes. , all semiconductor switching elements (12) to (15), (18)'
& off, and the hibernation state (state 203) has elapsed for a period of time T2 (state 204), the semiconductor switching elements (12), (75) '&off, and the semiconductor switching elements 13λ (14 The semiconductor switching element (18) is also turned off (
State 205), at this time a voltage of 10E1 is applied between the electrodes. When discharge starts between the electrodes due to this voltage (state 2061, the semiconductor switching element (18) is turned on, and the current I during discharge from the DC power supply R2 (71) is applied between the electrodes.
p is supplied (state 207), and state (205)
After time Tl has elapsed (state 208), whether or not there is a discharge, it is determined whether the semiconductor switching element (18) is turned on or off (state 208).
Regardless of whether they are turned off or not, the semiconductor switching elements (1, 2) to (15), and (18) are turned off again to enter a dormant state (state 2'091°) After a period of time T has elapsed in this resting state (state 210), returns to state (201'), and repeats the above-described cycle.
r Since R42 is selected to be sufficiently large compared to the resistance value of the resistor (19), the second DC power supply is turned on by turning on the semiconductor switching element (18) as shown in the current waveform in Figure 3 (bl). (7) The peak current value supplied from the first
The current, which is sufficiently high compared to the peak current value supplied from the DC power source (3) of the present invention, and which contributes to actual electrical discharge machining, is mostly supplied between the electrodes by the semiconductor switching element (18). Therefore, the average value of the voltage waveform of the inter-electrode voltage shown in FIG. A current flows from the electrode (2) to the electrode (11).

In addition, in the above embodiment, the first switching circuit generates voltage pulses of both positive and negative polarities, and after the discharge occurs,
A second switching circuit that supplies a current pulse in one direction between the electrodes was separately provided, but the resistance value of the current limiting resistor (17) was R112k, and the resistance value of the current limiting resistor (16) was R11.
If it is made sufficiently smaller than 1, the second switching circuit can be omitted and the same effect can be achieved using only the first switching circuit.

In addition, as shown in FIG.
The second semiconductor switching element (18) is connected to the electrode (1), the workpiece ( 2
), the voltage El is connected in series with the second DC power source (7) and the resistor (19) with the resistance value &, and the resistance value Rq'l is reduced by 4 mm.This makes the circuit simple. As shown in the flowchart in Figure 11) R5 and the voltage and current waveforms in Figure 6, the same operation as in the above embodiment can be performed.

Furthermore, in the above implementation ψ11, the rest time was fixed during the voltage pulse of both positive and negative polarities, but these were modified to the inter-electrode state and external signal within the range where the average value of the inter-electrode voltage was zero. It may be changed.

〔Effect of the invention〕

As explained above, the present invention is based on the following points: applying a voltage pulse having the same peak value in both positive and negative polarities between the electrode and the workpiece;
While the average type lE between the electrodes was set to zero, the current pulse was made so that the peak value in one direction (positive or negative) was sufficiently thicker than the other, so that the accuracy of the machined surface decreased due to the electrolytic current l.5 Electrolytic corrosion etc. This has the effect of enabling highly accurate and high-speed machining, especially in wire electric discharge machines that often use water as a machining fluid.

[Brief explanation of drawings]

FIG. 1 is a circuit configuration diagram showing an embodiment of the present invention, and FIG. 2 is a flowchart of the embodiment shown in FIG.
l, (bl is the current waveform of the embodiment shown in FIG. 1, (al is the voltage waveform diagram, fbl is the current waveform diagram, and FIG. 4 is the current waveform diagram) 5 is a flowchart of the embodiment shown in FIG. 4, FIG. 6 is a diagram showing the constant pressure/current waveform of the embodiment shown in FIG. (bl is a current waveform diagram, Figure 7 is a circuit configuration diagram of a conventional electric discharge machining power supply device,
Fig. 8 is a flowchart of the conventional device shown in Fig. 7, and Fig. 9 (al, (bl) is a flowchart of the conventional device shown in Fig. 7.
(al is 'F!t, Ff, waveform diagram. fbl is current waveform diagram. (1)...electrode, (2)...workpiece, (3)...・
・First DC power supply. +41. (81, (12) ~ (15), (18)...
semiconductor switching element, +51. (16), (17)
... Current limiting resistor, (61, (10), (21)
(25)...Drive circuit, (A)...Second DC power supply, +91. (19),...Resistor, (11), (2
6)...control circuit. Note that the same reference numerals in each figure indicate the same or corresponding parts. Agent Patent Attorney Sanro Kimura No. 1 Figure 2 Figure 3 Figure 6 Figure 7f! f 81st! r

Claims (1)

[Claims] In an electric discharge machine that performs electric discharge machining while supplying a pulse current to a machining gap formed between an electrode and a workpiece through a machining fluid by a switching element that repeatedly turns on and off periodically, the above-mentioned method is used. One or more first DC power supplies connected to the machining gap and the first DC power source and alternately generating a positive pulse voltage and a negative pulse voltage so that the average value of the voltage/time product in the machining gap is always zero. When a discharge occurs in the machining gap with either a positive pulse voltage or a negative pulse voltage, a current pulse of the same polarity as the current generated by the first switching element is applied to the machining gap. A power supply device for electrical discharge machining, comprising: a second DC power supply and a second switching element that supply the power to the electrical discharge machining device; and a control circuit that controls operations of the first switching element and the second switching element.