JPS6279914A - Electric discharge machine - Google Patents

Abstract

PURPOSE:To prevent a phenomenon interrupting an electric discharge machining current, by switching a peak current value in the initial step to be controlled in accordance with a level of the preset value for the electric discharge machining current. CONSTITUTION:In a step number comparing output circuit 6, a binary counter 16 is loaded by an initial reset pulse LD to binary input data D0-D5 with 1, when binary setting step numbers N0-N5 are 7 or less (electric discharge machining current preset value in 4.5A or less), while 3, when said numbers are 8 or more (said current preset value in 5A or more), thereafter a count up is performed by a step period pulse ST. By the step number comparing output circuit 6 having a function as in the above, output terminals P0-P6 drive switching elements S0-S6 to be turned on or off. As a result, an electric discharge machining current is prevented from being interrupted on the half way because a peak current in the initial step of the electric discharge machining current can be increased to a high value even when an electro static stray capacity is provided between a machining electrode 2 and a work 3.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention connects a DC voltage source, a switching element, a current limiting resistor, and an interelectrode power supply feeder in series between a processing electrode and a workpiece. The present invention relates to controlling the machining current of an electric discharge machining apparatus that applies a pulse voltage and drives a machining electrode to machine a workpiece.

[Conventional technology]

In a conventional device of this kind, when increasing the current value at the initial stage of the electrical discharge machining current in a stepwise manner, the peak current value at the first step is fixed and is a constant value. A conventional device will be explained with reference to FIGS. 3 to 10. In Figure 3,
(1) is a DC power supply and is set to voltage V. (2) is a processing electrode, which is connected to the DC voltage source (1). (
3) is a workpiece, which is subjected to electrical discharge machining by a machining electrode (2) K attached to an electrode drive device (4). Workpiece (3
) is connected to the other half of the DC voltage source (1) connected in series with the resistors RO to R6 and the switching elements SO to S6'.

Switch element SO is IA, switch element S1 is 0, 5
A, switch element S2 is IA, switch element S3 is 2
A, switch element S4 carries a peak current of 4 A, switch element S5 carries a peak current of 8 A, and switch element S6 carries a peak current of 16 A.

(6) is a step number comparison output circuit, and output terminals PO to P
6 drives the switch elements SO to S6 to ON or OFF. The step number is input as a binary value to input terminals NO to N5. (5) is a step period output circuit which outputs a step period pulse signal STt to the step number comparison output circuit (6). The step period is input as a binary value to the input terminals TO to T6. It also outputs a reset signal LD that notifies the start of the step operation. (7) is an oscillation circuit that receives a pulse signal PS, a 10 MHz clock signal CK, and an interelectrode discharge detection signal DSt-S.

Figure 4 shows the step cycle output circuit (5) in Figure 3.
FIG. In Figure 4, (9) is a 7-bit binary counter, and (8) is a step period of 2.
Decimal value TO~T6 and output QO of binary counter (9)~
Comparators for determining the size of Q6, (10a) to (10d)
are D-flip-flops, (11a) to (i 1 b
) HAND Kate, (13H2 Human power NAND
K), (13 is an inverter, and α is a 6-person NAND gate.

Figure 5 shows the step number comparison output circuit (6
) is a circuit diagram showing details of the circuit. In FIG. 5, ae is a 6-bit binary counter, (15 is the binary value NO~N5 of the step number and the output QO~ of the binary counter CIE9.
A comparator that determines the size of Q5, (1η is a three-man melon gate, (18m) to (18g) are switch element drivers.

In addition, the binary value of the step number (hereinafter referred to as the binary setting step number) NO to N5 is the binary integer value divided by the value t-0,5A, which is the value obtained by subtracting one person from the set value of the electrical discharge machining current. It is.

Next, various operations will be explained with reference to FIGS. 3 to 5 and 6 to 8. In FIG. 3, the peak current flowing through the switching elements SO to S6 is determined by the ratio between the resistors RO to R6 and the machining voltage E obtained by subtracting the voltage between discharge electrodes from the voltage V of the DC voltage source (1). These current peak currents are IA and switch element S1 when switch element SO is turned on.
When they turn on simultaneously, 1.5 A increases by being added to the ON'l or OF'F of the switching elements SO to S6.

In addition, ON and OFF of the above-mentioned switch elements SO to S6
F is controlled by the outputs PO to P6 of the step number comparison output circuit (6).

Below, the outputs PO to P6 of the step number comparison output circuit (6)
An example will be explained with reference to FIGS. 4 to 7. In FIG. 4, PS is at logic 1 (6) while applying a voltage between the discharge electrodes with a pulse signal.

When a discharge occurs between the discharge electrodes and a current begins to flow, the machining current signal DS becomes logic 1 (6). At this time clock signal C
Logic 1 (B) is latched in the υD-flip-flop (10C) by K, and the initial reset signal LD is set to 3-manual NA.
It is output from ND gate I. After this, the binary counter (9
) is loaded with an initial value Q and counted using a signal obtained by dividing the clock CK by 172, and the count data appears at the outputs QO to Q6 of the binary counter (9). The output data QO to Q6 of the binary counter (9) and the step period binary data TO to T6 are compared by the magnitude comparator (8), and the output data of the binary counter (9) becomes equal to the step period binary data. or becomes much larger, the OA (1m output) of the magnitude comparator (8) becomes logic 1 (2) and O
A>, the output becomes logic 0■.

As a result, step period pulse (ST) iE2 - human power N
At the same time as the output from the AND game [3, 0 is loaded into the binary counter (9). This situation is shown in the time chart of FIG. Clock CK is 10 MHz, step period binary data is 2, TO=0, TI=1,
In this example, T2=O1T3=0, T4=0, T5=0, T6=0, and the step period pulse ST is output at a period of 0.4 μS.

The step period pulse ST is sent to a step number comparison output circuit (6) whose details are shown in FIG. In Fig. 5, PS is a pulse signal that connects the switch element driver (18a).
~(18g) and outputs the switch signal PO. LD and ST are signals from the step period output circuit, which are an initial reset pulse and a step period pulse, respectively. After the binary counter IIQ is loaded with 0 by the initial reset pulse LD, it is counted up by the step periodic pulse ST. A binary counter (10 counts up is a binary counter (1
e output QO~Q5 and binary setting step number NO~N5e
It is limited by the output 0Ak8 of the comparing magnitude comparator 09, and 2
When the output data of the binary counter (1e becomes equal to or larger than the binary set step number data, 3-Manual A
Close the ND gate circle and stop the operation of the binary counter (IF5).

The inputs to the switch element drivers (18b) to (18g) are the outputs QO to Q5 of the binary counter and the switch signal P.
Output to 1 to P6. The time chart in Fig. 7 shows the number of binary setting steps: 6, N0=0°N1=1, N2=1
, N5=0, N4=0, and N5=O. The machining current flows for one person according to the pulse signal PS, and then increases by 0.5 A as the count progresses. The seventh ST pulse is not counted.

[Problem that the invention seeks to solve]

In the conventional electric discharge machining apparatus as described above, the initial current value of the electric discharge machining current is set to a constant value of 1 A, with the peak current value of the first step being fixed as shown in FIG. , 5A in steps. By the way, when the set value of the electric discharge machining current is large, the stray capacitance i existing between the machining electrode and the workpiece increases, and as shown in FIG. 9(a), the first step at the start of electric discharge An inrush current that is larger than the peak current value flows, and the vibration causes a phenomenon in which the electric discharge machining current is interrupted.

The magnitude of the rush current tends to increase in proportion to the magnitude of the set value of the electrical discharge machining current.

When the electrical discharge machining current having the set pulse width is interrupted midway, the pulse width of the electrical discharge machining current becomes the result of the electrical discharge machining current having a shorter width than the set pulse width flowing twice. As shown in Figure 10, when the electric discharge machining current is the same set current, it is known that the electrode wear ratio increases as the pulse width of the electric discharge machining current becomes shorter. In this case, the electrode consumption ratio is large due to machining with an electric discharge machining current having a pulse width shorter than the setting, resulting in problems such as unmachined parts and a decrease in the number of times the machining electrode is used.

The present invention was made to solve this problem, and an object of the present invention is to provide an electric discharge machining apparatus in which the electric discharge machining current is not interrupted midway even when the set value of the electric discharge machining current is large.

[Means for solving problems]

The electric discharge machining apparatus according to the present invention, when increasing the current value in steps at the beginning of applying the electric discharge machining current, adjusts the peak current value of the first step according to the magnitude of the set value of the electric discharge machining current. When the current setting value is large, the peak current value of the first step is changed to a large value, and when the electric discharge machining current setting value is small, the peak current value of the first step is switched to a small value.

[Effect]

In this invention, when the current value is increased in steps at the initial stage of application of the electrical discharge machining current, the peak current value of the first step is switched according to the magnitude of the set value of the electrical discharge machining current. It is possible to prevent interruptions in the current from the start.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. 1st
Fig. 2 is a circuit diagram showing a step number comparison output circuit in an embodiment of the present invention, Fig. 2 shows an ideal waveform of the electric discharge machining current in an embodiment of the invention, and Fig. 2(a) shows the binary setting step number. The waveform diagram when is 7 or less, Figure 2 (b) is 2
Waveform diagram when the number of forward setting steps is 8 or more, Figure 9 (b
) is a waveform chart showing the actual waveform of the electrical discharge machining current in one embodiment of the present invention.

In Fig. 1, the parts with the same symbols as in Fig. 5 indicate the same parts, (11 is a three-man OR gate, and outputs a logic 1 OR gate when the binary value NO~N5 of the step number is a value of 8 or more. If the value is 7 or less, a logical 0 color is output. 6-bit binary counter (L61 binary input data DO~D
DO of 5 is connected to logic 1 output, Dl is OR gate 0
output or connected. Further, D2 to D5 are connected to logic 0 (0).

In this invention, the circuit configuration of the step number comparison output circuit shown in FIG. 1 is different from the conventional one shown in FIG. This is the same as the conventional device shown in FIG.

Next, the operation will be explained.

In FIG. 1, PS controls all switch element drivers (18a) to (18g) using pulse signals, and also outputs a switch signal PO.

LD and ST are signals from the step period output circuit,
They are an initial reset pulse and a step period pulse, respectively.

Binary counter (Ie9 is υ by the initial reset pulse LD)
, if the binary setting step number NO~N5 is 7 or less, that is, if the set value of the electric discharge machining current is 4.5A or less, 1.
However, when the number of binary setting steps is 8 or more, that is, when the set value of the electric discharge machining current is 5A or more, 3 is Do-D5.
After being loaded into the register, it is counted up by the step period pulse ST. Binary counter (The count up number of Ie is a magnitude comparator that compares the output QO to Q5 of binary counter αe with the number of binary setting steps No-N5e + 15
When the output data A≧8 of the binary counter fIQ becomes equal to or becomes larger than the binary set step number data, the 3-manual AND gate α7) is closed and the operation of the binary counter αe is stopped. make it stop. Inputs to the switch element drivers (18b) to (18g) are outputs QO to Q5 of binary counters, which output switch signals P1 to P6.

As a result, the waveform of the electric discharge machining current will be as shown in Figure #c2 (a) or Figure (b) in the ideal case 7 where there is no stray capacitance between the machining electrode and the workpiece. . In addition, even if there is stray capacitance between the machining electrode and the workpiece, the peak current of the first step of the electric discharge machining current is increased as shown in Figure 9 (b). , the current is not interrupted midway as shown by the solid line.

Furthermore, as the set value of the electric discharge machining current increases, the stray capacitance between the machining electrode and the workpiece increases, and even if a large inrush current flows at the start of electric discharge, as shown by the broken line B. Since the peak current value of the first step can be increased, the electric discharge machining current will not be interrupted even if there is vibration due to the rush current.

〔Effect of the invention〕

In accordance with the above-described process, the present invention includes a switching control circuit that switches and controls the peak current value of the first step of the electrical discharge machining current, which increases the current value stepwise, in accordance with the magnitude of the set value of the electrical discharge machining current. Therefore, it is possible to prevent the phenomenon in which the electrical discharge machining current is interrupted at the time when the first step current rises at the start of electrical discharge.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing a step number comparison output circuit in an embodiment of the present invention, Fig. 2 shows an ideal waveform of the electrical discharge machining current in an embodiment of the invention, and Fig. 2(a) shows a binary setting. Waveform diagram when the number of steps is 7 or less, Figure 2 (b)
is a waveform diagram when the number of binary steps is 8 or more, FIG. 6 is a configuration diagram showing an example of an electrical discharge machining device, FIG. 4 is a circuit diagram showing details of the step cycle output circuit shown in FIG. 6, and FIG. The figure is a circuit diagram showing details of the step number comparison output circuit shown in Figure 6, Figure 6 is a time chart of the operation of the step cycle output circuit, Figure 7 is a time chart of the operation of the step number comparison output circuit, and Figure 8 is a time chart of the operation of the step number comparison output circuit. The figure is a waveform diagram showing the ideal waveform of the electrical discharge machining current of a conventional device, FIG. 9(a) is a waveform diagram showing the actual waveform of the electrical discharge machining current of the conventional device, and FIG. FIG. 10 is a waveform diagram showing the actual waveform of the electrical discharge machining current in the example, and is a graph showing an example of the characteristics of the electrode consumption ratio in electrical discharge machining. In the figure, (1) is a DC power supply, (2) is a processing electrode,
(3) is the workpiece, (4) is the electrode drive device, (5) is the step period output circuit, (6) is the step number comparison output circuit, (7) is the oscillation circuit, 5O-86 is the switch element, RO
~R6 is a current limiting resistor. In the drawings, the same reference numerals indicate the same or similar metal parts. Agent Patent Attorney Tadashi Sato 1st Figure 6: Hired 1st person, 1st person, 1st year, 2nd figure (a) (b) 4th part, 5th vJ

Claims (2)

[Claims] (1) A machining electrode and a workpiece are opposed to each other with a small gap between them via the machining fluid, and an electric discharge machining pulse current is applied between the machining electrode and the workpiece, and the electric discharge machining pulse is In an electrical discharge machining device that performs electrical discharge machining by increasing the current value at the initial stage of the current in a stepwise manner, switching is performed to control the peak current value of the first step in accordance with the magnitude of the set value of the electrical discharge machining current. An electrical discharge machining device characterized by being equipped with a control circuit. (2) The peak current value of the first step of the electric discharge machining pulse current that increases the current value in steps is initially set to a value that is an integral multiple of 0.5A that is less than the set value of the electric discharge machining current. An electric discharge machining apparatus according to claim 1.