JP3113305B2 - Electric discharge machine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric discharge machine, and more particularly to an electric discharge machine suitable for improving machining characteristics in finishing and fine machining (hereinafter, simply referred to as finishing).

[0002]

2. Description of the Related Art An electric discharge machine applies a machining pulse to a machining gap between a machining electrode and a workpiece to generate an intermittent arc discharge, and heat generated at that time causes a surface of the workpiece to be processed. (Processed surface) is melted and removed to perform required processing on the workpiece. In finish machining in such electric discharge machining, it is necessary to reduce the amount of machining of the workpiece by applying each machining pulse in order to reduce the surface roughness of the machining surface. For this reason, in the finishing processing, the processing is generally performed by setting the processing current flowing in the processing gap to a minimum value that can be maintained by the arc discharge. Therefore, an arc discharge generated in the machining gap during machining may be interrupted for some reason, that is, a so-called arc break may occur.

[0003]

In the above-mentioned conventional electric discharge machining, when an arc break occurs, the machining current flowing in the machining gap becomes shorter than the continuous application time of the machining current set as the machining condition. Then, as is generally known, the pulse width of the machining current (continuous application time)
And the consumption rate of the machining electrode are in inverse proportion, the consumption of the machining electrode is increased and the shape accuracy of the workpiece is reduced. In addition, in the case of arc break, the processing amount varies to make the processing energy for each processing current pulse non-uniform,
The surface roughness of the workpiece is also made non-uniform. Further, when an arc break occurs, the processing is interrupted, so that the processing speed is reduced. An object of the present invention is to provide an electric discharge machine capable of improving machining characteristics (shape accuracy of a workpiece, uniformity of a machined surface roughness, machining speed) in finishing machining.

[0004]

In order to achieve the above-mentioned object, the present invention provides a method for forming a gap between a workpiece and a processing electrode.
A pulse-like voltage based on a preset machining condition is applied to the machining control unit to generate an intermittent arc discharge having a predetermined discharge current value, perform machining, and detect a discharge state of the machining gap. In the electric discharge machine
When the duration included in the predetermined number of discharges is predetermined
Count the number of discharges shorter than the interval, and the counted value is a predetermined value
In the above case, the value of the discharge current is increased.

[0005]

The duration included in the predetermined number of discharges is determined in advance.
Count the number of discharges shorter than the specified time, and
If the value is equal to or more than the predetermined value, the value of the discharge current is increased , so that it is difficult to break the arc.

[0006]

FIG. 1 shows an embodiment of an electric discharge machine according to the present invention.
FIG. As shown in FIG. 1, the electric discharge machine of the present invention, based on a machining control unit A, a detection unit B for detecting a discharge state, and a discharge state detected by the detection unit B, determines the frequency of occurrence of arc breakage. The processing control unit A includes a calculating unit C for calculating and a determining unit D for determining whether or not the processing conditions need to be changed based on a preset reference value R. Are connected so as to face each other at a required machining gap.

[0007] The machining control unit A is configured as follows. Numeral control device 3 sets processing conditions (the peak value of the voltage of the processing pulse and the pause time, the peak value of the processing current and the continuous application time K, etc.). Reference numeral 4 denotes a variable output type DC power supply, which is connected to the numerical controller 3, the processing electrode 2 is connected to the positive electrode side, and the switching transistor 5 and the variable resistor 6 connected in series to the negative electrode side. The workpiece 1 is connected via the. Further, the resistance value of the variable resistor 6 is changed by the numerical controller 3. Reference numeral 7 denotes a control circuit which is connected to the numerical control device 3 and a detection circuit 8 described later, and controls on / off of the transistor 5 based on a command from the numerical control device 3 and a detection signal from the detection circuit 8.

[0008] The detection section B is configured as follows.
A detection circuit 8 is connected to the DC power supply 4 in parallel with the workpiece 1 and the processing electrode 2 so as to detect a voltage in the processing gap, and is connected to the control circuit 7. Reference numeral 9 denotes an oscillator, which is several MHZ to several tens MHZ (for example, 20 MHz).
MHZ). An AND circuit 10 is connected to the detection circuit 8 and the oscillator 9. A control circuit 11 is connected to the detection circuit 8. A counter circuit 12 is connected to the AND circuit 10 and the control circuit 11. A latch circuit 13 is connected to the control circuit 11 and the counter circuit 12. A setting circuit 14 sets a ratio L (determined by required machining characteristics or the like) between the arc discharge duration time and the arc break time.
An arithmetic circuit 15 is connected to the numerical control device 3 and the setting circuit 14, and obtains a judgment reference value M for judging arc breakage. Reference numeral 16 denotes a discrimination circuit, and the control circuit 11, the latch circuit 1
3 and the setting circuit 15 to determine the presence or absence of an arc break.

[0009] The calculation unit C is configured as follows.
A ring counter circuit 17 is connected to the detection circuit 8. A control circuit 18 is connected to the ring counter circuit 17. A counter circuit 19 is connected to the determination circuit 16 and the control circuit 18. A latch circuit 20 is connected to the control circuit 18 and the counter circuit 19.

[0010] The determination unit D is configured as follows. 21
Is a setting circuit in which the allowable frequency of occurrence of arc break is set as a reference value R. 22 is a judgment circuit, and the latch circuit 2
0, connected to the setting circuit 21 to determine whether or not the processing conditions need to be changed, and apply the output to the numerical controller 3.

With such a configuration, the numerical controller 3 controls the voltage of the DC power supply 4 based on preset processing conditions,
The resistance value of the resistor 6 is set, and the application time K of the machining current is applied to the control circuit 7 (the time from the first fall of each machining pulse applied to the machining gap until the application of the machining pulse is interrupted).
And the pause time of the machining pulse, and the arithmetic circuit 1
5, the continuous application time K is output. When the control circuit 7 turns on the transistor 5, the DC power supply 4 applies a processing pulse having a set voltage to the processing gap via the transistor 5 and the resistor 6. When an arc discharge occurs in the machining gap, the machining voltage drops as shown by a waveform b in FIG. The detection circuit 8 outputs to the control circuit 7 a detection signal that has detected the falling of the machining pulse. The control circuit 7
When a detection signal that detects the first fall of each processing pulse is input from the detection circuit 8, the transistor 5 is turned on from this time t1 until the continuous application time K of the processing current set by the numerical controller 3. Then turn off. Then, the transistor 5 is turned on after the pause time of the machining pulse of the voltage set by the numerical controller 3. By repeating the above operation, the DC power supply 4 applies a processing pulse to the processing gap as shown by the waveform a.

When an arc discharge occurs at time t1, a machining current flows through the machining gap as shown by a waveform c, and the machining voltage falls as shown by a waveform b. If an arc break occurs during the application of the machining pulse, the machining current is cut off as shown by the waveform c, and the machining voltage rises as shown by the waveform b. While the control circuit 7 turns on the transistor 5 when the processing voltage shown in the waveform b is lower than the preset reference value Vb while the control circuit 7 is on, the detection circuit 8 considers that the processing current is flowing and shows the waveform c. A voltage as shown by a waveform d that is the same as the machining current is generated, and the voltage is output to the AND circuit 10 and the control circuit 11. AND circuit 10
An AND condition is applied between a clock such as a waveform e input from the oscillator 9 and a voltage d shown in the waveform d input from the detection circuit 8 to output a clock such as a waveform f indicating intermittent arc discharge. . The counter circuit 12 receives the clocks f ₁ , f ₂ , f ₃ , f ₄ inputted from the AND circuit 10.
Count. The control circuit 11, the voltage input from the detection circuit 8 (waveform d) falls in its time t _2, the
The latch signal is output to the latch circuit 13, then the clear signal is output to the counter circuit 12, and the determination command is output to the determination circuit 16. The latch circuit 13 stores the number of clocks (J = 4) applied from the counter circuit 12 when the latch signal is input from the control circuit 11. When the clear signal is input from the control circuit 11, the counter circuit 12 resets the number of clocks counted so far (J = 4). The arithmetic circuit 15 converts the continuous application time (converted to the number of clocks oscillated from the oscillator 9; for example, K = 10) of the machining current input from the numerical controller 3 to the ratio (for example, K = 10) input from the setting circuit 14. L = 60%) to determine a criterion value (number of pulses M = 6) of arc break. When the determination command is input from the control circuit 11 or when input from the latch circuit 13, the determination circuit 16 determines the number J of clocks input from the latch circuit 13 and the determination reference value M input from the arithmetic circuit 15. And when the number J of clocks is smaller than or equal to the criterion value M, it is detected as an arc break. In this embodiment, since the number of clocks (J = 4) is smaller than the criterion value (M = 6), it is detected as a broken arc, and a detection signal g _{1 of the} broken arc is sent to the counter circuit 19 as shown in a waveform g. Output. Similarly, the discrimination circuit 16 outputs the arc break detection circuits g ₁ to g ₅ to the counter circuit 19. Counter circuit 1
9, to the detection signal g ₁ without the arc interruption input from the determination circuit 16 counts the g _5. The ring counter circuit 17
The pulses d ₁ to d _{7 of the} waveform d input from the detection circuit 8
, And the counted value (P = 7) is replaced with a preset value (Q =
If 6) is exceeded, a carry signal is output to the control circuit 18 and the values counted so far are reset. Control circuit 18
When the carry signal is input from the ring counter circuit 17, the latch signal is output to the latch circuit 20 and then the clear signal is output to the counter circuit 19. Latch circuit 20
Stores the number (N = 5) of arc cut detection signals applied from the counter circuit 19 when the latch signal is input from the control circuit 18. When the clear signal is input from the control circuit 18, the counter circuit 19 resets the number of arc break detection signals counted so far. The determination circuit 22 compares the number N of the detection signals of the arc interruption input from the latch circuit 20 with the reference value R input from the setting circuit 21, and the number N of the detection signals is larger than or equal to the reference value R. At this time, the control signal h ₁ shown in the waveform h is output to the numerical controller 3. In this embodiment, since the number of detection signals (N = 5) of the arc break is equal to the reference value (R = 5),
The control signal h ₁ is output to the numerical controller 3. Numerical controller 3, the control signal h ₁ is input from the determination circuit 22, to reduce the value of the resistor 6 to reduce the arc interruption, to increase the peak value of the machining current in the processing conditions.
As described above, according to the present embodiment, the processing conditions are set such that the peak value of the processing current is increased so that the frequency of occurrence of arc breaks is reduced. Uniformity, processing speed) can be improved.

[0013]

As described above, according to the present embodiment,
By applying a pulse-like voltage based on the processing conditions set in advance to the processing control unit in the processing gap between the workpiece and the processing electrode, generating an intermittent arc discharge having a predetermined discharge current value. In the electric discharge machine which performs the machining and detects the discharge state of the machining gap, a predetermined discharge
The duration included in the number of calls is shorter than the predetermined time
Count the number of discharges, and if the counted value is
In this case, since the value of the discharge current is increased, the shape accuracy of the workpiece, the uniformity of the processed surface roughness, the processing speed can be improved, and the processing speed can be increased.

[Brief description of the drawings]

FIG. 1 is a block diagram of an electric discharge machine according to the present invention.

FIG. 2 is a waveform chart for explaining the operation of the electric discharge machine of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Workpiece 2 Processing electrode A Processing control part B Detection part C Calculation part D Judgment part

Claims (1)

(57) [Claims] An intermittent arc in which a pulse-like voltage is applied to a machining gap between a workpiece and a machining electrode based on machining conditions preset in a machining control unit, and a discharge current value is predetermined. In the electric discharge machine, which performs the machining by generating the electric discharge and detects the electric discharge state of the machining gap, when the duration included in the predetermined number of discharges is predetermined.
Count the number of discharges shorter than the interval, and the counted value is a predetermined value
In the above case, the value of the discharge current is increased.