JPH04322910A - Electric discharge machine - Google Patents

Abstract

PURPOSE:To enhance the machining characteristic during finishing or fine electric discharge machining. CONSTITUTION:During finishing or fine machining by an electric discharge machine, a machining control section A applies machining pulses through a machining gap between a workpiece 1 and a machining electrode 2 under a preset machining condition. Accordingly, arcs are generated in the machining gap. A detecting section B detects an electric discharge condition in the machining gap. A calculating section C counts numbers of cycles of generation of pulses and cut-off of arcs, and calculates a frequency N of occurrence of cut-off of arcs. A determining section D delivers a control signal h1 to the machining control section A if the frequency H of occurrence of cut-off arcs exceeds a reference value P. When the control signal h1 is inputted, the machining control section A decreases the value of a resistance 6, the peak value of machining current is set to be high so as to change the machining condition by which the frequency of cut-off of arcs is reduced.

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 machining and micromachining (hereinafter simply referred to as finishing machining).

0002

[Prior Art] Electrical discharge machines apply machining pulses to the machining gap between a machining electrode and a workpiece to generate intermittent arc discharge, and the heat generated at that time causes the surface of the workpiece to (processed surface) is melted and removed to perform the required processing on the workpiece. In finishing machining in such electrical discharge machining, in order to reduce the surface roughness of the machined surface, it is necessary to reduce the amount of machining of the workpiece by applying each machining pulse. For this reason, in general, finishing machining is performed by setting the machining current flowing through the machining gap to the minimum value that can maintain arc discharge. For this reason, arc discharge generated in the machining gap during machining may be interrupted for some reason, so-called arc breakage.

0003

In the above-mentioned conventional electric discharge machining finishing process, when arc breakage occurs, the machining current flowing through 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 (continuous application time) of the machining current
Since the consumption rate of the machining electrode is inversely proportional to the consumption rate of the machining electrode, the consumption of the machining electrode increases and the shape accuracy of the workpiece decreases. In addition, arc breakage causes variations in machining amount due to uneven machining energy for each machining current pulse.
The roughness of the machined surface of the workpiece is also made non-uniform. Furthermore, when arc breakage occurs, machining is interrupted, resulting in a decrease in machining speed. An object of the present invention is to provide an electric discharge machine that can improve machining characteristics (shape accuracy of a workpiece, uniformity of machined surface roughness, and machining speed) in finishing machining.

0004

[Means for Solving the Problems] In order to achieve the above object, the configuration of an electric discharge machine of the present invention will be explained using FIG. 1 corresponding to an embodiment. In the figure, 1 is a workpiece. Reference numeral 2 denotes a machining electrode, which faces the workpiece 1 with a required machining gap. A is a machining control unit that applies machining pulses to the machining gap based on preset machining conditions. B is a detection unit that detects the discharge state of the machining gap. C is a calculating section connected to the detecting section B to calculate the frequency of occurrence of arc breakage. Reference numeral D denotes a determination section, which is connected to the calculation section C, determines whether or not it is necessary to change the machining conditions, and applies this determination result to the machining control section A.

[0005]

[Operation] Then, the machining control section A applies a machining pulse to the machining gap between the workpiece 1 and the machining electrode 2. Then, arc discharge occurs in the machining gap. Detector B detects the discharge state of the machining gap. The calculation unit C counts the number of occurrences of the machining current pulse and arc breakage detected by the detection unit B, and determines the number N of occurrences of the arc breakage. The determination unit D compares the number of arc breakage occurrences N input from the calculation unit C with a reference value R, and if the number of occurrences N is greater than or equal to the reference value R, outputs a control signal to the processing control unit A. . When the control signal from the determination section D is input, the processing control section A changes the settings of the processing conditions so that the number of arc breakage occurrences N is reduced. As mentioned above,
Since the machining conditions are changed so that the number of occurrences of arc breakage is reduced, the machining characteristics can be improved.

[0006]

[Example] An example of the electric discharge machine of the present invention is shown below in Fig. 1.
This will be explained with reference to FIG. As shown in FIG. 1, the electric discharge machine of the present invention includes a machining control section A, a detection section B that detects the discharge state, and a detection section B that detects the frequency of occurrence of arc breakage based on the discharge state detected by the detection section B. It consists of a calculation unit C that performs calculations, and a determination unit D that determines whether or not to change the machining conditions based on a preset reference value R. are connected so as to face each other with the required machining gap.

The processing control section A is constructed as follows. 3 is a numerical control device in which machining conditions (peak value and pause time of machining pulse voltage, peak value of machining current, continuous application time K, etc.) are set. Reference numeral 4 denotes a variable output DC power supply, which is connected to the numerical control device 3, with a processing electrode 2 connected to its positive terminal, and a switching transistor 5 and a variable resistor 6 connected in series to its negative terminal. The workpiece 1 is connected via the. Further, the resistance value of the variable resistor 6 is changed by the numerical control device 3. A control circuit 7 is connected to the numerical control device 3 and a detection circuit 8 to be 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.

Detector B is constructed as follows. A detection circuit 8 is connected to the DC power source 4 in parallel with the workpiece 1 and the machining electrode 2 so as to detect the voltage in the machining gap, and is also connected to the control circuit 7. 9 is an oscillator, which generates several MHz to several tens of MHz (for example, 20
A clock with a period of MHZ) is oscillated. 10 is an AND circuit connected to the detection circuit 8 and the oscillator 9. Reference numeral 11 denotes a control circuit, which is connected to the detection circuit 8. 12 is a counter circuit, which 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. Reference numeral 14 denotes a setting circuit in which a ratio L between the duration of arc discharge and the time of arc breakage (determined by the required machining characteristics, etc.) is set. Reference numeral 15 denotes an arithmetic circuit, which is connected to the numerical control device 3 and the setting circuit 14, and calculates a criterion value M for determining arc breakage. 16 is a discrimination circuit, which includes a control circuit 11 and a latch circuit 1.
3 and the setting circuit 15, and determines whether or not an arc is broken.

The calculation section C is configured as follows. 17 is a ring counter circuit, which 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.

The determining section D is constructed as follows. 21
is a setting circuit in which the allowable frequency of arc breakage occurrence is set as a reference value R. 22 is a judgment circuit, and latch circuit 2
0, is connected to the setting circuit 21, determines whether or not it is necessary to change the machining conditions, and applies the output to the numerical control device 3.

With such a configuration, the numerical control device 3 controls the voltage of the DC power source 4 and
The resistance value of the resistor 6 is set, and the machining current is continuously applied to the control circuit 7 for a duration K (time from the first fall of each machining pulse applied to the machining gap until the application of the machining pulse is interrupted).
and setting the pause time of the processing pulse, and the calculation 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 machining pulse of a set voltage to the machining gap via the transistor 5 and the resistor 6. When arc discharge occurs in the machining gap, the machining voltage drops as shown by waveform b in FIG. The detection circuit 8 outputs a detection signal that detects the falling edge of the processing pulse to the control circuit 7. The control circuit 7 is
When the detection signal that detected the first fall of each machining pulse was input from the detection circuit 8, the transistor 5 was turned on from time t1 until the continuous application time K of the machining current set by the numerical control device 3. Then turn it off. Then, after a pause time of the machining pulse of the voltage set by the numerical control device 3, the transistor 5 is turned on. By repeating the above operation, the DC power supply 4 applies a machining pulse to the machining gap as shown by waveform a.

When arc discharge occurs at time t1, a machining current flows through the machining gap as shown by waveform c, and a machining voltage decreases as shown by waveform b. Furthermore, if arc breakage occurs during the application of a machining pulse, the machining current is cut off as shown in waveform c, and the machining voltage increases as shown in waveform b. The detection circuit 8 considers that a machining current is flowing when the machining voltage shown in waveform b is lower than a preset reference value Vb while the control circuit 7 turns on the transistor 5, and the machining current is shown in waveform c. Generate a voltage as shown in waveform d, which is the same as the machining current, and apply the voltage to AND circuit 1.
0 and output to the control circuit 11. The AND circuit 10 performs an AND condition between a clock as shown in a waveform e input from the oscillator 9 and a voltage as shown in a waveform d input from the detection circuit 8, and performs an AND condition as shown in a waveform f indicating intermittent arc discharge. Outputs a clock. The counter circuit 12 receives clocks f1, f2, f3, f input from the AND circuit 10.
Count 4. When the voltage (waveform d) inputted from the detection circuit 8 falls, the control circuit 11 outputs a latch signal to the latch circuit 13 at time t2, and then outputs a clear signal to the counter circuit 12, and makes a determination. The command is output to the discrimination circuit 16. The latch circuit 13 stores the number of clocks (J=4) being applied from the counter circuit 12 when the latch signal is input from the control circuit 11. When the counter circuit 12 receives a clear signal from the control circuit 11, it resets the number of clocks counted so far (J=4). The arithmetic circuit 15 calculates the continuous application time of the machining current input from the numerical control device 3 (converted into the number of clocks oscillated from the oscillator 9; for example, K=10) and the ratio input from the setting circuit 14 (for example, L = 60%) to determine the criterion value for arc breakage (number of pulses M = 6)
seek. The determination circuit 16 receives the number J of clocks input from the latch circuit 13 and the determination reference value M input from the arithmetic circuit 15 when the determination command is input from the control circuit 11 or from the latch circuit 13. When the number J of clocks is smaller than or equal to the judgment reference value M,
Detected as arc breakage. In this example, since the number of clocks (J=4) is smaller than the judgment reference value (M=6),
It is detected as an arc breakage, and an arc breakage detection signal g1 is output to the counter circuit 19 as shown in the waveform g. Similarly, the discrimination circuit 16 outputs arc breakage detection circuits g1 to g5 to the counter circuit 19. The counter circuit 19 counts arc breakage detection signals g1 to g5 inputted from the discrimination circuit 16. Ring counter circuit 17
counts the pulses d1 to d7 of the waveform d input from the detection circuit 8, and outputs a carry signal to the control circuit 18 when the counted value (P=7) exceeds a preset value (Q=6). After that, reset the value counted up to that point. When the carry signal is input from the ring counter circuit 17 , the control circuit 18 outputs a latch signal to the latch circuit 20 and then outputs a clear signal to the counter circuit 19 . The latch circuit 20 stores the number of arc breakage detection signals (N=5) applied from the counter circuit 19 when the latch signal is input from the control circuit 18. Counter circuit 19
When the clear signal is input from the control circuit 18, the number of arc breakage detection signals counted up to that point is reset. The determination circuit 22 compares the number N of arc breakage detection signals inputted from the latch circuit 20 and the reference value R inputted from the setting circuit 21, and determines whether the number N of detection signals is greater than or equal to the reference value R. At this time, a control signal h1 having a waveform h is output to the numerical control device 3. In this embodiment, since the number of arc breakage detection signals (N=5) and the reference value (R=5) are equal, the control signal h1 is output to the numerical control device 3. When the control signal h1 is input from the determination circuit 22, the numerical control device 3 decreases the value of the resistor 6 to reduce arc breakage, and increases the peak value of the machining current in the machining conditions. As described above, according to this embodiment, the machining conditions are set to increase the peak value of the machining current so that the frequency of arc breakage is reduced. uniformity of thickness and processing speed).

[0013]

As described above, according to the present invention, machining pulses are applied to the machining gap between the workpiece and the machining electrode based on the machining conditions preset in the machining control section, and In an electric discharge machine that performs machining by generating arc discharge, a detection unit detects the discharge state of the machining gap, and the frequency of occurrence of arc breakage is determined based on the discharge state detected by this detection unit. A calculating section compares the arc breakage occurrence frequency determined by the calculating section with a preset reference value to determine whether or not the machining conditions need to be changed, and applies this determination result to the machining control section. Since the determination unit is provided and the peak value of the machining current is increased so that the frequency of occurrence of arc breakage is reduced, the machining characteristics can be improved.

[Brief explanation of drawings]

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

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

[Explanation of symbols]

1 Workpiece 2 Processing electrode A Processing control section B Detection part C Calculation part D Judgment section

Claims (1)

[Claims] [Claim 1] Machining is performed by applying a machining pulse to a machining gap between a workpiece and a machining electrode based on machining conditions preset in a machining control section to generate intermittent arc discharge. In the electrical discharge machine, there is a detection unit that detects the discharge state of the machining gap, a calculation unit that calculates the frequency of occurrence of arc breakage based on the discharge state detected by the detection unit, and an arc breakage frequency determined by the calculation unit. Electrical discharge machining characterized by comprising: a determination unit that determines whether or not the machining conditions need to be changed by comparing the frequency of occurrence with a preset reference value, and applies this determination result to the machining control unit. Machine.