JPH06262435A - Electric discharge machining method and device - Google Patents

Abstract

PURPOSE:To solve a problem of worsening machining efficiency due to generating improper servo reference voltage by decreasing impedance of a machining gap in the case of electric discharge machining by water machining fluid. CONSTITUTION:Whether a characteristic part of the last stage electrolytic condition appears or not is discriminated by an evaluating part 19, and in the case of performing servo control in a machining condition different from a spark discharge, a servo reference value capable of obtaining a machining gap length such as enabled to generate the spark discharge is given by a servo control part 16.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a die-sinking electric discharge machining method and apparatus for electric discharge die-sinking a workpiece using water or a so-called water-based machining fluid based on water.

[0002]

2. Description of the Related Art It is known that when an electric discharge machining apparatus is used to perform electric discharge machining of a workpiece using a water-based machining liquid, tar is likely to be generated in a machining gap. Since this tar has conductivity, the impedance of the machining gap locally decreases as the tar accumulates, and when electrolytic current or arc current flows, the machining speed decreases. There arises a problem that the processed surface of the work piece is deteriorated.

In particular, under a processing condition such as a finishing processing area where processing is performed with a small processing current, the value of the current limiting resistor of the power source is set to a large value, so that the internal impedance of the power source becomes large and the accumulation of tar. If the impedance of the electrical discharge machining gap decreases due to ionization of the machining fluid (reduction of the specific resistance), the level of the voltage applied to the machining gap decreases, and the phenomenon that the voltage becomes smaller than the servo reference voltage value tends to occur. ing. Further, when the electrolysis current starts to flow continuously, the electrolysis voltage waveform is higher than the normal discharge voltage waveform, and the average value of the machining voltage rises, and the servo control detection means determines that the gap voltage is in the normal machining state and the discharge is performed. Servo control continues even if it is not installed.
In this way, in a machining area where machining is performed with a small machining current, the servo reference voltage becomes improper due to the decrease in impedance in the machining gap, which prevents machining from proceeding. However, it has a peculiar problem that a finished surface cannot be obtained.

Therefore, in order to solve this kind of problem, it is necessary to remove tars or ions generated between the electrodes. Therefore, for example, in Japanese Unexamined Patent Publication No. 4-101722, the impedance state of the electric discharge machining gap is detected every time the machining pulse voltage is applied, and the polarity of the machining voltage is switched according to the detection result, so that a long time can be obtained. A configuration is disclosed that ensures a stable and stable discharge state.

[0005]

However, according to this conventional technique, the impedance state of the machining gap is detected every time the machining pulse voltage is applied, and the electrolytic state of the machining liquid in the machining gap is discriminated each time. In addition to the problem that the polarity of the machining voltage is frequently switched, the machining speed is rather reduced, and under the condition that a small machining current is used, the machining progresses even if the polarity is switched for the above reason. There is a problem that it may disappear and fall into an electrolysis state.

This will be described with reference to FIG. 5, which characteristically shows the waveforms of various machining voltages that appear in the machining gap when electric discharge machining is performed using an aqueous machining liquid.

FIG. 5A shows a state in which the no-load standby time changes variously and that there is no no-load standby time, but spark discharge is occurring (second waveform from the right). Spark discharge shows about 30V. Further, the average gap voltage and the servo reference voltage are in proper states, and the electric discharge machining is continuously performed.

FIG. 5B shows a voltage waveform when spark discharge and electrolysis occur in the machining gap.
In this case, there is almost no no-load standby time that appears before the start of spark discharge, and the voltage waveform appears when tar is starting to be generated between the electrodes or the specific resistance value of the gap decreases. In this state, the servo control is still within a range in which the average voltage of the machining gap is compared with the servo reference voltage. In order to avoid this situation, the machining can be continued by supplying the bipolar pulse of the prior art.

FIG. 5 (c) shows a state in which tar and the like are further generated and the specific resistance value between the electrodes is lowered, and discharge is no longer generated, and leakage current from the electrode (waveform at the left end) and electrolysis are generated. A voltage waveform higher than the spark discharge voltage can be seen, which indicates that the current and the current have started to flow.

In this state, the gap average voltage and the servo reference voltage are in agreement with each other, and although the spark discharge is not generated, the servo control system determines that the machining state is optimum. It cannot be avoided from the state. Moreover, in such a gap state, the supply voltage is divided by the internal current limiting resistance in the power source and the specific resistance value of the gap, and a sufficient voltage is not applied to the machining gap to cause discharge in the gap. Further, if the divided voltage value matches the servo reference voltage value, the machining itself will not be performed.

As can be seen from FIG. 5, the conventional servo detection device cannot distinguish the states (a), (b) and (c), and the servo control is performed as it is. It causes a problem.

It is therefore an object of the present invention to provide an improved electrical discharge machining method and apparatus which can solve the above mentioned problems in the prior art.

[0013]

In order to solve the above problems, it is necessary to perform servo control according to various states shown in FIG. Therefore, in the present invention, attention is paid to the characteristic part of the terminal electrolysis state, and when the servo control is performed in a machining state different from the spark discharge, the machining gap that enables the spark discharge to occur. The servo reference value is changed so that the length can be obtained.

The feature of the method of the present invention based on this technical idea is that it occurs in the electric discharge machining gap between the workpiece and the electrode in the electric discharge machining method of electric discharge machining a workpiece using an aqueous machining liquid. A detection step of detecting a gap voltage within a predetermined time and a no-load standby time in response to the machining gap voltage; and a step of determining a voltage level during a no-load standby based on the detection result obtained in the detection step, From the detection result of the gap voltage, a step of obtaining a generation rate of a voltage higher than a discharge voltage within a predetermined time, and determining an electrolysis state from a generation rate of a machining voltage whose no-load standby time is a predetermined value or less and higher than the discharge voltage It has a step and a step of changing and controlling the machining gap length to a gap length at which electric discharge is generated when the electrolysis state continues for a predetermined time or longer.

On the other hand, the feature of the apparatus of the present invention is that in an electric discharge machining apparatus for die-sinking electric discharge machining of a workpiece using a water-based machining liquid, an electric discharge machining gap between the workpiece and the machining electrode. And a first calculating means for calculating an average machining voltage based on the gap average voltage and required machining parameters. Second calculating means for calculating an average discharge standby time from the discharge standby time, and evaluation means for evaluating an electrolytic state of the aqueous machining liquid in the electrical discharge machining gap based on the average machining voltage and the average discharge standby time. And adjusting means for adjusting the servo reference voltage for relative servo feed control between the workpiece and the processing electrode according to the evaluation result of the evaluating means.

[0016]

The discharge waiting time and the gap average voltage are detected from the machining gap voltage, and the average machining voltage and the average discharge standby voltage are calculated. Based on this calculation result, the electrolysis state of the water-based machining fluid in the electric discharge machining gap is evaluated. The servo reference voltage for relative servo feed control of the machining electrode is adjusted according to the evaluation result, and appropriate servo feed according to the electrolytic state is performed.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of a die-sinking electric discharge machining apparatus according to the present invention. In FIG. 1, 1 is a workpiece, 2 is a processing electrode, 3 is a DC power source, 4 is a power limiting resistor, 5 is a switching transistor, and the switching transistor 5 is controlled to be turned on and off as described later. As a result, a machining pulse voltage is applied to the electric discharge machining gap G between the workpiece 1 and the machining electrode 2. The workpiece 1 is placed in a processing tank 7 filled with a water-based processing liquid 6, and sparks for processing are provided between the processing electrode 2 and the workpiece 1 via the water-based processing liquid 6. It is configured to generate a discharge.

The feeding operation of the servo motor 8 for feeding the machining electrode 2 and the turning on of the switching transistor 5,
In order to control the OFF operation and control the spark discharge generated in the electric discharge machining gap G via the water-based machining liquid 6, a control unit generally designated by reference numeral 10 is provided.

In the control unit 10, 11 is a processing condition parameter input unit for inputting processing condition parameters, and 12 is C
PU21, RAM22 for storing processing procedure, data, etc.
The ROM 23 and an input / output control unit for controlling input / output, and a detection unit 13 for detecting a machining gap voltage and an average machining voltage generated in the electric discharge machining gap G in response to a voltage generated between the workpiece 1 and the machining electrode 2. , 14 is a pulse control unit that controls and outputs the discharge pulse based on the input of the processing condition parameter, 15 is an operation command output unit that outputs the electrolytic evaluation result obtained as described later, the processing condition parameter, etc. A servo control unit for performing relative servo feed control between the workpiece 1 and the machining electrode 2, and 17 is a motor drive unit for driving a servomotor in response to a signal from the servo control unit 16. Relative servo feed with the electrode 2 is performed by the servo motor 8.

The average discharge standby time is calculated in the calculation section 18 from the data GV indicating the machining gap voltage detected in the detection section 13 and the discharge pulse signal PS given from the pulse control section 14. Contents of the processing condition parameter PM output from the operation command output unit 15 and the detection unit 1
The data KV indicating the average machining voltage detected by No. 3 and the data WT indicating the average discharge standby time calculated by the calculator 18 are supplied to the electrolysis evaluator 19 for evaluating the electrolysis state of the aqueous machining liquid 6 in the machining gap G. Has been given.

The detection unit 13 has a predetermined time (for example, 10 mse).
It has a circuit for detecting the machining gap voltage and the average machining voltage in c). In the calculation unit 18, from the discharge pulse signal PS given by the pulse control unit 14, the number of gate pulses for the switching transistor 5 within a given sampling period (for example, 10 msec),
And a counter that counts the integrated number of discharge standby times from the data GV indicating the machining gap voltage from the detection unit 13, and obtains the total of the discharge standby times within the sampling period from the counter value of the integrated number of discharge standby times, The average discharge standby time is calculated by dividing by the number of gate pulses.

This will be described with reference to the waveform chart shown in FIG. (A) is a waveform of the gate pulse GP given from the pulse control unit 14 to the switching transistor 5, (b) is a machining pulse given to the machining gap G by the switching transistor 5 turned on and off in response to the gate pulse GP. It is a waveform of the gap voltage V generated by the voltage. Here, τw is the standby time, τon is the discharge time, and τoff is the application stop time of the machining pulse. (C) is a waveform of the discharge period signal AL that is high level only during the period of τon, and the discharge period signal AL is generated in the detection unit 13. (D) is a waveform of a reference clock CL from a reference pulse generator (not shown) provided in the control unit 10, and (e) is a waveform of a sampling pulse SP generated based on the reference clock CL in the calculation unit 18, (F) shows the gate pulse GP, the discharge period signal AL,
And a waveform of a waiting time integration pulse AP having a reference clock pulse corresponding to each waiting time in response to the reference clock CL.

The waiting time integration pulse AP can be easily obtained by using, for example, the gate circuit shown in FIG. The standby time integration pulse AP thus obtained is defined by the sampling pulse SP 1
By counting only the time of the sampling cycle ST, it is possible to obtain data according to the total waiting time in one sampling cycle.

In the example of FIG. 2, assuming that the frequency of the reference clock is 1 MHz, the number of gates in one sampling period is 3, and the total discharge waiting time is 6 (μse).
Therefore, the content of the data TW indicating the average discharge standby time is 6/3 = 2 (μsec).

The electrolysis evaluation unit 19 includes data KV indicating the average machining voltage from the detection unit 13, data TW indicating the average discharge standby time from the calculation unit 19, and the machining condition parameter input unit 1.
Data ON / OFF for setting the ON time ON and OFF time OFF (see FIG. 2) of the switching transistor 5 input to 1 are input via the input / output control unit 12 and the operation command output unit 15. Electrolysis evaluation unit 1
In 9, the electrolysis is evaluated based on these input data, that is, the degree of electrolysis occurring in the machining gap G is evaluated.

In this embodiment, the electrolysis evaluation is carried out in three stages, and first, as a first means, it is judged whether or not the discharge waiting time τw, which is a feature of the electrolysis waveform, is below a predetermined value.
Therefore, the average discharge standby time calculated by the calculation unit 18 is compared with a predetermined time, and if the average discharge standby time is less than the predetermined time, it is determined that there is no discharge standby time. However, this predetermined time is set to such a time that an error does not occur in the evaluation in the second stage described below.

In this embodiment, this predetermined time is 1 μsec.
Therefore, the determination as to whether or not TW> 1 (μsec) ... (1) is executed by an appropriate means as the determination in the first step.

If the electrolysis waveform is judged in the first stage, then in the second stage, another characteristic of the electrolysis state, that is, "the electrolysis voltage is higher than the discharge voltage", is then applied. It is determined whether or not the state is the electrolysis state. Therefore, the set ON time A and the set OF
F time B, gap voltage C during rest time (inspect the voltage when actually falling into an electrolytic state and use that value), average machining voltage D within the sampling period TS, gate pulse within the sampling period TS Number E, sampling time TS is F
Then, the average electrolysis voltage VM is expressed by VM = [F × D−B × C × E−C × {F−E × (A + B)}] / (A × E) (2). The average electrolysis voltage VM obtained from the above equation is compared with a predetermined voltage (for example, 50 V), and if VM is equal to or higher than the predetermined voltage, the electrolysis state is determined.

However, a circuit for sampling the electrolysis voltage within the time A for each pulse within the sampling time F and a calculating means for calculating the average electrolysis voltage VM by obtaining the sum of the sampling data within the sampling time F are provided. When it has, the VM value can be obtained as a value obtained by dividing the total sum of the sampling data in the sampling time F by the number of samplings in the time F.

Finally, from the results of the first and second steps of the electrolysis evaluation, the rate at which the electrolysis state occurs within a fixed time (for example, 30 sec) is obtained to evaluate whether the electrolysis state is the terminal electrolysis state. For this reason, the first
Let Xn be the number of times that the waveform is not electrolyzed in the stage, Yn be the number of times that the electrolysis state is not in the second stage within the certain time, and Zn be the number of times that the electrolysis state is in the electrolysis state. Zn / (Xn + Yn + Zn) ≧ 0.7 (3) It is determined whether or not the terminal electrolysis state.

As a result, the state between the electrodes is the terminal electrolysis state (for example, the ratio of the electrolysis state within a certain time is 70%).
%), It is determined that the relative servo feed between the poles is abnormal, and a signal for adjusting the servo reference voltage is output from the operation command output unit 15 to the servo control unit 16 via the input / output control unit 12. To be done. According to the signal, the servo motor 8 is driven by the output from the motor drive unit 17 to adjust the servo reference voltage for relative servo feed control between the poles to continue the machining.

When the high-speed polarity switching circuit disclosed in Japanese Patent Laid-Open No. 4-101722 is provided, the operation command output unit 15 outputs a drive signal for the high-speed polarity switching circuit to continue the machining. Good.

The control unit 10 has the configuration shown in FIG.
A part of them can be replaced and configured by a microcomputer system. FIG. 4 shows a flowchart of a control program for covering a part of the operation of the control unit 10 when the control unit 10 is replaced with a known microcomputer system.

The flowchart will be described below. At the start of the program, sampling is started in step 31, and in steps 32 and 33, the gap voltage and the discharge waiting time are detected. In step 34, it is determined whether or not sampling has been performed for 10 (msec). If the result of this determination is YES, then sampling is stopped in step 35.

In the next step 36, the average discharge standby time is calculated, and in step 37 it is judged whether or not τw <1. If τw <1 is not established, step 42 is entered, and after it is determined that the discharge waveform is present, the number of discharge waveforms An + Bn is calculated,
Step 44 is entered. On the other hand, if τw ≦ 1, step 38 is entered, the average electrolysis voltage VM is calculated, and it is determined in step 39 whether VM is 50 V or higher. V
If M <50, step 42 is entered, and if VM ≧ 50, it is determined in step 40 that there is an electrolytic waveform, and in step 41, the number Cn of electrolytic waveforms is calculated.

When the number of electrolysis or discharge waveforms is calculated in this way, step 44 is entered to judge whether the sampling integration time exceeds 30 (msec).
If not exceeded, step 45 is entered, sampling is resumed, and steps 32 and 33 are returned to. On the other hand, if the sampling integration time exceeds 30 (msec),
Step 46 is entered.

Here, it is determined whether or not Cn / (An + Bn + Cn) ≧ 0.7 (4). That is, it is determined whether or not the number of electrolysis waveforms is 70% or more of the whole. If the result of this determination is YES, step 47 is entered to lower the servo reference voltage, and a transition is made from the electrolytic state to the discharge state. On the other hand, the determination result of step 46 is N
If it is O, the servo reference voltage remains at the set value calculated by the servo control unit 16 in step 48, and the execution of this program ends. As described above, according to the present invention, when the gap specific resistance value is reduced due to the electrolysis phenomenon or the generation of tar, the servo reference voltage value is lowered by 5 to 10 V to change the machining gap length to a value at which electric discharge occurs, Processing can be continued.

[0039]

According to the present invention, paying attention to the characteristic portion of the terminal electrolysis state, when the servo control is performed in a machining state different from the spark discharge, the machining gap length is set to the spark discharge. Since the servo reference value is changed so that it can be generated, even if a machining state in which an electrolytic current flows in the electric discharge machining gap, this can be immediately eliminated, and In comparison, the processing efficiency can be significantly improved.

[Brief description of drawings]

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

FIG. 2 is a waveform diagram showing waveforms of signals at various parts of the apparatus shown in FIG.

FIG. 3 is a circuit diagram showing an example of a circuit for obtaining a waiting time integration pulse.

FIG. 4 is a flowchart showing a control program used when a part of the configuration of the control unit in FIG. 1 is replaced with a microcomputer.

FIG. 5 is a waveform diagram for explaining how an electric discharge machining pulse waveform generated in an electric discharge machining gap changes according to a machining gap state at that time.

[Explanation of symbols]

 1 Workpiece 2 Machining electrode 6 Water-based machining fluid G Electric discharge machining gap 10 Control section 13 Detection section 16 Servo control section 18 Calculation section 19 Electrolytic evaluation section GV, KV, WT data PM Processing condition parameters

Claims (2)

[Claims] 1. An electric discharge machining method for electric discharge machining a workpiece using a water-based machining liquid, which is responsive to a machining gap voltage generated in an electric discharge gap between the workpiece and an electrode, and which has a no-load waiting time and a predetermined period. A detection step of detecting the gap voltage within the time, a step of determining the voltage level during no-load standby based on the detection result obtained in the detection step, and a discharge within a predetermined time from the detection result of the gap voltage. A step of obtaining a generation rate of a voltage higher than a voltage, a step of determining an electrolysis state from a generation rate of a machining voltage whose unloaded standby time is a predetermined value or less and higher than a discharge voltage, and the electrolysis state continued for a predetermined time or more. In this case, the electric discharge machining method includes a step of changing and controlling the machining gap length to a gap length at which electric discharge is generated. 2. An electric discharge machining apparatus for die-sinking electric discharge machining of a workpiece using a water-based machining liquid, which responds to a machining gap voltage generated in an electric discharge machining gap between the workpiece and a machining electrode. A detection unit for detecting the discharge standby time and the gap average voltage within a predetermined time period, a first calculation means for calculating the average machining voltage based on the gap average voltage and required machining parameters, and an average discharge from the discharge standby time. Second to calculate the waiting time
Between the calculation means, the evaluation means for evaluating the electrolytic state of the aqueous machining liquid in the electric discharge machining gap based on the average machining voltage and the average electric discharge standby time, and between the workpiece and the machining electrode. An electric discharge machining apparatus, comprising: an adjusting unit for adjusting a servo reference voltage for relative servo feed control according to an evaluation result of the evaluating unit.