JPS5927295B2 - Electric discharge machining equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electric discharge machining state detection device that changes machining conditions according to the state of a machining gap and outputs a signal for optimally controlling the state of the machining gap.

In general, in electrical discharge machining, the state of the machining gap changes very easily, and even if a pulse with certain electrical conditions is applied between the machining edges, not all of the pulse energy necessarily contributes to machining. It is very easy to change depending on the condition, and there are cases where applying too much pulse energy to the machining gap actually worsens the condition and makes machining impossible.

Therefore, in actual machining, the state of the machining gap can be monitored by observing the movement of the needle of the indicator to see the progress of machining, or by electrically detecting the machining voltage appearing in the machining gap. Usually, it is often determined how much pulse energy, or in this case, machining current, should be applied to the machining gap.

However, since such work is highly subjective and requires experience, it is generally considered to be a highly advanced technology, so automating such work is important in terms of labor saving and product processing. This is very advantageous in terms of uniformity. When automatically controlling the machining current or automatically changing other machining conditions according to the state of the machining gap, the present invention always maintains the machining gap at an optimum level and optimizes machining characteristics and machining efficiency. This invention relates to an electrical discharge machining detection device that outputs a signal to control the electrical discharge machining process.

Examples will be described below using figures.

That is, in FIG. 1, 1 is an electrode, and 2 is a workpiece, which faces the electrode 1 and forms a very narrow machining gap therebetween.

The pulsed current flowing through this machining gap is applied via a resistor 5 by converting the current from a DC power supply 3 into pulses by a switch element 4 . 6 is a control device for turning the switch element 4 from 0N to 0FF, and this device 6 controls the pulse time width,
The rest time width or current heater value can be freely selected.

Further, the electrical conditions of this control device 6 are also controlled by an output signal from a control device 7 which detects the voltage in the machining gap and calculates or evaluates this detection signal based on a certain method. Furthermore, the output signal of the control device 7 is sent to a machining fluid control device 8 and an average machining voltage control device 9, which are also sent to the machining voltage control device 9, respectively, and can control the machining fluid pressure, flow rate, and average machining voltage, respectively. It's becoming like that. 1
0 is a hose 11 for supplying machining fluid, and a hose 11 is connected to the electrode 1.
It is a joint that connects to.

The voltage across the machining gap is averaged through a filter composed of a resistor 12 and a capacitor 13, compared with the output voltage (Vh) of the average machining voltage control device 9, and a current proportional to the difference voltage is sent to the hydraulic servo valve 14. The current is applied to the control coil 15.

The variable resistor 16 is for changing the current. The amount of oil controlled by the servo valve 14 is sent to the servo cylinder 17 to control the machining gap length.

Further, in the average machining current control device 9, the voltage of the DC power source 18 is divided into various voltages by a resistor 19, and a desired voltage is selected by a rotary switch 20. The contacts of the mouth switch 20 are stepped by applying an impulse to its coil 21 as an input. In this case, the rotary switch 20 is used to switch the voltage, but the same switching is possible using a motor, a slide resistor, or the like. Now, the voltage and current waveforms appearing in the machining gap in FIG. 1 are normally as shown in FIG. 2, where a is the voltage waveform and b is the current waveform.

Even when a voltage pulse is applied to the machining gap, discharge often does not occur immediately; no-load voltage 22 appears for a certain period of time, and then discharge 23 occurs and discharge current 24 flows.
The discharge 23 stops when the pause time 25 is reached. Generally, the appearance of the no-load voltage 22 means that the dielectric strength in the machining gap has fully recovered during the rest period, and in such a case, the discharge is well distributed and the electrode 1 or the workpiece is It is unlikely that a steady arc will occur that would cause damage to 2.

However, when the application time of this no-load voltage 22 becomes longer, and the voltage pulse width 26 is constant, the duration of the discharge 23, that is, the time width of the current pulse 24 becomes shorter, so the average machining current 27 becomes smaller, and the machining speed decreases. Not only does this decrease, but when copper or graphite electrode materials are used, electrode wear and other processing characteristics are also greatly affected. Therefore, it is preferable that the voltage waveform in the machining gap is not O, but a discharge generation form in which there is a no-load voltage that does not last longer than a certain amount of time.

The present invention relates to an electric discharge machining detection apparatus for realizing a control method for ensuring that the ideal electric discharge generation form as described above always occurs in a machining gap, and the principle thereof will be explained below.

That is, as shown in FIG. 3, the voltage pulse width is divided into three time regions τ1, τ2, and τ3, and three types of machining states can be detected depending on in which region the discharge occurs.

That is, if τ is the time from when a voltage is applied to the machining gap until the occurrence of electric discharge, the case can be classified as a hit. (1) O≦τ≦τbi...A short circuit has occurred or the dielectric strength of the machining gap has not recovered. (1
1) τ1≦τ≦τ1+τ2...When there is no-load voltage for an appropriate period of time, and the contribution to the load is the largest. 0[1
) τ1+τ2≦τ≦τ1+τ2+τ3...When the no-load voltage application time is relatively long or no discharge occurs at all during the pulse voltage application time.

Therefore, we counted how many of the above three types of discharge forms occurred over a relatively long period of time, and calculated the number in order as Sl,
S2 and S3, the average occurrence rate λ in the case of the ideal discharge generation form (11) is as follows.

A large λ means that the contribution of pulses to machining is high, that is, there are many effective pulses, and when machining is performed under such conditions, the state of the machining gap is stable. At the same time, the machining efficiency is close to its maximum.

Therefore, in actual machining, the electrical conditions of the current or voltage pulse are adjusted so that the above-mentioned λ exceeds a certain value, or so that the maximum value of λ corresponding to the constantly changing machining gap conditions is obtained. The highest machining efficiency can be obtained by performing so-called adaptive control of electric discharge machining by changing the machining fluid pressure, flow rate, and control conditions of the servo mechanism for the machining gap.

FIG. 4 shows the main part of the present invention, and is an embodiment for determining the numerical value λ that is satisfied by the above formula.

In this figure, 7 is a discharge shape detection circuit that generates pulses according to the discharge shape. Cl, C2, C3, and C4 are all decimal counters, and by using two of them in series, it is possible to count up to 100. REG is a register that performs temporary storage according to input commands, and DAC is a digital-to-analog converter. Furthermore, when a pulse is applied to the machining gap, one of the signals Sl, S2, and S3 is always generated. Therefore, (S1+S2+S3) is a signal generated in synchronization with the above pulse. The same thing can be done by directly counting the number of applied pulses, but in the present invention, the total number of applied pulses is counted using S1 to S3 used for servo control. In addition, counters C3, C
Terminals A, B, C, I) and A, D in 4 are terminals from which outputs are output when the count number is 1, 2, 4, 8, and 9, and R is a reset terminal. The principle of operation in Fig. 4 is that when the number of pulses reaches a predetermined number (100 in this case), a command is issued to the output terminal 28 of the counter C2, and this command causes the contents of the counters C3 and C4 of the signal S2 to be transferred to the register REG. It is immediately converted into an output signal Vλ as a voltage by a digital-to-analog converter DAC.

Counters C3 and C4 are reset after their contents are moved to register REG. Now, if the count number of the counter is 100, and the digital quantity equivalent to 100 is converted to an analog quantity, Vλ = 10 (V).
The occurrence rate λ of the signal S2 is linearly determined between 0 and 10 CV).

Therefore, by displaying this output signal Vλ and providing feedback to the power supply system, machining fluid system, and even servo system so that it exceeds the desired value, the highest machining efficiency can be obtained depending on the state of the machining gap. . The value of the numerical value λ is 0.7 to 0.
A value of 8 or more is desirable, but it varies depending on the electrode material, workpiece material, and electrode shape. As described in detail above, according to the present invention, the machining gap can always be maintained at an optimum level, and machining characteristics and machining efficiency can be optimized, and the effects thereof are extremely large.

[Brief explanation of the drawing]

Fig. 1 is an embodiment diagram for explaining the operating principle of the device based on the present invention, Fig. 2 is a general voltage waveform diagram appearing in the electric discharge machining gap, and Fig. 3 is a diagram for explaining the present invention. Fourth
The figure is an explanatory diagram of main parts in the embodiment of FIG. 1. Note that the same reference numerals in the figures indicate the same or equivalent parts. 1... Electrode, 2... Workpiece, 4...
...Switch element, 6...Control circuit, 7.
...Control circuit that performs calculation or evaluation, 8...
... Machining liquid control device, 9 ... Average machining voltage control circuit, 14 ... Hydraulic servo valve, 15.
... Control coil, 17 ... Hydraulic cylinder, 18 ... DC power supply, 19 ... Resistor,
20... mouth switch, 21...
Coil, τ1, τ2, τ3... Time domain in which the voltage pulse width is divided into three, number of pulses when discharge occurs in the time domain of S1, S2, S3゜゜゜゜゛τ1, τ2, τ3, respectively, λ...Exponent determined by a predetermined division formula, Cl, C2, C3, C4...Counter, REG...Luzister, DAC...Digital-to-analog conversion vessel.

Claims (1)

[Claims] 1 Applying a controlled pulse voltage to a machining gap where an electrode and a workpiece face each other to generate an electric discharge in the machining gap,
In a device for detecting an electric discharge machining state in an electric discharge machining apparatus that supplies a repetitive machining pulse current, an elapsed time from the application of the controlled pulse voltage to the machining gap until the generation of electric discharge is from a first predetermined time. a first time period that is short, a second time period that is longer than the first predetermined time period and shorter than the second predetermined time period; and a second time period that is longer than the second predetermined time period, or the application of the controlled pulse voltage. A discharge shape detection circuit that divides the time into a third time region in which no discharge occurs, detects the occurrence of discharge in each time region, and outputs the discharge shape detection circuit, and counts the total number of pulses applied to the machining gap. comprising a first counter and a second counter that counts the number of pulses at which discharge occurs in a second time domain;
An electrical discharge machining state detection device, characterized in that, when the first counter counts a predetermined number, the content of the second counter is output as an evaluation function of electrical discharge machining.