JPS5815249B2 - Hoden Kakousouchi - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides an electric discharge machining apparatus that performs machining by intermittently supplying machining pulses to the machining gap between a tool electrode and a workpiece by controlling a switch element on and off. The present invention relates to a device for detecting abnormal machining such as.

When machining a workpiece using spark discharge, continuous arc discharge may occur if the gap between the electrode and the workpiece is not sufficiently deionized, or if the machining tip bridges the electrode and the workpiece. This may damage the workpiece and the electrode.

Such continuous arc discharge is harmful to machining, and there is a need to promptly detect it.

The present invention utilizes the fact that the discharge space terminal voltage during discharge differs between normal spark discharge and continuous arc discharge, and by comparing these terminal voltages, arc discharge or other abnormal discharge can be determined. It is characterized by:

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows the spark discharge voltage waveform between the workpiece and the electrode.

In the figure, τ is machining voltage application time, τ is discharge delay time, τ
indicates the discharge time.

As shown in Fig. 2, this discharge voltage changes moment by moment from the start of discharge as the discharge time elapses and approaches a certain value, and also depends on the electrode material, the material of the workpiece, the peak current value, etc.
It is generally known that the values are different.

The present invention aims to provide a device for evaluating and detecting continuous arc discharge regardless of such differences in materials and peak current values.

That is, during the applied pulse voltage in the first discharge at the start of machining, a certain time T (hereinafter referred to as track time T) from the end time of the delay time.

), the discharge voltage Va is measured and memorized, this voltage Va is used as a reference value, and compared with the voltage Vr at the track time T of each discharge, and this difference value is detected to determine abnormal discharge. The significance of this is as follows.

In other words, if the reference voltage is set from the second discharge after the start of machining, the machining gap between the tool electrode and the workpiece may not be deionized sufficiently, or the machining tip may not connect the tool electrode and the workpiece. There is a large possibility of bridging, and the reference voltage cannot be set accurately. However, if the reference voltage is set from the first discharge at the start of machining, the above factors will not occur and the reference voltage can be set accurately, so it is reliable. This method has the advantage that abnormal continuous discharge can be detected.

FIG. 3 shows a block diagram of the apparatus according to the present invention, in which 1 is a tool electrode, 2 is a workpiece, 3 is a DC power supply, and 4 is an intermittent power supply voltage applied to the electrode 1 and workpiece 2. 5 is an oscillator such as a multivibrator.

Further, 6 is a resistor arranged in parallel with the machining gap to detect the discharge voltage in the gap, 7 is a discharge delay time detection circuit, and the electrode 1
After applying a voltage to the workpiece 2, a start pulse is generated as shown in FIGS.

Reference numeral 9 denotes a voltage comparison circuit which closes the gate circuit 10 when the discharge voltage (the voltage during the τp period in FIG. 4A) and the voltage of the sawtooth wave shown in FIG. 4C match.

In this way, the pulses generated by the reference pulse generation circuit 11 are passed through the gate circuit 10 to the counter circuit 12 from the time when the start pulse is output after the discharge delay time τ0 ends.
Counting is started at , one counting is completed at the time when the discharge voltage and the sawtooth wave match, and the pulse train that has passed once during the track time T shown in Fig. 4d is counted by the counting circuit 12. .

The value counted by the first discharge at the start of machining is stored in the initial value storage circuit 13, and this value is held as a reference value until the power is turned off or the conditions are changed. Evaluate the discharge of

With the above configuration, in the first discharge after the start of machining, a certain time (track time T
), the discharge voltage is stored and becomes the reference voltage, but in the case of a short circuit between poles or continuous arc discharge, the discharge voltage is lower than the spark discharge voltage, so
As the track time T becomes shorter, the number of pulses passing through the gate circuit 10 decreases, and if the evaluation circuit 14 compares the count value of these pulses with a reference value, it becomes possible to detect abnormal discharge.

As described above, according to the apparatus of the present invention, machining current, workpiece material,
The spark discharge voltage, which changes depending on the electrode material, etc., is set each time the machining conditions are changed or the electrode is replaced, so the reference voltage can be set accurately depending on various conditions, and abnormal continuous discharge can be reliably detected. It is.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the machining gap voltage waveform, Fig. 2 is a diagram showing the relationship between discharge voltage and discharge duration, Fig. 3 is a block diagram showing an embodiment of the present invention, and Fig. 4 is a diagram showing the relationship between discharge voltage and discharge duration. 3 is a timing chart showing the operation of each part of FIG. DESCRIPTION OF SYMBOLS 1... Tool electrode, 2... Workpiece, 3... DC power supply, 4... Switching element, 5... Oscillator, 6...
...Resistor, 7...Discharge delay time detection circuit, 8...
Sawtooth wave generation circuit, 9...Voltage comparison circuit, 10...
Gate circuit, 11... Reference pulse generation circuit, 12...
- Counter, 13...Initial value storage circuit, 14...Evaluation circuit, τ...Machining voltage application time, τ0...Discharge delay time, τp...Discharge time.

Claims (1)

[Claims] 1. In electrical discharge machining equipment that intermittently applies a voltage to the machining gap between the tool electrode and the workpiece and measures the voltage during discharge to detect abnormal discharge, a delay occurs during the applied pulse voltage at the start of machining. A circuit that measures and stores the discharge voltage after a predetermined time elapses from the time end time, a circuit that detects the discharge voltage after the predetermined time elapses from the delay time end time during the applied pulse voltage of each discharge, and a circuit that detects the discharge voltage after the predetermined time elapses from the delay time end time. An electrical discharge machining apparatus comprising: a circuit that determines abnormal discharge by comparing a voltage stored at the time with each discharge voltage detected.