JPH0547326B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to improvements in electrical discharge machining equipment and wire cut electrical discharge machining equipment.

Conventionally, when machining carbide materials in electrical discharge machining, when increasing the machining speed with consumable electrodes, when cutting wire, etc., it has been possible to combine capacitor discharge with a transistor switching circuit as a power source for machining. As a result, the charging speed of the capacitor can be increased, the discharge repetition frequency can be increased, and the peak value of the discharge current can be increased to an extent that cannot be obtained by switching pulses, thereby improving the machining speed.

However, in order to charge the capacitor at a high speed, the charging resistance is set to a very small value, so when arc discharge occurs in the machining gap, current flows directly from the switching pulse power source into the gap, which can cause wire cuts and damage to the machining process. Accuracy decreases.

The present invention was invented in order to quickly and accurately detect abnormalities in the machining gap in order to quickly control the pulse power supply, servo feed, etc. in the event of such an arc or short circuit. A circuit for detecting a waveform signal based on a current in the circuit, and a circuit for detecting a waveform signal based on a current in a circuit connecting the capacitor and the processing gap,
A circuit for detecting a current waveform signal provided in the charging circuit of the capacitor and a circuit for detecting a current waveform signal provided in the discharging circuit are provided, and the detected current waveform signals of both the detection circuits are compared and the current waveform signal detected by the two detection circuits is compared. The present invention is characterized in that a comparison circuit is provided which detects deterioration of the machining gap condition and outputs a control signal in accordance with approximation of both detected current waveform signals to a predetermined level or higher.

The present invention will be explained below with reference to an embodiment of the drawings. A wire electrode 1 is supplied from a reel 2 and wound onto a reel 3. It moves between the guides 4 on the way, and electrical discharge machining is performed on the workpiece 5 facing this part. Reference numeral 6 denotes a table that fixedly supports the workpiece, and processing is normally performed by giving processing shape feed to this table using NC control. 7 is a power supply for processing energy supply,
8 is an on/off transistor switch, and 9 is a pulser that generates a gate pulse for switching. A series circuit of a power source 7 and a switch 8 is connected in parallel to the machining gap between the wire electrode 1 and the workpiece 5. 10 is a capacitor connected in parallel to the machining gap, 11 is a detection circuit that detects a waveform signal based on the current flowing between the switching pulse power supply by switch 8 and the capacitor 10, and 12 is between the capacitor 10 and the machining gap. This is a detection circuit that detects a waveform signal based on the current flowing through the circuit. 13 is a comparison circuit that compares the detection waveform signals of both detection circuits 11 and 12 to determine the discharge state of the machining gap; 14 is a comparison output output based on the discrimination comparison output of the comparison circuit 13, which determines the discharge state. This is a control device that controls the pulser 9 when an abnormality such as an arc or a short circuit is detected, and restores normality by increasing the pause width τoff of the gate pulse.

A wire cut is processed by applying pulse discharge to the gap facing the workpiece 5 while moving the wire electrode 1 in the direction of the arrow, and the pulse voltage is turned on and off by the transistor switch 8 according to the pulse 8. As a result, the capacitor 10 is charged and discharged, and a pulse current with an increased peak value of the discharge current is discharged.
At this time, the power supply voltage is increased and the charging current is increased to rapidly charge the capacitor 10, and the number of discharge repetitions can be increased to perform high-speed electrical discharge machining. Even if this rapid charging and discharging of the capacitor 10 is repeated, stable electric discharge machining can be performed by the power switch 8 repeating on/off switching of the on-pulse τon and the off-pulse τoff.

Therefore, the switching pulse current is detected by the detection circuit 1.
1 and the discharge current of the circuit connecting the capacitor 10 and the machining gap are respectively detected by the detection circuit 12, and the detected waveform signals of both circuits are compared by the comparison circuit 13. If normal pulse discharge is performed in the machining gap between the workpiece 5 and the workpiece 5, there is a phase difference between the waveform signals of the detection circuits 11 and 12, and there is also a difference in current peak value, waveform, etc.
In other words, the capacitor charging/discharging machining circuit used in electrical discharge machining accumulates (charges) discharged power from a charging/discharging power source via a charging circuit in a capacitor over time, and then uses this charged charge (voltage) between electrodes and It is applied to the discharge gap between the workpieces and is emitted as a discharge having a large discharge current amplitude value within a shorter (discharge) time after the start of discharge in the discharge gap. In general, the charging circuit can be configured using various circuit elements compared to the discharge circuit (as long as there are no special low electrode consumption machining conditions), but during normal charging and discharging, that is, normal discharge machining. In some cases, the charging time (time constant: Tc) is significantly longer than the discharging time (time constant: TD) (Tc》
TD) and, on the other hand, the discharge current amplitude value (IDP) is significantly larger than the maximum charging current value (ICP) (IDP》ICP), and electrical discharge machining is performed by repeating charging and discharging. Matters related to capacitor charging and discharging are, for example, published in April 1963.
This is well known, as is evident from ``Revised Electrical Discharge Machining'', co-authored by Seizaburo Otori and Nao Fujikura, published by Coronasha Co., Ltd. on May 15, 2017, especially the description regarding capacitor discharge (pages 25 to 47).

Therefore, according to the present invention, the detection circuits 11,1
Since each current of the charging circuit and discharging circuit of the capacitor 10 is detected as a waveform signal by 2, one or both of the time width of the charging and discharging time or the peak value of the charging and discharging current is detected and the comparison circuit 13
You can compare and determine the size relationship of each,
Therefore, by setting some discrimination criteria for the comparison, it is possible to know the charging/discharging state of the capacitor, that is, the charging/discharging characteristics, and by extension, the discharge state in the discharge gap or the discharge machining. This will allow you to know the status.

Therefore, in the present invention, the current waveform detection circuit 11 is provided in the charging circuit and the discharging circuit of the capacitor 10, respectively.
12 is provided, and the comparator circuit 13 compares the detection waveform signals of charging and discharging each time the capacitor 10 is charged, thereby determining the electrical discharge machining state and outputting a control signal. Comparison and analysis of the current waveform signals in the circuit 13 are performed, for example, as follows from the relationship of the above-mentioned basic characteristics of the charging and discharging current waveforms of the capacitor.

There are various ways to detect and compare the length of charging time and the length of discharging time (width of discharge pulse) as characteristics of charge/discharge current, but for example, when the charging and discharging currents exceed a certain value, The gate is opened for the period of time, and the clock pulses are cumulatively counted.
Each count is adjusted according to a preset appropriate ratio (for example, the count number on the discharge side is multiplied by n) and compared or calculated, and the magnitude relationship, and furthermore, the degree of magnitude, etc. is output as a signal. Similarly, when detecting and comparing the amplitude of the charging current and the amplitude of the discharging current as characteristics of the charging/discharging current, for example, the discharging current signal is detected during the period when the discharging current exceeds a certain value. The count digital signal counted by A/D conversion and the charging current are applied for a period almost the same as the A/D conversion period of the discharge current scheduled during normal machining. The D-converted and counted count digital signal is adjusted as necessary at an appropriate ratio set in advance, compared or calculated, and the magnitude relationship and degree of magnitude are output as signals to determine the electrical discharge machining status and the relevant This is used to determine the state of discharge pulses, etc.

As mentioned above, generally speaking, the quality of charging and discharging of a capacitor is better as there is a difference between the length of charging and discharging time and the amplitude (magnitude) of charging and discharging current. This can be determined by the frequency or rate of occurrence, and if the machining gap is narrower than the desired expected value or if the contamination with machining debris progresses, the degree of difference between the charging and discharging currents will decrease, and the machining gap will be short-circuited. Or, if a short circuit occurs due to machining debris or the like, the charging current becomes the discharging current (short circuit current), so the difference between the charging and discharging currents disappears.

Therefore, the detection output signal determined by the comparator circuit 13 applies a normal/abnormal signal to the control device 14, and when an abnormal discharge occurs, the off-pulse width τoff of the pulser 9 is increased to restore normality; , τoff
Machining speed is increased by short-circuiting and controlling to increase discharge repetition. Above, we have described an embodiment in which normal and abnormal discharges are detected based on the phase difference of the detection waveform signals, but similar effects can be obtained by comparing and determining the waveform of the current peak value or the current waveform itself. It will be done.

The detection signal from the comparison circuit 13 can also be used to control the servo drive device for the machining gap, control the jet of machining fluid from a nozzle (not shown), control the running speed of the wire electrode 1, and when applying forced vibration to the wire. The vibration control can be performed. Further, for manual control thereof, the output of the comparator circuit 13 can be supplied to and displayed on a display device.

As described above, the present invention includes a circuit that detects the current of the circuit that connects the pulse power source and the capacitor, and a circuit that detects the current of the circuit that connects the capacitor and the machining gap, and compares the signals of both detection circuits. Then, the discharge state in the machining gap is determined and detected by comparing and determining the phase difference, peak value, waveform, etc. Therefore, it is possible to detect the discharge state extremely accurately, and the control of the pulsar etc. can be performed appropriately by detection. This has the effect that electrical discharge machining using capacitor discharge can be performed at high speed and with high efficiency.

Note that the current detection circuit may be any type of circuit that measures the voltage drop across a resistor or detects a magnetic field generated by a pulse current.

[Brief explanation of the drawing]

The drawing is a circuit configuration diagram of an embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... Wire electrode, 5... Workpiece, 7... Power supply, 8
...Switch, 9...Pulser, 10...Capacitor, 1
1, 12... Current detection circuit, 13... Comparison circuit.

Claims (1)

[Claims] 1. A charging/discharging capacitor is connected in parallel to a machining gap formed by facing each other between an electrode and a workpiece, and the opening/closing of the capacitor is controlled by a DC power supply at a set on/off time width. In an electric discharge machining apparatus that charges via a switch element, the capacitor has a charging circuit for detecting a current waveform signal, and a discharging circuit for detecting a current waveform signal. and a comparison circuit that compares the detected current waveform signals of both the detection circuits, detects deterioration of the machining gap condition and outputs a control signal according to the approximation of both the detected current waveform signals to a predetermined level or higher. An electrical discharge machining device characterized by: