JPH0230810B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a machining power source for a wire-cut electrical discharge machining device, and in particular, a pulse voltage higher than a discharge voltage is applied between a workpiece and a wire electrode passing through the workpiece. The present invention relates to a machining power supply for a wire-cut electric discharge machining apparatus that generates intermittent discharge between the machining gap between the workpiece and the wire electrode, and processes the workpiece using the discharge energy.

Conventionally, this type of processing power supply connects a capacitor in parallel between the poles formed by the workpiece and the wire electrode.
A switching element such as a transistor is opened and closed to supply a pulse voltage to the capacitor, and when a discharge occurs between the electrodes, the energy stored in the capacitor is released between the electrodes. By repeating this operation, the workpiece is processed. In this manner, in electrical discharge machining by charging and discharging a capacitor, discharge often occurs during charging, resulting in variations in individual discharge energy.

Generally, in electric discharge machining, the greater the individual discharge energy, the worse the machined surface roughness and the faster the machining speed. Therefore, in capacitor discharge, the machined surface roughness is determined by the discharge with the greatest energy.
Machining speed decreases due to frequent electrical discharges during the process.

In normal mold-forming electrical discharge machining equipment,
As disclosed in Publication No. 13195, by keeping the current peak value i _p and pulse width (discharge current duration) τ _p constant in a rectangular current waveform, the same energy can be supplied between the electrodes. It has been devised to increase the machining speed relative to the roughness of the machined surface. In the device disclosed in the above-mentioned publication, the current peak value is kept constant by opening and closing the switching element, and the pulse width τ _p is kept constant by detecting the discharge.

However, when a die-forming electrical discharge machining apparatus is applied to a wire-cut electrical discharge machining apparatus, the following disadvantages arise, making it unsuitable for practical use. That is, when machining is performed with the discharge current duration time τ _p and rest time τ _r set as machining conditions, the largest effective current will flow if a short circuit occurs. That is, assuming that the discharge current waveform is a rectangular wave with a peak value i _p and the duty factor is D, the effective value of a general current referred to in electric circuit theory, that is, the effective current value I _rns is I _rns = i _p・Defined as √.

Here, when a short circuit occurs, a current flows at the same time as voltage is applied, so the duty factor D is defined as D=τp/τp+τr, and the effective current value at this time, that is, at the time of a short circuit I _Anax becomes the largest, becomes.

In addition, during normal machining, there is a delay time between the application of voltage and the occurrence of discharge, so only a small current value can be passed. For example, if the average value of the delay time is τ _p , the effective value of the current I _rns is becomes.

When the discharge current waveform is made into a rectangular wave with a peak value i _p , the average current I is defined as i _p ·D. As a result of many experiments, the inventor determined that the maximum average current that can be supplied is
Normal machining is possible up to a current value equivalent to about half of I _nax , but if the machining feed speed is increased to flow a current of 1/2 I _nax or more, a short circuit will occur and machining will become unstable. I found out.

On the other hand, to increase the machining speed, increase the current peak value i _p or the discharge current duration τ _p and increase the maximum average current I _nax , but there is a limit to the effective value of the current that can be passed through the wire electrode. Yes, if a current with an effective value exceeding a certain value is applied, the wire will break. This limit current value is called the effective value of wire breakage limit current. Therefore, when selecting machining conditions, adjust the current peak value i _p , discharge current duration τ _p , and rest time τ _r so that the effective value I _Anax of the machining current at the time of short circuit is less than the effective value of the wire breakage limit current. The machining feed rate must be set so that it is approximately half or less of the average current during a short circuit. In particular, in wire cut electric discharge machining, the wire electrode vibrates, so short circuits often occur not only during machining, but also at corners and at the start of machining.
Therefore, the drawback of not being able to flow a large current becomes fatal, and the processing speed decreases.

The present invention has been made in view of the above-mentioned conventional problems, and its purpose is to increase the processing speed by changing the current supplied at the time of a short circuit to within the effective value of the wire breakage limit current. An object of the present invention is to provide a machining power source for a wire cut electrical discharge machining device.

In order to achieve this object, the present invention applies a pulse voltage higher than a discharge voltage between a workpiece and a wire electrode passed through the workpiece by a switching element, and connects the workpiece and the wire. A short circuit that detects a short circuit between the poles in a machining power supply for a wire-cut electrical discharge machining machine that generates discharge between the poles and processes the workpiece using the discharge energy generated by opening and closing a switching element or other switching elements. Detection means, discharge current duration,
It is equipped with a setting means for setting the rest time or a peak current value respectively in a normal state and in the case of a short circuit between poles, and a switching means for switching the setting means in response to a detection signal from the short circuit detection means. The setting means is switched from a normal state to a short circuit, and the set value at the time of a short circuit is such that the effective value of the current flowing between the electrodes does not exceed a certain determined value.

In addition, the set value at the time of short circuit is determined dynamically by selecting the wire diameter and wire material, and this can be changed by the flow rate of the machining fluid.

Hereinafter, preferred embodiments of the present invention will be described based on the drawings. In FIG. 1, a wire electrode designated by 10 is connected to an initial hole 12a made in a workpiece 12.
It is stretched between a supply reel and a take-up reel (not shown) provided on both sides of the workpiece. A switching element 14 such as a transistor, a current limiting resistor 16, and a DC power source 18 are connected in series to the electric path connecting the wire electrode 10 and the workpiece 12. The switching element 14 is a drive circuit 20
The opening and closing are controlled by the wire electrode 10 and the workpiece 12, and a pulse voltage is applied between the poles formed by the wire electrode 10 and the workpiece 12. The oscillation circuit 22 controls the drive circuit 20 and sets the ON time and OFF time of the switching element 14.

The respective outputs of the rest time selection circuit 24 and the post-short-circuit current supply rest time selection circuit 26 that set the rest time τ _r are supplied to the oscillation circuit 22 via the switching circuit 28 . The respective outputs of the discharge current duration selection circuit 30 and the short-circuit current duration selection circuit 32 that set the discharge current duration τ _p are supplied to the oscillation circuit 22 via the switching circuit 34.

The short circuit detection circuit 36 is connected between the wire electrode 10 and the workpiece 12, and detects a short circuit between them. In this case, there are various methods of detecting a short circuit, but for example, if the wire electrode 10 and the workpiece 12 are
A method of detecting a short circuit by applying voltage from a power source different from the processing power source between the
2, the signal A when the switching element 14 is ON
Then, the inter-electrode voltage and the voltage value lower than the discharge voltage are compared with a comparator, etc., and the signal B which is emitted when the inter-electrode voltage is low is received, and these signals A and B are logically obtained by using a logic circuit. There is a method in which the signal C is used as a short circuit detection signal. The latter method is superior in terms of detection speed. The short circuit detection circuit 36 controls the switching circuits 28 and 34 with the output signal when a short circuit is detected, and changes the rest time selection circuit 24 to the rest time selection circuit 26 after supplying the short circuit current, and the discharge current duration selection circuit 30 to the short circuit current duration selection circuit. At the same time as switching to the selection circuit 32, the output signal of the short circuit detection circuit 36 is switched to the oscillation circuit 22.
and is supplied to the switching circuit 44.

The discharge detection circuit 38 is connected between the wire electrode 10 and the workpiece 12, and its output is supplied to the oscillation circuit 22. The respective outputs of the discharge current peak value selection circuit 40 that selects the discharge current peak value i _p and the short circuit current peak value selection circuit 42 that selects the short circuit current peak value are connected to the drive circuit 2 via the switching circuit 44.
0. The switching circuit 44 is the short circuit detection circuit 3
When a short circuit detection signal is received from the discharge current peak value selection circuit 40, the short circuit current peak value selection circuit 4 is selected from the discharge current peak value selection circuit 40.
Can be switched to 2.

The peak current of the drive circuit 20 is changed depending on the number of switching elements 14 that are opened and closed. That is, when a short circuit between poles is detected by the short circuit detection circuit 36, the switching circuit 2 that receives the short circuit detection output
8, 34, and 44 to switch to the conditions at the time of short circuit. The pause time after supplying the short circuit current, the duration time of the short circuit current, the peak value of the short circuit current, etc. may be set in each selection circuit, but it is complicated to select them according to various situations.

Therefore, as a result of experiments conducted by the present applicant, it was found that it is sufficient to set constant conditions according to the wire diameter and wire material, regardless of the machining conditions during normal discharge. If the wire material and wire diameter are selected by the wire diameter and wire material selection circuit 46 in FIG. The short-circuit current is supplied to the peak value selection circuit 42, and the short-circuit current post-supply pause time, short-circuit current duration time, and short-circuit current peak value corresponding to the selected wire material and wire diameter are automatically set.

Each selection circuit 24, 26, 30, 32, 40, 4
2. The switching circuits 28, 34, 44 can be constructed relatively easily using gates or the like.

The embodiment of the present invention has such a configuration, and its operation will be explained below with reference to the waveform diagram of FIG. 2. In FIG. 2, a is a machining voltage waveform diagram, b is a machining current waveform diagram, and times are indicated at the top of the diagram as signals t ₀ to t ₁₁ . This FIG. 2 shows an example in which only the discharge current duration time is changed.

First, a voltage is applied between the poles at time _t1 ,
After the delay, when a discharge occurs at time t ₂ , a current flows between the electrodes for a discharge current duration time τ _p1 and the discharge is detected by the discharge detection circuit 38 . At time _t3 , counting of the rest time _τr is started, and at time _t4 , voltage is again applied between the electrodes. In the event of a short circuit, time t ₇ to _{t 9} progress, but when the switching element 14 is turned on at time t ₇ , no voltage is generated between the poles, so the short circuit detection circuit 36 determines that there is a short circuit, and uses this determination output to Switching circuit 28, 34, 4
Control 4. As a result, the circuit is switched to the short-circuit current duration selection circuit 32, and starts counting the short-circuit current duration time τ _p2 . At time _t8 , counting of the rest time _τr is started, and at time _t9 , the voltage is again applied between the electrodes. In this case, if the effective current value determined by the short-circuit current duration τ _p2 , rest time τ _r , and current peak value i _p is I _A , then The short-circuit current duration τ _p2 is determined so that the effective value of the current at the time of short circuit determined by the wire diameter and wire material, that is, the value that does not exceed the effective value I _AWnax of the wire breakage limit current. That is, the configuration is such that τ _p2 is automatically selected based on the wire diameter and wire material selection.

In this embodiment, the discharge current duration time τ _p is changed, but the rest time τ _r , the current peak value i _p or a combination thereof may be changed.

In addition, in the above embodiment, the conditions at the time of short circuit can be selected by selecting the wire diameter and wire material, but the effective value of the wire breakage limit current changes slightly depending on the amount of machining fluid flowing between the electrodes. Therefore, it is even more effective to make fine adjustments corresponding to the liquid volume.

As described above, the present invention changes the discharge current duration, rest time, peak current value, or a combination of these in the event of a short circuit, and prevents a current exceeding a certain determined effective current value from flowing. Wire breakage due to current can be prevented.

Also, when discharging after a normal delay time, the effective value of the wire breakage limit current I _AWnax Under the conditions, discharge current duration τ _p・rest time τ _r・
It becomes possible to select the current peak value i _p and the machining speed can be increased. Furthermore, since the energy supplied by each discharge can be made the same, effects such as an increase in machining speed for machining surface roughness can be obtained.

[Brief explanation of drawings]

FIG. 1 is a circuit configuration diagram showing an embodiment of a machining power supply for a wire-cut electrical discharge machining apparatus according to the present invention, and FIG.
The figure is a waveform diagram of the gap voltage and machining current when the discharge current duration is changed during a short circuit in the example circuit. 10 is a wire electrode, 12 is a workpiece, 14 is a switching element, 16 is a current limiting resistor, 18 is a DC power supply, 20 is a drive circuit, 22 is an oscillation circuit, 24
26 is a pause time selection circuit after short-circuit current supply, 30 is a discharge current duration selection circuit, 32 is a short-circuit current duration selection circuit, 36 is a short-circuit detection circuit, 38 is a discharge detection circuit, and 40 is a discharge 42 is a short-circuit current peak value selection circuit; 28, 34, and 44 are switching circuits; and 46 is a wire diameter and wire material selection circuit.

Claims (1)

[Claims] 1. A pulse voltage higher than a discharge voltage is applied between a workpiece and a wire electrode passing through the workpiece by opening and closing a switching element, and the workpiece and wire electrode are generate a discharge between the electrodes,
In a machining power source for a wire cut electric discharge machining apparatus that processes the workpiece using discharge energy generated by opening and closing of the switching element or other switching elements, the machining power supply includes a short circuit detection means for detecting a short circuit between the poles, and a discharge current duration and time. It is equipped with a setting means for setting a rest time or a peak current value respectively in a normal state and in the case of a short circuit between poles, and a switching means for switching the setting means according to a detection signal from the short circuit detection means. Wire cut electric discharge machining characterized in that the switching means switches the setting means from a normal state to a short circuit state, and the set value at the time of a short circuit is such that the effective value of the current flowing between the electrodes does not exceed a certain determined value. Processing power supply for equipment. 2. A machining power source for a wire-cut electrical discharge machining device, which automatically determines a set value at the time of a short circuit by selecting a wire diameter and wire material, in the device according to claim 1. 3. A machining power source for a wire-cut electrical discharge machining device, in which the set value at the time of a short circuit can be changed depending on the flow rate of machining fluid, in the device according to claim 1.