JPH01257514A - Power source for electric discharge machining - Google Patents

Abstract

PURPOSE:To improve a machining speed by a method wherein by using a detecting source for high output impedance, during a period in which a detecting pulse is applied, a standard for application of a main pulse is decided depending upon whether a gap voltage exceeds a given level. CONSTITUTION:A gate pulse generated from a gate pulse generating part 16 is fed to the gate of a transistor 4 for an auxiliary switch to turn ON and OFF the gate. In this case, a gap voltage VG is utilized as a detecting output. A time when the detecting output exceeds A reference voltage Vref is a time when conductivity is low (gap impedance is high). When conductivity is increased, gap impedance is lowered, and a detecting output value is decreased. As long as a state in which the detecting output exceeds the reference voltage Vref is continued during a period in which a detecting pulse is applied, it is decided that a gap state is in a good state even when a main pulse is applied, and a main source gate pulse generating part 15 is triggered to output a main.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a TIR device used in a wire electrical discharge machine or the like.

[Conventional technology]

In electric discharge machining, the electrical conductivity of the gap between the electrode and the workpiece, in other words the impedance, is determined by the machining tip,
Affected by various ions 8 generated gas and gap width, etc.
constantly changing. In order to generate a discharge that releases the energy required for electrical discharge machining, the discharge starting voltage must be increased. However, if the conductivity of the gap is high, there will be a lot of leakage current, and the voltage drop at the output impedance of the power supply will be large, making it impossible to increase the discharge starting voltage.Therefore, it is recommended to use a power supply with a low output impedance. It is considered. However, if the output impedance is small, a small change such as electrode deflection will trigger a sudden increase in conductivity or a short circuit, causing a large current to flow and the resulting Joule heat to damage the electrode and workpiece. hurt a lot. Therefore, conventionally, before applying a pulse (main pulse) for electrical discharge machining, the electrical conductivity of the gap has been checked in advance using a detection pulse. The method is to provide a detection power supply with high output impedance, apply a detection pulse to the gap, and apply the main pulse only when the detection pulse causes a discharge. FIG. 4 is a diagram showing the connection relationship between the output impedance of the power source and the gap impedance, and the two are connected in series. The voltage across the gap impedance, that is, the gear 7 voltage ■. is used as the detection output. Since the output impedance is high, if the gap impedance is small (that is, the conductivity of the gap is large),
The gap voltage ■ becomes small and no discharge occurs with the detection pulse. If the gap impedance is large (that is, the conductivity of the gap is small), the gear tooth voltage ■6 will also be large,
Discharges with detection pulse. That is, when a detection pulse from a power source with high output impedance is applied, it can be seen that if discharge occurs, the conductivity is low, and if it does not, the conductivity is high. Conventionally, this fact was utilized to apply the main pulse only when the conductivity was low.

[Problem that the invention is trying to solve] However,
The conventional technique described above has a problem in that the machining speed cannot be increased. (Explanation of the problem) When the detection pulse discharges, the gap is always in a state where it is possible to apply the main pulse for electrical discharge machining, and when there is no discharge, the main pulse should not always be applied. If this is not the case, it is unavoidable. However, in reality, it is true that when the detection pulse is discharged, the gap is in a state where it is okay to apply the main pulse, but when there is no discharge, the gap is always in a state where the main pulse should not be applied. Yes, but that's not necessarily the case. Although the electrical conductivity has increased somewhat, it may be possible to generate a discharge with sufficient energy even if the main pulse is applied to cause the discharge. In the conventional technology, such an opportunity is taken away, so the frequency of application of the main pulse is low, and the machining speed cannot be increased. In particular, when the opposing area between the electrode and the workpiece is large (for example, when the thickness of the workpiece is large in wire electrical discharge machining), the gap impedance becomes low, resulting in a decrease in machining speed. In order to increase the processing speed, it is necessary to take advantage of as many of the above-mentioned opportunities as possible, and one possible way to do this is to lower the output impedance of the detection power source and increase the partial pressure at the gap. Then, the range in which a discharge occurs with the sensing pulse is expanded, and some of the aforementioned opportunities are picked up. However, as the output impedance is lowered, T! flowing through the wire! L'ft increases, and the heating of the wire due to the detection pulse increases, which is undesirable.
There was a limit to how much it could be lowered. The present invention aims to solve the above-mentioned problems.

[Means to solve the problem]

In order to solve the above problem, the present invention uses the detection 1B with a large output impedance so that the wire is not heated by the current generated by the detection pulse, and also maintains a gap voltage at a predetermined level during the period when the detection pulse is applied. The following measures were taken based on the idea that whether or not the voltage exceeds the level should be used as a guideline for whether or not the main pulse should be applied. In other words, in a power supply device for electric discharge machining in which a detection pulse is applied from a detection source to the gap between an electrode and a workpiece to check the conductivity of the gap and then the main pulse is applied, the main power supply that supplies the main pulse is A detection power supply with a larger output impedance and a detection output obtained from the gap are based on a gap state that is barely enough to allow electrical discharge to occur for electrical discharge machining! 1! A comparator that outputs when the voltage exceeds the voltage, and a main power gate pulse that outputs the main pulse when the output of the comparator is still present after the fall of the gate pulse that outputs the detection pulse. The main WB'r--tobalance generating section is provided.

[For production]

In the present invention, instead of deciding whether to apply the main pulse based on whether a discharge occurred after applying the detection pulse,
Whether or not the main pulse is applied is determined depending on whether the gap voltage (2) exceeds a predetermined level when the detection pulse is applied. In other words, the level of the gap voltage (■) is determined in accordance with the state of the gap that is barely suitable for interfering with the electrical discharge that allows electrical discharge machining, and the detection pulse is applied when that level is reached. If the period (in other words, the period of the gate pulse) continues, the main pulse is applied. In this way, the main pulse will be applied even when it has conventionally been determined that the main pulse should not be applied. As a result, the main pulse is applied more frequently and the machining speed becomes faster.

【Example】

Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 shows a power supply device for electric discharge machining according to an embodiment of the present invention. In Fig. 1, 1 is the main power supply, 2 is the detection power supply, 3 is the main switch transistor, 4 is the sub switch transistor, 5 and 6 are diodes, 7.8 is the line inductance, 9 is the workpiece, and 10 is the communication line. electron, 11 is wire,
12 is a machining trajectory, 13 is a comparator, 14 is a reference voltage terminal,
15 is a main power gate pulse generation section, 15-1 is a time constant circuit section, 16 is a gate pulse generation section, and 17 is a resistor. The detection type R2 used in the present invention is different from the conventional one,
Use a power supply with significantly higher output impedance than the main power supply 1. The resistor 17 means that the output impedance of the detection power supply 2 is increased. The detection pulse for detecting the electrical conductivity of the gear is supplied through the path of detection power supply 2 - resistor 17 - sub-switch transistor 4 - workpiece 9 - wire 11 - conductor 10 - detection 'S#2. Ru. A gate pulse for turning on and off the sub-switch transistor 4 is supplied from a gate pulse generating section 16. Then, the detection output is transmitted to the comparator 13, and the reference voltage V
Compare with raf. The reference voltages ■ and □ are determined corresponding to the state of the gear 7 when it is barely suitable for causing electric discharge that allows electric discharge machining. Based on the output of the comparator 13, it is determined whether or not to supply the main pulse to the main power gate pulse generator 15; Specifically, the main power voltage pulse generation section 15 is configured with a monostable multi-pie break. Time constant circuit section 1
5-1 is for adjusting the pulse width of the monostable multivibrator. The main pulse is main power supply 1 - main switch transistor 3 →
It is supplied in the path: diode 5 - line inductance 7 - workpiece 9 - wire 11 - conductor 10 - main IT source 1. Electric discharge machining is performed by this main pulse. FIG. 2 is a waveform diagram for explaining the operation of the device shown in FIG. 1. Each of the waveforms in FIG. 2 is labeled with symbols .about.■, indicating that the waveforms are the waveforms corresponding to the symbols in FIG. Next, the gap state detection operation will be described in detail with reference to the waveforms shown in FIG. A gate pulse having a waveform (3) generated by the gate pulse generator 16 is supplied to the gate of the sub-switch transistor 4 to turn it on and off. When on, a sensing pulse is provided to the gap. The gear gear voltage V at this time is used as the detection output (waveform ■). The detection output becomes larger than the reference voltage V ref when the conductivity is small (the gap impedance is large). The waveform will exceed the level. When the conductivity increases, the gear impedance decreases, and the value of the detection output decreases as shown in waveform 2-4. As long as the state in which the reference voltage V r e f is exceeded continues during the application period of the detection pulse (which can be said to be during the application period of the gate pulse), the gap state is a state in which the main pulse can be applied. It is determined that there is. If this is not the case, it is determined that the main pulse should not be applied because the electrical conductivity of the gap has increased to a level that is not suitable for causing electric discharge in electrical discharge machining. The comparator 13 has a detection output of 1! It is provided to check whether the voltage V rat is exceeded, and its output is the second
It will look like Figure ■. FIG. 3 shows an enlarged view of the gate pulse and comparator output. (2) is the gate pulse, (2) is the comparator output, and P is the rear end portion (shaded portion) of the comparator output (2) that protrudes from the rear end of the gate pulse (2). The comparator output ■ in the case of FIG. 3 is an output when the detection output ■ exceeds the reference voltage V rsf, as in waveforms 7-1 and 7-4. The comparator output ■ is created based on the detection output ■, etc., but the stray capacitance of the gap, comparator 1
Due to the time delay in the 3rd class, the falling edge of the trailing edge is slightly delayed from the falling edge of the gate pulse ■. Therefore, the detection output is set to the reference voltage ■1. ．． Gate pulse when exceeding ■
When the change occurs during the period of , a protruding rear end portion P (shaded portion) is formed as shown in FIG. This rear end portion P serves as a trigger, and the main power supply gate pulse generator 15 issues a gate pulse that turns on the main switch transistor 3. This is because the gate pulse (2) is introduced from the gate pulse generator 16 to the main power supply gate pulse generator 15 as an inhibit input. Even if the comparator output ■ is input, it is not triggered during the period when the gate pulse ■ is input, and if the comparator output ■ remains after the gate pulse ■ is exhausted, that is, the rear end portion P
If exists, it is the main power gate pulse generator 15
(monostable multi-by-break) and outputs the main gate pulse ■. Therefore, the main pulse output has a waveform such as (2) that rises near the fall of the comparator output (2). When the waveform of the detection output (2) is 2-2 or 2-3, the rear end portion P does not exist, so the main gate pulse (2) is not output. In this way, the main pulse is applied when the sensed output exceeds the reference voltage V ref during the period of the gate pulse, and is not applied when it does not. As a result of the detection pulse and the main pulse being applied to the gap at different times, the waveform of the gap voltage becomes a waveform such as (2), which is a combination of both (2) and (2). The gap current has a waveform like ■.

【Effect of the invention】

As described above, according to the present invention, it is now possible to select cases in which it is acceptable to cause a discharge to occur, from among cases in which the application of the main pulse was conventionally treated as not appropriate. As a result, the frequency of main pulse application increased and the processing speed became faster. Note that since the output impedance of the detection NB is made large, the current caused by the detection pulse is small and the wire will not be overheated.

[Brief explanation of the drawing]

Fig. 1: Power supply device for electrical discharge machining according to an embodiment of the present invention Fig. 2: Waveform diagram for explaining the operation of the device shown in Fig. 1 Fig. 3: Gate pulse and comparator output Enlarged view 4th
Figure: In the figure showing the connection relationship between the output impedance of the power supply and the gap impedance, 1 is the main power supply, 2 is the detection power supply, 3 is the main switch transistor, 4 is the sub switch transistor, 5
．． 6 is a diode, 7 and 8 are line inductances, 9 is a workpiece, 1o is a conductor, 11 is a wire, 12 is a machining path, 13 is a comparator, 14 is a reference voltage terminal, 15 is a main power gate pulse generator, 15-1 is a time constant circuit section, 16 is a gate pulse generation section, and 17 is a resistor.

Claims (1)

[Claims] In an electrical discharge machining power supply device that applies a detection pulse to the gap between the electrode and the workpiece from a detection power supply to check the conductivity of the gap before applying the main pulse, the output impedance is determined by the main power supply that supplies the main pulse. and a comparator that outputs when the detection output obtained from the gap exceeds a reference voltage determined corresponding to the gap condition that is barely suitable for causing electrical discharge that enables electrical discharge machining. and a main power gate pulse generator that outputs a main power gate pulse for generating a main pulse when the output of the comparator is still present after the fall of the gate pulse for generating a detection pulse. Features of electrical discharge machining power supply device.