JPS591539B2 - Electric discharge machining equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides electrical discharge machining in which a machining pulse is repeatedly applied to a machining gap where an electrode and a workpiece face each other.
To accurately detect and determine whether the state of the discharge being performed is good or bad, that is, the change in the state of the machining gap, and whether it is good or bad;
Furthermore, the purpose is to control the machining conditions in the best possible manner.

In electrical discharge machining, machining pulses are controlled according to the gap state (discharge state), flow rate of machining fluid, electrical conductivity are controlled,
Electrode vibration when machining debris accumulates, cleaning work by pulling up the electrode, servo control to adjust gap length to follow machining,
It is necessary to perform the following optimally.

Conventionally, in order to detect the state of the machining gap, the discharge state, the quality of the discharge, etc., high frequency components (vibration components) present or included in the discharge voltage or current or signals containing high frequencies are detected and determined to determine the machining gap. It is known to inspect and determine the state of the battery and the discharge state.

This high frequency usually has a frequency of about 1 MHz to 30 MHz, and once an arc state is established, this high frequency component immediately disappears. Of course, this does not occur even due to a short circuit. Therefore, whether there is this high frequency component or not,
In addition, by detecting and determining the magnitude of the discharge, it is possible to accurately detect and judge the discharge state, thereby achieving the effect of optimally controlling each part as described above. It will be done. However, even if the machining fluid is the same, the material combination of the electrode and the workpiece, the machining pulse conditions, etc. are the same, the high frequency component can be generated and generated by changing the polarity of the discharge. changes.

The workpiece is usually a ferrous material such as steel, but when machining it with electrodes made of materials such as copper, graphite, silver-tungsten, copper-tungsten, etc. facing each other, experiments have shown that generally the electrode side is negative and the electrode side is negative. When performing a positive polarity discharge with the workpiece side being positive, the generation of high frequency vibration components is stronger, and the higher the high frequency voltage is, than when performing a reverse polarity discharge with the opposite polarity. During electrical discharge machining or when setting machining conditions, the discharge polarity can be selected arbitrarily and set to positive polarity for high-speed machining, and reverse polarity for electrodeless (low) wear machining. A typical electrical discharge machine is equipped with a polarity switching device so that the discharge polarity can be arbitrarily selected.

When the polarity is switched in this way, the state of high frequency generation changes as described above, and it is no longer possible to accurately determine whether the discharge state is good or bad by detecting it under certain conditions and determining it at a certain level. It ends up. The present invention improves this point.

In other words, the detection level or discrimination level for detecting and determining high-frequency vibration components generated in the machining gap due to electric discharge or signals containing high frequencies is set to an optimal value for when performing positive polarity discharge and when performing reverse polarity discharge, respectively. This feature is characterized in that this can be changed, selected and set in response to polarity switching. The present invention will be explained below with reference to an embodiment of the drawings. Reference numerals 1 and 2 denote an electrode and a workpiece, which face each other and form a machining gap.

3 is a voltage source that supplies machining power; 4 is a switch element such as a transistor, which is connected in series with the voltage source 3 and connected in parallel to the machining gap; Generate and supply machining pulses by off-switching.

5 is a pulser that generates and applies switch control pulses to switch 4. Although an independent oscillator may be used in some cases, the pulse width, pause width, frequency, etc. are controlled to change in response to detection signals such as voltage and current in the machining gap. A dependent oscillator may also be used.

In addition, the processing gap detection signal voltage may be converted into a pulse and used. 6 is a polarity switch inserted in the machining pulse supply circuit; 7 is a polarity switch inserted in the high-frequency vibration component detection circuit generated in the machining gap; these switches are switched together with the polarity switch 6 of the machining pulse supply circuit; Detection is switched to occur.

8 is a detection resistor constituting a signal detection circuit, and 9 is a high-pass filter, which detects only medium and high frequency components of the detection signal and inputs them to the next discrimination circuit 10.

The discrimination circuit 10 is configured to discriminate, for example, the average voltage of the high frequency vibration component by Schmitt or the like, and is provided with a discrimination level changeover switch 11. Reference numeral 12 denotes a condition setting device consisting of a memory element such as a ROM or RAM, which sets machining conditions corresponding to the target machining conditions, such as the material combination of the electrode and the workpiece, machining speed, machined surface roughness, electrode consumption ratio, etc. Conditions such as pulse width, pause width, peak value, polarity, feed rate for gap control, and other conditions are input and stored, and by selecting the target machining during machining, the control pulser 5 of the machining pulse can be controlled. The polarity switch 6 operates to select the polarity.

At the same time, the polarity switch 7 of the signal detection circuit is also switched, and the level switch 11 of the discrimination circuit is also carried out. Switch 4 on.
The machining pulses generated by the off control cause repeated electrical discharges in the machining gap, and as described above, high frequency waves are generated during normal machining due to these discharges.

The high frequency vibration component usually has a frequency of about 1 MHz to 30 MHz, and its size and strength change depending on the quality of the discharge state. The gap voltage during pulse discharge is the sum of the DC component, which is the sum of the anode drop voltage and the cathode drop voltage, plus the above-mentioned high frequency component, and the DC component has low sensitivity to changes in the discharge state and changes little. The high frequency component changes with high response in conjunction with the discharge state, and therefore, by detecting and determining this, the gap state (discharge state) can be properly detected. As described above, the generation of high frequency components differs depending on the discharge polarity even under the same conditions, and as shown in FIG. 2, which shows the voltage waveform of an 1-pulse discharge, the high frequency voltage is higher with positive polarity than with reverse polarity.

ΔV1 is a high frequency voltage of positive polarity discharge, Δ2 is a high frequency voltage of reverse polarity discharge, and Δ1>Δ2. Incidentally, to give an experimental example, pulse width 11TS~2000μS1 wave height value 3A~50
In the processing of the applied force in the range of 0 A, the material combination of the electrode and the workpiece is Cu-FelG (Graphite).
-Fe. ．． In each case in the AfW-Fe combination,
Approximately 0.5 in positive polarity when detecting the average voltage of high frequency components
V was about 0.2 in reverse polarity. Of course, the generated high-frequency voltage varies depending on the medium, particularly the molecular weight of the medium, but the tests were conducted under the same conditions. Therefore, when the discharge polarity is switched by the switch 6, the polarity of the signal detection circuit is switched from the gap, and the level is also switched 11 for discrimination.

The detection resistor 8 also detects the DC component shown in FIG. 2, and only the high frequency component is detected and input to the discrimination circuit 10 through the filter 9. In the case of positive polarity processing, the high frequency component voltage △V1 is added to the discrimination circuit 10 and discriminated, so the discrimination level is increased according to the input △1, and in the case of reverse polarity processing, △V2 is added to the discrimination circuit 10. The discrimination level is decreased according to the input ΔV2. By performing such discrimination level switching 11 in conjunction with polarity switching 6, high frequency discrimination can be performed at the optimum level according to the discharge polarity. Even if the generation state of high frequency components changes, the discharge state can be accurately determined and determined. In the figure, the pulser 5 for generating machining pulses, polarity switching 6, 7, discrimination level switching 11, etc. are all automatically switched by the signal from the condition setting device 12, but they cannot be switched manually. Of course, it is also possible to switch the selection.

Further, when changing the level, the value to be changed is set each time by the condition setting device 12 in response to not only polarity switching but also other conditions, and analog or digital level change control settings are performed by the setting signal. You can do it like this. As described above, by changing the discrimination level according to polarity switching, detecting and discriminating signals of high frequency components, and detecting the discharge state, accurate detection and discrimination can be performed, and the discrimination output of the discrimination circuit 10 is normally Although not shown, the counter
A preset counter, an up-down counter, etc. are used to count and collect a plurality of them, and then they are determined as a group. When the preset counter, etc. counts the number of presets, a determination calculation signal is output, and the quality of the discharge state and machining state is determined. ,
Furthermore, changes in machining status, overall trends, etc. are determined, and control is performed in accordance with the determination results.

In this way, the detection/judgment, aggregation, and arithmetic processing have the effect of collectively determining the pass/fail distribution and making an overall judgment. In addition, the detected and determined signals can be collected and arithmetic processed by comparing good discharges with bad discharges, comparing them with the number of discharges, or comparing them with time.

Then, using this detection discrimination output as a signal or a collective signal counted by a counter etc., for example, gap servo control, follow-up control, gap cleaning by registration process control, vibration control, pulse width of machining pulse, etc. pause width,
Control of frequency, duty factor, etc., media processing fluid control, jet pressure, flow velocity, flow rate control, as well as edge machining feed, tilt machining feed control, etc. are always performed optimally, ensuring stable machining under optimal conditions. In addition, machining effects such as speed, machining efficiency, and machining accuracy are greatly improved.

Note that the detection level of the detection circuit 8 may be changed without changing the discrimination level.

Further, it is of course possible to detect and discriminate a signal containing a high frequency vibration component as the signal to be detected and discriminated.

[Brief explanation of drawings]

FIG. 1 is a circuit configuration diagram of an embodiment of the present invention, and FIG. 2 is an explanatory diagram of discharge waveforms. 1 is an electrode, 2 is a workpiece, 3 is a power source, 4 is a switch, 5
1 is a balsa, 6 is a polarity switch, 7 is a polarity switch, 8 is a signal detection resistor, 9 is a filter, 10 is a discrimination circuit, 11 is a level switch, and 12 is a processing condition setting device.

Claims (1)

[Scope of Claims] 1. A machining gap in which an electrode and a workpiece face each other, a machining pulse power source that supplies machining pulses to the machining gap, a polarity switch inserted in a machining pulse supply circuit of the machining pulse power source, and the machining device. A detection circuit for a signal containing a high-frequency vibration component or high frequency generated by discharge in the gap, a discrimination circuit for discriminating a detection signal of the detection circuit, and a detection level or detection circuit for the detection circuit in response to polarity switching of the polarity switch. An electrical discharge machining device equipped with a level changing device that changes (switches) the discrimination level of a discrimination circuit. 2. The electric discharge machining apparatus according to claim 1, wherein the level change device is changed in conjunction with the polarity change of the polarity changer corresponding to the machining conditions.