JPS6227930B2 - - Google Patents

Description

Detailed Description of the Invention The present invention is applicable to electric discharge machining (including electrolytic erosion machining) in which machining is performed by repeatedly generating electric discharge using machining pulses in the machining gap between an electrode and a workpiece facing each other. The purpose of this invention is to accurately detect and determine whether the state of the machining gap is good or bad, that is, the change in the state of the machining gap, and whether it is good or bad, and to thereby optimally control the machining state.

In electrical discharge machining, machining pulses are controlled according to the gap state (discharge state), flow rate of machining fluid, control of electrical conductivity, electrode vibration when machining debris accumulates, cleaning work by pulling up the electrode, and gap length. It is necessary to optimally perform servo control, etc. to follow the machining. Conventionally, it has been known to utilize the presence or absence of a high frequency component (vibration component) generated in the voltage or current in the gap to detect the state of the machining gap, the quality of discharge, etc. As shown in the voltage waveform of FIG. 1, the high frequency component takes the form of a high frequency component voltage ΔV (amplitude) superimposed on the discharge sustaining voltage of the DC component of each pulse discharge. V _G - is the average voltage of the machining gap during pulse discharge. The superimposed high frequency component voltage usually has a frequency of about 1 MHz to 30 MHz, and once an arc state is established, this high frequency component disappears. Of course, this does not occur even due to a short circuit. Therefore, in the past, the presence or absence of this frequency component was detected and determined, and if a high frequency component was present, it was determined that the discharge was good, and if there was no high frequency component, it was determined that it was a bad discharge, and based on this, it was determined that the discharge was bad. I was trying to control it.

However, by simply detecting the presence or absence of high-frequency components as in the past, it is only possible to determine whether or not there is an arc discharge. etc., it was not possible to make an accurate judgment based on this.

However, subsequent research has revealed that even when electrical discharge machining is performed under the same machining conditions, there is a dependence on the average molecular weight of the machining fluid, which changes the generation of high-frequency components and the amplitude of the high-frequency component voltage.
In other words, in pure water with a small molecular weight (molecular weight 18), the high frequency component voltage △V is extremely small;
200 to 300), ΔV is large, and spindle oil (molecular weight ~700) produces an even larger ΔV.

The present invention has been proposed in view of this point. In other words, it depends on the molecular weight of the machining fluid, and as the molecular weight increases, the high frequency component voltage △V generated by discharge increases, so it is necessary to consider this relationship to determine whether or not it is normal. This makes it possible to accurately determine and control the discharge state.

FIG. 2 is a graph of the gap voltage of normal pulse discharge detected based on the experimental results of electric discharge machining using machining fluids with different molecular weights under the same machining conditions. The horizontal axis is the average molecular weight of the processing fluid, which is the average value of the molecular weight of the processing fluid depending on the mixing ratio. The vertical axis shows the machining gap voltage (peak value) Vm.
As shown in the figure, the gap voltage during the pulse discharge is the sum of the anode drop voltage Va and the cathode drop voltage Vc (Va+Vc) plus the DC component voltage and the high frequency component voltage ΔV (amplitude). That is, the high frequency component voltage ΔV is DC biased to form the machining gap voltage Vm with Vm=Va+Vc+ΔV. The high frequency component voltage ΔV has a frequency of about 1 to 30 MHz as described above, but this voltage ΔV increases depending on the molecular weight of the processing fluid.
According to experiments, when performing electrical discharge machining on SKD-11 material using a 6mmφ Cu electrode, τon = 150μs, τoff = 12
When electric discharge was performed under the machining conditions of μs, Ip = 10A, and each high frequency component voltage △V was measured corresponding to machining fluids with different molecular weights, pure water with a small molecular weight (molecular weight 10~
20), even during normal discharge, △V = 1V, which is extremely small.
For a processing fluid with an average molecular weight of 100 (approximately 1000), △V = 5V, for a processing fluid with an average molecular weight of approximately 300, △V = 8V, and when the average molecular weight is further increased to approximately 600, △ V=10V. Also, for kerosene with an average molecular weight of 200 to 300, △V≒
8V and spindle oil with an average molecular weight of about 700 △
V≒10V. Also polyvinyl alcohol,
Even when the average molecular weight was changed by mixing gelatin or the like, it was almost the same as ΔV in the case of polyethylene glycol. This is because the electrons emitted from the cathode are absorbed by the polymer in the medium, making the discharge easy to pulse and generate high frequencies. However, if the medium is a low molecule, there is nothing to absorb and interfere with the electrons, and the electrons are It is thought that if the number increases too much, the discharge will continue and the generation of high frequency components will decrease. Also, even if a high molecular weight medium is used in the future, if cracking or lower molecular weight occurs during processing,
It can be seen that the high frequency component voltage gradually decreases and finally reaches the arc. Further, it can be seen from the above that regardless of the type of machining fluid, a high frequency component voltage ΔV is generated corresponding to the average molecular weight of the machining fluid.

Since the high frequency component voltage generated during discharge is dependent on the average molecular weight of the machining fluid,
The discharge state can be accurately detected by setting a reference value corresponding to the molecular weight of the machining fluid to determine its quality.

The present invention will be explained below with reference to an embodiment of the drawings. In Figure 3, 1 is the machining gap formed by the electrode and the workpiece, and 2 is the machining pulse from a pulse power source that generates machining pulses by switching the voltage source on and off using a switch element such as a transistor. is repeatedly supplied and subjected to electrical discharge machining. 3 is a detection circuit that detects the voltage (or current) at each discharge caused by the machining pulse in the machining gap 1, and 4 is a high-pass filter circuit that detects only the high frequency component voltage △V (approximately 1 to 30 MHz) included in the detection signal. Pass through and output. Reference numeral 5 denotes an amplifier that amplifies the high frequency output ΔV that has passed through the filter and converts it into a proportional DC output voltage, and this output is compared and determined by the next comparison circuit 6. The comparison circuit 6 includes a preset circuit 7 according to the average molecular weight of the processing fluid.
A comparison reference signal is added from. This comparison circuit may use, for example, a Schmitt circuit. The Schmitt phase inversion voltage may be preset by the preset circuit 7. As explained in Fig. 2, this preset value (comparison reference value) is correspondingly small because △V is small when water with a small molecular weight is used as the machining fluid. When using a large liquid, set it to a large value in proportion to △V. Further, when the average molecular weight is controlled by adding a substance with a high molecular weight, the value shall be set in accordance with the value of the average molecular weight.

For example, using Figure 2, for processing using a processing fluid with an average molecular weight of 20, set the reference value to 1V and a molecular weight of 100.
For machining fluids with a molecular weight of 300, the standard value is 5V, for machining fluids with a molecular weight of 700, the standard value is 10V, and so on, depending on the molecular weight of the machining fluid. Set.

In this way, the preset reference signal and the detected signal from the amplifier 5 are added to the comparator circuit 6 and compared, and if the detected signal is equal to or greater than the set value, a signal is output, and the signal is sent to the pulse circuit. 8 to perform pulse conversion. That is, this pulse circuit 8
The output is a discharge with a predetermined high frequency component,
In addition, the high frequency component voltage ΔV is higher than a certain set value, indicating good discharge (OK). 9 is an up-down counter for comparing and collecting the detection discrimination signals, and 10 is a pulse circuit that converts the detection signal of the detection circuit 3 into a predetermined pulse; Change to 11
is a preset counter for counting the number of discharge pulses, which counts the number of discharges up to a predetermined preset number and outputs a signal proportional to the total number of discharges. The up-down counter 9 receives the OK signal and a signal proportional to the total number of discharges, for example.
It counts up with an OK signal and counts down with a signal proportional to the total number of discharges. Of course, the OK signals may also be collected up to a certain preset number by a preset counter (not shown) and added to the up-down counter 9.
During machining under normal electrical discharge machining conditions, the count number of the up-down counter 9, which counts signals proportional to the OK signal and the discharge number signal, is controlled by a preset counter so that it balances to a certain value.

Each pulse discharge that repeatedly occurs in machining gap 1 is
Various types of discharges are included, such as those containing high frequency components, arcs and short circuits, and the total number of these discharges is detected by the pulse circuit 10 and the preset counter 11 and added to the up-down counter 9. On the other hand, those containing high frequency components are separated by a filter 4, and further, a comparator circuit 6 discriminates whether the high frequency component voltage generated by the working fluid used is higher than a predetermined value. That is, for example, if a high molecular weight machining fluid is used, but only the high frequency component voltage is generated when a low molecular weight fluid is used, this can be considered as a good discharge,
This system distinguishes discharges that are one step away from becoming arc discharges even if high-frequency component voltages are detected and eliminates them.
Only discharges recognized as normal under the set machining fluid and machining conditions are applied to the up-down counter 9. The count of the up-down counter 9 displays the ratio of the number of OK discharges to the total number of discharges,
OK discharge is based on strict discrimination as mentioned above.
Since the number of discharges is counted, the output of the counter 9 allows extremely accurate detection of the discharge state and machining state. The up-down counter 9 counts up in response to the OK signal, so when the count increases, the discharge condition is good.
When the count number decreases, it indicates that the discharge condition is poor. The output of the counter 9 may be displayed on a display device, and this signal may be used to control processing conditions. The illustrated circuit 12 is a control circuit for the machining pulse power source 2, and controls the pulse width τon, pause width τoff, repetition frequency F, etc. of the machining pulse, but the control is performed by accurate detection of the discharge state. Therefore, appropriate control is always performed.

In addition, the detection circuit 3 of each electric discharge repeated in the machining gap
The detection may be performed over the entire period of one pulse discharge time, but it may also be checked at the beginning, middle, and end of the discharge. In this case, the pressure and temperature of the discharge column change over time, and the molecular weight of the high-frequency component changes due to decomposition due to the temperature of the medium, so the high-frequency component is detected and determined at a fixed time within about 15 μsec at the beginning of the discharge. This makes highly accurate detection possible.

Alternatively, the detection signal may be a signal voltage containing a high frequency component, and this detection signal voltage may be discriminated.

In addition, the logic circuit for determining the quality of the discharge state and machining state by detecting the high frequency component voltage or the signal voltage including the high frequency component voltage is as described above.
In addition to using the ratio between the OK signal and the total discharge number signal,
Ratio, difference, or
The ratio of the OK signal, a signal other than OK, etc. to the counting time signal, or the ratio of the OK signal to the arc/short circuit signal,
difference, and various other logic circuit configurations can be used.

Based on the discrimination of the discharge state by detecting this high frequency component voltage or signal voltage including a high frequency component, when the high frequency component voltage △V is reduced to a predetermined value or less due to a decrease in the molecular weight of the medium liquid, for example, the pause time τoff is determined. When measuring the recovery ^of the medium by controlling ^the
(100μs) pause control. This is the discharge response,
That is, a time based on ion and electron mobility is required to cause a discharge with vibration, and this time is approximately 10 ^-4 to 2×10 ^-4 sec.

Furthermore, based on the detected and discriminated signals, the molecular weight of the machining fluid may be controlled, for example, the addition of a high molecular weight solution to the pace fluid and the amount of addition may be controlled, and the jet velocity and flow rate of the machining fluid may be controlled. Further, vibration control, frequency and amplitude control of the electrodes, reciprocating motion control of the electrodes, servo control, etc. may be performed, and can be carried out optimally.

In any of the above controls, the detected high-frequency component voltage is discriminated at a reference level corresponding to the molecular weight of the medium processing fluid, the state of the machining gap is detected based on the output of this discrimination, and each part is controlled based on this. The detection accuracy of the machining state is high, and the effect is that optimal control can be performed at all times.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of a discharge voltage waveform, FIG. 2 is an explanatory graph of changes in the gap voltage (peak value) corresponding to the molecular weight of the medium, and FIG. 3 is a circuit configuration diagram of an embodiment of the present invention. △V...High frequency component voltage, 1...Machining gap, 2
...Processing pulse power supply, 3...Detection circuit, 4...Filter circuit, 5...Amplifier, 6...Comparison circuit, 7
...Preset circuit, 8...Pulse circuit, 9...
Up-down counter, 10...Pulse circuit, 1
1... Preset counter, 12... Control circuit.

Claims (1)

[Scope of Claims] 1 Machining by repeatedly applying pulse discharge to a machining gap to which machining fluid is supplied, and detecting a high frequency component voltage or a signal voltage containing a high frequency component present or included in the pulse discharge. In the electric discharge machining method in which machining is performed while monitoring the electric discharge state or the state of the machining gap, the detected high frequency component voltage or the signal voltage containing the high frequency component is set in accordance with the molecular weight of the medium machining fluid. A discharge machining method characterized in that a discharge state or a machining gap state is detected based on the determination based on the reference level. 2. The electric discharge machining method according to claim 1, wherein the high frequency component voltage or the signal voltage containing the high frequency component is detected within 15 μs after the start of electric discharge. 3. The electric discharge machining method according to claim 1, wherein the high frequency component voltage or the detection signal voltage containing the high frequency component is determined within 15 μs after the start of electric discharge.