JPS6344490B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus for electrically cutting a workpiece using a wire electrode.

Machining workpieces using electrical energy has been widely used and is a well-known processing method, but a processing method that has been attracting attention as a recent technology uses wire-shaped electrodes to create a There is a so-called wire-cut electric discharge machining method in which a workpiece is machined using electrical energy like a ``string saw''.

FIG. 1 is a block diagram showing the operating principle of an apparatus for carrying out the wire cut electrical discharge machining method. A workpiece 1 faces a wire electrode 2 with an insulating liquid 3 interposed therebetween. The above-mentioned insulating liquid 3 will be hereinafter referred to as a processing liquid. The machining liquid is injected from a tank 4 by a pump 5 into the gap between the workpiece 1 and the wire electrode 2 through a nozzle 6. Workpiece 1 and wire electrode 2
The relative movement between the two is performed by moving the table 11 on which the workpiece 1 is placed. table 11
is driven by an X-axis drive motor 12 and a Y-axis drive motor 13. With the above configuration, the workpiece 1
The relative movement between the electrode 2 and the electrode 2 becomes a two-dimensional plane movement within the aforementioned X and Y axis planes. The wire electrode 2 is supplied by a wire supply reel 7, passes through the workpiece 1 in the lower wire guide 8A, and passes through the workpiece 1 in the upper guide 8B.
The wire is wound up by the wire winding/tension roller 10 via the electric energy supply section 9. The processing power supply 15 that supplies electrical energy is, for example, as in the present example, and includes a DC power supply 16, a switching element 17, and a current limiting resistor 19.
and a control circuit 20 that controls the switching element 17. 14 is X, Y
The control device drives and controls the drive motors 12 and 13 of the shafts, and uses a numerical control device, a copying device, or a control device using a computer.

Next, the operation of the conventional device will be explained.

In a normal machining state, a high frequency pulse voltage is applied from the machining power source 15, and a part of the workpiece 1 is melted and scattered by a discharge explosion caused by one pulse. In this case, the gap between the electrodes is gasified and ionized due to the high temperature, so a certain pause time is required before applying the next pulse voltage, and if this pause time is too short, the insulation between the electrodes will not recover sufficiently. Since this is not done, the discharge concentrates at the same location again, causing the wire electrode 2 to melt.

Therefore, with a normal machining power source, depending on the type of workpiece, plate thickness, etc., the electrical conditions such as the down time of the machining power source 15 are usually set to have enough margin to prevent wire breakage. . Therefore, the machining speed has to be considerably lower than the theoretical limit value, and furthermore, if the wire electrode 2 is not uniform and the thickness changes, or if there is a protrusion or scratch on a part of the wire and the discharge is concentrated. In this case, melting of the wire electrode 2 is unavoidable.

As described above, in the conventional wire-cut electric discharge machining apparatus, in order to prevent the wire electrode 2 from breaking, the output energy of the machining power source 15 is reduced, etc., so that the electric discharge is temporarily concentrated at one point on the wire electrode 2. The drawback was that the machining speed was extremely low because the wires were not broken even when the wires were cut.

The present invention has been made in view of the above-mentioned drawbacks of the conventional apparatus, and uses an inductance component between an electric energy feeding section and a discharge point in a workpiece to determine whether or not a discharge point is concentrated. Our goal is to analyze and judge the current waveform determined by this inductance, detect the occurrence of concentrated discharge, and control the discharge pause time to provide an extremely reliable wire-cut electrical discharge machining device that does not cause wire breakage. There is.

Hereinafter, the principle of the present invention will be explained using FIG. 2. In FIG. 2, CT is a current transformer for detecting the current I between electrodes. The value of the interelectrode current I has a different waveform depending on the inductance determined by the distance between the discharge point and the current feeder 9, and the distance between the feeder 9 and the discharge point is L ₁ , L ₂
If each inductance is l ₁ and l ₂ , then the current I between electrodes is expressed as follows.

However, R is the resistance value of the current limiting resistor 19, and E is the voltage of the DC power supply 16. Therefore, if the time from which the switching element 17 is turned on and the current I flows until it is turned off is T, then by measuring the current value at T until the switching element 17 is turned off, l ₁ and l ₂ can be found inversely. , furthermore, L ₁ and L ₂ can be determined. Therefore, if the discharge points are concentrated, the current value of the discharge current I at time T becomes approximately equal continuously. 30
is a detection device for detecting the presence or absence of discharge concentration based on the above principle, and the device 30 will be explained using the time chart in FIG. 3 and the block diagram in FIG. 4.

I in FIG. 3 is a current waveform between electrodes observed using a CT for current detection. Further, V _CE indicates the on/off state of the switching element 17. △T is switching element 1
7 is a signal output from the control circuit 20 when turned off.

In Fig. 4, the current signal S _I in Fig. 3 is
is held by the sampling hold circuit 31 at the timing ΔT, and this held value is temporarily stored as a digital value by the analog-to-digital converter 32 in the one-way latch circuit 33. This latch circuit 33 is configured to shift this signal to the next stage latch circuit 34 in response to the signal △T described above, so that the current value S _I at △T one timing before and the current value S S _I is calculated from the input and output values of the latch 34 as follows:
I can read it. Here, each signal is S _I
(t), S _I (t-1), and the difference is detected by a subtraction circuit or digital comparator 35. When there is a difference, that is, when there is no concentration of discharge, the counter 36 is reset, and when there is no difference, the counter 36 is reset. ,
That is, by adding an addition pulse to the counter 36 when there is a concentration of discharge, the contents of the counter 36 become
When the predetermined set value n is exceeded, continuous concentrated discharge n
It is now possible to detect when these events occur consecutively. In the example, △ is applied to the counting pulse of the counter.
T itself is used, and the reset is not applied in the case of concentrated discharge, so if n discharges are concentrated in succession and the set value n of the counter 36 is exceeded, the discharge concentration danger signal S is output. Also counter 36
Attach the digital-to-analog converter 37 to
By displaying this analog signal with a meter 38, a light emitting diode, etc., it is possible to visually confirm the state of concentration of discharge.

Figure 6 shows experimental data showing changes in inductance due to changes in discharge point, and the wire electrode diameter is 0.2φ.
The distance from the feeder 9 to the discharge point is L ₁ (mm),
The distance between the power source 15 and the feeder 9 is L ₀ (mm). Note that for the above section L ₀ , a coaxial cable or other extremely low inductance can be used, and it can be corrected as a fixed value of about 0.1 μH to 0.15 μH.

Further, FIG. 6 shows experimental data showing changes in inductance and changes in current, and this data was obtained when the resistance value R of the current limiting resistor 19 was 0.5Ω, the voltage E of the DC power supply 16 was 200V, and the switching element 17 was turned on. Then, the time T until the current I flows and turns off is
This is when the time is 0.4μsec.

Note that the resistance value of the wire electrode 2 is based on the wire electrode 2 that has a diameter of 0.2φ to 0.3φ and the length
Since it is about 0.04Ω at 200mm, it can be ignored compared to the resistance of 0.5Ω to 50Ω in the processing power source.

Now, by extending the off time of the switching element 17 based on the output obtained by the detection circuit, the period between discharges can be extended, and an ionization effect can be obtained. ,
One of the causes of discharge concentration can be eliminated. The circuit and method for this purpose will be explained with reference to FIG. Reference numeral 118 denotes an RS flip-flop, and when its output Q=1, the switching element 17 is turned on via the amplification amplifier 119. That is, it is an on time, and when Q=0, it is an off time. When Q=1
The output of the AND gate 120 is "0" until the on-time setting output τ _p of the on-time and off-time setting counter 121 becomes "1", but when τ _p becomes "1", the flip-flop 118 is reset. Therefore, Q becomes "0" and becomes off time. At the same time, the output of the AND gate 120 is sent to the oscillator OSC and the time setting counter 12 via the OR gate 122.
Since it is reset to 1, counting is performed from the beginning. Now, when Q = 0, it becomes = 1, so AND
Output 1 is not output until one of the gates of gate 123, that is, the output of OR gate 124 becomes "1". OR gate 124 and AND gate 125,1
26 controls the setting of the off time of the two systems, and when the above _SA is "0", τ ₁ is set to "1", and τ ₂ is set. In other words, according to the present invention, machining is performed with an off time of τ ₁ during normal discharge and τ ₂ during abnormal discharge, and when it is considered as an abnormal discharge, the pause time is suddenly extended to have a deionization effect, and the discharge is stopped. This device prevents concentration and wire breakage, and is characterized by detecting concentration of discharge by determining whether the current waveform during discharge is the same as the previous discharge current waveform. We provide processing control equipment that has never existed before.

In the above explanation, there are two types of off-time, τ ₁ and τ ₂ , but the counter 3 that detects the number of concentrated discharges
A similar effect can be obtained by continuously setting the off time according to the contents of 6.

[Brief explanation of the drawing]

Fig. 1 is a principle diagram of a conventional wire-cut electric discharge machining device, Fig. 2 is an explanatory diagram of the detection principle of the present invention, and Fig. 3 is a diagram illustrating the detection principle of the present invention.
The figure shows the relationship between the current waveform and the detection waveform, Figure 4 is a detection block diagram for detecting discharge concentration, Figure 5 is a circuit diagram for controlling the voltage applied between electrodes, and Figure 6 shows the change in inductance due to changes in the discharge point. Experimental data showing changes. FIG. 7 shows experimental data showing changes in inductance and changes in current. In the figure, 1 is the workpiece, 2
is a wire electrode, 9 is a feeder, CT is a current detector,
30 is a discharge concentration detection circuit. Note that the same reference numerals in the figures indicate the same or equivalent parts.

Claims (1)

[Claims] 1. In a wire cut electric discharge machining device that applies a pulsed voltage to the machining gap between the wire electrode and the workpiece and performs electrical discharge machining using the pulse, the electric discharge position between the wire electrode and the workpiece is set to the position of the wire electrode and the workpiece. It is equipped with a device that detects the current waveform which is a function of inductance at the discharge point, and also determines whether or not the discharge position is concentrated at one point, and outputs a signal based on this. A wire cut electric discharge machining apparatus characterized in that the pause time of the pulsed voltage is controlled to be changed.