JPS6247133B2 - - 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. The purpose of this invention is to analyze and judge the current waveform determined by this inductance, detect the occurrence of concentrated discharge, and provide an extremely reliable wire-cut electrical discharge machining device that does not cause wire breakage.

Hereinafter, the principle diagram 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
Assuming that each inductance is l ₁ and l ₂ , the inter-electrode current I is expressed as follows.

I ₁ = E/R (l-e _xp ^- 〓 ^t ) I ₂ = E/R (l-e _xp ^- 〓 ^t ) However, R is the resistance value of the current limiting resistor 19, and E is the voltage of the DC power supply 16. be. 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 in FIG.
_I is held by the sampling hold circuit 31 at the timing △T, and this held value is transferred to the analog/digital converter 32.
One-way latch circuit 33 as a digital value by
Temporarily memorize it. This latch circuit 33 is configured to shift this signal to the next stage latch circuit 34 in response to the aforementioned signal ΔT.
The current value S _I at ΔT before the timing and S _I at the next timing can be read from the input and output values of the latch 34. Here, each signal is defined as S _I (t) and S _I (t-1), and a difference is detected by a subtraction circuit or a digital comparator 35. When there is a difference, that is, when there is no concentration of discharge, a counter 36 When there is no difference, that is, when there is concentrated discharge, when the content of the counter 36 exceeds a predetermined set value n by adding an addition pulse to the counter 36, n consecutive concentrated discharges occur. It is now possible to detect what has happened. In the embodiment, △T itself is used as the counting pulse of the counter, and in the case of concentrated discharge, the reset is not applied. Therefore, if discharges are concentrated up to n consecutively, when the set value n of the counter 36 is exceeded, the concentrated discharge is detected. Danger signal S is output. Further, by attaching a digital-to-analog converter 37 to the counter 36 and displaying this analog signal on a meter 38 or a light emitting diode, it is possible to visually check the state of concentration of discharge.

As described above, it is possible to determine and control the concentration of discharge at one point using the value of the counter 36, and to know how many pulses have continuously generated concentrated discharge.

Figure 5 shows experimental data showing changes in inductance due to changes in discharge point.
Let φ be the distance from the feeder 9 to the discharge point L ₁
(mm), the distance between the power supply 15 and the feeder 9 is L ₀ (mm)
That is. It should be noted that for the above-mentioned section L ₀ , an extremely low inductance cable such as a coaxial cable 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 0.4
This is when it is set to μsec.

Note that the resistance value of the wire electrode 2 is approximately 0.04Ω when the diameter of the wire electrode 2 used in practical use is 0.2φ to 0.3φ and the length is 200mm. However, it can be ignored.

In the above embodiment, the circuit configuration uses the continuous amount of discharge concentration between the electrodes as a parameter, but it is not difficult to realize that the number of abnormal discharges (concentrated discharges) in a unit time is used as a discrimination parameter.

As described above, according to the present invention, the concentration of electric discharge in wire cut electric discharge machining can be properly detected, so that it is possible to grasp the precursor state of machining failure and wire breakage in terms of machining operation.

[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 experimental data showing changes in inductance due to changes in the discharge point, and Figure 6 is the diagram of the inductance. This is experimental data showing changes in current and current. In the figure, 1 is a workpiece, 2 is a wire electrode, 9 is a feeder, CT is a current detector, and 30 is a discharge concentration detection circuit diagram. 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. A wire cut discharge characterized by comprising a device that detects from a current waveform that is a function of inductance at a discharge point, determines whether the discharge position is concentrated at one point, and outputs a signal based on the determination. Processing equipment.