JP2616146B2 - Electric discharge machine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a position where an electric discharge occurs in an electric discharge machine,
The present invention relates to a detection device for detecting a change in a processing area of a workpiece.

[Prior Art] FIG. 4 is a schematic configuration diagram showing a conventional wire electric discharge machine. In the figure, 1 is a wire electrode, 2a and 2b are guide rollers, 3 is a workpiece, 4a and 4b are power supply portions for supplying power to the wire electrode 1, and 5a and 5b are formed of the wire electrode 1 and the workpiece 3. A working fluid supply nozzle for supplying a working fluid for stabilizing a discharge generated between the electrodes (gap), a processing power supply 6 for supplying power to the wire electrode 1 and the workpiece 3, and a wire electrode 7 for the wire electrode A voltage detection device for detecting a voltage applied between the workpiece 1 and the workpiece 3; a current detection shaft resistor 8 provided for detecting a current supplied from the processing power supply 6; A current detecting device for detecting a current flowing from the shunt resistor 8 into the circuit; a discriminating device 10 for discriminating a processing state of the wire electrode 1 and the workpiece 3 from an output of the voltage detecting device 7 and an output of the current detecting device 9 And 11 control the machining path, electric machining conditions, machining feed rate, etc. Control device.

Next, the operation of the conventional wire electric discharge machine will be described. The wire electrode 1 is sent in one direction while being held by guide rollers 2a and 2b and maintaining an appropriate tension by a brake (not shown) or the like. Further, the wire electrode 1 is always in contact with the power supply units 4a and 4b provided so as to sandwich the workpiece 3. The wire electric discharge machine causes a discharge between the wire electrode 1 and the workpiece 3 by causing the wire electrode 1 and the workpiece 3 to approach each other while applying a voltage from the machining power supply 6 between the wire electrode 1 and the workpiece 3. The workpiece 3 is processed. The reason that the workpiece 3 can be machined by the discharge generated between the wire electrode 1 and the workpiece 3 is that the discharge point at which the discharge occurs has a very high temperature and the workpiece 3
This is because the wire electrode 1 can be melted and scattered. The working fluid is supplied from the working fluid supply nozzles 5a and 5b in order to eliminate the melted and scattered working powder and cool the discharge point. Then, when the workpiece 3 is machined, it is necessary to detect the occurrence of electric discharge because the machining of the workpiece 3 is performed by repeating the discharge.
In order to detect the occurrence of this discharge, a voltage detecting device 7 for detecting a decrease in the voltage applied from the machining power supply 6 to the wire electrode 1 and the workpiece 3 or a current when a discharge current flows is detected. A current detection device 9 for detecting is provided.

Further, in order to process the workpiece 3 with high accuracy by the wire electric discharge machine, the wire electrode 1 when electric discharge occurs is required.
It is necessary to keep the distance between the wire electrode 1 and the workpiece 3 constant, and at the same time, it is necessary to prevent the wire electrode 1 and the workpiece 3 from coming into contact with each other and becoming unstable. In order to avoid this, the discriminating device 10 for discriminating the machining state between the electrode formed by the wire electrode 1 and the workpiece 3 from the output of the voltage detector 7 or the output of the current detector 9 stabilizes the electric discharge machining state. The degree is determined, and a signal output by the determination is sent to the control device 11. The control device 11 controls the machining feed rate so that the average machining voltage applied to the wire electrode 1 and the workpiece 3 is kept constant by a signal from the discriminating device 10. Is always constant, whereby the workpiece 3 can be machined with high precision.

[Problems to be Solved by the Invention] Since the above-described conventional wire electric discharge machine is configured as described above, it occurs when the plate thickness of the workpiece 3 changes suddenly or when electric discharge is concentrated. Since it is difficult to avoid an unstable state, there is a possibility that a failure may occur in the worst case where the wire electrode 1 is disconnected.

As a technique for avoiding the unstable state in which the discharge is concentrated as described above, as disclosed in Japanese Patent Application Laid-Open No. Sho 62-15017, the current flows to the power supply electrodes provided above and below the workpiece. Since the position of the discharge point of the generated discharge can be detected from the difference between the respective current values, a technique for avoiding an unstable state due to the concentration of the discharge based on the detected position has been proposed. However, even with such a technique, there is a disadvantage that the position of the discharge point cannot be detected when the processing area changes due to a change in the thickness of the workpiece or the like.

Further, as a method of detecting a change in the processing area caused by a change in the thickness of the workpiece or the like, a method of detecting that the processing feed speed changes due to the thickness of the workpiece or the like is used. It has been proposed, however, that when the machining conditions such as the machining current peak value and the average machining voltage value change, the machining feed rate also changes. It is necessary to provide the relationship of the feed speed as matrix data or to define the relationship functionally, but in this case, there is a problem that the data becomes enormous and the processing becomes complicated.

The present invention has been made in order to solve the above-described problems, and is capable of detecting a position where an electric discharge occurs and detecting a change in a plate thickness and a machining area of a workpiece. The aim is to obtain a device.

[Means for Solving the Problems] An electric discharge machining apparatus according to the present invention includes a pair of power supply units that supply power to a wire electrode provided at a position sandwiching a workpiece, and a pair of power supply units and the workpiece. , A pair of current detectors for detecting a value of a current flowing through each power supply unit, and a first calculator and a second calculator for calculating a difference and a sum of the current values of the two flowing through the respective current detectors A third unit for calculating a ratio between each operation result of the first and second operation units and a current value flowing through each current detector, or calculating a ratio of each operation result of the first and second operation units. And a change in the machining area such as the discharge position generated between the wire electrode and the workpiece and the thickness of the workpiece.

[Effect] The electric discharge machine according to the present invention calculates addition, subtraction, and current ratio of outputs of a pair of current detectors provided so as to sandwich a workpiece using first to third arithmetic units. By doing so, it is possible to detect a change in the machining area due to a change in a discharge position generated between the wire electrode and the workpiece and a change in the plate thickness of the workpiece.

Embodiment An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic configuration diagram showing a wire electric discharge machine according to an embodiment of the present invention, FIG. 2 is an enlarged view showing a main part of the wire electric discharge machine shown in FIG. 1, and FIG. It is explanatory drawing which shows the example of application of machining control in the wire electric discharge machine of the figure. In the figure, 1 is a wire electrode, 3 is a workpiece, 4a and 4b are feeding portions for supplying power to the wire electrode 1, 5a and
5b is a working fluid supply nozzle for supplying a working fluid for stabilizing a discharge generated between the gaps (gap) formed between the wire electrode 1 and the workpiece 3, and 6 is a working fluid supply nozzle.
Power supply for supplying power to the wire, 11 is a control device for controlling the processing trajectory, electric processing conditions, processing feed speed, etc., and 12 and 13 are power supply units 4a and 4b for supplying power to the wire electrode 1 and the workpiece 3
, A current detection current transformer coil of a current detector provided between the first and second calculators; 14 is a first computing unit for subtracting each output of the current detection current transformer coils 12, 13; 15 is a current detection current transformer coil 12; , 13 are added to each other, and 16 is the ratio of each output of the first and second arithmetic units 14 and 15, and the first and second arithmetic units 14, 15 and the current By calculating the ratio of the outputs of the detection AC coils 12 and 13 and the like, the discharge position generated between the wire electrode 1 and the workpiece 3 and the machining area such as the plate thickness of the workpiece 3 are detected. A third computing unit 20 is a discharge point of a discharge generated between the wire electrode 1 and the workpiece 3.

Next, the operation of the wire electric discharge machine according to the embodiment of the present invention will be described. Wire electrode 1 and workpiece 3
As shown in FIG. 2, the current flowing when a discharge occurs between the workpiece 3 and the wire electrode 1 through the discharge point 20 as shown in FIG.
And a circuit B that returns from the workpiece 3 to the machining power source 6 through the discharge point 20 via the discharge point 20 and the wire electrode 1 and returns to the machining power source 6 via the power supply unit 4b. In each of these two types of circuits A and B, current detection AC coils 12 and 13 are provided between the workpiece 3 and the power supply units 4a and 4b to detect the current flowing through each of the power supply units 4a and 4b. . The current flowing through each of the power supply units 4a and 4b is
, And convert the voltages into signals A and B, respectively. The first arithmetic unit 14 calculates the difference between the signals A and B to obtain a signal C. At the same time, the second arithmetic unit 15 calculates the sum of the two signals to obtain a signal D. The outputs of the first and second calculators 14 and 15 and the outputs of the current detection AC coils 12 and 13 are input to a third calculator 16 to calculate the respective ratios. The calculation result is as follows.

Here, the signal F is a power supply unit 4a for the entire current (signal D).
Signal G is the ratio of the current (signal B) flowing to the feeder 4b to the total current (signal D) Signal H is the current flowing to each feeder 4a, 4b to the total current (signal D) Ratio of difference (signal C) Signal I is obtained by averaging the absolute values of signal H and normalizing them.

 By using each of the above signals, (1) the discharge position can be detected by the signal H.

(2) The processed plate thickness (processed area) of the workpiece 3 according to the signal I
Can be detected.

(3) The direction of change in the thickness (machined area) of the workpiece 3 of the workpiece 3 can be detected from the signals F and G.

The above three types of detection signals (indicated by signal E in FIG. 1)
Is transmitted to the control device 11 for controlling the machining trajectory, the machining feed rate, the electric machining condition, etc., so that the machining control is difficult with the conventional apparatus of this kind. Processing control as shown below becomes possible.

Next, an application example of the processing control of the workpiece 3 shown in FIG. 3 will be described. First, a description will be given of a change in each signal when the plate thickness of the workpiece 3 becomes half from the middle as shown in the case (1). The wire electrode 1 is A
When moving from the point to the point B, the signal changes when the processing area, which is the plate thickness of the workpiece 3, changes (point C), the signal F and the signal I change, and the processing position of the workpiece 3 becomes a current. It is possible to detect that the processing area has decreased at the same time as it is shifted to the detection current transformer coil 13 side. When a change in the machining area occurs on the side opposite to the case (1) (not shown)
Can be detected by changing the signal G and the signal I.

Next, the signal change when the plate thickness of the workpiece 3 uniformly decreases in the vertical direction as shown in the case (2) is the signal F,
All of the signals G and I change, so that a change in the processing area can be detected.

As described above, in the embodiment according to the present invention, it is possible to easily detect a change in the machining area during the machining of the workpiece 3 and to detect the discharge position. Detection can be performed without being affected by the ratio operation of the first, second, and third arithmetic units 14, 15, and 16.

In the above-described embodiment, the case where the change in the plate thickness of the workpiece 3 is reduced from a thick portion to a thin portion is described. Conversely, the change in the plate thickness of the workpiece 3 is increased from a thin portion. In this case, it is needless to say that it can be detected in the same manner.

Further, in the above embodiment, since the direction of change in the processing area of the workpiece 3 can be detected, the processing accuracy can be improved by controlling the supply of the processing liquid based on this detection signal.

[Effects of the Invention] As described above, according to the electric discharge machining apparatus of the present invention, a pair of power supply units for supplying electric power to the wire electrode provided at a position sandwiching the workpiece, and each of the power supply units and the workpiece A pair of current detectors for detecting a current value flowing through each of the power supply units provided between the current detectors, a first calculator and a second calculator for calculating a difference and a sum of the current values of the two currents flowing through the respective current detectors Calculates the ratio of each calculation result of the first and second calculators to the value of the current flowing through each current detector, or calculates the ratio of each calculation result of the first and second calculators. Since the configuration is provided with the third arithmetic unit, the discharge position generated between the wire electrode and the workpiece, and changes in the processing area such as the plate thickness of the workpiece can be easily performed.
In addition, an excellent effect that accurate detection can be achieved.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing a wire electric discharge machine according to an embodiment of the present invention, FIG. 2 is an enlarged view showing a main part of the wire electric discharge machine shown in FIG. 1, and FIG. FIG. 4 is an explanatory diagram showing an application example of machining control in the wire electric discharge machine shown in FIG. 4, and FIG. 4 is a schematic configuration diagram showing a conventional wire electric discharge machine. In the drawing, 1 ... wire electrode, 2a, 2b ... guide roller, 3 ... workpiece, 4a, 4b ... power supply section, 5a, 5b ... working fluid supply nozzle, 6 ... working power supply, 7 ... voltage detecting device, 8 ... current detecting shunt resistor, 9 ... current detecting device, 10 ... discriminating device, 11 ... control device, 12, 13 ... current detecting current transformer coil, 14 The first computing unit,
15 ... second computing unit, 16 ... third computing unit, 20 ... discharge point. In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (1)

(57) [Claims] An electric discharge machine for applying a voltage to a minute gap between a wire electrode and a workpiece to perform electrical discharge machining on the workpiece, provided at a position sandwiching the workpiece, and provided on the wire electrode. A pair of power supply units for supplying electric power, a pair of current detectors for detecting a current value flowing through each of the power supply units, and a first computing unit for calculating a difference between the two current values flowing through the current detectors , A second computing unit that calculates the sum of the two current values flowing through the respective current detectors, the respective computation results of the first computing unit and the second computing unit, and the current value flowing through the respective current detectors A discharge position generated between the wire electrode and the workpiece, and a means for detecting a change in a processing area such as a plate thickness of the workpiece. Processing equipment.