JPH0138615B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an electric discharge machining apparatus, particularly an electric discharge machining apparatus that can automatically terminate machining by piercing a workpiece when cutting a workpiece. It is related to.

[Conventional technology]

Electrical discharge machining is a machining method in which an electrode and a workpiece are faced to each other through a gap, and a discharge phenomenon is generated while supplying machining fluid into the gap to machine the workpiece. BACKGROUND ART A punching process that can form a cutting die of a desired shape on a workpiece with high precision is suitable for processing various molds and other molds. however,
In conventional punching, it is not possible to automatically detect the point at which the tip of the electrode penetrates the workpiece, and electrical discharge machining with electrode feeding continues even though punching has finished. As a result, there was a disadvantage that the machining time increased, and furthermore, the side surface of the cutting die was over-machined, resulting in a significant decrease in machining accuracy. Conventionally, to detect electrode penetration,
The amount of electrode feeding had to be determined in advance, or the movement of the electrode had to be artificially monitored to perform processing.

FIG. 1 shows a conventional electrical discharge machining apparatus.

The electrode 10 and the workpiece 12 are opposed to each other with a gap in the machining fluid in the machining tank 14, and a machining voltage is supplied from a power supply unit 16 to the gap.

Here, the gap between the electrode 10 and the workpiece 12 is
It is adjusted by the servo voltage output from the servo voltage detection device 18.

That is, the servo voltage detection device 18 detects changes in the gap voltage, etc. during discharge based on the gap length fluctuation between the electrode 10 and the workpiece 12, and outputs a servo voltage to keep the gap voltage, etc. constant. The voltage is applied to the electrode position control mechanism, making it possible to perform electrical discharge machining while maintaining a constant gap.

Here, the servo voltage is converted and outputted so that the average voltage of the gap is 0V in the servo voltage, the no-load voltage is +6V, and the short circuit voltage is -6V.

Furthermore, in the machining tank 14, a machining fluid circulation device 2 is provided.
0 machining fluid is supplied by the machining fluid supply pump 22, and at this time, the machining fluid supply pump 22 and the machining tank 1
The pressure of the machining fluid is adjusted by the pressure value of the machining fluid pressure gauge 24 provided between the machining fluid pressure gauge 24 and the machining fluid pressure gauge 24 .

The conventional electrical discharge machining apparatus has the above-mentioned configuration, and maintains the gap constant by a servo voltage based on the gap voltage between the electrode 10 and the workpiece 12.
The electrode 10 is moved in the machining direction (downward in FIG. 1), and the workpiece 12 is caused by the electric discharge generated in the gap.
The cutting process was carried out.

As described above, when the workpiece 12 is punched using the conventional electrical discharge machining device, the electrode 10
Even after penetrating the electrode 2, the electrode 10 is still fed in the processing direction (downward in FIG. 1).
Therefore, the operator always has to touch the workpiece 1 of the electrode 10.
It was necessary to monitor the machining state of the electrode 10, control the moving speed of the electrode 10 using a dial gauge (not shown), etc., and manually stop the electrode 10 at the same time as the machining was completed, which was complicated. . In addition, if the amount of consumption (movement amount) of the electrode 10 is known in advance, a dial gauge and a limit switch (not shown) that are linked to the movement of the electrode 10 may be used.
In combination, the amount of movement of the electrode 10 is set in advance, and when the electrode 10 moves by the set amount of movement, processing is automatically completed.

[Problem to be solved by the invention]

As described above, in the conventional electric discharge machining apparatus, the operator constantly monitors the machining state of the electrode 10 on the workpiece 12, confirms when the electrode 10 has penetrated the workpiece 12, and finishes machining. Therefore, the work becomes complicated, and furthermore, the electrode 10
There will be variations in the feed amount. In particular, when drilling holes using a thin electrode 10, the electrode 1
The amount of feed after zero penetration causes the electrode 10 to wobble, making it difficult to ensure straightness, which has the disadvantage of having a large negative impact on the shape of the machined hole.

Furthermore, as mentioned above, if the amount of wear (the amount of movement) of the electrode 10 is known in advance, by combining a dial gauge and a limit switch (not shown) that are linked to the movement of the electrode 10, the completion of machining can be delayed to a certain extent. can be done automatically.
However, under the electrical conditions in general punching,
Since the electrode 10 is often consumed, it is difficult to determine the amount of consumption (movement amount) of the electrode 10 in advance.

As described above, in detecting the point in time when the electrode 10 penetrates the workpiece 12 and finishing the machining, the operator has to perform complicated work, which leads to a decrease in work efficiency and The current situation is hindering the promotion of automation of electrical discharge machining equipment.

The present invention has been made in view of the above-mentioned conventional problems, and its purpose is to ensure that the tip of the electrode 10 is connected to the workpiece 1.
It is an object of the present invention to provide an electrical discharge machining apparatus that can detect the point in time when the machining point 2 is penetrated and automatically terminate the machining.

[Means to solve the problem]

To achieve this objective, the present invention electrically detects changes in various machining conditions during electrical discharge machining in order to detect the point in time when the electrode penetrates the workpiece. This study focused on the fact that the servo voltage that controls the gap length between the electrode and the workpiece during machining and the electrode movement speed are the factors mentioned above.

The present invention provides a servo voltage detection device that outputs a servo voltage based on a gap voltage, and calculates an average value of the servo voltage per predetermined time as an actual average servo voltage value, and stores the actual average servo voltage value in advance. a servo voltage determination circuit that compares the actual average servo voltage value with a reference servo voltage value in each machining state and outputs an electrode penetration signal when the actual average servo voltage value matches the reference servo voltage value that indicates the state of penetration of the electrode into the workpiece; An electrode position detection device that detects the electrode position during processing, and a position detection signal from this detection device to detect the electrode speed from the change in electrode position per unit time, and move the electrode at high speed at a predetermined reference speed or higher. When it is determined that the electrode is in the state, the electrode movement speed determination circuit outputs the electrode high speed movement signal, and when the electrode penetration signal and electrode high speed movement signal of both the servo voltage determination circuit and the electrode movement speed determination circuit are input, the electrode movement speed determination circuit outputs the electrode high speed movement signal. The present invention is characterized by comprising a termination control circuit that outputs a termination signal.

〔Example〕

Hereinafter, preferred embodiments of the present invention will be described based on the drawings.

FIG. 2a shows an electric discharge machining apparatus according to the present invention, in which the same members as those in the conventional apparatus are given the same reference numerals and explanations thereof will be omitted.

In the example shown in the figure, the servo voltage is used as the first factor to detect the penetration state of the electrode, and for this purpose, the gap length is determined based on the gap voltage between the electrode and the workpiece during machining. A servo voltage detection device 18 outputs a servo voltage to be controlled, and calculates an actual average servo voltage value, which is an average servo voltage per predetermined time, from the output servo voltage, and uses the actual average servo voltage value to determine whether the electrode to be processed is A numerical control device 32 is provided which detects that the object has been penetrated and outputs a signal to the power supply unit 16 to end electrical discharge machining.

Then, as shown in FIG. 2b, the numerical control device 32 calculates the average value of the servo voltage output from the servo voltage detection device 18 per predetermined time and calculates it as an actual average servo voltage value. The converter 36 as a means, when the electrode approaches the workpiece before electric discharge machining, and during machining when electric discharge is generated between the electrode and the workpiece, the electrode and the workpiece are When a short circuit occurs due to abnormal contact with the workpiece,
and the servo voltages in four states when the electrode penetrates the workpiece are averaged and stored in advance as reference servo voltage values during free feeding, during machining, during short circuit, and during penetration, respectively. , the actual average servo voltage value output from the converter 36 and the air feeding stored in advance as described above;
Compares the standard servo voltage values in each machining state of machining, short circuit, and penetration, and outputs an electrode penetration signal when the actual average servo voltage value matches the reference servo voltage value in the state where the electrode penetrates the workpiece. A servo voltage determination circuit 38 is provided.

In this example, "H" indicating the electrode penetration state,
Two types of signals of "L" indicating the machining continuation state are output from the servo voltage determination circuit 38.

In general, machining conditions during electrical discharge machining can be roughly divided into:
It can be divided into four states: idle running, machining, short circuit, and penetration.

Next, the reference servo voltage value for each processing state,
Actual average servo voltage value and servo voltage judgment circuit 38
The relationship between the output signals will be explained with reference to FIG. 3a.

Examining the changes in servo voltage in each general machining state is as follows.

In the figure, the solid line shows the change in servo voltage during machining, the dashed line A represents the actual average servo voltage value obtained by averaging the servo voltage during idle running and penetration, and the dashed dotted line B represents the change in servo voltage during machining. It shows the actual average servo voltage value obtained by averaging the servo voltage at the time of short circuit.

As is clear from the figure, during idle running when the electrode 10 approaches the processing position of the workpiece 12 before machining, the electrode 10 and the workpiece 12
Since the electrode position control mechanism is far away from the
6V" is continuously output, and the average servo voltage is also "+
6V".

When the electrode 10 approaches the gap between the workpiece 12 and the workpiece 12 and discharge machining is performed, the servo voltage changes between +3V and -3V to maintain a predetermined gap length by minute vertical movements of the electrode. However, the average servo voltage is in the range of +3V to -3V. In addition, in the event of a short circuit in which the electrode 10 comes into abnormal contact with the workpiece 12, the servo voltage is changed from "+3V to -3V" to "-" by a short circuit avoidance control circuit (not shown).
6V'', the electrode 10 moves upward at high speed and performs an avoidance operation. Then, the electrode 10 and the workpiece 1
When the short-circuit condition is eliminated by separating the electrodes 10 and 2, the servo voltage changes from "-6V" to "+6V" and the electrode 10 moves downward again, returning to the normal machining state. Therefore, the average servo voltage during short circuit is "0V"
It will be nearby. Furthermore, just before the end of machining, the electrode 10 penetrates the workpiece 12 and moves further downward. That is, in the electrode penetration state, it becomes difficult for electric discharge to occur between the electrode 10 and the workpiece 12, and therefore,
The situation is as if the electrode 10 is far away from the workpiece. Therefore, the servo voltage changes from "+3V to -3V" to "+6V" and the no-load voltage "+6V" continues, so similarly,
The average servo voltage will be "+6V".

As mentioned above, the average servo voltage differs depending on each processing state, so if "+6V" is stored as the reference servo voltage value and the average servo voltage at the time of penetration is used as a judgment criterion, the penetration state of the electrode 10 can be automatically detected. can.

Therefore, the servo voltage during processing is output from the servo voltage detection device 18, the converter 36 calculates the average servo voltage per predetermined time, the actual average servo voltage value is obtained, and the servo voltage judgment circuit 38 calculates the average servo voltage value. Comparison is made with the reference servo voltage value "+6V" indicating the electrode penetration state stored in advance, and the electrode penetration signal is set to "H".
Alternatively, "L" can be output to the AND circuit 40 as an end control circuit to control the end of electrical discharge machining.

That is, the output of the servo voltage judgment circuit 38 is
As shown in Fig. 3b, the level is "H" when the electrode 10 is in the free running state and the penetrating state, and it is "L" when the electrode 10 is in the machining or short-circuit state, and the transition from the machining state to the penetrating state (L→H) is detected. It is possible to do so.

Furthermore, in the present invention, although the servo voltage value can be detected as described above, the servo voltage value is relatively unstable, and in particular, the voltage changes rapidly during machining, so errors are likely to occur in the output signal. , erroneous detection may occur if only the servo voltage value is used. Therefore, in the present invention, the distinction between processing and penetration is as follows:
It is characterized in that it is performed by a factor separate from the servo voltage.

The second factor for electrode penetration detection in the present invention is the electrode movement speed, and in order to electrically detect the electrode movement speed, an electrode position detection device 30 and an electrode movement speed are used as shown in FIG. 2b. A speed determination circuit 35 is provided.

The electrode movement speed and the corresponding output signal in each machining state (idle running, machining, short circuit, penetration) are shown in FIG. 3b.

In addition, in the examples, the electrode movement speed (high speed,
Depending on the speed (low speed), the output signal is “H” or “L”.
Indicated by the type of signal.

In embodiments, electrode position is used to detect electrode movement speed. Electrode position detection device 3
0 detects the position of the electrode 10, and this detected position signal of the electrode 10 is sent to the electrode moving speed determination circuit 3.
3. Then, the electrode movement speed determination circuit 33 processes the change in the position signal of the electrode 10 per unit time, determines the electrode movement speed, and outputs an "H" signal if the electrode 10 is moving at a high speed. If the speed is low, an "L" signal is output. Below, output signals corresponding to the electrode movement speed in each processing state are shown.

During idle running, the gap between the electrode 10 and the workpiece 12 is wide, so the electrode 10 moves downward at high speed. During this idle running, the output signal is "H"
maintain.

During machining, the electrode 10 moves downward at low speed while performing electrical discharge machining. During this processing, the output signal remains "L".

Further, in the event of a short circuit, the electrode 10 comes into contact with the workpiece 12, retreats upward at high speed to avoid contact, and then moves downward again at high speed. During this short circuit, the output signal remains at "H".

Furthermore, during penetration, the electrode 10 penetrates the workpiece 12 at a high speed and moves downward at an even higher speed. During this penetration, the output signal maintains "H".

The electrode moving speed and the corresponding output signal in each machining state (idle running, machining, short circuit, penetration) are as described above.During machining, the output signal becomes "L" due to the low speed, and On the other hand, when penetrating, the output signal becomes "H" as in the case of idle running and short circuit, so it is possible to easily distinguish between machining and penetrating from the second factor, "electrode moving speed."

The output signal from the servo voltage determination circuit 38 and the output signal from the electrode movement speed determination circuit 35 are supplied to an AND circuit 40 as an end control circuit.
The AND circuit 40 supplies a stop signal to the power supply unit 16 only when both of the supplied output signals are "H" to turn off the power and finish the machining.

Hereinafter, the operation of the AND circuit 40 in each machining state (idle running, machining, short circuit, through) will be explained.

The operation of the AND circuit 40 during idle running will be explained.

During idle running, the output signal from the servo voltage determination circuit 38 is "H", and the electrode moving speed range circuit 3
Although the output signal from 5 is "H", it is set in advance so that the AND circuit 40 does not supply a stop signal to the power supply unit 16 during idle running.

During processing, the output signal from the servo voltage determination circuit 38 and the output signal from the electrode movement speed determination circuit 35 are "L", so the AND circuit 40 does not supply a stop signal.

Furthermore, in the event of a short circuit, the output signal from the servo voltage determination circuit 38 is "L" and the output signal from the electrode movement speed determination circuit 35 is "H", so the AND circuit 40 does not supply a stop signal.

Furthermore, at the time of penetration, the output signal from the servo voltage determination circuit 38 is "H" and the output signal from the power supply moving speed range circuit 35 is "H", so the AND circuit 40 supplies a stop signal to the power supply unit 16. Then turn off the power and finish machining.

As described above, according to the electric discharge machining apparatus according to the present invention, it is possible to detect the point in time when the tip of the electrode 10 penetrates the workpiece 12 and automatically terminate the machining.

In the embodiment shown in FIGS. 2a and 2b, the converter 36 and the servo voltage judgment circuit 38 are provided in the electrode movement speed judgment circuit 35, the AND circuit 40, and the numerical control device 32, but the numerical control It is also possible to implement it separately and independently without providing it in the device 32.

Further, when the point of penetration is detected, the influence of wear of the electrode 10 can be eliminated by moving the electrode 10 by a certain amount in the direction of the deepest machining (downward in FIG. 2) and then finishing the machining. That is,
In electrical discharge machining, as machining progresses, the electrode 1
If only the tip of the electrode 10 is worn out and becomes thinner, and the tip of the electrode 10 passes through the workpiece 12, if the machining is immediately terminated, the through hole in the workpiece 12 will become smaller. Therefore, in this embodiment, an accurate through hole can be obtained by moving the electrode 10 through the part where the predetermined mold dimensions are maintained.

Furthermore, in FIG. 3b, when the electrode 10 is running idle before the discharge phenomenon occurs, the actual average servo voltage value becomes a signal "H" similar to that at the time of penetration. In order to prevent the supply of servo voltage to
By forming the system so that it is activated after detecting either the average machining current is 1A or more and the average machining voltage is 60V or less (i.e., with the occurrence of an electric discharge phenomenon), the electric discharge machining end signal is activated during idle running. There is no problem even if it becomes "H".

Further, the electric discharge machining apparatus according to the present invention can be used for cutting by electric discharge machining and for machining wire holes in a wire cut electric discharge machining apparatus.

〔Effect of the invention〕

As described above, according to the electric discharge machining apparatus according to the present invention, a servo voltage is output based on the gap voltage during machining, the average servo voltage per predetermined time is calculated, the actual average servo voltage value is determined, and the electrode is moved. By detecting the speed, the point at which the tip of the electrode penetrates the workpiece is detected and machining is automatically terminated. Although it is necessary to add a clock device to process changes in the electrode position signal per unit time to detect the electrode movement speed, it is possible to determine the state of the electrode movement speed with a configuration that does not have a memory device. Further, it is possible to always obtain an optimal and stable electrical discharge machining state, and to improve the shape accuracy of the machined hole. Furthermore, the operator does not have to do the complicated work of monitoring the machining status of the electrode on the workpiece and checking when the electrode has penetrated the workpiece, improving work efficiency and reducing discharge. Labor saving and automation of processing equipment will be promoted.

[Brief explanation of drawings]

Figure 1 is an explanatory diagram of a conventional electric discharge machining device,
Fig. a is an explanatory diagram of the electrical discharge machining apparatus according to the present invention;
Figure b is a circuit configuration diagram of a circuit for detecting electrode penetration according to the present invention, Figure 3a is a graph diagram showing the servo voltage during processing and the actual average servo voltage value, and Figure 3b is
It is an explanatory view showing an output signal of a detection factor in each processing state. The same members in each figure are given the same symbols, 10 is an electrode, 12 is a workpiece, 14 is a machining tank, 16 is a power supply unit, 18 is a servo voltage detection device, 20 is a machining fluid circulation device, and 22 is a machining device. A liquid supply pump, 24 a processing liquid pressure gauge, 30 an electrode position detection device, 32 a numerical control device, 35 an electrode movement speed determination circuit, 3
6 is a converter, 38 is a servo voltage determination circuit, and 40 is an AND circuit.

Claims (1)

[Claims] 1. A workpiece and an electrode are faced to each other through a gap,
In an electrical discharge machining device that processes a workpiece by producing an electrical discharge phenomenon in the gap, detecting the gap voltage between the electrode and the workpiece during machining and controlling the gap length based on the gap voltage. a servo voltage detection device that outputs a servo voltage applied to drive the electrode position control mechanism; and an average value of the servo voltage output from the servo voltage detection device per predetermined time is calculated as an actual average servo voltage value. a calculating means; averaging the servo voltages when the electrode penetrates the workpiece; storing the result in advance as a reference servo voltage value indicating the state of the electrode penetrating the workpiece; The actual average servo voltage value output from the calculation means is compared with the reference servo voltage value stored above, and if the actual average servo voltage value matches the standard servo voltage value indicating the state of the electrode penetrating the workpiece, the electrode A servo voltage judgment circuit that outputs a penetration signal, an electrode position detection device that detects the electrode position during processing, and an electrode position detection circuit that receives the electrode position detection signal detected by the electrode position detection device and determines the electrode position per unit time. an electrode movement speed determination circuit that detects the electrode speed from a change and outputs an electrode high-speed movement signal when it is determined that the electrode is moving at a high speed equal to or higher than a predetermined reference speed; and the servo voltage determination circuit and the electrode movement speed determination circuit. An electrical discharge machining apparatus comprising: a termination control circuit that outputs an electric discharge machining termination signal upon input of both an electrode penetration signal and an electrode high-speed movement signal.