JPH05309526A - Wire electric discharge machine - Google Patents

Abstract

PURPOSE:To control a wire electric discharge machine so as to prevent wire breakage of a wire electrode by setting a discharge rate, a ratio of discharge periodic signal to a discharge detection signal, as a standard. CONSTITUTION:Accumulated in a prescribed time of respective signals of a discharge detection signal which is outputted from a discharge detection circuit 38 for detecting discharge based on build-up of current caused by generation of discharge and a discharge periodic signal which is outputted by a discharge periodic output device 28 at every periods inputted beforehand, is computed by a computing counter and the rate of both accumulated is computed by CPU30 so that processing conditions are controlled based on the computing results.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wire electric discharge machining for machining a work piece by applying a predetermined voltage between the wire electrode and the work piece and moving the wire electrode and the work piece relative to each other. Regarding the machine.

[0002]

2. Description of the Related Art In a conventional wire electric discharge machine, as shown in FIG. 9, a work 10 and a wire electrode 12 for processing the work 10 are relatively moved by feed motors 14 and 16. The wire electrode 12 is stretched almost vertically by wire guides 18 and 20, and faces the work 10 with a machining gap.

The wire electrode 12 is connected to the power supply 26,
It is connected to the negative electrode of the machining power source 22 via a measuring device 72 described later and a switching element 24 (transistor), and the work 10 and the anode of the machining power source 22 are both grounded. The switching element 24 is a discharge cycle signal output device 2 that outputs a discharge cycle signal indicating permission of discharge.
8 is connected to the CPU 30 which controls the entire processing. When this discharge cycle signal is input to the switching element 24, the switching element 24 is turned on and discharge is permitted. Then, the work 10 and the wire electrode 12
A predetermined voltage is applied by the machining power supply 22 to the machining gap between and, and a discharge phenomenon occurs.

The measuring device 72 measures the discharge information and outputs the measured value data to the CPU 30 via the AD converter 74. Also, this C
Feed motors 14 and 16 are connected to the PU 30 via a motor drive circuit 32, and the CPU 30 stores a keyboard 34 for inputting processing conditions and the like, and input processing conditions and the like. The memory 36 is connected.

The control during machining of the wire electric discharge machine will be described below.

First, the operator inputs machining conditions such as table feed speed, machining energy, and cycle of the discharge cycle signal from the keyboard 34, and the machining conditions are stored in the memory 36. The CPU 30 causes the discharge cycle signal output device 28 to output a discharge cycle signal to the switching element 24 based on the input processing conditions, and turns on the switching element 24 to control the discharge permission. The discharge cycle signal input by the operator is, for example, a cycle of the discharge cycle signal when the plate thickness to be processed is large, and a cycle of the discharge cycle signal when the plate thickness is thin, depending on the processing efficiency and processing conditions. To increase. Alternatively, if the diameter of the wire electrode 12 used for machining is large, the cycle of the discharge cycle signal becomes small, and the wire electrode 12
If the diameter is small, the cycle of the discharge cycle signal is input large.

The CPU 30 also includes a motor drive circuit 32.
Feed motor 1 based on the processing conditions input via
4, 16 are controlled to relatively move the work 10 and the wire electrode 12. Thus, the work 10 and the wire electrode 12
A predetermined voltage is applied to the machining gap between and to generate a discharge phenomenon, and the measuring instrument 72 measures information about at least one discharge phenomenon such as current, voltage, and impedance between the work 10 and the wire electrode 12, Then, the measured value of the discharge phenomenon, which is analog data, is output to the CPU 30 via the AD converter 74 that converts the measured value into a digital signal. The CPU 30 determines the discharge state based on this discharge data. As a result, the relative movement between the work 10 and the wire electrode 12 is feedback-controlled according to a predetermined control.

First, the CPU 30 compares the above discharge data with a preset threshold value to determine the discharge state. This threshold value is a constant previously obtained by an experiment or the like as a standard that the discharge state changes and the discharge concentrates when the machining is continued as it is and the wire electrode 12 is broken. If the previous discharge data is greater than the threshold value, the CPU
30 determines that there is a risk that the wire electrode 12 may be broken or the processing accuracy may be reduced, and the motor drive circuit 32 may be used to drive the wire electrode 12 as shown in FIG.
As in 0, uniform control such as stopping the moving speed of the work 10 is performed.

In this way, a wire electric discharge machine is generally known which controls to prevent the wire electrode 12 from being broken and the machining accuracy from being lowered.

[0010]

However, if the machining conditions to be input, for example, the period of the discharge period signal or the relative moving speed of the wire electrode and the workpiece are changed, the allowable discharge state also changes, and the predetermined discharge condition is fixed. The threshold value set to the value is not a valid value for preventing the wire electrode from breaking, and if the set threshold value is set small, the measured discharge data will be It tends to be larger. Therefore, although there is a margin between the measured discharge state and the discharge state in which the wire electrode may be broken or the machining accuracy may be reduced, the moving speed of the workpiece is reduced and the machining time is reduced. There was a problem that it became longer.

On the contrary, when the preset threshold value is set to be large, it is difficult for the measured discharge data to be larger than the threshold value. Therefore, there is a problem that the machining is continued and finally the wire electrode is broken although the discharge state may cause the wire electrode to be broken.

The present invention has been made to solve the above-mentioned problems, and shortens the machining time by controlling the machining conditions according to the ratio of the discharge detection signal and the discharge cycle signal. An object of the present invention is to provide a wire electric discharge machine that prevents the wire electrode from breaking.

[0013]

To achieve this object, in a wire electric discharge machine of the present invention, as shown in FIG. 1, an electric discharge is generated in a machining gap formed between a wire electrode and a workpiece. Discharge cycle signal output means for outputting a discharge cycle signal for generating, discharge detection means for detecting the occurrence of discharge in the machining gap, and outputting a discharge detection signal,
While calculating the ratio of the discharge cycle signal and the discharge detection signal,
It is provided with an arithmetic means for outputting the data of the arithmetic result and a machining condition control means for controlling the machining condition when machining the workpiece based on the arithmetic result of the arithmetic means.

In order to achieve this object, claim 2 of the present invention
The wire electric discharge machine includes a machining condition control unit that controls machining conditions related to relative movement of the wire electrode and the workpiece.

In order to achieve this object, claim 3 of the present invention
The wire electric discharge machine includes a machining condition control unit that controls machining conditions related to the electric discharge cycle signal.

[0016]

In the wire electric discharge machine of the present invention having the above-described structure, the electric discharge cycle signal output means outputs the electric discharge cycle signal to generate an electric discharge in the machining gap formed between the wire electrode and the workpiece. The generation of discharge is permitted, and the discharge detection means detects the generation of discharge in the machining gap based on the discharge cycle signal and outputs a discharge detection signal. The calculation means calculates the ratio between the output discharge cycle signal and the discharge detection signal and outputs the data of the calculation result. The processing condition control means controls the processing conditions for processing the workpiece based on the calculation result of the calculation means.

In the wire electric discharge machine according to the second aspect of the present invention having the above structure, the machining condition control means controls the machining conditions relating to the relative movement of the wire electrode and the workpiece.

In the wire electric discharge machine according to the third aspect of the present invention having the above structure, the machining condition control means controls the machining conditions related to the electric discharge cycle signal.

[0019]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 2 is a schematic configuration diagram of a wire electric discharge machine embodying the present invention. The same components as those of the conventional example are designated by the same reference numerals, and the description thereof will be omitted.

In the wire electric discharge machine according to the present embodiment, as shown in FIG. 2, the electric discharge 26 between the work 10 and the machining power supply 22 detects the occurrence of electric discharge, and outputs a discharge detection signal. Detection circuit 38 and switching element 24
Are provided in that order. Further, the discharge detection circuit 38 includes an arithmetic counter 40 connected to the CPU 30.
Is connected so that a discharge detection signal can be output. A discharge cycle signal output device 28 connected to the CPU 30 is connected to the arithmetic counter 40 and the switching element 24 so that the discharge cycle signal is input in synchronization. The calculation counter 40 receives the discharge cycle signal from the discharge cycle signal output device 28 and the discharge detection signal from the discharge detection circuit 38, accumulates the respective numbers, and resets at a predetermined cycle by the reset signal from the CPU 30. To be done.

As shown in FIG. 3, the discharge detection circuit 38 is composed of an optical isolator Q, etc.
Electrical information of the electric current of the electric discharge for machining the workpiece 10 between the wire electrode 12 and the wire electrode 12 is converted into optical information. Then, this optical information is converted into electrical information again, and the occurrence of discharge is detected by this information. For example, as shown in FIG. 4, when the discharge cycle signal for permitting the discharge is output from the discharge cycle output device 28 at a constant interval input in advance, and the machining gap between the work 10 and the wire 12 is within a dischargeable distance. Discharge is permitted by the outputted discharge cycle signal, and a predetermined voltage is applied to this machining gap to cause a current to flow. At the rise of the current flowing at that time, the occurrence of discharge is detected by the discharge detection circuit 38 and a discharge detection signal is output. On the other hand, if the machining gap is not a distance that allows discharge,
Even if the discharge cycle signal is output and the discharge is permitted, the discharge does not occur. Then, the next discharge cycle signal is output after a fixed cycle, and the discharge is permitted. At that time, if the machining gap has a dischargeable distance, at that time, the discharge is generated, the occurrence of the discharge is detected, and the discharge is generated. The detection signal is output.

Next, the control operation will be described with reference to the flowchart of FIG.

First, when the processing conditions and the like are input from the keyboard, the processing is started. As step 1 (below,
The step is abbreviated as S. ), The CPU 30 sets n times (n is a constant) the discharge cycle set by the operator as a sampling time in the timer in order to measure the discharge state between the work 10 and the wire electrode 12. For example, if the discharge cycle is 10 μsec and the constant n is “100”, the sampling time is 1 msec. In next step S2, the arithmetic counter 40 is reset by the CPU 30, whereby the arithmetic counter 40 starts accumulating the number of times of input of the discharge detection signal and the discharge cycle signal. Next, in S3, the CPU 30 determines whether or not the previously set sampling time (= 1 msec) has elapsed, and when it has elapsed, in S4, the arithmetic counter 4
Both the counter values of the discharge detection signal and the discharge cycle signal accumulated at 0 are latched and read, and the ratio of the two counter values is calculated. At this time, the ratio calculated by the CPU 30 indicates the degree of concentration of discharge within a predetermined time,
The ratio is the discharge rate. Then, in S5, the CPU
30 controls various processing conditions based on this discharge rate.

For example, if the counter value of the discharge cycle signal within the sampling time is "100" and the counter value of the discharge detection signal is "70", the discharge rate is 70 in terms of percentage.
%. In this case, in S5, the CPU 30
Controls the moving speed of the work 10 via the motor drive circuit 32 according to the output signal. That is, as shown in FIG. 6, the vertical axis represents the moving speed of the work 10, and
The discharge rate is 70 according to the graph showing the discharge rate on the horizontal axis.
%, The moving speed of the work 10 is the reference command speed F
It is controlled to be "0.6F" which is 0.6 times the value of. Then, in S6, the CPU 30 determines whether or not the processing is completed, and if it is not completed, the above S2 to S5 are repeated, and if the determination in S6 is "YES", the operation is completed.

In this way, while recognizing the concentration of the discharge using the discharge rate as a guide and adjusting the moving speed of the work 10 according to the degree of the concentration, the concentration of the discharge is efficiently controlled, so that the optimum machining is performed. The speed can be maintained, the processing time can be shortened, and the discharge can be stably generated to prevent the wire electrode 12 from breaking.

In this embodiment, the discharge cycle signal output device 28 etc. are the discharge cycle signal output means of the present invention, the discharge detection circuit 38 etc. are the discharge detection means of the present invention, and the CPU 30 and the operation counter 40 etc. are the present invention. Computation means, CPU3
0 and the like constitute the processing condition control means of the present invention.

Next, a second embodiment will be described with reference to FIG. The same components as those in the first embodiment and the conventional example are designated by the same reference numerals and the description thereof will be omitted.

As shown in FIG. 7, the switching element 24 connected to the machining power supply 22 controls the output cycle of the discharge cycle signal output device 28 which outputs the discharge cycle signal and the discharge cycle signal. Discharge cycle signal control circuit 42
Is connected to the CPU 30 that controls the entire control. The discharge cycle signal control circuit 42 is controllably connected by the CPU 30 based on the discharge rate.

In the wire electric discharge machine of this embodiment, the electric discharge cycle signal control circuit 42 is the CPU 30.
The output cycle of the discharge cycle signal for permitting the discharge is controlled on the basis of the output signal of the discharge rate calculated in (3) to control the generation of the discharge between the work 10 and the wire electrode 12.

For example, as shown in FIG. 8, when the discharge rate is 70% along the graph showing the cycle of the discharge cycle signal on the vertical axis and the discharge rate on the horizontal axis, the discharge cycle signal The discharge cycle signal control circuit 42 controls the cycle of the discharge cycle signal based on the discharge rate so that the cycle becomes "1.4T" which is 1.4 times the command cycle T from the CPU 30.

Thus, while recognizing the concentration of discharge using the discharge rate as a guide, and adjusting the period of the discharge period signal according to the degree of concentration, the concentration of discharge is efficiently controlled, so that optimum machining is performed. The processing time can be shortened while maintaining the speed, and the occurrence of electric discharge can be stabilized to prevent disconnection of the wire electrode 12.

In this embodiment, the discharge cycle signal output device 2
8 and the like are the discharge cycle signal output means of the present invention, the discharge detection circuit 38 and the like are the discharge detection means of the present invention, and the CPU 30 and the arithmetic counter 40 are the arithmetic means of the present invention.
The discharge cycle signal control circuit 42 and the like constitute the processing condition control means of the present invention. In the present embodiment, the discharge cycle signal control circuit 42 is a circuit that delays the discharge cycle signal. However, it is not limited to this, one that does not output the signal itself by thinning out the number of discharge signals, or conversely reduces machining accuracy. Alternatively, a discharge cycle signal may be further output in order to increase the number of discharges and improve the machining efficiency within a range in which the wire electrode 12 is not broken.

In the first and second embodiments, the controlled object is linearly changed in the section where the discharge rate is 50% to 100%, but the section or the changing method is not limited to this. Further, although the motor drive circuit 32 is controlled by using the output signal from the arithmetic counter 40, by controlling the processing conditions such as processing energy, on-time, off-time, wire feed speed, and wire tension, Effective control is possible.

[0035]

As is apparent from the above description, the wire electric discharge machine of the present invention sets the machining condition to an arbitrary curve based on the ratio of the number of electric discharges generated in the machining gap to the number of electric discharge cycle signals. Since it is controlled in a uniform manner, the processing time can be shortened, and the concentration of electric discharge can be suppressed to prevent the wire electrode from breaking.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a wire electric discharge machine of the present invention.

FIG. 2 is a block diagram showing a first embodiment of the wire electric discharge machine of the present invention.

FIG. 3 is a schematic diagram of a circuit for detecting discharge according to an embodiment.

FIG. 4 is a diagram illustrating generation of a signal related to discharge detection according to an embodiment.

FIG. 5 is a flowchart showing the processing of the embodiment.

FIG. 6 is a graph showing the relationship between the discharge rate and the moving speed of the workpiece in the example.

FIG. 7 is a block diagram showing a second embodiment of the wire electric discharge machine of the present invention.

FIG. 8 is a graph showing the relationship between the discharge rate and the voltage application period in the example.

FIG. 9 is a block diagram showing a conventional wire electric discharge machine.

FIG. 10 is a graph showing the relationship between the threshold value of the measured value and the moving speed of the workpiece according to the related art.

[Explanation of symbols]

 10 Work 12 Wire Electrode 28 Discharge Cycle Signal Output Device 30 CPU 38 Discharge Detection Circuit 40 Operation Counter 42 Discharge Cycle Signal Control Circuit

Claims (3)

[Claims] 1. A wire electric discharge machine for machining a workpiece by applying a predetermined voltage between the wire electrode and the workpiece and moving the wire electrode and the workpiece relative to each other. A discharge cycle signal output means for outputting a discharge cycle signal for generating a discharge in a machining gap formed between the wire electrode and the workpiece, and detecting occurrence of a discharge in the machining gap, A discharge detection unit that outputs a discharge detection signal, and a calculation unit that calculates the ratio of the discharge cycle signal and the discharge detection signal, and outputs the data of the calculation result, based on the calculation result of the calculation unit, A wire electric discharge machine comprising: a machining condition control means for controlling machining conditions when machining a workpiece. 2. The processing condition for processing a workpiece controlled by the processing condition control means is a processing condition relating to relative movement of the wire electrode and the workpiece. Wire electric discharge machine described. 3. The wire electric discharge machine according to claim 1, wherein the processing condition for processing the workpiece controlled by the processing condition control means is a processing condition relating to the electric discharge cycle signal. ..