JP2564389B2 - Electric discharge machining method and device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an electric discharge machining method and an electric discharge machining apparatus for detecting an electric discharge state and controlling a pause time width and a peak current value of a machining pulse.

[Conventional technology]

In electric discharge machining, a machining pulse is applied to the machining electrode and the workpiece to cause electric discharge, and after a pause time (pause time width) of a predetermined width, the next machining pulse is applied to cause further electric discharge. As described above, machining is performed by causing electric discharge one after another. In electric discharge machining in which the shape electrode is opposed to the workpiece to transfer the electrode shape, the machining progresses only in a relatively small area at the tip of the electrode at the beginning of machining, so the average machining current may be small. Since the machining area expands as the machining progresses, it is necessary to increase the average machining current accordingly. Normally, the application time of the machining pulse is almost constant, and the average machining current is controlled by increasing or decreasing the pause time width and the peak current value.

When a large average machining current is applied from the beginning, the machining surface becomes rough, and when machining is performed with a relatively small average machining current to the end, the machining surface is good but inefficient.
However, controlling the average machining current by programming it in advance is not practical because it is difficult to calculate. Therefore, it is the current situation that the operator monitors the progress of machining and adjusts the machining current as appropriate, which is an obstacle to automation. It was. In order to solve this problem, Japanese Patent Publication Nos. 57-36096 and 57-36097
Japanese Patent Laid-Open Publication No. 2001-242242 discloses an electric discharge machining in which the pause time width of a machining pulse is increased when an abnormal state is detected by detecting an electric discharge state every moment and the pause time width of a machining pulse is shortened when a normal state is detected. A method is disclosed.

[Problems to be Solved by the Invention]

In the method described in the above publication, the pause time width of the machining pulse is increased or decreased stepwise in response to the detection of abnormality or normality of the discharge state. Therefore, the pause time width of the machining pulse constantly changes in a sawtooth shape. The problem with this method is that
There is no lower limit of the pause time width of the machining pulse (in other words, the control target value is 0 in order to increase the machining efficiency), the normal state is detected, and the pause time width of the machining pulse is shortened in steps. When going, this processing is always continued until an abnormal condition is detected. Therefore, the pause time width of the machining pulse changes in a sawtooth shape and vibrates near the point where the abnormal state is detected, and the actual machining is performed under the condition that the abnormal state is frequently generated. An object of the present invention is to provide an electric discharge machining method and an electric discharge machining apparatus in which a control system is stable and abnormal machining is unlikely to occur.

[Means for solving the problem]

In order to achieve the above-mentioned object, the principle of the present invention is to set the concept of a reference pause time width, increase the pause time width of a machining pulse when an abnormal state is detected, and then detect a normal state. The control is performed to shorten the pause time width of the machining pulse, the number of times of control is counted, and the reference pause time width itself is appropriately changed according to the result.

An electric discharge machining method according to a first aspect of the present invention applies a machining pulse to a machining electrode and a workpiece, increases the pause time width of the machining pulse when an abnormal state is detected by detecting an electric discharge state every moment, In an electric discharge machining method for performing control for shortening the pause time width of the machining pulse when a normal state is detected, a reference pause time width is preset, and the pause time width of the machining pulse is set when an abnormal state is detected. When the normal state is detected, the control is performed to shorten the pause time width of the machining pulse to the reference pause time width, and the pause time width of the machining pulse is shorter than the reference pause time width. The number of times of control for increasing or shortening to the reference pause time width is counted per unit time, and if the counted number of controls is below a predetermined allowable range, the reference of the machining pulse Shortening the stop time width, if exceeds characterized by increasing the reference pause time width of the machining pulses.

In the electric discharge machining method according to the second aspect of the present invention, a machining pulse is applied to the machining electrode and the workpiece, and when the abnormal state is detected by detecting the discharge state every moment, the pause time width of the machining pulse is increased, In an electric discharge machining method for performing control for shortening the pause time width of the machining pulse when a normal state is detected, a reference pause time width is preset, and the pause time width of the machining pulse is set when an abnormal state is detected. When the normal state is detected, the control is performed to shorten the pause time width of the machining pulse to the reference pause time width, and the pause time width of the machining pulse is shorter than the reference pause time width. The number of times of control for increasing or shortening to the reference pause time width is counted per unit time, and when the counted number of controls is below a predetermined allowable range, the peak of the machining pulse is counted. Increasing the current value, if exceeds, characterized in that to reduce the peak current value of the machining pulse.

In the electric discharge machining method according to the third aspect of the present invention, a machining pulse is applied to the machining electrode and the workpiece, and when the abnormal state is detected by detecting the discharge state every moment, the pause time width of the machining pulse is increased, In an electric discharge machining method for performing control for shortening the pause time width of the machining pulse when a normal state is detected, a reference pause time width is preset, and the pause time width of the machining pulse is set when an abnormal state is detected. When the normal state is detected, the control is performed to shorten the pause time width of the machining pulse to the reference pause time width, and the pause time width of the machining pulse is shorter than the reference pause time width. The number of times of control for increasing or shortening to the reference pause time width is counted per unit time, and if the counted number of controls is below a predetermined allowable range, the reference of the machining pulse The stop time width is shortened, and when it exceeds, the reference pause time width of the machining pulse is increased, and when the reference pause time width of the machining pulse is below a predetermined lower limit value, the peak current of the machining pulse. The value is increased, and when it exceeds a predetermined upper limit value, the peak current value of the machining pulse is controlled to be decreased.

According to a fourth aspect of the present invention, there is provided an electric discharge machining apparatus for applying a machining pulse to a machining electrode and a work piece, a detecting means for detecting an electric discharge state at every moment, and the machining when the detecting means detects an abnormal state. A pause time width control means for increasing the pause time width of a pulse from a preset reference pause time width and shortening the pause time width of the machining pulse to the reference pause time width when a normal state is detected, and the pause time. A control number counting means for counting the number of control times for increasing or shortening the pause time width of the machining pulse from the reference pause time width by the width control means, and counting by the control count counter means per unit time The control count counted by the control count counting means is compared with the predetermined control count and a permissible range of the control count for increasing or shortening the pause time width per unit time. If below the range, the shorter the reference pause time width, if exceeds, characterized by comprising a reference pause time width setting means for increasing the reference pause time width.

According to a fifth aspect of the present invention, there is provided an electric discharge machining apparatus for applying a machining pulse to a machining electrode and a work piece, a detecting means for detecting an electric discharge state at every moment, and the machining when the detecting means detects an abnormal state. A pause time width control means for increasing the pause time width of a pulse from a preset reference pause time width and shortening the pause time width of the machining pulse to the reference pause time width when a normal state is detected, and the pause time. A control number counting means for counting the number of control times for increasing or shortening the pause time width of the machining pulse from the reference pause time width by the width control means, and counting by the control count counter means per unit time The control count counted by the control count counting means is compared with the predetermined control count and a permissible range of the control count for increasing or shortening the pause time width per unit time. If below the range increases the peak current value of the machining pulses, if exceeds, characterized by comprising a peak current control means for reducing the peak current value of the machining pulse.

According to a sixth aspect of the present invention, there is provided an electric discharge machining apparatus for applying a machining pulse to a machining electrode and a work piece, a detection means for detecting a discharge state at every moment, and the machining when the abnormal state is detected by the detection means. A pause time width control means for increasing the pause time width of a pulse from a preset reference pause time width and shortening the pause time width of the machining pulse to the reference pause time width when a normal state is detected, and the pause time. A control number counting means for counting the number of control times for increasing or shortening the pause time width of the machining pulse from the reference pause time width by the width control means, and counting by the control count counter means per unit time The control count counted by the control count counting means is compared with the predetermined control count and a permissible range of the control count for increasing or shortening the pause time width per unit time. If it is below the range, the reference pause time width is shortened, and if it is above the range, the reference pause time width setting means for increasing the reference pause time width and the reference pause time width setting means are shortened or increased. A peak current control means for increasing the peak current value of the machining pulse when the standard pause time width is below a predetermined lower limit value and decreasing the peak current value of the machining pulse when it is above a predetermined upper limit value. And is provided.

[Action]

By shortening or increasing the reference pause time width in accordance with the number of times of control counted from the pause time width control means, the reference pause time width can be corrected to an optimum value according to the progress status of machining, and thus the machining efficiency can be improved. Can be raised.

The machining efficiency can also be increased by controlling the peak value of the machining pulse current in the same manner.

〔Example〕

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

FIG. 1 is a diagram showing a first embodiment of the present invention. The electric discharge machine is a frame (not shown) that supports the workpiece 10.
And a head 14 for supporting the tool electrode 12. head
A tool electrode 12 is arranged so as to face the workpiece 10 with a minute gap, and includes a servo drive mechanism for feeding. The tool electrode 12 is connected to the negative electrode of the machining power source 16, and the workpiece 10 is connected to the positive electrode of the machining power source 16.
A switching transistor 18 and a variable resistor 20 that limits the peak current are arranged between the machining power supply 16 and the workpiece 10. By controlling the switching transistor 18, a machining pulse having a peak current I _P can be generated in the machining power source 16 and the workpiece 10 as shown in FIG. 3, for example. There is a pause T _OFF between the machining pulse and the next machining pulse. The current application width of the machining pulse is almost constant value required to generate the optimum discharge.
The pause time width T _OFF can be changed as a control parameter. Therefore, the discharge state detecting means 22 is provided. In the embodiment, the discharge state detecting means 22 detects the voltage between the machining power source 16 and the workpiece 10,
The abnormal discharge state is detected from the fluctuation of the voltage between contacts. further,
There is a working fluid supply device (not shown) and the like.

Switching transistor 18 is a central processing unit (CPU)
And a computer having a memory. The means described below are mainly included in the computer. The quiescent time width control means 24 generates a command for controlling the quiescent time width T _OFF according to the setting conditions, the detection signal of the discharge state detection means 22, etc., and the pulse generation means 26 intermittently switches to the switching transistor 18 in response to this command. Send a signal to In the present invention, the reference pause time width setting means 28 sets the reference pause time width T _REF . The pause time width control means 24 also receives the output signal of the reference pause time width setting means 28. Further, the control number counting means 30 counts the increase / decrease control number of the pause time width by the pause time width control means 24 per unit time,
A signal is sent to the reference dwell time width setting means 28 to calculate the reference dwell time width T _REF . The processing condition setting means 32 is provided for setting processing conditions such as the processing pulse width, the initial value of the reference pause time width T _REF , the initial value of the peak current, etc., and is connected to the reference pause time width setting means 28. The processing condition setting means 32 can also be connected to the pause time width control means 24.

FIG. 2 is a flow chart for explaining the operation of the pause time width control means 24 and the method for counting the number of times of control. In step 40, it is determined whether the discharge state is abnormal or normal by referring to the detection signal of the discharge state detecting means 22. When it is determined that the state is not abnormal, that is, the state is normal, it is determined in step 41 whether the pause time width T _OFF is equal to the reference pause time width T _REF . If they are equal, the state is maintained and the control loop is returned to the beginning. If not, flag 1 in step 42
Set to 1.

This indicates that the pause time width T _OFF is larger than the reference pause time width T _REF and the pause time width T _OFF is shortened toward the reference pause time width T _REF . Next step
At 43, it is determined whether the flag 2 is 1 or 0. When the flag 2 is 1, it indicates that the pause time width T _OFF was increasing in the previous control loop. At this time, therefore, the flag 2 is set to 0 in step 44, and the control count is set in step 45. And add 1 to N ₁ . If the flag 2 is not 1 in step 43, that is, if it is 0, the quiescent time width T _OFF is in the direction of shortening as in the previous control loop, and therefore step 46 is directly executed without counting it as the number of times of control. In step 46, the operation of shortening the pause time width T _OFF by b is performed.

If it is determined in step 40 that the state is abnormal, step 47 is executed. That is, the pause time period T _OFF is declared to be increasing, and in step 48, the flag 1 is set in the previous control loop.
Is 1 is determined. If the flag 1 is 1, that is, the pause time width T _OFF is in the direction of shortening, step 49
Is reset with, and in step 50, 1 is added to N ₂ as the control count. Then, in step 51, the pause time width T _OFF is increased by a. If the flag 1 is not 1 in step 48, that is, if it is 0, the pause time width T _OFF is in the increasing direction as in the previous control loop, and therefore step 51 is directly executed without counting it as the control count. Here, the execution of the counting in step 45 or 50 is reset every unit time when the clock 54 (FIG. 4) is issued, and the counting result immediately before the reset is reported to the reference pause time width setting means 28. The number of times the quiescent time width T _OFF is shortened or increased is counted in steps 45 and 50, but in reality, it is sufficient to have either one.

FIG. 6 shows the pause time width when this pause time width control is performed in time series. For example, an abnormal state is detected at point A and the pause time width T _OFF is increased by a, and an abnormal state is also detected at the next point B and the pause time width T _OFF is increased by a. An abnormal condition was also detected at point C.
T _OFF is increased by a. Although the pause time width T _OFF is increased through three stages here, the pause time width T _OFF is continuously increased.
Since T _OFF is increased, the increased control count is 1
Count as times. Since it became normal at point D, the rest time width
T _OFF is shortened by b, and b is shortened one after another, and at point E, it is shortened to the standard pause time width T _REF . At the point F, the number of times of control increased or decreased per unit time was less than the allowable value, so the reference pause time width T _REF is shortened by c. At point G, the standard pause time width T _REF is further shortened by c,
At point H, it has increased by c.

FIG. 4 shows the details of the reference pause time width setting means 28. The reference pause time width setting means 28 sets the allowable range setting means 56 for setting the allowable range of the number of times of control, the counted number of times of control output from the number-of-controls counting means 30 and the allowable range output from the allowable-range setting means 56. It comprises a comparison calculation means 58 for performing a comparison calculation to obtain a reference pause time width T _REF to be changed next, and a reference pause time width register 60 for storing the result. The clock 54 gives a unit time signal to the control number counting means 30 and the comparison operation means 58.

FIG. 5 is a flow chart showing an example of correction setting of the reference pause time width T _REF by the reference pause time width calculating means 60. In step 61, it is judged whether or not the control number N output from the control number coefficient means 30 is larger than the upper limit value N _{MAX of the} allowable range output from the allowable range setting means 56, and if YES, the process proceeds to step 62. Reference rest time width T _REF
Increase by T _REF = T _REF + c. If the determination in step 61 is no, the process proceeds to step 63 and it is determined whether the control count N is smaller than the lower limit value N _{MIN of the} allowable range. If yes, go to step 64 and set the reference pause duration T _REF
Shorten by T _REF = T _REF −c. When the control count N is within the allowable range, the reference pause time width T _REF is maintained as it is.

Referring to FIG. 6, for example, at the point E, the number of control times N counted in a predetermined time before that is within the allowable range, so that it is maintained as it is, but at the point F, it is counted in the previous constant time. Since the control number N is below the allowable range, the reference pause time width T _REF is shortened by c, and at the point H, the control number N counted in a certain time before that is above the allowable range, the reference pause time width T _{REF. REF} is increased by c. As described above, the control count N is used as a parameter for checking the discharge state, and when the control count N is small, it can be determined that good electric discharge machining can be performed even if the reference pause time width T _REF is shortened. Reducing the reference pause time width T _REF is to increase the average machining current, and the machining time can be shortened.

FIG. 7 is a diagram showing a second embodiment of the present invention. Most of FIG. 7 is the same as FIG. 1, and a peak current control means 34 is added to the constituent elements of FIG. The peak current control means 34 acts on the variable resistor 20 to control the peak current I _P of the machining pulse. The control shown in FIG. 8 or 9 is executed for the peak current I _P of the machining pulse.

FIG. 8 is a diagram showing another embodiment of the electric discharge machining method of the present invention, in which the peak current I _P is corrected instead of the correction setting of the reference rest time width T _REF of FIG. Step 61,
Reference numeral 63 is for determining whether or not the counted number of times of control N is larger than the upper limit value N _MAX of the allowable range and smaller than the lower limit value N _{MIN of the} allowable range as in the case of FIG. If the control count N is larger than the upper limit value N _{MAX of the} allowable range, the routine proceeds to step 65, where the peak current I _P of the machining pulse is I _P = I _P −
It decreases with d. When the control count N is smaller than the lower limit value N _MIN of the permissible range of the permissible range, the routine proceeds to step 66, where the peak current I _P of the machining pulse is increased by I _P = I _P + d. Increasing the peak current I _P of the machining pulse is increasing the average machining current in the same manner as shortening the reference rest time width T _REF , and the machining time can be shortened.

FIG. 9 is a diagram showing still another embodiment of the electric discharge machining method of the present invention. Up to steps 61 to 64, the reference pause time width T _REF is set to increase or decrease as in the case of FIG. In addition to this, the peak current of the machining pulse similar to steps 65 and 66 in Fig. 8
It is a combination of controls that increase and decrease I _P. However, in FIG. 9, as a determination condition for the increase / decrease of the peak current I _P , in steps 67 and 68, whether the reference pause time width T _REF is larger than a predetermined upper limit T _MAX or less than a predetermined lower limit T _MIN . Is being determined. Reference pause time width T _REF
Is larger than the predetermined upper limit T _MAX , the peak current I _P of the machining pulse is reduced by I _P = I _P −d. When the reference rest time width T _REF is smaller than the predetermined lower limit T _MIN , the peak current I _P of the machining pulse is increased by I _P = I _P + d. In this way, by controlling by combining the reference rest time width T _REF and the peak current I _P , processing is performed with an average processing current according to the progress of processing, and the processing time is shortened while performing normal processing. You can

〔The invention's effect〕

As described above, according to the present invention, the reference pause time width is set, and when the normal state is detected after the abnormal state is detected, the control for shortening the pause time width of the machining pulse to the reference pause time width is performed. The number of control times for increasing or shortening the pause time width of the machining pulse is counted, and the reference pause time width or peak current is reduced or increased according to the counted number of controls, so the control system becomes stable and abnormal. It is possible to increase the processing efficiency while reducing the processing possibility.

[Brief description of drawings]

FIG. 1 is a block diagram showing an electric discharge machine according to the present invention, and FIG.
FIG. 4 is a flow chart showing the operation of the pause time width control means of FIG. 1 and a method of counting the number of times of control, FIG. 3 is a diagram for explaining the application of machining pulses, and FIG. 4 is the control number counting means of FIG. FIG. 5 is a block diagram showing a detailed configuration of the reference pause time width setting means, FIG. 5 is a flow chart showing the operation of the reference pause time width setting means, and FIG. 6 is an operation of the electric discharge machining apparatus shown in FIGS. 1 to 5. FIG. 7 is a configuration diagram similar to FIG. 1 of the second embodiment of the present invention, and FIG. 8 is a diagram showing the peak current in place of the control of the reference rest time width of the previous embodiment. A control flowchart, FIG. 9 is a flowchart of control performed by combining control of the reference rest time width and control of peak current. 10 …… Workpiece, 12 …… Processing electrode.

Claims (6)

(57) [Claims] 1. When a machining pulse is applied to a machining electrode and a workpiece and an abnormal state is detected by detecting a discharge state every moment, a pause time width of the machining pulse is increased to detect a normal state. In the electric discharge machining method in which control is performed to shorten the pause time width of the machining pulse, the reference pause time width is set in advance, and when the abnormal state is detected, the pause time width of the machining pulse is set to be smaller than the reference pause time width. When the normal state is increased, the control is performed to reduce the pause time width of the machining pulse to the reference pause time width, and the pause time width of the machining pulse is increased from the reference pause time width or the reference pause time. The number of control times to be shortened to the time width is counted per unit time, and when the counted number of control times is less than a predetermined allowable range, the reference pause time width is shortened and exceeds. In the case of the above, the electric discharge machining method for increasing the reference rest time width. 2. When a machining pulse is applied to the machining electrode and the workpiece and an abnormal state is detected by detecting a discharge state every moment, a pause time width of the machining pulse is increased to detect a normal state. In the electric discharge machining method in which control is performed to shorten the pause time width of the machining pulse, the reference pause time width is set in advance, and when the abnormal state is detected, the pause time width of the machining pulse is set to be smaller than the reference pause time width. When the normal state is increased, the control is performed to reduce the pause time width of the machining pulse to the reference pause time width, and the pause time width of the machining pulse is increased from the reference pause time width or the reference pause time. The number of times of control for shortening to the time width is counted per unit time, and when the counted number of times of control is below a predetermined allowable range, the peak current value of the machining pulse is increased, An electric discharge machining method of decreasing the peak current value of the machining pulse when the machining current is above the limit. 3. When a machining pulse is applied to the machining electrode and the workpiece and an abnormal state is detected by detecting the discharge state every moment, the pause time width of the machining pulse is increased to detect the normal state. In the electric discharge machining method in which control is performed to shorten the pause time width of the machining pulse, the reference pause time width is set in advance, and when the abnormal state is detected, the pause time width of the machining pulse is set to be smaller than the reference pause time width. When the normal state is increased, the control is performed to reduce the pause time width of the machining pulse to the reference pause time width, and the pause time width of the machining pulse is increased from the reference pause time width or the reference pause time. The number of control times to be shortened to the time width is counted per unit time, and when the counted number of control times is below a predetermined allowable range, the reference pause time width of the machining pulse is shortened. If the width of the machining pulse is shortened and exceeds, the reference pause time width of the machining pulse is increased, and if the reference pause time width of the machining pulse is below a predetermined lower limit value, the peak current value of the machining pulse is increased. However, when it exceeds a predetermined upper limit value, the electric discharge machining method is controlled so as to decrease the peak current value of the machining pulse. 4. A means for applying a machining pulse to a machining electrode and a work piece, a detecting means for detecting a discharge state every moment, and a pause time width of the machining pulse when an abnormal state is detected by the detecting means. Is increased from a preset reference dwell time width, and a dwell time width control means for shortening the dwell time width of the machining pulse to the reference dwell time width when a normal state is detected, and the dwell time width control means A control number counting means for counting the number of control times for increasing or shortening the pause time width of the machining pulse from the reference pause time width or to the reference pause time width; and the number of control times counted by the control count counter means per unit time in advance. The control count counted by the control count counting means is compared with the determined allowable range of the number of control times for increasing or shortening the pause time width per unit time and is below the allowable range. Electrical discharge machining apparatus, wherein the reference pause time width is shortened when it exceeds, and the reference pause time width is increased when it exceeds the reference pause time width. 5. A means for applying a machining pulse to a machining electrode and a work piece, a detecting means for detecting a discharge state every moment, and a pause time width of the machining pulse when an abnormal state is detected by the detecting means. Is increased from a preset reference dwell time width, and a dwell time width control means for shortening the dwell time width of the machining pulse to the reference dwell time width when a normal state is detected, and the dwell time width control means A control number counting means for counting the number of control times for increasing or shortening the pause time width of the machining pulse from the reference pause time width or to the reference pause time width; and the number of control times counted by the control count counter means per unit time in advance. The control count counted by the control count counting means is compared with the determined allowable range of the number of control times for increasing or shortening the pause time width per unit time and is below the allowable range. And a peak current control means for increasing the peak current value of the machining pulse and decreasing the peak current value of the machining pulse when it exceeds the peak current value. 6. A means for applying a machining pulse to a machining electrode and a work piece, a detecting means for detecting a momentary electric discharge state, and a pause time width of the machining pulse when an abnormal state is detected by the detecting means. Is increased from a preset reference dwell time width, and a dwell time width control means for shortening the dwell time width of the machining pulse to the reference dwell time width when a normal state is detected, and the dwell time width control means A control number counting means for counting the number of control times for increasing or shortening the pause time width of the machining pulse from the reference pause time width or to the reference pause time width; and the number of control times counted by the control count counter means per unit time in advance. The control count counted by the control count counting means is compared with the determined allowable range of the number of control times for increasing or shortening the pause time width per unit time and is below the allowable range. The reference pause time width is shortened by the reference pause time width, and the reference pause time width is increased by the reference pause time width when it exceeds the reference pause time width. Is lower than a predetermined lower limit value, the peak current value of the machining pulse is increased, and if it is higher than a predetermined upper limit value, the peak current value of the machining pulse is decreased. Electric discharge machine.