Control device for wire electrical discharge machining, wire electrical discharge machining machine, and control method for wire electrical discharge machining machine

Abstract

We provide a wire electrical discharge machining (EDM) machine that can achieve good straightness accuracy. [Solution] The wire electrical discharge machining machine includes a voltage application unit (50) that applies an induced voltage between the electrodes, an application control unit (76) that controls the voltage application unit (50) to repeatedly apply and stop the induced voltage, and a time change unit (78) that changes the time for which the induced voltage is applied. The application control unit (76) stops applying the induced voltage if a discharge occurs after the application of the induced voltage has started, or if the application cutoff time has elapsed without a discharge occurring after the application of the induced voltage has started, and the time change unit (78) changes the application cutoff time.

Description

Technical Field

[0001] The present invention relates to a wire electrical discharge machining apparatus.

Background Art

[0002] A wire electrical discharge machining apparatus applies an induced voltage for inducing discharge between a wire electrode and a workpiece. In this case, the wire electrical discharge machining apparatus performs servo feed control to move the wire electrode in the machining direction.

[0003] The gap amount between the wire electrode and the workpiece changes due to an electrostatic attraction force and a discharge repulsive force. The electrostatic attraction force is a force that attracts the wire electrode to the workpiece and occurs during the application of the induced voltage. The discharge repulsive force is a force that repels the wire electrode from the workpiece and occurs during the generation of discharge. If the electrostatic attraction force and the discharge repulsive force are balanced, the change in the gap amount between the wire electrode and the workpiece becomes small.

[0004] However, during machining, when the facing area between the wire electrode and the workpiece suddenly changes at a corner portion of the machining program, or when the flow of the machining fluid changes due to the machining environment (for example, the machining position within the workpiece) and the discharge of sludge deteriorates, etc. In this case, the frequency of discharge changes, the balance between the electrostatic attraction force and the discharge repulsive force is disrupted, and the straightness accuracy deteriorates.

[0005] The straightness accuracy refers to the difference between the maximum dimension and the minimum dimension in the thickness direction of the machined product. If this difference is large, the side surface of the machined product is in a bulging state or a concave state compared to the vertical side surface. Therefore, the smaller the difference between the maximum dimension and the minimum dimension in the thickness direction of the machined product, the better the straightness accuracy.

[0006] Japanese Patent No. 5739563 discloses a wire electrical discharge machining apparatus that stops applying an induced voltage between the electrodes when the discharge delay time, which is the duration of the voltage application state and the non-discharging state, is smaller than a predetermined reference value.

Prior Art Documents

Patent Documents

[0007] [Patent Document 1] Patent No. 5739563 [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] In the above-mentioned Patent Publication No. 5739563, if the discharge delay time is smaller than a predetermined reference value, the average voltage of the induced voltage applied per unit time decreases, and the electrostatic attraction force decreases. In this case, if the application of the induced voltage between the electrodes is stopped, the opportunity for discharge to occur changes, and the discharge repulsion force decreases.

[0009] However, when an induced voltage is repeatedly applied at intervals per unit time, the frequency of non-discharge tends to be higher than the frequency of discharge. In the above-mentioned Japanese Patent Publication No. 5739563, it is thought that the balance between electrostatic attraction and discharge repulsion becomes difficult to maintain because opportunities for discharge are lost. Therefore, obtaining good straightness accuracy is a challenge.

[0010] The present invention aims to solve the problems described above. [Means for solving the problem]

[0011] An aspect of the present invention is a wire electrical discharge machine that processes a workpiece by generating a discharge between the electrodes of the workpiece and a wire electrode, comprising: a voltage application unit that applies an induced voltage between the electrodes to induce the discharge; an application control unit that controls the voltage application unit to repeatedly apply the induced voltage and stop the application of the induced voltage; and a time change unit that changes the time for which the induced voltage is applied, wherein the application control unit stops applying the induced voltage when the discharge occurs after the application of the induced voltage has started, or when the application cutoff time has elapsed without the discharge occurring after the application of the induced voltage has started, and the time change unit changes the application cutoff time. [Effects of the Invention]

[0012] According to an aspect of the present invention, the average voltage of the induced voltage applied per unit time can be adjusted without changing the opportunity for discharge to occur. Therefore, it becomes easier to maintain a balance between the electrostatic attraction force and the discharge repulsion force, and as a result, good straightness accuracy can be obtained. [Brief explanation of the drawing]

[0013] [Figure 1] Figure 1 is a schematic diagram showing the configuration of a wire electrical discharge machining machine according to an embodiment. [Figure 2] Figure 2 is a block diagram showing the configuration of the machining control system of a wire electrical discharge machining machine according to the first embodiment. [Figure 3] Figure 3 shows the change in the induced voltage applied between the electrodes by the voltage application unit according to the control of the application control unit. [Figure 4] Figure 4A shows an example of the change in induced voltage when the application cutoff time in Figure 3 is shortened, and Figure 4B shows an example of the change in induced voltage when the application cutoff time in Figure 3 is lengthened. [Figure 5] Figure 5 is a graph showing the relationship between curvature and the application cutoff time. [Figure 6] Figure 6 is a block diagram showing the configuration of the machining control system of a wire electrical discharge machining machine according to the fourth embodiment. [Figure 7] Figure 7 is a block diagram showing the configuration of the machining control system of a wire electrical discharge machining machine according to the fifth embodiment. [Modes for carrying out the invention]

[0014] Figure 1 is a schematic diagram showing the configuration of a wire electrical discharge machining (EDM) machine 10. Figure 1 shows the X, Y, and Z directions, which are the drive directions of the axis of the wire electrical discharge machining machine 10. The X and Y directions are orthogonal to each other in the plane, and the Z direction is orthogonal to both the X and Y directions.

[0015] The wire electrical discharge machining tool 10 is a machine tool that machines a workpiece W by generating an electric discharge between the workpiece W and the wire electrode 12. The wire electrical discharge machining tool 10 includes a machining tool main body 14 and a machining fluid treatment device 16.

[0016] The material of the wire electrode 12 is, for example, a metal material such as tungsten-based, copper alloy-based, or brass-based. The material of the workpiece W is, for example, a metal material such as iron-based material or cemented carbide material. The workpiece W is also referred to as a work or a workpiece to be machined.

[0017] The machining tool main body 14 includes a supply system 20 and a recovery system 22. The supply system 20 supplies the wire electrode 12 toward the workpiece W. The recovery system 22 recovers the wire electrode 12 that has passed through the workpiece W.

[0018] The supply system 20 includes a wire bobbin 24, a torque motor 26, a brake shoe 28, a brake motor 30, and an upper die guide 32. The wire bobbin 24 winds the unused wire electrode 12. The torque motor 26 applies torque to the wire bobbin 24. The brake shoe 28 applies a braking force by friction to the wire electrode 12. The brake motor 30 applies a brake torque to the brake shoe 28. The upper die guide 32 guides the wire electrode 12 above the workpiece W. The upper die guide 32 has a support portion 32a that supports the wire electrode 12.

[0019] The recovery system 22 includes a lower die guide 34, pinch rollers 36, feed rollers 38, a feed motor, and a recovery box 42. The lower die guide 34 guides the wire electrode 12 below the workpiece W. The lower die guide 34 has a support portion 34a that supports the wire electrode 12 and a guide roller 34b that changes the direction of the wire electrode 12. The pinch rollers 36 and the feed rollers 38 sandwich the wire electrode 12. The feed motor 40 applies torque to the feed rollers 38. The recovery box 42 recovers the wire electrode 12 conveyed through the pinch rollers 36 and the feed rollers 38.

[0020] The machine tool main body 14 includes a machining tank 44 capable of storing a machining fluid. The machining fluid is a liquid such as deionized water used during machining. The machining tank 44 is placed on the base portion 46. An upper die guide 32 and a lower die guide 34 are arranged in the machining tank 44, and a workpiece W is provided between the upper die guide 32 and the lower die guide 34. The upper die guide 32, the lower die guide 34, and the workpiece W are immersed in the machining fluid stored in the machining tank 44.

[0021] At least one of the upper die guide 32 and the lower die guide 34 jets a clean machining fluid that does not contain sludge (machining chips) toward the space between the wire electrode 12 and the workpiece W. In this case, the space between the electrodes is filled with a clean liquid suitable for machining, and a decrease in machining accuracy due to sludge generated during machining is suppressed.

[0022] The machining fluid treatment device 16 is a device that adjusts the quality of the machining fluid. The machining fluid treatment device 16 removes sludge generated in the machining tank 44. Further, the machining fluid treatment device 16 adjusts the electrical resistivity, temperature, etc. The machining fluid whose quality has been adjusted by the machining fluid treatment device 16 is returned to the machining tank 44 again and jetted from at least one of the upper die guide 32 and the lower die guide 34 toward the space between the electrodes.

[0023] Hereinafter, several embodiments will be described with respect to the machining control system of the wire electrical discharge machining machine 10.

[0024] [First Embodiment] FIG. 2 is a block diagram showing the configuration of the machining control system of the wire electrical discharge machining machine 10 according to the first embodiment. The wire electrical discharge machining machine 10 further includes a voltage application unit 50, a control device 52, and a voltage detection unit 64.

[0025] The voltage application unit 50 applies an induced voltage for inducing discharge between the wire electrode 12 and the workpiece W. The voltage application unit 50 includes a power source 60 and a switching element 62. The voltage detection unit 64 measures the induced voltage applied between the electrodes.

[0026] The power supply 60 is a voltage source for applying an induced voltage between the wire electrode 61A, which is in contact with the wire electrode 12, and the workpiece electrode 61B, which is in contact with the workpiece W. The switching element 62 switches between applying the induced voltage between the electrodes and stopping the application of the induced voltage. The switching element 62 is controlled by the control device 52.

[0027] The control device 52 includes a signal processing unit 70, a storage medium 72, and a clock unit 74. The signal processing unit 70 includes a processor such as a CPU or GPU. The storage medium 72 includes volatile memory such as RAM and non-volatile memory such as ROM, flash memory, or hard disk. At least a portion of the storage medium 72 may be provided in the signal processing unit 70.

[0028] The signal processing unit 70 controls the motors that drive the upper die guide 32 and the lower die guide 34 based on the machining program stored in the storage medium 72. In this case, the signal processing unit 70 moves the wire electrode 12 relative to the workpiece W in at least one of the X and Y directions along the machining path defined in the machining program. Alternatively, the signal processing unit 70 may control the motor that drives the table on which the workpiece W is fixed, instead of controlling the motors that drive the upper die guide 32 and the lower die guide 34.

[0029] The signal processing unit 70 controls the torque motor 26 and the feed motor 40. In this case, the signal processing unit 70 applies torque to the wire bobbin 24 and the feed roller 38, causing the wire electrode 12 in contact with the wire bobbin 24 and the feed roller 38 to move in the direction of travel. The direction of travel of the wire electrode 12 (-Z direction) and the direction of movement of the wire electrode 12 relative to the workpiece W (X direction, Y direction) are intersecting.

[0030] The signal processing unit 70 includes an application control unit 76 and a time modification unit 78. The application control unit 76 and the time modification unit 78 may be implemented by the signal processing unit 70 processing a program stored in a storage medium 72. Alternatively, at least one of the application control unit 76 and the time modification unit 78 may be implemented by an integrated circuit such as an ASIC or FPGA. Alternatively, at least one of the application control unit 76 and the time modification unit 78 may be configured by an electronic circuit including discrete devices.

[0031] The voltage application control unit 76 controls the switching element 62 of the voltage application unit 50 based on the induced voltage measured by the voltage detection unit 64 and the time measured by the clock unit 74, to repeatedly apply the induced voltage between the poles and stop applying the induced voltage. When the switching element 62 switches from off to on, the induced voltage is applied between the poles. On the other hand, when the switching element 62 switches from on to off, the application of the induced voltage between the poles is stopped.

[0032] Figure 3 shows the change in the induced voltage applied between the electrodes by the voltage application unit 50 according to the control of the application control unit 76. When the application control unit 76 turns on the switching element 62, it monitors the induced voltage measured by the voltage detection unit 64. When discharge occurs, the induced voltage drops rapidly. The discharge delay time T1, from the start of induced voltage application until discharge occurs, is undefined.

[0033] When the induced voltage falls below a predetermined voltage value, the application control unit 76 turns off the switching element 62. After a pause time T2 has elapsed since turning off the switching element 62, the application control unit 76 turns on the switching element 62 again and applies the induced voltage between the electrodes. The pause time T2 is the time from when the application of the induced voltage is stopped until when the application of the induced voltage is started again. This pause time T2 is stored in the storage medium 72.

[0034] On the other hand, there are cases where discharge does not occur even when the switching element 62 is turned on and an induced voltage is applied between the electrodes. In this case, the application control unit 76 turns off the switching element 62 after the application cutoff time T3 has elapsed since turning on the switching element 62. After the pause time T2 has elapsed since turning off the switching element 62, the application control unit 76 turns on the switching element 62 again and applies an induced voltage between the electrodes.

[0035] The application cutoff time T3 is the time from when the application of the induced voltage is started until it is forcibly stopped, in the case that no discharge occurs. This application cutoff time T3 is stored in the storage medium 72. The application cutoff time T3 stored in the storage medium 72 is changed as appropriate by the time change unit 78. In other words, the application cutoff time T3 is a variable. Note that the pause time T2 stored in the storage medium 72 is not changed by the time change unit 78 in this embodiment. In other words, the pause time T2 is a constant.

[0036] Figures 4A and 4B show examples of changes in induced voltage when the application cutoff time T3 in Figure 3 is changed. Figure 4A shows an example where the application cutoff time T3 is shortened, and Figure 4B shows an example where the application cutoff time T3 is lengthened. The time change unit 78 changes the application cutoff time T3 based on information indicating the frequency of discharge occurring in a unit time (predetermined measurement time) UT.

[0037] In this embodiment, the information indicating the frequency of discharges occurring in a unit time UT is the number of discharges occurring in a unit time UT. In this case, the time change unit 78 calculates the number of discharges occurring in a unit time UT based on the induced voltage measured by the voltage detection unit 64 and the time measured by the clock unit 74, and the more discharges there are, the longer the application cutoff time T3 is made.

[0038] The number of discharges correlates with the frequency of discharges, indicating the frequency of discharges occurring per unit time UT. A higher number of discharges indicates a higher discharge frequency. A higher discharge frequency lowers the average voltage of the induced voltage per unit time UT. Therefore, a higher number of discharges tends to increase the discharge repulsion force and decrease the electrostatic attraction force. On the other hand, since no discharge occurs at the application termination time T3, even if the application continues during the pause time T2 after the application termination time T3, the occurrence of discharges will hardly increase. Therefore, the discharge repulsion force remains virtually unchanged even if the application termination time T3 is extended. Conversely, as the application termination time T3 increases, the average voltage of the induced voltage per unit time UT rises, and the electrostatic attraction force tends to increase.

[0039] Thus, by increasing the number of discharges and lengthening the application cutoff time T3, the average voltage can be increased without changing the opportunities for discharge to occur. Therefore, it becomes easier to maintain a balance between electrostatic attraction and discharge repulsion, resulting in good straightness accuracy.

[0040] The time change unit 78 may change the application cutoff time T3 while keeping the total time T4, which is the sum of the application cutoff time T3 and the pause time T2 immediately following the application cutoff time T3, constant. Keeping the total time T4 constant helps to suppress differences in the opportunities for discharge to occur per unit time UT between the case where the application cutoff time T3 is changed and the case where the application cutoff time T3 is not changed.

[0041] The time change unit 78 may change the applied cutoff time T3 during machining from the start to the end of machining, or it may change the applied cutoff time T3 only during machining of a part of the machining path. Examples of a part of the machining path include a corner section or a path specified by the operator. In this case, the time change unit 78 monitors the processing status of the machining program by the signal processing unit 70 and starts changing the applied cutoff time T3 at the start timing of machining of the corner section or the path specified by the operator. On the other hand, the time change unit 78 stops changing the applied cutoff time T3 at the end timing of machining of the corner section or the path specified by the operator.

[0042] [Second Embodiment] The second embodiment is the same as the first embodiment, except for the information indicating the frequency of discharges occurring in a unit time UT. Therefore, the description of the second embodiment will be limited to matters related to the information indicating the frequency of discharges occurring in a unit time UT. In the case of the second embodiment, the information indicating the frequency of discharges occurring in a unit time UT is the accumulated time of the discharge delay time T1 in the unit time UT. The time change unit 78 increases the application cutoff time T3 as this accumulated time decreases.

[0043] The cumulative discharge delay time T1 correlates with the discharge frequency and therefore indicates the frequency of discharge occurring per unit time UT. A shorter cumulative discharge delay time T1 corresponds to a higher discharge frequency. A higher discharge frequency lowers the average voltage of the induced voltage per unit time UT. For this reason, a shorter cumulative time tends to result in a stronger discharge repulsion force and a weaker electrostatic attraction force. On the other hand, since no discharge occurs at the application termination time T3, even if the application continues during the pause time T2 after the application termination time T3, the occurrence of discharge will hardly increase. Therefore, the discharge repulsion force remains virtually unchanged even if the application termination time T3 is extended. Conversely, as the application termination time T3 increases, the average voltage of the induced voltage per unit time UT rises, and the electrostatic attraction force tends to strengthen.

[0044] Thus, in the second embodiment, the shorter the integrated discharge delay time T1 in a unit time UT, the longer the application cutoff time T3 can be, thereby increasing the average voltage without changing the opportunity for discharge to occur. Therefore, similar to the first embodiment, it becomes easier to maintain a balance between the electrostatic attraction force and the discharge repulsion force, and as a result, good straightness accuracy can be obtained.

[0045] [Third Embodiment] In the third embodiment, information indicating the frequency of discharges occurring per unit time UT is replaced by the machining shape specified in the machining program. Therefore, the description of the third embodiment will be limited to matters related to the machining shape.

[0046] In the machining program, the machining shape can be specified as a straight section, an outer corner section, or an inner corner section. If an outer corner section is specified as the machining shape, the curvature (or radius of curvature) is specified in the machining program. An outer corner section is the machining path portion that protrudes outward after machining. When the machining shape is an outer corner section, the time change unit 78 shortens the applied cutoff time T3 as the curvature increases (or the radius of curvature decreases).

[0047] The curvature of the outer corner portion, specified in the machining program as the machined shape, correlates with the frequency of discharges, and therefore indicates the frequency of discharges occurring per unit time UT. The larger the curvature of the outer corner portion (or the smaller the radius of curvature), the lower the frequency of discharges. When the frequency of discharges is low, the average voltage of the induced voltage per unit time UT increases. For this reason, the larger the curvature of the outer corner portion (or the smaller the radius of curvature), the weaker the discharge repulsion force and the stronger the electrostatic attraction force tend to be. On the other hand, since no discharge occurs at the application cutoff time T3, shortening the application cutoff time T3 does not significantly change the opportunity for discharge to occur. Therefore, even if the application cutoff time T3 is shortened, the discharge repulsion force does not substantially change. Conversely, when the application cutoff time T3 is shortened, the average voltage of the induced voltage per unit time UT decreases, and the electrostatic attraction force tends to weaken.

[0048] Thus, when the processed shape is an outer corner, the larger the curvature (or the smaller the radius of curvature), the shorter the applied cutoff time T3, which allows the average voltage to be lowered without changing the opportunity for discharge to occur. Therefore, similar to the first embodiment, it becomes easier to maintain a balance between the electrostatic attraction force and the discharge repulsion force, and as a result, good straightness accuracy can be obtained.

[0049] On the other hand, when an inner corner is specified as the machining shape, the curvature (or radius of curvature) is specified in the machining program. An inner corner is a machining path portion that is concave inward after machining. When the machining shape is an inner corner, the time change unit 78 increases the applied cutoff time T3 as the curvature increases (or as the radius of curvature decreases).

[0050] The curvature of the inner corner, specified in the machining program as the machining shape, correlates with the frequency of discharges, and therefore indicates the frequency of discharges occurring per unit time UT. The larger the curvature of the inner corner (or the smaller the radius of curvature), the higher the frequency of discharges. When the frequency of discharges is high, the average voltage of the induced voltage per unit time UT decreases. For this reason, the larger the curvature of the inner corner (or the smaller the radius of curvature), the stronger the discharge repulsion force and the weaker the electrostatic attraction force tend to be. On the other hand, since no discharge occurs at the application termination time T3, even if the application continues during the rest time T2 after the application termination time T3, the occurrence of discharges will hardly increase. Therefore, even if the application termination time T3 is extended, the discharge repulsion force does not substantially change. Conversely, as the application termination time T3 is extended, the average voltage of the induced voltage per unit time UT increases, and the electrostatic attraction force tends to strengthen.

[0051] Thus, when the processed shape is an inner corner, the larger the curvature (or the smaller the radius of curvature), the longer the applied cutoff time T3 can be, thereby increasing the average voltage without changing the opportunity for discharge to occur. Therefore, similar to the first embodiment, it becomes easier to maintain a balance between the electrostatic attraction force and the discharge repulsion force, and as a result, good straightness accuracy can be obtained.

[0052] On the other hand, when a straight section is specified as the machining shape, the curvature (or radius of curvature) is not specified in the machining program. In this case, the time change unit 78 is set to a reference value for the applied cutoff time T3. The reference value is a predetermined constant and is stored in the storage medium 72.

[0053] Figure 5 is a graph showing the relationship between curvature and the applied cutoff time T3. The time change unit 78 may change the applied cutoff time T3 according to the control law "T3 = T0 + (-α × κ)".

[0054] [Fourth Embodiment] Figure 6 is a block diagram showing the configuration of the machining control system of the wire electrical discharge machining machine 10 according to the fourth embodiment. In Figure 6, components equivalent to those described in the first embodiment are denoted by the same reference numerals. In the fourth embodiment, explanations that overlap with those of the first embodiment are omitted. In the fourth embodiment, a display device 80, an input device 82, and a display control unit 84 are newly provided.

[0055] The display device 80 has a display screen and displays information supplied from the control device 52 on the display screen. Examples of the display device 80 include a liquid crystal display. The input device 82 supplies information to the control device 52 in response to the operator's operations. Examples of the input device 82 include a mouse, a keyboard, a touch panel placed on the display screen of the display device 80, and an operation panel provided on the housing of the main unit 14 of the wire electrical discharge machining machine 10.

[0056] The display control unit 84 is included in the signal processing unit 70 of the control device 52. The display control unit 84 may be implemented by the signal processing unit 70 processing a program stored in the storage medium 72. Alternatively, the display control unit 84 may be implemented by an integrated circuit such as an ASIC or FPGA. Furthermore, the display control unit 84 may be composed of an electronic circuit including discrete devices.

[0057] When the display control unit 84 receives a request from the input device 82 to change the degree of processing effectiveness, it controls the display device 80 to display multiple options indicating the degree of straightness accuracy effectiveness. For example, the display control unit 84 displays a first option, "slightly recess the central part of the plate thickness compared to normal," and a second option, "slightly bulge the central part of the plate thickness compared to normal." Note that plate thickness refers to the thickness of the processed product.

[0058] In this embodiment, the application cutoff time T3 is set in the storage medium 72 in association with each of a plurality of options indicating the degree of effectiveness of straightness accuracy. The application cutoff time T3 associated with each option is different from one another. For example, the application cutoff time T3 associated with the first option is longer than the application cutoff time T3 associated with the second option.

[0059] When one of the multiple options displayed on the display screen of the display device 80 is selected by the operator using the input device 82, a request to change the degree of effectiveness of the straightness accuracy based on that option is supplied from the input device 82 to the control device 52. In this case, the time change unit 78 changes the currently set application cutoff time T3 to the application cutoff time T3 corresponding to the degree of effectiveness of the straightness accuracy selected by the operator.

[0060] In this way, the setting of the applied cutoff time T3 is changed to correspond to the degree of processing effectiveness selected by the operator. This allows the applied cutoff time T3 to be set according to the operator's actions, even if the processing conditions change due to the material of the workpiece W, etc.

[0061] This embodiment may be applied to the second embodiment. In this case, the time modification unit 78 corrects the integrated time of the discharge delay time T1 in a unit time UT by multiplying the integrated time by a correction coefficient corresponding to the option selected by the operator.

[0062] Furthermore, this embodiment may be applied to a third embodiment. In this case, the time change unit 78 corrects the curvature (or radius of curvature) of the outer corner or inner corner by multiplying the curvature (or radius of curvature) by a correction coefficient corresponding to the option selected by the operator.

[0063] [Fifth Embodiment] Figure 7 is a block diagram showing the configuration of the machining control system of the wire electrical discharge machining machine 10 according to the fifth embodiment. In Figure 7, components equivalent to those described in the first embodiment are denoted by the same reference numerals. In the fifth embodiment, explanations that overlap with those of the first embodiment are omitted. In the fifth embodiment, a speed adjustment unit 86 is newly provided.

[0064] The speed adjustment unit 86 is included in the signal processing unit 70 of the control device 52. The speed adjustment unit 86 may be implemented by the signal processing unit 70 processing a program stored in the storage medium 72. Alternatively, the speed adjustment unit 86 may be implemented by an integrated circuit such as an ASIC or FPGA. Furthermore, the speed adjustment unit 86 may be composed of an electronic circuit including discrete devices.

[0065] The speed adjustment unit 86 controls a motor to move the wire electrode 12 relative to at least one of the X and Y directions, thereby adjusting the feed speed of the wire electrode 12. In this case, the speed adjustment unit 86 calculates the average voltage of the induced voltage in a unit time UT based on the induced voltage measured by the voltage detection unit 64 and the time measured by the clock unit 74. Furthermore, the speed adjustment unit 86 compares the calculated average voltage with a target value and adjusts the feed speed of the wire electrode 12 so that the deviation between the average voltage and the target value becomes small.

[0066] The target value is set as the dummy average voltage if the application cutoff time T3 is not changed. The dummy average voltage is set by the time change unit 78. In this case, the time change unit 78 calculates the dummy average voltage based on the average voltage actually calculated based on the induced voltage measured by the voltage detection unit 64 and the time measured by the clock unit 74, and the reference value of the application cutoff time T3. For example, the time change unit 78 calculates the difference time between the changed application cutoff time T3 and the reference value of the application cutoff time T3. Next, the time change unit 78 adds the accumulated time of the discharge delay time T1 in unit time UT to the calculated difference time to obtain a total time. Next, the time change unit 78 calculates the average of the induced voltage applied to the obtained total time as the dummy average voltage.

[0067] In this way, the feed rate of the wire electrode 12 is adjusted based on the dummy average voltage when the applied cutoff time T3 is not changed. This makes it possible to change the applied cutoff time T3 without changing the existing processing content in the speed adjustment unit 86.

[0068] This embodiment is not limited to the first embodiment, but can also be applied to the second, third, and fourth embodiments.

[0069] [Sixth Embodiment] The sixth embodiment is the same as the first embodiment, except for the time modification unit 78. Therefore, the description of the sixth embodiment will be limited to matters related to the time modification unit 78. In the case of the sixth embodiment, the time modification unit 78 changes the pause time T2 along with the application cutoff time T3 based on information indicating the frequency of discharge occurring in a unit time UT.

[0070] For example, the time adjustment unit 78 increases the application cutoff time T3 and the pause time T2 as the number of discharges increases. In this case, the degree to which the application cutoff time T3 is changed according to the number of discharges may be the same as or different from the degree to which the pause time T2 is changed according to the number of discharges.

[0071] Note that the pause time T2 may be the pause time T2 immediately following the discharge delay time T1, or the pause time T2 immediately following the application cutoff time T3. However, if the time change unit 78 changes the application cutoff time T3 while keeping the total time T4 constant, the pause time T2 is the pause time T2 immediately following the discharge delay time T1.

[0072] In this way, by changing the pause time T2 along with the application cutoff time T3, the amount of adjustment to the average voltage of the induced voltage applied per unit time UT can be increased compared to the case where only the application cutoff time T3 is changed.

[0073] This embodiment is not limited to the first embodiment, but can also be applied to the second, third, fourth, and fifth embodiments.

[0074] [Inventions obtained from embodiments and modifications] The inventions that can be understood from the above embodiments are described below.

[0075] (1) The present invention relates to a wire electrical discharge machine (10) that processes a workpiece (W) by generating a discharge between the electrodes of the workpiece and a wire electrode (12), comprising: a voltage application unit (50) that applies an induced voltage between the electrodes to induce the discharge; an application control unit (76) that controls the voltage application unit to repeatedly apply the induced voltage and stop the application of the induced voltage; and a time change unit (78) that changes the time for which the induced voltage is applied, wherein the application control unit stops applying the induced voltage when the discharge occurs after the application of the induced voltage has started, or when the application cutoff time (T3) has elapsed without the discharge occurring after the application of the induced voltage has started, and the time change unit changes the application cutoff time.

[0076] This allows for adjustment of the average voltage of the induced voltage applied per unit time without changing the opportunity for discharge to occur. Consequently, it becomes easier to maintain a balance between the electrostatic attraction force and the discharge repulsion force, resulting in good straightness accuracy.

[0077] (2) The present invention relates to a wire electrical discharge machine, wherein the time change unit may change the application cutoff time based on information indicating the frequency of the discharge occurring in a unit time (UT). This makes it possible to adjust the average voltage based on the frequency of the discharge.

[0078] (3) The present invention relates to a wire electrical discharge machine, wherein the information is the number of discharges generated per unit time, and the application control unit may increase the application cutoff time as the number of discharges increases. This makes it possible to set an appropriate application cutoff time according to the number of discharges.

[0079] (4) The present invention relates to a wire electrical discharge machine, wherein the information is the integrated discharge delay time (T1) in a unit time from the start of application of the induced voltage until the discharge occurs, and the application control unit may increase the application cutoff time as the integrated time decreases. This makes it possible to set an appropriate application cutoff time according to the discharge delay time.

[0080] (5) The present invention relates to a wire electrical discharge machining machine, wherein the time change unit may change the application cutoff time based on the machining shape specified in the machining program. This makes it possible to adjust the average voltage based on the machining shape.

[0081] (6) The present invention relates to a wire electrical discharge machining machine, wherein when the machining shape is an outer corner, the time change unit may shorten the application cutoff time as the radius of curvature decreases, and when the machining shape is an inner corner, the time change unit may lengthen the application cutoff time as the radius of curvature decreases. This makes it possible to set an appropriate application cutoff time according to the corner.

[0082] (7) The present invention relates to a wire electrical discharge machining machine, wherein the time change unit may change the application cutoff time based on the degree of straightness accuracy selected by the operator. This makes it possible to set the application cutoff time corresponding to the change in the machining conditions, such as the material of the workpiece, according to the operator's operation.

[0083] (8) The present invention relates to a wire electrical discharge machining machine, comprising a speed adjustment unit (86) for adjusting the feed rate of the relative position between the workpiece and the wire electrode, wherein the time change unit calculates a dummy average voltage based on the average voltage of the induced voltage applied per unit time and a reference value of the application cutoff time, and the speed adjustment unit may control the feed rate according to the dummy average voltage. This makes it possible to change the application cutoff time without changing the existing processing content in the speed adjustment unit.

[0084] (9) The present invention relates to a wire electrical discharge machine, wherein the time changing unit may keep the total time (T4) of the application cutoff time and the pause time (T2) from the time the application cutoff time has elapsed until the application of the induced voltage is restarted constant. This makes it possible to suppress differences in the opportunities for discharge to occur per unit time between the case where the application cutoff time is changed and the case where the application cutoff time is not changed.

[0085] (10) The present invention relates to a wire electrical discharge machining machine, wherein the application control unit applies the induced voltage again after a rest period has elapsed since the application of the induced voltage was stopped, and the time change unit may change the rest period along with the application cutoff time. This makes it possible to increase the amount of adjustment of the average voltage of the induced voltage applied per unit time compared to the case where only the application cutoff time is changed. [Explanation of Symbols]

[0086] 10...Wire EDM machine 12...Wire electrode 50...Voltage application unit 52...Control device 60...Power supply 62...Switching element 64...Voltage detection unit 70...Signal processing unit 72...Storage medium 74...Clock part 76...Application control unit 78...Time change unit 86…Speed ​​adjustment section

Claims

1. A wire electrical discharge machine (10) that processes a workpiece by generating an electrical discharge between the workpiece and the (W) wire electrode (12), A voltage application unit (50) is provided between the electrodes for applying an induced voltage to induce the discharge, An application control unit (76) controls the voltage application unit to repeatedly apply the induced voltage and stop applying the induced voltage, A time changing unit (78) that changes the time for which the induced voltage is applied, Equipped with, The application control unit stops applying the induced voltage if the discharge occurs after the application of the induced voltage has started, or if the application cutoff time (T3) has elapsed without the discharge occurring after the application of the induced voltage has started. The aforementioned time-changing unit changes the application cutoff time in a wire electrical discharge machining machine.

2. A wire electrical discharge machine according to claim 1, The aforementioned time-changing unit changes the application cutoff time based on information indicating the frequency of the discharge occurring in a unit time (UT) in a wire electrical discharge machine.

3. A wire electrical discharge machine according to claim 2, The aforementioned information is the number of discharges occurring per unit time, The application control unit increases the application cutoff time as the number of discharges increases, in a wire electrical discharge machine.

4. A wire electrical discharge machine according to claim 2, The aforementioned information is the integrated discharge delay time (T1) per unit time, from the start of application of the induced voltage until the discharge occurs. The application control unit of the wire electrical discharge machine increases the application cutoff time as the integration time decreases.

5. A wire electrical discharge machine according to claim 1, The aforementioned time-changing unit is a wire electrical discharge machine that changes the application cutoff time based on the machining shape specified in the machining program.

6. A wire electrical discharge machine according to claim 5, A wire electrical discharge machining machine, wherein, when the processed shape is an outer corner, the time adjustment unit shortens the applied cutoff time as the radius of curvature decreases, and when the processed shape is an inner corner, the time adjustment unit lengthens the applied cutoff time as the radius of curvature decreases.

7. A wire electrical discharge machine according to claim 1, The aforementioned time-changing unit changes the application cutoff time based on the degree of straightness accuracy selected by the operator in a wire electrical discharge machine.

8. A wire electrical discharge machine according to any one of claims 1 to 7, The system includes a speed adjustment unit that adjusts the feed rate of the relative position between the workpiece and the wire electrode, The time modification unit calculates a dummy average voltage based on the average voltage of the induced voltage applied per unit time and a reference value for the application cutoff time, assuming that the application cutoff time is not changed. The speed adjustment unit controls the feed rate according to the dummy average voltage in a wire electrical discharge machine.

9. A wire electrical discharge machine according to any one of claims 1 to 8, The time-changing unit maintains a constant total time (T4) consisting of the application cutoff time and the pause time (T2) from the time the application cutoff time has elapsed until the application of the induced voltage is restarted.

10. A wire electrical discharge machine according to any one of claims 1 to 9, The application control unit, after a rest period has elapsed since the application of the induced voltage was stopped, reapplies the induced voltage. The aforementioned time-changing unit changes the pause time along with the application cutoff time in a wire electrical discharge machining machine.

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