Control device for wire electric discharge machine and control method for electric discharge machining

Abstract

This control device for a wire electric discharge machine includes: a movement control unit that causes a wire electrode to move along a machining path; a voltage control unit that controls a machining power supply and applies a machining voltage across poles; and a machining control unit that maintains a non-discharge state in which discharge does not occur between the poles until the wire electrode reaches a first position on the machining path, that, upon the wire electrode reaching the first position, gradually increases the discharge density so that the discharge density of the discharge becomes a set value set as a machining condition, and that, upon the wire electrode reaching the first position again, gradually decreases the discharge density to achieve a non-discharge state.

Description

Wire electric discharge machine control device and electric discharge machining control method

[0001] The present disclosure relates to a control device for a wire electric discharge machine and a control method for electric discharge machining.

[0002] When a workpiece is subjected to finish machining using a wire electric discharge machine, overmachining is likely to occur. Japanese Patent Application Laid-Open No. 2011-83866 discloses a technique that can prevent overmachining from occurring.

[0003] There is a demand for a method for more effectively suppressing overmachining in finish machining of a workpiece using a wire electric discharge machine.

[0004] A first aspect of the present disclosure is a control device for a wire electric discharge machine that machines a workpiece by generating an electric discharge between electrodes of a wire electrode and the workpiece while moving the wire electrode along a machining path relative to the workpiece, the control device comprising: a movement control unit that moves the wire electrode along the machining path in accordance with a machining program; a voltage control unit that controls a machining power supply in accordance with machining conditions to apply a machining voltage between the electrodes; and a machining control unit that controls at least the voltage control unit of the movement control unit and the voltage control unit to maintain a non-discharge state in which no electric discharge occurs between the electrodes until the wire electrode reaches a first position on the machining path, gradually increase the electric discharge density of the electric discharges when the wire electrode reaches the first position so that the electric discharge density becomes a set value set as the machining condition, and gradually decrease the electric discharge density when the wire electrode reaches the first position again to return the non-discharge state between the electrodes.

[0005] A second aspect of the present disclosure is a control method for electric discharge machining by a control device of a wire electric discharge machine that machines a workpiece by moving a wire electrode along a machining path relative to the workpiece and generating an electric discharge between the electrodes of the wire electrode and the workpiece, the method including: a movement control step of moving the wire electrode along the machining path in accordance with a machining program; a voltage control step of controlling a machining power supply in accordance with machining conditions to apply a machining voltage between the electrodes; and a machining control step of maintaining a non-discharge state in which no electric discharge occurs between the electrodes until the wire electrode reaches a first position on the machining path, gradually increasing the discharge density of the electric discharges so that the discharge density becomes a set value set as the machining condition when the wire electrode reaches the first position again, and gradually decreasing the discharge density to bring the non-discharge state between the electrodes.

[0006] FIG. 1 is a diagram illustrating overmachining that can occur when a wire electrode moves through a position where an approach section, an escape section, and a machining path connect during finish machining. FIG. 2 is a diagram schematically illustrating the configuration of a control device for a wire electric discharge machine. FIG. 3 is a diagram illustrating an example of a machining path for finish machining and a predetermined section on the machining path. FIG. 4A is a graph showing changes in electrical discharge density between electrodes as the wire electrode moves. FIG. 4B is a graph showing the machining amount for each position of the wire electrode on the machining path. FIG. 5A is a diagram illustrating a pulse voltage applied to the machining path and a pause time in voltage application. FIG. 5B is a diagram illustrating the relationship between the pause time, electrical discharge density, and machining amount. FIG. 6 is a flowchart illustrating a procedure for electrical discharge machining control. FIG. 7 is a diagram illustrating the relationship between the moving speed of the wire electrode, electrical discharge density, and machining amount. FIG. 8 is a flowchart illustrating a procedure for electrical discharge machining control. FIG. 9 is a diagram illustrating a machining path for finish machining and a predetermined section on the machining path.

[0007] The wire electric discharge machine performs rough machining on a workpiece to remove a core from the workpiece, and then performs finish machining on the workpiece. Fig. 1 is a diagram for explaining overmachining that can occur during finish machining when a wire electrode E moves through a position Po where an approach section, an escape section (section Mc), and a machining path Rt are connected.

[0008] 1 shows a plan view of a workpiece W after rough machining. A core is removed in the rough machining, forming a hole H in the workpiece W. In finish machining after the rough machining, a wire electrode E of a wire electric discharge machine moves relative to the workpiece W along a machining path Rt on the inside of the hole H. The machining path Rt is determined along a machining surface Sp of the workpiece W that surrounds the hole H.

[0009] Before moving along the machining path Rt, the wire electrode E moves from the movement start position Ps to a position Po on the machining path Rt through a section Mc between the movement start position Ps included in the hole H and a position Po on the machining path Rt. In other words, the section Mc is used as an approach section from the movement start position Ps to the machining path Rt.

[0010] When the wire electrode E reaches the position Po, it moves from the position Po along the machining path Rt in a clockwise movement direction D. While the wire electrode E moves along the machining path Rt, an electric discharge occurs between the machining surface Sp and the wire electrode E. The workpiece W is subjected to a finish machining by this electric discharge.

[0011] After moving along the machining path Rt, the wire electrode E moves through a section Mc from the position Po to the movement start position Ps. That is, the section Mc is also used as an escape section from the position Po to the movement start position Ps.

[0012] When the disclosure of the above-mentioned Japanese Patent Application Laid-Open No. 2011-83866 is applied to the example shown in Fig. 1, discharge is turned off in the section Mc, which is the approach section and the escape section. Therefore, discharge is not performed while the wire electrode E is moving through the section Mc. The wire electrode E changes its moving direction at the position Po and moves along the machining path Rt.

[0013] After moving through the approach section (section Mc), the wire electrode E reaches position Po. At position Po, the movement direction of the wire electrode E is changed. The wire electrode E moves from position Po along the machining path Rt in movement direction D. The movement speed of the wire electrode E moving in movement direction D on the machining path Rt is low at position Po and gradually increases as the wire electrode E moves away from position Po. Because the movement speed of the wire electrode E at position Po is low, over-machining may occur in a region Spo facing position Po on the machining surface Sp before finish machining.

[0014] The wire electrode E moves along the machining path Rt in a movement direction D and reaches a position Po. At position Po, the movement direction of the wire electrode E changes. The wire electrode E moves through an escape section (section Mc) from position Po to a movement start position Ps. The movement speed of the wire electrode E moving in the movement direction D on the machining path Rt gradually decreases as the wire electrode E approaches position Po, and is low at position Po. Because the movement speed of the wire electrode E at position Po is low, overmachining may occur in the above-mentioned region Spo.

[0015] Furthermore, discharge occurs both times near the position Po where the wire electrode E passes twice. Therefore, overmachining may occur in the above-mentioned region Spo. As a result of overmachining occurring in the region Spo during finish machining, the partially machined surface So facing the position Po may be formed deeper than the machined surface Sp other than the partially machined surface So. In this case, the machining accuracy of the finish machining decreases.

[0016] An embodiment of a control device for a wire electric discharge machine that can prevent the occurrence of the above-mentioned overmachining will be described below. Figure 2 is a diagram schematically showing the configuration of a control device 20 for a wire electric discharge machine 10. The wire electric discharge machine 10 machines a workpiece W under the control of the control device 20.

[0017] The wire electric discharge machine 10 machines the workpiece W by generating an electric discharge between the wire electrode E and the workpiece W placed on the table B while moving the wire electrode E relative to the workpiece W along the machining path Rt. The wire electrode E can be moved relative to the workpiece W by moving either the wire electrode E or the table B relative to the other. An electric discharge between the electrodes can be generated by applying a machining voltage between the electrodes in accordance with the control of the machining power supply 30 by the control device 20.

[0018] The control device 20 controls the wire electric discharge machine 10. The control device 20 has a calculation unit 40 and a storage unit 42. The calculation unit 40 includes a processor such as a CPU (Central Processing Unit) or a GPU (Graphics Processing Unit). In other words, the calculation unit 40 includes a processing circuit.

[0019] The storage unit 42 includes volatile memory such as RAM (Random Access Memory) and non-volatile memory such as ROM (Read Only Memory) or flash memory. The volatile memory is used as working memory for the processor. The non-volatile memory stores control programs executed by the processor and other necessary information. The machining programs and machining conditions generated for the wire electric discharge machine 10 to machine the workpiece W are also stored in the non-volatile memory of the storage unit 42.

[0020] The calculation unit 40 has a movement control unit 50, a voltage control unit 52, and a processing control unit 54. The movement control unit 50, the voltage control unit 52, and the processing control unit 54 are realized by the calculation unit 40 executing a control program stored in the storage unit 42. At least a portion of the movement control unit 50, the voltage control unit 52, and the processing control unit 54 may be realized by an integrated circuit such as an ASIC (Application Specific Integrated Circuit) or an FPGA (Field Programmable Gate Array), or an electronic circuit including a discrete device.

[0021] The movement control unit 50 moves the wire electrode E along the machining path Rt in accordance with the machining program. The wire electrode E moves relative to the workpiece W. The machining path Rt includes at least one of a straight section and a curved section. In this embodiment, as will be described later with reference to FIG. 3 , the machining path Rt includes a curved section.

[0022] The movement control unit 50 moves the wire electrode E along the approach section before moving the wire electrode E along the machining path Rt. After moving the wire electrode E along the machining path Rt, the movement control unit 50 moves the wire electrode E along the escape section. The approach section and escape section in this embodiment will be described later with reference to FIG. 3. The movement control unit 50 moves the wire electrode E at a movement speed specified in the machining program.

[0023] The voltage control unit 52 controls the machining power supply 30 in accordance with the machining conditions to apply a machining voltage between the wire electrode E and the workpiece W. This allows discharge to occur between the electrodes. As will be described later with reference to FIG. 5A , the machining voltage is realized by combining a periodically repeated pulse voltage with a rest time between the application of the pulse voltage. The discharge density Y of the discharge between the electrodes can be changed by changing the magnitude, pulse width, pulse period (or number of pulses), or rest time of the pulse voltage.

[0024] The machining control unit 54 controls the movement control unit 50 and the voltage control unit 52 to generate discharge between the wire electrode E and the workpiece W, thereby machining the workpiece W. In this embodiment, the machining control unit 54 controls the voltage control unit 52 to change the rest time while the wire electrode E moves through a predetermined section on the machining path Rt, thereby gradually changing the discharge density Y of the above-mentioned discharge. The predetermined section will be described later with reference to FIG. 3 .

[0025] Fig. 3 is a diagram illustrating a machining path Rt for finish machining and a predetermined section Rs on the machining path Rt. Fig. 3 shows a plan view of a workpiece W having a hole H after rough machining. In finish machining, the wire electrode E of the wire electric discharge machine 10 moves relative to the workpiece W along the machining path Rt inside the hole H. The machining path Rt is determined along the machining surface Sp of the workpiece W that surrounds the hole H. In the example shown in Fig. 3, the machining path Rt includes a curved section Rtc.

[0026] Before moving along the machining path Rt, the wire electrode E moves through an approach section Ma from a movement start position Ps included in the hole H to a position Po on the machining path Rt. Hereinafter, the position Po on the machining path Rt will be referred to as a third position Po.

[0027] The movement control unit 50 moves the wire electrode E from the movement start position Ps to the third position Po in a non-discharge state in which no discharge occurs between the wire electrode E and the workpiece W. The non-discharge state is achieved by setting the discharge density Y of the discharge to zero. The control for setting the discharge density Y to zero will be described later with reference to FIG. 5B.

[0028] After moving through the approach section Ma, the wire electrode E reaches the third position Po without discharging. At the third position Po, the movement direction of the wire electrode E is changed. The movement control unit 50 moves the wire electrode E from the third position Po in a movement direction D along the machining path Rt without discharging. In this embodiment, the movement direction D is clockwise as shown in FIG. 3, but it may also be counterclockwise.

[0029] Since the wire electrode E is in a non-discharge state at and near the third position Po, no machining is performed in the region Spo facing the third position Po on the machining surface Sp before finish machining, and therefore no overmachining occurs. Hereinafter, machining of the workpiece W performed in the region Spo will be simply referred to as machining of the workpiece W at the third position Po. In other words, the machining amount A of the workpiece W at the third position Po is zero.

[0030] The movement control unit 50 moves the wire electrode E on the machining path Rt in a movement direction D from a third position Po on the machining path Rt toward a first position Pa on the machining path Rt. The first position Pa is a position away from the third position Po along the machining path Rt in the movement direction D of the wire electrode E. Until the wire electrode E reaches the first position Pa, the machining control unit 54 controls the voltage control unit 52 to maintain a non-discharge state. Therefore, the machining amount A of the workpiece W while the wire electrode E moves from the third position Po to the first position Pa is zero.

[0031] When the wire electrode E reaches the first position Pa, the machining control unit 54 controls the voltage control unit 52 to gradually increase the discharge density Y from zero while the wire electrode E moves through a predetermined section Rs. The predetermined section Rs is a section on the machining path Rt from the first position Pa to the second position Pb, both of which are on the machining path Rt.

[0032] The machining control unit 54 controls the voltage control unit 52 to gradually increase the discharge density Y so that the discharge density Y reaches the set value Yn set as a machining condition when the wire electrode E reaches the second position Pb.

[0033] Therefore, as the wire electrode E moves within the predetermined section Rs, discharge may occur between the electrodes. That is, the workpiece W may be machined at each position within the predetermined section Rs. The machining amount A of the workpiece W at each position within the predetermined section Rs gradually increases in accordance with the increase in discharge density Y as the wire electrode E moves from the first position Pa to the second position Pb. Note that the machining amount A of the workpiece W at each position within the predetermined section Rs refers to the machining amount of the workpiece W performed in each region on the machining surface Sp facing each position within the predetermined section Rs.

[0034] After moving through the predetermined section Rs, the wire electrode E moves on the machining path Rt, passes through the third position Po again, and reaches the first position Pa again. From the time the wire electrode E reaches the second position Pb, passes through the third position Po again, and reaches the first position Pa again, the machining control unit 54 controls the voltage control unit 52 to maintain the discharge density Y at the set value Yn set as a machining condition.

[0035] When the discharge density Y is maintained at the set value Yn, the machining amount A of the workpiece W is a constant amount An. Therefore, the machining amount A of the workpiece W at each position on the machining path Rt from the second position Pb to the first position Pa is a constant amount An. Note that the machining amount A of the workpiece W at each position on the machining path Rt from the second position Pb to the first position Pa refers to the machining amount of the workpiece W due to machining performed in each region on the machining surface Sp facing each position.

[0036] As described above, the machining amount A of the workpiece W at each position on the machining path Rt from the third position Po to the first position Pa was zero the previous time the wire electrode E passed through the section from the third position Po to the first position Pa. When the wire electrode E passes through the section again this time, the machining amount A is a constant amount An. Therefore, the total of the machining amounts A of the workpiece W at each position in the section is the constant amount An.

[0037] When the wire electrode E reaches the first position Pa again, the machining control unit 54 controls the voltage control unit 52 to gradually decrease the discharge density Y from the set value Yn to zero while the wire electrode E moves again through the predetermined section Rs. That is, the machining control unit 54 controls the voltage control unit 52 to gradually decrease the discharge density Y to bring the gap between the electrodes into a non-discharge state.

[0038] As the wire electrode E moves again within the predetermined section Rs, discharge may occur again between the electrodes. That is, machining of the workpiece W may be performed again at each position within the predetermined section Rs. The machining amount A of the workpiece W at each position within the predetermined section Rs gradually decreases in accordance with the decrease in discharge density Y as the wire electrode E moves again from the first position Pa to the second position Pb.

[0039] The wire electrode E moves again through the predetermined section Rs and then reaches the second position Pb again. When the wire electrode E reaches the second position Pb again, the discharge density Y returns to zero. The movement direction of the wire electrode E is changed at the second position Pb. The movement control unit 50 moves the wire electrode E from the second position Pb to the movement start position Ps in a non-discharge state. That is, the wire electrode E moves along the machining path Rt, and then moves through the escape section Me from the second position Pb to the movement start position Ps.

[0040] 3, the wire electrode E moves in a non-discharge state between the third position Po and the first position Pa, which is spaced apart from the third position Po along the machining path Rt in the moving direction D of the wire electrode E. Therefore, no overmachining occurs at the third position Po where the moving direction of the wire electrode E changes.

[0041] 4A is a graph showing a change in the discharge density Y between the electrodes accompanying the movement of the wire electrode E. When the position P of the wire electrode E is included in the approach section Ma from the movement start position Ps to the third position Po, a no-discharge state is maintained and therefore the discharge density Y is zero.

[0042] The discharge density Y is zero because the no-discharge state is maintained even when the position P of the wire electrode E is included in the section on the machining path Rt from the third position Po to the first position Pa. When the wire electrode E moves from the first position Pa to the second position Pb, the discharge density Y gradually increases from zero to the set value Yn described above.

[0043] When the position P of the wire electrode E is included in the section on the machining path Rt that starts from the second position Pb, passes through the third position Po, and then returns to the first position Pa, the discharge density Y is maintained at the set value Yn. When the wire electrode E moves again from the first position Pa to the second position Pb, the discharge density Y gradually decreases from the set value Yn to zero. When the position P of the wire electrode E reaches the second position Pb, the gap becomes non-dischargeable.

[0044] When the position P of the wire electrode E is included in the escape section Me from the second position Pb to the movement start position Ps, the discharge density Y is zero because a non-discharge state is maintained.

[0045] As described with reference to FIG. 4A , the machining control unit 54 maintains the no-discharge state until the wire electrode E reaches the first position Pa. When the wire electrode E reaches the first position Pa, the machining control unit 54 gradually increases the discharge density Y so that the discharge density Y reaches the set value Yn. The discharge density Y gradually increases while the wire electrode E moves through a predetermined section Rs from the first position Pa to the second position Pb. When the wire electrode E reaches the second position Pb, the discharge density Y reaches the set value Yn.

[0046] The discharge density Y is maintained at the set value Yn from when the wire electrode E reaches the second position Pb until when the wire electrode E reaches the first position Pa again. When the wire electrode E reaches the first position Pa again, the machining control unit 54 gradually reduces the discharge density Y to bring the gap between the electrodes into a non-discharge state.

[0047] Therefore, the moving direction of the wire electrode E while it is moving through the first position Pa at the start of discharge does not change at the first position Pa. The change in the discharge density Y is gradual in the predetermined section Rs after the start of discharge. Furthermore, the first position Pa of the wire electrode E where discharge starts and the second position Pb of the wire electrode E where discharge ends are different from each other. Therefore, overmachining is unlikely to occur.

[0048] 4B is a graph showing the machining amount A for each position P of the wire electrode E on the machining path Rt. When the position P of the wire electrode E is included in the approach section Ma and the escape section Me, machining of the workpiece W is not performed. Therefore, the graph shown in FIG. 4B shows the machining amount A when the position P of the wire electrode E is included in the machining path Rt. The machining amount A of the workpiece W at each position in sections other than the predetermined section Rs on the machining path Rt is a constant amount An because the discharge density Y is maintained at the set value Yn.

[0049] 4B shows a first machining amount A1 of the machining amount A of the workpiece W at each position P within the predetermined section Rs when the discharge density Y increases in the predetermined section Rs. The first machining amount A1 gradually increases in accordance with the increase in the discharge density Y that accompanies the movement of the wire electrode E from the first position Pa to the second position Pb.

[0050] 4B shows the second machining amount A2 of the workpiece W at each position P within the predetermined section Rs when the discharge density Y decreases in the predetermined section Rs. The second machining amount A2 gradually decreases in accordance with the decrease in the discharge density Y caused by the movement of the wire electrode E from the first position Pa to the second position Pb again.

[0051] As described above, the machining control unit 54 controls the voltage control unit 52 to control the increase and decrease of the discharge density Y. At that time, the increase and decrease of the discharge density Y are controlled so that the total machining amount of the first machining amount A1 and the second machining amount A2 becomes approximately the above-mentioned constant amount An. In the example shown in FIG. 4B , when the position P of the wire electrode E is at an arbitrary position Px within the predetermined section Rs, the first machining amount A1 takes a value A1x and the second machining amount A2 takes a value A2x. The sum of the value A1x and the value A2x becomes the constant amount An.

[0052] As explained using Figure 4B, the total machining amount of the first machining amount A1 when the discharge density Y increases in the predetermined section Rs and the second machining amount A2 when the discharge density Y decreases in the predetermined section Rs is approximately a constant amount An. In sections of the machining path Rt other than the predetermined section Rs, the discharge density Y is maintained at the set value Yn. The machining amount A of the workpiece W when the discharge density Y is maintained at the set value Yn is also a constant amount An. Therefore, it is possible to prevent over-machining from occurring over the entire machining surface Sp.

[0053] 5A is a diagram illustrating the pulse voltage Cv applied to the gap between the machining positions and the pause time Tp of the voltage application. The machining voltage applied to the gap between the machining positions is realized by combining the periodically repeated pulse voltage Cv and the pause time Tp of the application of the pulse voltage Cv. The voltage control unit 52 applies the pulse voltage Cv from the machining power supply 30 to the gap between the machining positions except during the pause time Tp. The voltage control unit 52 pauses the application of the pulse voltage Cv to the gap between the machining positions during the pause time Tp. In this way, the voltage control unit 52 can apply the machining voltage to the gap between the machining positions.

[0054] The discharge density Y of the discharge between the electrodes can be changed by changing the magnitude Vi of the pulse voltage Cv, the pulse width Cw of the pulse voltage Cv, the cycle Ct of the pulse voltage Cv, or the pause time Tp. In this embodiment, the machining control unit 54 controls the voltage control unit 52 to change the pause time Tp, thereby changing the discharge density Y of the discharge between the electrodes.

[0055] 5B is a diagram showing the relationship between the pause time Tp, the discharge density Y, and the machining amount A. When the discharge density Y is increased to a set value Yn, the machining control unit 54 controls the voltage control unit 52 to shorten the pause time Tp to a set time Tpn. As the discharge density Y increases, the machining amount A increases to a certain amount An. The set time Tpn is determined in advance by experimentation according to the set value Yn of the discharge density Y, which is set as a machining condition.

[0056] In order to maintain the discharge density Y at the set value Yn, the machining control unit 54 controls the voltage control unit 52 to maintain the pause time Tp at the set time Tpn. The machining amount A is a constant amount An. When the discharge density Y is to be reduced, the machining control unit 54 controls the voltage control unit 52 to extend the pause time Tp. As the discharge density Y is reduced, the machining amount A is reduced.

[0057] Assume that the machining control unit 54 controls the voltage control unit 52 to extend the pause time Tp, so that the pause time Tp reaches the predetermined time Tp0. In this case, the machining voltage drops to a level at which no discharge occurs between the electrodes. Therefore, the machining control unit 54 controls the voltage control unit 52 to make the pause time Tp equal to or longer than the predetermined time Tp0, thereby making it possible to make the discharge density Y zero. Since the discharge density Y is zero, the machining amount A is also zero. The predetermined time Tp0 is determined in advance through experimentation.

[0058] 6 is a flowchart illustrating a processing procedure for controlling electric discharge machining. This processing procedure is performed by the calculation unit 40 of the control device 20 executing a control program stored in the storage unit 42 in order to perform finish machining on the workpiece W. When this processing procedure is started, in step S1, the machining control unit 54 controls the voltage control unit 52 to set the pause time Tp in the application of the pulse voltage Cv to a predetermined time Tp0 and apply a machining voltage to the machining gap.

[0059] In step S2, the movement control unit 50 moves the wire electrode E from the movement start position Ps along the approach section Ma in a non-discharge state. In step S3, the movement control unit 50 determines whether the wire electrode E has reached a third position Po on the machining path Rt. If the result in step S3 is YES, the process proceeds to step S4. If the result in step S3 is NO, the process returns to step S3.

[0060] In step S4, the movement control unit 50 moves the wire electrode E from the third position Po in the movement direction D on the machining path Rt while maintaining the non-discharge state. In step S5, the movement control unit 50 determines whether the wire electrode E has reached the first position Pa on the machining path Rt. If the result of step S5 is YES, the process proceeds to step S6. If the result of step S5 is NO, the process returns to step S5.

[0061] In step S6, the machining control unit 54 controls the voltage control unit 52 to gradually shorten the pause time Tp of the application of the pulse voltage Cv to the set time Tpn. In step S7, the movement control unit 50 determines whether the wire electrode E has reached the second position Pb on the machining path Rt. If the answer is YES in step S7, the process proceeds to step S8. If the answer is NO in step S7, the process returns to step S6.

[0062] In step S8, the machining control unit 54 controls the voltage control unit 52 to stop shortening the pause time Tp of the application of the pulse voltage Cv. The pause time Tp is maintained at the set time Tpn. The discharge density Y is maintained at the set value Yn, and the machining amount A becomes a constant amount An. The movement of the wire electrode E continues thereafter.

[0063] In step S9, the movement control unit 50 determines whether the wire electrode E has reached the first position Pa on the machining path Rt again. If the result of step S9 is YES, the process proceeds to step S10. If the result of step S9 is NO, the process returns to step S9.

[0064] In step S10, the machining control unit 54 controls the voltage control unit 52 to gradually extend the pause time Tp of the application of the pulse voltage Cv to a predetermined time Tp0. In step S11, the movement control unit 50 determines whether the wire electrode E has reached the second position Pb on the machining path Rt again. If the answer is YES in step S11, the process proceeds to step S12. If the answer is NO in step S11, the process returns to step S10.

[0065] In step S12, the machining control unit 54 controls the voltage control unit 52 to stop extending the pause time Tp of the application of the pulse voltage Cv. The pause time Tp is maintained at a predetermined time Tp0. Even when the wire electrode E is located at the second position Pb, the gap between the electrodes is in a non-discharge state. The discharge density Y is maintained at zero, and the machining amount A also becomes zero.

[0066] In step S13, the movement control unit 50 moves the wire electrode E from the second position Pb to the movement start position Ps in a non-discharge state. When the process of step S13 is completed, this processing procedure ends.

[0067] In this embodiment, the discharge density Y of the discharge between the electrodes is changed by changing the pause time Tp of the application of the pulse voltage Cv, so that the occurrence of overmachining can be easily suppressed.

[0068] The above-described embodiment may be modified as follows: In the following modifications, explanations that overlap with the embodiment will be omitted.

[0069] (Variation 1) In the above-described embodiment, the machining voltage applied between the electrodes by the voltage control unit 52 is realized by a combination of a periodically repeated pulse voltage Cv and a rest time Tp in the application of the pulse voltage Cv. The machining control unit 54 controls the voltage control unit 52 to gradually change the rest time Tp while the wire electrode E moves through a predetermined section Rs on the machining path Rt, thereby gradually changing the discharge density Y of the discharge between the electrodes.

[0070] However, the machining control unit 54 may gradually change the discharge density Y of the discharge between the electrodes by controlling the movement control unit 50 to gradually change the movement speed of the wire electrode E while the wire electrode E moves through a predetermined section Rs on the machining path Rt. Fig. 7 is a diagram showing the relationship between the movement speed Z of the wire electrode E, the discharge density Y, and the machining amount A.

[0071] When the discharge density Y is increased, the machining control unit 54 controls the voltage control unit 52 to change the pause time Tp to a set time Tpz that is shorter than the predetermined time Tp0. This may cause discharge between the electrodes. The machining control unit 54 controls the movement control unit 50 to reduce the movement speed Z of the wire electrode E from a first speed Z1 to a second speed Z2. As the discharge density Y increases, the machining amount A increases. Note that the value of the movement speed Z corresponding to the discharge density Y and the set time Tpz of the pause time Tp are determined in advance through experiments.

[0072] When the discharge density Y is to be reduced, the machining control unit 54 controls the movement control unit 50 to increase the movement speed Z of the wire electrode E from the second speed Z2 to the first speed Z1. As the discharge density Y is reduced, the machining amount A is reduced. The machining control unit 54 controls the voltage control unit 52 to change the pause time Tp to a predetermined time Tp0. The value of the movement speed Z corresponding to the discharge density Y is determined in advance by experiment.

[0073] 8 is a flowchart illustrating a processing procedure for controlling electric discharge machining. This processing procedure is performed by the calculation unit 40 of the control device 20 executing a control program stored in the storage unit 42 for finish machining of the workpiece W. Steps similar to those described above with reference to FIG. 6 are given the same reference numerals, and descriptions thereof will be omitted where appropriate.

[0074] If step S5 is YES, the process proceeds to step S31. If step S5 is NO, the process returns to step S5. In step S31, the machining control unit 54 controls the voltage control unit 52 to change the pause time Tp of the application of the pulse voltage Cv to a set time Tpz. In step S32, the machining control unit 54 controls the movement control unit 50 to gradually reduce the movement speed Z of the wire electrode E from the first speed Z1 to the second speed Z2. When the process of step S32 is completed, the process proceeds to step S7.

[0075] If step S7 is YES, the process proceeds to step S33. If step S7 is NO, the process returns to step S31. In step S33, the machining control unit 54 controls the movement control unit 50 to stop the decrease in the movement speed Z of the wire electrode E. The movement speed Z is maintained at the second speed Z2. The discharge density Y is maintained at the set value Yn, and the machining amount A becomes a constant amount An. The movement of the wire electrode E continues thereafter. When the processing of step S33 is completed, the process proceeds to step S9.

[0076] If step S9 is YES, the process proceeds to step S34. If step S9 is NO, the process returns to step S9. In step S34, the machining control unit 54 controls the movement control unit 50 to gradually increase the movement speed Z of the wire electrode E from the second speed Z2 to the first speed Z1. When the process of step S34 is completed, the process proceeds to step S11.

[0077] If step S11 is YES, the process proceeds to step S35. If step S11 is NO, the process returns to step S34. In step S35, the machining control unit 54 controls the voltage control unit 52 to change the pause time Tp of the application of the pulse voltage Cv to a predetermined time Tp0. When the process of step S35 is completed, the process proceeds to step S13.

[0078] In the present modified example 1, the discharge density Y of the discharge between the electrodes is changed by changing the moving speed Z of the wire electrode E. Therefore, the occurrence of overmachining can be easily suppressed.

[0079] (Variation 2) In the above-described embodiment, the machining path Rt includes a curved section Rtc. However, the machining path Rt may also include a straight section. Fig. 9 is a diagram illustrating an example of a machining path Rt for finish machining and a predetermined section Rs on the machining path Rt. Fig. 9 shows a plan view of a workpiece W having a hole H after rough machining.

[0080] In finish machining, the wire electrode E of the wire electric discharge machine 10 moves relative to the workpiece W along a machining path Rt inside the hole H. The machining path Rt is determined along the machining surface Sp of the workpiece W that surrounds the hole H. The machining path Rt includes a straight section Rti.

[0081] Before moving along the machining path Rt, the wire electrode E moves through an approach section Ma from a movement start position Ps included in the hole H to a third position Po on the machining path Rt. The movement control unit 50 moves the wire electrode E from the movement start position Ps to the third position Po in a non-discharge state in which no discharge occurs between the wire electrode E and the workpiece W.

[0082] After moving through the approach section Ma, the wire electrode E reaches the third position Po while remaining in a non-discharge state. At the third position Po, the movement direction of the wire electrode E is changed. The movement control unit 50 moves the wire electrode E from the third position Po in a movement direction D along the machining path Rt while remaining in a non-discharge state. In this modified example 2, the movement direction D is counterclockwise as shown in FIG. 9 , but it may also be clockwise. The machining amount A of the workpiece W at the third position Po is zero.

[0083] The movement control unit 50 moves the wire electrode E on the machining path Rt in a movement direction D from a third position Po on the machining path Rt toward a first position Pa on the machining path Rt. The first position Pa is a position away from the third position Po along the machining path Rt in the movement direction D of the wire electrode E. Until the wire electrode E reaches the first position Pa, the machining control unit 54 controls the voltage control unit 52 to maintain a non-discharge state. Therefore, the machining amount A of the workpiece W while the wire electrode E moves from the third position Po to the first position Pa is zero.

[0084] When the wire electrode E reaches the first position Pa, the machining control unit 54 controls the voltage control unit 52 to gradually increase the discharge density Y from zero while the wire electrode E moves through the predetermined section Rs. The machining control unit 54 controls the voltage control unit 52 to gradually increase the discharge density Y so that the discharge density Y becomes the set value Yn set as a machining condition when the wire electrode E reaches the second position Pb.

[0085] Therefore, machining of the workpiece W can be performed at each position within the predetermined section Rs. The first machining amount A1 of the workpiece W at each position within the predetermined section Rs gradually increases in accordance with the increase in the discharge density Y accompanying the movement of the wire electrode E from the first position Pa to the second position Pb.

[0086] After moving through the predetermined section Rs, the wire electrode E moves on the machining path Rt, passes through the third position Po again, and reaches the first position Pa again. From the time the wire electrode E reaches the second position Pb, passes through the third position Po again, and reaches the first position Pa again, the machining control unit 54 controls the voltage control unit 52 to maintain the discharge density Y at the set value Yn set as a machining condition.

[0087] When the discharge density Y is maintained at the set value Yn, the machining amount A of the workpiece W is a constant amount An. Therefore, the machining amount A of the workpiece W at each position on the machining path Rt from the second position Pb to the first position Pa is a constant amount An. The machining amount A of the workpiece W at each position on the machining path Rt from the third position Po to the first position Pa is also a constant amount An.

[0088] When the wire electrode E reaches the first position Pa again, the machining control unit 54 controls the voltage control unit 52 to gradually decrease the discharge density Y from the set value Yn to zero while the wire electrode E moves again through the predetermined section Rs. That is, the machining control unit 54 controls the voltage control unit 52 to gradually decrease the discharge density Y to bring the gap between the electrodes into a non-discharge state.

[0089] As the wire electrode E moves again within the predetermined section Rs, machining of the workpiece W can be performed again at each position within the predetermined section Rs. The second machining amount A2 of the workpiece W at each position within the predetermined section Rs gradually decreases in accordance with the decrease in the discharge density Y as the wire electrode E moves again from the first position Pa to the second position Pb. The total machining amount of the first machining amount A1 and the second machining amount A2 is approximately the constant amount An described above.

[0090] The wire electrode E moves again through the predetermined section Rs and then reaches the second position Pb again. When the wire electrode E reaches the second position Pb again, the discharge density Y returns to zero. The movement direction of the wire electrode E is changed at the second position Pb. The movement control unit 50 moves the wire electrode E from the second position Pb to the movement start position Ps in a non-discharge state. That is, the wire electrode E moves along the machining path Rt, and then moves through the escape section Me from the second position Pb to the movement start position Ps.

[0091] In the present modified example 2, the machining route Rt includes at least one of a curved section Rtc and a straight section Rti. Therefore, regardless of the section shape of the machining route Rt, it is possible to suppress the occurrence of over-machining.

[0092] The above-described first and second modifications may be combined as appropriate within a range that does not cause a contradiction.

[0093] At least one of the above-described embodiments and modifications can more effectively prevent over-machining from occurring when the wire electric discharge machine 10 finishes the workpiece W.

[0094] The following additional notes are disclosed regarding the above-described embodiment and modifications.

[0095] (Supplementary Note 1) A control device (20) of the present disclosure is a control device for a wire electric discharge machine (10) that machines a workpiece (W) by generating an electric discharge between electrodes of the wire electrode and the workpiece while moving the wire electrode (E) along a machining path (Rt) relative to the workpiece (W), and includes: a movement control unit (50) that moves the wire electrode along the machining path in accordance with a machining program; a voltage control unit (52) that controls a machining power supply (30) in accordance with machining conditions to apply a machining voltage between the electrodes; and a machining control unit (54) that controls at least the voltage control unit of the movement control unit and the voltage control unit to maintain a non-discharge state in which no electric discharge occurs between the electrodes until the wire electrode reaches a first position (Pa) on the machining path, gradually increase a discharge density (Y) of the discharges when the wire electrode reaches the first position so that the discharge density (Y) becomes a set value (Yn) set as the machining condition, and gradually decrease the discharge density when the wire electrode reaches the first position again to bring the non-discharge state between the electrodes.

[0096] (Supplementary Note 2) In the control device for a wire electric discharge machine described in Supplementary Note 1, the machining control unit may gradually increase the discharge density while the wire electrode moves through a predetermined section (Rs) from the first position to a second position (Pb) on the machining path, the machining control unit controls at least one of the movement control unit and the voltage control unit to maintain the discharge density at the set value from the time the wire electrode reaches the second position until it reaches the first position again, and the machining control unit may gradually decrease the discharge density while the wire electrode moves again through the predetermined section from the first position to the second position where it has reached again.

[0097] (Supplementary Note 3) In the control device for a wire electric discharge machine described in Supplementary Note 2, the machining control unit may control the increase and decrease of the discharge density so that the total machining amount (A) of the workpiece at each position (P) within the predetermined section, consisting of a first machining amount (A1) when the discharge density increases in the predetermined section and a second machining amount (A2) when the discharge density decreases in the predetermined section, is the machining amount corresponding to the machining amount of the workpiece when the discharge density is maintained at the set value.

[0098] (Appendix 4) In the control device for a wire electric discharge machine described in Appendix 1, the movement control unit may move the wire electrode in the non-discharge state from a movement start position (Ps) of the wire electrode to a third position (Po) on the machining path, and the first position may be a position away from the third position in the movement direction (D) of the wire electrode along the machining path.

[0099] (Supplementary Note 5) In the control device for a wire electric discharge machine described in any one of Supplementary Notes 1 to 4, the voltage control unit may apply a pulse voltage (Cv) from a machining power supply to the gap except during a pause time (Tp), and may apply the machining voltage to the gap by pausing the application of the pulse voltage to the gap during the pause time, and in the non-discharge state, the machining control unit may control the voltage control unit to set the pause time to a predetermined time (Tp0) or more, thereby setting the discharge density to zero.

[0100] (Supplementary Note 6) In the control device for a wire electric discharge machine described in Supplementary Note 5, when the discharge density is increased, the machining control unit may control the voltage control unit to shorten the pause time, and when the discharge density is decreased, the machining control unit may control the voltage control unit to extend the pause time.

[0101] (Appendix 7) In the control device for a wire electric discharge machine described in Appendix 5, when the discharge density is to be increased, the machining control unit may control the movement control unit to reduce the movement speed (Z) of the wire electrode, and when the discharge density is to be decreased, the machining control unit may control the movement control unit to increase the movement speed.

[0102] (Supplementary Note 8) In the control device for a wire electric discharge machine described in Supplementary Note 1, the machining path may include at least one of a straight section (Rti) and a curved section (Rtc).

[0103] (Appendix 9) A control method disclosed herein is a control method for electric discharge machining by a control device of a wire electric discharge machine that machines a workpiece by generating an electric discharge between electrodes of a wire electrode and the workpiece while moving the wire electrode along a machining path relative to the workpiece, and includes: a movement control step of moving the wire electrode along the machining path in accordance with a machining program; a voltage control step of controlling a machining power supply in accordance with machining conditions to apply a machining voltage between the electrodes; and a machining control step of maintaining a non-discharge state in which no electric discharge occurs between the electrodes until the wire electrode reaches a first position on the machining path, gradually increasing the discharge density of the electric discharges so that the discharge density becomes a set value set as the machining condition when the wire electrode reaches the first position again, and gradually decreasing the discharge density to bring the non-discharge state between the electrodes.

[0104] Although the present disclosure has been described in detail, the present disclosure is not limited to the individual embodiments described above. Various additions, substitutions, modifications, partial deletions, etc. are possible in these embodiments without departing from the gist of the present disclosure or the spirit of the present disclosure derived from the content of the claims and their equivalents. These embodiments can also be implemented in combination. For example, in the above-described embodiments, the order of each operation and the order of each process are shown as examples and are not limited to these. The same applies when numerical values ​​or mathematical expressions are used in the description of the above-described embodiments.

[0105] DESCRIPTION OF SYMBOLS 10... Wire electric discharge machine 20... Control device 30... Machining power supply 40... Calculation unit 42... Storage unit 50... Movement control unit 52... Voltage control unit 54... Machining control unit

Claims

1. A control device for a wire electric discharge machine that machines a workpiece by generating an electric discharge between electrodes of a wire electrode and the workpiece while moving the wire electrode along a machining path relative to the workpiece, comprising: a movement control unit that moves the wire electrode along the machining path in accordance with a machining program; a voltage control unit that controls a machining power supply in accordance with machining conditions to apply a machining voltage between the electrodes; and a machining control unit that controls at least the voltage control unit of the movement control unit and the voltage control unit to maintain a non-discharge state in which no electric discharge occurs between the electrodes until the wire electrode reaches a first position on the machining path, gradually increase the electric discharge density of the electric discharges when the wire electrode reaches the first position so that the electric discharge density becomes a set value set as the machining condition, and gradually decrease the electric discharge density when the wire electrode reaches the first position again to return the non-discharge state between the electrodes.

2. A control device for a wire electric discharge machine according to claim 1, wherein the machining control unit gradually increases the discharge density while the wire electrode moves through a predetermined distance from the first position to a second position on the machining path, the machining control unit controls at least one of the movement control unit and the voltage control unit to maintain the discharge density at the set value from the time the wire electrode reaches the second position until it reaches the first position again, and the machining control unit gradually decreases the discharge density while the wire electrode moves through the predetermined distance again from the first position to the second position where it has reached again.

3. A control device for a wire electric discharge machine according to claim 2, wherein the machining control unit controls the increase and decrease of the discharge density so that the total machining amount of the workpiece at each position within the specified section, consisting of a first machining amount when the discharge density increases in the specified section and a second machining amount when the discharge density decreases in the specified section, is the machining amount corresponding to the machining amount of the workpiece when the discharge density is maintained at the set value.

4. A control device for a wire electric discharge machine according to claim 1, wherein the movement control unit moves the wire electrode in the non-discharge state from a movement start position of the wire electrode to a third position on the machining path, and the first position is a position away from the third position in the movement direction of the wire electrode along the machining path.

5. A control device for a wire electric discharge machine according to any one of claims 1 to 4, wherein the voltage control unit applies a pulse voltage from a machining power supply to the machining gap except during pauses, and suspends application of the pulse voltage to the machining gap during the pauses, thereby applying the machining voltage to the machining gap, and in the non-discharge state, the machining control unit controls the voltage control unit to make the pause time a predetermined time or longer, thereby reducing the discharge density to zero.

6. A control device for a wire electric discharge machine according to claim 5, wherein, when the discharge density is to be increased, the machining control unit controls the voltage control unit to shorten the pause time, and when the discharge density is to be decreased, the machining control unit controls the voltage control unit to extend the pause time.

7. A control device for a wire electric discharge machine according to claim 5, wherein, when the discharge density is to be increased, the machining control unit controls the movement control unit to reduce the movement speed of the wire electrode, and when the discharge density is to be decreased, the machining control unit controls the movement control unit to increase the movement speed.

8. A control device for a wire electric discharge machine according to claim 1, wherein the machining path includes at least one of a straight section and a curved section.

9. A control method for electric discharge machining by a control device of a wire electric discharge machine that machines a workpiece by generating an electric discharge between electrodes of a wire electrode and the workpiece while moving the wire electrode along a machining path relative to the workpiece, the control method comprising: a movement control step of moving the wire electrode along the machining path in accordance with a machining program; a voltage control step of controlling a machining power supply in accordance with machining conditions to apply a machining voltage between the electrodes; and a machining control step of maintaining a non-discharge state in which no electric discharge occurs between the electrodes until the wire electrode reaches a first position on the machining path, gradually increasing the discharge density of the electric discharges so that the discharge density becomes a set value set as the machining condition when the wire electrode reaches the first position again, and gradually decreasing the discharge density to bring the non-discharge state between the electrodes.

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