Electrical Discharge Machining Machine

Abstract

The electric discharge machine includes a power supply cable having a first conductor electrically connected to the electric discharge machining electrode and a second conductor electrically connected to the work table, and a ground wire having a third conductor electrically connecting the second conductor to a frame ground.

Description

[Technical Field]

[0001] The present disclosure relates to electrical discharge machines. [Background technology]

[0002] Japanese Patent No. 5804056 discloses an electric discharge machining device (electrical discharge machine) that applies high-frequency pulses to an electrode gap between a machining electrode and a workpiece via a coaxial cable. Summary of the Invention

[0003] Recently, there has been a demand for better electrical discharge machines.

[0004] The present disclosure aims to solve the above-mentioned problems.

[0005] An aspect of the present disclosure is an electric discharge machining machine comprising a power supply cable having a first conductor electrically connected to an electric discharge machining electrode and a second conductor electrically connected to a work table, and a ground wire having a third conductor electrically connecting the second conductor to a frame ground.

[0006] According to the present disclosure, a better electric discharge machine can be provided. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a schematic diagram of an electric discharge machine according to the first embodiment. [Figure 2] FIG. 2 is a schematic diagram of an electric discharge machine according to the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0008] The electrical discharge machine disclosed herein includes a power supply cable having a first conductor electrically connected to the electrical discharge machining electrode and a second conductor electrically connected to the work table. The power supply cable applies a voltage between the electrical discharge machining electrode and a workpiece attached to the work table. When an electrical discharge occurs between the electrical discharge machining electrode and the workpiece, a machining current flows from the machining power supply through the first conductor between the electrical discharge machining electrode and the workpiece, and then returns to the machining power supply as a return current through the second conductor.

[0009] When the impedance of the first conductor and the impedance of the second conductor are equal, the magnitude of the return current is the same as the magnitude of the machining current, and the direction of the return current is opposite to the direction of the machining current. Therefore, the electromagnetic field generated in the first conductor can be canceled out by the electromagnetic field generated in the second conductor, reducing noise generation in the power supply cable.

[0010] The power supply cable is made up of a coaxial cable. In a coaxial cable, the inner conductor is the first conductor and the outer conductor is the second conductor. By configuring the first conductor and the second conductor within the coaxial cable, the difference in impedance between the first conductor and the second conductor can be reduced.

[0011] However, because the connection destination of the first conductor and the connection destination of the second conductor are located far apart, it is not possible to construct the entire power feeder cable using coaxial cable. In the portion of the power feeder cable that is not composed of coaxial cable, the path along which the first conductor is wired is different from the path along which the second conductor is wired, and therefore the lengths of the first conductor and the second conductor may differ. In this case, the difference between the impedance of the first conductor and the impedance of the second conductor becomes large.

[0012] Furthermore, the impedance of the power supply cable increases in proportion to the frequency of the pulse current (machining current) flowing from the machining power supply to the power supply cable. Therefore, the higher the frequency of the pulse current flowing from the machining power supply to the power supply cable, the greater the difference in impedance between the first conductor and the second conductor.

[0013] As a result, the electromagnetic field generated in the first conductor cannot be sufficiently canceled out by the electromagnetic field generated in the second conductor, and there is a risk that noise generation in the power supply cable cannot be sufficiently suppressed.

[0014] In the electric discharge machine of the present disclosure, current generated due to noise occurring in the power supply cable can be released to the earth.

[0015] [First embodiment] [Configuration of EDM machine] FIG. 1 is a schematic diagram of an electric discharge machine 10 according to a first embodiment. The electric discharge machine 10 of this embodiment is a wire electric discharge machine. The electric discharge machine 10 is not limited to a wire electric discharge machine. The electric discharge machine 10 may be a die-sinker electric discharge machine, a small-hole electric discharge machine, or the like.

[0016] The electric discharge machine 10 generates an electric discharge by applying a voltage between the electric discharge machining electrode 12 and the workpiece 14. The space between the electric discharge machining electrode 12 and the workpiece 14 is sometimes referred to as the electrode gap. When the electric discharge machine 10 is a wire electric discharge machine, the electric discharge machining electrode 12 is a wire electrode.

[0017] The workpiece 14, which is the object to be machined, is placed on a work table 16. As the workpiece 14 moves together with the work table 16, the electric discharge machining electrode 12 moves relative to the workpiece 14. By generating an electric discharge between the electrodes and moving the electric discharge machining electrode 12 relative to the workpiece 14, the workpiece 14 can be machined into any shape.

[0018] The electric discharge machine 10 includes a machining power supply 18. The machining power supply 18 generates a pulse current and passes the pulse current to the electric discharge machining electrode 12 via a power supply cable 20a (upper power supply cable) and a power supply cable 20b (lower power supply cable). Hereinafter, when there is no need to distinguish between the power supply cable 20a and the power supply cable 20b, they will be referred to as the power supply cable 20.

[0019] The power supply cable 20 has a first conductor 22 and a second conductor 24. The first conductor 22 is electrically connected to the electric discharge machining electrode 12 via a power supply die 26. The first conductor 22 may not be directly connected to the power supply die 26 but may be connected via another member. The second conductor 24 is electrically connected to the work table 16. The second conductor 24 may not be directly connected to the work table 16 but may be connected via another member. When a workpiece 14 is placed on the work table 16, the second conductor 24 is also electrically connected to the workpiece 14.

[0020] The majority of the feeder cable 20 is made up of a coaxial cable 28. Within the coaxial cable 28, the first conductor 22 is the inner conductor of the coaxial cable 28, and the second conductor 24 is the outer conductor of the coaxial cable 28.

[0021] The tip of the first conductor 22 extending outward from the coaxial cable 28 is connected to the power supply die 26. The tip of the second conductor 24 extending outward from the coaxial cable 28 is connected to the work table 16.

[0022] The electric discharge machine 10 includes a ground wire 30. The ground wire 30 has a third conductor 32. The third conductor 32 electrically connects the second conductor 24 to a frame ground 34. At least a portion of the third conductor 32 may be made of a braided conductor. The frame ground 34 is a portion of the electric discharge machine 10 that is made of a cast metal. The frame ground 34 is grounded.

[0023] One end of the third conductor 32 is connected to the second conductor 24 extending outward from the coaxial cable 28. Most of the second conductor 24 extending outward from the coaxial cable 28 is covered with an insulating coating. The third conductor 32 is connected to the portion of the second conductor 24 that is not covered with the coating.

[0024] The other end of the third conductor 32 is connected to a frame ground 34 via a capacitor 36. Most of the third conductor 32 is covered with an insulating coating. The capacitor 36 is connected to the portion of the third conductor 32 that is not covered with the coating.

[0025] The worktable 16 is electrically connected to a frame ground 34 by a conductive path 38 separate from the ground wire 30 .

[0026] [Action and effect] When a discharge occurs between the poles, a machining current flows from the machining power supply 18 through the first conductor 22 to the poles, and the machining current returns to the machining power supply 18 through the second conductor 24 as a return current.

[0027] When the impedance of the first conductor 22 and the impedance of the second conductor 24 are equal, the magnitude of the return current is the same as the magnitude of the machining current, and the direction of the return current is opposite to the direction of the machining current. Therefore, the electromagnetic field generated in the first conductor 22 can be canceled out by the electromagnetic field generated in the second conductor 24, and noise generation in the power supply cable 20 can be reduced.

[0028] In the portion of the power feed cable 20 that is configured with the coaxial cable 28, the difference in impedance between the first conductor 22, which is the inner conductor, and the second conductor 24, which is the outer conductor, is small. However, in the portion of the power feed cable 20 that extends from the coaxial cable 28 to the outside for connection to the power feed die 26 and the work table 16, the first conductor 22 and the second conductor 24 must be routed along separate paths. Therefore, the lengths of the first conductor 22 and the second conductor 24 may differ, which increases the difference in impedance between the first conductor 22 and the second conductor 24. As a result, the electromagnetic field generated in the first conductor 22 cannot be sufficiently canceled out by the electromagnetic field generated in the second conductor 24, and noise generation in the power feed cable 20 may not be sufficiently suppressed.

[0029] Therefore, the electric discharge machine 10 of this embodiment is provided with a third conductor 32 that electrically connects the second conductor 24 to the frame ground 34. This allows current caused by noise generated in the power supply cable 20 to be sent from the third conductor 32 to the frame ground 34 and then released to earth. Hereinafter, the current caused by noise generated in the power supply cable 20 may be referred to as noise current.

[0030] This makes it possible to prevent noise generated in the power supply cable 20 from being emitted to the outside of the electric discharge machine 10. It also makes it possible to prevent noise generated in the power supply cable 20 from affecting other devices of the electric discharge machine 10.

[0031] When the second conductor 24 and the frame ground 34 are directly connected by the third conductor 32, part of the machining current flows from the third conductor 32 to the frame ground 34. As mentioned above, the frame ground 34 is a part of the electric discharge machine 10 that is made of a cast metal. A ball screw is installed in this part that is made of a cast metal. Therefore, the machining current may flow through the ball screw.

[0032] If a relatively large current flows through a ball screw, damage may occur to the nut, screw shaft, balls, etc. that make up the ball screw. Therefore, if machining current flows through the ball screw, there is a risk that the reliability of the ball screw will be impaired.

[0033] Furthermore, a part of the machining current flows from the third conductor 32 to the frame ground 34, which may change the voltage waveform and current waveform between the workpieces. This may affect the machining performance of the workpiece 14.

[0034] Therefore, in the electric discharge machine 10 of this embodiment, the third conductor 32 is connected to the frame ground 34 via the capacitor 36 .

[0035] The frequency of the noise current is often higher than the frequency of the machining current. By selecting the capacitance of the capacitor 36 according to the frequency of the noise current, the capacitor 36 can be used as a high-pass filter. By connecting the third conductor 32 to the frame ground 34 via the capacitor 36, the noise current having a higher frequency than the machining current can be passed through the frame ground 34, thereby suppressing the machining current flowing through the frame ground 34.

[0036] This makes it possible to prevent damage to the ball screw and also to reduce the effect on the machining performance of the workpiece 14.

[0037] Second Embodiment 2 is a schematic diagram of an electric discharge machine 10 according to a second embodiment. The electric discharge machine 10 according to this embodiment differs from the electric discharge machine 10 according to the first embodiment in that a plurality of capacitors 36 are provided between the third conductor 32 and the frame ground 34.

[0038] As shown in Fig. 2, a plurality of capacitors 36 are arranged in parallel. Each capacitor 36 has a different capacitance. A switch 40 is provided for each capacitor 36. The switch 40 is provided between the third conductor 32 and the capacitor 36. The switch 40 switches between a connection state in which the third conductor 32 and the capacitor 36 are electrically connected, and a disconnection state in which the third conductor 32 and the capacitor 36 are electrically disconnected.

[0039] The switch 40 may be provided between the frame ground 34 and the capacitor 36. In this case, the switch 40 switches between a connection state in which the frame ground 34 and the capacitor 36 are electrically connected and a disconnection state in which the frame ground 34 and the capacitor 36 are electrically disconnected.

[0040] Other configurations of the electric discharge machine 10 of this embodiment are the same as those of the electric discharge machine 10 of the first embodiment.

[0041] [Action and effect] The frequency of the generated noise current differs depending on the individual electric discharge machine 10. Furthermore, the frequency of the machining current differs depending on the machining stage of the workpiece 14 (rough machining, finish machining, etc.).

[0042] In this embodiment, the capacitor 36 electrically connected to the third conductor 32 is selected depending on the frequency of the noise current and the frequency of the machining current. This allows the noise current to flow to the frame ground 34 and prevents the machining current from flowing to the frame ground 34.

[0043] The following additional notes are further disclosed regarding the above embodiment.

[0044] (Appendix 1) The electric discharge machine (10) of the present disclosure includes a power supply cable (20) having a first conductor (22) electrically connected to the electric discharge machining electrode (12) and a second conductor (24) electrically connected to the work table (16), and a ground wire (30) having a third conductor (32) electrically connecting the second conductor to a frame ground (34).

[0045] (Appendix 2) In the electric discharge machine described in Supplementary Note 1, the third conductor may be connected to a portion of the second conductor that is not covered with a coating.

[0046] (Appendix 3) In the electric discharge machine according to Supplementary Note 1 or 2, the third conductor may be connected to the frame ground via a capacitor (36).

[0047] (Appendix 4) In the electric discharge machine described in Supplementary Note 3, the capacitor may be connected to a portion of the third conductor that is not covered with a coating.

[0048] (Appendix 5) In the electric discharge machine described in Supplementary Note 3 or 4, the capacitor may be provided between an end of the third conductor and the frame ground.

[0049] (Appendix 6) In the electric discharge machine described in any one of Appendices 3 to 5, a plurality of the capacitors may be provided, and a switch (40) may be provided for each of the plurality of capacitors, switching between a connection state in which the third conductor and the capacitor are electrically connected and a disconnection state in which the third conductor and the capacitor are electrically disconnected.

[0050] (Appendix 7) In the electric discharge machine described in any one of Appendices 3 to 5, a plurality of the capacitors may be provided, and a switch may be provided for each of the plurality of capacitors to switch between a connection state in which the frame ground and the capacitor are electrically connected and a disconnection state in which the frame ground and the capacitor are electrically disconnected.

[0051] (Appendix 8) In the electric discharge machine according to any one of Supplementary Notes 1 to 7, the work table may be electrically connected to the frame ground via a conductive path (38) separate from the grounding wire.

[0052] (Appendix 9) In the electric discharge machine described in any one of Supplementary Notes 1 to 8, the power supply cable may be a coaxial cable (28), the first conductor may be an inner conductor of the coaxial cable, and the second conductor may be an outer conductor of the coaxial cable.

[0053] (Appendix 10) In the electric discharge machine according to any one of Supplementary Notes 1 to 9, the third conductor may be made of a braided conductor.

[0054] 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. [Explanation of symbols]

[0055] 10...Electric discharge machine 12...Electrode for electrical discharge machining 16...Work table 20...Power supply cable 22...First conductor 24...Second conductor 28...Coaxial cable 30...Ground wire 32...Third conductor 34...Frame ground 36...Capacitor 38...Conduction path 40...Switch

Claims

1. a power supply cable having a first conductor electrically connected to the electric discharge machining electrode and a second conductor electrically connected to the work table; a ground line having a third conductor electrically connecting the second conductor to a frame ground; An electric discharge machine comprising:

2. 2. The electric discharge machine according to claim 1, The third conductor is connected to a portion of the second conductor that is not covered with a coating.

3. 3. The electric discharge machine according to claim 1, The third conductor is connected to the frame ground via a capacitor.

4. 4. The electric discharge machine according to claim 3, The capacitor is connected to a portion of the third conductor that is not covered with a coating.

5. 4. The electric discharge machine according to claim 3, The capacitor is provided between the end of the third conductor and the frame ground.

6. 4. The electric discharge machine according to claim 3, A plurality of the capacitors are provided, an electric discharge machine, wherein a switch is provided for each of the plurality of capacitors, the switch switching between a connection state in which the third conductor and the capacitor are electrically connected and a disconnection state in which the third conductor and the capacitor are electrically disconnected.

7. 4. The electric discharge machine according to claim 3, A plurality of the capacitors are provided, an electric discharge machine, wherein a switch is provided for each of the plurality of capacitors, the switch switching between a connection state in which the frame ground and the capacitor are electrically connected and a disconnection state in which the frame ground and the capacitor are electrically disconnected.

8. 3. The electric discharge machine according to claim 1, The electric discharge machine, wherein the work table is further electrically connected to the frame ground via a conductive path separate from the ground wire.

9. 3. The electric discharge machine according to claim 1, the power supply cable is a coaxial cable, the first conductor is an inner conductor of the coaxial cable, The second conductor is the outer conductor of the coaxial cable.

10. 3. The electric discharge machine according to claim 1, The third conductor is a braided conductor.

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