System, method and program for cutting carbon fiber-reinforced resin

Abstract

To realize high-quality cutting work of CFRP and improvement in tool life more securely.SOLUTION: A system 1 that cuts a workpiece W1 made of carbon fiber-reinforced resin comprises: a discharge circuit 10 which applies discharge voltage between a discharge electrode 20 and the surface of the workpiece; a machine tool 30 having a workpiece holding part 37 holding the workpiece and a tool holding part 33 holding a tool 32 which cuts the workpiece, where the discharge circuit generates atmospheric discharge by applying discharge voltage to the discharge electrode in the state where a minute gap G1 is provided between a tip part 20a of the discharge electrode and the surface of the workpiece, the discharge electrode performs electric discharge machining to the surface of the workpiece by atmospheric discharge by moving along the surface of the workpiece after discharge voltage is applied from the discharge circuit, and the machine tool cuts the surface of the workpiece after electric discharge machining by atmospheric discharge by using a tool.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a system, method, and program for cutting carbon fiber reinforced resin. [Background technology]

[0002] Carbon Fiber Reinforced Plastics (hereinafter, also referred to as CFRP) is known as a high-strength, lightweight material. CFRP has excellent strength, elastic modulus, heat resistance, and various durability properties, and therefore can contribute to making products stronger, lighter, and smaller, and is therefore used in many industrial fields, such as automobiles, aircraft, and medical devices.

[0003] However, CFRP is a difficult-to-cut material due to the carbon fibers contained as reinforcing materials, so tool wear is likely to occur during cutting, and there are concerns about the generation of burrs on the machined surface and the deterioration of the finished dimensions and finished surface. For example, Patent Document 1 discloses a related technique for reducing tool wear and unevenness on the finished surface when machining CFRP, in which a CFRP laminate is immersed in a machining fluid, a discharge voltage is generated using a discharge circuit, and the machining area of ​​the laminate is thermally machined. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2022-034938 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, because CFRP is a layered composite material made of carbon fibers and matrix resin, there is a concern that the processing fluid will penetrate between the layers of the CFRP during the submerged processing process, resulting in a deterioration in the quality of the CFRP after cutting due to delamination, etc.

[0006] The present disclosure has been made in consideration of the above-mentioned problems, and aims to more reliably achieve high-quality cutting of CFRP and improve tool life. [Means for solving the problem]

[0007] One aspect of the present disclosure is a system for cutting a workpiece made of carbon fiber reinforced resin, the system comprising: a discharge circuit that applies a discharge voltage between a discharge electrode and a surface of the workpiece; and a lathe having a workpiece holding portion that holds the workpiece and a tool holding portion that holds a tool for cutting the workpiece, wherein the discharge circuit generates an air discharge by applying the discharge voltage to the discharge electrode with a small gap between a tip of the discharge electrode and the surface of the workpiece, the discharge electrode moves along the surface of the workpiece after the discharge voltage is applied from the discharge circuit, thereby performing electric discharge machining on the surface of the workpiece by the air discharge, and the lathe uses the tool to cut the surface of the workpiece after electric discharge machining by the air discharge.

[0008] According to one aspect of the present disclosure, electric discharge machining is performed by air discharge on the surface of a workpiece made of CFRP to cut the carbon fibers on the surface side of the CFRP, and then the area where the carbon fibers have been cut is cut with a lathe tool, thereby more reliably achieving high-quality cutting of CFRP and improving tool life.

[0009] Another aspect of the present disclosure is a method for cutting a workpiece made of carbon fiber reinforced resin, comprising: applying a discharge voltage to a surface of the workpiece via a discharge electrode to perform electric discharge machining on the surface of the workpiece by air discharge; and cutting the surface of the workpiece after the electric discharge machining with a lathe tool, wherein, when performing the electric discharge machining by air discharge, the discharge electrode is moved along the surface of the workpiece with a small gap provided between the surface of the workpiece and the tip of the discharge electrode. According to this method, the surface of the workpiece is first subjected to electric discharge machining by air discharge, and then the surface of the workpiece after the electric discharge machining is cut with a lathe, so that high-quality cutting of CFRP and improvement of tool life can be more reliably achieved.

[0010] Yet another aspect of the present disclosure is a program configured to be executed by at least one processor and including instructions for executing the method, which performs electric discharge machining of a surface of a workpiece by air discharge and then cuts the surface of the workpiece after electric discharge machining using a lathe, thereby more reliably realizing high-quality cutting of CFRP and improving tool life. Effect of the Invention

[0011] According to the present disclosure, it is possible to more reliably achieve high-quality cutting of CFRP and improve tool life. [Brief description of the drawings]

[0012] [Figure 1] 1 is a block diagram showing a schematic configuration of a system according to a first embodiment. [Diagram 2] FIG. 2 is a plan view showing the configuration of a discharge electrode used in the system according to the first embodiment. [Diagram 3] FIG. 2 is an enlarged view of part III in FIG. [Figure 4] FIG. 4A is a perspective view of a workpiece holder provided in the system according to the first embodiment, and FIG. 4B is a perspective view showing a state in which a workpiece is held by a workpiece jig. [Diagram 5]FIG. 5A is a perspective view showing a state in which a tool jig is attached to a tool used in an NC lathe provided in the system according to the first embodiment, and FIG. 5B is a cross-sectional view showing a state in which the tool holding portion holds the tool. [Figure 6] FIG. 6A is an oblique view showing a state in which a discharge electrode is attached to a tool used in an NC lathe provided in the system according to the first embodiment, and FIG. 6B is a cross-sectional view showing a state in which the tool holding portion holds the discharge electrode via the tool and a tool jig. [Figure 7] 1 is a block diagram showing a schematic configuration of a discharge circuit provided in the system according to the first embodiment. [Figure 8] FIG. 2 is a diagram showing an outline of an operational flow of a method for cutting a workpiece made of CFRP by the system according to the first embodiment. [Figure 9] FIG. 9A is a front view of a tool unit with an integrated discharge electrode provided in the system according to the second embodiment, and FIG. 9B is a side view of the tool unit with an integrated discharge electrode provided in the system according to the second embodiment. [Figure 10] 10A is a front view of the cutting operation of a workpiece by a tool unit with an integrated discharge electrode provided in a system according to a second embodiment, and 10B is a side view of the cutting operation of a workpiece by a tool unit with an integrated discharge electrode provided in a system according to the second embodiment. [Figure 11] 11A is a front view of the discharge breakdown operation of a workpiece by a discharge electrode provided in the system according to the third embodiment, and 11B is a side view of the cutting processing operation of the workpiece by a tool provided in the system according to the third embodiment. [Figure 12] 12A is a front view of the discharge breakdown operation of a workpiece by a non-cutting part of a tool provided in the system of the third embodiment, and 10B is a side view of the cutting processing operation of a workpiece by a cutting part of a tool provided in the system of the third embodiment. [Figure 13] 13A is a photograph showing an example of a tool used in a comparative example, and 13B is a photograph showing an example of the appearance of a workpiece after electric discharge machining in the comparative example. [Figure 14]14A is a photograph showing an example of the appearance of the workpiece after electric discharge machining in Example 1, and 14B is a photograph showing an example of the appearance of the workpiece after cutting in Example 1. [Figure 15] 11 is a photograph showing an example of the appearance of a workpiece after electric discharge machining in Example 2. [Figure 16] 16A is a photograph showing an example of the appearance of the workpiece after discharge-assisted machining in Comparative Example 2, and 16B is a photograph showing an example of the appearance of the workpiece after cutting in Comparative Example 2. [Figure 17] 17A is a photograph showing a cross section of a high speed steel tool subjected to cutting after electric discharge assisted machining in Comparative Example 2, and 17B is a photograph showing a cross section of a high speed steel tool subjected to cutting without electric discharge assisted machining. [Figure 18] 18A is a photograph showing an example of the appearance of the workpiece after discharge assisted machining in Example 3, and 18B is a photograph showing an example of the appearance of the workpiece after cutting in Example 3. [Figure 19] 19A is a photograph showing an example of remaining fibers in a workpiece that was cut after discharge-assisted machining in Example 3, and 19B is a photograph showing an example of remaining fibers in a workpiece that was cut without discharge-assisted machining. [Figure 20] 20A is a photograph showing a cross section of a high speed steel tool subjected to cutting after electric discharge assisted machining in Example 3, and 20B is a photograph showing a cross section of a high speed steel tool subjected to cutting without electric discharge assisted machining. [Figure 21] 21A is a photograph showing an example of the appearance of the workpiece after discharge assisted machining in Example 4, and 21B is a photograph showing an example of the appearance of the workpiece after cutting in Example 4. [Figure 22] 22A is a photograph showing an example of remaining fibers in a workpiece that was cut after discharge-assisted machining in Example 4, and 22B is a photograph showing an example of remaining fibers in a workpiece that was cut without discharge-assisted machining. [Figure 23] 23A is a photograph showing a cross section of a high speed steel tool subjected to cutting after electric discharge assisted machining in Example 4, and 23B is a photograph showing a cross section of a high speed steel tool subjected to cutting without electric discharge assisted machining. [Figure 24]13 is a photograph showing an example of the appearance of a workpiece after electric discharge machining in Example 5. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] A preferred embodiment of the present disclosure will be described in detail below. The embodiment described below does not unduly limit the contents of the present disclosure described in the claims, and all of the configurations described in the embodiment are not necessarily essential as a solution to the present disclosure.

[0014] In the following description, terms indicating directions such as "upper", "lower", "left" and "right" are used for convenience of description and do not limit the method or manner of use. Terms such as "first" and "nth" (n is an integer) following "first" in this specification and claims are used as identifying terms to distinguish different elements and do not indicate a specific order or superiority or inferiority.

[0015] The terms used in the following description are intended to describe specific embodiments only and are not intended to limit the scope of the present disclosure. Elements according to an aspect described in the present specification and claims are intended to include the plural form unless the context clearly dictates that they are singular or plural.

[0016] The term "and / or" is intended to refer to and include any and all possible combinations of one or more of the associated listed elements. For example, "A or B" means "A, B, or both A and B." "A," "B," and "both A and B" all respectively satisfy "A or B."

[0017] The terms "includes", "including", "comprises" and / or "comprising" used in this specification and in the claims are intended to specify the presence of features, operations, elements, steps, but do not exclude the presence or addition of one or more other features, operations, elements, steps, and / or groups thereof.

[0018] All embodiments and optional embodiments included in this disclosure may be combined with each other to form new embodiments. In addition, all technical features and optional technical features included in this disclosure may be combined with each other to form new technical features.

[0019] System 1 Configuration

[0020] The configuration of the system according to the first embodiment of the present disclosure will be described with reference to the drawings. Fig. 1 is a block diagram showing a schematic configuration of the system according to the first embodiment, Fig. 2 is a plan view showing a configuration of a discharge electrode used in the system according to the first embodiment, and Fig. 3 is an enlarged view of part III in Fig. 1.

[0021] The system 1 of this embodiment is a system for cutting a workpiece W1 made of carbon fiber reinforced plastic (CFRP). The system 1 is characterized in that when cutting a round bar-shaped workpiece W1, discharge assisted machining is performed on the surface of the workpiece W1 using a discharge circuit 10 and a discharge electrode 20, and then turning is performed using an NC lathe 30. In the system 1 of this embodiment, an NC lathe 30 is used for cutting using a tool such as a cutting tool with a cutting tip attached to the tip side of a shank that becomes a handle fixed to the machine. However, the machine tool used in the system 1 is not limited to the NC lathe 30, and other general-purpose lathes capable of cutting and turning, and other machine tools using rotary cutting tools such as end mill processing and drill processing can also be applied.

[0022] The "surface" of the workpiece W1 referred to in this disclosure includes all surfaces (external surfaces) constituting the outer shape of the workpiece W1, and examples thereof include the outer surface of the workpiece, the end face of the workpiece, and the cut surface of the workpiece, but are not limited thereto. In addition, the shape of the workpiece W1 is not particularly limited as long as it is a shape that can be machined by a machine tool, and examples thereof may include a plate material, a bar material, and any other shape.

[0023] The CFRP applied to the cutting process by the system 1 of this embodiment includes both CFRTS (Carbon Fiber Reinforced Thermosetting Plastic) using a thermosetting resin as the base material and CFRTP (Carbon Fiber Reinforced Thermo Plastic) using a thermoplastic resin as the base material. The CFRP applied to the cutting process by the system 1 can be applied to CFRP containing continuous fibers with approximately constant carbon fiber length, and other types of CFRP containing discontinuous fibers with variations in carbon fiber length, regardless of whether it is CFRTS or CFRTP.

[0024] The NC lathe 30 is a machine tool in which a numerical control device is incorporated in a general-purpose lathe, and a control unit 40 executes a program set in advance, thereby computer-controlling operations such as the rotation and movement of the workpiece W1, the movement of the tool 32, and the replacement of the tool 32. As shown in FIG. 1, the NC lathe 30 has a collet chuck 37 provided on a support unit 31a at one end of the bed 31. The collet chuck 37 functions as a workpiece holder that holds the workpiece W1. The collet chuck 37 is fixed to a spindle 39 provided on the support unit 31a. The collet chuck 37 and the workpiece W1 held by the collet chuck 37 are controlled by a drive motor (not shown) to rotate via the spindle 39 at a predetermined peripheral speed. The holding of the workpiece W1 by the collet chuck 37 includes both a direct holding mode and an indirect holding mode in which the workpiece W1 is held via a desired member.

[0025] As shown in FIG. 1, the NC lathe 30 is provided with a turret 33 at a position facing the collet chuck 37. The turret 33 functions as a tool holding unit that holds the tool 32. The turret 33 is a swivel-type tool rest that can support one or more tools 32, and is supported by a saddle 35 via a support shaft 34. The turret 33 can be replaced with a desired tool 32 to be used in cutting by rotating. The saddle 35 is supported by a frame 36 and can be moved in the width direction of the bed 31 (Y-axis direction shown in FIG. 1) via a motor (not shown). The frame 36 is supported by the bed 31 and can be moved in the length direction of the bed 31 (X-axis direction shown in FIG. 1) via a motor (not shown). The holding of the tool 32 by the turret 33 includes both a direct holding mode and an indirect holding mode in which the tool 32 is held via a desired member.

[0026] In this way, the NC lathe 30 moves the turret 33 holding the tool 32 in the X-axis and Y-axis directions in accordance with a previously set program while bringing the desired tool 32 into contact with the workpiece W1, thereby enabling the workpiece W1 rotating at a predetermined peripheral speed to be efficiently and accurately turned into a desired shape. Note that the NC lathe 30 only needs to be configured so that the turret 33 holding the tool 32 can be moved in the X-axis and Y-axis directions, and therefore the drive mechanism for the turret 33 is not limited to the configuration described above.

[0027] The NC lathe 30 further includes a gas supply unit 33a that supplies an assist gas toward the workpiece W1 after cutting. The gas supply unit 33a supplies a gas such as nitrogen or air as an assist gas toward the workpiece W1 after cutting. The gas supply unit 33a is provided, for example, near the turret 33, and removes chips after cutting and cools the workpiece W1 by supplying the assist gas toward the workpiece W1 after cutting.

[0028] Therefore, even if the discharge electrode 20 performs discharge-assisted machining by air discharge on the surface of the workpiece W1 and then performs cutting with the tool 32 of the NC lathe 30, measures can be taken against heat generated during discharge-assisted machining and against cutting chips generated during cutting. The location of the gas supply unit 33a is not limited to the vicinity of the turret 33, and it may be installed in another location as long as it is a position where assist gas can be supplied to the workpiece W1 after cutting.

[0029] The discharge circuit 10 has a function of applying a discharge voltage between the discharge electrode 20 and the surface of the workpiece W1. In this embodiment, the discharge circuit 10 is characterized in that it is controlled to apply a discharge voltage of 10 V or less to the discharge electrode 20. The discharge circuit 10 is electrically connected to the discharge electrode 20 and the workpiece W1, thereby applying a discharge voltage between the discharge electrode 20 and the workpiece W1 and generating an air discharge between the tip 20a of the discharge electrode 20 and the surface of the workpiece W1.

[0030] Specifically, the discharge circuit 10 has one conductor 10a directly connected to, for example, any portion on the base end side of the discharge electrode 20 by screwing or the like, and the other conductor 10b connected to a carbon brush or the like (not shown) that enables power supply to the rotating body, and is connected to the surface of the workpiece W1 via the carbon brush to supply power. At this time, the carbon brush is fixed near the collet chuck 37 via an insulating material (not shown). The detailed configuration of the discharge circuit 10 will be described later.

[0031] The discharge electrode 20 is configured as a needle-shaped electrode. Specifically, the discharge electrode 20 has a main body 20c with a diameter of 2 mm, and a cross section of the main body 20c is round or elliptical, and has a needle-like shape that protrudes in an elongated manner. The discharge electrode 20 is also configured of a good conductor having a certain degree of hardness, such as copper or cemented carbide. Furthermore, the discharge electrode 20 is configured to be attachable to a tool 32 held by a turret 33. Specifically, as shown in FIG. 2, the discharge electrode 20 has a connecting portion 20b on the base end side of the main body 20c, which has the same shape and size as a cutting tip 32a attached to the tip side of the tool 32 of the NC lathe 30, and has, for example, a substantially triangular shape with rounded corners. That is, the discharge electrode 20 is configured to protrude in a needle shape from one end of the connecting portion 20b toward the tip portion 20a of the main body 20c of the discharge electrode 20.

[0032] In addition, as long as the main body 20c of the discharge electrode 20 is configured in a needle shape, the cross-sectional shape is not limited to a round or elliptical shape, and may be other shapes such as a semicircular shape, a polygonal shape, etc. In the present embodiment, the discharge electrode 20 is a needle-shaped electrode with the main body 20c having a diameter of 2 mm, but as long as the main body 20c of the discharge electrode 20 is configured to protrude in an elongated manner from the connecting portion 20b, the diameter of the main body 20c is not limited to 2 mm, and may be, for example, about 1.8 to 2.5 mm.

[0033] In this way, the discharge electrode 20 is configured to be attachable to a mounting portion of the cutting tip 32a provided on the tip side of the tool 32 held via the turret 33. The shape of the connecting portion 20b of the discharge electrode 20 is not limited to a substantially triangular shape, and may be other shapes and sizes as long as it is configured to be replaceable with the cutting tip 32a attached to the tool 32 to be used.

[0034] As shown in FIG. 3, a discharge voltage is applied from the discharge circuit 10 to the discharge electrode 20 with a minute gap G1 of, for example, 40 to 50 μm between the tip 20a and the surface of the workpiece W1. The discharge electrode 20 moves in the feed direction of the tool 32 along the surface of the workpiece W1 to perform electric discharge machining on the surface of the workpiece W1. When a discharge voltage is applied from the discharge circuit 10 to the discharge electrode 20, an air discharge occurs in which electricity flows through the air in the minute gap G1 between the tip 20a of the discharge electrode 20 and the surface of the workpiece W1, and a dielectric breakdown phenomenon occurs due to the air discharge. In this embodiment, electric discharge machining is performed in which carbon fibers are cut at a depth of several tens of μm from the surface of the CFRP constituting the workpiece W1 by the force of the dielectric breakdown phenomenon caused by the air discharge at the site of the minute gap G1 that becomes the discharge gap. That is, the force of the dielectric breakdown phenomenon caused by the air discharge cuts the carbon fibers from the surface of the CFRP to a discharge depth of 20 to 60 μm, forming an electric discharge processed layer (cut carbon fiber portion).

[0035] In this system 1, when cutting the workpiece W1, electric discharge machining is performed on the surface side of the hard CFRP using the electric discharge circuit 10 and the electric discharge electrode 20, and then turning is performed on the part where the carbon fibers have been cut using the tool 32 of the NC lathe 30. Therefore, the tool 32 of the NC lathe 30 cuts the electric discharge machined layer where the hardness has been reduced by cutting the carbon fibers at a depth of 20 to 60 μm from the surface of the CFRP, thereby suppressing wear of the tool 32, reducing the occurrence of burrs, and achieving high-quality turning with improved surface properties.

[0036] System 1 Insulation

[0037] Next, the insulation process of the system 1 according to the first embodiment of the present disclosure will be described with reference to the drawings. FIG. 4A is a perspective view of a workpiece holder included in the system according to the first embodiment, and FIG. 4B is a perspective view showing a state in which the workpiece is held by a workpiece jig. FIG. 5A is a perspective view of a state in which a tool jig is attached to a tool used in the NC lathe included in the system according to the first embodiment, and FIG. 5B is a cross-sectional view showing a state in which the tool holder holds the tool. FIG. 6A is a perspective view of a state in which a discharge electrode is attached to a tool used in the NC lathe included in the system according to the first embodiment, and FIG. 6B is a cross-sectional view showing a state in which the tool holder holds the discharge electrode via the tool and the tool jig.

[0038] In the NC lathe 30, in order to prevent leakage current when performing electric discharge assisted machining using the discharge circuit 10 and the discharge electrode 20, insulation is performed between the workpiece W1 and the collet chuck 37 and between the discharge electrode 20 and the turret 33. Specifically, the cylindrical collet chuck 37 shown in Fig. 4A holds the workpiece W1, which is a cylindrical rod, via a thick disk-shaped workpiece jig 38 shown in Fig. 4B, which is made of an insulating material such as polyacetal, thereby insulating the workpiece W1 from the collet chuck 37. The NC lathe 30 is capable of cutting in the same manner as when turning other workpieces by the normal NC lathe 30, by the collet chuck 37 gripping the workpiece jig 38 and the workpiece jig 38 gripping the workpiece W1.

[0039] On the other hand, insulation between the discharge electrode 20 and the turret 33 is performed by insulating the tool 32 to which the discharge electrode 20 is attached and the turret 33. Specifically, as shown in Fig. 5A, the base end side of the tool 32 is covered with a tool jig 33b made of an insulating material such as glass fiber reinforced resin, and then, when attaching the tool 32 to the turret 33, the tool 32 is fixed with a bolt 33c as shown in Fig. 5B. In this way, the turret 33 is insulated from the tool 32 by holding the base end side of the tool 32 via the tool jig 33b made of an insulating material.

[0040] Similarly, as shown in Fig. 6A, the base end side of the tool 32 in which the discharge electrode 20 is attached to the portion where the cutting tip 32a was provided is covered with a tool jig 33b made of an insulating material such as glass fiber reinforced resin, and then, when the tool 32 is attached to the turret 33, it is fixed with a bolt 33c as shown in Fig. 6B. In this manner, the discharge electrode 20 is attached to the tip side of the tool 32 held by the turret 33 via the tool jig 33b, thereby insulating the discharge electrode 20 from the turret 33. Note that, with regard to the insulation between the discharge electrode 20 and the turret 33, it is sufficient that such insulation is performed only on at least the tool 32 in which the discharge electrode 20 is attached in place of the cutting tip 32a, among the tools 32 held by the turret 33.

[0041] Schematic configuration of the discharge circuit 10

[0042] Next, a schematic configuration of a discharge circuit provided in the system of the first embodiment of the present disclosure will be described with reference to the drawings. Fig. 7 is a block diagram showing a schematic configuration of a discharge circuit provided in the system of the first embodiment.

[0043] The discharge circuit 10 is a HALS discharge circuit used for performing electric discharge machining by applying a discharge voltage to the surface of a workpiece W1 via a discharge electrode 20. As shown in Fig. 4, the discharge circuit 10 includes a microcontroller 11, a general-purpose logic IC 12, a photocoupler 13, a half-bridge driver 14, a DC power supply 15, a three-terminal regulator 16, a variable DC power supply 17, and a MOSFET element 18. The discharge circuit 10 is controlled by the microcontroller 11 independently of the control unit 40 of the NC lathe 30, and can also be synchronized by the microcontroller 11.

[0044] The microcontroller 11 is a microcomputer such as ESP32 (manufactured by Espressif Systems) and has a function of controlling the frequency and duty ratio of the pulse wave output from the MOSFET element 18. The microcontroller 11 is capable of adjusting the discharge depth, which is an index of the strength of the electric discharge machining, by adjusting the frequency and duty ratio of the pulse wave it outputs. In this embodiment, the microcontroller 11 is connected to a general-purpose logic IC 12, and a pulse wave with an amplitude of, for example, +3.3V and an arbitrary discharge frequency and duty ratio is output from the microcontroller 11 and applied to the general-purpose logic IC 12.

[0045] The general-purpose logic IC 12 is an integrated circuit consisting of a hex inverter and the like, which is provided between the microcontroller 11 and the photocoupler 13. The general-purpose logic IC 12 functions, for example, as a buffer amplifier circuit, and outputs a pulse wave of +3.3V voltage as a voltage of +5V to apply it to the photocoupler 13.

[0046] The DC power supply 15 is connected to the three-terminal regulator 16 and the half-bridge driver 14, and the three-terminal regulator 16 is provided between the DC power supply 15 and the photocoupler 13. The voltage of +15 V output from the DC power supply 15 is converted to a voltage of +5 V using the three-terminal regulator 16, for example, and applied to the photocoupler 13.

[0047] The photocoupler 13 is an element that has the function of transmitting a signal while maintaining electrical insulation by converting an electric signal into light inside and then converting it back into an electric signal. In this embodiment, the photocoupler 13 is provided before the half-bridge driver 14 as shown in Fig. 4, thereby electrically insulating the circuit following the photocoupler 13 from the microcontroller 11, so that the microcontroller 11 can be protected even if a large voltage or current flows. The drive voltage of the photocoupler 13 is, for example, +5V, and a pulse wave having an amplitude of +5V is applied from the photocoupler 13 to the half-bridge driver 14.

[0048] Also, for example, a voltage of +15V output from DC power supply 15 is applied to half-bridge driver 14, and the amplitude of the pulse wave is converted from +5V to +15V, which is applied to MOSFET element 18 functioning as a switching semiconductor that outputs a pulsed discharge voltage. Half-bridge driver 14 converts the amplitude of the pulse wave to +15V, for example, to apply it to the gate of MOSFET element 18, thereby ensuring the voltage of +15V required for switching.

[0049] Thereafter, for example, a discharge voltage of +10V output from a variable DC power supply 17 with a maximum voltage of 400V is applied to the MOSFET element 18, and is applied as a pulse wave to the discharge electrode 20. In this manner, the discharge circuit 10 is controlled to apply a voltage of 10V or less to the discharge electrode 20. Note that other switching semiconductors such as an IGBT element may be used as the switching semiconductor that outputs the pulsed discharge voltage. However, since the discharge circuit 10 of the present system 1 is used to output a low-voltage pulse waveform voltage, it is preferable to use a MOSFET element 18 with excellent low-temperature voltage characteristics as the switching semiconductor used in the output stage of the discharge circuit 10.

[0050] Method Operation Flow

[0051] Next, the method for cutting a workpiece made of CFRP according to the first embodiment of the present disclosure will be described with reference to the drawings. Fig. 8 is a diagram showing an outline of the operation flow of the method for cutting a workpiece made of CFRP by the system according to the first embodiment.

[0052] The method for cutting a workpiece made of CFRP according to the first embodiment is executed by a program that operates a computer that serves as the control unit 40 that controls the NC lathe 30. The program that executes the method for cutting a workpiece made of CFRP is a program that causes at least one processor (computer device) to execute cutting of a workpiece W1 made of CFRP. The program that executes the method for cutting a workpiece made of CFRP according to the present embodiment causes the computer device that serves as the control unit 40 of the NC lathe 30 to execute the operation flow shown in FIG.

[0053] When cutting a workpiece W1 made of CFRP, first, a discharge voltage is applied from the discharge circuit 10 to the discharge electrode 20 (step S1). As described above, the discharge circuit 10 is configured to be able to apply a discharge voltage of a predetermined magnitude between the discharge electrode 20 and the surface of the workpiece W1. In this embodiment, the discharge circuit 10 is computer-controlled by the control unit 40 of the NC lathe 30 so as to apply a discharge voltage of 10 V or less between the discharge electrode 20 and the surface of the workpiece W1.

[0054] After applying the discharge voltage to the discharge electrode 20, the turret 33 of the NC lathe 30 is then moved in the length direction and height direction of the bed 31 while the tip 20a of the needle-shaped discharge electrode 20 is brought close to the workpiece W1 (step S2). In the method of cutting the workpiece W1 of the present disclosure, in order to cause a dielectric breakdown phenomenon due to air discharge, it is necessary to apply the discharge voltage from the discharge circuit 10 to the discharge electrode 20 in a state in which a minute gap G1, which becomes a discharge gap, is provided between the tip 20a of the discharge electrode 20 and the surface of the workpiece W1. For this reason, the discharge electrode 20 is brought close to the workpiece W1 so that the minute gap G1 between the tip 20a of the discharge electrode 20 and the surface of the workpiece W1 is, for example, 40 to 50 μm.

[0055] Thereafter, the turret 33 of the NC lathe 30 is moved in the length direction of the bed 31 to move the discharge electrode 20 along the surface of the workpiece W1 in the feed direction of the tool 32 (step S3). The NC lathe 30 applies a discharge voltage between the discharge electrode 20 attached to the turret 33 and the surface of the workpiece W1, and then controls the operation so that the discharge electrode 20 advances in the feed direction while maintaining a minute gap G1 between the discharge electrode 20 and the workpiece W1.

[0056] In this way, by controlling the operation of the discharge electrode 20, the minute gap G1 between the tip 20a of the needle-shaped discharge electrode 20 and the surface of the workpiece W1 becomes a discharge gap, and a dielectric breakdown phenomenon occurs due to air discharge caused by electricity flowing through the air in the minute gap G1. Then, the force of the dielectric breakdown phenomenon caused by the air discharge performs electric discharge machining in which the carbon fibers are cut at a depth of 20 to 60 μm from the surface of the workpiece W1 made of CFRP.

[0057] Thereafter, the spindle 34 of the turret 33 is rotated to change the tool for machining the workpiece W1 from the discharge electrode 20 to a desired tool 32 (step S4). Then, the turret 33 of the NC lathe 30 is moved in the length direction of the bed 31 to move the tool 32 in the feed direction of the tool 32 along the surface of the workpiece W1 after the electric discharge machining (step S5). As a result, the carbon fibers on the surface side of the CFRP are cut, and the cut and fluffy carbon fibers are cut and removed by the tool 32 from the workpiece W1 after the electric discharge machining, which has a reduced hardness, thereby enabling efficient cutting of the CFRP.

[0058] Functions and Effects of the Embodiments

[0059] Next, the operation and effects of the system 1 and method for cutting a workpiece made of carbon fiber reinforced resin according to the first embodiment of the present disclosure will be described.

[0060] The present inventors have conducted extensive research to solve the problem of achieving high-quality cutting of CFRP and improving tool life, and have discovered the following phenomenon. That is, the present inventors have found that when a discharge voltage is applied between the tip 20a of the discharge electrode 20 and the surface of the workpiece W1 made of CFRP with a minute gap G1 provided between the tip 20a and the surface of the workpiece W1, an air discharge occurs in the air at the minute gap G1. The present inventors have also found that the force of the dielectric breakdown phenomenon caused by the air discharge can cut carbon fibers to a depth of several tens of μm from the surface of the CFRP.

[0061] For this reason, in the system 1 and method of the first embodiment, discharge-assisted machining by air discharge is performed on the surface of the CFRP to be cut material W1 using the discharge circuit 10 and the discharge electrode 20, and then cutting is performed with the tool 32 of the NC lathe 30. As a result, the carbon fibers covered from the surface side of the hard CFRP by the discharge-assisted machining by air discharge are cut to a depth of 20 to 60 μm from the surface of the workpiece W1, and then the discharge-machined layer (carbon fiber cut portion) in which the carbon fibers are cut and the hardness is reduced is cut with the tool 32 of the NC lathe 30. For this reason, since the hard CFRP is not directly cut with the tool 32, wear of the tool 32 is suppressed, and the remaining fibers on the surface of the workpiece W1 are efficiently removed to reduce the occurrence of burrs, thereby realizing high-quality cutting with good surface properties.

[0062] Furthermore, in the system 1 and method of the first embodiment, unlike electric discharge machining using submerged machining, electric discharge machining using air discharge is performed in a dry environment without immersion in liquid, and then cutting is performed with the tool 32 of the NC lathe 30. This reduces the risk of delamination occurring due to infiltration of machining liquid between the layers of CFRP, as occurs with submerged electric discharge machining, and therefore makes it possible to suppress deterioration in quality due to delamination of CFRP after cutting.

[0063] In addition, the inventors have conducted intensive research to solve the above-mentioned problems, and have found that by applying a discharge voltage of 10V or less to the discharge electrode 20, which is a needle-shaped electrode made of copper or cemented carbide and has a diameter of, for example, 2 mm, the air in the minute gap G1 between the tip 20a of the discharge electrode 20 and the surface of the workpiece W1 becomes a discharge gap, and an air discharge occurs. Therefore, even under low voltage conditions of 10V or less, an air discharge can be generated in the air in the minute gap G1 on the tip side of the discharge electrode 20, and the carbon fibers are cut to a depth of several tens of μm from the surface of the CFRP by the force of the dielectric breakdown phenomenon caused by the air discharge, so that electric discharge machining can be performed with low power consumption and safety in mind. In addition, since an air discharge can be generated in the minute gap G1 that becomes the discharge gap even under low voltage conditions of 10V or less, it is possible to perform electric discharge-assisted machining of CFRP more generally and safely without requiring a high-voltage power supply for electric discharge machining.

[0064] Furthermore, the present inventors have conducted extensive research to solve the above-mentioned problems, and have found that when performing electric discharge machining of CFRP with a discharge electrode 20 consisting of a needle-shaped electrode using an NC lathe 30, the suitable value of the minute gap G1 between the tip 20a of the discharge electrode 20 and the surface of the workpiece W1 is at least 50 μm or less. In particular, it has been found that when the minute gap G1, which is the discharge gap, is 40 μm and a voltage of 10 V or less is applied, carbon fibers can be stably cut from the surface of the CFRP to a depth of 40 μm. If the minute gap G1 is greater than 50 μm, no air discharge is generated that is strong enough to cause a dielectric breakdown phenomenon capable of cutting the carbon fibers on the surface of the CFRP.

[0065] Moreover, in the system 1 and method of the first embodiment, the discharge electrode 20 is configured to be attachable to a tool 32 held by a turret 33 of an NC lathe 30. Specifically, the discharge electrode 20 has a connecting portion 20b on the base end side that has the same shape and size as the cutting tip 32a of the tool 32 attached to the turret 33, and is configured to be attachable to an installation portion of the cutting tip 32a of the tool 32.

[0066] As a result, the discharge electrode 20 can be attached in exchange for the cutting tip 32a at the tip end of one of the tools 32 held by the turret 33, so that discharge assisted machining using the discharge electrode 20 and normal cutting machining using the tool 32 can be easily performed on a single NC lathe 30. This allows stable machining with less variation in the cutting of CFRP, and makes it easy to realize efficient mass production of CFRP cutting.

[0067] In the system 1 of the first embodiment, the NC lathe 30 is insulated between the workpiece W1 and the collet chuck 37 and between the discharge electrode 20 and the turret 33. Specifically, the collet chuck 37 is insulated from the workpiece W1 by holding the workpiece W1 via a workpiece jig 38 made of an insulating material. Meanwhile, the discharge electrode 20 is insulated from the turret 33 by being placed on the tip side of the tool 32 held by the turret 33 via a tool jig 33b made of an insulating material. By thus insulating the NC lathe 30, it becomes possible to prevent leakage current when performing electric discharge assisted machining using the discharge circuit 10 and the discharge electrode 20 by using the NC lathe 30.

[0068] Furthermore, the system 1 of the first embodiment is characterized by further including a gas supply unit 33a that supplies assist gas toward the workpiece W1 after cutting by the NC lathe 30. By providing the gas supply unit 33a that supplies assist gas toward the workpiece W1 in this manner, it becomes possible to air-cool the heat generated during discharge-assisted machining by air discharge and to remove chips generated during cutting by the tool 32 of the NC lathe 30.

[0069] In addition, non-contact processing using submerged machining, which is seen in related technologies of electrical discharge machining, is difficult to perform fine precision processing. In particular, in the medical device field, the demand for micro-machined products using CFRP is increasing, so there is a growing need for cutting processing using NC lathes that can perform precise mass-production turning processing. However, when normal cutting processing of CFRP is performed using tools of NC lathes, the carbon fibers contained in CFRP as a reinforcing material cause wear of the tools, which causes problems such as burrs on the CFRP to be cut (W1) and deterioration of the finished dimensions and finished surface.

[0070] In contrast, in the system 1 and method of the first embodiment, one NC lathe 30 is used to perform discharge-assisted machining, which is a pretreatment for cutting CFRP, and then the CFRP is cut. Specifically, the system 1 and method utilizes the NC lathe 30 that has been insulated as described above, and first performs discharge-assisted machining of CFRP under low-voltage conditions using the discharge circuit 10 and the discharge electrode 20, and cuts the carbon fibers to a depth of several tens of μm from the surface of the CFRP by dielectric breakdown. Then, the carbon fibers of the CFRP are cut, and cutting (turning) is performed on the discharge-machined layer (carbon fiber cut portion) with reduced hardness (after cutting the carbon fibers) using a normal tool 32 of the NC lathe 30.

[0071] In this way, in the system 1 and method of the first embodiment, after discharge-assisted machining by the discharge electrode 20 under low voltage conditions, normal turning is performed by the tool 32 of the NC lathe 30, which reduces wear on the cutting edge of the tool 32, suppresses the occurrence of burrs, and enables high-quality turning with good surface properties. In addition, since discharge-assisted machining of CFRP is performed using one NC lathe 30 to reduce the hardness of the part to be cut, and then cutting is performed with the tool 32, it becomes possible to mass-produce micro-machined products using CFRP with good precision, even without using a tool made of a high-hardness material such as cemented carbide.

[0072] Second embodiment (Figs. 9 and 10)

[0073] The configuration of a tool unit with an integrated discharge electrode included in a system according to a second embodiment of the present disclosure will be described with reference to the drawings. Fig. 9A is a front view of the tool unit with an integrated discharge electrode included in the system according to the second embodiment, and Fig. 9B is a side view of the tool unit with an integrated discharge electrode included in the system according to the second embodiment.

[0074] The system 2 of this embodiment is characterized in that discharge assisted machining and cutting of CFRP, which is a workpiece, can be performed continuously using a discharge electrode integrated tool unit 100 in which a discharge electrode 120 and a tool 132 are held by an insulating holder 133. The insulating holder 133 is formed of an insulating material such as glass fiber reinforced resin, and functions as a tool holding part that holds the tool 132, and at the same time, has a function of holding the discharge electrode 120. In this embodiment, the configurations of the discharge circuit 10 and the NC lathe 30 other than the discharge electrode integrated tool unit 100 are similar to those of the first embodiment described above, so their description will be omitted.

[0075] 9A, the discharge electrode-integrated tool unit 100 has a tool 132 for cutting a workpiece provided at one longitudinal end of an insulating holder 133, and a roller electrode 110 serving as a power supply electrode for supplying power to the workpiece provided at the other longitudinal end of the insulating holder 133. A needle-shaped discharge electrode 120 is provided between the tool 132 and the roller electrode 110 in the longitudinal direction of the insulating holder 133.

[0076] The base end side of the discharge electrode 120 is connected to the discharge circuit 10 (see FIG. 1) by an electric wire (not shown). In this embodiment, the discharge electrode 120 is adapted to adjust the minute gap (electrode distance) between the tip of the discharge electrode 120 and the surface of the workpiece W1 to a desired size by an electrode distance adjustment mechanism 122 built into the insulating holder 133. The electrode distance adjustment mechanism 122 may be, for example, a mechanism using a feed screw or a mechanism that automates gap adjustment according to the discharge current using a shape memory alloy spring. The electrode distance adjustment mechanism 122 adjusts the minute gap between the tip of the discharge electrode 120 and the surface of the workpiece W1 to a desired size of, for example, 20 to 40 μm, at least 50 μm or less. In this way, by providing the electrode distance adjustment mechanism 122, a stable discharge gap between the discharge electrode 120 and the surface of the workpiece W1 can be maintained.

[0077] The roller electrode 110 is formed in a roller shape from a conductive material such as graphite, and is attached to an insulating holder 133 via a support member 112 also made of a conductive material such as graphite, as shown in FIG. 9B. The support member 112 is formed of an elastically deformable spring or the like. The base end side of the support member 112 of the roller electrode 110 is connected to the discharge circuit 10 (see FIG. 1) by an electric wire (not shown). The roller electrode 110 is configured in this way, so that it can supply electricity to a workpiece that is elastically in contact with the roller electrode 110 with a desired pressing force.

[0078] Next, the cutting operation of the workpiece by the discharge electrode-integrated tool unit provided in the system of this embodiment will be described with reference to the drawings. Fig. 10A is a front view of the cutting operation of the workpiece by the discharge electrode-integrated tool unit provided in the system of this embodiment, and Fig. 10B is a side view of the cutting operation of the workpiece by the discharge electrode-integrated tool unit.

[0079] In the system 2 of this embodiment, as shown in Fig. 10A, the discharge electrode integrated tool unit 100 is brought close to the workpiece W1 so that the longitudinal direction of the insulating holder 133 is aligned with the rotation direction of the workpiece W1. At this time, the roller electrode 110 first comes into contact with the rotating workpiece W1 to supply power to the workpiece W1, and then the discharge electrode 120 located downstream performs dielectric breakdown treatment on the surface of the workpiece W1 by air discharge while maintaining a desired discharge gap. Then, the tool 132 located downstream of the discharge electrode 120 cuts the carbon fibers constituting the workpiece W1 made of CFRP that have been dielectrically broken down and cut by the discharge electrode 120, and the remaining resin that is the base material of the CFRP.

[0080] 10B, by moving the discharge electrode integrated tool unit 100 close to the workpiece W1 in the feed direction of the workpiece W1, cutting can be performed in the rotation axis direction (feed direction) of the workpiece W1 rotatably held by the collet chuck 137. In this manner, in this embodiment, the discharge electrode integrated tool unit 100 is used to continuously perform the following steps: power supply to the workpiece W1 by the roller electrode 110, dielectric breakdown due to air discharge on the surface of the workpiece W1 by the discharge electrode 120, and cutting (turning) of the workpiece W1 after dielectric breakdown by the tool 132.

[0081] Therefore, by using the discharge electrode integrated tool unit 100, it becomes possible to feed power to the surface of the workpiece W1 and perform insulation breakdown by air discharge, and then continuously perform cutting of the workpiece W1 after cutting the carbon fibers with the tool 132. That is, compared with the system 1 of the first embodiment, the system 2 of this embodiment does not require a process of replacing the discharge electrode 120 with the tool 132, so that discharge-assisted turning can be realized more efficiently and continuously in a short time. In addition, the discharge electrode integrated tool unit 100 maintains the roller electrode 110, the discharge electrode 120, and the tool 132 in a state where they are arranged at a predetermined interval, so that it is possible to prevent the roller electrode 110, the discharge electrode 120, and the tool 132 from interfering with each other. Therefore, it becomes possible to continuously perform discharge-assisted machining using the discharge electrode 120 and cutting using the tool 132 in a stable state.

[0082] Third embodiment (Figs. 11 and 12)

[0083] The discharge breakdown operation of the workpiece by the system according to the third embodiment of the present disclosure will be described with reference to the drawings. Fig. 11A is a front view of the discharge breakdown operation of the workpiece by the discharge electrode provided in the system according to the third embodiment, and Fig. 11B is a side view of the cutting operation of the workpiece by the tool provided in the system according to the third embodiment.

[0084] Unlike the first and second embodiments which use an NC lathe 30 as the machine tool, the system 3 of this embodiment is applied to a machine tool which performs cutting processing using a rotary cutting tool 232, such as end mill processing or drill processing.

[0085] That is, in the system 3 of this embodiment, first, as shown in Fig. 11A, a discharge electrode 220 made of a needle electrode performs dielectric breakdown by air discharge on the surface of the workpiece W1, cutting the carbon fibers on the surface layer side of the workpiece W1 made of CFRP. Then, as shown in Fig. 11B, a rotary cutting tool 232 such as an end mill performs cutting processing on the workpiece W1 after the carbon fibers are cut, thereby cutting and removing the cut carbon fibers and base material of the workpiece W1 made of CFRP. In this way, in this embodiment, electric discharge assisted machining is applied to a machine tool that performs end mill machining and drill machining.

[0086] In addition, the system 3 of this embodiment can perform cutting processing of the cross section of the workpiece W1 only by the rotary cutting tool 232 by connecting the non-cutting part 232b at the base end side of the cutting part 232a provided at the tip side of the rotary cutting tool 232 to the discharge circuit 10 (FIG. 1) with an electric wire (not shown). Specifically, as shown in FIG. 12A, the rotary cutting tool 232 first cuts the carbon fibers at the cross section of the workpiece W1 by using the non-cutting part 232b as a discharge electrode that performs insulation breakdown by air discharge on the cross section of the workpiece W1. Then, the rotary cutting tool 232 is raised, and the cross section of the workpiece W1 from which the carbon fibers have been cut is cut by the cutting part 232a, and the cut carbon fibers and the base material of the workpiece W1 are cut and removed.

[0087] In this manner, in this embodiment, the rotary cutting tool 232 is moved in the thickness direction of the cross section of the workpiece W1, and the non-cutting portion 232b and the cutting portion 232a of the rotary cutting tool 232 are oscillated, so that the dielectric breakdown and cutting process of the cross section of the workpiece W1 due to air discharge can be intermittently and repeatedly performed. Therefore, even if a rotary cutting tool 232 such as an end mill is used, the discharge-assisted machining of the workpiece W1 made of CFRP can be efficiently performed. In particular, when cutting the cross section of the workpiece W1, the non-cutting portion 232b of the rotary cutting tool 232 such as an end mill is connected to the discharge circuit 10 so that electricity can be passed therethrough, and by oscillating the rotary cutting tool 232 up and down, the dielectric breakdown and cutting process of the cross section of the workpiece W1 due to air discharge can be efficiently and repeatedly performed. EXAMPLES

[0088] Next, the system 1 and the method according to the first embodiment of the present disclosure will be described in detail with reference to examples. Note that the first embodiment of the present disclosure is not limited to these examples.

[0089] (Advance preparation) In order to perform electric discharge assisted cutting using the system 1 and method according to the first embodiment of the present disclosure, an NC lathe (GSL-10 manufactured by Takamatsu Machine Industry Co., Ltd.) was used, and insulation was performed between the workpiece W1 to be cut and the collet chuck (see FIG. 4), and between the turret and the tool holder (see FIG. 5). In addition, a discharge circuit shown in FIG. 7 was produced as a pulse discharge circuit for performing electric discharge assisted machining of CFRP.

[0090] Comparative Example 1 As Comparative Example 1, a discharge electrode having the same shape and size as the cutting tip of the tool of the NC lathe was attached to the tool, and the discharge depth was confirmed by performing discharge-assisted machining while changing the discharge voltage from 10 to 50 V with a minute interval G1, which is the discharge gap, set to 15 μm. In Comparative Example 1, as shown in FIG. 13A, a copper tip having a substantially triangular apex with R0.8 mm was used as the discharge electrode. In addition, CFRP made of CFRTS with a vinyl ester matrix was used as the workpiece. The discharge voltage applied at this time was an AC voltage with a discharge frequency of 1 kHz, a duty ratio of 0.01, and a pulse wave with a rectangular waveform. In addition, the feed speed of the discharge electrode was 0.15 mm / rev, and the peripheral speed of the workpiece to be machined by discharge-assisted machining was 2 m / min.

[0091] As shown in Table 1 below, the discharge depth was 205 μm when the discharge voltage was 50 V, whereas the discharge depth was 200 μm when the discharge voltage was 40 V, 195 μm when the discharge voltage was 30 V, 160 μm when the discharge voltage was 20 V, and 50 μm when the discharge voltage was 10 V. This confirmed that the lower the discharge voltage, the shallower the discharge depth.

[0092] [Table 1]

[0093] Next, the copper tip shown in Fig. 13A was used to perform electrical discharge machining at each discharge voltage, and the appearance of the surface of the workpiece after electrical discharge machining was confirmed. As shown in Fig. 13B, when the discharge voltage was 20 to 50 V, the carbon fibers on the surface side of the CFRP were cut, but when the discharge voltage was 10 V, the carbon fibers on the surface side of the CFRP were hardly cut. From this, it was found that when the discharge electrode has the same shape and size as the cutting tip of the NC lathe tool, when the discharge voltage is 10 V, the force of the insulation breakdown phenomenon due to air discharge that is strong enough to cut the carbon fibers of the CFRP is not generated.

[0094] Example 1 In Example 1, a copper needle electrode with a diameter of 2 mm was attached to the tool as the discharge electrode, and the discharge assisted machining was performed with a minute interval G1 of 45 μm, which was the discharge gap, and a discharge voltage of 10 V. At this time, a CFRP made of vinyl ester CFRTS matrix was used as the workpiece. The applied discharge voltage was an AC voltage with a discharge frequency of 1 kHz, a duty ratio of 0.01, and a pulse waveform of a rectangular wave. Furthermore, the feed rate of the discharge electrode was 0.15 mm / rev, and the peripheral speed of the workpiece to be cut by the discharge assisted cutting was 2 m / min. Then, after the discharge assisted machining, cutting was performed using a tool with a cutting tip made of high speed steel with a substantially triangular shape of R0.8 mm attached to the tip.

[0095] When a copper needle electrode with a diameter of 2 mm was used as the discharge electrode, the center of both sides of the workpiece was the cut portion P1 where the carbon fibers on the surface side of the CFRP were cut, as shown in Fig. 14A. This shows that when a copper needle electrode with a diameter of 2 mm was used as the discharge electrode and the discharge gap was set to 45 μm, even when the discharge voltage was a low voltage of 10 V, a dielectric breakdown phenomenon force was generated due to air discharge that was strong enough to cut the carbon fibers on the surface side of the CFRP.

[0096] Furthermore, when the cut portion P1 where the carbon fibers were cut was cut using a normal tool after performing the EDM, a high-quality machined surface P2 with good surface properties with few burrs or remaining fibers was obtained, as shown in Fig. 14B. This shows that when EDM is performed using a discharge voltage of 10 V, a discharge gap of 45 μm, and a copper needle electrode with a diameter of 2 mm as the discharge electrode, and then cutting is performed using a normal tool, high-quality turning can be performed with good surface properties with few burrs or remaining fibers.

[0097] Example 2 In Example 2, a copper needle electrode with a diameter of 2 mm was attached to the tool as a discharge electrode, and the minute interval G1, which was the discharge gap, was set to 50 μm, and the discharge voltage was changed by decreasing it by 1 V to a value of 10 V or less, and discharge-assisted machining was performed. At this time, CFRP made of vinyl ester CFRTS matrix was used as the workpiece. The applied discharge voltage was an AC voltage with a discharge frequency of 1 kHz, a duty ratio of 0.01, and a pulse waveform of a square wave. Furthermore, the feed rate of the discharge electrode was 0.15 mm / rev, and the peripheral speed of the workpiece to be cut by discharge-assisted cutting was 2 m / min. Then, after discharge-assisted machining, cutting was performed using a tool with a cutting tip made of high-speed steel with a substantially triangular shape and R0.8 mm attached to the tip.

[0098] After performing electrical discharge machining at each discharge voltage using a copper needle electrode with a diameter of 2 mm as the discharge electrode, the appearance of the surface of the workpiece after electrical discharge machining was confirmed. As shown in FIG. 15, slight cutting of the carbon fibers on the surface side of the CFRP began to be observed from a discharge voltage of 7 V, and cutting of the carbon fibers on the surface side of the CFRP was clearly observed at discharge voltages of 8 to 10 V. However, when the discharge voltage was 6 V or less, no air discharge occurred even when the discharge gap was changed, so electrical discharge-assisted machining could not be performed. From this, it was found that a discharge voltage of at least 7 V or more is required to perform electrical discharge-assisted machining at a low discharge voltage using a copper needle electrode with a diameter of 2 mm as the discharge electrode with a discharge gap of 50 μm.

[0099] Furthermore, when the discharge depth at each discharge voltage was confirmed, it was found that the discharge depth was 40 μm at a discharge voltage of 8 V, 50 μm at a discharge voltage of 9 V, and 55 μm at a discharge voltage of 10 V. This shows that in the discharge voltage range of 10 V or less where discharge-assisted machining can be performed, a shallow discharge depth of 40 to 55 μm, which is suitable for precision machining of CFRP, can be ensured.

[0100] From the results of Examples 1 and 2 and Comparative Example 1, it was found that the carbon fibers on the surface side of the CFRP can be cut by performing discharge assisted machining using a copper needle electrode with a diameter of 2 mm and a discharge gap of 40 to 50 μm as the discharge electrode, even under low-voltage conditions with a discharge voltage of 10 V or less. Therefore, it was found that when cutting is performed with a tool of an NC lathe after discharge assisted machining, it is possible to perform high-quality turning with improved surface properties while suppressing the generation of burrs.

[0101] Comparative Example 2 As Comparative Example 2, a copper tip with an approximately triangular apex of R0.4 mm was attached to the tool as a discharge electrode, and the minute interval G1, which is the discharge gap, was set to 5 μm, and discharge assisted machining was performed at a discharge voltage of 10 V. At this time, CFRP made of vinyl ester CFRTS matrix was used as the workpiece. The applied discharge voltage was an AC voltage with a discharge frequency of 1 kHz, a duty ratio of 0.01, and a pulse waveform of a rectangular wave. Furthermore, the feed speed of the discharge electrode was 0.15 mm / rev, and the peripheral speed of the workpiece to be cut with discharge assisted cutting was 2 m / min. Then, after discharge assisted machining, cutting was performed using a tool with a cutting tip made of high speed steel with an approximately triangular apex of R0.4 mm attached to the tip. Thereafter, in order to confirm the wear suppression effect of the tool, a laser microscope (LEXT OLS 4100 made by OYLMPUS) was used to measure the wear of the high speed steel tool that had been cut to the same cutting depth after cutting with discharge assistance and after cutting without discharge assistance.

[0102] When a copper tip with a roughly triangular apex and a radius of 0.4 mm was used as the discharge electrode, the center of both sides of the workpiece was cut off at a cut part P3 where the carbon fibers on the surface side of the CFRP were cut off, as shown in Fig. 16A. However, because the discharge assisted machining was performed under conditions with a small discharge gap of 5 μm, the discharge depth was 70 μm, which was somewhat deep, and it was found that shallow discharge assisted machining with good controllability could not be performed. In addition, when the cut part P3 where the carbon fibers were cut off was cut off with a normal tool after the discharge assisted machining, a cut surface P4 with relatively few burrs and remaining fibers and somewhat better surface quality was obtained, as shown in Fig. 16B.

[0103] Next, when the cross section of the high-speed steel tool that had been subjected to cutting after EDM was observed with a laser microscope, the maximum wear width was 10.1 μm and the wear depth was 6.8 μm on the cutting face SU1 shown in Fig. 17A with EDM. In contrast, when the cross section of the high-speed steel tool that had been subjected to cutting without EDM was observed with a laser microscope, the maximum wear width was 101.3 μm and the wear depth was 14.1 μm on the cutting face SU2 shown in Fig. 17B with only cutting. From this, the effect of reducing tool wear in EDM was confirmed in Comparative Example 2 as well.

[0104] Example 3 In Example 3, a needle-shaped electrode made of cemented carbide with a diameter of 2.2 mm was attached to the tool as a discharge electrode, and discharge-assisted machining was performed with a minute gap G1 of 40 μm, a discharge voltage of 10 V, and a workpiece. At this time, CFRP with a vinyl ester matrix CFRTS was used as the workpiece. The applied discharge voltage was an AC voltage with a discharge frequency of 1 kHz, a duty ratio of 0.01, and a square pulse waveform. The feed rate of the discharge electrode was 0.15 mm / rev, and the peripheral speed of the workpiece to be cut with discharge-assisted cutting was 2 m / min. Then, after discharge-assisted machining, cutting was performed using a tool with a cutting tip made of high-speed steel with a roughly triangular shape and R0.4 mm attached to the tip.

[0105] When a 2.2 mm diameter cemented carbide needle electrode was used as the discharge electrode, the carbon fibers in the center of both sides of the surface of the CFRP were cut to form cut portion P5, as shown in Figure 18A. This shows that when a 2.2 mm diameter cemented carbide needle electrode was used as the discharge electrode and the discharge gap was set to 40 μm, even when the discharge voltage was as low as 10 V, a dielectric breakdown phenomenon force was generated due to air discharge that was strong enough to cut the carbon fibers on the surface side of the CFRP. In addition, since the discharge depth was 50 μm, it was found that shallow discharge-assisted machining with good controllability was performed.

[0106] Furthermore, when the cut portion P5 where the carbon fibers were cut was cut using a normal tool after performing the EDM, a high-quality machined surface P6 with good surface properties with few burrs or remaining fibers was obtained, as shown in Fig. 18B. This shows that when EDM is performed using a discharge voltage of 10V, a discharge gap of 45μm, and a 2.2mm diameter cemented carbide needle electrode as the discharge electrode, and then cutting is performed using a normal tool, high-quality turning can be performed with good surface properties with few burrs or remaining fibers.

[0107] In addition, in order to confirm the effect of suppressing remaining fibers by the discharge-assisted machining, the length of remaining fibers and the surface roughness (Rz, Ra) of the workpiece after cutting with discharge-assisted machining and after cutting without discharge-assisted machining were measured using a laser microscope. When the remaining fibers of the workpiece that was cut after discharge-assisted machining were observed, as shown in FIG. 19A, the maximum remaining fiber length L1 was 52.6 μm, the maximum height roughness Rz was 71.342 μm, and the arithmetic mean roughness Ra was 13.192 μm. In contrast, when the remaining fibers of the workpiece that was cut without discharge-assisted machining were observed, as shown in FIG. 19B, the maximum remaining fiber length L2 was 1322.2 μm, the maximum height roughness Rz was 161.741 μm, and the arithmetic mean roughness Ra was 28.864 μm. From this, it was confirmed that in Example 3, the workpiece was cut with high precision according to the dimensions by the cutting after discharge-assisted machining.

[0108] After that, the wear of the high-speed steel tool that had been cut to the same cutting depth after cutting with and without discharge-assisted machining in Example 3 was measured using a laser microscope. When the cross section of the high-speed steel tool that had been cut after discharge-assisted machining was observed with a laser microscope, the maximum wear width was 9.4 μm and the wear depth was 5.9 μm in the cutting with discharge-assisted machining on the rake face SU3 shown in FIG. 20A. In contrast, when the cross section of the high-speed steel tool that had been cut without discharge-assisted machining was observed with a laser microscope, the maximum wear width was 12.6 μm and the wear depth was 19.7 μm in the cutting only on the rake face SU4 shown in FIG. 20B. From this, the effect of reducing tool wear in cutting after discharge-assisted machining was confirmed in Example 3.

[0109] Example 4 In Example 4, a copper needle electrode with a diameter of 2 mm was attached to the tool as a discharge electrode, and discharge-assisted machining was performed with a minute gap G1 of 45 μm, a discharge voltage of 10 V, and a workpiece. At this time, a CFRP with a vinyl ester matrix CFRTS was used as the workpiece. The applied discharge voltage was an AC voltage with a discharge frequency of 1 kHz, a duty ratio of 0.01, and a square pulse waveform. The feed rate of the discharge electrode was 0.15 mm / rev, and the peripheral speed of the workpiece to be cut with discharge-assisted cutting was 2 m / min. Then, after discharge-assisted machining, cutting was performed using a tool with a cutting tip made of high-speed steel with a substantially triangular shape and R0.4 mm attached to the tip.

[0110] When a copper needle electrode with a diameter of 2 mm was used as the discharge electrode, the carbon fibers in the center of both sides of the surface of the CFRP were cut to form cut portion P7, as shown in Figure 21A. This shows that when a copper needle electrode with a diameter of 2 mm was used as the discharge electrode and the discharge gap was set to 45 μm, even when the discharge voltage was a low voltage of 10 V, a dielectric breakdown phenomenon force was generated due to air discharge that was strong enough to cut the carbon fibers on the surface side of the CFRP. In addition, since the discharge depth was 50 μm, it was found that shallow discharge-assisted machining with good controllability was performed.

[0111] Furthermore, when the cut portion P7 where the carbon fibers were cut was cut using a normal tool after performing the EDM, a high-quality machined surface P8 with good surface properties with few burrs or remaining fibers was obtained, as shown in Fig. 21B. This shows that when EDM is performed using a discharge voltage of 10V, a discharge gap of 45μm, and a copper needle electrode with a diameter of 2mm as the discharge electrode, and then cutting is performed using a normal tool, high-quality turning can be performed with good surface properties with few burrs or remaining fibers.

[0112] In addition, in order to confirm the effect of suppressing remaining fibers by the discharge-assisted machining, the length of remaining fibers and the surface roughness (Rz, Ra) of the workpiece after cutting with discharge-assisted machining and after cutting without discharge-assisted machining were measured using a laser microscope. When the remaining fibers of the workpiece that was cut after discharge-assisted machining were observed, as shown in FIG. 22A, the maximum remaining fiber length L3 was 278.0 μm, the maximum height roughness Rz was 83.4 μm, and the arithmetic mean roughness Ra was 16.4 μm. In contrast, when the remaining fibers of the workpiece that was cut without discharge-assisted machining were observed, as shown in FIG. 22B, the maximum remaining fiber length L4 was 2163.7 μm, the maximum height roughness Rz was 166.5 μm, and the arithmetic mean roughness Ra was 28.5 μm. From this, it was confirmed that in Example 4, the surface shape of the workpiece can be cut with high precision according to the dimensions by the discharge-assisted cutting.

[0113] After that, the wear of the high-speed steel tool that had been cut to the same cutting depth after cutting with and without discharge assistance in Example 4 was measured using a laser microscope. When the cross section of the high-speed steel tool that had been cut after discharge assistance was observed with a laser microscope, the maximum wear width was 9.4 μm and the wear depth was 7.3 μm in the discharge-assisted cutting process on the rake face SU5 shown in FIG. 23A. In contrast, when the cross section of the high-speed steel tool that had been cut without discharge assistance was observed with a laser microscope, the maximum wear width was 64.8 μm and the wear depth was 40.6 μm in the cutting process alone on the rake face SU6 shown in FIG. 23B. From this, the effect of reducing tool wear in discharge-assisted cutting was confirmed in Example 4.

[0114] From the results of Examples 3 and 4 and Comparative Example 2, it was found that the carbon fibers on the surface side of the CFRP could be cut by performing discharge assisted machining using a discharge gap of 40 to 50 μm, a cemented carbide needle electrode having a diameter of 2.2 mm, and a copper needle electrode having a diameter of 2 mm as the discharge electrode, even under low-voltage conditions with a discharge voltage of 10 V or less. In other words, it was found that discharge assisted machining can be performed under low-voltage conditions whether the needle electrode constituting the discharge electrode is made of copper, which has excellent conductivity, or cemented carbide, which has excellent wear resistance.

[0115] For this reason, it was found that if cutting is performed with a high-speed steel tool on an NC lathe after discharge-assisted machining using these discharge electrodes, the generation of burrs can be suppressed and high-quality cutting with improved surface properties can be performed.In addition, it was found that wear on the cutting edge of the high-speed steel tool can be reduced because the carbon fibers on the surface side of the CFRP are cut by discharge-assisted machining to reduce the hardness of the area to be cut, and then cutting is performed with a high-speed steel tool on an NC lathe.

[0116] Example 5 In Example 5, the feasibility of discharge-assisted machining at a discharge voltage of 10V or less was verified. Specifically, a copper needle electrode with a diameter of 2mm was attached to the tool as the discharge electrode, and the discharge voltage was changed to 10V or less while the minute interval G1, which is the discharge gap, was set to 50μm, and discharge-assisted machining was performed for 10 revolutions of the workpiece to confirm the discharge depth. At this time, CFRP made of vinyl ester CFRTS matrix was used as the workpiece. The applied discharge voltage was an AC voltage with a discharge frequency of 1kHz, a duty ratio of 0.01, and a pulse waveform of a square wave. The feed rate of the discharge electrode was 0.15mm / rev, and the peripheral speed of the workpiece to be cut with discharge-assisted cutting was 2m / min. Then, after discharge-assisted machining, cutting was performed using a tool with a cutting tip made of high-speed steel with a roughly triangular shape of R0.4mm attached to the tip.

[0117] In Example 5, a copper needle electrode with a diameter of 2 mm was used as the discharge electrode to perform discharge-assisted machining at each discharge voltage, and the appearance of the surface of the workpiece after discharge-assisted machining was confirmed. As shown in FIG. 24, when the discharge voltage was 10V, 9V, and 8V, the carbon fibers on the surface of the workpiece were cut with discharge depths of 55 μm, 50 μm, and 40 μm, respectively. Furthermore, when the discharge voltage was 7V, the carbon fibers on the surface of the workpiece were partially cut, but when the discharge voltage was 6V or less, the carbon fibers could not be cut. From this, it was found that when the discharge electrode was a copper needle electrode with a diameter of 2 mm, discharge-assisted machining for cutting the carbon fibers on the surface side of the workpiece made of CFRP was possible from a discharge voltage of 7V, and discharge-assisted machining was impossible when the discharge voltage was 6V or less.

[0118] Although each embodiment and each example of the present disclosure have been described in detail above, it will be readily apparent to those skilled in the art that many modifications are possible without substantially departing from the novel features and effects of the present disclosure. Therefore, all such modifications are intended to be included within the scope of the present disclosure.

[0119] For example, a term described at least once in the specification or drawings together with a different term having a broader meaning or the same meaning can be replaced with that different term anywhere in the specification or drawings. In addition, the configuration and operation of the system are not limited to those described in each embodiment and each example of the present disclosure, and various modifications are possible. [Explanation of symbols]

[0120] 1, 2, 3 System 10 Discharge circuit 10a conductor 10b conductor 11 Microcontrollers 12 General-purpose logic ICs 13 Photocoupler 14 Half-bridge drivers 15 DC power supply 16 3-Terminal Regulator 17 Variable DC power supply 18 MOSFET elements 20 Discharge electrode 20a Tip 20b Connecting part 20c Main body 30 NC lathe (lathe) 31 Bed 31a Support part 32 Tools 32a Cutting tip 33 Turret (tool holding part) 33a Gas supply section 33b Tool Jig 33c Bolt 34 Spindle 35 Saddle 36 Frames 37 Collet chuck (workpiece holding part) 38 Jig for cutting materials 39 Main shaft 40 Control section 100 Discharge electrode integrated tool unit 110 Roller electrode (power supply electrode) 112 Support part 120 Discharge electrode 122 Pole distance adjustment mechanism 132 Tools 133 Insulating holder 137 Collet chuck (workpiece holding part) 220 Discharge electrode 232 Rotary cutting tools 232a Cutting section 232b Non-cutting part

Claims

1. In a system for cutting a workpiece made of carbon fiber reinforced resin, A discharge circuit that applies a discharge voltage between a discharge electrode and the surface of the workpiece; a machine tool having a workpiece holding portion for holding the workpiece and a tool holding portion for holding a tool for cutting the workpiece, the discharge circuit applies the discharge voltage to the discharge electrode in a state where a small gap is provided between the tip of the discharge electrode and the surface of the workpiece, thereby generating an air discharge; the discharge electrode performs electric discharge machining on the surface of the workpiece by moving along the surface of the workpiece after the discharge voltage is applied from the discharge circuit, and The machine tool performs cutting processing on the surface of the workpiece after the electric discharge processing by the air discharge using the tool. system.

2. The discharge circuit is controlled to apply a discharge voltage of 10 V or less to the discharge electrode. The system of claim 1 .

3. The discharge electrode is a needle-shaped electrode. The system of claim 1 .

4. The minute interval is at least 50 μm or less. The system of claim 1 .

5. The discharge electrode is configured to be attachable to the tool held by the tool holding portion. The system of claim 1 .

6. In the machine tool, insulation is performed between the workpiece and the workpiece holding portion, and between the discharge electrode and the tool holding portion. The system of claim 5.

7. The workpiece holding portion holds the workpiece via a workpiece jig made of an insulating material, thereby insulating the workpiece from the workpiece. The system of claim 6.

8. the tool holding portion holds a base end side of the tool via a tool jig formed of an insulating material, The discharge electrode is installed on the tip side of the tool held via the tool jig, thereby insulating the discharge electrode from the tool holding portion. The system of claim 6.

9. The discharge electrode is configured to be attachable to a cutting tip installation site provided on the tip side of the tool held via the tool jig. The system of claim 8.

10. the tool holding portion is an insulating holder formed of an insulating material, The insulating holder holds the tool and the discharge electrode. The system of claim 1 .

11. the insulating holder further holds a power supply electrode for supplying power to the workpiece; The discharge electrode is provided between the power supply electrode and the tool. The system of claim 10.

12. the insulating holder is provided with an inter-electrode distance adjustment mechanism capable of adjusting the size of the minute gap between the tip of the discharge electrode and the surface of the workpiece; The system of claim 10.

13. The cutting machine further includes a gas supply unit that supplies an assist gas toward the workpiece after cutting by the machine tool. A system according to any one of claims 1 to 9.

14. A method for cutting a workpiece made of carbon fiber reinforced resin, comprising the steps of: applying a discharge voltage between a discharge electrode and the surface of the workpiece to perform electric discharge machining on the surface of the workpiece by air discharge; and cutting the surface of the workpiece after the electric discharge machining with a tool of a machine tool; When performing the electric discharge machining by the air discharge, the discharge electrode is moved along the surface of the workpiece while a small gap is provided between the surface of the workpiece and a tip end of the discharge electrode. method.

15. The tool is a rotary cutting tool that is rotationally driven to cut the workpiece with a cutting portion at a tip end thereof. The method of claim 14.

16. The rotary cutting tool uses a non-cutting portion provided on a base end side of the cutting portion as the discharge electrode for electric discharge machining of a cross section of the workpiece, and then cuts the cross section with the cutting portion. The method of claim 15.

17. A program configured to be executed by at least one processor, comprising: comprising instructions for carrying out the method according to any one of claims 14 to 16, program.

Images