Wire electric discharge machining apparatus, wire electric discharge machining method, and wafer manufacturing method

Abstract

The wire electric discharge machining device includes a pair of wire parallel guide rollers arranged on both sides of the workpiece to sandwich the workpiece, and having a plurality of wire guide grooves formed at equal intervals on the outer peripheral side surfaces, into which a plurality of traveling cutting wires are fitted to restrict the movement of the plurality of cutting wires; parallel wire tensioning position measuring units (52a, 52b) that measure the distance between a measurement reference plane set parallel to an imaginary plane including the plurality of cutting wires and wire electrodes that constitute the plurality of cutting wires; a wire guide groove disengagement detection unit (53) that detects the occurrence of a change in distance based on the measurement results of the parallel wire tensioning position measuring units (52a, 52b); and a wire state determination unit (54) that determines, based on the detection results of the wire guide groove disengagement detection unit (53), whether the state is a wire disengaged state in which at least one cutting wire is disengaged from the wire guide groove, or a wire contact state in which all cutting wires are in contact with the wire guide groove.

Description

[Technical Field]

[0001] The present disclosure relates to a wire electric discharge machining apparatus, a wire electric discharge machining method, and a wafer manufacturing method that perform electric discharge machining using a wire electrode to simultaneously cut out a plurality of plate-shaped members from a workpiece. [Background technology]

[0002] Multi-wire electrical discharge machining devices generate electric discharges between multiple wire electrodes and the workpiece, allowing multiple plate-shaped components to be cut out simultaneously from the workpiece. Multi-wire electrical discharge machining devices are used, for example, in semiconductor manufacturing processes, for slicing multiple wafers from an ingot. If an abnormality occurring near the electrodes of a multi-wire electrical discharge machining device is discovered late, various problems can occur, including unstable electrical discharge machining, broken wire electrodes, uneven thickness of the cut plate-shaped components, and reduced surface accuracy of the plate-shaped components. For these reasons, various anomaly detection technologies for multi-wire electrical discharge machining devices have been developed.

[0003] Patent Document 1 describes a multi-wire electric discharge machining apparatus that includes a high-frequency pulse power supply unit that applies a high-frequency pulse voltage to a parallel wire section and a base and has short-circuit determination means that determines whether a short circuit has occurred between the wires of the parallel wire section and the workpiece, and a control means.The short-circuit determination means determines that a short circuit has occurred if the time from the start of application of the high-frequency pulse voltage to the start of an increase in the value of the current flowing between the wire and the workpiece is less than a predetermined standard. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-87395 Summary of the Invention [Problem to be solved by the invention]

[0005] Some multi-wire electric discharge machines are provided with a pair of guide rollers arranged on either side of the workpiece to sandwich the workpiece and prevent the cutting wires from shifting position so that the distance between the parallel cutting wires does not change from the start to the end of machining. In this case, multiple wire guide grooves are machined into the surfaces of the guide rollers to define the distance between the parallel wire electrodes.

[0006] When multiple wire electrodes run in parallel to simultaneously cut out multiple plate-shaped components from a workpiece, the wire electrodes may lift up from the wire guide groove. Possible causes of wire electrode lift include the flow of machining fluid supplied between the electrodes during machining, the repulsive force of discharge, eccentricity during rotation of the guide mechanism, which has wire guide grooves formed on the cylindrical side surface that align the wire electrodes at intervals determined by the thickness of the plate-shaped components being cut out, and foreign matter accumulated in the wire guide groove.

[0007] The wire electrode that has lifted up from the wire guide groove may deviate from the wire guide groove due to the external force exemplified above, etc. As a result, the multiple wire electrodes cannot run parallel to each other at a predetermined interval, and the thickness of the plate-shaped member cut out from the ingot becomes uneven, resulting in a decrease in productivity of the plate-shaped member.

[0008] Furthermore, when a wire electrode deviates from the wire guide groove, its parallel running becomes unstable, which in turn makes the electrical discharge machining unstable and makes the wire electrode more susceptible to breakage. Furthermore, if a wire electrode breaks and the broken wire electrode is reconnected to continue electrical discharge machining, the resulting machining groove is machined by the wire electrode that deviated from the wire guide groove and is shifted from the position that would have been formed by the parallel wire electrodes, making it difficult to resume electrical discharge machining from the position of the breakage. For this reason, detecting abnormalities is important in multi-wire electrical discharge machining devices.

[0009] However, the multi-wire electric discharge machining device described in Patent Document 1 detects abnormalities based on the current value between the electrodes, and therefore has the problem of being unable to detect defects that are not reflected in the current value, and therefore unable to accurately detect defects caused by misalignment of the wire electrodes.

[0010] The present disclosure has been made in view of the above, and has an object to provide a wire electric discharge machining apparatus that can accurately detect defects caused by misalignment of the wire electrode. [Means for solving the problem]

[0011] In order to solve the above-mentioned problems and achieve the object, the present disclosure provides a wire electric discharge machining apparatus that generates electric discharges between a plurality of traveling cutting wires and a workpiece, uses energy from the electric discharges to electric discharge machine the workpiece, and simultaneously cuts a plurality of wafers from the workpiece. The wire electric discharge machining apparatus includes a wire electrode having a plurality of cutting wires that are spaced apart in parallel and include portions that face the workpiece, a power supply unit that generates electric discharges between the plurality of cutting wires and the workpiece, a pair of wire parallel guide rollers that are arranged on both sides of the workpiece to sandwich the workpiece, and that have a plurality of equally spaced wire guide grooves formed in their outer peripheral surfaces that receive the traveling cutting wires and limit their movement, and a parallel wire tension position measurement unit that measures the distance between a measurement reference plane set parallel to an imaginary plane that includes the plurality of cutting wires and the wire electrodes that make up the plurality of cutting wires. The wire electric discharge machining device includes a wire guide groove disengagement detection unit that detects the occurrence of a change in distance based on the measurement results of the parallel wire tension position measurement unit, a wire state determination unit that determines whether the state is a wire disengagement state in which at least one cutting wire portion is disengaged from the wire guide groove, or a wire contact state in which all cutting wire portions are in contact with the wire guide groove, based on the detection results of the wire state determination unit, and a machining control unit that controls the stopping or continuation of electric discharge machining based on the determination results of the wire state determination unit. [Effects of the Invention]

[0012] According to the present disclosure, it is possible to obtain an advantageous effect of providing a wire electric discharge machining apparatus that can accurately detect defects caused by misalignment of the wire electrode. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a conceptual diagram showing a configuration example of a wire electric discharge machining apparatus according to a first embodiment. [Figure 2] FIG. 1 is a schematic diagram illustrating a configuration example of a wire tension state monitoring unit of a wire electric discharge machining apparatus according to a first embodiment; [Figure 3] FIG. 1 is a perspective view showing an example of installation of a parallel wire tension position measurement unit relative to a cutting wire unit in a wire electric discharge machining apparatus according to a first embodiment; [Figure 4] FIG. 1 is a block diagram showing an example of the configuration of a control unit and a wire tension state monitoring unit included in a wire electric discharge machining apparatus according to a first embodiment. [Figure 5] FIG. 1 is a diagram showing the positional relationship between a wire parallel guide roller, a parallel wire portion, and a guide roller holder in the wire electric discharge machining apparatus according to the first embodiment. [Figure 6] FIG. 1 is a schematic diagram showing parallel wires stretched over a plurality of wire guide grooves in a wire parallel guide roller included in the wire electric discharge machining apparatus according to the first embodiment; [Figure 7] FIG. 10 is a first schematic diagram illustrating an example of a state in which parallel wire portions are displaced from wire guide grooves in a wire parallel guide roller included in the wire electric discharge machining apparatus according to the first embodiment; [Figure 8] FIG. 2 is a second schematic diagram illustrating an example of a state in which the parallel wire portions are displaced from the wire guide grooves in the wire parallel guide roller included in the wire electric discharge machining apparatus according to the first embodiment; [Figure 9] FIG. 7 is a diagram showing an example of a detection value of a wire guide groove deviation detection unit in the state shown in FIG. 6. [Figure 10] FIG. 8 is a diagram showing an example of a detection value of a wire guide groove deviation detection unit in the state shown in FIG. 7; [Figure 11] FIG. 9 is a diagram showing an example of a detection value of a wire guide groove deviation detection unit in the state shown in FIG. 8 . [Figure 12]1 is a flowchart showing an operation during cutting of the wire electric discharge machining device according to the first embodiment; [Figure 13] FIG. 10 is a schematic diagram showing a configuration example of a wire contact machining state monitoring unit of a wire electric discharge machining device according to a second embodiment. [Figure 14] FIG. 10 is a block diagram showing an example of the configuration of a control unit and a wire contact machining state monitoring unit included in a wire electric discharge machining apparatus according to a second embodiment. [Figure 15] 10 is a characteristic diagram showing the timing of switching between application of machining voltage and wire contact detection in a wire electric discharge machining device according to a second embodiment. [Figure 16] FIG. 10 is a schematic diagram showing an example of a state in which parallel wire portions are disengaged from wire guide grooves in a wire parallel guide roller of a wire electric discharge machining device according to a second embodiment. [Figure 17] FIG. 17 is a conceptual diagram showing a detection value corresponding to the wire disconnection state in FIG. 16 and a state determination corresponding to the detection value. [Figure 18] FIG. 1 is a diagram showing a configuration in which the functions of the control unit according to the first and second embodiments are realized by hardware. [Figure 19] FIG. 1 is a diagram showing a configuration in which the functions of the control unit according to the first and second embodiments are realized by software. DETAILED DESCRIPTION OF THE INVENTION

[0014] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A wire electric discharge machining apparatus, a wire electric discharge machining method, and a wafer manufacturing method according to embodiments will be described in detail below with reference to the accompanying drawings.

[0015] Embodiment 1 Multi-wire electric discharge machining devices are used, for example, in semiconductor manufacturing processes, for slicing multiple semiconductor wafers from an ingot at once, i.e., for batch cutting of multiple semiconductor wafers. In multi-wire electric discharge machining devices, thin plates to be batch cut are cut by electric discharges generated between multiple cutting wires that are spaced apart from each other and arranged in parallel facing the workpiece. For this reason, in multi-wire electric discharge machining devices, the distance between the parallel cutting wires significantly affects the thickness of the thin plates to be cut.

[0016] Therefore, the multi-wire electric discharge machining device is provided with a pair of wire parallel guide rollers arranged on either side of the workpiece to sandwich the workpiece and prevent the mutual separation distance of the parallel cutting wire portions from changing from the start to the end of machining, and to prevent the cutting wire portions from shifting position.

[0017] The surface of the wire parallel guide roller is machined with multiple V-shaped wire guide grooves that define the distance between each wire electrode section. A wire electrode is placed in each wire guide groove and stretched between the pair of wire parallel guide rollers to form the cutting wire section.

[0018] The wire guide grooves are formed in the surface of the wire parallel guide rollers at a distance designed to cut out the thin plates to the desired thickness during electrical discharge cutting. The pair of wire parallel guide rollers restrain the multiple wire electrodes so that the distance between the multiple wire electrodes is maintained while allowing the cutting wires to travel in parallel during electrical discharge cutting.

[0019] In thin plate machining using a multi-wire electric discharge machining device, machining fluid is sprayed from a nozzle toward the machining groove along the tension direction of the cutting wire. When cutting a cylindrical ingot, the flow rate of the machining fluid is adjusted according to the cutting thickness. However, adjusting the flow rate of the machining fluid can cause vibrations in the wire electrode and fluctuations in the tension of the wire electrode. Furthermore, increasing the discharge energy to speed up the electric discharge cutting process increases the repulsive force caused by the discharge. The increased repulsive force caused by the discharge also causes vibrations in the wire electrode and fluctuations in the tension of the wire electrode. Alternatively, foreign matter such as machining chips generated during cutting can get caught in the wire guide groove of the wire parallel guide roller, resulting in a locally shallow wire electrode placement in the wire guide groove.

[0020] Furthermore, the wire electrode is pushed out and bent in the direction opposite to the direction of the ingot's machining surface by the impact force of the discharge. The direction of the ingot's machining surface is the direction in which the wire electrode processes the ingot, and the direction in which the wire electrode cuts the ingot. The direction opposite to the direction of the ingot's machining surface can be called the counter-machining direction or counter-cutting direction. In other words, the wire electrode is pushed out and bent in the counter-machining direction by the impact force of the discharge. The impact force of the discharge that pushes the wire electrode in the counter-machining direction is called the discharge repulsion force.

[0021] Due to the various disturbances described above, the wire electrode is pressed against one slope of the V-shaped wire guide groove rather than against the deepest part of the wire guide groove, and even falls out of the wire guide groove and continues to run on the outer circumferential surface of the wire parallel guide roller between the adjacent wire guide grooves. As a result, as the electric discharge cutting process with the cutting wire progresses, areas where the thickness suddenly changes occur in the thin plate processed thereafter, making it impossible to cut thin plates of uniform thickness in a single operation.

[0022] In the case of semiconductor wafers, if even a part of the semiconductor wafer is cracked or chipped, it will cause problems such as a decrease in yield in the polishing process of the sliced ​​semiconductor wafer or in the semiconductor manufacturing process after the polishing process. For this reason, cracks or chips in semiconductor wafers are a factor that significantly reduces the commercial value of the semiconductor wafers.

[0023] Specifically, in electrical discharge cutting, which uses a wire electrode to simultaneously cut multiple plate-like members from a workpiece, the flow rate of machining fluid supplied to the gap between thin plates being formed is increased to improve the discharge of chips generated by the discharge and the cooling of the wire heated by the discharge energy. This increases the pressure of the machining fluid flow on the wire electrode, causing it to vibrate. The wire electrode is also vibrated by the repulsive force of the discharge, which is proportional to the discharge energy. The wire electrode is also vibrated by chips accumulated in the wire guide groove of the wire parallel guide roller or by chips clogging the wire guide groove. The vibrated wire electrode during cutting may move away from its restraining position at the deepest V-groove in the wire guide groove, resulting in cutting the workpiece at a parallel spacing different from the design value.

[0024] At the position where the wire electrode is misaligned, the machined groove formed in the workpiece is bent from the designed position, resulting in a misalignment of the machined groove. The misaligned portion of the machined groove acts as a resistance to the inflow and outflow of machining fluid supplied into the machined groove, making it difficult for the machining fluid in the machined groove to be replaced. As a result, in electrical discharge cutting after the wire electrode is misaligned, the machining state becomes unstable, electrical discharge cutting performance deteriorates, the thickness of thin plates becomes uneven, and wire breakage becomes more likely.

[0025] When the workpiece is, for example, an ingot made of silicon carbide (SiC) crystal or an ingot made of gallium nitride (GaN) crystal, the diameter of the semiconductor wafer increases. As the diameter of the wafer increases, the distance between the pair of parallel wire guide rollers increases, which makes the wire electrode more likely to bend and cause it to come off the wire guide groove of the wire parallel guide roller.

[0026] Hereinafter, the thin plate separated by the cutting process will be referred to as a wafer.

[0027] FIG. 1 is a conceptual diagram showing a configuration example of a wire electric discharge machining apparatus 1000 according to the first embodiment. FIG. 2 is a schematic diagram showing a configuration example of a wire tension state monitoring unit 400 of the wire electric discharge machining apparatus 1000 according to the first embodiment. FIG. 2 shows the positional relationship between the workpiece W, wire parallel guide rollers 51a and 51b, guide roller holders 55a and 55b, nozzles 7a and 7b, vibration-damping guide rollers 4a and 4b, and a power supply unit 200. FIG. 2 also shows a state in which wire electric discharge cutting on a cylindrical workpiece W by the cutting wire unit 1b has progressed to a position approximately half the diameter of the workpiece W. FIG. 2 does not show the thin plate machining stabilization unit 70. FIG. 3 is a perspective view showing an example of installation of a parallel wire tension position measuring unit 52a relative to the cutting wire unit 1b in the wire electric discharge machining apparatus 1000 according to the first embodiment. FIG. 3 also shows the positional relationship between the workpiece W and the wire parallel guide rollers 51a and 51b, guide roller holders 55a and 55b, nozzles 7a and 7b, vibration-damping guide rollers 4a and 4b, and a power supply unit 200. Ruwa 1 shows a state in which the cutting wire portion 1b stretched between the ear parallel guide rollers 51a and 51b passes above the guide roller holder 55a.

[0028] The wire electric discharge machining apparatus 1000 is a multi-wire electric discharge machining apparatus that performs electric discharge cutting using a wire electrode 1. In Figures 2 and 3, arrow 101 indicates the traveling direction of the cutting wire 1b. In Figure 2, arrow 102 indicates the flow direction of the machining fluid.

[0029] FIG. 1 shows the x-axis, y-axis, and z-axis of a three-axis Cartesian coordinate system. The y-axis direction corresponds to the traveling direction of the wire electrode 1 over the workpiece W, i.e., the traveling direction of the wire electrode 1 relative to the workpiece W placed in the wire electric discharge machining apparatus 1000. The z-axis direction corresponds to the height direction of the wire electric discharge machining apparatus 1000. The height direction of the wire electric discharge machining apparatus 1000 corresponds to the up-down direction, i.e., the vertical direction. The x-axis direction corresponds to the direction in which the wire electrode 1 is arranged in parallel over the workpiece W, i.e., the direction in which the wire electrode 1 is arranged in parallel with the workpiece W placed in the wire electric discharge machining apparatus 1000. The x-axis direction can be said to be parallel to the longitudinal direction of the workpiece W placed in the wire electric discharge machining apparatus 1000.

[0030] The wire electric discharge machining apparatus 1000 includes a machining mechanism unit 100 that performs electric discharge cutting on a workpiece W using a wire electrode 1, a power supply unit 200 that supplies power, a control unit 300 that controls the wire electric discharge machining apparatus 1000, and a wire tension state monitoring unit 400. The wire electric discharge machining apparatus 1000 cuts out a plurality of plate-shaped members from the workpiece W at once. Examples of materials for the workpiece W include tungsten, molybdenum, silicon carbide, single crystal silicon, single crystal silicon carbide, gallium nitride, and polycrystalline silicon. Silicon carbide is also called silicon carbide. Hereinafter, electric discharge cutting may be simply referred to as cutting.

[0031] The processing mechanism 100 includes a plurality of guide rollers 2, a bobbin 3, vibration-damping guide rollers 4a, 4b, nozzles 7a, 7b, bobbin rotation control devices 8a, 8b, traverse control devices 9a, 9b, and a cutting and feeding stage 10. The plurality of guide rollers 2 are made up of guide roller 2a, guide roller 2b, guide roller 2c, and guide roller 2d. The bobbin 3 is made up of bobbin 3a and bobbin 3b.

[0032] The multiple guide rollers 2 guide the travel of the wire electrode 1. Each of the guide rollers 2a, 2b, 2c, and 2d is installed so that it can rotate around its own rotation axis. The guide rollers 2a, 2b, 2c, and 2d are spaced apart from one another and arranged so that their rotation axes are parallel to one another. Because the rotation axes of the guide rollers 2a, 2b, 2c, and 2d are parallel to one another, the wire electrode 1 can travel with high precision. The rotation axes of the guide rollers 2a, 2b, 2c, and 2d are arranged parallel to the x-axis.

[0033] A single wire electrode 1 is wound around guide rollers 2a, 2b, 2c, and 2d multiple times at intervals in the direction of the rotation axis of each of the guide rollers 2a, 2b, 2c, and 2d. These wire electrodes 1 are collectively referred to as the parallel wire section 1a. The portion of the parallel wire section 1a facing the workpiece W is referred to as the cutting wire section 1b. The cutting wire section 1b is made up of multiple parallel wire sections 1a arranged in parallel. The cutting wire sections 1b are preferably installed parallel to each other.

[0034] A plurality of wire guide grooves 2e are formed at equal intervals on the surfaces of the guide rollers 2a, 2b, 2c, and 2d. The wire electrode 1 is wound around the surfaces of the guide rollers 2a, 2b, 2c, and 2d along the plurality of wire guide grooves 2e, and the guide rollers 2a, 2b, 2c, and 2d maintain constant spacing between the wire electrodes 1, i.e., the spacing between the wire electrodes 1 of the parallel wire portions 1a. By arranging the cutting wire portions 1b parallel to one another and at equal intervals, the wire electric discharge machining apparatus 1000 can ensure that the thicknesses of the plurality of plate-shaped members cut out from the workpiece W are equal and that the cross sections of the plurality of plate-shaped members are parallel. The number of guide rollers 2 does not necessarily have to be four; it may be three or less, or five or more.

[0035] The bobbins 3a and 3b run the wire electrode 1 by unwinding and winding the wire electrode 1. The bobbin 3a unwinds the wire electrode 1. The bobbin 3b winds the wire electrode 1. The bobbin rotation control device 8a and the traverse control device 9a control the bobbin 3a. The bobbin rotation control device 8b and the traverse control device 9b control the bobbin 3b.

[0036] The bobbin rotation control device 8a controls the rotation of the bobbin 3a and controls the travel of the wire electrode 1. The bobbin rotation control device 8a controls, for example, the travel direction and travel speed of the wire electrode 1. The bobbin rotation control device 8b controls the rotation of the bobbin 3b and controls the travel of the wire electrode 1. The bobbin rotation control device 8b controls, for example, the travel direction and travel speed of the wire electrode 1.

[0037] The traverse control device 9a controls the position of the bobbin 3a in the x-axis direction in correspondence with the unwinding position of the wire electrode 1. The traverse control device 9b controls the position of the bobbin 3b in the x-axis direction in correspondence with the winding position of the wire electrode 1. The position control of the bobbins 3a and 3b by the traverse control devices 9a and 9b is called traverse control. The traverse control enables the bobbins 3a and 3b to travel the wire electrode 1 stably and with high precision.

[0038] The wire electrode 1 unwound from the bobbin 3a is wound around the guide roller 2b, the guide roller 2a, the guide roller 2d, and the guide roller 2c in this order, and then continues to be wound around the guide roller 2b again. In this way, the wire electrode 1 makes multiple revolutions between the guide rollers 2a, 2b, 2c, and 2d before being wound onto the bobbin 3b.

[0039] The workpiece W is placed on a workpiece fixing plate 42 fixed to a cutting feed stage 10, which will be described later. The workpiece fixing plate 42 to which the workpiece W is fixed is disposed between the wire parallel guide roller 51a and the wire parallel guide roller 51b in the y-axis direction.

[0040] The wire parallel guide rollers 51a and 51b are arranged on either side of the workpiece W in the y-axis direction, sandwiching the workpiece W therebetween. The wire parallel guide rollers 51a and 51b are also installed between the vibration-damping guide roller 4a and the vibration-damping guide roller 4b in the y-axis direction. The wire parallel guide rollers 51a and 51b limit the movement of the wire electrode 1 in the x-axis direction. Specifically, the wire parallel guide rollers 51a and 51b limit the movement of the parallel wire portion 1a and the cutting wire portion 1b in the x-axis direction.

[0041] Like the guide rollers 2a, 2b, 2c, and 2d, the wire parallel guide rollers 51a and 51b each have a rotation axis and are installed so as to be rotatable around their respective rotation axes. The wire parallel guide rollers 51a and 51b are spaced apart from each other in the y-axis direction and are arranged so that their rotation axes are parallel to each other. Because the rotation axes of the wire parallel guide rollers 51a and 51b are parallel to each other, the wire electrode 1 can be run with high precision. The rotation axes of the wire parallel guide rollers 51a and 51b are arranged parallel to the x-axis.

[0042] A plurality of wire guide grooves 51c are formed on the surfaces of the wire parallel guide rollers 51a, 51b at equal intervals, at pre-designed intervals. The wire electrodes 1 run on the surfaces of the wire parallel guide rollers 51a, 51b along the plurality of wire guide grooves 51c, and the wire parallel guide rollers 51a, 51b thereby maintain constant spacing between the wire electrodes 1, i.e., the spacing between the wire electrodes 1 of the parallel wire portions 1a. By arranging the cutting wire portions 1b parallel to one another and at equal intervals, the wire electric discharge machining apparatus 1000 can equalize the thicknesses of the plurality of plate-shaped members cut out from the workpiece W and make the cross sections of the plurality of plate-shaped members parallel.

[0043] That is, the wire parallel guide rollers 51a, 51b guide the parallel wire portion 1a and the cutting wire portion 1b of the wire electrode 1, which are wound multiple times at equal intervals in the direction of the rotation axis of each of the guide rollers 2a, 2b, 2c, 2d and run spaced apart from each other, thereby suppressing vibration of the parallel wire portion 1a in the section of the cutting thickness of the workpiece W. As a result, the wire parallel guide rollers 51a, 51b can maintain the arrangement spacing of the parallel wire portions 1a and the cutting wire portions 1b with high precision, allowing the parallel wire portions 1a and the cutting wire portions 1b to run.

[0044] As shown in FIG. 2, the wire parallel guide rollers 51a and 51b are supported by a pair of guide roller holders 55a and 55b that are equipped with bearings that support the wire parallel guide rollers 51a and 51b so that the wire parallel guide rollers 51a and 51b can rotate around their respective rotation axes.

[0045] The pair of guide roller holders 55a, 55b are fixed to either side of the workpiece W so that the workpiece W is sandwiched in the y-axis direction and the rotation axes of the wire parallel guide rollers 51a, 51b are arranged parallel to the x-axis direction. As shown in FIG. 3 , the guide roller holder 55a supports the rotation axis 51a2 of the wire parallel guide roller 51a with the upper end portion 51a1 of the wire parallel guide roller 51a protruding upward from the upper surface 55a1 of the guide roller holder 55a, thereby supporting the wire parallel guide roller 51a. Similarly, the guide roller holder 55b supports the rotation axis of the wire parallel guide roller 51b with the upper end portion (not shown) of the wire parallel guide roller 51b protruding upward from the upper surface (not shown) of the guide roller holder 55b, thereby supporting the wire parallel guide roller 51b.

[0046] Nozzle 7a is disposed between vibration-damping guide roller 4a and workpiece W in the y-axis direction. Nozzle 7b is disposed between vibration-damping guide roller 4b and workpiece W in the y-axis direction. Each of nozzles 7a and 7b is disposed above the parallel wire portions 1a, sandwiching the parallel wire portions 1a between itself and wire parallel guide rollers 51a and 51b, and spaced apart from the parallel wire portions 1a in the z-axis direction. Machining fluid supplied from a machining fluid supply pipe 62 is filled inside the nozzles 7a and 7b. Each of nozzles 7a and 7b has machining fluid ejection holes 7c that eject the machining fluid filled inside toward the workpiece W in the thin plate machining stabilization unit 70. The parallel wire portions 1a travel below the machining fluid ejection holes 7c of nozzles 7a and 7b.

[0047] A machining fluid tank and a pump may be connected to the nozzles 7a and 7b. Alternatively, the thin plate machining stabilization unit 70, to which the workpiece W is fixed, may be placed inside a machining tank containing machining fluid, and the electric discharge machining may be performed with the workpiece W immersed in the machining fluid.

[0048] In the wire electric discharge machining apparatus 1000, the wire parallel guide rollers 51a, 51b restrict the movement of the wire electrode 1 in the x-axis direction, and further, the vibration-damping guide rollers 4a, 4b restrict the movement of the wire electrode 1 in the z-axis direction, thereby suppressing vibration of the wire electrode 1 in the cutting wire portion 1b. Note that, although the portion of the parallel wire portion 1a facing the workpiece W is referred to as the cutting wire portion 1b above, the portions of the parallel wire portion 1a on the wire parallel guide rollers 51a and 51b, and the portions between the wire parallel guide rollers 51a and 51b, will also be referred to as the cutting wire portion 1b. Note that, in the wire electric discharge machining apparatus 1000, the vibration-damping guide rollers 4a and 4b may be omitted.

[0049] The cutting feed stage 10 changes the relative position between the workpiece W and the cutting wire 1b. Specifically, the cutting feed stage 10 changes the relative position between the cutting wire 1b and a workpiece fixing plate 42 to which the workpiece W is fixed. In the first embodiment, the position of the cutting wire 1b is fixed in the z-axis direction, and the cutting feed stage 10 is movable in the z-axis direction. The cutting feed stage 10 moves the workpiece W in the vertical direction. The wire electric discharge machining device 1000 cuts the workpiece W by moving the cutting feed stage 10 in the vertical direction to move the workpiece W closer to or farther away from the cutting wire 1b. Furthermore, by electric discharge machining of the workpiece W, a machined groove is formed in the workpiece W along the cutting wire 1b. The cutting feed stage 10 may be movable in the x-axis, y-axis, and z-axis directions.

[0050] The machining mechanism 100 may include components such as a guide pulley that suppresses vibration of the wire electrode 1, a load cell that measures the tension of the wire electrode 1, and a dancer roller that controls the tension of the wire electrode 1. The machining mechanism 100 may use the load cell and the dancer roller to maintain the tension of the wire electrode 1 within a range suitable for the running of the wire electrode 1. For example, the dancer roller may control the tension of the wire electrode 1 by changing the payout speed and winding speed of the wire electrode 1.

[0051] The power supply section 200 includes a machining power source 5 and electronic supply units 6a and 6b. The machining power source 5 supplies power to the wire electrode 1 via the electronic supply units 6a and 6b connected to the wire electrode 1. The machining power source 5 also supplies power to the workpiece W via a machining fluid rectifying plate 71a, which will be described later. The electronic supply units 6a and 6b, which serve as power supply means, are an assembly of multiple electronic supply units 11. The electronic supply units 11 are insulated from one another. Each wire electrode 1 of the cutting wire portion 1b is supplied with power from the electronic supply units 11, and a machining current flows through each wire electrode 1. The machining power source 5, which serves as power supply means, has its power supply side terminals electrically connected to the electronic supply units 6a and 6b, respectively, and its ground side terminal electrically connected to the workpiece W. Therefore, a voltage pulse output from the machining power source 5 is applied between the wire electrode 1 of the cutting wire portion 1b and the workpiece W. The machining power source 5, the multiple electronic supply units 11, and the workpiece W W and is the power supply line 12a, 12b The electrical connection is made by

[0052] The thin plate processing stabilization unit 70 is a mechanism that prevents poor power supply to each thin plate during cutting. The thin plate processing stabilization unit 70 is disposed between the vibration-damping guide roller 4a and the vibration-damping guide roller 4b, and between the nozzles 7a and 7b. The thin plate processing stabilization unit 70 includes a pair of machining fluid rectification plates 71a and 71b, and a workpiece holder 72.

[0053] The pair of machining fluid rectifying plates 71, machining fluid rectifying plate 71a and machining fluid rectifying plate 71b, are electrically conductive and arranged parallel to the traveling direction of cutting wire 1b to rectify the flow of machining fluid. Machining fluid rectifying plate 71a and machining fluid rectifying plate 71b are arranged between nozzle 7a and nozzle 7b. Machining fluid rectifying plate 71a and machining fluid rectifying plate 71b have a plate-like or rectangular parallelepiped shape and are arranged with their opposing surfaces parallel to each other.

[0054] The machining fluid rectifying plate 71a is the first of the pair of machining fluid rectifying plates 71, and is connected to the machining power source 5. As a result, power is supplied from the electric discharge machining power source to the workpiece W from the machining fluid rectifying plate 71a, which is in contact with the end face of the workpiece W.

[0055] The machining fluid rectifying plate 71b is the second of the pair of machining fluid rectifying plates 71, and is positioned parallel to the machining fluid rectifying plate 71a with the workpiece W fixed to the workpiece fixing plate 42 sandwiched between it and the machining fluid rectifying plate 71a.

[0056] Machining fluid rectifying plate 71b is in close contact with workpiece W and, together with machining fluid rectifying plate 71a, forms a flow path that guides machining fluid supplied from nozzles 7a and 7b toward workpiece W. Machining fluid is supplied from nozzles 7a and 7b toward workpiece W through the gap between machining fluid rectifying plate 71a and machining fluid rectifying plate 71b. This prevents the machining fluid from diffusing in the thickness direction of the thin plate being formed, i.e., in the x-axis direction.

[0057] In the wire electric discharge machining apparatus 1000, the machining fluid supplied from the nozzles 7a, 7b is rectified as described above, thereby suppressing diffusion of the machining fluid and reducing the possibility of the thin plate being shaken by the machining fluid and cracking during formation.

[0058] The workpiece W is sandwiched between the machining fluid rectifying plates 71a and 71b and is placed and fixed on the workpiece fixing plate 42 inside the thin plate machining stabilizing section 70. The workpiece W is fixed on the workpiece fixing plate 42 by a jig (not shown) for fixing the workpiece W placed on the cutting feed stage 10.

[0059] When the workpiece W is a material for semiconductor wafers, the workpiece W is often formed into a cylindrical shape in advance so that the cut thin plate will be a circular thin plate. Here, the curved cylindrical side surface of the cylindrical workpiece W is referred to as the outer circumferential side surface. The workpiece W is placed on the workpiece fixing plate 42 inside the thin plate processing stabilization unit 70 so that the outer circumferential side surface faces the cutting wire portion 1b. The workpiece W is cut into rings by the cutting wire portion 1b, and a thin plate, a wafer, is processed from the workpiece W.

[0060] A certain voltage is applied to the gap between the cutting wire 1b and the workpiece W. When the gap reaches a certain value, an electric discharge occurs between the electrodes, causing the cutting wire 1b to heat up and melt the workpiece W, resulting in multiple plate-like members being cut out all at once. When machining fluid is supplied to the gap between the workpiece W and the cutting wire 1b during cutting, machining debris generated between the workpiece W and the cutting wire 1b can be discharged outside the gap. Because this machining debris can cause a short circuit between the workpiece W and the cutting wire 1b, supplying machining fluid can reduce the frequency of short circuits.

[0061] The workpiece holder 72 holds down the multiple thin plates in the process of being formed from the outer peripheral side of the multiple thin plates at the cut start side, thereby collectively fixing the multiple thin plates in the process of being formed. By collectively fixing the multiple thin plates in the process of being formed, the workpiece holder 72 can suppress shaking of the multiple thin plates due to vibration of the workpiece W generated by the hydraulic pressure of the machining fluid flow that is applied to the cut surfaces of the multiple thin plates.

[0062] The wire tension state monitoring unit 400 monitors the tension state of the parallel wire portion 1a during cutting. FIG. 4 is a block diagram showing an example configuration of the control unit 300 and the wire tension state monitoring unit 400 provided in the wire electric discharge machining apparatus 1000 according to the first embodiment. The wire tension state monitoring unit 400 includes parallel wire tension position measuring units 52a and 52b, a wire guide groove deviation detecting unit 53, and a wire state determining unit 54. The parallel wire tension position measuring units 52a and 52b are connected to the wire guide groove deviation detecting unit 53. The wire guide groove deviation detecting unit 53 is connected to the wire state determining unit 54. The wire state determining unit 54 is connected to the machining control device 31 of the control unit 300. These components constitute the wire tension state monitoring unit 400 for the cutting wire portion 1b.

[0063] The pair of parallel wire tensioning position measuring units 52a, 52b are installed on guide roller holders 55a, 55b as shown in Figures 2 and 3. The pair of parallel wire tensioning position measuring units 52a, 52b are installed on the guide roller holders 55a, 55b in a state facing the wire electrode 1 that is tensioned in the wire guide grooves 51c of the wire parallel guide rollers 51a, 51b and runs parallel to each other.

[0064] The parallel wire tension position measuring unit 52a is disposed in the guide roller holder 55a at a position corresponding to the gap between the pair of wire parallel guide rollers 51a, 51b and above which the cutting wire 1b passes. That is, the parallel wire tension position measuring unit 52a is disposed in the guide roller holder 55a at a position closer to the workpiece W than the wire parallel guide roller 51a in the y-axis direction and below the cutting wire 1b.

[0065] The parallel wire tension position measuring unit 52b is disposed in the guide roller holder 55b at a position corresponding to the gap between the pair of wire parallel guide rollers 51a, 51b and above which the cutting wire 1b passes. That is, the parallel wire tension position measuring unit 52b is disposed in the guide roller holder 55b at a position closer to the workpiece W than the wire parallel guide roller 51b in the y-axis direction and below the cutting wire 1b.

[0066] The cutting wire 1b passes above the guide roller holders 55a, 55b. In the height direction, the distance between the cutting wire 1b and the upper surface of each of the guide roller holders 55a, 55b is set to 1 mm or less. Therefore, the end faces of the sensors of the parallel wire position measuring units 52a, 52b installed on the guide roller holders 55a, 55b are installed so as to be at approximately the same height as the upper surfaces of the guide roller holders 55a, 55b. The end faces of the sensors of the parallel wire position measuring units 52a, 52b are the upper surfaces of the parallel wire position measuring units 52a, 52b. In the example shown in FIG. 3, the upper surface 52a1, which is the end face of the sensor of the parallel wire position measuring unit 52a, is installed so as to be at approximately the same height as the upper surface 55a1 of the guide roller holder 55a.

[0067] In addition, as long as it is within a range that does not interfere with the cutting wire portion 1b and is within the detection capability range of the sensors of the parallel wire tensioning position measuring units 52a, 52b, the installation positions of the parallel wire tensioning position measuring units 52a, 52b in the height direction do not necessarily have to be set so that the distance from the upper surface of each of the guide roller holders 55a, 55b is 1 mm or less.

[0068] During the cutting process, the pair of parallel wire position measuring units 52a, 52b measure the height distance L to the parallel wire section 1a facing the parallel wire position measuring units 52a, 52b at a predetermined cycle and monitor changes in the distance L. The height distance L to the parallel wire section 1a facing the parallel wire position measuring units 52a, 52b can be expressed as the height distance L between the parallel wire section 1a and the upper surfaces 55a1 of the guide roller holders 55a, 55b, which serve as a predetermined measurement reference plane. That is, during the cutting process, each of the pair of parallel wire position measuring units 52a, 52b measures the height distance L between the parallel wire section 1a and the upper surfaces 55a1 of the guide roller holders 55a, 55b, which serve as a predetermined measurement reference plane.

[0069] The pair of parallel wire position measuring units 52a, 52b use the upper surfaces 55a1 of the guide roller holders 55a, 55b, which are approximately parallel to the same virtual plane including the wire electrodes 1 of the cutting wire unit 1b arranged in parallel between the pair of wire parallel guide rollers 51a, 51b, as a predetermined measurement reference plane, and the height position of the upper surfaces 52a1 of the parallel wire position measuring units 52a, which are the tips of the detection units of the parallel wire position measuring units 52a, 52b, is set in accordance with the height of the measurement reference plane. ,52b This is the end face of the sensor.

[0070] Therefore, the pair of parallel wire position measuring units 52a, 52b measure the distance L in the height direction between the tips of the detection units of the pair of parallel wire position measuring units 52a, 52b and the parallel wire portion 1a at a predetermined cycle. The pair of parallel wire position measuring units 52a, 52b then measure the distance L between a measurement reference plane set parallel to an imaginary plane including the multiple cutting wire portions 1b and the wire electrodes 1 that constitute the multiple cutting wire portions 1b. The pair of parallel wire position measuring units 52a, 52b transmit information on the measurement result, that is, the distance L, to the wire guide groove displacement detecting unit 53.

[0071] The pair of parallel wire tension position measuring units 52a, 52b includes at least one of an eddy current displacement sensor, a capacitance displacement sensor, a current detection sensor, and a contact detection displacement sensor as a sensor, and measures the distance L using the sensor.

[0072] The wire guide groove deviation detection unit 53 detects occurrence of a change in the distance L detected by the parallel wire position measurement units 52a, 52b that exceeds a predetermined standard, based on the measurement results of the parallel wire position measurement units 52a, 52b. That is, the wire guide groove deviation detection unit 53 acquires the measurement results of the distance L in the height direction between the parallel wire position measurement units 52a, 52b and the parallel wire section 1a. Then, the wire guide groove deviation detection unit 53 compares the acquired measurement results of the distance L with a distance threshold, which is a predetermined standard, to detect occurrence of a change in the distance L that exceeds the distance threshold. That is, the wire guide groove deviation detection unit 53 detects occurrence of a change in the distance L that exceeds the predetermined standard.

[0073] FIG. 5 is a diagram showing the positional relationship between the wire parallel guide roller 51a, the parallel wire portion 1a, and the guide roller holder 55a in the wire electric discharge machining apparatus 1000 according to the first embodiment. FIG. 5 shows a longitudinal cross section of the wire parallel guide roller 51a and the parallel wire portion 1a taken along line VV in FIG. 3, and the positional relationship between the guide roller holder 55a. That is, FIG. 5 shows the positional relationship between the guide roller holder 55a and a longitudinal cross section passing through the rotation axis 51a2 of the wire parallel guide roller 51a when the parallel wire portion 1a and the wire parallel guide roller 51a stretched between the wire parallel guide rollers 51a and 51b are viewed from the direction of arrow 103 in FIG. 3. FIG. 5 also shows a state in which the parallel wire portion 1a is caught in the multiple wire guide grooves 51c in the wire parallel guide roller 51a. FIG. 5 also shows a plane 43, which is a virtual same plane including the wire electrodes 1 of the parallel wire portion 1a arranged in parallel between the pair of wire parallel guide rollers 51a and 51b.

[0074] Fig. 6 is a schematic diagram showing the parallel wire portion 1a stretched in the wire guide grooves 51c of the wire parallel guide rollers 51a and 51b included in the wire electric discharge machining apparatus 1000 according to the first embodiment. Fig. 6 corresponds to a part of Fig. 5. Fig. 6 shows the normal state in which the parallel wire portion 1a is fitted in the deepest part of the wire guide groove 51c.

[0075] 7 is a first schematic diagram showing an example of a state in which the parallel wire portions 1a have come out of the wire guide grooves 51c of the wire parallel guide rollers 51a, 51b included in the wire electric discharge machining apparatus 1000 according to the first embodiment. Fig. 7 shows an abnormal state in which some of the parallel wire portions 1a have come out of the wire guide grooves 51c of the wire parallel guide roller 51a due to the disturbance described above and have climbed onto the outer peripheral surface 51d of the wire parallel guide roller 51a.

[0076] Fig. 8 is a second schematic diagram showing an example of a state in which the parallel wire portion 1a has come out of the wire guide groove 51c in the wire parallel guide roller 51a included in the wire electric discharge machining apparatus 1000 according to the first embodiment. Fig. 8 shows a state in which the parallel wire portion 1a that has come out of the wire guide groove 51c in the state shown in Fig. 7 has moved further and is now fitted into the adjacent wire guide groove 51c.

[0077] FIG. 9 is a diagram showing an example of the detection value of the wire guide groove deviation detection unit 53 in the state shown in FIG. 6. FIG. 10 is a diagram showing an example of the detection value of the wire guide groove deviation detection unit 53 in the state shown in FIG. 7. FIG. 11 is a diagram showing an example of the detection value of the wire guide groove deviation detection unit 53 in the state shown in FIG. 8. FIGS. 9 to 11 correspond to the tensioned state of the parallel wire section 1a and show, in graph form, the detected value of the distance L in the height direction between the parallel wire section 1a facing the parallel wire tension position measurement units 52a and 52b, converted into an electrical signal. The horizontal axis in FIGS. 9 to 11 represents the measurement time. The vertical axis in FIGS. 9 to 11 represents the detected value of the distance L converted into an electrical signal.

[0078] The distance L between the parallel wire portion 1a and the detection unit of each of the parallel wire position measuring units 52a, 52b is determined by the position of the wire guide groove 51c in the height direction and does not fluctuate significantly when the electric discharge machining is stable. However, due to external disturbances such as changes in the flow of machining fluid caused by changes in machining conditions or fluctuations in wire tension caused by increases in electric discharge energy, abnormalities in the alignment of the parallel wire portion 1a may occur, as shown in Figures 7 and 8.

[0079] Specifically, during cutting in the wire electric discharge machining apparatus 1000, machining fluid is sprayed from the nozzles 7a and 7b toward the machining groove along the tension direction of the parallel wire portion 1a. When cutting a cylindrical workpiece W, the flow rate of the machining fluid is adjusted according to the cutting thickness. However, adjusting the flow rate of the machining fluid can cause vibration of the parallel wire portion 1a and fluctuations in the tension of the parallel wire portion 1a. Furthermore, increasing the discharge energy to speed up the electric discharge machining increases the repulsive force caused by the discharge. The increase in the repulsive force caused by the discharge also causes vibration of the parallel wire portion 1a and fluctuations in the tension of the parallel wire portion 1a. Alternatively, foreign matter such as machining chips generated during cutting can get caught in the wire guide grooves 51c of the wire parallel guide rollers 51a and 51b, resulting in a localized shallowness of the parallel wire portion 1a in the wire guide grooves 51c.

[0080] Furthermore, during cutting in the wire electric discharge machining apparatus 1000, the parallel wire portions 1a are pushed out and bent in the direction opposite to the direction of the machining surface of the workpiece W by the impact force of the electric discharge. The direction of the machining surface of the workpiece W is the direction in which the parallel wire portions 1a machine the workpiece W. The direction opposite to the direction of the machining surface of the workpiece W can be said to be the opposite machining direction. In other words, the parallel wire portions 1a are pushed out and bent in the opposite machining direction by the impact force of the electric discharge during cutting. The impact force of the electric discharge that pushes the parallel wire portions 1a in the opposite machining direction during cutting is called the discharge repulsion force.

[0081] During cutting in the wire electric discharge machining apparatus 1000, the above-mentioned disturbance causes the parallel wire part 1a to be pressed against one slope of the V-shaped wire guide groove 51c rather than against the deepest part of the wire guide groove 51c of the wire parallel guide rollers 51a, 51b, and further to come out of the wire guide groove 51c and continue running on the outer circumferential surface 51d of the wire parallel guide rollers 51a, 51b between the adjacent wire guide grooves 51c. As a result, as electric discharge machining by the parallel wire part 1a progresses, areas where the thickness suddenly changes occur in the thin plate machined thereafter, making it impossible to cut thin plates with a uniform thickness in a single operation.

[0082] 9, it can be seen that the distance L remains constant at distance L1, indicating that the parallel wire portion 1a is normally stuck in the deepest part of the wire guide groove 51c. FIG. 10 shows that the distance L begins to change to distance L2 from time T1, indicating that the parallel wire portion 1a begins to disengage from the wire guide groove 51c of the wire parallel guide rollers 51a and 51b and climbs onto the outer peripheral surface 51d of the wire parallel guide roller 51a. FIG. 11 also shows that the distance L2 begins to change to distance L3 from time T2, indicating that the parallel wire portion 1a, having disengaged from the wire guide groove 51c, continues to move and becomes stuck in the adjacent wire guide groove 51c.

[0083] That is, in the wire tension state of the parallel wire portion 1a shown in Fig. 6, all of the wire electrodes 1 are tensioned while being fitted into the wire guide grooves 51c. Therefore, the detected value of the distance L by the parallel wire tension position measuring units 52a and 52b is a constant distance L1, as shown in Fig. 9.

[0084] In Figure 7, when the wire electrode 1 of the parallel wire section 1a comes off from some of the multiple wire guide grooves 51c, the detection value of the parallel wire tensioning position measuring units 52a and 52b changes from the steady-state distance L1 to the distance L2 as shown in Figure 10, and the wire guide groove detachment detection unit 53 detects that an abnormality has occurred in the wire tensioning state of the parallel wire section 1a.

[0085] In Figure 8, the wire electrode 1 of the parallel wire portion 1a, which has come out of the wire guide groove 51c, gets stuck in the adjacent wire guide groove 51c, causing the detection value of the parallel wire tensioning position measuring units 52a and 52b to change from distance L2 to distance L3 as shown in Figure 11, and the wire guide groove dislocation detection unit 53 detects that a change has occurred in the wire tensioning state of the parallel wire portion 1a.

[0086] As described above, during cutting, the parallel wire position measuring units 52a and 52b detect changes in the distance L, which indicates the position of the parallel wire section 1a in the height direction. The parallel wire position measuring units 52a and 52b then send the measurement results, ie, the detected value of the distance L, to the wire guide groove deviation detecting unit 53. The wire guide groove deviation detecting unit 53 converts the detected values ​​of the parallel wire position measuring units 52a and 52b into electrical signals and calculates the change in the distance L as a difference ΔL. In the example of FIG. 7, the change from distance L1 to distance L2 is calculated as the difference ΔL.

[0087] When the difference ΔL exceeds a predetermined criterion, the wire guide groove deviation detection unit 53 transmits information about the difference ΔL to the wire condition determination unit 54, thereby notifying the wire condition determination unit 54 of the occurrence of a change in the distance L that exceeds the predetermined criterion. The predetermined criterion is stored in the wire guide groove deviation detection unit 53.

[0088] Based on the detection result from the wire guide groove disengagement detector 53, the wire state determiner 54 determines whether at least one parallel wire portion 1a is disengaged from the wire guide groove 51c, i.e., whether all parallel wire portions 1a are in contact with the wire guide groove 51c, i.e., whether they are in a wire disengaged state. The wire state determiner 54 compares the difference ΔL transmitted from the wire guide groove disengagement detector 53 with a predetermined reference value of the distance L to determine whether the tension state of the parallel wire portions 1a has changed. If the difference ΔL exceeds the predetermined reference value of the distance L, the wire state determiner 54 determines that there has been a change in the tension state of the parallel wire portions 1a, i.e., the tension state of the cutting wire portions 1b. In this case, a parallel abnormality has occurred in the wire electrode 1. If the difference ΔL does not exceed the predetermined reference value of the distance L, the wire state determiner 54 determines that there has been no change in the tension state of the parallel wire portions 1a, i.e., the tension state of the cutting wire portions 1b.

[0089] The wire state determination unit 54 transmits parallel wire tension state information ps, which is the determination result and state monitoring information, to the processing control device 31 of the control unit 300.

[0090] The control unit 300 controls the entire wire electric discharge machining apparatus 1000. The control unit 300 controls the entire wire electric discharge machining apparatus 1000 based on the state monitoring information transmitted from the wire state determination unit 54 of the wire tension state monitoring unit 400. The control unit 300 includes a machining control unit 31, an electric discharge waveform control unit 32, a cutting stage drive control unit 34, and a wire travel control unit 35.

[0091] The machining control device 31 controls the discharge waveform control device 32, the cutting stage drive control device 34, and the wire travel control device 35 based on the parallel wire tension state information ps acquired from the wire state determination unit 54 of the wire tension state monitoring unit 400.

[0092] The discharge waveform control device 32 controls the machining power source 5 based on the discharge waveform command wc input from the machining control device 31, and controls the voltage waveform applied to the machining gap or the current waveform flowing in the machining gap.

[0093] The wire travel control device 35 drives and controls the bobbin rotation control devices 8a and 8b based on the wire electrode travel command rc input from the machining control device 31, thereby controlling the travel of the wire electrode 1. Furthermore, the wire travel control device 35 drives and controls the traverse control devices 9a and 9b based on the wire electrode travel command rc input from the machining control device 31, thereby controlling the traverse control.

[0094] The cutting stage drive control device 34 drives the cutting feed stage 10 based on a stage command sc input from the processing control device 31, and controls the relative position between the workpiece W and the cutting wire portion 1b.

[0095] FIG. 12 is a flowchart showing the operation of the wire electric discharge machining apparatus 1000 according to the first embodiment during cutting.

[0096] When cutting starts, a parallel-wire position measuring step is performed in step S110. That is, the parallel-wire position measuring units 52a and 52b measure the distance L between the measurement reference plane, which is set parallel to the imaginary plane including the plurality of cutting wires 1b as described above, and the wire electrodes 1 that constitute the plurality of cutting wires 1b. The parallel-wire position measuring units 52a and 52b transmit information on the measurement result, that is, the distance L, to the wire guide groove displacement detecting unit 53.

[0097] Next, in step S120, a wire guide groove deviation detection process is performed. That is, the wire guide groove deviation detection unit 53 detects the occurrence of a change in the distance L based on the measurement results of the parallel wire tension position measurement units 52a and 52b as described above. The wire guide groove deviation detection unit 53 calculates the change in the distance L as a difference ΔL. If the difference ΔL exceeds a predetermined standard, the wire guide groove deviation detection unit 53 transmits information about the difference ΔL to the wire condition determination unit 54.

[0098] Next, in step S130, a wire state determination step is performed. That is, the wire state determination unit 54 determines whether at least one wire electrode 1 of the parallel wire portion 1a is in a wire-disengaged state where it is disengaged from the wire guide groove 51c, or whether all wire electrodes 1 of the parallel wire portion 1a are in a wire-contact state where they are in contact with the wire guide groove 51c, based on the detection result of the wire guide groove disengagement detection unit 53. When the wire state determination unit 54 determines that there has been a change in the tension state of the parallel wire portion 1a, it transmits parallel wire tension state information ps, which is state monitoring information, to the machining control device 31 of the control unit 300.

[0099] Next, in step S140, a machining control step is performed. That is, the machining control device 31 controls the stop or continuation of electric discharge machining based on the parallel wire tension state information ps, which is the determination result of the wire state determination unit 54. The machining control device 31 controls the continuation of electric discharge machining when the parallel wire tension state information ps indicates that there is no change in the tension state of the parallel wire portion 1a, i.e., the tension state of the cutting wire portion 1b. The machining control device 31 controls the stop of electric discharge machining when the parallel wire tension state information ps indicates that there is a change in the tension state of the parallel wire portion 1a, i.e., the tension state of the cutting wire portion 1b. That is, the machining control device 31 stops wire electric discharge machining simultaneously with the occurrence of a parallel abnormality in the wire electrode 1.

[0100] As described above, the wire electric discharge machining apparatus 1000 according to the first embodiment can detect an abnormal parallel state caused by the wire electrode 1 of the parallel wire portion 1a being displaced from the wire guide groove 51c immediately after the abnormal parallel state occurs. The abnormal parallel state is an abnormal state in which the multiple wire electrodes 1 of the cutting wire portion 1b, which are normally stretched parallel and at equal intervals between the pair of wire parallel guide rollers 51a, 51b, are no longer stretched parallel and at equal intervals. In other words, the wire electric discharge machining apparatus 1000 can accurately and promptly detect misalignment of the wire electrodes 1, and can accurately and promptly detect defects caused by the misalignment of the wire electrodes 1. The wire electric discharge machining apparatus 1000 can detect a parallel abnormality caused by some of the wire electrodes 1 of the parallel wire section 1a coming out of the wire guide groove 51c immediately after the abnormality occurs, and wire electric discharge machining is stopped immediately upon occurrence of the parallel abnormality of the wire electrodes 1. This prevents a large amount of thin plate whose thickness fluctuates during cutting due to electric discharge machining in which the parallel distance between the wire electrodes 1 of the parallel wire section 1a changes during cutting.

[0101] Furthermore, since the wire electric discharge machining apparatus 1000 stops cutting immediately upon occurrence of an abnormality in the parallel alignment of the wire electrode 1, the formation of abnormal portions on the surface of the thin plate being cut can be minimized. As a result, after the parallel state of the parallel wire portions 1a has been repaired, the wire electric discharge machining apparatus 1000 can resume cutting from the machining stop position without causing unstable machining, improving the machining accuracy of the thin plate and increasing the yield of thin plate machining. Therefore, when cutting a semiconductor ingot, for example, the wire electric discharge machining apparatus 1000 does not waste expensive semiconductor crystals and can reduce wafer production costs.

[0102] Furthermore, the wire electric discharge machining apparatus 1000 can stop cutting early when the parallel wire portion 1a is in an abnormal parallel state, thereby preventing the formation of serpentine portions in the machining groove of the workpiece W, which reduces the amount of machining fluid supplied between the electrodes during cutting and hinders the discharge of machining chips, and can prevent the wire electrode 1 from breaking.

[0103] Furthermore, in the wire electric discharge machining apparatus 1000, the parallel-wire tensioning position measuring units 52a, 52b are provided with at least one of an eddy current displacement sensor, a capacitance displacement sensor, an electrical conduction detection sensor, and a contact detection displacement sensor as a sensor, and measure the distance L using the sensor. This allows the wire electric discharge machining apparatus 1000 to accurately and promptly detect an abnormal parallel state caused by some of the wire electrodes 1 of the parallel wire portion 1a coming out of the wire guide grooves 51c immediately after the abnormal parallel state occurs.

[0104] Therefore, the wire electric discharge machining apparatus 1000 according to the first embodiment has the advantage of being able to accurately detect defects caused by misalignment of the wire electrode 1. Furthermore, the wire electric discharge machining apparatus 1000 has the advantage of being able to uniformize the thickness of thin plates that are cut collectively from the workpieces W.

[0105] Embodiment 2 In the second embodiment, other functions of the wire electric discharge machining apparatus 1000 will be described. The wire electric discharge machining apparatus 1000, which cuts thin plates all at once using the cutting wire 1b, supplies machining power individually from a machining power supply 5 to each of the wire electrodes 1 of the parallel wire section 1a that run in parallel at predetermined intervals. The machining power is supplied in pulses to each of the wire electrodes 1 of the parallel wire section 1a, and is supplied only during a predetermined power supply time or voltage application time.

[0106] For example, a predetermined interval of pause time during which no voltage is applied is set between pulsed voltages. Furthermore, the machining power supply 5 uses a system in which multiple power supply devices are combined to enable power-on and power-off operations in a short time in order to respond to high-frequency pulse oscillation commands for supplying machining power to the wire electrodes 1 of the parallel wire part 1a. In such a machining power supply 5, depending on the timing of switching from an off state in which machining power is not applied to each of the wire electrodes 1 of the parallel wire part 1a to an on state in which machining power is applied to each of the wire electrodes 1 of the parallel wire part 1a, a power short circuit may occur in which the power supplies are simultaneously turned on, damaging the power supplies.

[0107] In wire electric discharge machining apparatus 1000, to avoid the possibility of such damage to the power supply devices, in addition to an off time during which no power is applied to wire electrode 1 of parallel wire section 1a, a time called dead time is also set during which voltage application to all combined power supply devices is turned off. As described above, pulse power supply from machining power supply 5 to each power supply 11 or power supply units 6a, 6b is controlled by machining control device 31 and discharge waveform control device 32.

[0108] During cutting in the wire electric discharge machining apparatus 1000, a voltage pulse is applied between each wire electrode 1 of the parallel wire unit 1a and the workpiece W via a power supply 11 connected to the machining power supply 5 by power supply lines 12a and 12b, generating a discharge. The discharge waveform of the discharge generated between the wire electrode 1 of the cutting wire unit 1b and the workpiece W varies depending on the distance between the wire electrode 1 of the cutting wire unit 1b and the workpiece W at the time the machining power supply is applied.

[0109] The discharge waveform has a relatively low peak when the wire electrode 1 of the cutting wire part 1b and the workpiece W are relatively far apart at the time when the machining power is applied, i.e., when the electrode distance between the wire electrode 1 of the cutting wire part 1b and the workpiece W at the time when the machining power is applied is relatively long. On the other hand, the discharge waveform has a relatively high peak when the wire electrode 1 of the cutting wire part 1b and the workpiece W are relatively close at the time when the machining power is applied, i.e., when the electrode distance between the wire electrode 1 of the cutting wire part 1b and the workpiece W at the time when the machining power is applied is relatively short. When the electrode distance between the wire electrode 1 of the cutting wire part 1b and the workpiece W at the time when the machining power is applied is an appropriate electrode distance, the discharge waveform has a peak intermediate between that of an open state and that of a short-circuit state.

[0110] Here, we will explain the "open state" and "short state." When a machining power supply pulse is applied between the cutting wire 1b and the workpiece W, the magnitude of the generated discharge pulse changes depending on the distance between the cutting wire 1b and the workpiece W, i.e., depending on the inter-electrode distance. If the inter-electrode distance, which is the gap between the cutting wire 1b and the workpiece W, is large, discharge is unlikely to occur between the electrodes, and if no discharge occurs, no discharge current will flow. This state in which no discharge occurs between the electrodes and no discharge current flows is defined as the "open state."

[0111] In the open state, the discharge voltage waveform during the pulse application time maintains the applied voltage level, and the discharge current waveform is low. However, depending on the resistivity of the deionized water used as the machining fluid, i.e., the electrical conductivity of the deionized water, and the magnitude of the insulation resistance between adjacent power supply electrodes 11, a small amount of discharge current may be detected as a leakage current.

[0112] On the other hand, if the cutting wire 1b comes too close to the workpiece W or comes into contact with the workpiece W, a discharge occurs between the electrodes almost simultaneously with the application of the pulse, and a large discharge current flows because the insulation resistance between the electrodes is small. This state is defined as a "short-circuit state."

[0113] In the wire electric discharge machining apparatus 1000 that employs a method of performing electric discharge machining in deionized water, the gap between the electrodes is insulated by the resistivity of the deionized water present between the electrodes. However, as the gap between the electrodes narrows, the resistivity between the electrodes decreases, so a discharge current with less resistance loss or a machining for A state is reached in which the current supplied from the power supply 5 flows between the electrodes. In this state, the discharge voltage drops significantly, and the discharge current assumes a waveform with a high peak.

[0114] The "state where the wire electrode 1b and the workpiece W are at an appropriate electrode distance" is classified as a state where the electrode distance is neither in the short-circuit state nor the open-circuit state. Because it is difficult to directly measure the electrode distance during cutting, the wire electric discharge machining apparatus 1000 constantly monitors the state of the generated discharge waveform. When the wire electric discharge machining apparatus 1000 detects a tendency in the discharge waveform to transition from a state where a discharge state that is neither an open-circuit state nor a short-circuit state continues to occur to an "open state" or a "short-circuit state," it maintains a stable discharge state by adjusting various conditions such as the applied voltage, machining current, discharge frequency, voltage application pulse time, and pulse application pause time.

[0115] The wire electric discharge machining device 1000 monitors the discharge waveforms as described above, estimates the state of the gap between the wire electrode 1 of the cutting wire portion 1b and the workpiece W during cutting, and controls the cutting so that many discharge waveforms that stabilize the cutting are generated.

[0116] The machining control device 31 transmits command information to the discharge waveform control device 32 to instruct the oscillation frequency of the discharge pulse during electric discharge machining or the on-time and off-time of the discharge pulse, and controls the discharge energy supplied from the machining power supply 5 to the gap between the wire electrode 1 of the cutting wire portion 1b and the workpiece W. The machining control device 31 transmits command information to the cutting stage drive control device 34 to instruct the machining feed speed, and controls the gap distance.

[0117] When machining thin plates using the wire electric discharge machining device 1000 as described above, for example, in the case of a workpiece W having a relatively high resistivity, such as a material for semiconductor wafers, a situation rarely occurs in which electric discharge machining continues even when the cutting wire 1b is in complete contact with the workpiece W. This situation occurs when the machining current flowing through the cutting wire 1b when the cutting wire 1b is in complete contact with the workpiece W is not a pulse oscillation condition with a heat quantity sufficient to melt the wire electrode 1, or when a short circuit occurs between the cutting wire 1b and the workpiece W in a portion of the cutting wire 1b, but normal inter-electrode discharge occurs in other portions of the cutting wire 1b, causing electric discharge cutting to continue, and is caused by the inability to accurately observe or determine the situation in which the short circuit continues.

[0118] As described above, if the cutting wire 1b and the workpiece W are short-circuited and the cutting process of the thin plate continues with the cutting wire 1b remaining in contact with the workpiece W without breaking, the wire electrode 1 of the cutting wire 1b in contact with the workpiece W will not continue cutting beyond the position where the wire electrode 1 is short-circuited with the workpiece W. Despite this situation, the wire electrode 1 of the cutting wire 1b that is short-circuited with the workpiece W continues to rise while being pulled up together with the workpiece W by the cutting feed stage 10 while in contact with the workpiece W.

[0119] In the second embodiment, the wire electric discharge machining apparatus 1000 includes a wire contact machining state monitoring unit 500. Fig. 13 is a schematic diagram showing an example of the configuration of the wire contact machining state monitoring unit 500 of the wire electric discharge machining apparatus 1000 in the second embodiment. Fig. 13 shows a state in which the wire electrode 1 comes into contact with the workpiece W and short-circuits when wire electric discharge machining using the cutting wire portion 1b on the cylindrical workpiece W has progressed to a position approximately half the diameter of the workpiece W. Also, Fig. 13 does not show the thin plate machining stabilization unit 70. Also, Fig. 13 does not show the configuration of the wire tension state monitoring unit 400.

[0120] The wire contact machining state monitoring unit 500 monitors the contact state between the parallel wire portion 1a and the nozzles 7a, 7b during cutting. Fig. 14 is a block diagram showing an example configuration of the control unit 300 and wire contact machining state monitoring unit 500 provided in the wire electric discharge machining apparatus 1000 according to the second embodiment. The wire contact machining state monitoring unit 500 includes nozzle contact detection devices 75a, 75b, a wire contact detection circuit switching device 76, and a wire contact determination device 77.

[0121] The nozzle contact detection devices 75a, 75b are connected to a wire contact detection circuit switching device 76 and the nozzles 7a, 7b. The wire contact detection circuit switching device 76 is connected to the nozzle contact detection devices 75a, 75b, a wire contact determination device 77, and a discharge waveform control device 32 of the control unit 300. The wire contact determination device 77 is connected to the nozzle contact detection devices 75a, 75b, the power feeders 12a, 12b connecting the machining power source 5 and the power feeder 11, or to the machining power source 5, and the machining control device 31 of the control unit 300. This constitutes a wire contact machining state monitoring unit 500.

[0122] The nozzle contact detection devices 75a, 75b detect a characteristic value related to the potential difference between the nozzles 7a, 7b and the electron supply 11. Specifically, the nozzle contact detection devices 75a, 75b detect the current, voltage, or resistance value in the wire contact detection circuit. The nozzle contact detection devices 75a, 75b transmit the detection results, that is, information on the current, voltage, or resistance value in the wire contact detection circuit, to the wire contact determination device 77.

[0123] The wire contact detection circuit is composed of nozzle contact detection devices 75a and 75b, nozzles 7a and 7b, cutting wire 1b, power supply 11, power supply lines 12a and 12b, and wire contact determination device 77. Power is supplied to the wire contact detection circuit from wire contact detection power supply 74 under the control of wire contact detection circuit switching device 76.

[0124] The wire contact detection circuit switching device 76 controls the opening and closing of the wire contact detection circuit. The wire contact detection circuit switching device 76 connects the wire contact detection circuit, i.e., closes the wire contact detection circuit, during the machining power-off time when no machining voltage is applied between the poles. The wire contact detection circuit switching device 76 also disconnects the wire contact detection circuit, i.e., opens the wire contact detection circuit, during the machining power-on time when machining voltage is applied between the poles.

[0125] The wire contact determination device 77 monitors changes in the current value, voltage value, or resistance value in the wire contact detection circuit. When the wire contact determination device 77 detects a change in the current value, voltage value, or resistance value in the wire contact detection circuit, it determines that short-circuit machining is continuing due to undetected contact between the wire electrode 1 of the parallel wire portion 1a and the nozzles 7a, 7b, and sends a signal uc indicating a contact machining state to the machining control device 31.

[0126] The cutting wire 1b, which is normally tensioned between the pair of wire parallel guide rollers 51a, 51b, is maintained in a linear tensioned state between the pair of wire parallel guide rollers 51a, 51b while spaced apart from the workpiece W. Meanwhile, the wire electrode 1 of the cutting wire 1b, which is being raised by the cutting feed stage 10 while in contact with the workpiece W, eventually comes into contact with the nozzles 7a, 7b, with which it should not normally come into contact. Figure 13 shows a state in which the wire electrode 1 of the cutting wire 1b, which is being raised by the cutting feed stage 10 while in contact with the workpiece W, comes into contact with the nozzles 7a, 7b, with which it should not normally come into contact.

[0127] Fig. 15 is a characteristic diagram showing the timing of switching between machining voltage application and wire contact detection in wire electric discharge machining apparatus 1000 according to Embodiment 2. Fig. 15 shows the waveforms of a machining power supply application command pulse and a wire contact detection pulse.

[0128] The machining power supply application command pulse is a command pulse that the discharge waveform control device 32 issues to the machining power supply 5 to command the timing of application of the machining voltage.

[0129] The wire contact detection pulse is supplied from the wire contact detection power supply 74 to the wire contact detection circuit and to the wire electrode 1 of the cutting wire portion 1b. The workpiece W is It is a pulse power supply that supplies power to the detection power supply to detect contact. The wire contact detection pulse is a pulse that is oscillated in the opposite phase to the machining power supply application command pulse, which is a command pulse that commands the timing of application of the machining voltage to the machining gap by the machining power supply 5. The wire contact detection pulse can also be called a wire contact detection circuit switching command pulse that switches the open / close status of the wire contact detection circuit.

[0130] When the machining power supply 5 receives a machining power supply application command pulse, which is a command pulse that commands the timing of applying a machining voltage, from the discharge waveform control device 32, it supplies power to each power supply 11 based on the machining power supply application command pulse, and supplies power individually to each of the parallel wire portions 1a. As a result, a voltage is applied between the cutting wire portion 1b and the workpiece W.

[0131] When the machining power supply application command pulse from the discharge waveform control device 32 is in a LOW state, the period during which the machining power supply application command pulse is in a LOW state corresponds to a machining power supply off time P2. During the machining power supply off time P2, the machining power supply 5 is in a machining power off state in which no power is supplied to each power supply 11, and no machining voltage is applied between the cutting wire portion 1b and the workpiece W.

[0132] When the machining power supply application command pulse goes to a HIGH state after a machining power supply-off time P2 in which no machining voltage is applied, the period during which the machining power supply application command pulse is in a HIGH state becomes a machining power application time P1. During the machining power application time P1, the machining power supply is in an ON state in which power is supplied from the machining power supply 5 to each of the power supply electrodes 11, and a machining voltage is applied between the cutting wire 1b and the workpiece W. If a discharge occurs between the electrodes while the machining power supply application command pulse is in a HIGH state, a machining current is supplied from the machining power supply 5 to the power supply electrodes 11.

[0133] While the voltage application operation to the machining gap as described above is repeated, a command pulse tc is sent from the discharge waveform control device 32 to the wire contact detection circuit switching device 76.

[0134] The wire contact detection circuit switching device 76 connects the wire contact detection circuit during a machining power-off time P2 when no machining voltage is applied between the poles, i.e., when the machining power supply application command pulse sent from the discharge waveform control device 32 to the machining power supply 5 is in a LOW state. The wire contact detection circuit switching device 76 also disconnects the wire contact detection circuit during a machining power-on time when the machining power supply application command pulse sent from the discharge waveform control device 32 to the machining power supply 5 is in a HIGH state and a machining voltage is applied between the poles, i.e., during a machining power supply application time P1.

[0135] Machining power-off time P2 corresponds to the period during which the wire contact detection pulse is in a HIGH state. The period during which the wire contact detection pulse is in a LOW state corresponds to detection power-off time P3, during which no detection power is supplied to the wire contact detection circuit. The period during which the wire contact detection pulse is in a HIGH state corresponds to short-circuit detection time P4, during which the detection power is supplied to the wire contact detection circuit and the presence or absence of a short circuit between the workpiece W and the cutting wire 1b is detected. The period from time T11 onward corresponds to short-circuit processing duration P5, during which cutting is performed with the cutting wire 1b completely short-circuited to the workpiece W.

[0136] The waveform of the short-circuit processing duration P5 during which cutting processing is performed with the cutting wire 1b completely short-circuited with the workpiece W is present in the wire contact detection pulse. The wire contact detection pulse is generated by the wire contact detection power supply 74 and is input to the wire electrode 1 of the cutting wire 1b. The workpiece W is This is a waveform that supplies power to a detection power source for detecting contact.

[0137] If a power supply for detecting potential changes corresponding to the contact state of the cutting wire 1b with the workpiece W could be constantly applied to the wire contact detection circuit, the configuration of the oscillator circuit and detection processing system would be simplified. However, because the machining power supply is also applied to the cutting wire 1b and the workpiece W in addition to the detection power supply, two types of power supply, the detection power supply and the machining power supply, are supplied to the cutting wire 1b and the workpiece W. For this reason, it is necessary to prevent a situation in which two types of voltage, the detection power supply and the machining power supply, are simultaneously applied to the cutting wire 1b and the workpiece W.

[0138] Therefore, in the wire electric discharge machining apparatus 1000, as a measure to prevent a state in which two types of voltages, one from the detection power supply and the other from the machining power supply, are simultaneously applied to the cutting wire 1b and the workpiece W, a method is adopted in which a wire contact detection pulse is applied to the cutting wire 1b and the workpiece W during a no-load time when no pulsed machining voltage is applied. If the cutting wire 1b is not in contact with the workpiece W, the wire contact detection circuit does not close, and therefore no current supplied from the wire contact detection power supply 74 flows in the wire contact detection circuit, and no voltage drop occurs, so the voltage applied to the wire contact detection circuit is high, i.e., in the HIGH state.

[0139] On the other hand, when the cutting wire 1b comes into contact with the workpiece W, the wire contact detection circuit is closed via the conductive workpiece W. In this case, the potential detected by the nozzle contact detection devices 75a, 75b is lower than when the cutting wire 1b and the workpiece W are not in contact with each other, i.e., it is in a LOW state.

[0140] Therefore, in the wire electrical discharge machining apparatus 1000, it is possible to determine whether the cutting wire portion 1b and the workpiece W are in contact or out of contact based on the voltage state detected by the nozzle contact detection devices 75a, 75b, for example, based on whether the voltage pulse applied to the wire contact detection circuit is in a HIGH state or a LOW state, as shown in FIG. 15.

[0141] In normal electric discharge machining, the cutting wire 1b does not come into contact with the nozzles 7a, 7b, and the wire contact detection circuit is open. On the other hand, as described above, when contact of the cutting wire 1b with the workpiece W is not detected, the cutting stage drive control device 34 continues to feed the cutting wire 1b, and the pulled-up cutting wire 1b comes into contact with the metal nozzles 7a, 7b, which closes the wire contact detection circuit.

[0142] The wire contact determination device 77 detects a change in the current value, voltage value, or resistance value in the wire contact detection circuit when the wire contact detection circuit is connected by the wire contact detection circuit switching device 76. The wire contact determination device 77 detects a change in the current value, voltage value, or resistance value of the wire contact detection circuit by comparing the current value, voltage value, or resistance value in the wire contact detection circuit detected when the wire contact detection circuit is connected by the wire contact detection circuit switching device 76 with a predetermined reference value for the current value, voltage value, or resistance value.

[0143] The predetermined reference value for the current value, voltage value, or resistance value is the current value, voltage value, or resistance value of the wire contact detection circuit when the cutting wire portion 1b comes into contact with the workpiece W and is pulled up to contact the metal nozzles 7a, 7b.

[0144] If the detected current value, voltage value, or resistance value in the wire contact detection circuit exceeds the corresponding reference value, wire contact determination device 77 determines that there is a change in the current value, voltage value, or resistance value, and determines that a change in the current value, voltage value, or resistance value in the wire contact detection circuit has been detected.If the detected current value, voltage value, or resistance value in the wire contact detection circuit does not exceed the corresponding reference value, wire contact determination device 77 determines that there is no change in the current value, voltage value, or resistance value, and determines that no change in the current value, voltage value, or resistance value in the wire contact detection circuit has been detected.

[0145] When the wire contact determination device 77 detects a change in the current value, voltage value, or resistance value of the wire contact detection circuit, it determines that there is a continuous short-circuit machining state in which cutting is being performed with a short circuit between the workpiece W and the cutting wire 1b due to a lack of contact detection between the wire electrode 1 of the parallel wire portion 1a and the nozzles 7a, 7b. The continuous short-circuit machining state can be said to be a contact machining state in which cutting is being performed with the workpiece W and the cutting wire 1b in contact. The wire contact determination device 77 then transmits a signal uc indicating the contact machining state to the machining control device 31.

[0146] When the machining control device 31 receives the signal uc indicating the contact machining state, it commands the discharge waveform control device 32 to stop oscillation of the machining power supply 5, the wire travel control device 35 to stop wire travel, and the cutting stage drive control device 34 to stop the cutting feed stage 10, based on the signal uc. That is, based on the signal uc, the machining control device 31 controls the stopping of application of voltage to the machining gap, the stopping of travel of the wire electrode 1, and the stopping of movement of the cutting feed stage 10 and the workpiece W, thereby stopping the cutting process.

[0147] The wire contact detection power supply 74 applies the detection power supply to the wire contact detection circuit so that it is not applied simultaneously with the machining power supply supplied between the poles from the machining power supply 5. In other words, the wire contact detection power supply 74 supplies the wire contact power supply to the wire contact detection circuit with a wire contact detection pulse.

[0148] If the wire contact detection circuit remains connected even for a short time while machining power is being applied between the poles from the machining power supply 5, the machining power supply will also be connected to the wire contact detection circuit from the power supply 11 or the power feeders 12a and 12b, which could damage the devices that make up the wire contact detection circuit. Alternatively, if the wire contact detection circuit remains connected even for a short time while machining power is being applied between the poles, the power supply for detecting the machining power application command pulse will be applied to the poles, which could make the electric discharge machining unstable.

[0149] For this reason, the wire contact detection power supply 74: Wire contact detection pulse Not only is it oscillated with a pulse of the opposite phase to the machining power supply command pulse, but as shown in FIG. 15, there are set periods in which neither the machining power supply command pulse nor the wire contact detection pulse is in the ON state: a period Δt1 of several hundred nanoseconds immediately after the machining power supply command pulse changes from HIGH to LOW, and a period Δt2 of several hundred nanoseconds immediately before the pulse changes from LOW to HIGH.

[0150] The machining power supply application command pulse sent from the discharge waveform control device 32 to the machining power supply 5 is also sent to the wire contact detection circuit switching device 76. The wire contact detection circuit switching device 76 refers to the machining power supply application command pulse and opens and closes the wire contact detection circuit based on the timing of application of the pulsed voltage from the machining power supply 5 to the power supply 11.

[0151] FIG. 16 is a schematic diagram showing an example of a state in which the parallel wire portion 1a is disengaged from the wire guide groove 51c of the wire parallel guide roller 51a of the wire electric discharge machining apparatus 1000 according to the second embodiment. FIG. 16 shows a longitudinal cross section of the nozzle 7a, the parallel wire portion 1a stretched between the wire parallel guide rollers 51a and 51b, and the wire parallel guide roller 51a, passing through the rotation axis 51a2 of the wire parallel guide roller 51a. FIG. 16 also shows a state in which, as cutting continues with a portion of the wire electrode 1a of the parallel wire portion 1a in contact with the workpiece W, the parallel wire portion 1a stretched in the wire guide groove 51c rises up and eventually comes into contact with the nozzle 7a. As cutting continues, the nozzle 7a is cut. In FIG. 16, the parallel wire portion 1a disengaged from the wire guide groove 51c is indicated by a white circle.

[0152] Fig. 17 is a conceptual diagram showing detection values ​​corresponding to the wire disengagement state in Fig. 16 and state determinations corresponding to the detection values. The detection value D is the current value, voltage value, or resistance value in the wire contact detection circuit when the wire contact detection circuit is connected by the wire contact detection circuit switching device 76. Fig. 17 schematically shows, by means of detection values, the monitoring status of the wire contact machining state monitoring unit 500 of the wire electric discharge machining apparatus 1000 regarding the behavior of the parallel wire portion 1a that has disengaged from the wire guide groove 51c in Fig. 16.

[0153] In FIG. 16, in the steady state, the parallel wire portion 1a is stuck in the deepest part of the wire guide groove 51c, and normal cutting is being performed (State A). Subsequently, a situation occurs in which a portion of the wire electrode 1 of the parallel wire portion 1a shorts out to the workpiece W, and cutting continues while the wire electrode 1 remains in contact with the workpiece W without breaking. As a result, as the workpiece W, to which the wire electrode 1 of the parallel wire portion 1a is in contact, is fed by the cutting feed stage 10, the wire electrode 1 begins to lift off the wire guide groove 51c, creating an abnormal tension state (State B). If cutting continues without resolving the abnormal tension state, the lifted wire electrode 1 eventually comes into contact with the nozzle 7a (State C). As cutting continues, the wire electrode 1 in contact with the nozzle 7a scrapes against the nozzle 7a as it travels, cutting the nozzle 7a and forming a cut groove Wz in the nozzle 7a. If State C continues, the wire electrode 1 will break.

[0154] The same phenomenon as above also occurs with the nozzle 7b, the parallel wire portion 1a stretched between the wire parallel guide rollers 51a and 51b, and the wire parallel guide roller 51b.

[0155] In FIG. 17, the state A is a steady state in which there is no abnormality in the wire tension state, and then the state B is reached in which the wire electrode 1 comes into contact with the nozzle 7a. CAt this time, in the wire contact machining state monitoring unit 500, the detection value D changes from the detection value D1 in the steady state to the detection value D2, and the wire contact determination device 77 detects the occurrence of state C, which is a state in which the wire is in contact with the nozzle 7a. When the wire contact detection circuit switching device 76 connects the wire contact detection circuit, the wire contact determination device 77 detects the occurrence of state C based on the detection value in the nozzle contact detection device 75a.

[0156] The wire contact determination device 77 transmits a signal uc indicating the contact machining state to the machining control device 31. Based on the signal uc, the machining control device 31 instructs the discharge waveform control device 32 to stop oscillation of the machining power supply 5, the wire travel control device 35 to stop wire travel, and the cutting stage drive control device 34 to stop the cutting feed stage 10. Alternatively, upon receiving the signal uc indicating the contact machining state from the wire contact determination device 77, the machining control device 31 instructs the discharge waveform control device 32 to temporarily suspend oscillation of the machining power supply 5 or to control the oscillation frequency of the machining power supply 5 to rapidly reduce its oscillation frequency, or instructs the wire travel control device 35 to reverse the feed direction of the wire electrode 1 by the cutting stage drive control device 34 from the cutting advance direction and rapidly retract the cutting feed stage 10 (state D in FIGS. 16 and 17 ). That is, based on the signal uc, the machining control device 31 controls the retraction operation to eliminate the short circuit by reversing the feed direction of the cutting stage drive control device 34 from the cutting advance direction. As a result, the wire electric discharge machining apparatus 1000 can return the wire electrode 1 that has become abnormally stretched to the wire guide groove 51c without interrupting the cutting process.

[0157] Furthermore, if the retraction operation to eliminate the short circuit is not performed based on the signal uc, the machining control device 31 stops the power supply to all of the parallel wire portions 1a and stops the cutting process. This allows the machining control device 31 to stop the cutting process immediately when a parallel abnormality occurs in the wire electrode 1.

[0158] As described above, according to the second embodiment, it is possible to detect when a part of the wire electrode 1 of the parallel wire portion 1a comes out of the wire guide groove 51c and comes into contact with the nozzles 7a, 7b, and to stop the cutting process at the point when the wire electrode 1 comes into contact with the nozzles 7a, 7b. As a result, according to the second embodiment, it is possible to prevent damage to the nozzles 7a, 7b and other peripheral devices constituting the wire electric discharge machining apparatus 1000 due to friction of the wire electrode 1.

[0159] Furthermore, according to the second embodiment, when the wire electrode 1, which has come out of the wire guide groove 51c, comes into contact with the nozzles 7a, 7b, breakage of the wire electrode 1 due to the oscillation control of the machining power supply 5 is prevented. That is, when the wire electrode 1, which has come out of the wire guide groove 51c, comes into contact with the nozzles 7a, 7b, the wire electric discharge machining device 1000 performs control to temporarily suspend the oscillation of the machining power supply 5 or performs oscillation frequency control to suddenly reduce the oscillation frequency of the machining power supply 5, thereby preventing breakage of the wire electrode 1 due to continuation of cutting in a contact machining state.

[0160] Furthermore, according to the second embodiment, when the wire electrode 1 that has come out of the wire guide groove 51c comes into contact with the nozzles 7a, 7b, the cutting feed stage 10 is driven and controlled to retract the wire electrode 1 from the wire contact state, so that the wire electrode 1 that has become abnormally stretched can be returned into the wire guide groove 51c without interrupting the cutting process.

[0161] Furthermore, according to the second embodiment, the wire electric discharge machining apparatus 1000 stops cutting immediately upon occurrence of a parallelism abnormality in the wire electrode 1, thereby minimizing machining in the state where the wire electrode 1 is in contact and minimizing abnormal portions formed on the surface of the thin plate during cutting. As a result, the wire electric discharge machining apparatus 1000 can resume machining after correcting the abnormal tension state of the wire electrode 1 and the power supply state to the wire electrode 1, and can resume cutting from the machining stop position without causing unstable machining, improving the machining accuracy of the thin plate and improving the yield of thin plate machining. Therefore, when cutting a semiconductor ingot, for example, the wire electric discharge machining apparatus 1000 does not waste expensive semiconductor crystals and can reduce wafer production costs.

[0162] Furthermore, according to the second embodiment, cutting of the workpiece W due to friction of the wire electrode 1 in contact with the workpiece W is prevented, which prevents the formation of meandering grooves in the workpiece W, which reduce the amount of machining fluid supplied to the electrode gap during cutting and hinder the discharge of machining debris, thereby preventing wire breakage. As a result, when cutting semiconductor ingots, for example, the wire electric discharge machining apparatus 1000 can improve the yield of thin plate machining without wasting expensive semiconductor crystals, and reduce wafer production costs.

[0163] Therefore, the second embodiment has the advantage of providing a wire electric discharge machining apparatus 1000 that can accurately detect defects caused by misalignment of the wire electrode 1. The second embodiment also has the advantage of making uniform the thickness of thin plates that are cut collectively from the workpiece W. The second embodiment also has the advantage of preventing damage to devices included in the wire electric discharge machining apparatus 1000 that would be caused by a short-circuited wire electrode 1.

[0164] Next, the hardware configuration of each of the control units 80 according to the first and second embodiments will be described. The control unit 80 according to the first and second embodiments corresponds to the control unit 300 and the wire tension state monitoring unit 400 in the first and second embodiments, and the wire contact processing state monitoring unit 500 in the second embodiment. Each function of the control unit 80 according to the first and second embodiments is realized by a processing circuit. The processing circuit may be dedicated hardware, or may be a processing unit that executes a program stored in a storage device.

[0165] When the processing circuit is dedicated hardware, the processing circuit may be a single circuit, a composite circuit, a programmed processor, a parallel programmed processor, an application specific integrated circuit, a field programmable gate array, or a combination thereof. Figure 18 is a diagram showing a configuration in which the functions of the control unit according to the first and second embodiments are realized by hardware. The processing circuit 81 incorporates a logic circuit 81a that realizes the functions of the control unit 80.

[0166] When the processing circuit 81 is a processing device, the functions of the control unit 80 are realized by software, firmware, or a combination of software and firmware.

[0167] FIG. 19 is a diagram illustrating a configuration in which the functions of the control unit according to the first and second embodiments are implemented by software. The processing circuit 81 includes a processor 811 that executes a program 81b, a random access memory 812 that the processor 811 uses as a work area, and a storage device 813 that stores the program 81b. The processor 811 loads the program 81b stored in the storage device 813 onto the random access memory 812 and executes it, thereby realizing the functions of the control unit 80. The software or firmware is written in a programming language and stored in the storage device 813. The processor 811 may be, but is not limited to, a central processing unit. The storage device 813 may be a semiconductor memory such as a random access memory (RAM), a read-only memory (ROM), a flash memory, an erasable programmable read-only memory (EPROM), or an electrically erasable programmable read-only memory (EEPROM). The semiconductor memory may be either a non-volatile memory or a volatile memory. In addition to semiconductor memory, a magnetic disk, a flexible disk, an optical disk, a compact disk, a mini disk, or a DVD (Digital Versatile Disc) can be applied to the storage device 813. The processor 811 may output data such as a calculation result to the storage device 813 for storage, or may store the data in an auxiliary storage device (not shown) via the random access memory 812. By integrating the processor 811, the random access memory 812, and the storage device 813 on one chip, the functions of the control unit 80 can be realized by a microcomputer.

[0168] The processing circuit 81 realizes the functions of the control unit 80 by reading and executing the program 81b stored in the storage device 813. It can also be said that the program 81b causes the computer to execute the procedures and methods for realizing the functions of the control unit 80.

[0169] The processing circuit 81 may be configured so that some of the functions of the control unit 80 are realized by dedicated hardware, and some of the functions of the control unit 80 are realized by software or firmware.

[0170] In this way, the processing circuitry 81 can realize each of the above-described functions by hardware, software, firmware, or a combination of these.

[0171] The configurations shown in the above embodiments are merely examples, and may be combined with other known technologies, or different embodiments may be combined with each other. It is also possible to omit or modify parts of the configurations as long as they do not deviate from the gist of the invention. [Explanation of symbols]

[0172] 1 wire electrode, 1a parallel wire portion, 1b cutting wire portion, 2, 2a, 2b, 2c, 2d guide roller, 2e, 51c wire guide groove, 3, 3a, 3b bobbin, 4a, 4b vibration-damping guide roller, 5 machining power source, 6a, 6b power supply unit, 7a, 7b nozzle, 7c machining fluid ejection hole, 8a, 8b bobbin rotation control device, 9a, 9b traverse control device, 10 cutting feed stage, 11 power supply, 12a, 12b power supply line, 31 machining control device, 32 discharge waveform control device, 34 cutting stage drive control device, 35 wire travel control device, 42 workpiece fixing plate, 43 flat surface, 51a, 51b wire parallel guide roller, 51a1 upper end portion, 51a2 rotating shaft, 51d outer circumferential surface, 52a, 52b Parallel wire tension position measurement unit, 52a1, 55a1 upper surface, 53 wire guide groove deviation detection unit, 54 wire state determination unit, 55a, 55b guide roller holder, 62 machining fluid supply pipe, 70 thin plate machining stabilization unit, 71, 71a, 71b machining fluid rectification plate, 72 workpiece holder, 74 power supply for wire contact detection, 75a, 75b nozzle contact detection device, 76 wire contact detection circuit switching device, 77 wire contact determination device, 100 machining mechanism unit, 101, 102, 103 arrow, 200 power supply unit, 300 control unit, 400 wire tension state monitoring unit, 500 wire contact machining state monitoring unit, 1000 wire electric discharge machining device, L, L1, L2, L3 distance, P1 machining power application time, P2 machining power off time, W workpiece, Wz cutting groove.

Claims

1. A wire electric discharge machining apparatus for simultaneously cutting a plurality of wafers from a workpiece by generating electric discharges between a plurality of traveling cutting wires and the workpiece and machining the workpiece with energy from the electric discharges, comprising: a wire electrode having a plurality of the cutting wire portions, each including a portion facing the workpiece and spaced apart from each other in parallel; a power supply unit that generates an electric discharge between the cutting wires and the workpiece; a pair of wire parallel guide rollers disposed on both sides of the workpiece so as to sandwich the workpiece, the wire parallel guide rollers having a plurality of wire guide grooves formed at equal intervals on the outer circumferential side surfaces into which the traveling cutting wire portions are fitted to limit the movement of the cutting wire portions; a parallel-wire tension position measuring unit that measures a distance between a measurement reference plane that is set parallel to a virtual plane including the plurality of cutting wires and the wire electrodes that constitute the plurality of cutting wires; a wire guide groove deviation detection unit that detects occurrence of a change in the distance based on a measurement result by the parallel wire tension position measurement unit; a wire state determination unit that determines whether at least one of the cutting wire portions is in a wire-disengaged state where it is disengaged from the wire guide groove, or whether all of the cutting wire portions are in a wire-contact state where they are in contact with the wire guide groove, based on a detection result by the wire guide groove disengagement detection unit; a machining control unit that controls whether to stop or continue electric discharge machining based on a determination result of the wire state determination unit; A wire electric discharge machining apparatus comprising:

2. the parallel-wire-stretching-position measuring unit is provided with at least one of an eddy-current-type displacement sensor, a capacitance-type displacement sensor, an electrical-current-detection-type sensor, and a contact-detection-type displacement sensor to measure the distance; 2. The wire electric discharge machining apparatus according to claim 1 .

3. the machining control unit stops electric discharge machining when the wire state determination unit determines that the wire is in the disconnected state; 2. The wire electric discharge machining apparatus according to claim 1 .

4. the power supply unit includes a machining power source and a power supply connected to the cutting wire unit to supply power from the machining power source to the cutting wire unit; a nozzle disposed above the cutting wires in a state in which the cutting wires are sandwiched between the wire parallel guide roller and the nozzle and spaced apart from the cutting wires, the nozzle supplying a machining fluid to a gap between the cutting wires and the workpiece; a wire contact detection circuit that detects contact between the nozzle and the cutting wire based on a potential difference between the nozzle and the power supply; Equipped with the machining control unit stops electric discharge machining when the wire contact detection circuit detects contact between the nozzle and the cutting wire; 4. The wire electric discharge machining apparatus according to claim 1,

5. a cutting feed stage that changes a relative position between the workpiece and the cutting wire portion, the machining control unit stops power supply to all of the cutting wires and stops electric discharge machining when contact between the nozzle and the cutting wires is detected and a retraction operation for eliminating a short circuit is not performed by reversing the feed direction of the cutting feed stage from the cutting progress direction of the workpiece; 5. The wire electric discharge machining apparatus according to claim 4,

6. A wire electric discharge machining method for simultaneously cutting a plurality of wafers from a workpiece by generating electric discharges between a plurality of traveling cutting wires and the workpiece and machining the workpiece with energy from the electric discharges, comprising: a parallel wire tension position measuring step of measuring a distance between a measurement reference plane set parallel to a virtual plane including the plurality of cutting wire portions and a wire electrode constituting the plurality of cutting wire portions; a wire guide groove deviation detection step of detecting the occurrence of a change in the distance based on a measurement result in the parallel wire tension position measurement step; a wire state determination step of determining whether at least one of the cutting wire portions is in a wire-disengaged state where it is disengaged from the wire guide groove, or whether all of the cutting wire portions are in a wire-contact state where they are in contact with the wire guide groove, based on a detection result in the wire guide groove disengagement detection step; a machining control step of controlling whether to stop or continue electric discharge machining based on a result of the wire condition determination step; A wire electric discharge machining method comprising:

7. in the machining control step, when a contact between the cutting wires and a nozzle that is disposed above the cutting wires and supplies machining fluid to a gap between the cutting wires and the workpiece is detected in a state in which the cutting wires are sandwiched between a pair of wire parallel guide rollers that are disposed on both sides of the workpiece so as to sandwich the workpiece and that have a plurality of wire guide grooves formed at equal intervals on the outer peripheral side surface into which the cutting wires are fitted and that limit the movement of the cutting wires, and that are spaced apart from the cutting wires, and when a retraction operation for eliminating a short circuit is not performed in which a feed direction of a cutting feed stage that changes a relative position between the workpiece and the cutting wires is reversed from a cutting progress direction of the workpiece, the retraction operation being performed, the retraction operation being performed to reverse a feed direction of a cutting feed stage that changes a relative position between the workpiece and the cutting wires from a cutting progress direction of the workpiece, the retraction operation being performed to stop power supply to all of the cutting wires and stop electric discharge machining; 7. The wire electric discharge machining method according to claim 6, further comprising:

8. 8. The wire electric discharge machining method according to claim 6 or 7, wherein a plurality of wafers are cut out from the workpiece at the same time; A method for manufacturing a wafer, comprising the steps of:

9. The workpiece is a semiconductor ingot, The wafer is a semiconductor wafer; The method for manufacturing a wafer according to claim 8 ,

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