Grinder and grinding wheel correction method

Abstract

Provided is a grinder for grinding a workpiece, the grinder comprising: a first grinding wheel having a first diameter; a second grinding wheel having a second diameter and having a grain size finer than that of the first grinding wheel; a grinding wheel shaft to which the first grinding wheel and the second grinding wheel are mounted side by side; a dresser for performing wheel correction on the first grinding wheel and the second grinding wheel; and a control part for performing wheel correction on the first grinding wheel and the second grinding wheel by using the dresser while rotating the grinding wheel shaft. The control part executes a first correction process of performing wheel correction so that the first diameter of the first grinding wheel is larger than the second diameter of the second grinding wheel prior to grinding the workpiece using the first grinding wheel, and / or a second correction process of performing wheel correction so that the second diameter of the second grinding wheel is larger than the first diameter of the first grinding wheel prior to grinding the workpiece using the second grinding wheel.

Description

Grinding machine and grinding wheel adjustment method

[0001] The present disclosure relates to a grinding machine and a grinding wheel dressing method.

[0002] Patent Document 1 discloses a numerically controlled grinding machine equipped with multiple grinding wheels. When forming multiple tapers on a workpiece, this grinding machine calculates a correction amount for the grinding wheels in accordance with the rotation angle of the wheel head, and corrects the grinding wheels by an amount equivalent to the correction amount to create steps in the grinding wheels.

[0003] Publication No. 6-27334

[0004] In grinding a workpiece, it is common for the workpiece to be rough-ground and then finished-ground. Conventionally, it has been necessary to change the grinding wheel attached to the grinding machine between rough grinding and finish grinding, which has been a time-consuming process.

[0005] The present disclosure can be realized in the following forms.

[0006] (1) According to a first aspect of the present disclosure, there is provided a grinding machine for grinding a workpiece, the grinding machine including: a first grinding wheel having a first diameter; a second grinding wheel having a second diameter and a finer grit than the first grinding wheel; a grinding wheel stalk to which the first grinding wheel and the second grinding wheel are attached side by side; a dresser for dressing the first grinding wheel and the second grinding wheel; and a control unit for dressing the first grinding wheel and the second grinding wheel using the dresser while rotating the grinding wheel stalk, the control unit performing at least one of a first dressing process for dressing the first grinding wheel so that the first diameter of the first grinding wheel is larger than the second diameter of the second grinding wheel before grinding the workpiece with the first grinding wheel; and a second dressing process for dressing the second grinding wheel so that the second diameter of the second grinding wheel is larger than the first diameter of the first grinding wheel before grinding the workpiece with the second grinding wheel. According to the grinding machine of this embodiment, by adjusting the grinding wheels so that the first grinding wheel and the second grinding wheel have different diameters, rough grinding using the first grinding wheel or finish grinding using the second grinding wheel can be performed without replacing the grinding wheels attached to the grinding machine. This reduces the user's effort to replace the grinding wheels attached to the grinding machine. (2) In the grinding machine of the above embodiment, the control unit may perform the second adjustment process after performing the first adjustment process. According to the grinding machine of this embodiment, rough grinding using the first grinding wheel can be performed on the workpiece, followed by finish grinding using the second grinding wheel. (3) In the grinding machine of the above embodiment, the control unit may adjust both the first grinding wheel and the second grinding wheel in each of the first adjustment process and the second adjustment process. According to the grinding machine of this embodiment, the first grinding wheel for rough grinding is adjusted immediately before rough grinding, and the second grinding wheel for finish grinding is adjusted immediately before finish grinding, thereby enabling the workpiece to be machined with high precision.(4) In the grinding machine of the above aspect, the control unit may perform at least one of the following: increasing the feed rate of the dresser relative to the second grinding wheel in the first dressing process compared to the feed amount of the dresser relative to the second grinding wheel in the second dressing process; increasing the cut-in amount of the dresser relative to the second grinding wheel in the first dressing process compared to the cut-in amount of the dresser relative to the second grinding wheel in the second dressing process; increasing the feed rate of the dresser relative to the first grinding wheel in the second dressing process compared to the feed rate of the dresser relative to the first grinding wheel in the first dressing process; and increasing the cut-in amount of the dresser relative to the first grinding wheel in the second dressing process compared to the cut-in amount of the dresser relative to the first grinding wheel in the first dressing process. According to this aspect of the grinding machine, the diameter of the second grinding wheel can be quickly reduced in the first dressing process. Alternatively, the diameter of the first grinding wheel can be quickly reduced in the second dressing process. (5) In the grinding machine of the above aspect, the control unit may, in the first dressing process, dress the second grinding wheel but not dress the first grinding wheel, and, in the second dressing process, dress the first grinding wheel but not dress the second grinding wheel. The grinding machine of this aspect can reduce the amount of wear on the first grinding wheel and the second grinding wheel. (6) In the grinding machine of the above aspect, the control unit may repeatedly execute the first dressing process and the second dressing process, and grind a plurality of workpieces with the first grinding wheel and the second grinding wheel. The grinding machine of this aspect can further reduce the effort required to replace the grinding wheels. (7) According to a second aspect of the present disclosure, there is provided a grinding wheel dressing method for a first grinding wheel and a second grinding wheel attached side by side to a grinding wheel spindle.In this grinding wheel dressing method, the first grinding wheel has a first diameter, and the second grinding wheel has a second diameter and a finer grit size than the first grinding wheel, and the grinding wheel dressing method includes at least one of: prior to grinding a workpiece using the first grinding wheel, dressing the grinding wheel using a dresser so that the first diameter of the first grinding wheel is larger than the second diameter of the second grinding wheel; and prior to grinding the workpiece using the second grinding wheel, dressing the grinding wheel using the dresser so that the second diameter of the second grinding wheel is larger than the first diameter of the first grinding wheel. The present disclosure is not limited to the above-mentioned grinding machine and grinding wheel dressing method, but can be realized in various forms, such as a grinding machine control method, a computer program for implementing the control method, and a non-transitory tangible recording medium on which the computer program is recorded in a computer-readable manner.

[0007] FIG. 1 is an explanatory diagram showing a schematic configuration of a grinding machine. FIG. 2 is a flowchart of a grinding process. FIG. 3 is an explanatory diagram of a first correction process in a first embodiment. FIG. 4 is an explanatory diagram of a rough grinding process. FIG. 5 is an explanatory diagram of a second correction process in the first embodiment. FIG. 6 is an explanatory diagram of a finish grinding process. FIG. 7 is a flowchart of a grinding process in a second embodiment. FIG. 8 is an explanatory diagram of an initial correction process in the second embodiment. FIG. 9 is an explanatory diagram of a second correction process in the second embodiment. FIG. 10 is an explanatory diagram of a first correction process in the second embodiment.

[0008] A. First Embodiment: Fig. 1 is an explanatory diagram showing the schematic configuration of a grinding machine 100. Fig. 1 shows arrows representing three mutually orthogonal coordinate axes, the X, Y, and Z axes. The Z and X axes are coordinate axes parallel to the horizontal plane. The Y axis is a coordinate axis parallel to the vertical direction. When specifying the orientation of a direction, positive and negative signs are used in combination to indicate the direction, with "+" representing the positive direction indicated by the arrow and "-" representing the negative direction opposite to the direction indicated by the arrow.

[0009] The grinding machine 100 is configured as a cylindrical grinding machine that rotates a cylindrical workpiece W about an axis RX of the workpiece W and approaches the rotating grinding wheel 33 in a cutting direction that intersects with the axis RX, thereby grinding the outer circumferential surface of the workpiece W with the grinding wheel 33. More specifically, the grinding machine 100 grinds the outer circumferential surface of the workpiece W by bringing the grinding wheel 33 into contact with the workpiece W and moving the workpiece W and the grinding wheel 33 relative to each other. In this embodiment, the cutting direction is the -X direction. The axis RX is also along the Z axis. The workpiece W is made of, for example, metal or ceramic. The workpiece W may have any shape that has a cylindrical portion.

[0010] The grinding machine 100 includes a bed 10 , a support unit 20 , a wheel head 30 , a table moving device 40 , a wheel head moving device 50 , a dresser 60 , a control unit 70 , and drive circuits 81 , 82 , and 83 .

[0011] The bed 10 supports the support unit 20, the wheel head 30, the table moving device 40, and the wheel head moving device 50. The bed 10 is made of, for example, cast iron. On the upper surface of the bed 10, a sliding surface is formed for the support unit 20 to move along the Z-axis direction, and a sliding surface is formed for the wheel head 30 to move along the X-axis direction.

[0012] The support unit 20 includes a table 21, a spindle unit 22, and a tailstock 28. The support unit 20 supports the workpiece W so that the workpiece W can rotate about an axis RX.

[0013] The table 21 is disposed on the upper surface of the bed 10. A spindle unit 22 and a tailstock 28 are attached to the upper surface of the table 21.

[0014] The spindle device 22 is disposed on the −Z direction side of the workpiece W. The spindle device 22 applies a rotational force to the workpiece W. The spindle device 22 includes a headstock 23, a spindle 24, a chuck 25, and a spindle rotation motor 26.

[0015] The headstock 23 is fixed on the table 21 and supports the spindle 24 rotatably about the axis RX. The chuck 25 is fixed to the tip of the spindle 24 and grips the end of the workpiece W on the -Z direction side. The spindle rotation motor 26 rotates under the control of the control unit 70 and drives the spindle 24 to rotate. The rotation of the spindle 24 causes the workpiece W to rotate about the axis RX. The rotation speed of the spindle 24 is controlled by controlling the rotation speed of the spindle rotation motor 26. The spindle rotation motor 26 has a spindle encoder 27. The rotation speed signal of the spindle encoder 27 is fed back to the drive circuit 81.

[0016] The tailstock 28 is disposed opposite the headstock 23 in the Z-axis direction with the workpiece W sandwiched therebetween. The tailstock 28 includes a center 29. The center 29 supports the end of the workpiece W on the +Z direction side so that the workpiece W can rotate around the axis RX.

[0017] The wheel head 30 is disposed on the upper surface of the bed 10. The wheel head 30 includes a first grinding wheel 31, a second grinding wheel 32, a grinding wheel spindle 34, and a grinding wheel spindle rotation motor 35.

[0018] The first grinding wheel 31 and the second grinding wheel 32 rotate about their respective axes to grind the outer peripheral surface of the workpiece W. The first grinding wheel 31 and the second grinding wheel 32 are attached side by side via a spacer to a grinding wheel shaft 34 so that their respective axes coincide. Hereinafter, when the first grinding wheel 31 and the second grinding wheel 32 are referred to interchangeably, they will be simply referred to as grinding wheels 33.

[0019] The grinding wheel 33 has a core and a grinding wheel layer. The core is disk-shaped and made of metal such as iron. The core is detachably connected to the grinding wheel spindle 34 by a grinding wheel flange or the like. The grinding wheel layer is disk-shaped and provided on the outer periphery of the core. The grinding wheel layer is formed by mixing abrasive grains and a binder and baking the mixture. For example, CBN (cubic boron nitride) or diamond is used as the abrasive grains. The grinding wheel layer comes into contact with the workpiece W, thereby grinding the outer periphery of the workpiece W.

[0020] The first grinding wheel 31 and the second grinding wheel 32 have different grain sizes. In this embodiment, the grain size of the second grinding wheel 32 is finer than the grain size of the first grinding wheel 31. In other words, the size of the abrasive grains contained in the grinding wheel layer of the second grinding wheel 32 is smaller than the size of the abrasive grains contained in the grinding wheel layer of the first grinding wheel 31. The first grinding wheel 31 is mainly used for rough grinding, and the second grinding wheel 32 is mainly used for finish grinding.

[0021] The first grinding wheel 31 has a first diameter d1. The second grinding wheel 32 has a second diameter d2. The first diameter d1 of the first grinding wheel 31 and the second diameter d2 of the second grinding wheel 32 are each adjusted in a grinding process described below.

[0022] The grinding wheel spindle 34 supports the first grinding wheel 31 and the second grinding wheel 32 rotatably around their axes. The grinding wheel spindle 34 is rotatably supported on the wheel head 30 via bearings (not shown). The first grinding wheel 31 and the second grinding wheel 32 are attached to the grinding wheel spindle 34 so that the axis of the first grinding wheel 31, the axis of the second grinding wheel 32, and the grinding wheel rotation axis BX, which is the axis of the grinding wheel spindle 34, are aligned. The direction of the grinding wheel rotation axis BX is parallel to the Z-axis.

[0023] The grinding wheel spindle rotation motor 35 is built into the grinding wheel head 30 coaxially with the grinding wheel spindle 34. The grinding wheel spindle rotation motor 35 drives the grinding wheel spindle 34 to rotate about the grinding wheel rotation axis BX. The rotation speed of the grinding wheel spindle rotation motor 35 is controlled by the control unit 70. As the grinding wheel spindle 34 is driven to rotate, the first grinding wheel 31 and the second grinding wheel 32 are driven to rotate about the grinding wheel rotation axis BX.

[0024] The table moving device 40 is connected to the table 21 and moves the table 21 along the Z-axis direction. The table moving device 40 has a table moving motor 41. The table moving motor 41 generates a driving force for moving the table 21 under the control of the control unit 70, and controls the position of the table 21. The table moving motor 41 has a table encoder 42. A position signal from the table encoder 42 is fed back to the drive circuit 82.

[0025] The wheel head moving device 50 is connected to the wheel head 30 and moves the wheel head 30 along the X-axis direction. The wheel head moving device 50 has a wheel head moving motor 51. The wheel head moving motor 51 generates a driving force for moving the wheel head 30 under the control of the control unit 70, and controls the position of the wheel head 30. The wheel head moving motor 51 has a wheel head encoder 52. A position signal from the wheel head encoder 52 is fed back to the drive circuit 83.

[0026] The dresser 60 is a device that performs grinding wheel dressing for the first grinding wheel 31 and the second grinding wheel 32. In this disclosure, grinding wheel dressing refers to truing. Note that grinding wheel dressing may include not only truing but also dressing. The dresser 60 is, for example, a single-element dresser or a multi-element dresser equipped with a single diamond element for dressing the outer peripheral surface of the grinding wheel 33. The dresser 60 is fixed to the headstock 23. In other words, the dresser 60 is supported by the table 21 via the headstock 23. The dresser 60 is given a driving force by the table movement motor 41 via the table 21 and moves in the Z direction.

[0027] The control unit 70 controls the operation of the grinding machine 100. The control unit 70 includes a CPU 71 and a storage unit 72. The storage unit 72 stores a program for operating the grinding machine 100. More specifically, the storage unit 72 stores a program for executing a processing process for grinding a workpiece W, for example. The CPU 71 executes the program stored in the storage unit 72, thereby causing the control unit 70 to realize various functions. The control unit 70 may include a display unit formed of a liquid crystal display or the like, and an input unit formed of a keyboard and buttons.

[0028] The control unit 70 controls the rotation speed of the grinding wheel spindle 34, i.e., the rotation speed of the grinding wheel 33, by controlling the rotation speed of the grinding wheel spindle rotation motor 35. The control unit 70 outputs drive commands to drive circuits 81, 82, and 83. The drive circuit 81 controls the operation of the spindle rotation motor 26 in response to the command from the control unit 70. The drive circuit 82 controls the operation of the table movement motor 41 in response to the command from the control unit 70. The drive circuit 83 controls the operation of the wheel head movement motor 51 in response to the command from the control unit 70.

[0029] 2 is a flowchart of a grinding process for a workpiece W. By performing the grinding process shown in FIG. 2, a grinding wheel dressing method for the first grinding wheel 31 and the second grinding wheel 32 is realized.

[0030] In step S100, the control unit 70 executes a first correction process. The first correction process is a process for correcting the grindstones so that the first diameter d1 of the first grindstone 31 is larger than the second diameter d2 of the second grindstone 32.

[0031] 3 is an explanatory diagram of the first adjustment process in the first embodiment. In the first adjustment process in the first embodiment, the control unit 70 adjusts both the first grinding wheel 31 and the second grinding wheel 32 using the dresser 60 so that the first diameter d1 of the first grinding wheel 31 is larger than the second diameter d2 of the second grinding wheel 32. In Fig. 3, the relative positional change of the dresser 60 with respect to the first grinding wheel 31 and the second grinding wheel 32 during the first adjustment process is shown by a dashed line.

[0032] The control unit 70 controls the grinding wheel spindle rotation motor 35 to rotate the first grinding wheel 31 and the second grinding wheel 32 at a predetermined grinding wheel dressing speed, while controlling the grinding wheel head movement motor 51 and the table movement motor 41 to control the relative position of the dresser 60 with respect to the first grinding wheel 31 and the second grinding wheel 32, thereby performing grinding wheel dressing. The control unit 70 controls the grinding wheel head movement motor 51 to control the cutting amount of the dresser 60 with respect to the first grinding wheel 31 and the second grinding wheel 32. The control unit 70 also controls the table movement motor 41 to control the feed speed of the dresser 60.

[0033] In the first correction process of the first embodiment, the control unit 70 corrects the first grinding wheel 31 under first correction conditions, and corrects the second grinding wheel 32 under second correction conditions. The first correction conditions include the feed rate, cutting amount, and number of cuttings of the dresser 60 for using the first grinding wheel 31 for rough grinding. The second correction conditions include the feed rate, cutting amount, and number of cuttings of the dresser 60 for making the second grinding wheel 32 have a smaller diameter than the first grinding wheel 31. In the first embodiment, the second correction conditions include at least one of the feed rate in (1) and the cutting amount in (2) below. (1) A feed rate that is faster than the normal feed rate for using the second grinding wheel 32 for finish grinding (in other words, a feed rate that is faster than the feed rate under the fourth correction condition described below). (2) A depth of cut greater than the normal depth of cut for using the second grinding wheel 32 for finish grinding (in other words, a depth of cut greater than the depth of cut under the fourth correction condition described later).

[0034] In the rough grinding process in step S110, which will be described later, the second grinding wheel 32 for finish grinding is not used. Therefore, as in (1) and (2) above, by grinding the second grinding wheel 32 at a faster feed rate or with a larger depth of cut than usual, the second grinding wheel 32 can be quickly shaped to a smaller diameter than the first grinding wheel 31. Generally, the feed rate of the dresser 60 for using the first grinding wheel 31 as a grinding wheel for rough grinding is faster than the feed rate for using the second grinding wheel 32 as a grinding wheel for finish grinding, and the depth of cut of the dresser 60 for using the first grinding wheel 31 as a grinding wheel for rough grinding is larger than the depth of cut for using the second grinding wheel 32 as a grinding wheel for finish grinding.

[0035] In step S110 of FIG. 2, the control unit 70 executes a rough grinding process in which the workpiece W is roughly ground using the first grindstone 31.

[0036] 4 is an explanatory diagram of the rough grinding process. As a result of the first correction process in step S100, the first diameter d1 of the first grinding wheel 31 is larger than the second diameter d2 of the second grinding wheel 32. Therefore, in the rough grinding process, the second grinding wheel 32 does not come into contact with the workpiece W, and only the first grinding wheel 31 comes into contact with the workpiece W. Therefore, the first grinding wheel 31, which has a coarse grain size, performs rough grinding on the workpiece W.

[0037] 2, the control unit 70 executes a second correction process. The second correction process is a process for correcting the grinding wheel so that the second diameter d2 of the second grinding wheel 32 is larger than the first diameter d1 of the first grinding wheel 31.

[0038] 5 is an explanatory diagram of the second dressing process in the first embodiment. In the first embodiment, the control unit 70 dresses both the first grinding wheel 31 and the second grinding wheel 32 using the dresser 60 so that the second diameter d2 of the second grinding wheel 32 is larger than the first diameter d1 of the first grinding wheel 31. In Fig. 5, the relative positional change of the dresser 60 with respect to the first grinding wheel 31 and the second grinding wheel 32 during the second dressing process is shown by a dashed line.

[0039] In the second adjustment process of the first embodiment, the control unit 70 adjusts the first grinding wheel 31 under the third adjustment condition, and adjusts the second grinding wheel 32 under the fourth adjustment condition. The fourth adjustment condition includes the feed rate, cutting amount, and number of cuttings of the dresser 60 for using the second grinding wheel 32 for finish grinding. The third adjustment condition includes the feed rate, cutting amount, and number of cuttings of the dresser 60 for making the diameter of the first grinding wheel 31 smaller than that of the second grinding wheel 32. In the first embodiment, the third adjustment condition includes at least one of the feed rate in (3) and the cutting rate in (4) below. (3) A feed rate that is faster than the normal feed rate for using the first grinding wheel 31 for rough grinding (in other words, a rate faster than the feed rate under the first adjustment condition). (4) A cutting depth greater than the normal cutting depth for using the first grinding wheel 31 for rough grinding (in other words, a cutting depth greater than the cutting depth under the first correction condition).

[0040] In the finish grinding process in step S130 described later, the first grinding wheel 31 for rough grinding is not used. Therefore, as in (3) and (4) above, by adjusting the first grinding wheel 31 with a faster feed rate or a larger depth of cut than usual, the first grinding wheel 31 can be quickly shaped to a smaller diameter than the second grinding wheel 32.

[0041] In step S130 of FIG. 2, the control unit 70 executes a finish grinding process in which the workpiece W is finish-ground using the second grinding wheel 32.

[0042] 6 is an explanatory diagram of the finish grinding process. As a result of the second adjustment process in step S120, the second diameter d2 of the second grinding wheel 32 is larger than the first diameter d1 of the first grinding wheel 31. Therefore, in the finish grinding process, the first grinding wheel 31 does not come into contact with the workpiece W, and only the second grinding wheel 32 comes into contact with the workpiece W. Therefore, the second grinding wheel 32, which has a finer grain size, performs finish grinding on the workpiece W.

[0043] According to the first embodiment described above, before rough grinding of the workpiece W using the first grinding wheel 31, grinding wheel adjustment is performed so that the first diameter d1 of the first grinding wheel 31 is larger than the second diameter d2 of the second grinding wheel 32. Furthermore, before finish grinding of the workpiece W using the second grinding wheel 32, grinding wheel adjustment is performed so that the second diameter d2 of the second grinding wheel 32 is larger than the first diameter d1 of the first grinding wheel 31. In this manner, in the first embodiment, grinding wheel adjustment is performed so that the diameters of the first grinding wheel 31 and the second grinding wheel 32 are different. Therefore, rough grinding using the first grinding wheel 31 and finish grinding using the second grinding wheel 32 can be performed without replacing the grinding wheel 33 attached to the grinding machine 100. As a result, the user can reduce the effort required to replace the grinding wheel 33 attached to the grinding machine 100. Furthermore, according to the first embodiment, since there is no need to replace the grinding wheel 33 between rough grinding and finish grinding, the processing time for the workpiece W can be shortened, thereby reducing the unit price of the product.

[0044] In the first embodiment, the control unit 70 performs a first correction process to make the first grinding wheel 31, which has a coarse grain size, larger in diameter than the second grinding wheel 32, and then performs a second correction process to make the second grinding wheel 32, which has a finer grain size, larger in diameter than the first grinding wheel 31. Therefore, the workpiece W can be subjected to rough grinding and then finish grinding.

[0045] In the first embodiment, the control unit 70 performs grinding wheel correction on both the first grinding wheel 31 and the second grinding wheel 32 in each of the first correction process and the second correction process. As a result, the first grinding wheel 31 for rough grinding is corrected immediately before rough grinding, and the second grinding wheel 32 for finish grinding is corrected immediately before finish grinding, so that the workpiece W can be machined with high precision.

[0046] Furthermore, in the first embodiment, the control unit 70 performs the grinding wheel dressing process in the first dressing process according to the second dressing condition described above, thereby implementing at least one of the following (i) and (ii). Therefore, the diameter of the second grinding wheel 32 can be quickly reduced in the first dressing process. Furthermore, the control unit 70 performs the grinding wheel dressing process in the second dressing process according to the third dressing condition described above, thereby implementing at least one of the following (iii) and (iv). Therefore, the diameter of the first grinding wheel 31 can be quickly reduced in the second dressing process. (i) The feed rate of the dresser 60 with respect to the second grinding wheel 32 in the first dressing process is made faster than the feed amount of the dresser 60 with respect to the second grinding wheel 32 in the second dressing process. (ii) The cutting depth of the dresser 60 with respect to the second grinding wheel 32 in the first dressing process is made larger than the cutting depth of the dresser 60 with respect to the second grinding wheel 32 in the second dressing process. (iii) The feed speed of the dresser 60 relative to the first grinding wheel 31 in the second adjustment process is made faster than the feed speed of the dresser 60 relative to the first grinding wheel 31 in the first adjustment process. (iv) The cutting depth of the dresser 60 relative to the first grinding wheel 31 in the second adjustment process is made larger than the cutting depth of the dresser 60 relative to the first grinding wheel 31 in the first adjustment process.

[0047] B. Second Embodiment: The second embodiment differs from the first embodiment in the grinding process of the workpiece W. The configuration of each part of the grinding machine 100 in the second embodiment is the same as that in the first embodiment.

[0048] 7 is a flowchart of the grinding process of the workpiece W in the second embodiment. In step S200, the control unit 70 executes an initial correction process.

[0049] 8 is an explanatory diagram of the initial dressing process in the second embodiment. In the first embodiment, the control unit 70 uses the dresser 60 to dress both the first grinding wheel 31 and the second grinding wheel 32 so that the first diameter d1 of the first grinding wheel 31 is larger than the second diameter d2 of the second grinding wheel 32. In Fig. 8, the relative position change of the dresser 60 in the initial dressing process is indicated by a dashed line.

[0050] In the initial adjustment process of the second embodiment, the control unit 70 adjusts the first grinding wheel 31 under the fifth adjustment condition, and adjusts the second grinding wheel 32 under the sixth adjustment condition. The fifth adjustment condition includes the feed rate, the depth of cut, and the number of cuts of the dresser 60 for using the first grinding wheel 31 for rough grinding. The sixth adjustment condition includes the feed rate, the depth of cut, and the number of cuts of the dresser 60 for using the second grinding wheel 32 for finish grinding while making the diameter of the second grinding wheel 32 smaller than that of the first grinding wheel 31.

[0051] In step S210 of Fig. 7, the control unit 70 executes a rough grinding process in which rough grinding is performed on the workpiece W using the first grinding wheel 31. The rough grinding process in the second embodiment has the same processing content as the rough grinding process in the first embodiment shown in Fig. 4. Due to the initial correction process in step S200, the first diameter d1 of the first grinding wheel 31 is larger than the second diameter d2 of the second grinding wheel 32. Therefore, in the rough grinding process, the second grinding wheel 32 does not come into contact with the workpiece W, and only the first grinding wheel 31 comes into contact with the workpiece W. Therefore, rough grinding is performed on the workpiece W using the first grinding wheel 31, which has a coarse grain size.

[0052] 7, the control unit 70 executes a second correction process. Similar to the second correction process in the first embodiment, the second correction process in the second embodiment is a process for correcting the grinding wheel so that the second diameter d2 of the second grinding wheel 32 is larger than the first diameter d1 of the first grinding wheel 31.

[0053] 9 is an explanatory diagram of the second adjustment process in the second embodiment. In the second embodiment, the control unit 70 uses the dresser 60 to adjust only the first grinding wheel 31 so that the second diameter d2 of the second grinding wheel 32 is larger than the first diameter d1 of the first grinding wheel 31. That is, in the second adjustment process in the second embodiment, the control unit 70 adjusts the first grinding wheel 31 so that the first diameter d1 of the first grinding wheel 31 is smaller than the second diameter d2 of the second grinding wheel 32, but does not adjust the second grinding wheel 32. In FIG. 9, the relative position change of the dresser 60 during the second adjustment process is indicated by a dashed line. In the second adjustment process in the second embodiment, the control unit 70 adjusts the first grinding wheel 31 under the seventh adjustment condition. The seventh adjustment condition includes the feed rate, cutting depth, and number of cuttings of the dresser 60 for using the first grinding wheel 31 for rough grinding while making the diameter of the first grinding wheel 31 smaller than that of the second grinding wheel 32 .

[0054] In step S230 of Fig. 7, the control unit 70 executes a finish grinding process in which the workpiece W is finish-ground using the second grinding wheel 32. The finish grinding process in the second embodiment has the same process content as the finish grinding process in the first embodiment shown in Fig. 6. As a result of the second correction process in step S220, the second diameter d2 of the second grinding wheel 32 is larger than the first diameter d1 of the first grinding wheel 31. Therefore, in the finish grinding process, the first grinding wheel 31 does not come into contact with the workpiece W, and only the second grinding wheel 32 comes into contact with the workpiece W. Therefore, the workpiece W is finish-ground using the second grinding wheel 32, which has a finer grain size.

[0055] 7, the control unit 70 executes a first correction process. Similar to the first correction process in the first embodiment, the first correction process in the second embodiment is a process for correcting the grinding wheels so that the first diameter d1 of the first grinding wheel 31 is larger than the second diameter d2 of the second grinding wheel 32.

[0056] 10 is an explanatory diagram of the first adjustment process in the second embodiment. In the first adjustment process in the second embodiment, the control unit 70 uses the dresser 60 to adjust only the second grinding wheel 32 so that the first diameter d1 of the first grinding wheel 31 is larger than the second diameter d2 of the second grinding wheel 32. That is, in the first adjustment process in the second embodiment, the control unit 70 adjusts the second grinding wheel 32 so that the second diameter d2 of the second grinding wheel 32 is smaller than the first diameter d1 of the first grinding wheel 31, but does not adjust the first grinding wheel 31. In FIG. 10, the relative position change of the dresser 60 during the first adjustment process is indicated by a dashed line. In the first adjustment process in the second embodiment, the control unit 70 adjusts the second grinding wheel 32 under the eighth adjustment condition. The eighth adjustment condition includes the feed rate, cutting depth, and number of cuttings of the dresser 60 for using the second grinding wheel 32 for finish grinding while making the diameter of the second grinding wheel 32 smaller than that of the first grinding wheel 31 .

[0057] In step S250 of FIG. 7 , the control unit 70 determines whether the first grinding wheel 31 and the second grinding wheel 32 have reached their service lives. If the first grinding wheel 31 and the second grinding wheel 32 have reached their service lives, the control unit 70 terminates the grinding process. If the first grinding wheel 31 and the second grinding wheel 32 have not reached their service lives, the control unit 70 returns the process to step S210 to perform the grinding process on another workpiece W. In step S240 before the process returns to step S210, the first adjustment process is performed, and grinding wheel adjustment is performed so that the first diameter d1 of the first grinding wheel 31 is larger than the second diameter d2 of the second grinding wheel 32. Therefore, the control unit 70 can perform the rough grinding process in step S210 without re-executing the initial adjustment process in step S200. In step S250 in this embodiment, the control unit 70 determines that the first grinding wheel 31 and the second grinding wheel 32 have reached the end of their lives when the processes from step S210 to step S240 have been repeated a predetermined number of times. Alternatively, the control unit 70 may determine the end of their lives by using a sensor such as an acoustic emission (AE) sensor attached to the grinding machine 100.

[0058] According to the second embodiment described above, similarly to the first embodiment, it is possible to reduce the time and effort required for the user to replace the grinding wheel 33 attached to the grinding machine 100. Furthermore, since there is no need to replace the grinding wheel 33 between rough grinding and finish grinding, it is possible to shorten the processing time for the workpiece W, thereby reducing the unit price of the product.

[0059] Furthermore, in the second embodiment, only one of the first grinding wheel 31 and the second grinding wheel 32 is dressed in each of the first dressing process and the second dressing process. Therefore, the amount of wear on the first grinding wheel 31 and the second grinding wheel 32 can be reduced compared to when both the first grinding wheel 31 and the second grinding wheel 32 are dressed in each of the first dressing process and the second dressing process. As a result, the first grinding wheel 31 and the second grinding wheel 32 can be used repeatedly for grinding multiple workpieces W.

[0060] In the second embodiment, the first correction process and the second correction process are repeatedly performed, and a plurality of workpieces W are ground by the first grindstone 31 and the second grindstone 32. Therefore, the effort required for replacing the grindstone 33 can be further reduced.

[0061] In the second embodiment, if it is determined in step S250 of Fig. 7 that the grinding wheel 33 has not reached the end of its life, the process returns to step S210, thereby repeatedly grinding a plurality of workpieces W. Alternatively, step S250 of Fig. 7 may be omitted. In this way, the grinding process of Fig. 7 is performed on one workpiece W.

[0062] C. Other Embodiments: (C-1) In each of the above embodiments, the grinding machine 100 is equipped with two grinding wheels 33 having different grain sizes. Alternatively, the grinding machine 100 may be equipped with three or more grinding wheels 33 having different grain sizes. In this case, the control unit 70 performs grinding wheel adjustment prior to grinding so that the diameter of the grinding wheel 33 to be used in the grinding process is maximized.

[0063] (C-2) In the first embodiment described above, the control unit 70 performs both the rough grinding process and the finish grinding process in the grinding process. In contrast, the control unit 70 may perform only one of the rough grinding process or the finish grinding process in the grinding process. When performing only the rough grinding process, the control unit 70 performs the first correction process prior to the rough grinding process. When performing only the finish grinding process, the control unit 70 performs the second correction process prior to the finish grinding process.

[0064] (C-3) In each of the above embodiments, the grinding machine 100 is a cylindrical grinding machine. However, the grinding machine 100 may be an internal grinding machine, a centerless grinding machine, or a surface grinding machine.

[0065] (C-4) In the second embodiment, the control unit 70 determines that the first grinding wheel 31 and the second grinding wheel 32 have reached the end of their lives and terminates the grinding process when the processing from step S210 to step S240 has been repeated a predetermined number of times. However, the control unit 70 may set the number of times to repeat the processing from step S210 to step S240, taking into consideration the amount of processing determined from the amount of movement of the grinding wheel head 30, the material of the workpiece W, etc. Furthermore, the control unit 70 may not stop the repetition of the processes from step S210 to step S240 when it determines that the first grinding wheel 31 and the second grinding wheel 32 have reached the end of their lifespan, but may stop the repetition of the processes from step S210 to step S240, for example, by measuring the workpiece W using a sizing device provided on the grinding machine 100 and detecting that the processing time has become longer for the same amount of processing, or by measuring the relationship between the movement amount of the grinding wheel head movement motor 51 and the current (power) of the grinding wheel spindle rotation motor 35 and detecting that the current (power) has increased for the same amount of movement, or that the drive power of each part has increased.

[0066] The present disclosure is not limited to the above-described embodiments and can be realized in various configurations without departing from the spirit thereof. For example, the technical features in the embodiments corresponding to the technical features in each aspect described in the Summary of the Invention section can be appropriately replaced or combined to solve some or all of the above-described problems or achieve some or all of the above-described effects. Furthermore, if a technical feature is not described as essential in this specification, it can be appropriately deleted.

[0067] DESCRIPTION OF SYMBOLS 10...bed, 20...support part, 21...table, 22...spindle device, 23...headstock, 24...spindle, 25...chuck, 26...spindle rotation motor, 27...spindle encoder, 28...tailstock, 29...center, 30...grinding wheel head, 31...first grinding wheel, 32...second grinding wheel, 33...grinding wheel, 34...grinding wheel spindle, 35...grinding wheel spindle rotation motor, 40...table moving device, 41...table moving motor, 42...table encoder, 50...grinding wheel head moving device, 51...grinding wheel head moving motor, 52...grinding wheel head encoder, 60...dresser, 70...control part, 71...CPU, 72...storage part, 81...drive circuit, 82...drive circuit, 83...drive circuit, 100...grinding machine

Claims

1. A grinding machine for grinding a workpiece, comprising: a first grinding wheel having a first diameter; a second grinding wheel having a second diameter and a finer grit than the first grinding wheel; a grinding wheel spindle on which the first grinding wheel and the second grinding wheel are mounted side by side; a dresser for dressing the first grinding wheel and the second grinding wheel; and a control unit that dresses the first grinding wheel and the second grinding wheel using the dresser while rotating the grinding wheel spindle, wherein the control unit performs at least one of: a first dressing process that dresses the first grinding wheel so that the first diameter of the first grinding wheel is larger than the second diameter of the second grinding wheel before grinding the workpiece with the first grinding wheel; and a second dressing process that dresses the second grinding wheel so that the second diameter of the second grinding wheel is larger than the first diameter of the first grinding wheel before grinding the workpiece with the second grinding wheel.

2. A grinding machine according to claim 1, wherein the control unit executes the second correction process after executing the first correction process.

3. A grinding machine according to claim 1, wherein the control unit adjusts both the first grinding wheel and the second grinding wheel in each of the first adjustment process and the second adjustment process.

4. A grinding machine according to claim 3, wherein the control unit performs at least one of the following: making the feed speed of the dresser relative to the second grinding wheel in the first adjustment process faster than the feed amount of the dresser relative to the second grinding wheel in the second adjustment process; making the cut-in amount of the dresser relative to the second grinding wheel in the first adjustment process larger than the cut-in amount of the dresser relative to the second grinding wheel in the second adjustment process; making the feed speed of the dresser relative to the first grinding wheel in the second adjustment process faster than the feed speed of the dresser relative to the first grinding wheel in the first adjustment process; and making the cut-in amount of the dresser relative to the first grinding wheel in the second adjustment process larger than the cut-in amount of the dresser relative to the first grinding wheel in the first adjustment process.

5. A grinding machine according to claim 1, wherein the control unit, in the first adjustment process, adjusts the second grinding wheel but not the first grinding wheel, and, in the second adjustment process, adjusts the first grinding wheel but not the second grinding wheel.

6. A grinding machine according to claim 5, wherein the control unit repeatedly executes the first correction process and the second correction process, and grinds a plurality of workpieces with the first grindstone and the second grindstone.

7. A method for dressing a first grinding wheel and a second grinding wheel attached side by side to a grinding wheel spindle, wherein the first grinding wheel has a first diameter, and the second grinding wheel has a second diameter and is finer in grain size than the first grinding wheel, the method comprising at least one of: dressing the grinding wheels using a dresser before grinding a workpiece with the first grinding wheel so that the first diameter of the first grinding wheel is larger than the second diameter of the second grinding wheel; and dressing the grinding wheels using the dresser before grinding the workpiece with the second grinding wheel so that the second diameter of the second grinding wheel is larger than the first diameter of the first grinding wheel.

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