JP2007237333A - Abrasive wheel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To highly efficiently perform rough grinding the surface of a workpiece and finish grinding it to an ultra highly accurate surface roughness with one piece of abrasive wheel. <P>SOLUTION: The abrasive wheel has an abrasive chip 11 for rough grinding and an abrasive chip 12 for finish grinding different in properties having an abrasive wheel layer bonding abrasive grains. The abrasive chip for rough grinding and the abrasive chip for finish grinding are randomly attached to the outer peripheral surface of a disc-like core 13 as a non-square shape having a curve of a profile shape of these abrasive chips. The displacement amount in the load direction of the grinding surface of the abrasive chip to the load acting on the grinding surface of the abrasive chip toward the inner side of the abrasive wheel is larger in the abrasive chip for finish grinding than the abrasive chip for rough fringing. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a grinding wheel in which a plurality of types of grinding stone chips having different properties suitable for rough grinding and finish grinding of a workpiece are randomly attached to the outer peripheral surface of a disk-shaped core.

  Conventionally, in order to grind the surface of a workpiece to a high-precision surface roughness, two grinding wheel platforms are provided in the grinding machine, and a grinding wheel for rough grinding is provided on one grinding wheel table and the other grinding wheel table is finished. Each grinding wheel is supported so that it can be rotated, and after the workpiece is roughly ground with high grinding efficiency by the rough grinding wheel, it is finish ground to a high-precision surface roughness by the finishing grinding wheel. I have to. In addition, when the surface of the camshaft is required to have a particularly high surface roughness, the surface roughness may be improved by lapping with lapping tape after rough grinding with a grinding wheel. It has been broken.

Further, in the centerless roll grinder, as described in Patent Document 1, a wide combination grindstone made up of a rough grindstone 11a, a medium grindstone 11b, and a finish grindstone 11c is used as the grindstone 11, and an adjustment wheel 13 is used. In addition, while the roll 2 supported and rotated by the knife blade 14 passes between the grinding wheel 11 and the adjusting wheel 13, rough polishing, intermediate polishing and finish polishing are performed in one pass.
Japanese Patent Laid-Open No. 11-104940 (page 4, FIGS. 2, 3)

  However, in the above conventional grinding machine, after rough grinding with a grinding wheel for rough grinding, finish grinding or lapping is performed with a grinding wheel for finishing grinding or a lapping tape. Time required to move from the position facing the grinding wheel to the position facing the grinding wheel for finishing grinding or the wrapping tape is required, and there is a problem that the grinding time becomes long and the grinding machine becomes expensive.

  Further, in the centerless grinding machine as described in Patent Document 1, if the cutting amount of the grinding wheel is made very fine, the roll 2 cannot be fed in the axial direction. There was a problem that it could not be ground to roughness.

  The present invention has been made to solve the above-described conventional problems, and a single grinding wheel can be used to efficiently grind the surface of a workpiece with high efficiency and finish to an ultra-high precision surface roughness. The purpose is to enable grinding.

  In order to solve the above-mentioned problems, the structural features of the invention described in claim 1 include a grindstone tip for rough grinding and a grindstone tip for finish grinding having different properties having a grindstone layer combined with abrasive grains, The contour shape of the rough grinding wheel tip and the finishing grinding wheel tip is made into a non-square shape having a curve, and is randomly attached to the outer peripheral surface of the disk-shaped core, and acts on the grinding surface of the grinding wheel tip toward the inside of the grinding wheel. The amount of displacement in the load direction of the grinding surface of the grindstone tip with respect to the load is greater in the finish grinding grindstone tip than in the rough grinding grindstone tip.

  A structural feature of the invention according to claim 2 is that, in claim 1, the non-square shape having the curve is a circle or an ellipse.

  A structural feature of the invention according to claim 3 is that, in claim 1 or 2, the Young's modulus of the binder of the grinding wheel tip is smaller in the finish grinding wheel than in the rough grinding wheel tip. It is.

  The structural feature of the invention according to claim 4 is the abrasive grain of at least one of the grinding wheel tip for rough grinding and the grinding stone tip for finish grinding in any one of claims 1 to 3. Is a superabrasive grain.

  According to the invention according to claim 1 configured as described above, during rough grinding, the load acting on the grinding wheel is large, and the load by which the workpiece presses the grinding wheel tip toward the inside of the grinding wheel is large. Therefore, the grinding wheel tip for finish grinding is elastically deformed and escapes to the inside of the grinding wheel, and the workpiece is roughly ground by the grinding surface of the grinding wheel tip for rough grinding that is hard to be elastically deformed. Since the load acting on the grinding wheel during finish grinding is reduced, the ground surface of the grinding wheel tip for finish grinding is elastically restored so that it protrudes outward from the grinding surface of the grinding wheel tip for rough grinding. Done. In this way, it is possible to efficiently perform from rough grinding to finish grinding with a single grinding wheel, and to finish-grind the surface of the workpiece to an ultra-high precision surface roughness.

  In addition, since the contour shape of the grindstone tip is a non-square shape with a curve, there is no regularity in the arrangement of the grindstone tips, so that the grinding process is not interrupted and the surface roughness of the grinding surface is reduced. It is possible to improve and prevent uneven wear of the grinding wheel.

  According to the invention according to claim 2 configured as described above, since the non-square shape having a curve is a circle or an ellipse, the occupation area of the grindstone tip can be increased, and the area calculation of the grindstone tip can also be performed. It can be done easily.

  According to the invention according to claim 3 configured as described above, since the Young's modulus of the binder of the grinding wheel tip is smaller in the grinding wheel for finishing grinding than the grinding wheel tip for rough grinding, the grinding wheel tip toward the inside of the grinding wheel. The amount of displacement of the grinding surface of the grinding wheel tip with respect to the load acting on the grinding surface of the finish grinding wheel tip is larger than that of the rough grinding wheel tip, and the effect similar to that of the invention described in claim 1 is achieved with a simple configuration. Can be played.

  According to the invention according to claim 4 configured as described above, the abrasive grains of at least one of the rough grinding wheel tip and the finish grinding grinding wheel chip are superabrasive grains. The number of the workpieces can be reduced and the workpiece can be efficiently ground.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. The grinding wheel G shown in FIG. 1 and FIG. 2 has an outer periphery of a disk-shaped core 13 in which rough grinding wheel tips 11 and finish grinding grinding stone tips 12 having different properties are formed of a metal such as iron, aluminum alloy, or titanium alloy. The configuration is affixed to the surface 13a. The grinding wheel tip 11 for rough grinding and the grinding stone tip 12 for finish grinding are formed in an elliptical shape, and are randomly formed on the outer peripheral surface 13a of the disk-shaped core 13 so that the major axis of the ellipse is parallel to the rotational axis direction of the grinding wheel G. Is arranged. By making the rough grinding wheel tip 11 and the finish grinding wheel tip 12 into an elliptical shape, the rough grinding wheel tip 11 and the finish grinding wheel tip 12 are arranged in the circumferential direction and the axial direction of the outer peripheral surface 13a of the disk-shaped core 13. It is possible to arrange them randomly and easily, and the area occupied by the grindstone tips 11 and 12 with respect to the area of the outer peripheral surface 13a of the disk-shaped core 13 can be increased. Moreover, since the regularity is lost as compared with the ones in which rectangular grindstone chips are alternately arranged in the circumferential direction, the grinding process is not interrupted, and the surface roughness of the workpiece to be ground can be improved. At the same time, uneven wear of the grinding wheel G can be prevented.

  In the grindstone tip 11 for rough grinding, for example, a grindstone layer 16 in which superabrasive grains 14 such as CBN and diamond are bonded with a binder 15 is formed on the outer peripheral side, and an underlayer 17 that does not contain superabrasive grains is formed of the grindstone layer 16. It is molded integrally on the inside. As an example, the grindstone layer 16 is formed by binding CBN abrasive grains having a particle size of # 80 with a vitrifado binder 15 to a thickness of 3 to 5 mm with a concentration of 200. The underlayer 17 is obtained by bonding the base particles 18 with a vitrifado binder 15 to a thickness of 1 to 3 mm.

  In the production of the grindstone tip 11 for rough grinding, the grindstone layer powder in which the superabrasive grains 14 and the vitrifado binder 15 constituting the grindstone layer 16 are mixed is filled in an elliptical press lower mold with a uniform thickness, The elliptical grinding wheel layer 16 is temporarily formed by temporary pressing with the first upper die. The ground layer powder containing the ground particles 18 is filled to an even thickness on the upper side of the temporarily pressed molded grinding wheel layer powder, and the ground layer powder and the grinding wheel layer powder are simultaneously formed by the second upper mold. The ground layer 17 is pressed and integrally formed on the inner side of the grindstone layer 16, and an elliptical rough grinding grindstone chip is press-molded. The press-molded rough grinding wheel tip is dried and fired to complete an elliptical rough grinding wheel tip 11.

  The grinding wheel tip 12 for finish grinding is formed, for example, by bonding general abrasive grains 19 such as WA and GC with a binder 20 having a Young's modulus smaller than the binder 15 of the grinding wheel tip 11 for rough grinding. A WA abrasive grain having a particle size of # 800 is bonded to a thickness of 4 to 8 mm with a concentration of 30 by the resinoid binder 20 and formed into an elliptical shape.

  The oval rough grinding wheel tip 11 and the finish grinding wheel tip 12 of the same thickness formed in this way are randomly arranged on the outer circumferential surface 13a of the disc-shaped core 13 in the circumferential direction and the axial direction, The bottom surface of the ground layer 17 of the grinding wheel tip 11 for grinding and the bottom surface of the grinding wheel tip 12 for finish grinding are attached to the outer peripheral surface 13a of the disk-shaped core 13 with an adhesive made of epoxy resin.

  In this case, since the Young's modulus of the resinoid binder 20 of the finish grinding wheel tip 12 is smaller than the vitrified binder 15 of the grinding wheel tip 11 for rough grinding, the grinding wheel tip 11 for coarse grinding toward the center of rotation inside the grinding wheel G. Further, the amount of displacement in the load direction of the grinding surface of the grinding wheel tip relative to the load acting on the outer peripheral surface of the grinding wheel tip 12 for finish grinding is larger in the grinding stone tip 12 for finishing grinding than in the grinding wheel tip 11 for rough grinding. The adjacent rough grinding wheel tip 11 and finish grinding wheel tip 12 can be elastically deformed independently in the load direction, respectively, between the elliptical rough grinding wheel tip 11 and finish grinding wheel tip 12. Are left as voids, or the voids are filled with a soft resin rich in elasticity, for example, ethylene tetrafluoride.

  The distribution ratio of the grinding wheel tip 11 for rough grinding and the grinding wheel tip 12 for finish grinding can be arbitrarily changed according to the application of the grinding wheel G. Generally, the grindstone tip 11 for rough grinding and the grindstone tip 12 for finish grinding are equally distributed (50:50). For example, when the machining allowance is large, the grinding efficiency (grinding time) is emphasized. When performing the above-described grinding process or when finishing accuracy is not required, the distribution rate of the rough grinding wheel tip 11 is made larger than that of the finishing grinding wheel tip 12, and the grinding efficiency is emphasized. On the contrary, when the machining allowance is small and the finishing accuracy is strictly required, the distribution ratio of the grinding wheel tip 12 for finishing grinding is made larger than that of the grinding wheel tip 11 for rough grinding, and the grinding accuracy is emphasized. The Even if the machining allowance is large, if finishing accuracy is required, the rough grinding wheel tip 11 and the finish grinding wheel tip 12 are equally distributed. However, in any case, the distribution density of the grindstone tip 11 for rough grinding and the grindstone tip 12 for finish grinding is always kept uniform.

  Next, a grinding machine 10 for grinding the workpiece W by mounting the grinding wheel G having the above-described configuration will be described with reference to FIG.

  A table 27 is supported on the bed 26 so as to be movable in the horizontal Z-axis direction, and is moved in the Z-axis direction by a servo motor 28 via a ball screw. A headstock 29 and a tailstock 30 are arranged on the table 27 so as to face each other, so that the workpiece W can rotate around an axis parallel to the Z-axis direction between the headstock 29 and the tailstock 30. Is supported by the center. A spindle 31 is rotatably supported on the spindle stock 29 and is driven to rotate by a servo motor 32 for driving the spindle. The workpiece W is connected to the main shaft 31 via a drive fitting or the like and is driven to rotate. A truing tool 33 for truing the grinding wheel G is coaxially fixed to the tip of the main shaft 31.

  On the bed 26, a grindstone base 34 is supported so as to be movable in a horizontal X-axis direction orthogonal to the moving direction of the table 27, and is moved in the X-axis direction by a servo motor 35 via a ball screw. A grinding wheel shaft 36 is rotatably supported on the grinding wheel base 34, and is rotationally driven by a servo motor 37 for driving the grinding wheel via a belt transmission mechanism. A grinding wheel G is fitted at the tip of the grinding wheel shaft 36 with a center hole drilled in the disk-shaped core 13 and fixed by a bolt.

  The CNC device 40 is connected to the drive units 41 to 44 of the servo motors 28, 32, 35, and 37, respectively. The CNC device 40 executes the truing NC program during truing and trues the grinding wheel G with the truing tool 33, and executes the grinding NC program during grinding and rough grinding the workpiece W with the grinding wheel G. Finish grinding.

  Next, the operation of the grinding machine 10 in the above-described embodiment will be described mainly based on FIGS. FIG. 4 schematically shows the operation of truing the grinding wheel G provided with the grinding wheel tip 11 for rough grinding and the grinding wheel tip 12 for finish grinding with the truing tool 33, and FIG. 5 shows the grinding wheel. The operation | movement which rough-grinds and finish-grinds the workpiece W by G is typically shown.

  When truing the grinding wheel G, the CNC device 40 executes a truing NC program, and outputs a rotation command to rotate the grinding wheel G at a high rotational speed to the drive unit 44 of the servo motor 37 for driving the grinding wheel. A rotation command for rotating the truing tool 33 with respect to the grinding wheel G at a predetermined peripheral speed suitable for truing is output to the drive unit 42 of the servo motor 32 for driving the spindle.

  Next, a forward command for cutting and advancing the grinding wheel base 34 in the X-axis direction is output to the drive unit 43 of the servo motor 35, and the grinding surface of the grinding wheel G is advanced by the truing cutting amount with respect to the outer peripheral surface of the truing tool 33. . In this state, a feed command for relatively moving the table 27 and the grindstone table 34 at the truing speed is output to the drive units 41 and 43 of the servo motors 28 and 35, whereby the truing tool 33 is positioned at the position of the two-dot chain line in FIG. The traverse to the left in the figure is traversed by a predetermined amount, and the grinding surface of the grinding wheel G is trued.

  During truing of the grinding wheel G, the grinding wheel tip 12 for finishing grinding is more centrifugally expanded than the grinding wheel tip 11 for rough grinding due to the high-speed rotation of the grinding wheel G. However, since the load pressing the grinding surfaces 11a, 12a of the grinding wheel tip 11 for rough grinding and the grinding wheel tip 12 for finishing grinding toward the rotation center inside the grinding wheel G is large, as shown in FIG. The grindstone tip 12 is pushed and elastically deformed by the truing tool 33 and escapes to the rotation center side of the grinding wheel G. For this reason, the grinding wheel tip 11 for rough grinding is trued more than the grinding wheel tip 12 for finish grinding.

  When the truing of the grinding wheel tip 12 for finish grinding is completed and is not pushed by the truing tool 33, the grinding wheel tip 12 for finishing grinding is elastically restored as shown in part A of FIG. As for the grinding surface, the grinding surface 12a of the finish grinding wheel tip 12 is slightly larger in diameter than the grinding surface 11a of the rough grinding wheel tip 11.

  When the workpiece W is roughly ground by the grinding wheel G, the CNC device 40 executes a rough grinding NC program, and gives a rotation command to rotate the grinding wheel G at a low rotational speed. And a rotation command for rotating the workpiece W at a peripheral speed suitable for rough grinding is output to the drive unit 42 of the servo motor 32 for driving the spindle.

  When the grinding wheel G is moved to a position facing the grinding part of the workpiece W (state shown in FIG. 5A), a command to move the grinding wheel base 34 forward in the X-axis direction at the coarse grinding feed speed is given by the servo motor 35. To the drive unit 43, and the workpiece W is roughly ground. At the time of such rough grinding, as shown in FIG. 5 (B), the cutting amount (removal allowance) Z1 of the grinding wheel G into the workpiece W is large, and the workpiece W passes the grinding surfaces 11a and 12a of the grinding stone chips 11 and 12. Since the load pressed toward the rotation center side of the grinding wheel G is large, the grinding wheel tip 12 for finish grinding is elastically deformed and escapes toward the rotation center side of the grinding wheel G. For this reason, the grinding wheel tip 12 for finishing grinding hardly participates in the grinding process, and the workpiece W is roughly ground by the grinding surface 11a of the grinding wheel tip 11 for rough grinding with high efficiency.

  When the rough grinding of the workpiece W is completed, the CNC device 40 executes the NC program for finish grinding in order to finish grinding the workpiece W by the grinding wheel G. A rotation command for rotating at a high rotation speed is output to the drive unit 44 of the servo motor 37 for driving the grindstone, and a command for moving the grindstone table 34 forward in the X-axis direction at the finish grinding feed speed is a drive unit 43 for the servo motor 35. Output to.

  As a result, the workpiece W is finish-grinded. At the time of such finish-grinding, as shown in FIG. 5C, the cutting amount (removal allowance) Z2 of the grinding wheel G to the workpiece W is small. The load applied to the grinding wheel tip 11 for grinding and the grinding wheel tip 12 for finish grinding is reduced. Therefore, the grinding wheel tip 12 for finishing grinding that has escaped toward the center of rotation of the grinding wheel G during rough grinding is restored elastically, and the centrifugal expansion action due to the increase in the rotational speed of the grinding wheel G is combined with the finishing. The grinding surface 12 a of the grinding wheel tip 12 has a larger diameter than the grinding surface 11 a of the rough grinding wheel tip 11. Thereby, the grinding surface 12a of the grindstone tip 12 for finish grinding is held in a state of slightly projecting outward of the grinding wheel G from the grinding surface 11a of the grindstone tip 11 for rough grinding, and the workpiece W has an elliptical finish. The ground surface 12a of the grinding wheel tip 12 for grinding is subjected to finish grinding with high accuracy.

  That is, since the rough grinding wheel tip 11 and the finish grinding wheel tip 12 have an elliptical shape, there is no regularity in the arrangement of the grinding wheel tips, and the grinding process is not interrupted. Therefore, the surface roughness and waviness accuracy of the grinding surface of the workpiece W can be improved, and uneven wear of the grinding wheel G can be prevented. As a result, in particular, the surface roughness of the workpiece W in finish grinding can be increased to an accuracy of, for example, 0.2 μmRa or less.

  When the workpiece to be ground by the grinding wheel G is a cam surface of a camshaft, the movement of the grinding wheel base 34 is controlled in synchronism with the rotation of the camshaft, so that A desired cam profile can be ground with high accuracy without lapping.

  According to the above-described embodiment, the grinding wheel G can perform grinding with high efficiency and high accuracy in one process from rough grinding to finish grinding. Moreover, since the grindstone tips 11 and 12 have an elliptical shape, there is no regularity in the arrangement of the grindstone tips as in the prior art, and the grinding process is not interrupted. Therefore, the processing quality (surface roughness and waviness accuracy) of the workpiece W can be improved. In addition, since the grindstone tips 11 and 12 have an elliptical shape, the grindstone tips 11 and 12 are randomly arranged in the circumferential direction and the axial direction of the outer peripheral surface 13a of the disc-shaped core 13 at a distribution rate according to the purpose of grinding. In addition, the occupied area with respect to the area of the outer peripheral surface 13a of the disk-shaped core 13 can be increased, the abrasive distribution density can be improved, and the surface roughness of the workpiece W in the finish grinding can be lapped. Even if it does not perform, it becomes possible to raise to a desired precision easily.

  In the above-described embodiment, the rough grinding wheel tip 11 and the finish grinding wheel tip 12 are configured to have an elliptical shape, and the major axis of the ellipse is arranged parallel to the rotational axis direction of the grinding wheel G. However, the major axis of the ellipse may be an arbitrary angle between the rotation axis direction of the grinding wheel G and an angle perpendicular to the rotation axis direction, and the shape of the grindstone tips 11 and 12 is not limited to the elliptical shape, and is circular. Or a combination of an ellipse and a circle. Thus, by making the grindstone chips 11 and 12 elliptical or circular, the total area of the grindstone chips 11 and 12 involved in the grinding process can be easily calculated, and the distribution density of the grindstone chips 11 and 12 is increased. Is easy to set.

  However, the shape of the grindstone tips 11 and 12 is not necessarily limited to an elliptical shape or a circular shape because regularity can be eliminated if the contour shape is a non-square shape having a curve.

  In the above-described embodiment, the example in which the rough grinding stone tip 11 and the finish grinding grinding stone tip 12 are randomly arranged on the outer circumferential surface 13a of the disk-shaped core 13 in the axial direction and the circumferential direction has been described. An assembly in which the rough grinding wheel tip 11 is disposed along the axial direction and the circumferential direction, and an assembly in which the finish grinding grinding wheel tip 12 is disposed along the axial direction and the circumferential direction are combined into the disk-shaped core 13. It may be arranged alternately in the circumferential direction.

  Further, in the above-described embodiment, the rough grinding wheel tip 11 is composed of a CBN grinding wheel or the like in which superabrasive grains are bonded with the vitrifado binder 15, and the finishing grinding wheel chip 12 is made of WA abrasive grains or the like with a resinoid binder. As described in the example constituted by the ordinary grindstone bonded at 20, the rough grinding wheel tip 11 can be composed of a metal grindstone or an electrodeposition grindstone, and the finish grinding grindstone tip 12 is composed of superabrasive grains. You can also. Further, the rough grinding grindstone tip 11 does not necessarily have a two-layer structure of the grindstone layer 16 and the base layer 17, and may include only one grindstone layer.

  In the above-described embodiment, the displacement in the load direction of the grinding surfaces 11a, 12a of the grinding wheel tips 11, 12 with respect to the load acting on the grinding surfaces 11a, 12a of the grinding wheel tips 11, 12 toward the inside of the grinding wheel G. As a means to make the amount of the grinding wheel tip 12 for finishing grinding larger than the grinding wheel tip 11 for rough grinding, the Young's modulus of the binder (resinoid binder) 20 of the grinding wheel tip 12 for finishing grinding is used for rough grinding. Although the Young's modulus is smaller than the Young's modulus of the binder (vitrified binder) 15 of the grindstone chip 11, the present invention is not limited to this, and the Young's modulus can be freely changed depending on the binder ratio and the type of the binder. Is possible. For example, the grindstone tip 12 for finish grinding is composed of a grindstone layer in which superabrasive grains are bonded with a vitrified binder and an underlayer integrally formed by overlapping the grindstone layer. The Young's modulus may be made smaller than the Young's modulus of the foundation layer 17 of the grindstone tip for rough grinding. Further, the Young's modulus can be finely adjusted by changing the thickness of the grindstone tips 11 and 12.

1 is an external view of a grinding wheel showing an embodiment of the present invention. It is a fragmentary sectional view of the grinding wheel cut | disconnected along the II-II line | wire of FIG. It is a top view of the cylindrical grinding machine provided with the grinding wheel of FIG. It is a figure which shows the truing cycle which truws a grinding wheel. It is a figure which shows the grinding process cycle which rough-grinds and finish-grinds a workpiece with a grinding wheel.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Grinding machine, 11 ... Grinding wheel chip for rough grinding, 12 ... Grinding wheel chip for finish grinding, 13 ... Disc-shaped core, 14 ... Superabrasive grain, 15 ... Vitrified binder , 16 ... Grinding wheel layer, 17 ... Undercoat layer, 19 ... General abrasive, 20 ... Resinoid binder, 27 ... Table, 29 ... Headstock, 30 ... Tailstock 33, truing tool, 34 ... grinding wheel base, 28, 32, 35, 37 ... servo motor, 40 ... CNC device, G ... grinding wheel, W ... workpiece.

Claims (4)

  The grinding wheel tip for rough grinding and the grinding wheel tip for finish grinding with different properties having a grinding wheel layer combined with abrasive grains are provided, and the contour shape of the grinding wheel tip for rough grinding and the grinding wheel for finish grinding is a non-square shape with a curve. The amount of displacement in the load direction of the grinding surface of the grinding wheel tip relative to the load acting on the grinding surface of the grinding wheel tip toward the inner side of the grinding wheel is randomly attached to the outer peripheral surface of the disk-shaped core from the rough grinding wheel tip A grinding wheel characterized in that the grinding wheel tip for finish grinding is larger.    The grinding wheel according to claim 1, wherein the non-square shape having the curve is a circle or an ellipse.    3. The grinding wheel according to claim 1, wherein the finish grinding wheel has a Young's modulus smaller than that of the rough grinding wheel tip according to claim 1.    4. The grinding wheel according to claim 1, wherein the abrasive grains of at least one of the grinding wheel tip for rough grinding and the grinding stone tip for finish grinding are superabrasive grains. 5.

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