JP2008114338A - Grinding wheel with inclined groove and manufacturing method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To easily carve inclined grooves inclined toward the axis of rotation on the abrasive grain layer of a grinding wheel by machining at a low cost. <P>SOLUTION: A plurality of inclined grooves are carved on the abrasive grain layer of the grinding wheel by repeating a groove-machining process in which the inclined grooves from the grinding surface to the underlayer of the grinding wheel are linearly carved on the abrasive grain layer by machining by moving a tool onto the grinding wheel in a straight line toward the inclined angle direction of the inclined grooves and an indexing process in which the grinding wheel is rotated in an indexing manner by an angle corresponding to the number of the inclined grooves. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method of manufacturing a grindstone with an inclined groove in which an inclined groove is formed on a segment type grindstone chip affixed to a core.

  An abrasive layer containing superabrasive grains such as diamond or cubic boron nitride is formed on the outer peripheral surface of a disk-shaped core that is driven to rotate about the axis, and a predetermined width and depth are formed on the outer peripheral surface of the abrasive layer. Patent Document 1 discloses a grooved grindstone in which an inclined groove having a thickness is engraved with an inclination of about 25 to 45 degrees with respect to the axis of the core. According to such a grooved grindstone, the grinding liquid can be effectively introduced to the grinding point along the inclined groove, and the removal amount by grinding is about 1.5 times that of the grindstone without the inclined groove. It is possible to increase the grinding efficiency.

In addition, the grinding fluid supplied to the grinding point generates dynamic pressure between the workpiece and the grinding wheel, and this dynamic pressure prevents the workpiece from being displaced relative to the grinding wheel to prevent deterioration in machining accuracy and efficiency. In order to achieve this, it is considered to provide a groove on the grinding surface of the grindstone to release the dynamic pressure.
JP 2000-354969 (paragraphs [0007], [0026], FIG. 1)

  In order to engrave the inclined groove on the grinding surface of the grindstone in a curved shape by machining, it is necessary to perform simultaneous three-axis control, which requires a long time for the groove processing and increases the cost.

  An object of the present invention is to easily engrave an inclined groove inclined with respect to the rotation axis at a low cost by machining in an abrasive layer of a grindstone.

  In order to solve the above-mentioned problem, the structural feature of the invention according to claim 1 is that superabrasive grains are applied to a core mounted on a grindstone shaft that is rotatably supported around a grinding wheel base of a grinding machine. A plurality of grindstone chips having an abrasive grain layer are affixed, and a grinding surface formed on the abrasive grain layer abuts a workpiece supported by a workpiece support device of the grinder so as to be rotationally driven at a grinding point. In the grindstone to be ground, a plurality of inclined grooves linearly engraved in the abrasive layer by a tool that is linearly fed in the inclination angle direction of the inclined groove with respect to the grindstone, and linearly in the abrasive layer. It is engraved.

  The structural feature of the invention according to claim 2 is that, in claim 1, the inclined groove is engraved in the abrasive grain layer by the linearly fed tool from the grinding surface to the base layer. It is.

  The structural feature of the invention according to claim 3 is that in claim 1 or 2, the inclined groove is terminated before both side surfaces of the abrasive grain layer parallel to the circumferential direction of the grindstone.

  The structural feature of the invention according to claim 4 is that, in claim 3, the length of the inclined groove in the rotational axis direction of the grindstone is longer than the length of the grinding point in the axial direction.

  A structural feature of the invention according to claim 5 is that: a core that is mounted on a grindstone shaft that is rotatably supported around a rotation axis on a grindstone base of a grinding machine; A grinding point is formed by attaching a plurality of grindstone chips made of a base layer not containing abrasive grains, and a grinding surface formed on the abrasive grain layer is rotatably supported by a workpiece support device of the grinding machine. In the manufacturing method of a grindstone that abuts and grinds, a groove is formed by linearly engraving an inclined groove in the abrasive layer by machining a tool in a straight line in the inclination angle direction of the inclined groove with respect to the grindstone. By repeating the step, the indexing step of indexing and rotating the grindstone by an angle corresponding to the number of the inclined grooves, the groove processing step and the indexing step, a plurality of the inclined grooves, the abrasive grains It is to engrave in the layer.

  The structural feature of the invention according to claim 6 is that, in claim 5, the inclined groove is engraved in a straight line from the grinding surface to the underlayer in the abrasive grain layer.

  According to the first aspect of the present invention, the inclined grooves are linearly engraved in the abrasive layer by a tool that is linearly fed in the inclination angle direction of the inclined grooves with respect to the grindstone, and a plurality of the inclined grooves are provided. Therefore, compared to a grindstone with a slanted groove, the grindstone with a slanted groove with multiple slanted grooves engraved on the grinding surface in order to shorten the processing time and reduce the cost, and to improve the processing accuracy and efficiency. Can be provided at low cost in a short time.

  According to the second aspect of the present invention, since the inclined grooves are linearly engraved in the abrasive grain layer from the ground surface to the base layer, the entire thickness of the abrasive grain layer can be effectively used for grinding. , The life of the wheel will be longer.

  According to the invention of claim 3, since the inclined groove terminates in front of both side surfaces of the abrasive grain layer parallel to the circumferential direction of the grindstone, the acute angle portion of the abrasive grain layer sandwiched between the inclined groove and the side surface is eliminated. It is possible to prevent the acute angle portion from being damaged by the grinding load.

  According to the invention of claim 4, since the length of the inclined groove in the grinding wheel rotation axis direction is longer than the length of the grinding point in the axial direction, the entire length of the workpiece is ground with high precision under the same grinding conditions. Can do.

  According to the fifth aspect of the present invention, since the tool is linearly fed in the direction of the inclination angle of the inclined groove with respect to the grindstone, the inclined groove is engraved linearly by machining in the abrasive layer of the grindstone. Compared with the case of processing the groove in a curved line, the processing time can be shortened and processing can be performed at low cost. Thereby, the grindstone by which the some inclined groove was engraved on the grinding surface can be provided at low cost.

  According to the sixth aspect of the invention, since the inclined groove is linearly engraved in the abrasive grain layer from the grinding surface to the base layer, the entire thickness of the abrasive grain layer can be effectively used for grinding. It is possible to provide an inclined grooved grindstone having a long lifetime at low cost.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a grindstone 10 including a segment type grindstone tip 11. The grindstone tip 11 of the grindstone 10 is formed with an abrasive grain layer 12 in which superabrasive grains are bonded by vitrified bonding on the outer peripheral side. A base layer 13 not included is integrally formed so as to overlap the inside of the abrasive grain layer 12. In the grindstone 10, a plurality of arc-shaped grindstone chips 11 composed of an abrasive grain layer 12 and an underlayer 13 are arranged on the outer peripheral surface of a disk-shaped core 14 formed of a metal such as iron or aluminum, or a resin. The base layer 13 is configured to be attached to the core 14 with an adhesive on the bottom surface. The grindstone 10 is attached by a core 14 to a grindstone shaft 32 that is supported on a grindstone base 31 of a grinder 30 shown in FIG. A workpiece W is rotatably supported on the workpiece support device 33 of the grinding machine 30, and the grinding surface 15 formed on the abrasive layer 12 of the grindstone 10 by the advance of the grindstone table 31 is applied to the workpiece W at a grinding point P. The outer peripheral surface of the workpiece W is ground by abutting with the above.

FIG. 3 shows an arc-shaped grindstone tip 11, and the abrasive grain layer 12 is obtained by bonding superabrasive grains 16 such as CBN and diamond to a thickness of 4 to 6 mm with vitrified bonds 17. For adjustment, particles such as aluminum oxide (Al ₂ O ₃ ) may be mixed as an aggregate instead of superabrasive grains. The underlayer 13 is obtained by bonding the underlayer particles 19 with a vitrified bond 17 to a thickness of 2 to 4 mm. When vitrified bond 17 is employed, the chip characteristics are excellent due to the characteristics of the pores, and the sharpness is improved, so that the amount of grinding wheel wear can be reduced and grinding can be performed to a good surface roughness. However, as the binder, in addition to the vitrified bond 17, a resin bond or a metal bond can be used.

  As shown in FIG. 4, the grinding surface 15 of the grindstone 10 has a plurality of inclined grooves 20 having a width b that is inclined with respect to the circumferential direction of the grindstone, and at least one inclined groove 20 regardless of the rotational phase of the grindstone 10. It is engraved so as to pass the grinding point P up and down. As described above, when at least one inclined groove 20 always passes through the grinding point P, the dynamic pressure generated between the grinding surface 15 and the workpiece W by the grinding liquid supplied to the grinding point P is reduced at the grinding point. The workpiece W is released from both above and below, and the workpiece W is not displaced in a direction away from the grindstone 10 to increase the workpiece size, so that the grinding accuracy, particularly roundness, is improved. If at least one inclined groove 20 does not always pass through the grinding point P, the dynamic pressure is not released below the grinding point P if the inclined groove 20 is opened only above the grinding point P. Similarly, if the inclined groove 20 is opened only downward, the dynamic pressure of the grinding fluid is not released above the grinding point P. The inclined groove 20 passes through both side surfaces 21 and 22 of the abrasive grain layer 12 parallel to the circumferential direction of the grindstone and is carved on the grinding surface 15. As shown in FIG. 5, each of the plurality of inclined grooves 20 is machined with a cutting tool to a depth h from the grinding surface 15 to the base layer 13 and is engraved in a straight line on the abrasive grain layer 12. Yes.

  The conditions for easily creating the inclined groove 20 that can effectively prevent the generation of dynamic pressure of the grinding fluid supplied to the grinding point P and ensure high grinding accuracy and a long grinding wheel life will be described below. Street. Regardless of the rotational phase of the grindstone 10, the inclined groove 20 should pass at least one, preferably two or more grinding points P within the width of the workpiece W, that is, the length of the grinding point P in the axial direction. The groove circumferential width c, which is the width of the inclined groove 20 in the circumferential direction of the grindstone, is preferably shorter because the interval between the superabrasive grains 16 exposed on the grinding surface 15 is increased by the groove circumferential width c. In order to reduce the number of processing steps, it is better that the number of grooves is small. The pitch of the inclined grooves 20 in the circumferential direction of the grindstone is preferably longer because the pitch between the inclined grooves 20 is difficult to process and the strength of the grindstone tip 11 is reduced. It is better not to make the total area of the inclined grooves 20 too large since increasing the size will reduce the number of superabrasive grains 16 involved in grinding and increase the amount of grinding wheel wear.

  In consideration of these conditions, for example, a method for determining the number n of the inclined grooves 20 and the inclination angle α, which are suitable when the workpiece W having a width of 15 mm is plunge cut ground with the grindstone 10 having an outer diameter of 350 mm, will be described below. . The inclination angle α is an angle formed between the inclined groove 20 and the side surface 21 of the abrasive layer 12, that is, the circumferential direction of the grindstone, and the length of the grinding point P in the axial direction is 15 mm, which is the same as the width of the workpiece W.

  The width b in the groove normal direction of the inclined groove 20 is about 1 mm in order to reduce the groove circumferential width c, which is the length of the inclined groove 20 in the circumferential direction of the grindstone in consideration of the strength of the grindstone for grinding. It is good to do. The relationship between the groove circumferential width c and the inclination angle α of the inclined groove 20 is as shown in FIG. 6. When the inclination angle α is larger than about 15 degrees, the groove circumferential width c is reduced, and superabrasion by the inclined groove 20 is performed. The spread of the interval between the grains 16 can be kept small.

  As shown in FIG. 7, for example, in the range d in which the outer peripheral grinding surface 15 (outer diameter 350 mm) of the grindstone 10 is in contact with the workpiece W (width 15 mm), for example, two inclined grooves 20 are related to the rotational phase of the grindstone 10. When the grinding point P having the same length in the axial direction as the width of the workpiece W is passed, the relationship between the inclination angle α and the number n of the inclined grooves 20 is shown in FIG. FIG. 9 shows the relationship between the pitch 20 in the circumferential direction of the grindstone 20 and FIG. 10 shows the relationship between the inclination angle α and the area reduction rate of the grinding surface 15 by the inclined grooves 20. As is apparent from FIG. 9, when the inclination angle α is smaller than about 15 degrees, the pitch p in the circumferential direction of the grindstone of the inclined groove 20 becomes sufficiently large, so that the processing of the inclined groove 20 is not hindered. Further, as shown in FIG. 10, when the inclination angle α is smaller than about 15 degrees, the reduction rate of the area of the grinding surface 15 by the inclined grooves 20 can be reduced. As shown in FIG. 8, when the inclination angle α is about 15 degrees, the number n of the inclined grooves 20 can be reduced. Considering these, it is preferable to set the inclination angle α to a value in the vicinity of 15 degrees.

  In this way, when the workpiece W having a width of 15 mm is subjected to plunge cut grinding with the grindstone 10 having an outer diameter of 350 mm, the width of the workpiece W, that is, within the length in the axial direction of the grinding point P, regardless of the rotational phase of the grindstone 10. In the example of the specifications of the inclined groove 20 determined so that the two inclined grooves 20 pass the grinding point P, the groove width b is 1 mm, the groove depth h is 6 mm, the inclination angle α is 15 degrees, the number n There are 39.

  Next, a method of manufacturing a grindstone with an inclined groove will be described with reference to FIG. The grindstone chip 11 is created by a known method and is affixed to the core 14 to create the grindstone 10 (step 41). As described above, based on the outer diameter of the grindstone 10, the width of the workpiece W, the number of the inclined grooves 20 that always pass through the grinding point P within the axial length of the grinding point P regardless of the rotational phase of the grindstone 10, and the like. Thus, the origin of the inclined groove 20 is determined (step 42). The inclined groove 20 is machined on the outer peripheral grinding surface 15 of the grindstone 10 with a grindstone for grooving in accordance with the determined specifications of the inclined groove 20 (step 43).

  This machining can be performed using a known groove processing apparatus 50 shown in FIG. In the grooving apparatus 50, for example, a grindstone base 53 that supports a grindstone shaft 52 on which a grindstone 51 for grooving is mounted in a horizontal plane so that the grindstone shaft 52 can be driven to rotate about an axis parallel to the Z axis is provided on a column 54 in the vertical Y-axis direction. The column 54 is placed on the bed 55 so as to be movable in the Z-axis direction, and the work table 56 is opposed to the column 54 on the bed and is perpendicular to the Z-axis in the horizontal plane. It is mounted so as to be movable in the direction. A rotary table 57 is supported on the work table 56 so as to be indexed and rotatable about a vertical axis, and a spindle base 60 that supports a spindle 59 provided with a jig 58 so as to be capable of rotational positioning in a horizontal plane is fixed on the rotary table 57. Has been.

  The inclined groove 20 is processed by rotating and positioning the main shaft 59 so that the grindstone 10 is coaxially fixed to the main shaft 59 via the jig 58 and the inclined groove 20 to be processed first is positioned above the rotation axis of the main shaft 59. Is done. The rotary table 57 is indexed and rotated so that the axis of the main shaft 59 is inclined by the inclination angle α of the inclined groove 20 with respect to the Z axis so that the direction of the side surface of the grindstone 51 for grooving coincides with the direction of the inclined groove 20. Is done. The wheel base is positioned so that the column 54 is positioned in the Z-axis direction so that the grooving grindstone 51 is aligned with the inclined groove 20 to be machined first, and the lower end surface of the grooving grindstone 51 coincides with the bottom surface of the inclined groove 20. 53 is lowered and positioned in the Y-axis direction. When the work table 56 is ground and fed in the X-axis direction, the grooving grindstone 51 is linearly fed with respect to the grindstone 10 in the direction of the slant angle α of the slanted groove 20, and the grindstone circumference 12 of the grindstone 10 is moved around the grindstone. An inclined groove 20 inclined with respect to the direction is cut in a straight line by machining from the grinding surface 15 to the underlayer 13 (see FIG. 5). Subsequently, if the number of the inclined grooves 20 is n, the main shaft 59 is rotationally positioned by 360 / n, and the above operation is repeated to engrave n inclined grooves 20.

  When the inclined groove 20 is engraved on the grinding surface 15 of the grindstone 10 by machining with the grooving grindstone 51, the holding force of the superabrasive grains 16 exposed on the grinding surface 15 is machined at the side walls 23 and 24 of the inclined groove 20. And the interval between the superabrasive grains 16 exposed on the grinding surface 15 is widened by the groove circumferential width c of the inclined grooves 20, so that the superabrasive grains The acting grinding load increases, and it is easy to drop off and chip. In order to prevent such superabrasive grains 16 from falling off and chipping, the abrasive grain layer 12 is reinforced with an adhesive 25 on the side walls 24 at the rear of each inclined groove 20 in the grinding wheel rotation direction. The side wall 24 is reinforced by the adhesive 25 by impregnating the side wall 24 with an adhesive such as an epoxy resin or a phenolic resin, or applying the brush 24 with a brush (step 44). In addition, you may make it reinforce the side wall 23 behind the grindstone rotation direction of the inclination groove | channel 20, and the side surfaces 21 and 22 of the abrasive grain layer 12 with an adhesive agent as needed.

  Next, the operation of the grindstone 10 produced by the method for producing the inclined grooved grindstone of this embodiment will be described. The grindstone 10 is mounted on a grindstone shaft 32 supported on a grindstone base 31 of a grinding machine 30 shown in FIG. 2 by a core 14 and is driven to rotate. It is supported and rotated. The coolant is supplied from the coolant nozzle 35 attached to the grindstone cover 34 to the grinding point P between the grindstone 10 and the workpiece W, and the grindstone base 31 is ground and fed toward the workpiece W. Is ground. In this case, since the plurality of inclined grooves 20 that are inclined with respect to the circumferential direction of the grindstone always pass at least two grinding points P regardless of the rotational phase of the grindstone 10, the grinding fluid supplied to the grinding point P is ground. The dynamic pressure generated between 15 and the workpiece W can be released from above and below the grinding point P. As a result, the workpiece W is not displaced in the direction away from the grindstone 10 to increase the size of the workpiece W, and the grinding accuracy, particularly roundness, can be increased.

  As an example of the grinding process, CBN abrasive grains having a grain size of # 120 are bonded by vitrified bond 17 with a concentration of 150 to form the abrasive grain layer 12, and the abrasive grain layer 12 does not contain superabrasive grains. Normal line when a hardened steel cam (workpiece W) having a width of 15 mm is ground by a grindstone having an outer diameter of 350 mm, on which a grindstone tip 11 formed integrally with the formation 13 is stuck to a steel core 14 Assuming that the grinding resistance in the direction and the profile accuracy are 100, 39 inclined grooves 20 having a groove width b of 1 mm, a groove depth h of 6 mm, and an inclination angle α of 15 degrees are formed on the outer peripheral grinding surface 15 of the grindstone. When the same cam was ground with the inclined grooved grindstone 10, the grinding resistance in the normal direction was reduced to 77 and the profile accuracy was improved to 20 (see FIG. 13).

  In the above-described embodiment, the width of the workpiece W is smaller than the width of the grindstone 10, and the specifications of the inclined groove 20 are obtained assuming that the length of the grinding point P in the axial direction is equal to the width of the workpiece W. However, when the width of the workpiece W is larger than the width of the grindstone 10, the specifications of the inclined groove 20 are obtained assuming that the length of the grinding point P in the axial direction is equal to the width of the grindstone.

  In the above embodiment, the inclined groove 20 is engraved in the abrasive grain layer 12 by machining from the grinding surface 15 to the underlayer 13, but only the abrasive layer 12 at a depth without reaching the underlayer 13. May be engraved.

  Moreover, in the said embodiment, although the inclination groove | channel 20 penetrates the both side surfaces 21 and 22 of the abrasive grain layer 12 parallel to a grindstone circumferential direction, it is engraved in the grinding surface 15, as shown in FIG. The inclined groove 20 may be terminated before the both side surfaces 21 and 22 of the abrasive grain layer 12. In this way, since the acute angle portion of the abrasive grain layer 12 sandwiched between the inclined groove 20 and the side surfaces 21 and 22 can be eliminated, it is possible to prevent the acute angle portion from being damaged by a grinding load. In this case, when the length of the inclined groove 20 in the grinding wheel rotation axis direction is longer than the length of the grinding point P in the axial direction, the workpiece W can be ground with high precision under the same grinding conditions over the entire length. .

  In the above embodiment, at least two grinding points P are passed through the inclined grooves 20 regardless of the rotational phase of the grinding stone 10 in the fired grindstone chips, but at least one grinding point P is passed. You may do it.

  In addition, the present invention can be used in a grindstone with a slanted groove for effectively introducing a grinding fluid along a slanted groove to a grinding point and a manufacturing method thereof.

The whole figure of the grindstone which consists of a segment type grindstone tip which shows an embodiment of the invention. The figure which shows the state which grinds a workpiece with the grinder equipped with the grindstone with an inclined groove. The figure which shows a grindstone chip. The figure which shows the state which engraved the some inclined groove | channel on the grinding surface of the grindstone so that at least 1 inclined groove might always pass a grinding point. The figure which shows the state by which the inclined groove | channel was engraved in the abrasive grain layer. The figure which shows the relationship between the groove circumferential width of an inclination groove | channel, and an inclination angle. The figure which shows the state engraved so that two inclined grooves may always pass the grinding point which has the length of the same axial direction as the width | variety of a workpiece. The graph which shows the relationship between the inclination angle of an inclination groove | channel, and the number. The figure which shows the relationship between the inclination-angle of an inclination groove | channel, and the pitch of a grindstone circumferential direction. The figure which shows the relationship between the inclination angle of an inclination groove | channel, and the reduction rate of the area of a grinding surface. The figure which shows the process of manufacturing an inclined grooved grindstone. The figure which shows a groove processing apparatus. The figure which shows the ratio which the grinding resistance and profile precision of a normal direction improve with a grindstone with an inclined groove | channel. The figure which shows the state which an inclined groove | channel terminates before the both sides | surfaces of an abrasive grain layer.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Whetstone, 11 ... Whetstone tip, 12 ... Abrasive grain layer, 13 ... Underlayer, 14 ... Core, 15 ... Grinding surface, 16 ... Superabrasive grain, 17 ... Vitrified bond, 20 ... Inclined groove, 21, 22 ... Side, 23, 24 ... Side wall, 25 ... Adhesive, 30 ... Grinding machine, 31 ... Grinding head, 32 ... Grinding wheel shaft, 33 ... Workpiece support device, 35 ... Coolant nozzle, 50 ... Grooving device, 51 ... Grinding wheel (tool), 58 ... Jig, 59 ... spindle, P ... grinding point, W ... workpiece, α ... tilt angle.

Claims (6)

A plurality of grindstone chips having an abrasive layer containing superabrasive grains are affixed to a core that is mounted on a grindstone shaft that is rotatably supported around an axis on a grinding wheel head of a grinding machine, and formed on the abrasive grain layer. In a grindstone that grinds a workpiece with a ground surface abutting at a grinding point on a workpiece supported so as to be rotationally driven by the workpiece support device of the grinding machine,
A plurality of inclined grooves, which are linearly engraved in the abrasive grain layer, are linearly engraved in the abrasive grain layer by a tool that is linearly fed with respect to the grindstone in the inclination angle direction of the inclined groove. A whetstone with inclined grooves.   2. The grindstone with an inclined groove according to claim 1, wherein the inclined groove is engraved in the abrasive layer by the linearly fed tool from the ground surface to the base layer.   The inclined grooved grindstone according to claim 1 or 2, wherein the inclined groove terminates in front of both side surfaces of the abrasive grain layer parallel to the circumferential direction of the grindstone.   4. The inclined grooved grindstone according to claim 3, wherein the length of the inclined groove in the rotation axis direction of the grindstone is longer than the length of the grinding point in the axial direction. A plurality of grindstone chips comprising an abrasive layer containing superabrasive grains and a base layer not containing superabrasive grains on a core mounted on a grindstone spindle supported so as to be rotationally driven around a rotational axis on a grinding wheel head of a grinding machine In the method of manufacturing a grindstone, wherein a grinding surface formed on the abrasive layer is abutted at a grinding point to grind a workpiece supported so as to be rotationally driven by a workpiece support device of the grinding machine.
A grooving step of linearly engraving the abrasive layer in the abrasive layer by linearly feeding a tool in the direction of the inclination angle of the inclined groove with respect to the grindstone;
An indexing step of indexing and rotating the grindstone by an angle corresponding to the number of the inclined grooves;
A method for manufacturing a grindstone with inclined grooves, wherein a plurality of the inclined grooves are formed in the abrasive layer by repeating the groove processing step and the indexing step.   6. The method for producing a grindstone with a slanted groove according to claim 5, wherein the slanted groove is linearly engraved in the abrasive grain layer from the ground surface to the base layer.

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