JP2018043312A - Cup type vitrified grind stone for grind stone - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cup type grind stone for performing grinding working of brittle material such as a semiconductor substrate which makes specular working possible, continues satisfactory sharpness and prevents a grinding mark from being put on a center part of a work-piece.SOLUTION: A grind stone segment 3 of extremely soft class hardness of which porosity as volume ratio obtained by binding composite abrasive grains provided by combining hard abrasive grains such as diamond abrasive grains and soft abrasive grains such as cerium oxide of which respective particle sizes are 3 μm or less with a vitrified bond is 55% or more is provided. The grind stone segment 3 has innumerably existing fine pores opened to an outer part, and the grind stone configures a cup type grind stone which is arranged such that a rotation locus of polish surface draws a ring having a fixed width on a position deviated to the outer circumferential side of one surface of a base metal 2 assuming a disc shape and is joined. Therein, the grind stone segment 3 is arranged such that a distance from a center of the base metal 2 to radial direction inner/outer ends of the grind stone is changed during one round through an outer circumferential part of the base metal.SELECTED DRAWING: Figure 9

Description

  The present invention relates to a cup-type grindstone for a grinder, and more particularly, to a cup-type vitrified grindstone for a grinder that enables high-quality mirror finishing by using ultrafine particles (average particle size 0.1 to 3 μm). .

  One type of grinding wheel is a cup-type grinding wheel. As a conventional example of the cup-type grinding wheel, for example, those described in Patent Documents 1 to 3 below are known.

  When processing a wafer such as a semiconductor substrate, if the grindstone segment (called a cutting edge) attached to the end face of the peripheral wall of the cup-shaped base is advanced to the rotation center of the wafer, the edge of the grindstone segment Since the portion always passes through the same track, a wrinkle is created at a location where the rotational peripheral speed at the center of the wafer is extremely reduced, and the processing accuracy deteriorates.

  Therefore, the grinding wheel described in Patent Document 1 does not have a device that swings the grindstone so that the grindstone segment swings in and out in the radial direction of the grindstone when rotating the grindstone by arranging the grindstone segments in a distorted circle shape. The above-mentioned problems can be solved by using a grinding machine.

  Moreover, the cup type grindstone described in Patent Documents 2 and 3 achieves the same effect as the grindstone of Patent Document 1 with an easily manufactured structure by combining two types of grindstone segments having different widths.

No. 7-5983 JP-A-11-207634 JP-A-11-207635

  The objects to be processed in recent grinding processes are various, such as alumina, sapphire, silicon carbide, silicon nitride, gallium nitride, aluminum nitride, lithium niobate, lithium tantalate, cordierite, special glass, and PCD. Across.

  The grinding process is required to reduce the processing time, and the required processing surface roughness tends to be mirrored. Even in such a situation, high-precision and damage-free processing is demanded with the aim of reducing the burden of the lapping / polishing process in the subsequent process and greatly reducing the process time.

  For mirror finishing, it is considered effective to make the abrasive grains of the grinding wheel to be used fine, but the ultra-fine grinding of the grinding stones in the grinding process has not yet been put to practical use because the sharpness is extremely reduced. is there.

  Further, in the processing using the cup-type grinding wheel, the center of the orbit of the grinding surface of the rotating grinding wheel always passes through the center of the rotating workpiece, so that a grinding pattern as shown in FIG. There is a tendency that wrinkles are generated by the edges of the workpiece, and the surface roughness of the center of the workpiece is extremely deteriorated (see the photograph of FIG. 17 showing the trajectory accumulation pattern of the grindstone edge and the properties of the actual machining surface in FIG. 16).

  Regarding the abrasive grains of the grindstone, conventionally, the area that can be efficiently processed by grinding machine processing is limited to No. 2000 (abrasive grain diameter of 8 μm). In that case, in the fine particle region, the sharpness is extremely lowered, and the surface roughness corresponding to the particle size cannot be obtained.

  The grinding wheel disclosed in Patent Document 1 is a grinding wheel called a grinding mark (polishing pattern) generated at the center of a workpiece by causing the grinding wheel segment to swing in and out in the radial direction of the grinding wheel as the grinding wheel rotates. However, since the grindstone has a special shape of a strain circle, its manufacture is not easy.

  Moreover, although the grindstone of the said patent document 2 and 3 has a structure which is easy to manufacture compared with the grindstone of patent document 1, since these use two types of grindstone segments, when considering productivity and manufacturing cost, it is still. There is room for improvement.

  In addition, Patent Documents 1 to 3 do not mention any abrasive grains of the grindstone. As described above, it is difficult to reduce the burden of the lapping / polishing process in the subsequent process with a grindstone of about 2000, which has been regarded as a limit.

  In view of the above-mentioned present state of the art, in grinding processing, development of whetstones that do not degrade sharpness even when using abrasive grains in the finer particle region (0.1 to 3 μm) and generation of wrinkles (especially grinding marks at the center of the workpiece) The development of a grindstone that does not occur is desired.

  Accordingly, an object of the present invention is to realize and provide a cup-type grindstone for a grinding machine that can be mirror-finished, can prevent a reduction in sharpness, and can prevent wrinkles at the center of the workpiece.

In order to solve the above-mentioned problems, in the present invention, the porosity in a volume ratio in which composite abrasive grains, each of which is a combination of hard abrasive grains and soft abrasive grains each having a grain size of 3 μm or less, are bonded by a low melting point vitrified bond, There is a grindstone with an extremely soft hardness of 55% or more, and the grindstone has numerous fine pores open to the outside on the surface that becomes the polishing surface, and the grindstone is a single side of a disk-shaped base metal A cup-type vitrified grindstone for a grinding machine, which is joined with a rotation locus of a polishing surface in a position deviating to the outer peripheral side of the ring so as to describe a ring having a certain width,
For a grinding machine in which the disposition of the grindstone is such that the distance from the center of the base metal to the radially outer end of the grindstone and the distance from the radially inner end of the grindstone change during one round of the outer peripheral portion of the base metal A cup-type vitrified grinding wheel is provided.

Preferred forms of such cup-type vitrified grinding wheels for grinding machines are listed below.
1) The relationship between the grindstone particle size, RL hardness of the grindstone, and the strength of the grindstone expressed by the bending strength with a one-point load at two points is set as shown in the table below.

2) The hard abrasive grains of the composite abrasive grains are diamond abrasive grains or cubic boron nitride abrasive grains, the soft abrasive grains are cerium oxide, silica, barium sulfate or zirconium oxide, and the volume of the hard abrasive grains The ratio in the ratio of 50 to 90% and the volume ratio of the soft abrasive grains is 10 to 50%.

3) The said grindstone is comprised combining several grindstone segments of the same shape and the same size, and each dimension of each grindstone segment is width: 3-6 mm, length: 9-30 mm, thickness: 5-10 mm Yes, the grindstone segments are arranged with a gap of 1-10 mm in the circumferential direction.

4) The grindstone segment extends linearly in the length direction, and both ends in the length direction are R surfaces.

5) The arrangement of the grindstone segments is based on a polygon having a side of a convex arc of constant curvature, and a plurality of grindstone segments are arranged along each side of the polygon so as to draw a pseudo convex arc, A grindstone segment at an adjacent position in each corner is arranged in a separated state with a predetermined angle.
6) The polygon is an odd-numbered regular polygon, and a plurality of grindstone segments are arranged along the sides of the convex arcs of the regular polygon. When the number of corners of the polygon is n, the polygons are arranged in a separated state with an angle X determined by the equation {X = 180 ° × (n−2) ÷ n}. The odd-numbered regular polygon is particularly preferably a pentagon.
7) The amount of change between the distance from the center of the base metal to the radially outer end of the grindstone and the distance from the radially inner end of the base metal to the outer circumference of the base metal is 0.5 to 2 mm larger than the grindstone width. The whetstone segments are arranged so as to be.

  Even a grindstone using ultrafine abrasive grains of 3 μm or less is required to have excellent sharpness. Therefore, in the present invention, low melting point vitrified composite abrasive grains in which hard abrasive grains such as diamond abrasive grains and cubic boron nitride abrasive grains and soft abrasive grains such as cerium oxide, silica, barium sulfate or zirconium oxide are combined. A very soft hardness grindstone bonded with a bond was adopted.

  This grindstone is obtained by firing a mixture of composite abrasive grains and a low melting point vitrified bond at a temperature of 900 ° C. or lower.

  By mixing soft abrasive grains, the gap between the abrasive grains can be increased. Moreover, by combining soft abrasive grains and hard abrasive grains with vitrified bonds, micro-crushing is likely to occur, and good sharpness can be maintained. In addition, a mechanochemical reaction can be expected.

  The mixing ratio of the soft abrasive grains to the hard abrasive grains is suitably 10 to 50% by mass ratio. If it is this ratio, an abrasive grain space | interval can be ensured and an abrasive grain penetration capability can also be improved.

  The grindstone structure is a porous structure having a high porosity of 55% or more while having a low binder ratio of 6 to 12%. The porous structure allows good chip discharge and sharpness. Sustainability.

  Also, for the problem of deterioration of grinding marks and surface roughness at the center of the workpiece, the distance from the center of the base metal to the radially outer end of the grindstone and the distance from the radially inner end is the outer circumference of the base metal. Since it changes during one round of the part (while the grindstone makes one revolution), the edge of the grindstone does not pass the same track.

  Due to the change in the distance, the position of the edge fluctuates between the inner side and the outer side in the radial direction as the cup-type grindstone rotates, thereby causing a deviation in the track accumulation pattern of the grindstone edge and the center of the workpiece. The generation of grinding marks and the deterioration of surface roughness at the part are suppressed.

  The change in the distance can be easily imparted by combining a plurality of grindstone segments having the same shape and the same size to form a polished surface.

  The arrangement of the grindstone segments is based on a polygon having convex arc sides with a constant curvature, and a plurality of grindstone segments are arranged along each side of the polygon so as to draw a pseudo convex arc. The distance from the center of the base metal to the inner and outer ends in the radial direction of the grinding wheel can be changed during one round of the circumference of the base metal by arranging the grindstone segments at adjacent positions in a separated state at a predetermined angle. it can.

  The predetermined angle X mentioned here is an angle obtained by the equation {X = 180 ° × (n−2) ÷ n} where n is the number of regular polygons.

  When the basic polygon is an odd-numbered polygon, it is easy to avoid a situation in which the polishing surface passes through the same track. The basic polygon is a regular pentagon, and a plurality of grindstone segments are arranged along the side of each convex arc of the regular pentagon, and the grindstone segments at adjacent positions in each corner portion are spaced apart at an angle of 108 °. In particular, those arranged in (1) exhibited the most excellent effects in comprehensive evaluations such as prevention of grinding marks at the center of the workpiece, improvement of surface roughness, increase in machining allowance, and wear resistance.

  Each grindstone segment that extends linearly is less likely to be distorted during manufacturing, and it is easy to ensure high dimensional accuracy. The individual dimensions of each grindstone segment are suitably width: 3 to 6 mm, length: 9 to 30 mm, and thickness: 5 to 10 mm. Further, the shape of each grindstone segment has both ends in the length direction. What is an R surface is good.

  If both ends in the length direction of the grindstone segment are R surfaces, the biting on the machined surface gradually spreads, so that deep wrinkles that are thought to occur from the grindstone edge are unlikely to occur.

  Good results have been obtained in the actual cutting test by arranging the grindstone segments with a gap of 1 to 10 mm in the circumferential direction.

It is a perspective view which shows an example of the cup type grindstone (pseudo polygon grindstone) of this invention. It is a top view of the cup type grindstone of FIG. It is a front view which shows the other example of the cup type grindstone (pseudo polygon grindstone) of this invention. It is a front view which shows the further another example of the cup type grindstone (pseudo polygon grindstone) of this invention. It is a front view which shows the further another example of the cup type grindstone (pseudo polygon grindstone) of this invention. It is a front view which shows the further another example of the cup type grindstone (pseudo polygon grindstone) of this invention. It is a front view which shows the further another example of the cup type grindstone (pseudo polygon grindstone) of this invention. It is a front view which shows the further another example of the cup type grindstone (pseudo polygon grindstone) of this invention. It is a front view which shows an example of the state which arranged the grindstone segment along the side of each convex arc of a polygon. It is a front view which shows an example of the cup type grindstone which arranged the block-shaped grindstone segment on the same perfect circle. It is a front view which shows the turbo type cup type grindstone which arranged the grindstone segment in the tangential direction with respect to the circle | round | yen concentric with the metal base. It is a front view which shows the continuous type cup-type grindstone which arranged the grindstone segment along the circle | round | yen concentric with the metal base. It is a perspective view which shows the preferable shape of a grindstone segment. It is a processing image figure of vertical grinding by a grinding machine. It is explanatory drawing of the grinding pattern whose track | orbit of the edge of a grindstone is a single track | truck passing through the center of a process part. FIG. 16 is a track integration diagram of a grindstone edge in the grinding pattern of FIG. 15. It is a figure (photograph) which shows the property of the actual processing surface which shows the grinding mark produced in the center of a workpiece with the grinding pattern of FIG. It is a figure which shows the movement amount of the locus | trajectory of the grinding | polishing surface by the process with the cup type grindstone of this invention, and the track | orbit center of a grindstone. FIG. 19 is a track integration diagram of a grindstone edge in the grinding pattern of FIG. 18. It is a figure (photograph) which shows the property of the actual processing surface by the cup type grindstone of this invention. It is a figure (photograph) which shows the property of the actual processing surface by a block type grindstone. It is a figure (photograph) which shows the property of the actual processing surface by a turbo type grindstone. It is a figure (photograph) which shows the property of the actual processing surface by a continuous type grindstone. It is a figure (photograph) which shows the property of the actual processing surface by a pseudo pentagonal grindstone.

  Embodiments of a cup-type vitrified grindstone for a grinding machine according to the present invention will be described below with reference to the accompanying drawings.

  The cup type vitrified grindstone for a grinding machine (hereinafter abbreviated as cup type grindstone) 1 shown in FIGS. 1 to 8 is located at a position biased toward the outer peripheral side of one side of a base metal (disk-shaped wheel) 2. A large number of the grindstone segments 3 are joined in such a manner that the rotation trajectory D (see FIG. 18) of the polishing surface is arranged so as to draw a ring having a certain width.

  FIG. 2 is a front view showing the arrangement state of the grindstone segments 3 of the cup-type vitrified grindstone of FIG. 1 in an easy-to-understand manner. Since the cup-type vitrified grindstone of FIG. 1 is the same product, FIG.

  The arrangement pattern of each grindstone segment 3 is a polygon having a side of a convex arc having a constant curvature in each of the embodiments of FIGS. 1 to 8, and a plurality of grindstone segments 3 along each side of the polygon. Are arranged so as to draw a pseudo-convex arc, and the grindstone segments 3 and 3 at adjacent positions in each corner portion are angle X determined by the above-described formula {X = 180 ° × (n−2) ÷ n}. Are arranged in a separated state.

  As a result, the distance from the center O (see FIG. 9) of the base metal 2 to the inner and outer ends in the radial direction of the grindstone (grindstone segment 3) changes while making one round of the outer peripheral portion of the base metal.

  The cup-shaped grindstone 1 of FIGS. 1 and 2 has a regular polygon as a regular triangle, the cup-shaped grindstone 1 of FIG. 3 has a regular polygon as a regular square, and the cup-shaped grindstone 1 of FIGS. 4 to 6 has a basic shape. 7 is a regular pentagon, the cup-shaped grindstone 1 of FIG. 7 has a regular polygon of a regular hexagon, and the cup-shaped grindstone 1 of FIG. 8 has a regular polygon of a regular heptagon.

  The cup-type grindstone 1 shown in FIGS. 4 to 6 has a radius R = 150 mm (FIG. 4), a radius R = 135 mm (FIG. 5), and a convex arc side S (see FIG. 9) between adjacent corners of a pentagon. A plurality of grindstone segments 3 are arranged so as to draw a pseudo arc along each side with a radius R = 190 mm (FIG. 6).

  The grindstone segment 3 is a composite abrasive in which hard abrasive grains (diamond abrasive grains or cubic boron nitride abrasive grains) each having a particle size of 3 μm or less and soft abrasive grains (cerium oxide, silica, barium sulfate or zirconium oxide) are combined. Is a grindstone of extremely soft hardness in which is bonded with a low melting point vitrified bond.

  The volume ratio of hard abrasive grains to soft abrasive grains is 50 to 90% for the former and 10 to 50% for the latter.

  Each grindstone segment 3 is made of the same material, and has the same shape and size. Therefore, the kind of grindstone segment 3 employ | adopted for the same cup type grindstone is integrated into one kind, and it is excellent in productivity and manufacturing cost compared with the grindstone of the said patent documents 2 and 3.

  Further, the shape is not curved, and as shown in FIG. 13, a shape linearly extending in the length direction is used, and it is easy to mold. In addition, the straight line also has an effect that the grindstone swings in a minute amount during processing. Furthermore, the both ends in the length direction are R surfaces as shown in FIG. 13, and deep wrinkles are unlikely to occur on the workpiece due to the edges.

  In addition, since the grindstone segments 3 having the same shape and the same size are arranged in a predetermined pattern and joined to the base metal 2, manufacture is easier than the grindstone of the Patent Document 1.

  A cup-type grindstone having the shape shown in FIGS. Further, as a comparative example, a block-type grindstone (see FIG. 10), a turbo-type grindstone (see FIG. 11), and a continuous grindstone (see FIG. 12), which are conventional standards, were also prepared.

<Whetstone used>
Abrasive grain size of 2-4 μm (4000 mesh) to 0-2 μm (8000 mesh) for intermediate finishing on a grinding machine (to ensure 8-20 μm machining allowance and 5-20 nmRa or less on the processed surface) ) Grindstone (grindstone segment).

  Also, for finishing (securing 1-5 μm machining allowance and mirror surface of 2 nmRa or less), grindstones (grinding stone segments) with an abrasive grain size of 0-1 μm (10000 mesh) to 0-0.5 μm (20000 mesh) Was used.

The abrasive grains are alumina (Al ₂ O ₃ ), sapphire (Al ₂ O ₃ ), silicon carbide (SiC), silicon nitride (Si ₃ N ₄ ), gallium nitride (GaN), zirconia (ZrO ₂ ), aluminum nitride (AlN ), Lithium tantalate (LiTaO ₃ ), lithium niobate (LiNbO ₃ ), silicon (silicon, Si), quartz, quartz (SiO ₂ ) cordierite (2MgO, 2Al ₂ O ₃ , 5SiO ₂ ), WC-Co series For grinding of brittle materials such as cemented carbides such as alloys, PCD (diamond sintered body), PCBN (CBN sintered body) and glass, diamond abrasive grains are used as hard abrasive grains. Uses CBN (hexagonal boron nitride) abrasive grains.

  Soft abrasive grains are used to increase the spacing between hard abrasive grains (diamonds and CBN), to assist machining by mechanochemical reaction, and to improve surface roughness. Silica, cerium oxide, barium sulfate, and oxidation Use chromium, zirconium oxide or the like. These soft abrasive grains can be used according to the material to be processed.

  The grindstone bonding degree generally applies an extremely soft hardness, but varies depending on the grain size of the abrasive grains used. That is, the finer the abrasive grains, the greater the number of particles even at the same concentration, and the narrower the gap between the abrasive grains. For this reason, the finer the grain, the greater the need to widen the abrasive grain spacing. As a result, the grindstone bond inevitably has a low setting.

The particle size and hardness adjustment were as shown in Table 2.
The grindstone hardness was measured using a Rockwell superficial hardness tester with a steel ball indenter of 3.175 mm, a standard load of 29.4 N, and a test load of 196 N.
Table 2 shows the conformity hardness for each particle size.

<Use shape>
Three basic shapes No. A to No. C shown in Table 3 and No. D to No. N in Table 3 were used. No. D to No. N are grinding wheel width W (horizontal width): 3 patterns of 3 mm, 4 mm and 5 mm, gap interval between grinding wheel segments G: 3 patterns of 0 mm, 3 mm and 6 mm, movement of the grinding stone shown in FIG. The movement D of the trajectory D and the center of the trajectory is a grindstone having a shape set to 3 patterns of −2 mm, +0.5 mm, and +6 mm with respect to the grindstone width W.

<Evaluation test>
The type of grindstone used was No. 4000 (abrasive grain average particle size: 2.5 μm), and in order to see the type of abrasive grains, the two types in Table 4 (Example A and Comparative Example A) were used, and No. 8000 (Abrasive) In order to confirm the influence of hardness and the effect of shape, the three types shown in Table 4 (Example B and Comparative Examples B and C) were used.

Example A and Comparative Example A have the same contents except for the type of abrasive grains. In Example A, composite abrasive grains having diamond abrasive grains of about 63.5% and SiO ₂ soft abrasive grains of about 36.5% in a volume ratio shown in Table 4 were used. On the other hand, Comparative Example A was made of diamond abrasive grains alone (MD).

No. 8000 was an SHS grindstone containing about 63.5% diamond abrasive grains and 36.5% SiO ₂ soft abrasive grains in volume ratio. In order to confirm the effect of sharpness due to the grinding wheel hardness, one point is Comparative Example C in which the amount of the binder is 0.30 parts by weight with respect to 1 part by weight of the abrasive grains and Example B and Comparative Example B in which the amount is 0.2 parts by weight. Example B and Comparative Example B were prepared in the same quality.

The grindstone strength is a grindstone with an extremely low bending strength of 9.1 MPa.
The other point was to prepare 13 different shapes using the quality of Example B and Comparative Example B, and evaluated the reduction of polishing marks and the improvement of surface roughness at the center of the workpiece due to the shape effect.

  The shape of the grindstone is the block type of FIG. 10, the turbo type of FIG. 11, the continuous type of FIG. 12 (the above is a comparative example), the arc triangle type of FIG. 2, the arc quadrangle type of FIG. An arc pentagon type, an arc hexagon type shown in FIG. 7, and an arc heptagon type shown in FIG. 8 were used.

  For the arc pentagon type, the grindstone width W (width) is 3 patterns, 3 mm, 4 mm, and 5 mm, the gap G between the segments is 3 patterns, 0 mm, 3 mm, and 6 mm, and the movement trajectory of the grindstone and the movement amount of the trajectory center are 2 mm ( Three patterns of FIG. 5), 4.5 mm (FIG. 4), and 10 mm (FIG. 5) were used.

  2 to 8, the radius of the side of the convex arc circumscribing the grindstone segment 3 is R = 130 mm for the grindstone of FIG. 1 (FIG. 2), R = 138 mm for the grindstone of FIG. 4 for the grindstone of FIG. 4, R = 135 mm for the grindstone of FIG. 5, R = 190 mm for the grindstone of FIG. 6, R = 170 mm for the grindstone of FIG. 7, and R = 185 mm for the grindstone of FIG. did.

  These dimensions vary depending on the number of polygonal corners and the movement trajectory of the grindstone and the amount of movement of the orbit center.

  The amount of movement of the polishing surface at the center of the track (the amount of wobbling in the radial direction between the radially inner end and the radially outer end of the grinding wheel) was based on the grinding wheel width +0.5 mm.

The binders used in Examples and Comparative Examples are the same, and their compositions are as shown in Table 5.

  Moreover, the binder ratio with respect to 1 part by mass of unit abrasive grains is 0.25 parts by weight in Example A and Comparative Example A, 0.30 parts by weight in Comparative Example C, and Examples B and Comparative Example B have the same quality. 0.2 parts by weight.

  After the abrasive grains and the binder were uniformly mixed, they were compression molded into predetermined dimensions of each shape, dried and fired. The firing temperature was maintained for 3 hours at the maximum firing temperature of 720 ° C. under the same conditions in the examples and comparative examples. After the abrasive grains and the binder were uniformly mixed, they were compression molded into predetermined dimensions of each shape, dried and fired.

  Table 4 shows the grinding wheel structure (volume ratio, concentration), grinding wheel strength and hardness of the obtained grinding wheel segment. The grindstone strength was measured using an autograph AG-X manufactured by Shimadzu Corporation under the conditions of two-point support, one-point load, and a span of 30 mm.

  The grinding wheel hardness was a value measured using a Rockwell superficial hardness tester under conditions of a steel ball indenter of 3.175 mm, a standard load of 29.4 N, and a test load of 196 N.

<Use shape>
A total of 10 types of grindstone shapes with dimensions of a grindstone outer diameter of 252 mm and an inner diameter of 95 mm were used as shown in FIGS. 2 to 8 and FIGS. 10 to 12.

  For No. 4000 (average particle size 2.5 μm), only a comparison of sharpness was made with a normal block type. For the No. 8000 (average particle size 1 μ) grindstone, two types were selected, one point from the past The softness hardness whetstone used, and another point, an extremely softness whetstone was manufactured and the sharpness was compared.

  Moreover, the bonding shape of the grindstone segments was varied in 13 ways, and the effect of reducing wrinkles / polishing marks on the workpiece by each shape was confirmed.

<Test equipment used for evaluation>
The workpiece A (4 inch size silicon carbide wafer) was processed using a vertical grinder manufactured by Nippon Engis whose main part is shown in FIG. The details of the polishing machine and the processing conditions are summarized in Table 6.

  Reference numeral 4 in FIG. 14 denotes a main spindle of a polishing machine equipped with a cup-type grindstone, and reference numeral 5 denotes a rotary table that holds the workpiece A and rotates it at a fixed position.

<Actual cutting test>
In the actual cutting test, the surface of the workpiece A (4 inch silicon carbide) was ground.
For the work A, the same grinding as the pre-processing is performed using a vitrified grindstone with a diamond grain size of 22 to 36 μm (600 mesh) and a concentration 140, and the surface roughness of the surface of the work is obtained. Was unified to 0.8 μmRa (center line average roughness).

  The dimensions of the cup-type grindstone used were an outer diameter of 252 mm, an inner diameter of 95 mm, and a grindstone segment thickness of 5 mm.

  As for the type of quality of the grindstone, the effect of adding soft abrasive grains was confirmed using two types of grindstones having a number of 4000 (average particle size 2.5 μm), including those containing soft abrasive grains.

  Moreover, about the grindstone of No. 8000 (average particle diameter: 1 micrometer), 2 types with different grindstone hardness were used. For this # 8000 grindstone, soft grindstone quality was adopted and the grindstone shape was divided into 13 types.

  The rotational speed of the grindstone was unified to 2000 rpm, and the rotational speed of the workpiece A was 50 rpm and 100 rpm.

  The cutting speed was set to 36 μm for the No. 4000 grindstone and 30 μm for the No. 8000 grindstone, and the spark-out was 10 seconds.

The evaluation was performed by confirming the machining allowance, the grinding wheel wear amount, the finished surface roughness, and the presence or absence of the polishing pattern (wrinkles). The finished surface roughness was measured using a laser microscope (VK-X100 manufactured by Keyence).
The evaluation results are shown in Table 7.

<From actual cutting test results>
1. Influence by soft abrasive grains From Comparative Example 1 and Reference Example 1 in which the effect of soft abrasive grains was compared with a No. 4000 (average particle diameter: 2.5 μm) grindstone having comparable hardness, as in Comparative Example 1 When diamond abrasive grains are used alone as hard abrasive grains, the cutting allowance is as low as 8.2 μm at a cutting speed of 0.3 μm / sec, and the surface is rubbed with the workpiece, resulting in poor sharpness. I understand that.

  Since the grindstone is clogged, the wear amount of the grindstone is as small as 1.5 μm, but the performance as a grindstone is not exhibited at all.

  On the other hand, the grinding wheel of Reference Example 1 to which soft abrasive grains are added has a large machining allowance of 21.6 μm regardless of the fine grains, is excellent in sharpness, has a small grinding wheel wear amount of 1.9 μm, and is in a good state, and has a finished surface roughness. It can be seen that the roughness corresponding to the particle size is ensured and functions effectively as a grindstone, and has a performance sufficient for practical use.

2. Effect of grinding wheel hardness Among the two qualities tested with different hardness at No. 8000 (average particle size 1 μm), the quality of Comparative Example 2 was 2.5 μm, regardless of the soft quality of RL hardness −54. It is small, and the wear amount of the grinding wheel is as small as 1.8 μm, but it is in a clogged state, and it can be said that it is a grindstone that still has a poor sharpness in grinding processing in the ultrafine grain region with normal soft hardness.

  On the other hand, the grindstone with hardness H of Reference Example 2 has an RL hardness of -121 and extremely soft quality, but has a good machining allowance of 8.4 μm despite being a block type. The amount of wear of the grinding wheel is as high as 11.9 μm, and it can be said that a very soft quality (−50 or less, normal product does not have −50 or less) is effective for the grinding wheel in the ultrafine grain region.

3. Influence by grinding wheel shape The improvement measure of grinding marks by shape was performed with a grinding wheel of No. 8000 (average particle size 1 μm). Comparative Examples 3 to 4, Reference Example 2 and Examples 3 to 14 are comparison targets.

_3-1 ) Comparative Example 2 (block type)
The block type has the same level as the other shapes in terms of surface area of the grinding wheel, but the number of grinding wheel edges is short, and the number of grinding wheel edges increases accordingly. Although it is an excellent shape, on the other hand, the amount of wear of the grinding wheel is large, and the finished surface roughness is also poor, and a grinding mark is placed in the center of the workpiece (see FIG. 21).

3 ₂₎ ... Comparative Example 3 (turbo)
The turbo type has a large grinding wheel surface area and excellent wear resistance, but has a small machining allowance, poor finished surface roughness, and a grinding mark in the center of the workpiece (see FIG. 22).

_3-3) ... Comparative Example 4 (continuous type)
The continuous type is good in terms of stock and has excellent wear resistance. Although the finished surface roughness is good and the grinding wheel shape is the best among the comparative examples, no improvement is seen with respect to the grinding mark at the center of the workpiece (see FIG. 23).

  The example is based on the continuous type which is the best of the comparative examples, and the grinding pattern in which the grinding wheel trajectory center of the rotating grinding wheel (FIG. 14) always passes through the center of the rotating workpiece A is eliminated. That is, the center of the grindstone track moves in the radial direction as the grindstone rotates, and the grindstone has a shape in which the edges do not pass through the same trajectory.

_3-4) ... Example 3 (arc triangular in Figure 2: the grindstone width W = 4 mm, the inter-segment gap G = 3 mm, the radial moving distance L = 4.5 mm of the track center as shown in FIG. 18).
The arc center of the grindstone moves in the radial direction as it rotates and the edges do not pass through the same trajectory (polygonal shape; all examples are regular polygons). In the design of = 130, the moving amount L at the center of the orbit of the grindstone is set to 4.5 mm.

  The machining allowance of this cup-type grindstone is as good as 7.9 μm, and the wear amount of the grindstone is as good as 5.3 μm. Finished surface roughness has been improved and the grinding mark in the center has also disappeared.

_3-5 ) Example 4 (circular quadrangular shape: grinding wheel width W = 4 mm, inter-segment gap G = 3 mm, radial movement amount L = 4.5 mm at the center of the track).
An even-numbered polygonal arc quadrangular shape which is one corner larger than that of the third embodiment is R = 138. In this product, the machining allowance is slightly lower than in Example 3, and the grinding wheel wear amount is slightly increased. The surface roughness other than the center is the same, but a little grinding mark remains in the center of the workpiece, and the surface roughness is slightly poor at 12 nmRa.

_3-6) ... Example 5 (arc pentagonal: grindstone width W = 3 mm, the inter-segment gap G = 3 mm, the radial movement of the track center L = 3.5 mm).
This is an odd-numbered polygonal arc pentagon shape that is one more corner than Example 4. In this product, since the grindstone width W was set to 3 mm, the radial movement amount L at the center of the track was set to 3.5 mm. The machining allowance is as good as 10.5 μm.

  The amount of wear of the grinding wheel is slightly large at 8.1 μm. The surface roughness other than the center is 9 nmRa, the surface roughness of the center is 10 nmRa, and no grinding mark is seen (see FIG. 24).

_3-7) ... Example 6 (arc pentagonal: grindstone width W = 4 mm, the inter-segment gap G = 0 mm, the radial moving distance L = 4.5 mm of the track center).
This is the same polygonal arc pentagon shape as the fifth embodiment. In this product, the radial movement amount L at the center of the orbit is set to 4.5 mm because the grindstone width W is set to 4 mm. The machining allowance is as good as 10.1 μm.

  The grinding wheel wear is as small as 6.5 μm. The surface roughness other than the central portion is 9 nmRa. Further, the surface roughness of the central portion is 11 nmRa, which is slightly rough.

_3-8) ... Example 7 (arc pentagonal: grindstone width W = 4 mm, the inter-segment gap G = 3 mm, the radial moving distance L = 4.5 mm of the track center).
This is an odd-numbered polygonal arc pentagon type as in the sixth embodiment. In this product, the gap G between the segments was widened to 3 mm so that the abrasive powder was easily discharged to the outside. Since the grindstone width W was set to 4 mm, the radial movement amount L at the center of the track was set to 4.5 mm as in Example 6.

  The machining allowance is 9.4 μm, the sharpness is good, and the wear amount of the grinding wheel is as small as 5.4 μm, which is good. The surface roughness of the workpiece other than the central portion is 7 nmRa, and the central portion has a surface roughness of 8 nmRa, and the best results are obtained.

  Since the polishing surface has a fluctuating shape, no grinding mark is formed at the center of the workpiece, and a uniform processed surface is obtained.

_3-9) ... Example 8 (was processed set at approximately half of Example 6 the rotational speed of the workpiece using the same cup-shaped grinding wheel as in Example 6).
In the processing under these conditions, the sharpness is improved and the machining allowance is as large as 11 μm, but the wear amount of the grindstone is 7.8 μm and is slightly increased.

  Perhaps due to the effect of soft processing, the roughness of the finished surface is significantly improved to 5 nmRa at the center as well as at the center of the workpiece. No grinding mark is seen at the center of the workpiece.

_3-10) ... Example 9 (arc pentagonal: grindstone width W = 4 mm, the inter-segment gap G = 3 mm, the radial moving distance L = 2 mm of the track center).
This is also the odd-numbered polygonal arc pentagon type as in the sixth embodiment. The difference from the sixth embodiment is that the amount of radial movement at the center of the orbit is halved.

  The machining allowance of this product is as good as 9 μm, and the grinding wheel wear amount is as small as 5.4 μm. The surface roughness of the workpiece other than the central portion is 7 nmRa, the surface roughness of the central portion is also 8 nmRa, and no grinding mark is observed at the central portion.

_3-11) ... Example 10 (arc pentagonal: grindstone width W = 4 mm, the inter-segment gap G = 3 mm, the radial moving distance L = 10 mm of the track center).
This is also the odd-numbered polygonal arc pentagon type as in the sixth embodiment. The radial movement amount L at the center of the orbit is increased to 10 mm.

  In this product, the machining allowance is reduced to 5.7 μm, but the wear amount of the grindstone is as small as 6.3 μm, which is good. The surface roughness of the workpiece other than the central portion is 9 nmRa, which is reasonable, but the central portion has a poor surface roughness of 13 nmRa, and some grinding marks are generated in the central portion.

_3-12) ... Example 11 (arc pentagonal: grindstone width W = 4 mm, the inter-segment gap G = 6 mm, the radial moving distance L = 4.5 mm of the track center).
In this example, the inter-segment gap G is expanded to 6 mm with respect to Example 6.

  In this product, the machining allowance is reduced to 6.8 μm, and the grinding wheel wear amount is increased to 12.5 μm. The surface roughness of the workpiece other than the center is 11 nmRa, and the surface roughness of the center is not so good as 12 nmRa. The grinding mark in the center could not be confirmed. This is thought to be due to the fact that the processing surface pressure increased because the total surface area of the grindstone (the total area of the polishing surface) became narrow, and this was affected.

_3-13) ... Example 12 (arc pentagonal: grindstone width W = 5 mm, the inter-segment gap G = 3 mm, the radial movement of the track center L = 5.5 mm).
Compared to Example 6, the grinding wheel width W is increased to 5 mm to increase the grinding wheel surface area. Since the grindstone width W is 5 mm, the radial movement amount L at the center of the track is also increased to 5.5 mm.

  The machining allowance with this product is reasonable at 7.5 μm, and the amount of wear on the grindstone is as small as 4.9 μm. The surface roughness of the workpiece other than the center portion was 9 nmRa, the surface roughness of the center portion was 10 nmRa, and the grinding mark in the center portion could not be confirmed. Contrary to Example 10, it is considered that the processing surface pressure was lowered due to the increase in the total surface area of the grindstone, and this was affected.

_3-14) ... Example 13 (arc hexagonal type: grindstone width W = 4 mm, the inter-segment gap G = 3 mm, the radial moving distance L = 4.5 mm of the track center).
This is an arc hexagonal cup-type grindstone in which the number of polygons is further increased to an even number.

  This product has a reasonable machining allowance of 7.5 μm, and has a small grinding wheel wear amount of 5.5 μm. The surface roughness of the workpiece other than the central portion was relatively good at 9 nmRa, but the surface roughness at the central portion was slightly rough at 13 nmRa, and some grinding marks were also confirmed.

_3-15) ... Example 14 (arc heptagon type: grindstone width W = 4 mm, the inter-segment gap G = 3 mm, the radial moving distance L = 4.5 mm of the track center).
This is an odd-numbered arc heptagonal cup-type grindstone with more polygonal corners.

  The machining allowance of this product is as good as 8.3 μm, and the wear amount of the grindstone is as small as 6.1 μm. The surface roughness other than the central portion of the workpiece and the surface roughness of the central portion are both as good as 9 nmRa, and the grinding mark at the central portion of the workpiece was not confirmed.

・ Summary a. Reference Example 1 ⇔ Comparative Example 1
When grinding silicon carbide (SiC) with a fine-grained grindstone (average particle size 2.5 μm), it is effective to add soft abrasive grains instead of diamond abrasive grains alone.

b. Reference Example 2 ⇔ Comparative Example 2
In the ultrafine grain region No. 8000 (average abrasive grain size 1 μm), an extremely soft hardness grindstone in which the porosity is increased and the grindstone hardness is shifted to a softer quality is effective.

c. Reference Example 2 and Comparative Examples 2-4
When the grindstone is evenly applied on the circumference of a perfect circle, the problem of generating a grinding mark in the center cannot be solved in any of the block type, turbo type, and continuous type.

d. When the grinding wheel is made into a pseudo polygon and the center of the trajectory (distance from the rotation center to the radially inner end and the outer end) moves (displaces) while the grinding wheel rotates once (Examples 3 to 14).

d _-1 ) ... Effects due to orbit center displacement Grinding wheel width + 0.5 (if the grinding wheel width W = 4 mm, the movement amount L is 4.5 mm) and the movement amount is halved to 2 mm. Although the difference is not seen, when the moving amount L is increased to 10 mm, the machining allowance is reduced, and the grinding mark in the center portion is slightly generated.

d- ₂ ) ... Effect of odd-numbered and even-numbered angles The even-angled array configuration is the same as the odd-numbered surface with respect to the surface roughness excluding the central portion, but there is a tendency that the grinding mark in the central portion is slightly generated. Impairs roughness. Experimental results show that odd angles are more preferred.

d ₋₃ ) ... Influence of grinding wheel width (3, 4.5 mm) Grinding wheel width W = 3 mm is excellent in machining allowance, but the amount of grinding wheel wear is somewhat large, and the surface roughness of the processed surface is also slightly deteriorated.
On the other hand, when the grindstone width is 5 mm, the wear resistance is slightly reduced, but the wear resistance is improved. The balance between the machining allowance and the wear resistance is a product with a width of 4 mm, which has good surface roughness.

d _-4 ) ... Effect of grinding wheel segment gap G (0, 3.6 mm) Products with a grinding wheel segment gap G of 0 have good machining allowance and grinding wheel wear, but are slightly inferior in surface roughness. However, no grinding mark is seen at the center of the workpiece.

  On the other hand, in the products in which the gap G between the grindstone segments is 6 mm (too much), a reduction in machining allowance and an increase in the wear amount of the grindstone are seen, and the surface roughness of the processed surface tends to deteriorate. Accordingly, it is not preferable to make the gap G between the grindstone segments too much, but the grinding mark at the center of the workpiece is also eliminated by machining with this product.

  As for the gap G between the grindstone segments, 3 mm is good in all of the machining allowance, wear resistance, and finished surface roughness, and it is possible to realize processing without a grinding mark at the center of the workpiece.

DESCRIPTION OF SYMBOLS 1 Cup type grindstone 2 Base metal 3 Grinding wheel segment 4 Grinding wheel spindle 5 Grinding wheel rotation table A Workpiece M Grinding mark W Grinding wheel width G Gap gap between grinding wheel segments L Movement amount of the grinding wheel track center S Polygonal convexity Arc side

Claims (8)

It has a grindstone with an extremely soft hardness with a porosity of 55% or more in a volume ratio in which composite abrasive grains, each of which has a particle size of 3 μm or less, combined with hard abrasive grains and soft abrasive grains are combined with a low melting point vitrified bond. The grinding wheel has numerous fine pores open to the outside on the surface that becomes the polishing surface, and the grinding wheel rotates in a position that is biased to the outer peripheral side of one side of the disk-shaped base metal. Is a cup-type vitrified grindstone for a grinder joined in an arrangement that describes a ring having a certain width, and the arrangement of the grindstone is as follows:
A cup-type vitrified grindstone for a grinding machine, wherein the distance from the center of the base metal to the radially outer end of the grindstone and the distance from the radially inner end of the base metal change during one round of the outer peripheral portion of the base metal. The grinding according to claim 1, wherein the relationship between the grindstone particle size, the average grind particle size, the RL hardness, and the grindstone strength expressed by the bending strength at a one-point load at two points is set as shown in the following table. Cup type vitrified grinding wheel for board.
  The hard abrasive grains of the composite abrasive grains are diamond abrasive grains or cubic boron nitride abrasive grains, the soft abrasive grains are cerium oxide, silica, barium sulfate or zirconium oxide, and the ratio of the hard abrasive grains in the volume ratio The cup type vitrified grindstone for a grinding machine according to claim 1 or 2, wherein the ratio of the soft abrasive grains in the volume ratio is 10 to 50%.   The grindstone is configured by combining a plurality of grindstone segments of the same shape and the same size, and the individual dimensions of each grindstone segment are width: 3-6 mm, length: 9-30 mm, thickness: 5-10 mm, The cup type vitrified grindstone for grinding machines according to any one of claims 1 to 3, wherein the grindstone segments are arranged with a gap of 1 to 10 mm in the circumferential direction.   The cup type vitrified grindstone for a grinding machine according to claim 4, wherein the grindstone segment extends linearly and both ends in the length direction are R surfaces.   The arrangement of the grindstone segments is based on a polygon having a convex arc side having a constant curvature, and a plurality of grindstone segments are arranged along each side of the polygon so as to draw a pseudo convex arc. The grindstone cup-type vitrified grindstone according to any one of claims 1 to 5, wherein the grindstone segments at positions adjacent to each other in the portion are arranged at a predetermined angle.   The polygon is an odd-numbered regular polygon, and a plurality of grindstone segments are arranged along the side of each convex arc of the regular polygon, and the grindstone segments at positions adjacent to each corner portion are regular polygons. The cup type vitrified grindstone for a grinder according to claim 6, wherein the cup type vitrified grindstone for a grinding machine is arranged in a separated state with an angle X determined by an expression of {X = 180 ° × (n-2) ÷ n}, where n is the number of corners. .   The amount of change between the distance from the center of the base metal to the radially outer end of the grindstone and the distance from the radially inner end of the base metal to the outer circumference of the base metal is 0.5 to 2 mm larger than the lateral width of the grindstone. The grindstone cup type vitrified grindstone according to any one of claims 4 to 7, wherein the grindstone segments are arranged as described above.