GRINDING WHEEL AND GRINDING METHOD

BACKGROUND OF THE INVENTION
Field of the Invention

The present invention relates to a grinding wheel and a grinding method, which are useful in grinding workpieces.

Description of the Related Art

A plurality of device chips that include devices such as integrated circuits (ICs) or large scale integration (LSI) circuits respectively therein are obtained by dividing a plate-shaped workpiece, which is formed with the devices thereon and is typified by a semiconductor wafer, along scribe lines (streets). Such device chips are incorporated in various kinds of electronic equipment represented by personal computers and mobile phones. Along with a move toward smaller and thinner electronic equipment in recent years, there is also a growing demand for smaller and thinner device chips. A method is therefore used to thin workpieces by grinding them with grinding stones.

For the grinding of a workpiece, a grinding machine is used, which includes a chuck table that holds the workpiece, and a grinding unit that grinds the workpiece held on the chuck table. The grinding unit of the grinding machine includes a wheel mount fixed on a distal end portion of a spindle that acts as a rotating shaft, and a grinding wheel that includes grinding stones for grinding the workpiece is mounted on the wheel mount (see, for example, JP 2014-124690A). By bringing the grinding stones into contact, at grinding surfaces thereof, with the workpiece while rotating the grinding wheel, the workpiece is ground.

SUMMARY OF THE INVENTION

After such a grinding wheel is mounted on the grinding machine, dressing of the grinding wheel is performed. The dressing of the grinding wheel is an essential work to be performed for setting and truing the grinding surface, but leads to a reduction in productivity because the grinding on the grinding machine is suspended when the dressing is performed. It has hence been desired to establish a method that allows the dressing of the grinding wheel to be performed without reducing the productivity.

The present invention therefore has, as objects thereof, the provision of a grinding wheel and a grinding method which allow dressing to be performed without a reduction in productivity.

In accordance with a first aspect of the present invention, there is provided a grinding wheel for grinding a workpiece, including an annular wheel base and a plurality of grinding stones arrayed in an annular pattern on a side of one surface of the wheel base. The grinding stones each include a base portion having a mounting surface where the base portion is mounted on the wheel base, and a wear-accelerated portion that has a grinding surface to be brought into contact with the workpiece and is more prone to wearing than the base portion.

Preferably, the wear-accelerated portion may have a higher brittleness than that of the base portion. Preferably, the wear-accelerated portion may have a lower Vickers hardness than that of the base portion.

Preferably, the wear-accelerated portion may be made from the same material as that of the base portion, and a plurality of grooves may be formed on a side of the grinding surface of the wear-accelerated portion. Preferably, the wear-accelerated portion may be made from the same material as that of the base portion and may have a shape with a cross-sectional area that is parallel to the mounting surface and is progressively reduced toward the grinding surface.

Preferably, the wear-accelerated portion may have a higher porosity than that of the base portion.

Preferably, the wear-accelerated portion may have a thickness of 5 μm or greater and 15 μm or smaller in a direction from the grinding surface toward the base portion.

In accordance with a second aspect of the present invention, there is provided a grinding method of a workpiece with a grinding wheel. The grinding wheel includes an annular wheel base and a plurality of grinding stones arrayed in an annular pattern on a side of one surface of the wheel base. The grinding stones each include a base portion having a mounting surface where the base portion is mounted on the wheel base, and a wear-accelerated portion that has a grinding surface to be brought into contact with the workpiece and is more prone to wearing than the base portion. The grinding method includes grinding the workpiece at a surface thereof by the wear-accelerated portion, and after the wear-accelerated portion has been lost, grinding the workpiece by the base portion.

The grinding wheel according to the first aspect of the present invention has the base portion and the wear-accelerated portion, the wear-accelerated portion being more prone to wearing than the base portion, and the wear-accelerated portion comes into contact with the workpiece at an initial stage of the grinding of the workpiece. When the grinding of the workpiece is started by the grinding wheel in accordance with the grinding method of the second aspect of the present invention, the wear-accelerated portion therefore appropriately wears, and the grinding wheel is dressed along with the grinding of the workpiece. As appreciated from the foregoing, a grinding wheel and a grinding method, which can perform dressing without a reduction in productivity, are provided according to the first and second aspects of the present invention.

The above and other objects, features and advantages of the present invention and the manner of realizing them will become more apparent, and the invention itself will best be understood from a study of the following description and appended claims with reference to the attached drawings showing a preferred embodiment of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view schematically depicting a grinding machine;

FIG. 2 is a perspective view schematically depicting a first example of a grinding wheel according to an embodiment of the first aspect of the present invention;

FIG. 3 is a cross-sectional view schematically depicting the first example of the grinding wheel;

FIG. 4 is a side view depicting, on an enlarged scale, one of grinding stones of the grinding wheel of FIGS. 2 and 3;

FIG. 5 is a side view schematically depicting the grinding wheel of FIGS. 2 and 3 and a workpiece before grinding the workpiece;

FIG. 6 is a side view schematically depicting how wear-accelerated portions of the grinding stones of the grinding wheel of FIG. 5 are worn in the course of grinding the workpiece;

FIG. 7 is a side view similar to FIG. 6 and schematically depicts a situation after loss of the wear-accelerated portions in the course of grinding the workpiece;

FIG. 8 is a cross-sectional view schematically depicting a second example of the grinding wheel according to the embodiment of the first aspect of the present invention;

FIG. 9 is a side view depicting, on an enlarged scale, one of grinding stones of the grinding wheel of FIG. 8;

FIG. 10 is a cross-sectional view schematically depicting a third example of the grinding wheel according to the embodiment of the first aspect of the present invention;

FIG. 11 is a side view depicting, on an enlarged scale, one of grinding stones of the grinding wheel of FIG. 10;

FIG. 12 is a side view schematically depicting one of grinding stones of a fourth example of the grinding wheel according to the embodiment of the first aspect of the present invention; and

FIG. 13 is a flow diagram illustrating an example of a grinding method according to an embodiment of the second aspect of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference to FIGS. 1 through 12 of the attached drawings, a description will be made of first to fourth examples of a grinding wheel according to an embodiment of the first aspect of the present invention. First, a description will be made about a configuration example of a grinding machine including two grinding wheels of different kinds according to this embodiment. FIG. 1 is a perspective view schematically depicting a grinding machine 2 that grinds a workpiece 11. It is to be noted that, in FIG. 1, an X-axis direction (first horizontal direction, left-right direction of the grinding machine 2) and a Y-axis direction (second horizontal direction, front-rear direction of the grinding machine 2) are directions perpendicular to each other. It is also to be noted that a Z-axis direction (processing feed direction; height direction, vertical direction, or up-down direction of the grinding machine 2) is a direction perpendicular to the X-axis direction and Y-axis direction.

The grinding machine 2 includes a bed 4 supporting or accommodating individual elements that configure the grinding machine 2. On a side of an upper surface of a front end section of the bed 4, a recessed portion 4a is disposed. Inside of the recessed portion 4a, a transfer unit (transfer mechanism) 6 is disposed to transfer the workpiece 11. Used as the transfer unit 6 is, for example, a transfer robot on which robot hands (end effectors) capable of holding the workpiece 11 are secured.

On opposite sides of the transfer unit 6, cassette placing areas 8A and 8B are disposed respectively. On the cassette placing areas 8A and 8B, cassettes 10A and 10B which can each accommodate a plurality of workpieces 11 are arranged. The cassettes 10A and 10B can each accommodate the workpieces 11 to be ground by the grinding machine 2 (the workpieces 11 before grinding) or the workpieces 11 ground by the grinding machine 2 (the workpieces 11 after grinding).

For example, the workpiece 11 is a disk-shaped wafer made from a semiconductor material such as single crystal silicon and includes a front surface (first surface) 11a and a back surface (second surface) 11b, which are substantially parallel to each other. The workpiece 11 is defined into a plurality of rectangular regions by a plurality of streets (scribe lines) arrayed in a grid pattern so that they intersect together. Further, the individual regions defined by the streets on a side of the front surface 11a of the workpiece 11 are formed with devices (not depicted) such as ICs, LSI circuits, light emitting diodes (LEDs), or micro electro mechanical systems (MEMS) devices.

By dividing the workpiece 11 along the streets with a processing machine such as a cutting machine or a laser processing machine, a plurality of devices chips are manufactured with the devices included respectively therein. Further, by grinding and thinning the workpiece 11 before or after its division with the grinding machine 2, thinned device chips are obtained.

No limitations are however imposed on the kind, material, size, shape, construction, and the like of the workpiece 11. For example, the workpiece 11 may be a substrate (wafer) made from a semiconductor (GaAs, InP, GaN, SiC, or the like) other than silicon, glass, ceramic, resin, metal, or the like. Further, no limitations are imposed either on the kind, number, shape, construction, size, arrangement, and the like of the devices formed on the workpiece 11, and no devices may be formed on the workpiece 11.

Moreover, the workpiece 11 may be a package substrate such as a chip size package (CSP) substrate or a quad flat non-leaded package (QFN) substrate. The package substrate is formed, for example, by sealing, with a resin layer (mold resin), a plurality of device chips mounted on a predetermined substrate. By dividing and singulating the package substrate, package devices are manufactured including the packaged device chips respectively.

Obliquely rearward from the recessed portion 4a, a position alignment mechanism (alignment mechanism) 12 is disposed. Desired one of the workpieces 11 accommodated in the cassette 10A or 10B is transferred to the position alignment mechanism 12 by the transfer unit 6. The position alignment mechanism 12 then clamps the workpiece 11 and arranges it at a predetermined position.

At a position adjacent the position alignment mechanism 12, a transfer unit (transfer mechanism, loading arm) 14 is disposed to transfer the workpiece 11. The transfer unit 14 includes, for example, a suction pad that holds the workpiece 11 under suction on a side of an upper surface thereof. After holding, by the holding pad, the workpiece 11 that has been subjected to an alignment by the position alignment mechanism 12, the transfer unit 14 causes the suction pad to swing so that the workpiece 11 is transferred rearward.

In rear of the transfer unit 14, a disk-shaped turn table 16 is disposed. To the turn table 16, a rotary drive source (not depicted) such as a motor is connected to rotate the turn table 16 about an axis of rotation that is substantially parallel to the Z-axis direction.

Above the turn table 16, a plurality of chuck tables (holding tables) 18 are disposed to hold the workpiece 11. In FIG. 1, an example is depicted in which three chuck tables 18 are arranged at substantially equal intervals (120° intervals) along a peripheral direction of the turn table 16. No limitation is however imposed on the number of the chuck tables 18.

The turn table 16 depicted in FIG. 1 is configured to rotate both clockwise and counterclockwise as seen in a plan view. Each chuck table 18 is sequentially positioned by way of a transfer position A, a coarse grinding position (first grinding position) B, and a finish grinding position (second grinding position) C, and again at the transfer position A. It is to be noted that the turn table 16 may be configured to rotate in only one of the clockwise and counterclockwise as seen in the plan view.

In vicinities of the coarse grinding position B and finish grinding position C, thickness gauges 26 are disposed, respectively, to measure the thickness of the workpiece 11 held on the chuck table 18. The thickness gauges 26 each include, for example, a first height gauge that measures the height of an upper surface of the workpiece 11 held on the chuck table 18, and a second height gauge that measures the height of an upper surface of the chuck table 18.

In rear of the coarse grinding position B and finish grinding position C, columnar support structures 28A and 28B are arranged respectively. On a side of a front surface of the support structure 28A, a moving unit (moving mechanism) 30A is disposed, and on a side of a front surface of the support structure 28B, a moving unit (moving mechanism) 30B is disposed.

The moving units 30A and 30B each include a pair of guide rails 32 arranged along the Z-axis direction. On the paired guide rails 32, a plate-shaped moving plate 34 is fitted in such a manner as to be slidable along the guide rails 32.

On a side of a rear surface (back surface) of the moving plate 34, a nut portion (not depicted) is disposed. Maintained in threaded engagement with this nut portion is a ball screw 36 that is arranged along the Z-axis direction between the paired guide rails 32. To an upper end portion of the ball screw 36, a pulse motor 38 is connected to rotate the ball screw 36. When the ball screw 36 is rotated by the pulse motor 38, the moving plate 34 is moved along the Z-axis direction.

On the moving plate 34 of the moving unit 30A, a grinding unit (coarse grinding unit) 40A is mounted to apply coarse grinding to the workpiece 11. The grinding unit 40A grinds the workpiece 11 which is held on the chuck table 18 positioned at the coarse grinding position B. On the moving plate 34 of the moving unit 30B, on the other hand, a grinding unit (finish grinding unit) 40B is mounted to apply finish grinding to the workpiece 11. The grinding unit 40B grinds the workpiece 11 which is held on the chuck table 18 positioned at the finish grinding position C.

The grinding units 40A and 40B include housings 42, respectively, which are formed in a hollow cylindrical shape. Each housing 42 is fixed on a side of a front surface of the corresponding moving plate 34. In the housing 42, a cylindrical spindle 44 (see FIG. 5) arranged along the Z-axis direction is accommodated, and the spindle 44 is exposed at a distal end portion (lower end portion) thereof from the housing 42. To a proximal end portion (upper end portion) of the spindle 44, on the other hand, a motor 46 is connected to rotate the spindle 44. On the distal end portion of the spindle 44, a disk-shaped wheel mount 48 made of metal or the like is fixed.

On a side of a lower surface of the wheel mount 48 of the grinding unit 40A, a grinding wheel (coarse grinding wheel) 50A for coarse grinding is mounted. On a side of a lower surface of the wheel mount 48 of the grinding unit 40B, on the other hand, a grinding wheel for finish grinding (finish grinding wheel) 50B is mounted. The grinding wheels 50A and 50B are processing tools which are each detachably mounted on the wheel mount 48 to grind the workpiece 11. For example, the grinding wheels 50A and 50B are each fixed on the corresponding wheel mount 48 by fixtures such as fastening bolts. As a consequence, the grinding wheels 50A and 50B are mounted on the distal end portions of the spindles 44, respectively. About details of the grinding wheels 50A and 50B, a description will be made subsequently herein.

The moving unit 30A lifts up or down the grinding unit 40A along the Z-axis direction, whereby the chuck table 18, which is positioned at the coarse grinding position B, and the grinding wheel 50A are caused to separate or approach each other along the Z-axis direction. Similarly, the moving unit 30B lifts up or down the grinding unit 40B along the Z-axis direction, whereby the chuck table 18, which is positioned at the finish grinding position C, and the grinding wheel 50B are caused to separate or approach each other along the Z-axis direction.

As depicted in FIG. 1, at a position adjacent the transfer unit 14 in the X-axis direction, a transfer unit (transfer mechanism, unloading arm) 66 is disposed to transfer the workpiece 11. The transfer unit 66 includes, for example, a suction pad that holds the workpiece 11 under suction on the side of the upper surface thereof. After holding by the holding pad the workpiece 11 that is held on the chuck table 18 arranged at the transfer position A, the transfer unit 66 causes the suction pad to swing so that the workpiece 11 is transferred forward.

On a forward side of the transfer unit 66, a rinsing unit (rinsing system, rinsing device) 68 is disposed to rinse the workpiece 11. The rinsing unit 68 rinses the workpiece 11 transferred from the chuck table 18 by the transfer unit 66. The rinsing unit 68 includes, for example, a spinner table that rotates with the workpiece 11 held thereon, and a nozzle that supplies a rinsing liquid (pure water or the like) to the workpiece 11 held on the spinner table.

In addition, the grinding machine 2 also includes a controller (control unit, control section, control system) 64 connected to the individual elements (transfer unit 6, position alignment mechanism 12, transfer unit 14, turn table 16, chuck tables 18, thickness gauges 26, moving units 30A and 30B, grinding units 40A and 40B, transfer unit 66, rinsing unit 68, and the like) that configure the grinding machine 2. The controller 64 controls operations of the grinding machine 2 by outputting control signals to the individual elements of the grinding machine 2.

For example, the controller 64 is configured by a computer and includes a processing section that performs processing needed to operate the grinding machine 2, and a storage section that stores various kinds of information (data, programs, and the like) to be used in the operation of the grinding machine 2. The processing section includes a processor such as a central processing unit (CPU). On the other hand, the storage section includes a memory such as a read only memory (ROM) or a random access memory (RAM).

When the workpiece 11 is ground by the grinding machine 2, the cassette 10A or 10B with a plurality of workpieces 11 accommodated therein is first placed on the cassette placing area 8A or 8B. Then, the desired one of the workpieces 11 is transferred from the cassette 10A or 10B to the position alignment mechanism 12 by the transfer unit 6, and a position alignment of the workpiece 11 is performed by the position alignment mechanism 12. After that, the workpiece 11 is transferred by the transfer unit 14 to the chuck table 18 arranged at the transfer position A and is held on the chuck table 18.

The turn table 16 is next rotated clockwise to position the chuck table 18 with the workpiece 11 held thereon at the coarse grinding position B. The workpiece 11 is then ground by the grinding wheel 50A mounted on the grinding unit 40A. As a consequence, coarse grinding is applied to the workpiece 11.

The turn table 16 is further rotated clockwise to position the chuck table 18 with the workpiece 11 held thereon at the finish grinding position C. The workpiece 11 is then ground by the grinding wheel 50B mounted on the grinding unit 40B. As a consequence, finish grinding is applied to the workpiece 11.

Upon completion of the grinding of the workpiece 11, the turn table 16 is rotated clockwise to again position the chuck table 18 with the workpiece 11 held thereon at the transfer position A. The workpiece 11 is then transferred by the transfer unit 66 from on the chuck table 18 to the rinsing unit 68 and is rinsed by the rinsing unit 68. The workpiece 11 after the rinsing is transferred by the transfer unit 6 and is placed again in the cassette 10A or 10B.

A description will next be made about the grinding wheels 50A and 50B. It is to be noted that the description will hereinafter be made taking, as an example, the grinding wheel 50A for coarse grinding, but the grinding wheel 50B for finish grinding can also have a similar configuration. FIG. 2 is a perspective view schematically depicting a first example of the grinding wheel 50A, FIG. 3 is a cross-sectional view schematically depicting the first example of the grinding wheel 50A, and FIG. 4 is a side view depicting, on an enlarged scale, one of a plurality of grinding stones 54 of the grinding wheel 50A of FIGS. 2 and 3.

As depicted in FIG. 2, the grinding wheel 50A includes an annular wheel base 52. The wheel base 52 is made of metal such as aluminum or stainless steel and is formed with substantially the same diameter as the wheel mount 48. On a side of a lower surface of the wheel base 52, the grinding stones 54 are fixed. For example, the grinding stones 54 are each formed in a parallelepiped shape and are arrayed at substantially equal intervals in an annular pattern along a peripheral direction of the wheel base 52.

As depicted in FIG. 4, each grinding stone 54 includes a base portion 56 having a mounting surface 58 where the base portion 56 is mounted on the wheel base 52, and a wear-accelerated portion 60 having a grinding surface 62 that is directed toward a side opposite to the mounting surface 58 and is brought into contact with the workpiece 11. The base portion 56 is formed, for example, in a parallelepiped shape. On the other hand, the wear-accelerated portion 60 is configured to be more prone to wearing than the base portion 56.

Using, as the material of the wear-accelerated portion 60, a material having a higher brittleness than that of the material of the base portion 56, for example, the wear-accelerated portion 60 is made prone to wearing compared with the base portion 56. As an alternative, using, as the material of the wear-accelerated portion 60, a material having a lower Vickers hardness than that of the material of the base portion 56, the wear-accelerated portion 60 is made prone to wearing compared with the base portion 56.

If the wear-accelerated portion 60 is made from the same material as that of the base portion 56, on the other hand, the wear-accelerated portion 60 is formed to have a shape with a cross-sectional area that is parallel to the mounting surface 58 and is progressively reduced toward the grinding surface 62. The wear-accelerated portion 60 is made prone to wearing compared with the base portion 56, for example, by forming the wear-accelerated portion 60 in a dome shape or truncated cone shape having a progressively reduced cross-sectional area toward a side of the grinding surface 62. Similarly, the wear-accelerated portion 60 is also made prone to wearing compared with the base portion 56 when the wear-accelerated portion 60 has a higher porosity than that of the base portion 56.

No particular limitations are imposed on the materials of the base portion 56 and wear-accelerated portion 60. For example, the base portion 56 and wear-accelerated portion 60 are made from a material containing abrasive grits made of diamond, cubic boron nitride (cBN), or the like, and a binder (bonding material), such as a metal bond, resin bond, or vitrified bond, that keeps the abrasive grits fixed. It is to be noted that the number and array of the grinding stones 54 can be set as desired.

The wear-accelerated portion 60 preferably has such a thickness that the wear-accelerated portion 60 is completely lost before the grinding of a single workpiece 11 is completed. By setting the thickness a to such a thickness, the single workpiece 11 will be ground by both the wear-accelerated portion 60 and the base portion 56. Preferably, the thickness a of the wear-accelerated portion 60 is, for example, 5 μm or greater and 15 μm or smaller.

A description will next be made about behavior, which occurs by making the wear-accelerated portion 60 more prone to wearing than the base portion 56, and its effects. FIG. 5 is a side view schematically depicting the grinding wheel 50A and the workpiece 11, before grinding the workpiece 11. FIG. 6 is a side view schematically depicting how the wear-accelerated portion 60 is worn in the course of grinding the workpiece 11. FIG. 7 is a side view similar to FIG. 6 and schematically depicts a situation after the loss of the wear-accelerated portions 60 in the course of grinding the workpiece 11.

As depicted in FIG. 5, the spindle 44 and the grinding wheel 50A are caused to rotate about an axis of rotation substantially parallel to the Z-axis direction when the motor 46 is rotated. As a consequence, the grinding stones 54 each rotate along an annular rotation path (track) centering around the axis of rotation of the spindle 44 and grinding wheel 50A.

As also depicted in FIG. 5, a clearance c occurs between the wheel mount 48 and the grinding wheel 50A if any foreign matter exists, for example, between the wheel mount 48 and the grinding wheel 50A when the grinding wheel 50A is attached to the wheel mount 48. As a result, the grinding surfaces 62 of the grinding stones 54 are inclined with respect to the front surface (to-be-ground surface) 11a of the workpiece 11. Described specifically, the grinding surfaces 62 are actually inclined with respect to the grinding surfaces 62 in ideal conditions under which the front surface 11a of the workpiece 11 can be appropriately ground, and an offset of an amount b is formed between the actual grinding surfaces 62 and the ideal grinding surfaces.

If the workpiece 11 is ground with such an offset amount b existing, two kinds of areas occur on the front surface 11a of the workpiece 11, one being in contact with some of the grinding stones 54, and the other out of contact with the remaining grinding stones 54. As a consequence, a problem may arise in that the workpiece 11 is lowered in quality. Described more specifically, there are, for example, problems of increases of variations occurring in surface roughness among a plurality of workpieces 11 and also of in-plane variations occurring in surface roughness within a single workpiece 11.

As depicted in FIG. 6, the grinding wheel 50A of this embodiment is configured such that the wear-accelerated portions 60 come into contact with the workpiece 11 at an initial stage of the grinding of the workpiece 11. When the grinding of the workpiece 11 by the grinding wheel 50A is started, the wear-accelerated portions 60 therefore appropriately wear so that the grinding wheel 50A is dressed along with the grinding of the workpiece 11. As a result, lower surfaces of the grinding stones 54 come close to the ideal grinding surfaces, and therefore the effects of the offset amount b are substantially eliminated.

With the grinding machine and grinding method of the related art, a step is needed to provide and grind dummy workpieces before grinding workpieces, in order to perform dressing (setting, truing) of the grinding wheels. In contrast to this, the use of the grinding wheel 50A of this embodiment obviates any special work for dressing the grinding wheel 50A as mentioned above, so that dressing can be performed concurrently with the grinding of the workpiece 11. The grinding wheel of this embodiment can therefore avoid reduction of productivity.

The grinding wheel 50A of this embodiment exhibits particularly pronounced advantageous effects if the frequency of replacements for the grinding wheel 50A is high and the frequency of work for dressing hence becomes high, for example, if workpieces 11 made from a hard material are ground or in a similar situation. In the grinding wheel 50A of this embodiment, the wear-accelerated portions 60 are formed, as mentioned above, with such a thickness that they are completely removed by grinding a single piece of workpiece 11. In continuation to the grinding of the workpiece 11 by the wear-accelerated portions 60, the same workpiece 11 is therefore continuously ground by the base portions 56. The quality of the workpiece 11 can hence be maintained equal to that in the related art.

It is to be noted that the thickness of each wear-accelerated portion 60 in a direction from the grinding surface 62 toward the base portion 56 (the thickness a in FIG. 4) may preferably be adjusted according to a mounting tolerance of the grinding wheel 50A. For example, the thickness of each wear-accelerated portion 60 may preferably be set to the mounting tolerance or greater. If the wear-accelerated portions 60 have an excessively large thickness, the grinding of a single piece of workpiece 11 is completed without complete loss of the wear-accelerated portions 60. If this is the case, the quality tends to differ between the workpiece 11 ground by only the wear-accelerated portions 60 and the workpiece 11 further ground by the base portions 56 after the wear-accelerated portions 60 have been lost completely. The wear-accelerated portions 60 are therefore preferably set to such a thickness that they are completely lost before completion of the grinding of a single piece of workpiece 11.

This means that the wear-accelerated portions 60 are each formed to such a thickness as to be completely removed by grinding a single piece of workpiece 11. In continuation to the grinding of the workpiece 11 by the wear-accelerated portions 60, the same workpiece 11 is therefore ground by the base portions 56. As a result, it is hence easier to maintain constant quality among a plurality of workpieces 11.

A description will next be made about other examples of the grinding stones 54. FIG. 8 is a cross-sectional view schematically depicting a second example of the grinding wheel according to the embodiment of the first aspect of the present invention, and FIG. 9 is a side view depicting, on an enlarged scale, one of grinding stones of the grinding wheel of FIG. 8. As depicted in FIGS. 8 and 9, each wear-accelerated portion 60 is provided in the grinding surface 62 thereof with a plurality of grooves. Owing to such a shape of each wear-accelerated portion 60, the wear-accelerated portion 60 has a smaller cross-sectional area in the direction parallel to the mounting surface 58 (see FIG. 4) than that of the base portion 56, so that the wear-accelerated portion 60 is more prone to wearing than the base portion 56.

FIG. 10 is a cross-sectional view schematically depicting a third example of the grinding wheel according to the embodiment of the first aspect of the present invention, and FIG. 11 is a side view depicting, on an enlarged scale, one of grinding stones of FIG. 10. As depicted in FIGS. 10 and 11, each wear-accelerated portion 60 has a dome shape in the third example. In other words, each wear-accelerated portion 60 has a shape tapered toward the grinding surface 62 so as to have a smaller cross-sectional area, in the direction parallel to the mounting surface 58 (see FIG. 4), toward the grinding surface 62. Owing to such a shape of each wear-accelerated portion 60, the cross-sectional area of the wear-accelerated portion 60 in the direction parallel to the mounting surface 58 is smaller than that of the base portion 56 especially on the side of the grinding surface 62, and therefore the wear-accelerated portion 60 is more prone to wearing on the side of the grinding surface 62 thereof than the base portion 56.

FIG. 12 is a side view schematically depicting one of grinding stones of a fourth example of the grinding wheel according to the embodiment of the first aspect of the present invention. As depicted in FIG. 12, each wear-accelerated portion 60 has a truncated square cone shape in the fourth example. In other words, each wear-accelerated portion 60 has a shape tapered toward the grinding surface 62 so as to have a smaller cross-sectional area, in the direction parallel to the mounting surface 58 (see FIG. 4), toward the grinding surface 62. Owing to such a shape of each wear-accelerated portion 60, the cross-sectional area of the wear-accelerated portion 60 in the direction parallel to the mounting surface 58 is smaller than that of the base portion 56 especially on the side of the grinding surface 62, and therefore the wear-accelerated portion 60 is more prone to wearing on the side of the grinding surface 62 thereof than the base portion 56.

Referring to FIG. 13 of the attached drawings, a description will next be made about a grinding method according to an embodiment of the second aspect of the present invention. FIG. 13 is a flow diagram illustrating an example of the grinding method according to the embodiment of the second aspect of the present invention. As illustrated in FIG. 13, the grinding method of this embodiment has a step (S1) of attaching the grinding wheel 50A to the wheel mount 48, a step (S2) of transferring the workpiece 11 to the coarse grinding position B, a first grinding step (S3), and a second grinding step (S4).

If the grinding wheel 50B for finish grinding is configured similar to the above-mentioned grinding wheel 50A for coarse grinding, however, the grinding wheel 50A can be replaced to the grinding wheel 50B in the step S1, and the coarse grinding position B can be replaced to the finish grinding position C in the step S2.

In the grinding method of this embodiment, the above-mentioned grinding machine 2 in the embodiment of the first aspect of the present invention is used. When grinding of the workpiece 11 is started, the grinding machine 2 grinds the workpiece 11 by the wear-accelerated portions 60 of the grinding stones 54 in the first grinding step (S3). As the wear-accelerated portions 60 are configured to be prone to wearing, dressing of the grinding wheel 50A proceeds concurrently with the grinding of the workpiece 11. After the wear-accelerated portions 60 have been lost by wear, the grinding machine 2 continuously grinds the workpiece 11 by the base portions 56 of the grinding stones 54 in the second grinding step (S4).

As mentioned above, the grinding method according to the embodiment of the second aspect of the present invention can perform dressing without a reduction in productivity.

Moreover, the construction, method, and the like according to the above-described embodiments can be practiced with appropriate changes or modifications within the scope not departing from the objects of the present invention.

The present invention is not limited to the details of the above described preferred embodiments. The scope of the invention is defined by the appended claims and all changes and modifications as fall within the equivalence of the scope of the claims are therefore to be embraced by the invention.

GRINDING WHEEL AND GRINDING METHOD

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Description

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Priority Claims (1)