Abrading – Rigid tool – Rotary disk
Reexamination Certificate
2002-04-19
2004-02-17
Morgan, Eileen P. (Department: 3723)
Abrading
Rigid tool
Rotary disk
C451S550000
Reexamination Certificate
active
06692343
ABSTRACT:
TECHNICAL FIELD
The present invention generally relates to a superabrasive wheel, and more specifically, it relates to a superabrasive wheel for mirror finishing employed for mirror-finishing a hard brittle material such as silicon, glass, ceramics, ferrite, rock crystal, cemented carbide or the like.
BACKGROUND ART
Recently, high-precision mirror finishing of a material is required following abrupt technical innovation such as high integration of a semiconductor device or ultraprecision in working of ceramics, glass, ferrite or the like. Such mirror finishing is generally performed by grinding referred to as lapping. More specifically, free abrasive grains mixed into a lapping solution are fed between a lapping surface plate and a workpiece and rubbed with each other while applying pressure to the lapping surface plate and the workpiece in this grinding, for grinding the workpiece due to rolling and scratching actions of the free abrasive grains and providing a highly precise mirror-finished surface on the workpiece. In this lapping, however, a large quantity of free abrasive grains are consumed to result in a large quantity of mixture, referred to as sludge, of used freed abrasive grains, chips caused by cutting the workpiece and the lapping solution, disadvantageously leading to deterioration of the working environment and pollution.
Therefore, mirror finishing employing fixed fine superabrasive grains is actively studied/developed as a method substitutable for the aforementioned grinding employing free abrasive grains. As such mirror finishing employing fixed fine superabrasive grains, well known is machining with a resin bond superabrasive wheel elastically holding superabrasive grains of several &mgr;m in mean grain size or ELID (electrolytic in-progress dressing) grinding of dressing a metal bond superabrasive wheel while electrolytically dissolving a bond material for grinding a material with the metal bond superabrasive wheel.
In the aforementioned machining employing a resin bond superabrasive wheel, however, the sharpness of a grindstone is deteriorated due to the fine superabrasive grains, and the grindstone is so remarkably worn that the worked surface of a workpiece is readily changed in shape or reduced in precision and the grindstone must be frequently trued and dressed.
In the aforementioned working method employing a metal bond superabrasive wheel, the rigidity of the metal bond material is so high that superabrasive grains finer than those in the resin bond superabrasive wheel must be used for obtaining a mirror-finished state substantially identical to the worked surface of the workpiece obtained by the machining employing the resin bond superabrasive wheel, to result in further deterioration of the sharpness of the grindstone.
In order to solve the problem of sharpness, a vitrified bond may be used as the binder while reducing the area of a superabrasive layer. For example, a number of grooves may be formed in a superabrasive layer employing a vitrified bond as the binder, so that superabrasive layers contributing to grinding are formed at intervals from each other. When employing a superabrasive wheel formed with such superabrasive layers, not only the conventional grinding employing free abrasive grains can be changed to grinding employing fixed superabrasive grains but also a vitrified bond superabrasive wheel for mirror finishing having remarkably excellent sharpness and a long life can be provided by performing truing and dressing with a diamond rotary dresser (hereinafter referred to as an RD). This is because large-volume pores of the vitrified bond serve as chip pockets for smoothly discharging chips and enabling highly efficient machining, so that the workpiece can be mirror-finished with small surface roughness.
In the aforementioned vitrified bond superabrasive wheel for mirror finishing, a plurality of segment superabrasive layers are arranged along the peripheral direction of an annular base plate at intervals from each other. Depending on the size or the shape of the segments, however, superabrasive grains crushed or falling during mirror finishing or shavings may be caught between the superabrasive layers and the workpiece, to cause scratches on the surface of the workpiece. Further, a long time is required for a step of removing such scratches.
For example, Japanese Patent No. 2976806 proposes a structure of a segment grindstone. This segment grindstone is formed with segment fixing grooves so that a plurality of abrasive layer segments are engaged in the segment fixing grooves respectively. When performing grinding with the segment grindstone having such a structure, however, the segment fixing grooves are clogged with shavings, and dischargeability for such shavings is extremely deteriorated.
Japanese Patent Laying-Open No. 54-137789 (1979) proposes a structure of a segment type grindstone for surface grinding. In the segment type grindstone disclosed in this gazette, superabrasive layers are formed by sintering superabrasive grains with a binder such as a metal bond or a resin bond. When arranging superabrasive layers of plate segments shown in
FIG. 4
or
FIG. 6
of this gazette along the peripheral direction of an annular base plate at intervals from each other, grinding resistance is disadvantageously increased due to the metal bond or the resin bond employed as the binder, although dischargeability for shavings is improved. Therefore, sharpness is deteriorated in grinding and the superabrasive layers are readily displaced from the base plate. The superabrasive layers are frequently displaced as the quantity of grinding is increased, to result in scratches. Consequently, the life of the grindstone is disadvantageously reduced.
The aforementioned gazette further proposes a structure of a segment type grindstone for surface grinding formed by arranging segment tips of cylindrically formed superabrasive layers along the peripheral direction of an annular base plate at intervals from each other in FIG.
1
. However, although such cylindrical superabrasive layers are hardly displaced from the base plate in grinding, the inner sides of the cylindrical superabrasive layers are readily clogged with shavings and dischargeability for such shavings is disadvantageously deteriorated.
Accordingly, an object of the present invention is, in order to solve the aforementioned problems, to provide a superabrasive wheel for mirror finishing improved in dischargeability for superabrasive grains crushed or falling during mirror finishing or shavings to hardly cause scratches, capable of performing efficient machining and also capable of preventing scratches caused by displacement of a segment superabrasive layer by rendering the superabrasive layer hardly displaceable from a base plate.
SUMMARY OF INVENTION
According to a first aspect of the present invention, a superabrasive wheel for mirror finishing, comprising an annular base plate having an end surface and a plurality of superabrasive layers or members, each having a peripheral end surface, arranged along the peripheral direction of this annular base plate at intervals from each other and fixed onto the end surface of the base plate, has the following characteristics. Each of the plurality of superabrasive layers or members has a flat plate shape, and is so arranged that the peripheral end surface is substantially parallel to the rotary shaft of the superabrasive wheel. A surface defined by the thickness of the flat plate shape of each of the plurality of superabrasive layers, i.e., a surface along the direction of the thickness of the flat plate shape is fixed onto the end surface of the base plate. Superabrasive grains are bonded by a binder of a vitrified bond in the superabrasive layers.
In the superabrasive wheel having the aforementioned structure, the surface defined by the thickness is fixed onto the end surface of the base plate in each of the superabrasive layers having the flat plate shape, whereby sufficient clearances can be defined between the superabrasive layers and dischargeability
Hirata Takahiro
Okanishi Yukio
A.L.M.T. Corp.
Fasse W. F.
Fasse W. G.
Morgan Eileen P.
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