Abstract:
A grinding wheel having hollow particles, along with abrasive grains, fixed by a bonding material. The abrasive grains may be diamond grains. The hollow particles may consist essentially of silica. The bonding material may be electrodeposited nickel. The grinding wheel is manufactured by performing an abrasive grain electrodeposition step of immersing a base, with a plating surface being pointed upward, in a plating solution, in which the abrasive grains having a larger specific gravity than the plating solution are dispersed, to deposit the abrasive grains settling in the plating solution on the plating surface, and also deposit a plating metal on the plating surface; and a hollow particle electrodeposition step of immersing the base, with the plating surface being pointed downward, in a plating solution, in which the hollow particles having a smaller specific gravity than the plating solution are dispersed, to deposit the hollow particles floating in the plating solution on the plating surface, and also deposit a plating metal on the plating surface.

Description:
FIELD OF THE INVENTION  
       [0001]     This invention relates to a grinding wheel having abrasive grains, such as diamond grains, fixed thereto by a bonding material, and a method for manufacturing the grinding wheel.  
       DESCRIPTION OF THE PRIOR ART  
       [0002]     As well known among people skilled in the art, grinding wheels of various shapes, which comprise abrasive grains, such as diamond grains, fixed by a suitable bonding material such as a plating metal, are used for cutting and grinding hard and brittle materials, such as a silicon wafer, a sapphire wafer, a ceramics plate, and a glass plate.  
         [0003]     According to the inventor&#39;s experience, conventional grinding wheels of the above-mentioned forms have the abrasive grains firmly fixed. Thus, the abrasive grains decreased in cutting or grinding capacity are kept retained, without being suitably released, resulting in an excessively low self-sharpening effect. Hence, the conventional grinding wheels pose the problem that dressing has to be performed frequently in order to maintain high cutting or grinding capacity.  
       SUMMARY OF THE INVENTION  
       [0004]     It is a first object of the present invention, therefore, to provide a grinding wheel in which abrasive grains decreased in cutting or grinding capacity are suitably released to produce a sufficient self-sharpening effect.  
         [0005]     It is a second object of the present invention to provide a manufacturing method which can advantageously produce the above-described grinding wheel.  
         [0006]     Based on eager studies and experiments, the inventor has found that when hollow particles along with abrasive grains are fixed by a bonding material to produce a grinding wheel, the degree of fixing of the abrasive grains is suitably decreased because of the presence of the hollow particles, with the result that the abrasive grains decreased in cutting or grinding capacity are suitably released to exert a sufficient self-sharpening effect.  
         [0007]     According to a first aspect of the present invention, there is provided, as a grinding wheel for attaining the above first object, a grinding wheel having hollow particles, along with abrasive grains, fixed by a bonding material.  
         [0008]     Preferably, the abrasive grains comprise diamond grains, the hollow particles consist essentially of silica, and the bonding material is a plating metal. The metal is preferably nickel. It is preferred that the proportion by volume of the abrasive grains is 10 to 30%, especially 15 to 25%, and the proportion by volume of the hollow particles is 10 to 50%, especially 20 to 40%.  
         [0009]     According to a second aspect of the present invention, there is provided, as a manufacturing method for attaining the above second object, a method for manufacturing a grinding wheel having hollow particles, along with abrasive grains, electrodeposited, comprising:  
         [0010]     an abrasive grain electrodeposition step of immersing a base, with a plating surface thereof being pointed upward, in a plating solution, in which the abrasive grains having a larger specific gravity than the plating solution are dispersed, to deposit the abrasive grains settling in the plating solution on the plating surface, and also deposit a plating metal on the plating surface; and  
         [0011]     a hollow particle electrodeposition step of immersing the base, with the plating surface being pointed downward, in a plating solution, in which the hollow particles having a smaller specific gravity than the plating solution are dispersed, to deposit the hollow particles floating in the plating solution on the plating surface, and also deposit a plating metal on the plating surface.  
         [0012]     Preferably, the abrasive grain electrodeposition step and the hollow particle electrodeposition step are alternately repeated a plurality of times. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]      FIG. 1  is a schematic view showing an abrasive grain electrodeposition step in a preferred embodiment of the manufacturing method according to the present invention.  
         [0014]      FIG. 2  is a schematic view showing a hollow particle electrodeposition step in the preferred embodiment of the manufacturing method according to the present invention.  
         [0015]      FIG. 3  is a sectional view showing a state in which a grinding wheel is formed on a plating surface of a base by repeating the abrasive grain electrodeposition step, shown in  FIG. 1 , and the hollow particle electrodeposition step, shown in  FIG. 2 , alternately a plurality of times.  
         [0016]      FIG. 4  is an enlarged view showing a part of the grinding wheel shown in  FIG. 3 .  
         [0017]      FIG. 5  is a perspective view showing a cutting tool composed of the base and the grinding wheel.  
         [0018]      FIG. 6  is a perspective view showing a cutting tool composed of the grinding wheel alone.  
         [0019]      FIG. 7  is a schematic view showing the abrasive grain electrodeposition step in another embodiment of the manufacturing method according to the present invention.  
         [0020]      FIG. 8  is a schematic view showing the hollow particle electrodeposition step in still another embodiment of the manufacturing method according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0021]     The preferred embodiments of the present invention will now be described in greater detail with reference to the accompanying drawings.  
         [0022]      FIG. 1  schematically shows an abrasive grain electrodeposition step in a preferred embodiment of a method for manufacturing a grinding wheel constructed in accordance with the present invention. In this abrasive grain electrodeposition step, an electroplating device furnished with a plating tank  2  is used. The plating tank  2  accommodates a plating solution  4  such as a nickel sulfate solution. The plating solution  4  contains abrasive grains  6 . The plating tank  2  is provided with a stirring means  8  rotationally driven by a drive source  7  which may be an electric motor. A metal bar  10 , which is preferably made of nickel, is partly immersed in the plating solution  4 . A base  12 , which is formed from a suitable metal such as aluminum, is placed at the bottom of the plating tank  2 . The base  12  in the illustrated embodiment, as will be clearly understood by reference to  FIG. 3  along with  FIG. 1 , has an inverted truncated conical upper portion and a truncated conical lower portion, and has a substantially flat plating surface  14  formed on a side surface thereof (an upper surface in  FIGS. 1 and 3 ). A through-hole  16  is formed at the center of the base  12 . Prior to placement of the base  12  in the plating tank  2 , the base  12  has an entire surface (except the plating surface  14 ) coated with a masking material  18  composed of a suitable insulating material. The electroplating device is also equipped with a voltage application means  20  for applying a direct current voltage between the metal bar  10  and the base  12 . The voltage application means  20  includes a direct current voltage source  22  and an on/off switch  24 .  
         [0023]     In the abrasive grain electrodeposition step, the stirring means  8  is rotationally driven, with the switch  24  being open. As a result, the plating solution  4  containing the abrasive grains  6  is stirred to disperse the abrasive grains  6  in the plating solution  4 . In  FIG. 1 , only some of the dispersed abrasive grains  6  are schematically shown. Then, the rotational driving of the stirring means  8  is stopped, and the switch  24  is closed. In this situation, nickel is deposited on the plating surface  14  of the base  12  by an electroplating action to carry out plating. Since the specific gravity of the abrasive grains  6  is higher than the specific gravity of the plating solution  4 , the abrasive grains  6  dispersed in the plating solution  4  settle in the plating solution  4 , so that the abrasive grains  6  are also deposited on the plating surface  14  of the base  12 . Consequently, an abrasive grain electrodeposition layer comprising the abrasive grains  6  fixed by the nickel plating is formed on the plating surface  14  of the base  12 .  
         [0024]     The abrasive grains  6  may have a grain size of the order of 10 to 15 μm measured, for example, by the laser diffraction/scattering method.  
         [0025]      FIG. 2  schematically shows a hollow particle electrodeposition step in the preferred embodiment of the method for manufacturing the grinding wheel constructed in accordance with the present invention. In this hollow particle electrodeposition step as well, an electroplating device furnished with a plating tank  102  is used. The plating tank  102  accommodates a plating solution  104  such as a nickel sulfate solution. The plating solution  104  contains hollow particles  106 . The plating tank  102  is provided with a stirring means  108  rotationally driven by a drive source  107  which may be an electric motor. A metal bar  110 , which is preferably made of nickel, is partly immersed in the plating solution  104 . The base  12 , which has had the abrasive grain electrodeposition layer formed on the plating surface  14  in the aforementioned abrasive grain electrodeposition step, is immersed, with its plating surface  14  being pointed downward, in an upper layer part of the plating solution  104  accommodated in the plating tank  102 . The electroplating device is also equipped with a voltage application means  120  for applying a direct current voltage between the metal bar  110  and the base  12 . The voltage application means  120  includes a direct current voltage source  122  and an on/off switch  124 .  
         [0026]     In the hollow particle electrodeposition step, the stirring means  108  is rotationally driven, with the switch  124  being open. As a result, the plating solution  104  containing the hollow particles  106  is stirred to disperse the hollow particles  106  in the plating solution  104 . In  FIG. 2 , only some of the dispersed hollow particles  106  are schematically shown. Then, the rotational driving of the stirring means  108  is stopped, and the switch  124  is closed. In this situation, nickel is deposited on the plating surface  14  of the base  12  by an electroplating action to carry out plating. Since the specific gravity of the hollow particles  106  is lower than the specific gravity of the plating solution  104 , the hollow particles  106  dispersed in the plating solution  104  float in the plating solution  104 , so that the hollow particles  106  are also deposited on the plating surface  14  of the base  12 . Consequently, a hollow particle electrodeposition layer comprising the hollow particles  106  fixed by the nickel plating is formed on the plating surface  14  of the base  12 .  
         [0027]     Preferably, the hollow particles  106  are hollow spherical bodies consisting essentially of silica (proportion by weight: 60 to 80%), and have a particle size of the order of 20 to 50 μm measured, for example, by the laser diffraction/scattering method. Preferably usable as the hollow particles  106  are hollow particles marketed by Taiheiyo Cement under the trade name of “E-SPHERES”, hollow particles marketed by Towana under the trade name of “Shirasu-balloons”, hollow particles marketed by Public Strategy under the trade name of “SILAX BALLOON”, and hollow particles marketed by SUZUKI YUSHI INDUSTRIAL under the trade name of “GOD BALL”.  
         [0028]      FIG. 3  shows a state in which a grinding wheel  26  having the abrasive grains  6  and the hollow particles  106  fixed by the nickel plating by the above-described abrasive grain electrodeposition step and hollow particle electrodeposition step alternately repeated a plurality of times is disposed on the plating surface  14  of the base  12 .  FIG. 4  is an enlarged view showing a part of the grinding wheel  26 . In the grinding wheel  26 , as clearly understood from  FIG. 4 , the abrasive grains  6  and the hollow particles  106  are suitably dispersed in plated nickel  28 . Generally, the abrasive grains  6  account for 10 to 30% by volume, the hollow particles  106  account for 10 to 50% by volume, and the remainder being plated nickel, advantageously.  
         [0029]     When the masking material  18  is removed from the base  12  shown in  FIG. 3  and, further, a part of the base  12 , namely, an outer peripheral edge portion of the upper end of the base  12 , is removed in a manner well known per se, such as dissolution with a sodium hydroxide solution, a cutting tool  30  as shown in  FIG. 5  can be formed. The cutting tool  30  is composed of the base  12 , and the grinding wheel  26  disposed on a surface (i.e., the plating surface  14 ) of the base  12 , and an outer peripheral edge portion of the grinding wheel  26  protrudes from the base  12 . If the whole of the base  12  is removed, a cutting tool  32 , composed only of the grinding wheel  26  of an annular thin plate shape, can be formed, as shown in  FIG. 6 .  
         [0030]      FIG. 7  schematically shows an abrasive grain electrodeposition step in other embodiment of the method for manufacturing the grinding wheel constructed in accordance with the present invention. In the abrasive grain electrodeposition step shown in  FIG. 7  as well, an electroplating device furnished with a plating tank  202  is used. The plating tank  202  accommodates a plating solution  204  such as a nickel sulfate solution. The plating solution  204  contains hollow particles  106  along with abrasive grains  6 . The abrasive grains  6  and the hollow particles  106  are substantially the same as the abrasive grains  6  and the hollow particles  106  shown in FIGS.  1  to  3 . The plating tank  202  is provided with a stirring means  208  rotationally driven by a drive source  207  which may be an electric motor. A metal bar  210 , which is preferably made of nickel, is partly immersed in the plating solution  204 . A base  12  is immersed, with its plating surface  14  being pointed upward, in an intermediate portion in the depth direction of the plating solution  204  accommodated in the plating tank  202 . This base  12  is substantially the same as the base  12  illustrated in FIGS.  1  to  3 . The electroplating device is also equipped with a voltage application means  220  for applying a direct current voltage between the metal bar  210  and the base  12 . The voltage application means  220  includes a direct current voltage source  222  and an on/off switch  224 .  
         [0031]     In the abrasive grain electrodeposition step, the stirring means  208  is rotationally driven, with the switch  224  being open. As a result, the plating solution  204  containing the abrasive grains  6  and the hollow particles  106  is stirred to disperse the abrasive grains  6  and the hollow particles  106  in the plating solution  204 . Then, the rotational driving of the stirring means  208  is stopped, and the switch  224  is closed. In this situation, nickel is deposited on the plating surface  14  of the base  12  by an electroplating action to carry out plating. Since the specific gravity of the abrasive grains  6  is greater than the specific gravity of the plating solution  204 , the abrasive grains  6  dispersed in the plating solution  204  settle in the plating solution  204 , so that the abrasive grains  6  are deposited on the plating surface  14  of the base  12 . Consequently, an abrasive grain electrodeposition layer comprising the abrasive grains  6  fixed by the nickel plating is formed on the plating surface  14  of the base  12 . Since the specific gravity of the hollow particles  106  is lower than the specific gravity of the plating solution  204 , on the other hand, the hollow particles  106  float in the plating solution  204 , and do not deposit on the plating surface  14  of the base  12 .  
         [0032]     In the hollow particle electrodeposition step, the base  12  in the plating solution  204  is turned upside down to point downward the plating surface  14  of the base  12 , as shown in  FIG. 8 . Then, the stirring means  208  is rotationally driven, with the switch  224  being open. As a result, the plating solution  204  containing the abrasive grains  6  and the hollow particles  106  is stirred to disperse the abrasive grains  6  and the hollow particles  106  in the plating solution  204 . Then, the rotational driving of the stirring means  208  is stopped, and the switch  224  is closed. In this situation, nickel is deposited on the plating surface  14  of the base  12  by an electroplating action to carry out plating. Since the specific gravity of the hollow particles  106  is lower than the specific gravity of the plating solution  204 , the hollow particles  106  dispersed in the plating solution  204  float in the plating solution  204 , so that the hollow particles  106  are deposited on the plating surface  14  of the base  12 . Consequently, a hollow particle electrodeposition layer comprising the hollow particles  106  fixed by the nickel plating is formed on the plating surface  14  of the base  12 . The specific gravity of the abrasive grains  6  is greater than the specific gravity of the plating solution  204 . Thus, the abrasive grains  6  settle in the plating solution  204 , and do not deposit on the plating surface  14  of the base  12 .  
         [0033]     If the above-described abrasive grain electrodeposition step and hollow particle electrodeposition step are alternately repeated a plurality of times, the grinding wheel  26  having the abrasive grains  6  and the hollow particles  106  fixed by the nickel plating can be disposed on the plating surface  14  of the base  12 , as shown in  FIG. 3 .  
         [0034]     While the preferred embodiments of the grinding wheel constructed according to the present invention, and the preferred embodiments of the method for manufacturing the grinding wheel have been described in detail by reference to the accompanying drawings, it is to be understood that the invention is not limited to such embodiments, but various changes and modifications may be made without departing from the scope of the present invention.  
         [0035]     For example, the grinding wheel in the shape of an annular thin plate has been described. However, the grinding wheel of such a shape is not restrictive, and the present invention can be applied to grinding wheels of various shapes. Moreover, the electrodeposited grinding wheel having the abrasive grains and the hollow particles fixed by the plating metal has been described. However, the present invention can be applied to grinding wheels using bonding materials other than the plating metal, such as a resin-based bonding material and a vitrified bonding material.