Composite abrasive-articles and manufacturing method therefor

A composite abrasive-articles according to the present invention is obtained by: mixing diamond pieces of abrasive articles or cubic boron nitride pieces of abrasive articles and metal powder, molding this mixture into a uniformed small piece of abrasive articles, then or simultaneously with this molding, completely sintering the uniform small piece of abrasive articles after the molding, and mixing the completely sintered piece of abrasive articles after the sintering with resin, metal or glass of a low melting point so as to be solidified into a predetermined shape. In the composite abrasive-article of this type, the completely sintered piece of abrasion articles made of the diamond pieces of abrasion articles or cubic boron nitride piece of abrasive articles and metal powder is dispersed and solidified in a matrix made of either resin, metal, or glass having a low melting point. The composite abrasive-articles are preferably used for grinding, polishing, and/or cutting metal, ceramics, stone, or the like.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to composite abrasive-articles and a 
manufacturing method therefor exhibiting high efficiency and long life, 
the composite abrasive-articles being used for grinding, polishing, and 
cutting metal, ceramics, stone, or the like. 
2. Description of the Prior Art 
In general, composite abrasive-articles are used for grinding, polishing, 
and cutting metal, ceramics, stone, or the like, the composite 
abrasive-articles being manufactured by dispersing and solidifying a piece 
of abrasive article consisting of diamond abrasive or cubic boron nitride 
abrasive and metal powder in a matrix made of resin, metal, or glass of a 
low melting point. 
A conventional method of manufacturing composite abrasive-articles has been 
disclosed in Japanese Patent Laid-Open No. 50-153387, and another 
conventional method has been disclosed in Japanese Patent Publication No. 
60-3557. 
According to these inventions, a sintered body of abrasive and metal powder 
is pulverized in the manufacturing process so as to be small chips, the 
thus-obtained small chips being then dispersed and solidified in resin or 
the like. 
In particular, according to the invention disclosed in Japanese Patent 
Publication No. 60-3557, abrasive and metal powder are incompletely 
sintered so as to be readily pulverized in the latter manufacturing 
process. The powder is then screened for the adjustment of the particle 
size thereof. It then dispersed in resin or metal before being subjected 
to heat molding so that it is completely sintered. 
According to the above-described conventional invention, since massive and 
pulverized abrasive article pieces are formed by way of the pulverization 
performed in the manufacturing process after the sintering (the incomplete 
sintering), it is difficult to employ metal of the type displaying a high 
malleability and ductility as the metal which forms the abrasive article. 
Therefore, metal which can be readily pulverized, that is, brittle metal 
is necessarily employed. According to the invention disclosed in Japanese 
Patent Laid-Open No. 50-153387, since no particle-size adjustment is 
conducted, a problem of non-uniform abrasion and surface roughness of the 
ground surface arises due to the non-uniform distribution of the particle 
size in the produced abrasive-article obtained after the manufacturing 
process. Furthermore, according to the invention disclosed in Japanese 
Patent Publication No. 60-3557, the particle size adjustment of the 
abrasive which has been pulverized after the incomplete sintering is 
conducted, the particle size adjustment being conducted by means of a 
screen. However, the portion separated by the screening raises the cost, 
and the shape of the screened pieces of the abrasive articles cannot be 
made to be uniform in terms of the shape thereof. Furthermore, the 
particle size distribution ranges excessively widely. Therefore, the 
abrasive-article of the type described above encounters a problem of a 
difficulty of controlling the grinding ratio, cutting capability, and life 
thereof. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide composite 
abrasive-articles and a manufacturing method therefor from which the 
pulverization process which is arranged to be conducted after the 
sintering process can be eliminated for the purpose of raising the 
manufacturing yield whereby a piece of abrasive article exhibiting uniform 
shape and extremely narrow particle size distribution can be obtained. The 
thus-obtained piece of the abrasive article being able to form the 
composite abrasive-article, the grinding ratio and the life of which can 
be optionally controlled to correspond to the type of the substance to be 
ground (both substance to be polished and substance to be cut are 
included) and which exhibits an excellent grinding ratio and reduced 
grinding resistance. 
The method of manufacturing composite abrasive-articles according to the 
present invention comprises the following steps of: 
mixing diamond pieces of abrasive articles or cubic boron nitride pieces of 
abrasive articles and metal powder; 
molding the mixture into a uniform small piece of abrasive articles; 
then, or simultaneously with the molding, completely sintering the uniform 
small piece of abrasive articles which has been molded; and 
mixing a completely sintered piece of abrasive articles and any of resin, 
metal, or glass having a low melting point, whereby the mixture is 
solidified into a predetermined shape. 
The composite abrasive-articles obtained as described above are formed by 
way of dispersing and solidifying a completely sintered and uniform 
abrasive consisting of diamond abrasive or cubic boron nitride abrasive 
and metal powder in a matrix of resin, metal, or glass having a low 
melting point. 
The other objects and constructions will be clear from the following 
explanations.

DETAILED DESCRIPTION OF THE INVENTION 
The present invention will be explained in more detail hereinafter. 
According to the present invention, the term "uniform small piece of 
abrasive article" means a substance formed by mixed powders of diamond 
abrasive or cubic boron nitride abrasive and metal powder or paste 
prepared as a result of the kneading with a caking instrument, the uniform 
small piece of abrasive article being formed by a uniform non-sintered 
body having a constant shape without dimensional distribution. 
The metal powder according to the present invention is exemplified by a 
sole metal powder of copper, iron, nickel, or the like, a variety of alloy 
powders, and mixed powder of metals. Furthermore, powders of metals 
displaying malleability and ductility may be employed. In particular, it 
is preferable to employ Ni-Cu-Sn, Ni-Cu-Sn-P, Ni-Zn, Cu-Sn, and Cu-Su-Zn. 
The metal powder of the type described above and the diamond abrasive or 
cubic boron nitride (CBN) are mixed and are then molded. The molding is 
conducted in accordance with the screen printing method, perforated screen 
method, metal molding method, molding method, hot pressing method. 
Granulation method so that the uniform small piece of abrasive articles is 
formed. 
Then, a specific example of the molding method will be described. 
In the screen printing method and aperture plate printing method, a paste 
of a kneaded body obtained by kneading the above-described mixed powder 
and a caking aid such as polyvinyl alcohol is printed on a base such as a 
graphite plate or a ceramic plate that can withstand the sintering 
temperature, the base being formed on a plate having a predetermined 
pattern. As a result, the uniform small piece of abrasive articles can be 
formed. 
The metal molding method is arranged such that: a metal die and a punch are 
used and the mixed powder is enclosed in the die. Then, the thus-enclosed 
mixed powder is pressed by the punch so as to be solidified. As a result, 
a desired uniform small piece of abrasive articles is formed. 
The hot pressing method is arranged such that: a graphite die and a punch 
are used, and the mixed powder is enclosed in the die. Then, electricity 
is supplied to the graphite die with pressure applied with the punch. 
Alternatively, a metal die including a heater and a punch is used, and the 
mixed powder is enclosed in the die. Then, the heater is actuated with a 
pressure applied by the punch so as to solidify the mixed powder. As a 
result, a completely sintered small piece of abrasive articles is formed. 
The molding method is arranged such that: a mold having a predetermined 
shape is formed on the base such as a ceramic plate which can withstand 
the sintering temperature, the mold being formed by drilling or supersonic 
machining. Then, the above-described mixed powder is enclosed in the 
thus-formed mold, causing the uniform small piece of abrasive articles to 
be formed. 
The granulating method is arranged such that: the above-described mixed 
powder and liquid paraffin diluted and adjusted by, for example, an 
organic solvent, are kneaded and the thus-kneaded material is granulated 
to a predetermined shape by a commercially available granulating machine. 
As a result, the uniform small piece of abrasive articles is formed. 
The uniform small piece of abrasive articles may, of course, be prepared by 
any conventional method so far as the non-uniform distribution of the 
particle size can be prevented. For example, it may be prepared by means 
of a controlled atomization. 
The obtained uniform small piece of abrasive articles is then subjected to 
the sintering process. The sintering is conducted such that the uniform 
small piece of abrasive articles is completely sintered in an non-oxidized 
atmosphere such as hydrogen, ammonia cracked gas at a temperature above 
500.degree. C. As a result, the completely sintered small piece of 
abrasive articles is formed. When the uniform small piece of abrasive 
articles is formed by the hot pressing method, the sintering process can 
be eliminated since the complete sintering is conducted simultaneously 
with the molding. 
Then, the thus-obtained completely sintered small piece of abrasive 
articles and the material for the matrix are mixed so as to meet the 
purpose, the matrix material being exemplified by a resin such as a phenol 
resin and epoxy resin, all known types of metal that can be used for a 
usual metal bond abrasive article, and glass having a low melting point. 
This mixed material is then heated, hardened at room temperature, or 
molded by pressure so as to be molded into the shape of the abrasive 
article. As a result, the abrasive article is formed. A grinding aid may 
be added to the matrix, the grinding aid being exemplified by: diamond, 
CBN, SiC, alumina, fillers which are usually added to the resin bond 
abrasive articles such as calcium carbonate, and talc, and a solid 
lubricant (molybdenum disulfide, boron nitride, carbon, or the like). 
The thus-obtained composite abrasive-articles made of resin bond, metal 
bond, or vitrified bond are further composed by way of dispersing uniform 
small piece of abrasive articles which has been completely sintered and 
which displays no particle size distribution in the matrix thereof, the 
uniform small piece of abrasive articles being made of diamond 
abrasive-articles or cubic boron nitride abrasive and metal powder. That 
is, the completely sintered and uniform abrasive-articles are dispersed, 
the completely sintered and uniform abrasive-articles having extremely 
reduced particle size. 
The uniform small piece of abrasive-articles precomplete sintering, which 
is used for the composite abrasive-articles according to the present 
invention, is a piece of abrasive-article having a uniform diameter 
involving extremely reduced particle size distribution. Therefore, the 
completely sintered small piece of abrasive-articles obtained by 
completely sintering the former also displays the uniform diameter, it is 
then dispersed and solidified in the matrix. Therefore, the particle size 
of the piece of the abrasive-articles and the weight ratio of the same can 
be optionally arranged to meet the various way of usage of it. 
In order to realize a further uniform particle size of the completely 
sintered piece of abrasive-articles, it is preferable that the uniform 
small piece of abrasive-articles is formed by the screen printing method, 
perforated screen printing method, metal molding method, hot pressing 
method, or molding method. 
The accompanying drawing is a microphotograph of an enlargement of 20 times 
of an embodiment of the composite abrasive-articles according to the 
present invention, the composite abrasive-articles being obtained by 
forming a completely sintered piece of abrasive articles by using a 
uniform small piece of abrasive articles manufactured by the perforated 
screen printing method and by mixing it with resin before being enclosed 
into a predetermined mold. 
The completely sintered piece of abrasive-articles according to the present 
invention is arranged to be a uniformed cylindrical or disc like body 
having a size range of between .phi.0.1.times.0.1 and .phi.5.times.5 mm, 
preferably a range of between .phi.0.5.times.0.5 and .phi.3.times.3 mm in 
the case where it is molded by the screen printing method, perforated 
screen printed method, metal molding method, hot pressing method, or the 
molding method. On the other hand, in the case where the completely 
sintered piece of abrasive-articles is formed in accordance with the 
granulating method, it is arranged to be a spheric body having a size 
range between .phi.0.1 to .phi.5 mm, preferably range between .phi.0.3 to 
.phi.3 mm. 
Although the composite abrasive-articles shown in FIG. 1 use the completely 
sintered piece of abrasive-articles having the same size, another type of 
composite abrasive-articles may be employed, this composite 
abrasive-articles being formed such that two types of small pieces of 
abrasive articles, each type having individual particles sizes are 
dispersed and solidified in the matrix. According to this method, a 
further improved grinding performance can be obtained since the relatively 
large pieces of abrasive articles and relatively small pieces of abrasive 
articles can be dispersed in the matrix with a satisfactory balance 
arranged. 
Then, embodiments will be described. 
Embodiment 1 
60 parts of metal powder consisting of 15 wt % tin and a balance of copper 
and 40 parts of diamond powder having a mean particle size of 120.mu. were 
mixed, and then a solution obtained by dissolving PVB in an organic 
solvent was added so that a paste whose viscosity had been adjusted to be 
preferable for the printing was prepared. Then, a screen with perforations 
of .phi.1.3.times.0.4 t was disposed on a graphite plate having the 
thickness of 3 mm, then the above-described paste was printed by using a 
squeegee. As a result, a uniform small piece of abrasive articles of 
.phi.1.3.times.0.4 t was obtained. The thus-obtained uniform small piece 
of abrasive articles was completely sintered with the graphite plate at 
750.degree. C. for one hour in a hydrogen atmosphere. As a result, a 
planing resin-bonded abrasive-articles was manufactured from 30 parts of 
.phi.1.times.0.3 t completely sintered piece of abrasive articles with 
extremely reduced particle size distribution, 38 parts of diamond powder 
having an average particle size of 120.mu., and a balance of phenol resin. 
Another planing resin bond abrasive-article of .phi.205.times.10 w.times.3 
t consisting of 50 parts of diamond powder having a particle size of 
120.mu. and a balance of phenol resin was manufactured so as to be 
subjected to a comparison made with the planing resin bond 
abrasive-articles according to the present invention. 
These abrasive-articles were mounted on a reciprocating type grinder 
(PSG52DX) manufactured by Okamoto Machine Co., Ltd and a 99% alumina (200 
mm.times.200 mm.times.10 mmt) plate was ground under the following 
conditions, the result being shown in Table 1: 
______________________________________ 
Conditions 
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Wheel Speed 3000 rpm 
Table Speed 10 m/min 
Cross Feed 3 mm 
Downfeed 20 .mu.m/pass 
Coolant soluble type diluted by 
40 times 
______________________________________ 
TABLE 1 
______________________________________ 
Present Invention 
Comparative Example 
______________________________________ 
Grinding Ratio 
625 cc/cc 284 cc/cc 
Grinding Resistance 
13.5 kgf 17 kgf 
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Embodiment 2 
A mixture of 80 parts of metal powder consisting of 10 wt % tin, 17 wt % 
copper, 0.5 wt % phosphorus, and a balance of nickel and 20 parts of 
diamond powder having an average particle size of 45 .mu.m and 5%-water 
solution of PVA were mixed. Then, the thus-obtained mixture was introduced 
into to a commercially available granulating machine so that an .phi.1.1 
mm spheric uniform small piece of abrasive articles was obtained. It was 
then completely sintered at 900.degree. C. for one hour in ammonia cracked 
gas. 
As a result, chips of abrasive-articles of 20 w.times.30L.times.10 t were 
obtained from 40 parts of completely sintered piece of abrasive articles 
of .phi.0.8 mm obtained, 10 parts of calcium carbonate, and a balance of 
epoxy resin. The 15 chips were fixed to a bakelite plate in such a manner 
that 12 chips were fixed to the outermost circumferential direction and 3 
chips were fixed to the inner portion so as to grind the surface of 
granite. In order to make a comparison, comparative examples A and B of 
500 U.S. mesh manufactured by the other manufacturer were subjected to the 
similar surface grinding. 
An Isobe Stone grinder was used to grind 300 mm.times.300mm+10 mmt granite 
at a wheel speed of 500 rpm for 2 minutes with water used for cooling. The 
results are shown in Table 2. 
TABLE 2 
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present Comparative 
Comparative 
Invention 
Example A Example B 
______________________________________ 
Stock 202 g 147 g 110 g 
removal 
______________________________________ 
As is shown from Table 2, the present invention displays an improvement in 
the grinding performance by 30% or more with respect to comparative 
example A, and by 95% with respect to comparative example B. 
Embodiment 3 
90 wt % metal powder containing of 10 wt % tin and a balance of nickel and 
10 wt % diamond powder having a particle size of 170 U.S. mesh were mixed. 
Then, a perforated screen .phi.0.2.times.1.5 t in which a perforation was 
formed was placed on a graphite plate, this perforation being then filled 
with the above-described mixed powder. Then, the perforated screen plate 
was removed after it has been enclosed in this perforation, resulting in a 
uniform small piece of abrasive articles. The thus-obtained uniform small 
piece of abrasive articles was completely sintered with the graphite plate 
at 850.degree. C. for 1 hours in ammonia cracked gas. The thus-obtained 50 
parts of completely sintered piece of abrasive articles of 
.phi.1.5.times.1.0 t, 30 parts of silicon carbide which serves as an 
aggregate, and balance of boro-silicated glass were molded to form a body 
of outer diameter of 205 mm, inner diameter of 199 mm, and height of 10 mm 
so as to be sintered in air at 800.degree. C. The thus-obtained sintered 
body was adhered by an adhesive to an aluminum plate of outer diameter of 
198 mm.times.10 mm so that a vitrified bond grinding wheel containing 
completely sintered piece of abrasive articles was obtained. In order to 
make a comparison, a vitrified bond diamond abrasive-articles having the 
same composition but containing no completely-sintered piece of abrasive 
articles having the grain size of diamond of 170 U.S. mesh and a 
concentration of 75 (concentration of 100=4.4 cts/1 cc of 
abrasive-articles) was subjected to a test. The test was conducted by 
using a grinder similar to that employed in Embodiment 1 and ground under 
the same conditions as those for Embodiment 1. The results are shown in 
Table 3. As is shown from Table 3, the abrasive-articles according to the 
present invention displays an increase in grinding ratio (the value of 
ground work/value of reduction of the abrasive-articles) by 73%. 
TABLE 3 
______________________________________ 
Present Invention 
Comparative Example 
______________________________________ 
Grinding ratio 
295 cc/cc 170 cc/cc 
______________________________________ 
Embodiment 4 
Mixed powder consisting of 3 wt % zinc, 4 wt % of 40 U.S. mesh diamond 
pieces of abrasive article, and a balance of nickel was molded into a 
uniform small pieces of abrasive articles of .phi.1.times.1 t in 
accordance with the metal molding method. It was then completely sintered 
at 750.degree. C. for 0.5 hour in hydrogen atmosphere so that a completely 
sintered piece of abrasive articles (.phi.0.9.times.0.9 t) was obtained. 
Then, 55 parts of metal mixed powder consisting of 7 wt % tin, 45 wt % 
copper, 0.8 wt % phosphorus, and a balance of nickel, 45 parts of the 
above-described completely sintered piece of abrasive articles were mixed. 
The thus-obtained chip of 50L.times.10H.times.2.5W and having a curvature 
radius of 254 mm was sintered at 650.degree. C. for 15 minutes in air in 
accordance with the hot pressing method. Then, 22 chips containing the 
completely sintered piece of abrasive articles were fastened to the 
periphery of an iron plate having an outer diameter of 488 mm, at equal 
intervals by using silver solder so that a cut off wheel was obtained. In 
order to make a comparison, mixed powder consisting of 1.7 wt % zinc, 4 wt 
% tin, 0.4 wt % phosphorus, 25 wt % copper, 2 wt % diamond piece of 
abrasive articles of a particle size of 40 U.S. mesh, and a balance of 
nickel were prepared under the same conditions as those for the present 
invention by the same number. Thus, a cut off wheel of the same shape was 
manufactured for making a comparison. 
The thus-manufactured cut off wheel was used to cut granite of 100 
mm.times.100 mm.times.20 mm with a Maruto cutter MC-420 at a wheel speed 
of 1200 rpm with water used as a coolant. The electric power consumption 
was 2.4A with the cutter according to the present invention, while it was 
3.8A with the comparative example. 
Embodiment 5 
Mixed powder consisting of 10 wt % tin, 5 wt % diamond powder having the 
grain size of 200 U.S. mesh, and a balance of copper was prepared. Then, 
this mixed powder was enclosed in a graphite plate having a multiplicity 
of perforations of .phi.2.times.1 t. The graphite plate in which the mixed 
powder containing diamond was sintered in ammonia cracked gas at 
700.degree. C. for 1.5 hours. As a result, .phi.1.4.times.0.7 t completely 
sintered piece of abrasive articles whose particle size was uniform was 
obtained. 
Furthermore, mixed powder of a similar composition was enclosed in a 
graphite plate having a multiplicity of perforations of .phi.3.5.times.2.5 
t. Thus, completely sintered piece of abrasive articles of 
.phi.2.5.times.1.8 was obtained from the similar manufacturing conditions 
to the above-described conditions. 
Then, 20 chips of the abrasive-articles of 50L.times.5 t.times.5W 
(curvature radius 185 mm) were manufactured, the chip consisting of 30 
parts of .phi.1.4.times.0.7 t completely sintered piece of abrasive 
articles, 25 parts of f2.5.times.1.8 t completely sintered piece of 
abrasive articles, and a balance of epoxy resin. The thus-manufactured 
chips were fixed to an aluminum plate, in the cup shape having an outer 
diameter of 370 mm and inner diameter of 350 mm, at equal intervals by 
using an epoxy bond. 
In order to make a comparison, an abrasive-articles of the same shape 
consisting of 13 parts of 200 U.S. mesh diamond, 8.7 parts of calcium 
carbonate, and a balance of epoxy resin was manufactured. 
They were mounted on a vertical spindle grinding machine manufactured by 
Sansei Ltd. so that 99% alumina of 300 mm.times.300 mm.times.10 mmt was 
ground at 1500 rpm and down feed of 60 .mu./min. The abrasive articles of 
the comparative example overheated due to the grinding work 5 minutes 
after the start of the grinding, causing the color of the resin bond 
portion to be turn red. It was impossible to use it further. 
However, the abrasive-articles according to the present invention smoothly 
ground without no problem to 300 mm.times.300 mm.times.5 mmt' (83 
minutes). 
Embodiment 6 
Mixed powder consisting of 10 wt % tin, 20 wt % copper, 2 wt % diamond 
powder having the average grain size of 12.mu., and a balance of nickel 
was enclosed in a graphite mold in which a multiplicity of .phi.2 
perforations are formed. Then, this mixture was pressed from above and 
beneath by using .phi.2 punches under a load of 100 kg/cm.sup.2, and 
simultaneously electricity was supplied to the graphite mold so as to heat 
it at 650.degree. C. for 15 minutes. As a result, .phi.2.times.2 t 
uniformed and completely sintered piece of abrasive articles was obtained 
in accordance with the hot pressing method. 
A disc-like tool of .phi.120.times.5 t was manufactured by 60 parts of the 
obtained completely sintered piece of abrasive articles and a balance of 
epoxy resin. It was then adhered to a cast plate of .phi.120 with an epoxy 
bond so that a tool for polishing lens was manufactured. 
In order to make a comparison, a tool of the same shape was manufactured 
using an epoxy resin bond containing diamond powder having an average 
grain size of 12.mu. and a concentration of 10. 
Then, they were used to smooth .phi.60.times.10 t Bk-7 glass after they had 
been respectively mounted on Spherical lens grinding machine under 
conditions of 2 kgw, 300 rpm, and soluble type polishing liquid diluted by 
40 times for 15 minutes. As a result, the tool according to the present 
invention displayed the grindability of 4 .mu./sec, but the comparative 
example displayed 0.8 .mu./sec. 
As described above, and according to the present invention, a uniform small 
piece of abrasive article in which diamond powder or cubic boron nitride 
pieces of abrasive articles are dispersed in metal and uniform and 
completely sintered piece of abrasive articles which does not display 
extremely reduced particle size distribution and which is obtained from 
completely sintering the former can be obtained. Then, it is dispersed and 
solidified in resin, metal, or glass having a low melting point. As a 
result, the obtained composite abrasive-articles can be freely controlled 
in its grinding ratio and grinding performance. Furthermore, the 
controllable grinding ratio and grinding resistance displays a significant 
improvement with respect to conventional abrasive-articles. Therefore, the 
most suitable grinding work can be conducted to correspond to the types of 
the material to be ground (material to be ground or material to be cut) 
and the grinding conditions. As a result, working efficiency can be 
improved. Furthermore, a pulverization process can be eliminated from the 
manufacturing processes for the composite abrasive-articles regardless of 
the fact whether the sintering is complete or incomplete. A free and 
optional selection of type of metal can be conducted. Furthermore, since 
the composite abrasive-articles is formed by completely sintered piece of 
abrasive articles which can be perfectly used without involving the 
portion left from the screening work, the manufacturing yield can be 
improved and thereby the manufacturing processes can be reduced so that 
cheap composite abrasive-articles can be manufactured.