Development of Partially Ni-coated Diamond Abrasives
for Electroplated Tools
Yu Zhang1, Yasuhiro Tani2, Junji Murata3 and Takahiro Hashizume4
1
College of Science and Engineering, Ritsumeikan University, Japan, zhangyu@fc.ritsumei.ac.jp
2
College of Science and Engineering, Ritsumeikan University, Japan, tani@fc.ritsumei.ac.jp
3,4
College of Science and Engineering, Ritsumeikan University, Japan,
Abstract:
Electroplated diamond tools with superior proportional limit and wear resistance are developed for grinding hard and
brittle materials. Application of Ni-coated diamond abrasives is effective for high-speed manufacturing of
electroplated grinding tools. However, the sharpness of the grinding tool decreases because nickel membrane was
attached on the surface of abrasives. The phenomenon of abrasives aggregation is also serious. In this study, we
developed partially Ni-coated diamond abrasives. The production method of the partially Ni-coated abrasives was
described and the effect of application of the abrasives was investigated. As the result, the problems with using
Ni-coated abrasives or non-coated abrasives could be solved and the grindability of electroplated tools was improved.
Key words: Electroplating, Diamond tool, Grindability, Diamond abrasive, Grinding, Abrasive distribution
1．Introduction
Diamond tools are the most popular for machining hard and
brittle materials, silicon, glass, ceramics, cemented carbide, etc. A
diamond tool with fine grains and superior wear resistance is
adopted for finishing process of free-formed dies and molds. The
diamond grinding tools could be produced by an electroplating
process at low cost, so that has been in the mainstream in the
fabrication of diamond tools1)-5). To improve the shape accuracy and
grinding performance of the tool, a single layer of diamond abrasives
is electroplated on tool body. The electroplating process delivers a
homogeneous layer with diamonds embedded in nickel alloy with
high speed. In order to facilitate the adhesion of diamond abrasives,
the diamond abrasives are treated by electroless plating process and
coated by nickel membrane, generically. Therefore, the cutting
edges of the abrasive are coated with nickel membrane, grinding
performance of the diamond tools decreases. Moreover, a
phenomenon of abrasives aggregation generates usually and leads to
bad distribution of abrasives. In this paper, in order to solve those
problems, authors developed partially Ni-coated diamond abrasives,
which are produced from the commercially available full Ni-coated
diamond abrasives. The adhesion characteristics of partially
Ni-coated abrasives are discussed, too. The grindabilities of diamond
tools, which are fabricated by using Ni-coated abrasives or partially
Ni-coated abrasives or non-coated abrasives, are evaluated.
2. Growth of electrodeposited layer around diamond
abrasives
Sato6)7) discussed the growth of electrodeposited layer around
abrasives and the gripping force of abrasives which are coated by
metal membrane or not. Diamond abrasives coated with nickel
membrane are used wildly in composite electroplating process. As
shown in Fig.1(a), sharp cutting edges of Ni-coated diamond
abrasives are covered and hidden under the nickel membrane.
Therefore, the Ni-coated diamond abrasives are gripped strongly on
the tool body. In composite electroplating process, Ni-coated
abrasives are also deposited on the abrasives which were deposited
previously. That leads to the abrasives aggregation on the tool body.
Fig.1(b) shows the image of using non-coated diamond abrasives.
Because there is not any metal membrane on the non-coated
abrasives, the cutting edges and the abrasive distribution are better
than that of Ni-coated abrasives, but gripping force is weaker. If the
abrasives have both merits of the non-coated abrasives and the
Fig.1 Schematic view of growth of electrodeposited layer along
abrasive surface, (a) Non-coated diamond, (b) Ni-coated
diamond, (c) Partially Ni-coated diamond
Ni-coated abrasives, diamond tool that has shape cutting edges and
high gripping force could be produced as shown in Fig.1(c), authors
attempt to produce the partially Ni-coated diamond abrasives and
apply it in manufacturing diamond tools in this study.
3. Production of partially Ni-coated diamond abrasives
Partially Ni-coated diamond abrasives are newly developed to
overcome the problems with using the Ni-coated abrasives or the
non-coated ones. To produce the partially Ni-coated abrasives, a
portion of nickel membrane is stripped off from the full Ni-coated
abrasives. Fig.2 shows the schematic diagram of the making process
of partially Ni-coated diamond abrasives. Firstly, wax is thinly
painted on a stainless steel plate and half of the Ni-coated abrasives
are buried in the wax. Secondly, the stainless plate was soaked in a
nickel stripping bath. Table 1 shows the solution composition of the
stripping bath and the stripping conditions. The nickel coat which is
not buried in the wax is stripped off from the abrasives and sharp
cutting edges are exposed. Lastly, the stainless plate is soaked in
toluene solution for dissolving the wax. The diamond abrasives were
taken out by filter.
Fig.3 shows results of the surface elemental analysis of the
partially Ni-coated diamond abrasives with using energy dispersion
X-ray spectrograph (EDS). It was able to be confirmed that a partial
of diamond (carbon) exposed from the nickel membrane. Stripping
time is an important factor to control the removed mass of nickel
membrane. Fig.4 shows the percentage of atomic number of carbon
and nickel on the surface of the partial diamond abrasives which are
stripped off in 30, 40 and 50 minutes. The ratio of carbon increased
as stripping time. It is clarified that the nickel coat has almost
disappeared on the abrasives which are stripped off in 50 minutes.
Therefore, for producing the partially Ni-coated diamond abrasives
used in this study, the stripping time is set to 40 minutes.
4. Fabrication of electroplated diamond tools
4.1 Electroplating characteristics of various abrasives
Partially Ni-coated diamond abrasives, commercial available full
Ni-coated diamond abrasives and non-coated diamond abrasives are
used to fabricate tools. Cleaning of the substrate surface (tool body)
is conducted by acetone and then degreasing and acid pickling in
order. The electroplating processes are carried out in 3 steps,
pre-plating, complex plating and after-plating. Cleaning with distilled
water between various steps is carried out not to bring the former
solution to the solution of the next step.
In this study, carbon steel (JIS S45C) is used for tool body which
is 10mm in diameter and 50mm in length. The electroplating bathes
are shown in Table 2. A nickel/phosphorus (Ni/P) electroplating bath
(sulfamate bath) is used in the complex plating, which is composed
Fig.2 Production process of partially Ni-coated diamond abrasives
Fig.4 Ratio of Carbon and Nickel atom on the surface of
partially Ni-coated diamond abrasives
Table 2
Fig.3 Elemental analysis of surface of partially Ni-coated
diamond, (a) SEM image, (b) Nickel, (C) Carbon
Table 1 Stripping conditions
Composition of bath and plating conduction
with nickel sulfamate, nickel chloride, boric acid, phosphorous acid,
Saccharin and diamond abrasives. Particle size of all diamond
abrasives is 30~40μm. A Watt’s both is used to pre-plating and
after-plating. The experiments are performed at 60 ℃ in complex
plating and at 50 ℃ in pre-plating and after-plating The pH level
was regulated in 3.5 to 4.0 for all baths.
The schematic diagram of electroplating setup was shown in Fig.4.
Three nickel round bars as anode were fixed on the inner wall of
beaker. The tool body as cathode was attached on lower part of a
shaft which was rotated by agitator. The upper part of shaft was
connected to an electronic power supply with an electric cable. The
current density was set to 15A/dm2 and the plating time was set at
120s in the pre-plating and the after-plating process. For the complex
plating, the current density was set to 20A/dm2 and the plating time
is set to 30s.
The distribution of 3 kinds of diamond abrasives on tools was
shown in Fig.5. It was known that, in the case of using full Ni-coated
diamond abrasives, a large amount of abrasives deposited on the tool
body, but these abrasives show non-uniform distribution and
aggregated on the tool body. On the other hand, the non-coated
diamond abrasives almost deposited. In contrast to the former 2
kinds of abrasives, a lot of partially Ni-coated diamond abrasives
deposited and the distribution of abrasive is much more uniform on
the tool, though the amount of abrasives was a little lower than that
of full Ni-coated ones.
To evaluate numerically the distribution of abrasives, 200 areas
were selected randomly on the surface of tools and the number of
abrasives deposited in 150μm square was counted. If 2 or more
abrasives connected together, the abrasives are judged to aggregate.
The number of abrasives aggregated was also counted. The
statistical results are in Fig.6. Looking at the aggregation percentage
of full Ni-coated abrasives, it amounts to about 90%. In case of
partially Ni-coated diamond abrasives, the amount of abrasives
aggregated was nearly 70% reduced. In the case of non-coated
diamond abrasives, the percentage of agglutinated abrasives is 30%
or so, but the areas deposited none abrasive are too large, about 50%.
The distribution of partially Ni-coated diamond abrasives is the best
uniform on the tools among 3 kinds of abrasives.
To increase the density of partially Ni-coated diamond abrasives
on tool, complex plating time was extended from 30s to 60s and 90s.
Fig.7 shows the distribution of partially Ni-coated diamond
abrasives in different complex plating time. As the complex plating
time increase, the rate of abrasives aggregation also became higher.
It was also known that the areas contained 9 or more abrasives were
less than 10% with using the partially Ni-coated abrasives than that
of the full Ni-coated abrasives. It was clarified that, the areas existing
none abrasive with using partially Ni-coated diamond abrasive and
Ni-coated one were in equivalent level. In case of using the
non-coated abrasives, the areas existing none abrasive are very large
and accounted about 50%. Therefore, it was proved that the
agglutination of abrasives could be restrained and the distribution of
abrasives could be improved with using partially Ni-coated diamond
abrasives.
Fig.8 shows the partially Ni-coated diamond abrasives on the tool.
It could be observed that the part with nickel coat adheres to the tool
and the part without nickel coat faces outwardly. Therefore, as the
sharp cutting edges face outwardly, we thought that the tool have
high grinding ability and that would be discussed in the following.
Fig.4 Schematic diagram of electroplating setup
Fig.5 Photographs of diamond abrasives on tool surface
(a) Ni-coated diamond, (b) Non-coated diamond,
(c) Partially Ni-coated diamond
Fig.6 Distribution of various abrasives on surface of tools
Fig.7 Distribution of abrasives in different complex plating time
4.2 Grinding characteristics of electroplated diamond tools
In order to investigate the grinding ability of tools electroplated
with different diamond abrasives, grinding experiments were carried
out on soda glass with dimensions of 30mm×50mm×4mm.The
abrasive density on the each tool was set to150 abrasive/mm2 with
regulating complex electroplating time. Even if the complex
electroplating time is increased, the abrasive density is still low with
using non-coated diamond abrasives. We increased the
concentration of non-coated abrasives in the complex electroplating
bath.
Fig.9 shows the schematic diagram of grinding. A grinding center
made by Hitachi tool was used to grind a soda glass. Spindle rotation
speed was set to 2000rpm. Cutting depth and feed speed were set to
30μm and 30mm/min, respectively. The grinding force was
measured by a dynamometer (9257B, Kistler Japan Co., Ltd.). The
normal grinding force was used to evaluate the grinding ability of
tools, which are fabricated with using full Ni-coated abrasives,
partially Ni-coated abrasives or non-coated abrasives.
Fig.10 shows the grinding forces with using different diamond
abrasives. For the tool with using the non-coated abrasives, the
grinding force increased with grinding passes. The reason is thought
that the gripping force of non-coated abrasives is weak and the
abrasives dropped off from the tool in grinding process. The
gripping force of full or partially Ni-coated abrasives is higher than
that of non-coated abrasives. The grinding force of partially
Ni-coated abrasives is smaller than that of the full Ni-coated ones.
Therefore, the diamond tools fabricated with using the partially
Ni-coated abrasives has high gripping force and shape cutting edges.
5. Conclusions
In this study, with the aim of improving the grinding ability of
diamond tools, partially Ni-coated diamond abrasives were
developed. By comparing non-coated and full Ni-coated diamond
abrasives, the grinding ability and the electroplating characteristics of
partially Ni-coated diamond abrasives was investigated. The results
can be summarized as follows:
1) Partially Ni-coated abrasive is able to fabricate from full
Ni-coated abrasives. The best stripping off time is 40 minutes.
2) The deposition speed of partially Ni-coated abrasives is a little
lower than that of full Ni-coated abrasives. The abrasive
distribution of partially Ni-coated abrasives is better than that
of full Ni-coated abrasives. Though the aggregation of
non-coated diamond abrasives almost occurs, the deposition
speed of abrasives was too low for fabricating tools efficiently.
3) It was confirmed that the grinding ability of the tool used the
partially Ni-coated abrasives is smallest in this study. The
partially Ni-coated diamond abrasives are most suitable to
fabricate diamond tools.
Fig.8 SEM photograph of partially Ni-coated diamond on the tool
Fig.9 Schematic diagram of grinding
Fig.10 Grinding force of tools with different abrasives
[4]
[5]
[6]
References
[1] C. Heinzel, K. Rickens., 2009, CIRP Annals - Manufacturing
Technology, Vol.58, No. 1 (C series), pp. 315-318.
[2] Heung-Kil Park, Hiromichi Onikura, Osamu Ohnishi, Ahmad
Sharifuddin., 2010, Development of micro-diamond tools
through electroless composite plating and investigation into
micro-machining characteristics, Vol.34, No.3, pp. 376-386.
[3] T. Semba, H. Sato., 2000, Development of Electroformed
Diamond Tool with Fine Grains Covered with Metal Oxide
[7]
Coating, CIRP Annals - Manufacturing Technology, Vol.49,
No. 1 (C series), pp. 157-160.
Kinji Sato, Kazuo Suzuki., 1982, Manufacture of Electrodeposit Diamond Wheel and Its Grinding Action, Journal of
The Surface Finishing Society of Japan, Vol.33, No.6,
pp.285-290
Hidetaka Hayashi, 2000, Particle Composition Mechanism of
Composite Plating, The Journal of the Surface Finishing
Society of Japan Vol.51, No.11, pp.1062-1068. (in Japanese).
Kinji Sato, Toshio Yokoyama, Kazuo Suzuki., 1995, Holding
Force of Nickel Layer for Single Grit on Electrodeposited
Diamond Wheel, The Journal of the Surface Finishing Society
of Japan, Vol.46, No.4, pp.371-374. (in Japanese).
T. Semba, H. Sato., Tomoyuki Saiki, 2004, Development of
Electroforming Technique for Fabricating Electroformed
Diamond Tool with High Grain Density, The Japan Society of
Mechanical Engineers, (C series), Vol.70, No.694, pp.18491854. (in Japanese).