Development of Partially Ni-coated for Electroplated

Yu Zhang1, Yasuhiro Tani2, Junji Murata3 and Takahiro Hashizume4 1 College of Science and Engineering, Ritsumeikan University, Japan, [email protected] 2 College of Science and Engineering, Ritsumeikan University, Japan, [email protected] 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 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 , Grinding, Abrasive distribution

1．Introduction shown in Fig.1(a), sharp edges of Ni-coated diamond Diamond tools are the most popular for machining hard and abrasives are covered and hidden under the nickel membrane. brittle materials, silicon, glass, ceramics, cemented carbide, etc. A Therefore, the Ni-coated diamond abrasives are gripped strongly on diamond tool with fine grains and superior wear resistance is the tool body. In composite electroplating process, Ni-coated adopted for finishing process of free-formed dies and molds. The abrasives are also deposited on the abrasives which were deposited diamond grinding tools could be produced by an electroplating previously. That leads to the abrasives aggregation on the tool body. process at low cost, so that has been in the mainstream in the Fig.1(b) shows the image of using non-coated diamond abrasives. fabrication of diamond tools1)-5). To improve the shape accuracy and Because there is not any metal membrane on the non-coated grinding performance of the tool, a single layer of diamond abrasives abrasives, the cutting edges and the abrasive distribution are better is electroplated on tool body. The electroplating process delivers a than that of Ni-coated abrasives, but gripping force is weaker. If the homogeneous layer with embedded in nickel alloy with abrasives have both merits of the non-coated abrasives and the 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 6)7) Sato discussed the growth of electrodeposited layer around Fig.1 Schematic view of growth of electrodeposited layer along abrasives and the gripping force of abrasives which are coated by abrasive surface, (a) Non-coated diamond, (b) Ni-coated metal membrane or not. Diamond abrasives coated with nickel diamond, (c) Partially Ni-coated diamond membrane are used wildly in composite electroplating process. As

Ni-coated abrasives, diamond tool that has shape cutting edges and X-ray spectrograph (EDS). It was able to be confirmed that a partial high gripping force could be produced as shown in Fig.1(c), authors of diamond (carbon) exposed from the nickel membrane. Stripping attempt to produce the partially Ni-coated diamond abrasives and time is an important factor to control the removed mass of nickel apply it in manufacturing diamond tools in this study. membrane. Fig.4 shows the percentage of atomic number of carbon and nickel on the surface of the partial diamond abrasives which are 3. Production of partially Ni-coated diamond abrasives stripped off in 30, 40 and 50 minutes. The ratio of carbon increased Partially Ni-coated diamond abrasives are newly developed to as stripping time. It is clarified that the nickel coat has almost overcome the problems with using the Ni-coated abrasives or the disappeared on the abrasives which are stripped off in 50 minutes. non-coated ones. To produce the partially Ni-coated abrasives, a Therefore, for producing the partially Ni-coated diamond abrasives portion of nickel membrane is stripped off from the full Ni-coated used in this study, the stripping time is set to 40 minutes. abrasives. Fig.2 shows the schematic diagram of the making process of partially Ni-coated diamond abrasives. Firstly, wax is thinly 4. Fabrication of electroplated diamond tools painted on a stainless steel plate and half of the Ni-coated abrasives 4.1 Electroplating characteristics of various abrasives are buried in the wax. Secondly, the stainless plate was soaked in a Partially Ni-coated diamond abrasives, commercial available full nickel stripping bath. Table 1 shows the solution composition of the Ni-coated diamond abrasives and non-coated diamond abrasives are stripping bath and the stripping conditions. The nickel coat which is used to fabricate tools. Cleaning of the substrate surface (tool body) not buried in the wax is stripped off from the abrasives and sharp is conducted by acetone and then degreasing and acid pickling in cutting edges are exposed. Lastly, the stainless plate is soaked in order. The electroplating processes are carried out in 3 steps, toluene solution for dissolving the wax. The diamond abrasives were pre-plating, complex plating and after-plating. Cleaning with distilled taken out by filter. water between various steps is carried out not to bring the former Fig.3 shows results of the surface elemental analysis of the solution to the solution of the next step. partially Ni-coated diamond abrasives with using energy dispersion 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 Composition of bath and plating conduction

Fig.3 Elemental analysis of surface of partially Ni-coated diamond, (a) SEM image, (b) Nickel, (C) Carbon

Table 1 Stripping conditions

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 Fig.4 Schematic diagram of electroplating setup 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 Fig.5 Photographs of diamond abrasives on tool surface were selected randomly on the surface of tools and the number of (a) Ni-coated diamond, (b) Non-coated diamond, abrasives deposited in 150μm square was counted. If 2 or more (c) Partially Ni-coated diamond 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 Fig.6 Distribution of various abrasives on surface of tools 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 Fig.7 Distribution of abrasives in different complex plating time high grinding ability and that would be discussed in the following.

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.8 SEM photograph of partially Ni-coated diamond on the tool 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 Fig.9 Schematic diagram of grinding 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. Fig.10 Grinding force of tools with different abrasives 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 Coating, CIRP Annals - Manufacturing Technology, Vol.49, of full Ni-coated abrasives. Though the aggregation of No. 1 (C series), pp. 157-160. non-coated diamond abrasives almost occurs, the deposition [4] Kinji Sato, Kazuo Suzuki., 1982, Manufacture of Electro- speed of abrasives was too low for fabricating tools efficiently. deposit Diamond Wheel and Its Grinding Action, Journal of 3) It was confirmed that the grinding ability of the tool used the The Surface Finishing Society of Japan, Vol.33, No.6, partially Ni-coated abrasives is smallest in this study. The pp.285-290 partially Ni-coated diamond abrasives are most suitable to [5] Hidetaka Hayashi, 2000, Particle Composition Mechanism of fabricate diamond tools. Composite Plating, The Journal of the Surface Finishing Society of Japan Vol.51, No.11, pp.1062-1068. (in Japanese). [6] Kinji Sato, Toshio Yokoyama, Kazuo Suzuki., 1995, Holding References Force of Nickel Layer for Single Grit on Electrodeposited [1] C. Heinzel, K. Rickens., 2009, CIRP Annals - Manufacturing Diamond Wheel, The Journal of the Surface Finishing Society Technology, Vol.58, No. 1 (C series), pp. 315-318. of Japan, Vol.46, No.4, pp.371-374. (in Japanese). [2] Heung-Kil Park, Hiromichi Onikura, Osamu Ohnishi, Ahmad [7] T. Semba, H. Sato ., Tomoyuki Saiki, 2004, Development of Sharifuddin., 2010, Development of micro-diamond tools Electroforming Technique for Fabricating Electroformed through electroless composite plating and investigation into Diamond Tool with High Grain Density, The Japan Society of micro-machining characteristics, Vol.34, No.3, pp. 376-386. Mechanical Engineers, (C series), Vol.70, No.694, pp.1849- [3] T. Semba, H. Sato ., 2000, Development of Electroformed 1854. (in Japanese). Diamond Tool with Fine Grains Covered with Metal Oxide