DEVELOPMENT OF A MICRO DIAMOND GRINDING TOOL BY COMPOUND PROCESS
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30-10-2010, 10:36 AM
DEVELOPMENT OF A MICRO DIAMOND GRINDING
TOOL BY COMPOUND PROCESS
College Of Engineering, Trivandrum
DEVELOPMENT OF A MICRO DIAMOND GRINDING.docx (Size: 2.2 MB / Downloads: 129)
INDEX OF CONTENTS
Topics Page No
1. INTRODUCTION -1
2. EXPERIMENTAL HARDWARE -3
2.1. Developed Tabletop Machining Center. -3
2.2. Design of the Miniature Electroforming Tank. -4
3. EXPERIMENTAL PROCEDURES -6
3.1. Influence of the Anodic Shape. -6
3.2. Experiment for the Best Electroforming Zone. -7
3.3. Micro-Tool Shaft Machining. -10
3.4. Effect of the Funnel Mold. -11
4. RESULT -14
5. VERIFICATION OF MICRO DIAMOND GRINDING TOOL -16
6. CONCLUSIONS -19
7. REFERENCES -20
LIST OF FIGURES
Name Page No
Fig.1. Developed tabletop hybrid machining center -3
Fig.2. Principle of WEDG -4
Fig.3. Proposed miniature electroforming tank -5
Fig.4. Identifying the best electroforming zone, Substrate placed horizontally -7
Fig.5. Distribution of current density -8
Fig.6. Comparison of amounts of diamond grains -9
Fig.7. Various micro-tool shafts after micro-EDM -10
Fig.8. Design and test of the miniature funnel mold -12
Fig.9. Comparison of diamond grain content with and without the funnel mold -13
Fig.10. Finished various micro-diamond tools -14
Fig.11. Close-up view of the electroformed diamond layer -15
Fig.12. Illustration of the micro-grinding -16
Fig.13. Finish-grinding the inner taper surface -17
Fig.14. Surface roughness on the inner taper surface -18
The development of integrates micro-Electron Discharge Machining (micro-EDM) with precision composite electroforming technique is presented to efficiently produce a micro-grinding tool. First, the metal substrate is cut down to 50µm diameter using WEDG, and then the micro-diamonds with 0–2µm grain is plated on the surface of the substrate by composite electroforming. The good circularity of the diamond tool can be obtained by arranging the nickel spherules array on the anode. To allow the diamond grains to converge toward the cathode and to increase the amount and the distribution rate of the diamond grains on the cathode a novel miniature funnel mold is designed. The thickness of the electroformed layer is controlled to within 25µm. A micro-ZrO2 ceramic ferrule is grinded to verify the proposed approach. The surface roughness of Ra = 0.08µm is obtained. This tool, which depends on machining applications, can be applied during the final machining. Applications include dental drilling tools, components, precise tools, medical instruments, communications systems, and are utilized by the national defence industry. The developed micro-tool is utilized to machine hard and brittle materials, such as optical glass, fine ceramics, and tungsten carbide, and for micro-cutting or nano-grinding
Micro-manufacturing processes are not only used for the production of micro-systems but increasingly also for the machining of surfaces, the surface being influenced by the dimensions and the shape of the integrated structures. They are applied in optical, electronic, precise tools, medical instruments and communications systems, these micro-parts and structures are required to develop and fabricate low-cost tools that are micro-sized and have increased wear resistance. A machining mechanism cannot be applied to micro-parts and structures due to thermal stress, thermal deformation and the surface degenerating layer of the machined material. The production of these components is usually done by manufacturing technologies originated in semiconductor processing. To avoid the technological and economical limitations of these processes, cutting and non-conventional processes well known from the macroscopic world are increasingly applied in micro-technology.
This study presents the development of a high-speed electroformed micro diamond grinding tool with thick nickel-diamond coatings with micro-Electron Discharge Machining (micro-EDM). The developed micro-tool is utilized to machine hard and brittle materials, such as optical glass, ﬁne ceramics, and tungsten carbide, and for micro-cutting or nano-grinding. The tool shaft surface provides a reposed base for the floating diamonds. Nickel ions and diamond grains are combined via an electrochemical mechanism to a composite electroformed layer that has two phases: the continuous phase of the metal bonder made of pure nickel, and the discontinuous phase of grinding grain which is fixed with a micro-diamond.
To increase the diamonds per unit area and the amount of exposed cutting edge thereby improving the cutting properties and tool life, a diamond grain 0–2µm in diameter is employed. This reduces micro-miniaturizing of tool and increases the lifetime of the tool. The combined force of the diamond can be enhanced by nickel due to ions piling up one by one. Additionally, micro-tool strength is increased. The ﬁxed diamond with the nickel layer for cementing forms the cutter. To increase the strength of the proposed micro-grinding tool, the tool shaft is made of tungsten carbide in ultra-fine particles. Its diameter is reduced to only 50µm by micro-EDM
2. EXPERIMENTAL HARDWARE
The experiment is carried out in two stages. First, the micro-tool shaft is cut to required dimension by using micro-EDM. Second, the thick nickel-diamond coating is plated on the shaft by composite electroforming.
2.1. Developed Tabletop Machining Center
The work material of fine tungsten carbide, 300μm in diameter is cut down to the required dimensions using the developed tabletop machining center (Fig.1). The machining center with 10 nm resolution, due to its modularized design, can perform general micro-milling, micro-EDM, micro-high speed milling, micro-EDM milling, and micro-measurement on-line, a swell as micro-wire-EDM.
Fig.1. Developed tabletop hybrid machining center 
This study uses only on micro-EDM. The metal substrate is easily machined to a very small diameter using the designed WEDG (Wire Electro Discharge Grinding) this is also good to producing accurate circularity and cylindricity (Fig. 2). 
Fig.2. Principle of WEDG 
2.2. Design of the Miniature Electroforming Tank
A miniature composite working tank with a perfect convectional design is constructed (Fig. 3) for the electroforming process and also for the good dispersive effect of the diamond grains in the electroforming liquid, so that a uniform composite electroforming layer is acquired. This design has the following advantages.
1. It is simple and inexpensive
2. Provides an airtight circulation space for creating a non-directional convectional liquid, 3. Increasing the displacement of nickel ions and dispersion of diamond grains
4. It saves the electroforming solution and diamonds
The concentration of the electroforming solution can be kept stable with no change during the whole experiment. A partition is given in the tank to resists flushing, minimizes turbulent flow and improves deposition efficiency in the cathode. This partition in the working tank separates the zone of the flushing liquid from the depositing diamond. And also reduce the energy with which the solution impacts the micro-substrate, and the diamond grains are then uniformly dispersed in the tank. The liquid is flow to the electroforming zone through an array of micro-holes and the gap between the partition’s plate and tank’s bottom. Then the some liquid flows upward and circulates within the working tank, and some flows out of the working tank is pumped and delivered back into the tank through the top using a micro-DC motor. The electroforming solution he liquid entrance is below the liquid surface to eliminate excessive spraying and turbulent flow.
Fig.3. Proposed miniature electroforming tank 
3. EXPERIMENTAL PROCEDURES
3.1. Inﬂuence of the Anodic Shape
The circularity is very important in the time of formation of micro grinding tool. The shape and dimensional accuracies of the machined hole and surfaces are affected during machining when micro-tool circularity is poor. It is difficult to make good circularity on the micro-grinding tool with an average diameter 150µm. the shape of pure nickel in the anode affects the correct form of the electroformed diamond tool. The shapes, including (a) single block, (b) double blocks, © holed block, and (d) spherules array, of the nickel in the anode is applied and tested individually.
In the same experimental parameters, the best circularity is achieved when using the spherules array. Due to the volume of the nickel spherule is small enough so that it can provide a good dissolution rate and keep a low dissolution voltage. Thus the nickel ions can have a good and uniform precipitation in the anode. With the convectional design for the electroforming solution, the nickel ions have good fluidity and are steadily and non-directionally deposited on the substrate. From this experiment, good circularity of the micro-tool can be obtained with spherules array. Therefore the spherules array of pure nickel in the anode is used to make the micro diamond grinding tool in this study. To increase the diamonds per unit area and the amount of exposed cutting edge there by improving the cutting properties and tool life a diamond grain 0–2μm in diameter is employed.
3.2. Experiment for the Best Electroforming Zone
In the electroforming process the plating of diamond is not carried out uniformly on the tool shaft. will differ with different electroforming zones in the tank. Therefore to find out the best electroforming zone, that is the zone with highly filled diamond grains. Laddered and horizontal electroforming is tested to identify the proper electroforming zone (Fig. 4). The four micro-pillared metal substrates, including A, B, C and D, are lined up and placed horizontally on the conducting post in the cathode, and the interval between the pillars is 30mm. 
Fig.4. Identifying the best electroforming zone, Substrate placed horizontally 
Fig. 5 shows the distribution of current density on the substrate and the result of the appearance of the product. The electroformed substrate is shaped like a mushroom head at the free end of the substrate. It causes poor form accuracy on the micro-diamond tool. The strongest current density is located at the sharp corner so the mushroom head is formed at these corners on the free end. There are three approaches used to prevent the current crowding effect. They are
1. Lengthening the distance between the cathode and anode
2. Filleting on the end corner of the substrate
3. And using a non-conducting material such as PMMA to disconnect from the strongest current density
Fig.5. Distribution of current density 
The experiment is conducted and the result obtained at different zone is shown in Fig. 6. The SEM photograph is used to comparisons of the amount of diamonds at different zone in the experiment. A comparatively good result for the amount and distribution rate of diamonds exists in zone C because that zone has the lowest flush of electroforming liquid and is proper distance away from the anode. Only some diamonds are plated onto the substrate in zones A, B and D. It is due to the undue flush generated in these zones. And non-fine and non-smooth texture is produced on the surface of electroformed layer in zones A and B due to there is a small distance between the two zones and the anode. The excessive current density causes the rough surface on the electroformed layer to occur. Hence the C zone is selected for the main electroforming zone because the chances of catching and ﬁxing the diamonds are increased in the zone C.
Fig.6. Comparison of amounts of diamond grains 
3.3. Micro-Tool Shaft Machining
The tool shaft surface provides a reposed base for the floating diamonds. To increase the strength of the proposed micro grinding tool, the tool shaft is made of tungsten carbide in ultra-fine particles. The outer diameter of the grinding tool is designed fromØ100µm to Ø200µm; hence the shaft diameter is machined by WEDG  to between Ø50µm and Ø150µm to electroform the abrasives on a single side up to a 25µm thickness, which provides quantities of sufficient diamond grains for ﬁne ﬁnishing. The substrates of the micro-grinding tools have various shapes is made for the different application some of them are shown in fig-(1) straight, (2) ﬂuted and (3) tapered (4)Fluted (Fig. 7).
Fig.7.Various micro-tool shafts after micro-EDM 
3.4. Effect of the Funnel Mold
In this experiment the diamond is plated on substrate surface by using electroforming process. Fixing of the micro-diamond grains on the metal cathode is based on probability. Because there is no control of micro diamond grain in the electroforming tank the diamonds covered continuously by nickel ions once the diamond grain is fixed. A composite electroformed layer that has two phases: the continuous phase of the metal bonder made of pure nickel, and the discontinuous phase of grinding grain which is fixed with a micro-diamond. The combined force of the diamond can be enhanced by nickel due to ions piling up one by one.
Through a continuous process, the diamonds are joined with the substrate permanently when the nickel coating thickness exceeds the diamond radius. This is due to the fact that there is only a physical relationship not a chemical reaction between nickel ions and diamond grains. The combination of nickel ions and diamonds is not controlled by a chemical reaction. So for controlling and increase the concentration of diamond grains a funnel mold is made is shown in Fig.8. The funnel mold is partitioned into two sections by a gap. The gap is adjustable to allow the diamond grains and nickel electroforming solution to exit from the gap. It is also increase the displacement of nickel ions and the distribution of diamond grains on the cathode
Fig.8. Design and test of the miniature funnel mold 
The mold’s entrance is designed as an inner tapered hole through which diamond grains ﬂow, increases gradually when scattered diamond grains drop slowly from the top to the bottom of the working tank. The funnel mold is located on the cathode, the substrate becomes surrounded by number of diamond grains since many diamond grains collect around the cathode. So the probability of ﬁxing diamond grains onto the substrate surfaces largely increases. Fig. 8 shows the testing of electroforming by using funnel mold. While using of material such as PMMA to make the funnel mold, it also used as a non-electrically conductive material to separate from the high current density and there by reduce the current crowding effect.
Fig. 9 shows the experimental results. It shows that there is less number of diamond grains are plated on the substrate without the funnel mold. While electroforming is done with funnel mold the amount of diamond grains plated on the shaft surface is large enough and the grains are uniformly distributed on the metal substrate, and more diamonds are covered by the nickel layer. Experimental results verify that the miniature funnel mold increases the concentration and distribution of diamond grains. And it will also reduce the flushing of electroforming solution, the energy with which the solution impacts the micro substrate.
Fig.9. Comparison of diamond grain content with and without the funnel mold 
The two kinds of micro-metal tools are fabricated in accordance with the above mentioned conditions. Fig.10 displays various ﬁnished micro-grinding tools. These tools are used for the ﬁne grinding of micro-holes, slots, and other applications. Fig. 11 is a magniﬁcation of the electroformed surface. The electroformed layer with a thickness of 25µm can be accurately obtained. As for the electroformed diamonds, they belong to a multilayer structure. In fig. 11 it will show a layer of micro diamond grain with nickel coating it will have thickness of 25µm.
Fig.10.Finished various micro-diamond tools 
The insight figure in Fig. 11 shows the ﬁnished surface of a micro-grinding tool. These diamond grains are electroformed non-directionally into the nickel layer, some of diamonds are partially visible on the electroformed surface, and some are fully embedded into the electroformed layer. Due to the nickel ions piling up one by one, a good combined strength between the micro-diamond grain and the nickel layer can be achieved. To increase the diamonds per unit area and the amount of exposed cutting edge thereby improving the cutting properties and tool life a diamond grain 0–2μm in diameter is employed.
Fig.11. Close-up view of the electroformed diamond layer 
5. VERIFICATION OF MICRO DIAMOND GRINDING TOOL
For verification of the surface roughness a surface machined by micro diamond grinding tool a ferrule which is made of ZrO2 ceramic is ﬁnely grinded. The micro-ferrule and the micro-tapered grinding tool are tightly clamped by the micro-chucks. The revolutions of the micro-work piece and micro-tool are at 500 and 100,000 rpm, respectively, besides opposite rotating in direction. The micro-diamond grinding tool is slowly fed along the inner taper direction. The illustration of the micro-grinding is shown in Fig. 12.
Fig.12. (a) Illustration of the micro-grinding 
Two kinds of different micro-diamond tools in grain diameter are employed to compare the grinding surfaces. The diamond grain-diameters of the micro-tool are 15–20µm and 0–2µm respectively. Each cutting depth is accurately controlled within 1µm during fine grinding process after rough grinding.
The finish-grinding inner taper surface is shown and the close-up view of the SEM photograph is used to comparison between the rough and fine grinding. It is displayed in Fig. 13. The different between the two surface roughnesses is obtained. The more surface roughness is obtained when using fine grinding with a diamond grain size 0–2µm.
Fig.13. Finish-grinding the inner taper surface 
The surface roughness, inspected by a 3D surface proﬁling system (SNU Precision Company, Korea) is given in Fig. 14, and the surface roughness is
Ra = 0.085µm.
Fig.14. Surface roughness on the inner taper surface 
The development of integrates micro-Electron Discharge Machining (micro-EDM) with precision composite electroforming technique was conducted to efficiently produce a micro-grinding tool. The experiment is carried out in two stages. First, the micro-tool shaft is cut using micro-EDM. Second, the micro-diamond grain is plated on the shaft by composite electroforming.
Fine tungsten carbide is machined using micro EDM in a tabletop machining center. A composite working tank is constructed to increase the quantity of the electroformed diamond grains on the substrate. The partition in the tank is reduces flushing, minimizes turbulent flow, improves deposition efficiency in the cathode, sufficiently mixes the electroforming solution and saves diamond grains. The best circularity is improved by using the spherules array in the anode. To increase the amount and the distribution rate of the diamond grains on the cathode a novel miniature funnel mold is developed. By means of the proposed composite electroforming tank and funnel mold, the nickel ions and diamond grains are smoothly and tightly plated on to the substrate surface. Due to the nickel ions piling up one by one, a good combined strength between the micro-diamond grain and the nickel layer can be achieved.
The developed technology is verified on the ceramic component and it is successful to obtain a good surface roughness on the micro component. And can be applied quickly and cost-effectively when fabricating miniature and precise dies, tools and parts. It is also used for the flexible manufacture of cylindrical hole components of hard materials, which are used for the mass production of micro-structured components by forming processes as forming tools.
1. Shun-Tong Chena, Ming-Yi Tsai, Yun-Cheng Lai, Ching-Chang Liu, Development of a micro diamond grinding tool by compound process, Materials Processing Technology (209), 2009, 4698–4703
2. Gatzen, H.H., Maetzig, J.C., 1997, Nano grinding. Precision Eng. 21, 1997, 134–139.
3. Masuzawa, T., Fujino, M., Kobayashi, K., Suzuki, T., Wire electro-discharge grinding for micro-machining. CIRP Ann. 34 (1), 1985. 431–434.
4. Semba, T., Sato, H., Development of electroformed diamond tool with ﬁne grains covered with metal oxide coating. CIRP Ann. 49 (1), 2000.157–160.
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