Fabrication of Porous Metal Bonded Diamond Grinding Wheels for Flat-Surface Nanomachining
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Fabrication of
Porous Metal Bonded Diamond Grinding Wheels for Flat-Surface Nanomachining
Koji Matsumaru and Atsushi Takata Introduction The articles thus far in this MRS Bulletin issue on Emerging Methods for Micro- and Nanofabrication have addressed the creation of structures or devices on a small scale. What is implicit in some of these articles is that a substrate of sufficient flatness is available upon which to build these structures in a controlled way. A related area, therefore, is the formation of these flat surfaces, as well as the development of the tools to make them. Many new advanced materials, such as engineering ceramics and electronic materials, are hard or tough and thus challenging to machine to the desired flatness. The resulting high machining costs inhibit their use in manufacturing. For functional devices such as semiconductor electronics and magnetic recording media, submicrometeror nanometer-scale surface roughness is required, and these demands are becoming even more severe as the critical feature sizes decrease and the performance of these devices improves. A number of techniques are available to make flat surfaces, such as chemical– mechanical polishing, elastic emission machining, magnetic abrasive finishing, and grinding with electrolytic in-process dressing.1 But these techniques require special equipment or devices to make flat surfaces. In this article, we give an example of how to refine the flatness of the starting
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substrate by improving a simple tool, the grinding wheel, which is commonly used for rough machining due to its high removal rates. In order to achieve submicrometer flatness and roughness by means of this technique, it is necessary to improve the grinding machine’s stiffness and precision. In particular, we have developed porous cast-iron bonded diamond grinding wheels to machine hard materials. These grinding wheels, and the techniques for using them, rely critically on a knowledge of fabrication techniques for porous materials.2–5
balanced in order to satisfy the requirements of a given application. Here we describe a new grinding wheel developed to optimize the anchoring force of abrasive grains against the bridging matrix. The newly developed grinding wheel is expected to have a higher protrusion height than in conventional grinding wheels. The wheel uses a cast-iron powder to form the skeleton matrix. Diamonds in conventional grinding wheels are held mechanically by the matrix material, but are easily removed during machining due to poor bonding strength. Stronger anchoring effects can be achieved by bonding abrasive diamond grains to the skeleton cast-iron matrix through a chemical reaction, which produces a carburized layer by diffusion of carbon (Figure 1b). Figure 2 shows scanning electron micrographs of a cross section of a porous grinding wheel. More dimples are observed on the diamond surfaces bonded to cast iron of 3.0 mass% carbon concentration, as shown in Figure 2a, than on the diamond surfaces bonded to cast iron of 4.0 mass% carbon concentrat
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