| Summary: | 博士 === 國立中山大學 === 機械與機電工程學系研究所 === 102 === A diamond film with thickness of several microns is usually deposited by chemical vapor deposition method. To deposit the diamond film by this method, its operating parameters have to be precisely controlled. Otherwise, the rough souface of the diamond film is grown with non-uniform thickness, resulting in limitations on the applications. Hence, a surface machining process is required.
A feasibility study to grinding diamond film is conducted by Composite Electro-plating In-process Sharpening (CEPIS) method. A nickel plate as the anode is located on the top of a copper disc horizontally as the cathode. Both are connected to DC power supply and immersed in a nickel chloride bath containing diamond grits of 10 μm as an electrolyte, so that metal ions with diamond grits are deposited onto a grinder in process to expose fresh sharp grains. Results show that the removal rate of the diamond film increases with increasing current density, and the highest removal rate is about 3.8 times higher than that of the traditional grinding method. Meanwhile, the coating thickness on the disc is maintained or slightly increased.
Next, effects of various operating parameters, such as current densities, bath compositions, and diamond grit sizes, on the grinding characteristics of CEPIS method are studied. Results show that a distribution model of the diamond grits in the coating layer is deduced, and it can be demonstrated as body-centered tetragonal structure. To promote optimum grinding efficiency, a high variation rate in the surface roughness of diamond film and a small growth rate in the coating thickness are desired. To meet this demand, a current density is in the range of 2.5 to 7.5 ASD, a concentration of nickel chloride is in the range of 30 to 150 g/L, and the diamond grit size is larger than the column size on a diamond film surface. A two-stage CEPIS grinding procedure is used to grind the diamond film. A grit size of 25 μm is selected to conduct the CEPIS grinding for 30 min. Then, the operating conditions are switched to a grit size of 3 μm and a grinding time of 180 min. Finally, a mirror-like surface on the diamond film with an average surface roughness of 0.03 μm is obtained. Moreover, the grinding mechanism is deduced by observing the coating and diamond film surface during this process.
Finally, a pulse reversal current is introduced to this method to control the coating thickness on the grinding tool. The coating can be sharpen by composite electroplating and dressed by electrolyzing simultaneously, so that both sharpness and thickness of the coating is maintained. Effect of pulse reversal current on the grinding characteristics of the coating layer and the CVD diamond film is experimentally investigated. Results show that the surface roughness of diamond film is higher than that obtained by the positive pulse current, but the coating thickness on the tool can be efficiently controlled regardless of pulse reversal duration. The thickness of the coating layer can almost maintain constant at the pulse reversal duration of 1500 μs.
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