| Summary: | 碩士 === 東南科技大學 === 機械工程研究所 === 103 === In this study, electrochemical discharge machining (ECDM) is applied to drilling process of zirconia material. ECDM is a commonly used processing technique for insulation with hard and brittle property in recent years. It is not affected by the mechanical properties of the workpiece and is well suited for machining materials of high hardness, toughness and strength. ECDM involves high-temperature melting and accelerated chemical etching under the high electrical energy discharge on the electrode tip during electrolysis for material removal.
The workpiece used in the study is black zirconia of more than 96 % purity and mohs scale 8.7. With its hardness only lower than diamond and much higher than stainless steel, zirconia is replacing the metal material used in dental implant. Experiments were conducted using tungsten electrodes of 0.2 mm diameter, cut from 1 mm, at various applied voltages, mole concentrations and spindle speeds. Changes in ECDM efficiency of alpha-Al2O3 ceramic under difference parameter settings were examined using a white light interferometer and the variations in surface morphology were observed with a scanning electron microscope.
Experimental results show that a minimum hole diameter of 224 μm and depth of 122.9 μm can be obtained under the optimal machining conditions of applied voltage, 85 V ; mole concentration of phosphoric acid, 5M ; and spindle speed, 1000 rpm if under such conditions for 20 minutes. To achieve a better result, conditions are further changed to voltage, 83 V ; mole concentration of phosphoric acid, 15 M ; and spindle speed, 1000 rpm for 40 minutes, eventually boring through the zirconia with diameter of 304 μm at the front and 113 μm at the back of the hole respectively.
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