| Summary: | 博士 === 國立中央大學 === 機械工程研究所 === 95 === The micro-EDM can be used to machine complex shape conductive hard-to-machine materials with high precision, less material remove rate, micro stable energy. However, micro-EDM will cause recast layer, discharge craters and micro-cracks on the machined surface with poor surface quality. This affects the precision of diameter and the geometric shape. Moreover, the electrode wear not only will the dimension of the machined structure be changed, but also its shape is severely distorted. Unfortunately, the conventional grinding is difficult to refine the machined shape accuracy by inserting the tool into the micro-hole. To overcome these issues, novel hybrid processes combined with micro-EDM were applied to effectively machine a micro-structure with high accuracy and quality surface.
This study describes two hybrid processes that are micro-tool with ultrasonic vibration free abrasive grinding method and co-deposited micro-tool with grinding method. The circular and square micro-holes are investigated in this study. Experimental results show that the surface roughness of the micro-hole inner-wall can be well refined without micro-cracks and micro-craters by each of the proposed methods. For the circular micro-hole, using a helical micro-tool with ultrasonic vibration grinding method takes only 25 minutes to improve the machined surface from 1.35 to 0.58 µm Rmax, while using a co-deposited micro-tool grinding method can improve the machined surface roughness from 1.47 to 0.46 µm Rmax. By using a square micro-tool with ultrasonic vibration grinding method, the surface roughness of the square micro-hole inner-wall can be improved from 0.96 to 0.31 µm Rmax. Moreover, after EDM spherical forming, a micro-spherical tool is made by Ni-diamond co-deposition. A smooth surface of micro-spherical cavity can be gained using the micro-spherical diamond tool and better one has surface roughness 0.35 μm Rmax can be finished by combining with free abrasive grinding.
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