| dc.description.abstract | High precision micro-holes are one of the objectives that can be fabricated by micro machining method. Since micro-holes are widely used in the micro-valve, micro-fluidics, micro-sensor and micro-mould applications, an economical and effective method producing high accuracy micro-holes is focused in this thesis. Based on the traditional electrical discharge machining (EDM) principle, the micro-EDM can be utilized to fabricate conductive materials with high precision, less material remove rate, micro and stable energy state. Micro-EDM is an effective method to produce fine devices with complex shapes. Hard, brittle or tough materials are easily fabricated by this process. This noncontact manufacturing process is frequently used to produce micro-holes with diameter less than 100 ?m. 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, owing to the wear of the electrode during the process, not only will the dimension of the machined micro-hole be changed, but also its shape is severely distorted. Unfortunately, the conventional grinding is difficult to refine the machined surface by inserting the micro-tool into the micro-hole. To solve such problems, in this study, some different finishing methods, followed after the micro-EDM process, were developed to produce a superior refined surface of the micro-hole with almost no machining defects.
After the micro-hole is made by micro-EDM, four kinds of finishing methods will be applied to improve the surface quality of the micro-hole. The four finishing methods are helix grinding method (HG), high frequency dither grinding method (HFDG), ultrasonic vibration grinding method (UVG), and electropolishing method (EP). The shapes of the micro-holes investigated in this study are not only the circular type but also the special shape. Experimental results show that the surface roughness of the micro-hole can be well refined without micro-cracks by each of the proposed methods. For the circular shape of the micro-hole, the HFDG takes only 15 minutes to improve the work surface from 2.11 to 0.85 μm Rmax, while the HG and the UVG require 120 and 30 minutes respectively. By using UVG or EP, the surface roughness of the micro-hole with special shape can be improved from 0.957 μm Rmax (0.11μm Ra) to 0.31 μm Rmax (0.015μm Ra), which is measured by AFM. However, the EP takes only 5 minutes, while the UVG requires 45 minutes. | en_US |