| Summary: | 碩士 === 華梵大學 === 機電工程研究所 === 91 === ABSTRACT
A new laser machining technique developed from the concept of fracture machining was proposed to produce a micro-removal of ceramic material. A focused laser is scanned along a constant direction to generate micro-cracks on ceramic substrate, forming a fine crack network. A defocused laser is then scanned along the same path again. The laser heat generates tensile stresses that are concentrated at the tip of crack and induces the extension of the micro-cracks. Materials are removed due to the systematical linkage of the micro-cracks. The median cracks, radial cracks, and lateral cracks are formed on the material surface during the laser scribing process. The cracks will link together and form the chip-element, which is the fundamental unit of material removal. The minimum average length of the removed chip-element is about 0.1 mm and the thickness is about 0.02 mm. The surface quality is very good and the arithmetic average surface roughness is about 1.1 mm. The finite element software was used to analyze temperature and stress distribution. The SEM photographs of the machining surface and the acoustic emission data were obtained to analyze the micro-mechanism of the fracture machining process. The relationship between the surface quality and machining parameters was also discussed.
Finally, an acoustic emission system is applied to investigate the phenomena of cracks propagation and linkage during the fracture machining process. The AE sensor can detect a signal when crack is generated. The acoustic emission signal provides useful information about material removal mechanism. The AE signal parameters for investigations were peak amplitude and event counts. The crack formations of laser scribing and controlled fracture, and the crack linkage of laser milling were studied by using the acoustic emission technique.
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