| Summary: | 碩士 === 國立中興大學 === 機械工程學系所 === 94 === Granite is an excellent material as a reference datum for precision measurement due to its good physical properties. High-flatness mahcining process for granite is therefore an important technology for the granite industry. The material, however, is hard and brittle, not to mention that it is non-homogeneous, thus difficult to machine. This research is aimed to investigate the effects of machining parameters for high-flatness grinding and lapping of granite blocks. Experiments are designed by Taguchi method with translating speed, feed rate, and transversal feed as parameters for grinding process and with lapping pressure, lapping speed, and lapping times as parameters for lapping process. Grinding experiments are conducted in a horizontal-spindle gantry-type grinding machine. Experimental spices include a 1000mm1000mm150mm Rustenburg, an Indian Black of the same size, a 250mm×250mm×70mm Indian Black and a 600×mm400mm×120mm Zimbabwe Black granite blocks. Experimental results showed that best flatness and roughness are obtained under 21.7m/min translating speed, 0.05m/min feed rate and 5μm transversal feed. The flatness reached 15μm for Rustenburg and Indian Black, 2.25μm for the small Indian Black block, 3μm for Zimbabwe Black block. Surface roughness in Ra are 1.62μm for Rustenburg, 0.73μm for Indian Black, 0.61μm for small Indian Black and 0.62μm Ra for Zimbabwe Black. The results have been highly improved compared with granite ground by the commonly used vertical-spindle grinding machine. The purpose of lapping is to improve surface roughness. Experimental results showed that best roughness 0.67μm Ra for Rustenburg can be achieved under lapping pressure in 6.8kg, lapping speed in 40rpm and lapping once. The best roughness for the other three blocks can be reached under pressure 10.6kg, speed 40rpm and lapping twice. Surface roughness in Ra are 0.45μm for Indian Black, 0.5μm for small Indian Black and 0.54μm for Zimbabwe Black. Although surface flatness increases after lapping, they are still within the specifications in CNS-B6048 standard.
|
|---|
