| Summary: | 碩士 === 逢甲大學 === 材料科學所 === 91 === ABSTRACT
The goal of this thesis is to investigate the performance of microgrinding process of optical glasses using superabrasive grinding wheels (diamond and CBN) combined with ultrafine oxide abrasive (SiO2, CeO2, ZrO2, and Al2O3) slurry to achieve the ductile mode in material removal process. In the research work, a subsystem was installed, which supplies oxide abrasive slurry in the contact region between superabrasive wheel and glass workpiece and machining parameters including circulation flow rate, pumping pressure, and chilling of slurry can be manipulated during the microgrinding process.
The functions of dynamic abrasive slurry in terms of abrasion, debris removal, heat dissipation, and lubrication and potential tribochemical or chemino-mechanical reaction involved in the microgrinding process were thoroughly studied. The purpose of this work is to obtain better efficiency of ultrafine surface finish process associated with the surface quality of optical glasses. Effects of microgrinding on surface and sub-surface properties of optical glasses and the transition from brittle mode to ductile mode in material removal were explored. Furthermore, one of major interests is the interaction mechanism of optical glasses, ultrafine oxide abrasive slurry, and superabrasive wheel grinding process, which may lead to the ductile deformation at surface and subsurface regions. A dynamic balancing gauge for the microgrinding wheel was employed in order to understand how the machining operation conditions and wheel parameters affect the surface integrity of workpiece.
The glass workpiece after microgrinding was examined by materials analytical tools as well as optical instrument including SEM, EDS, AFM, XRD, XPS, and UV-Vis spectrometer to evaluate the variation of surface topology, grinding-induced damages in surface and subsurface, potential tribochemical reaction, and change of optical properties. The detailed mechanism for microgrinding process of optical glasses using superabrasive grinding wheel combined with ultrafine oxide abrasive slurry, accompanied with ultra-low table feed rate for various types of optical glasses is also proposed. In addition, the optimal microgrinding parameters were also examined in order to achieve better surface integrity and microgrinding efficiency for optical glasses in this work.
The results indicated that the enhanced machining efficiency and minimum machining damages incurred in the microgrinding process of optical glasses can be achieved by using superabrasive grinding wheels combined with ultrafine oxide abrasive (SiO2, CeO2, ZrO2, and Al2O3) slurry to achieve the ductile mode in material removal process. The minimum average surface roughness (Ra = 8.836 nm) of optical glass by AFM measurement was obtained from the microgrinding process using #1200 WA wheel associated with 1.3 □m sized Al2O3 free abrasive. In comparison, the minimum average surface roughness (Ra = 7.213 nm) was obtained from the microgrinding process using #5000 diamond wheel associated with 2.0 □m sized ZrO2 free abrasive. The polishing action by a wool felt wheel did not show any substantial material removal of optical glass samples, however, injection of free abrasive slurry (2.0 □m ZrO2) to assist the polishing action by a wool felt wheel would result in satisfactory effects on surface smoothness (Ra = 1.054 nm). The injection of various of oxide free abrasive slurries into the grinding contact zone between the wheel and optical glass workpiece was demonstrated as an effective means by exerting the addition wear of optical glass workpieces to illuminate the minute machining damage at glass sample surface, to produce the ductile mode of material removal, and to enhance the surface planarization by oxide free abrasives during the microgrinding process.
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