Institute for Systems Research
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Item Optimization of Machining Performance of Dental Ceramic Restorative Materials(1997) Le, Dung T.; Zhang, G.; ISRDental ceramics are gaining popularity because of their esthetics, strength, chemical durability, and bio-compatibility. However, the inherent brittleness of ceramics poses a challenge to the manufacturing community as the cracking formed during the material removal leads to premature clinical failures. Consequently, fabrication of excellent-fitting and durable dental prostheses calls for new and innovative processing technologies to minimize the formation of, micro-scale cracking.This thesis presents a combined analytical and experimental study with focus on optimizing the machining performance of a type of newly developed dental material. It is called DICOR/MGC, where MGC stands for machinable glass ceramic. The study starts from analyzing their microstructural characteristics to searching for the machining conditions that provide satisfactory performance in terms of surface finish and acceptable flexural strength. To gain a better understanding of the material removal mechanism(s), a dynamometer is designed to perform an on-line recording of the cutting force generated during machining. Method of using an environmental scanning electron microscope is employed to examine the machined surface texture and identify the machining induced cracking. Two major contributions of this thesis study are (1) the fundamental understanding of the relationships among the material microstructures, the machining parameters, and the material preparation on surface integrity of dental ceramics, and (2) the development of an architecture for searching machining conditions that optimize the machining performance of dental ceramics.
Item Control of Machining Induces Edge Chipping on Glass Ceramics(1996) Ng, S.J.; Le, Dung T.; Tucker, S.R.; Zhang, G.M.; ISREdge chipping is a phenomenon commonly observed during the machining of ceramic material. Characterization of edge chipping, both in macro and in micro scale, and correlating its formation to machining parameters form a basis for developing new and innovative technologies for controlling in machining induced damage. An experimental-based study using glass ceramic material is performed. Three types of edge chipping are identified. The SEM-sterephotography method and the finite element method are used to evaluate the edge chipping effect under a set of machining conditions. Significant findings are obtained and guidelines for controlling edge chipping during machining are suggested.Item Characterization of the Surface Texture Formed During the Machining of Ceramics(1995) Zhang, G.M.; Ng, S.J.; Le, Dung T.; Job, Lenox S.; ISRThis paper presents the development of a computer-based system to perform characterization of the surface texture formed during the machining of ceramic material. Techniques of image processing and computer graphics are employed to display vivid pictures of micro-scale details of the machined surfaces. Special attention is given to establishing the interrelations between the surface texture formation and the grain facet fracture induced by machining. Results obtained from microscopic analysis of the formed surface texture reveal that grain pullouts and cleavage, as a result of the progressive development of grain boundary micro-cracking, are two mechanisms responsible for the material removal process. The surface texture is an aggregation of macro and micro-scale fractured facets. A new performance index cavity density is introduced to quantify the combinational effect of material microstructure and the dynamic loading during machining on the micro-mechanisms of the material removal process.