published_or_final_version / abstract / Mechanical Engineering / Doctoral / Doctor of Philosophy

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OBJECTIVES: To evaluate the marginal chipping of anterior veneers made with CAD/CAM by calculating the chipping factor, to evaluate the failure load of different veneering materials and thicknesses under static loading and cyclic loading. MATERIALS AND METHODS: An ivorine central incisor was prepared to receive a traditional veneer. Using epoxy resin, 120 replication dies were made of the prepared tooth. Four ceramic materials were used; IPS Empress CAD, IPS e.max CAD, VITA ENAMIC and Lava Ultimate. Veneers were milled using a Sirona InLab MCXL at three different thicknesses, 0.4mm, 0.7mm and 1.0mm, n=10 for each group. Veneers were inspected under the light microscope to calculate the chipping factor (CF). All veneers were cemented to their tooth replicas using Variolink Veneer resin cement. Five specimens/group were loaded under compression using an Instron universal testing machine at a rate of 0.5 mm/minute until fracture. Another five specimens were subjected to cyclic loading at 30% of the mean fracture load for 30,000 cycles at frequency rate of 1 Hz, and then were loaded under compression to fracture. Modes of failure were recorded after each test. RESULTS: IPS Empress CAD 0.4mm CF was higher than all other groups, and VITA ENAMIC and Lava Ultimate 1.0mm CF were the lowest. There was a significant difference in the failure load of the IPS Empress CAD and IPS e.max CAD groups under static loading but not in VITA EANMIC and Lava Ultimate groups. Cyclic fatigue had no significant effect on the failure load of different veneering materials and thicknesses. CONCLUSIONS: Chipping factor decreases as the material thickness increases and can be used as an indicator of material machinability. IPS e.max CAD at 1.0mm had the highest static failure load value when compared to other materials. Cyclic fatigue did not affect the failure load values within the groups tested. / 2019-09-26T00:00:00Z

Tese de mestrado integrado. Engenharia Metalúrgica e de Materiais. Faculdade de Engenharia. Universidade do Porto. 2010

Trabalho realizado na empresa BringConcept, orientado pelo Prof. Dr. Casimiro de Andrade / Tese de Mestrado Integrado. Engenharia Metalúrgica e de Materiais. Faculdade de Engenharia. Universidade do Porto. 2013

Fabrication of a 3D structure and surface texture using excimer laser mask projection ablation processes typically requires the machine operator to develop a specific NC part program for the desired structure geometry, and also incorporate appropriate machine parameters to achieve the desired surface finish. The capability of the laser ablation process could therefore be significantly improved by developing a CAD/CAM system that automatically generates the NC part program using the 3D information of the CAD model of the desired structure. Accordingly, the focus of this research was to develop such a system that is, an effective CAD/CAM system specifically for excimer laser mask projection micromachining tools. To meet these requirements, a unique combination of commercially available systems was used to develop the new CAD/CAM system. The systems used comprised of a computer aided, feature based parametric design system (SolidWorks), together with its extended programming capabilities based on Automated Programming Interface (API) functions for Windows applications, and Visual Basic (VB) 6.0 programming utilities. The system's algorithms use a novel methodology to extract the 3D geometry of a microstructure. Two different techniques have been developed to extract the 3D data. First, where 3D geometry information from a CAD model was defined as a Stereolithography (STL) file, and second, where this information has been contained in a set of bit-map (BMP) files that represent a sliced or layered structure of a CAD model. Based on this, first an algorithm to create NC part programs to support Step-and-repeat micromachining technique was developed and then successfully extended to be applicable for another commonly used micromachining method, Workpiece-Dragging technique. The systems algorithms for both techniques are based on the raster-colour programming technique, resulting in substantially reduced mathematical complexity and computational time. This is the first time this approach has been used to support direct conversion of 3D geometry from a CAD model into an NC part program compatible with the excimer laser CNC controller. 2D mathematical models for controlling edge and stitching errors were also implemented in the system. An additional technique, named as 'Common Nest' has been developed with the aim to enable automatic NC part programming when microstructure design to be completed successfully, requires use of multiple complex mask patterns as a projection tool instead of just a single square aperture. The effectiveness of the system was verified by NC part program generation for several 3D microstructures and subsequent machining trials using polycarbonate (PC) and Polyethylene terephthalate (PET), and optimised processing parameters. Excellent agreement was obtained between the laser machined geometries and the microstructure CAD models. The Laser Scanning Confocal Microscope (LSCM) measured the lateral dimensions tolerance of 2m. The system was also successfully applied for a practical micro-engineering application, for the development of a microfluidics cell transportation device.

Thesis (M.S.)--Brigham Young University. Dept. of Mechanical Engineering, 2006. / Includes bibliographical references (p. 65-67).

Thesis (Ph. D.)--University of Hong Kong, 2006. / Title proper from title frame. Also available in printed format.

Thesis (M.S.)--University of Florida, 2002. / Title from title page of source document. Includes vita. Includes bibliographical references.