| Freeform surfaces give designers freedom in designing products with functional, aesthetic, and ergonomic surfaces. Among various fabrication processes, only the machining process can produce functional parts without compromise in quality. However, in conventional CAD/CAM systems, freeform surface machining is usually time consuming, information intensive, and prone to errors. The problems become even more critical in the circumstances of networked manufacturing and rapid prototyping.; In the thesis, philosophy, strategies, and algorithms are developed for freeform surface machining in networked rapid prototyping. The thesis mainly focuses on automatic manufacturability checking and low level process planning. The central ideas are eliminating manufacturability problems before process planning, and minimizing the overall machining time with the constraints of design specifications in the low level process planning. Specific points of discussion in the thesis include: (1) An overall strategy to achieve the manufacturability checking and process planning automation for freeform surface machining in networked rapid prototyping. (2) A representation of mesh surfaces that contains feature, geometry, connectivity, and spatial relation information and a subdivision scheme to refine mesh surfaces and obtain accurate geometric properties. (3) A two-phase process to check manufacturability problems before process planing: rule-based checking and feature-based checking. (4) An automatic process to map a manufacturable feature into machinable operations. The overall machining time is minimized by optimal tool selection and operation decomposition for multiple tools and tool path patterns. (5) A simulation tool for predicting form error in ball end milling, and a simulation-toolbased cutting parameter selection process that minimizes the machining time for a certain operation with the constraints of the design specifications.; The methodologies developed in the thesis have been implemented on an experimental test-bed to create the functional molds and dies in a late stage of a product development cycle. |
