Design analysis and redimensioning of prismatic parts for manufacturability

Abstract

To facilitate concurrent engineering, efficient and effective computer-based design assistant tools are imperative. However, tools based on current design for manufacturability approaches focus on the geometric and topological aspects of a design, like machining feature models of a design, feature approachability etc. Other aspects, like dimensions and tolerances, are not considered sufficiently. This thesis aims to narrow this gap by taking into account the impact of dimensioning and tolerancing on manufacturability. This is achieved by an approach which aids designers to (re)design for improved manufacturability. A system modifying design dimension schemes through changing design datums and tolerance values of some dimensions via proper dimension chains is developed. This system mainly consists of four modules: a module for searching alternative design dimension chains; a module for constraint generation; a module for manufacturability evaluation, which assesses the manufacturability for derived design dimension schemes; as well as an interface. A prototype of the so-called Design Rewriting System demonstrates the proposed approach. This system relies on a systematic approach investigating alternative dimensional specifications, and bases on a graph theoretical approach. Several concepts, such as explicit dimension, state of a dimension, and overall dimension graph, are discussed to facilitate the determination of alternative design dimension chains. In particular, a measure, that compares different types of geometric tolerances, is adopted as the manufacturability criterion to evaluate the manufacturability of generated designs. Meanwhile, an augmented torsor model is adopted to mathematically represent tolerance zones and accommodate the propagation of both size and geometric tolerances. In addition, manufacturability measures with regard to dimensioning are studied, and an 7