Towards Cost-Based Structural Optimisation: cost modelling and feature recognition for injection moulded components

Year: 2008
Author: Yao, Na
Supervisor: Parks, Geoff
Institution: University of Cambridge
Page(s): 183


Today’s competitive global markets have led to the cost of a product becoming one of the most crucial factors in deciding its success. Therefore, manufacturability and cost considerations must be incorporated explicitly in the design optimisation process. More importantly, a fundamental shift in the focus of the optimisation is necessary, away from ‘a performance-based objective and design constraints’, as at present, towards ‘a cost-based objective with performance and manufacturing constraints’. Injection moulding is a major processing technique for plastics fabrication, and moulded components are used in almost every type of manufactured product. This thesis aims to present an alternative approach to the design of optimal injection-moulded components, in which the cost of manufacture is considered as the principal objective. Medial Object Technology (MOT) provides an auxiliary shaped representation of a solid object based on the geometric proximity of its boundary entities. The geometric proximity information provided by MOT allows the development of a computationally efficient feature recognition algorithm, which in turn greatly simplifies the generation of detailed Computer Aided Engineering (CAE) models to suit the requirements of different simulation scenarios. This work presents an efficient algorithm for recognising the geometric features of injection-moulded components. The algorithm employs the medial objects of a solid model together with other information extracted from the model, in order to identify the ‘local’ features of components. By making use of the geometric features extracted directly from the input CAD model, an automatic cost estimation system has been developed to evaluate the total manufacturing cost of moulded components. The ability to estimate automatically the cost of a proposed design for an injection moulded component paves the way for its optimisation on the basis of cost. This research represents a transition from traditional Computer Aided Design (CAD) to CAE for a selected manufacturing process, and suggests a means of incorporating it into the downstream application, in order to facilitate structural optimisation design.

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