G. A. Britton

Feature-based CAD-CAE integration model for injection-moulded product design

One prominent characteristic of product design for injection-moulded parts is that design and analysis (e.g. flow simulation) go hand in hand to ensure that the design is manufacturable by the injection-moulding process. Despite the wide use of CAD and CAE systems, the two processes are still not integrated. There is no generic, unified model that allows both design and analysis information to be specified. In this paper, a feature-based CAD-CAE integration model is proposed to tackle the problem. The model comprises a hierarchy of CAD-CAE features such as part, wall, hole, rib, boss and treatment. The features are defined by their attributes and behaviours. With this model, information relating to both design and analysis can be specified and modified. The specified information from the design process is used to activate relevant CAE analysis routines, thus supporting integration from the CAD to the CAE process. If any of the specified design constraints is not satisfied from the CAE results, the initial model can be modified and the CAE analysis executed again. Hence, the model also supports integration from the CAE to the CAD process. A design case illustrates the bidirectional integration process.

Guiding functional design of mechanical products through rule-based causal behavioural reasoning

The paper presents a behaviour-driven functional (B-FES) modelling framework for functional design of mechanical products based on a rule-based causal behavioural reasoning step to guide the design process. A new representation scheme called rule-based behavioural representation (causal behavioural rules) was developed to facilitate causal behavioural reasoning, with which the interconnected physical behaviours can be reasoned out from a desired function. The behaviour schema was then used to select and arrange embodiments (abstractions of physical artefacts) to develop a set of potential concept variants. The proposed approach was not only useful in the creation of new configurations (combinations) from a library of standard physical behaviours, but also it might be used to generate specifications of new physical behaviours. A design case study of a terminal feeding unit is presented to demonstrate the practicality of the proposed approach.

An Industrial Implementation of Computer-Aided Tolerance Charting

This paper argues that tolerance charting is not relevant for design tolerancing, but that it is an effective tool for process planning. It also argues that the tolerance charting algorithm based on rooted tree graphs, developed by the authors, provides a very general and powerful representation technique for tolerance charting. The technique is explained in detail to show how it can encompass all practical manufacturing processes that affect dimensions. A computer-based implementation of this technique, called CATCH, has been developed and is currently being used by a company in Singapore for process planning.

Optimization of injection moulding conditions with user-definable objective functions based on a genetic algorithm

This paper applies a Genetic Algorithm (GA) method to optimize injection moulding conditions, such as melt temperature, mould temperature and injection time. A GA is very suitable for moulding conditions optimization where complex patterns of local minima are possible. Existing work in the literature has limited versatility because the optimization algorithm is hard-wired with specific objective function. However, for most of the practical applications, the appropriateness of optimization objective functions depends on each specific moulding problem. The paper develops a multi-objective GA optimization strategy, where the objective functions may be defined by the designers, including using different criteria and/or weights. For parts with general quality requirements, an objective function is also recommended with some quality measuring criteria, which are either more accurately represented or cover more moulding defects than those from existing simulation-based optimization approaches. The paper also elaborates on the effective GA attributes suited to moulding conditions optimization, such as population size, crossover rate and mutation rate. A case study demonstrates the effectiveness of the proposed approach and algorithm. The optimization results are compared with those from an exhaustive search method to determine the algorithms accuracy in finding global optimum. It is found to be favourable.

Optimal process plans for manufacturing and tolerance charting

Abstract A graph theoretical approach is presented that permits the calculation of optimal process plans from datum hierarchy trees, which are elegant representations of tolerance charts. The theory is developed for a cost function that minimizes machine and datum changes. Restrictions on the sequence of machining operations arising from technical constraints or the layout of a group cell are taken into account. The process plans are optimal with respect to a specified datum hierarchy tree, manufacturing constraints and cost function. It is shown that the number of possible plans for real industrial trees is very large, and therefore this kind of optimization is beyond the ability of a human process planner. Trial runs with industrial parts indicate that optimization can be performed by a computer within a time period that is acceptable for industrial use.

Design of a Feature-object-based Mechanical Assembly Library

AbstractIn this paper, a new feature-based assembly library for injection mould bases is presented. Assembly design feature-object modeling and configuration management are the key technologies developed. This library is an important functional module of QuickMould, which is a productivity software tool for plastic injection mould design. Interactions between the library and mould design processes are realized. This paper also covers the details about the design of the system and the realization of some major functions, with which, the process of traditional mould design is simplified and standardized. Consequently, the lead-time for plastic injection mould can be significantly shortened.

Techniques in Knowledge-Based Expert Systems for the Design of Engineering Systems

Engineering design is a process of inventing new physical products and systems to fulfill human needs. It is one of the most important and challenging phases in the development lifecycle of a product (Figure 1). Note that the figure depicts the feedback loops for design only; the other feedback loops have been omitted for clarity. Open image in new window Figure 1. Design process and the product lifecycle.

Modelling functional design information for injection mould design

Injection mould design is a complex process incorporating various aspects of design information and a variety of design activities. Specific requirements such as undercut mould design add difficulties to the problem because they often require innovation, which involves the conceptual stage of design problem solving. Modelling injection mould design from a functional perspective enables a higher level of design abstraction, thus facilitating a wider range of conceptual variants selection. In this paper, the authors discuss the essential aspects of functional design information in injection mould design and how they can be modelled. Functional design knowledge supporting the modelling process is also discussed and formalized, and a number of knowledge libraries are implemented. A side core mechanism design is used as an example to illustrate the proposed method and its usefulness.

Knowledge-based functional design of industrial robots

This paper presents an expert functional design model and software modeling environment for designing the architecture of industrial robots. The modeling environment comprises an integrated knowledge base, an inference engine, a working memory, and an explanation unit and is implemented in CLIPS. The functional design model is based on the authors’ behaviour-driven, function-environment-structure (B-FES) formalism, which has been tailored to meet the special requirements of industrial robot design. A universal robot template has been created and a library of typical components of a robot has been compiled. Nine customized templates were generated from the universal template. Web links to the websites of manufacturers/suppliers provide easy access to data on robot components. The architectural design solutions are assessed by a set of user-defined performance criteria, such as precision, flexibility and short cycle time. Application of the approach is demonstrated through a case study of the functional design of a printed circuit board assembly robot. The authors argue that this approach is new for configuring robots and can significantly reduce the time, effort and number of errors made.

A Review of the Evolution of a Graph Theoretic Approach to Computer Aided Process Planning

Abstract This paper describes the development of Computer Aided Process Planning methods at the University of Canterbury and Nanyang Technological University. Three methods are described: a generative system for milling operations, an interactive system for cylindrical parts, and a retrieval system using neural networks. They are based on tolerance analysis and, in particular our technique for tolerance charting using rooted tree digraphs.