Redesign methodology for mechanical assembly

Design for assembly is the concept of carrying out critical thought early in the design stage to create assembly easement at the production stage. In the aerospace industry, products have very long lives, frequently being optimised rather than introducing new products. This has meant older products, which are stable income generators, have not benefited from the latest design for assembly methods and manufacturing technology suffers from obsolescence. It has been established that a large percentage of overall product cost is determined at the design stage; thus, existing products suffer from preloaded costs. This paper takes existing design for assembly methodologies and analyses them with respect to the unique challenges involved in legacy product redesign. Several novel factors that contribute to redesign analysis are identified such obsolescence impact and a holistic operation difficulty assessment. A tool is developed to identify potential redesign for assembly projects. The tool is demonstrated through the application of real data and comparing against business decisions. The tool was found to provide a strong indication of where profitable projects may be launched

A methodology for aggregate assembly modelling and planning

The introduction of Concurrent Engineering highlights the need for a link between the early stages of product design and assembly planning. This thesis presents aggregate assembly process planning as a novel methodology to provide this link. The theory behind the research is to bring all aspects of product development together to consider assembly planning at the conceptual stage of design. Decisions taken during the early design stage not only have the greatest influence on production times and costs, but also should ensure that a design is easy to manufacture and assemble. An automated computer-based system has been developed to implement the methodology. The system generates aggregate assembly process plans which give details of feasible sequences, assembly process times and costs, resource requirements, and factory loadings. The Aggregate Assembly Modelling and Planning (AAMP) system employs object-oriented modelling techniques to represent designs, process planning knowledge, and assembly resources. The minimum information requirements have been identified, and a product model encompassing this data has been developed. An innovative factor of this thesis is to employ Assembly Feature Connections (AFCs) within the product model to represent assembly connectivity. Detailed generic assembly process models, functioning with limited design data, are used to calculate assembly criteria. The introduction of a detailed resource model to represent assembly facilities enables the system to calculate accurate assembly times, dependent on which resources are used within a factory, or even which factory is employed. A new algorithm uses the structure of the product model, process constraints and assembly rules to efficiently generate accurate assembly sequences. Another new algorithm loads the assembly operations onto workstations, ensuring that the capability and capacity are available. The aggregate assembly process planning functionality has been tested using products from industry, and has yielded accurate results that prove to be both technically feasible and realistic. Industrial response has been extremely favourable. Specific comments on the usefulness and simplicity of such a comprehensive system gives encouragement to the concept that aggregate assembly process planning provides the required link between the early stages of product design and assembly planning

Product and process information interactions in assembly decision support systems

A characteristic of concurrent engineering is the intensive information interchange between areas that are involved through the product life cycle. Shared information structures to integrate different software applications have become necessary to support effectively the interchange of information. While . much work has been done into the concepts of Product and Manufacturing Models, there is a need to make them able to support Assembly related activities. The research reported in this thesis explores and defines the structures of a Product Model and. a Manufacturing Model to support assembly related information. These information models support the product development process, especially during the early stages of the product life cycle. The structures defined for the models allow information interactions between them and with application software; these interactions are essential to support an effective concurrent environment. The Product Model is a source and repository of the product information, whilst the Manufacturing Model holds information about the manufacturing processes and resources of an enterprise. A combination of methods was proposed in order to define the structure for the information models. An experimental software system was created and used to show that the structure defined for the Product Model and the Manufacturing Model can support· a range of assembly-related software applications through the concurrent development of the product, system and process, from conceptual design through to planning. The applications implemented in the experimental system were Design for Assembly and Assembly Process Planning. The real data used for the tests was obtained from an industrial collaborator who manufactures large electrical machines. This research contributes to the understanding of. the general structural requirements of the decision support systems based on information models, and to the integration of Design for Assembly and Assembly Process Planning

Design guidelines for manufacturability

Matching the configuration of a product to available production capabilities during the design process directly affects product cost and hence product competitiveness. Existing approaches to improving manufacturability are helpful in the latter stages of the design process and usually involve corrective redesign. To avoid redesign, designers require appropriate guidance in the early stages of the design process. Guidelines, that is prescriptive recommendations for actions to address issues, are frequently used to provide this guidance. However, guideline sets are often poorly structured, incomplete, and the guidelines difficult to retrieve and apply. The overall aim of this research is to improve guidance to designers, particularly manufacturability guidance, early in the design process. Particular objectives of this research are to improve existing methods of guideline collection, storage, and retrieval. The research proceeded in the following pattern: - Case studies explored manufacturability problems in a small company. - Guideline support concepts were developed using a retrospective case study. - Collection concepts were developed with observational studies. - Storage approaches were developed using advanced composite guidelines. - A link-based retrieval technique was validated with a mechanical design protocol study. - Collection, storage, and retrieval methods were empirically tested. The results of this research were: - a technique to directly relate guidelines to the design process - a system of links relating guidelines to each other - an Action-Centred Guideline Approach - a preliminary software implementation of the approach - validation of the utility of the approach. The conclusions from this research are: - Guidance in the early stages of the design process can be improved through the use of structured guidelines. - The Action-Centred Guideline Approach improves the collection, storage, and retrieval of guidelines. - Empirical validation showed that guideline links are an effective means for improving guideline retrieval. - Further research is required in the areas of integrating the approach with other design tools, and in extending the link technique