Feature-based representation for assembly modelling

The need for a product model which can support the modelling requirements of a broad range of applications leads to the application of a feature-based model. An important requirement in feature-based design and manufacture is that a single feature representation should be capable of supporting a number of different applications. The capability of representing products composed of assemblies is seen to be necessary to serve the information needs of those applications. To achieve this aim it is an essential prerequisite to develop a formal structure for the representation of assembly information in a feature-based design system. This research addresses two basic questions related to the lack of a unified definition for features and the problem of representing assemblies in a feature-based representation. The intention is to extend the concept of designing with features by incorporating assembly information in addition to the geometrical and topological details of component parts. This allows models to be assembled using the assembly information within the feature definitions. Features in this research are defined as machined volumes which are represented in a hierarchical taxonomy. The taxonomy includes several types and profiles of features which cover a general range of machined parts. A hierarchical assembly structure is also defined in which features form basic entities in the assembly. Each feature includes information needed to establish assembly relationships among features in the form of mating relationships. An analysis of typical assemblies shows that assembly interfaces occur at the face level of the mating features and between features themselves. Three mating relationships between pairs of features have been defined (against, fits and align) and are represented in the form of expressions that can be used for evaluations. Various sub-types of these major mating relationships can be identified (e.g. tight fit, clearance fit, etc.) and represented through the use of qualifying attributes. Component Relation Graphs, Feature Relation Graphs and Face Mating Graphs have been developed to represent each level of interaction in an assembly, and assembly relationships are combined with knowledge on process planning into a Component Connectivity Graph. These graphs are used as the basis for deriving an integrated data structure which is used for defining classes for each level in the assembly hierarchy. The implementation of a prototype system has been facilitated by use of an object-oriented programming technique which provides a natural method of adding functionality to the geometric reasoning process of features and the complex relationships between the parts that make up the assembly. The feature-based model is embedded in an object-oriented solid modeller kernel, ACIS®. The research demonstrates the possibilities for a single feature representation to support multiple activities within a computer integrated manufacturing environment. Such a representation can form the basis of design improvement techniques and manufacturing planning as well as be a model to support the life cycle of the product

Feature-based representation for assembly modelling

The aim of building an assembly model is to describe the component geometry and to define the relationships between parts of the final assembly. This requires a representation of features which include all the information needed to assemble the products and a data structure which stores information on how all the components and features are connected in an assembly. This paper outlines the development of an assembly model based on an established feature representation and a hierarchical assembly structure. Information needed to establish assembly relationships among features are included in the form of mating conditions such as "against", "fits" and the mating of two faces. The model is embedded in an object-oriented solid modeller kernel. The aim is to achieve an efficient assembly model that can be used to generate feasible sets of assembly plans

A single representation to support assembly and process planning in feature-based design machined parts

The need for a product model that can support the modelling requirements of a broad range of applications leads to the application of a feature-based model within a computer aided design environment. An important requirement in feature-based design for manufacture is that a single feature representation should be capable of concurrently supporting a number of different applications. Assembly and process planning are seen as two crucial manufacturing applications and a formal structure for their representation in a feature-based design system is presented. This research addresses two basic questions relating to the lack of a unified definition for features and the establishment of a feature-based representation for assembly. Thus the concept of designing with features is extended by incorporating assembly and process planning information with the geometrical and topological details of component parts. A prototype system has been implemented using an object-oriented programming technique which provides a convenient method for adding functionality to the geometric reasoning process of features and the complex relationships between the parts that make up the assembly. The feature-based model is embedded in the ACIS object-oriented solid modeller kernel

A representation of assembly and process planning knowledge for feature-based design

The need for a product model which can support the modelling requirements of a broad range of applications leads to the application of feature-based techniques. An important requirement in featurebased design and manufacture is that a single feature representation should be capable of supporting a number of different applications. Assembly and process planning are seen as two crucial applications and a formal structure for their representation in a feature-based design system is presented. This research described addresses two basic questions relating to the lack of a unified definition for features and the problem of representing assemblies in a feature-based representation. A prototype system has been implemented using object-oriented techniques which provide a natural method of adding functionality to the geometric reasoning process of features and the complex relationships between the parts that make up the assembly. The feature-based model has been implemented using the ACIS object-oriented solid modeller kernel

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

An intelligent knowledge based cost modelling system for innovative product development

This research work aims to develop an intelligent knowledge-based system for product cost modelling and design for automation at an early design stage of the product development cycle, that would enable designers/manufacturing planners to make more accurate estimates of the product cost. Consequently, a quicker response to customers’ expectations. The main objectives of the research are to: (1) develop a prototype system that assists an inexperienced designer to estimate the manufacturing cost of the product, (2) advise designers on how to eliminate design and manufacturing related conflicts that may arise during the product development process, (3) recommend the most economic assembly technique for the product in order to consider this technique during the design process and provide design improvement suggestions to simplify the assembly operations (i.e. to provide an opportunity for designers to design for assembly (DFA)), (4) apply a fuzzy logic approach to certain cases, and (5) evaluate the developed prototype system through five case studies. The developed system for cost modelling comprises of a CAD solid modelling system, a material selection module, knowledge-based system (KBS), process optimisation module, design for assembly module, cost estimation technique module, and a user interface. In addition, the system encompasses two types of databases, permanent (static) and temporary (dynamic). These databases are categorised into five separate groups of database, Feature database, Material database, Machinability database, Machine database, and Mould database. The system development process has passed through four major steps: firstly, constructing the knowledge-based and process optimisation system, secondly developing a design for assembly module. Thirdly, integrating the KBS with both material selection database and a CAD system. Finally, developing and implementing a ii fuzzy logic approach to generate reliable estimation of cost and to handle the uncertainty in cost estimation model that cannot be addressed by traditional analytical methods. The developed system has, besides estimating the total cost of a product, the capability to: (1) select a material as well as the machining processes, their sequence and machining parameters based on a set of design and production parameters that the user provides to the system, and (2) recommend the most economic assembly technique for a product and provide design improvement suggestion, in the early stages of the design process, based on a design feasibility technique. It provides recommendations when a design cannot be manufactured with the available manufacturing resources and capabilities. In addition, a feature-by-feature cost estimation report was generated using the system to highlight the features of high manufacturing cost. The system can be applied without the need for detailed design information, so that it can be implemented at an early design stage and consequently cost redesign, and longer lead-time can be avoided. One of the tangible advantages of this system is that it warns users of features that are costly and difficult to manufacture. In addition, the system is developed in such a way that, users can modify the product design at any stage of the design processes. This research dealt with cost modelling of both machined components and injection moulded components. The developed cost effective design environment was evaluated on real products, including a scientific calculator, a telephone handset, and two machined components. Conclusions drawn from the system indicated that the developed prototype system could help companies reducing product cost and lead time by estimating the total product cost throughout the entire product development cycle including assembly cost. Case studies demonstrated that designing a product using the developed system is more cost effective than using traditional systems. The cost estimated for a number of products used in the case studies was almost 10 to 15% less than cost estimated by the traditional system since the latter does not take into consideration process optimisation, design alternatives, nor design for assembly issue

Managing Variability in Assembly Lines

Every successful company have a diversified product portfolio based on their customer demand. Though products are branded as different variants, versions etc. most of them are similar products with little variations in their features or functions they perform. With the traditional, product centric approach to handle variation, new techniques like Clone and own were implemented in which engineers pick the most similar one available, copy it, make changes to it and present it as a new variant. Even though this approach employs reuse, but the savings occur once and only once. This project discussed how companies can exploit the commonality between the products, manage variability and get benefitted using concepts like feature based modelling, materialization etc. Feature based modelling was extensively being used in software industry, this paper focuses on using the same methods in manufacturing industry and improve the product lines for better efficiency. This project specifically investigates the assembly lines and how they can be programmed and documented to handle the portfolio of products efficiently through the entire Product Life Cycle using pure::variants, a leading variant-management tool. The use feature based modelling and variability management techniques through the assembly lines greatly reduces the evolution and development time of variants, improves cycle time and with project management documents like instruction Manuals, Bill of materials etc. Keywords: Central Variability Model (CVM), Feature based modelling, Pure Variants, Assembly Lines, Product Life Cycle

Review of research in feature-based design

Research in feature-based design is reviewed. Feature-based design is regarded as a key factor towards CAD/CAPP integration from a process planning point of view. From a design point of view, feature-based design offers possibilities for supporting the design process better than current CAD systems do. The evolution of feature definitions is briefly discussed. Features and their role in the design process and as representatives of design-objects and design-object knowledge are discussed. The main research issues related to feature-based design are outlined. These are: feature representation, features and tolerances, feature validation, multiple viewpoints towards features, features and standardization, and features and languages. An overview of some academic feature-based design systems is provided. Future research issues in feature-based design are outlined. The conclusion is that feature-based design is still in its infancy, and that more research is needed for a better support of the design process and better integration with manufacturing, although major advances have already been made

Conceptual Graphs in CAD

This paper elaborates on the use of conceptual graphs in a prototype of a computer based support system for re-design. Re-design support involves the modelling of assemblies and components. The requirements of the components to be modelled are a compromise between the functioning of the assembly and the manufacturability of the individual components. Conceptual graphs provide for an elegant way of representing both functioning and manufacturing aspects. In the prototype system, conceptual graphs are used for representing and defining assemblies, components and features as well as the relations between these entities. Constraints, such as kinematic, tolerance and manufacturing constraints are also represented using conceptual graphs

Incremental simulation modelling for Internet collaborative design

In order to support Web-based collaborative design in terms of transferring or updating models dynamically and efficiently, new incremental modelling and local updating strategies have been developed for simulation modelling application since simulation is more focused on visualisation effects than on geometry details. Based on an assembly connection concept, a drag-and-drop assembly method has also been proposed in simulation assembly. An assembly connection is defined as a group of assembly constraints and it makes assembly easier. A case study example is given to show the content of the proposed research