Feature validation in a feature-based design system

The Loughborough University of Technology Feature-Based Design System (LUTFBDS) allows detail design to be carried out in a computer aided design (CAD) environment by the addition of form features to stock material or part-machined components. An iconic user interface assists in the description parts in terms of a set of primitive features such as holes, pockets and slots or higher level compound features such as patterns of holes and counterbored holes. This feature representation is generated in parallel with the geometric data structure of the underlying boundary representation solid modeller. The feature representation is useful for a range of downstream manufacturing activities, but our research focusses on the integration of CAD with process planning. LUT-FBDS functions allows the designer or manufacturing engineer to progressively construct the final geometry of a part, and facilities are provided for the designer to modify parameters which relate to feature dimensions, location, orientation and relationships with other features. These changes may result in changes to the feature representation and hence there is a need for feature validation to ensure the integrity of the model

Component grouping for GT applications - a fuzzy clustering approach with validity measure

The variety of the currently available component grouping methodologies and algorithms provide a good theoretical basis for implementing GT principles in cellular manufacturing environments. However, the practical application of the grouping approaches can be further enhanced through extensions to the widely used grouping algorithms and the development of criteria for partitioning components into an 'optimum' number of groups. Extensions to the fuzzy clustering algorithm and a definition of a new validity measure are proposed in this paper. These are aimed at improving the practical applicability of the fuzzy clustering approach for family formation in cellular manufacturing environments. Component partitioning is based upon assessing the compactness of components within a group and overlapping between the component groups. The developed grouping methodology is experimentally demonstrated using an industrial case study and several well known component grouping examples from the published literature

Process capability models for equipment selection

Due to the increased complexity of modern manufacturing facilities and the increased demands for product variability and system flexibility there is a need for coherent formal representation of the basic knowledge domains supporting manufacturing applications such as equipment selection. The paper presents integrated framework for equipment selection based upon describing process capability at generic, machine tool and manufacturing system levels. The decision making process is designed as a sequence of steps for transforming component design information into processing requirements which are mapped into specific physical machines organised as a processing system

Component grouping for cell formation using resource elements

The work reported in this paper recognises that the traditional close association between components and a fixed route utilising a set of machine tools can no longer be relied upon as an appropriate basis for deciding component similarity and partitioning components into families in modern manufacturing applications. A new methodology for describing the capabilities of machine tools and machining facilities using generic capability units termed 'resource elements' is reported. REs are used to capture the processing requirements of components, assessing their similarity and a fuzzy grouping procedure is used for simultaneously grouping components and machine tools for cellular manufacturing applications. The reported results show that the use of resource elements leads to component groups that are more compact with better matching between processing requirements of components and the capabilities of the machine tools selected for their processing compared with the conventional machine-based approach

Geometric elements for tolerance definition in feature-based product models

Product modelling is an essential part of all computerised design and manufacturing activities. A precise mathematical model of the geometry of products is important, but must be supplemented with technological information such as the material, mechanical properties, functional specifications and tolerances. Modern CAD systems can model and manipulate components with complex geometry. However, technological information is represented as text symbols on the computer screen or drawing, and subsequent application programs are frequently unable to use this information effectively. This paper discusses this problem, and establishes the geometric elements required for the representation or dimensions and tolerances in a feature-based product modelling environment

A survey of virtual prototyping techniques for mechanical product development

Repeated, efficient, and extensive use of prototypes is a vital activity that can make the difference between successful and unsuccessful entry of new products into the competitive world market. In this respect, physical prototyping can prove to be very lengthy and expensive, especially if modifications resulting from design reviews involve tool redesign. The availability and affordability of advanced computer technology has paved the way for increasing utilization of prototypes that are digital and created in computer-based environments, i.e. they are virtual as opposed to being physical. The technology for using virtual prototypes was pioneered and adopted initially by large automotive and aerospace industries. Small-to-medium enterprises (SMEs) in the manufacturing industry also need to take virtual prototyping (VP) technology more seriously in order to exploit the benefits. VP is becoming very advanced and may eventually dominate the product development process. However, physical prototypes will still be required for the near future, albeit less frequently. This paper presents a general survey of the available VP techniques and highlights some of the most important developments and research issues while providing sources for further reference. The purpose of the paper is to provide potential SME users with a broad picture of the field of VP and to identify issues and information relevant to the deployment and implementation of VP technology

A design by features approach to the building of feature data models for process planning

As research and development in Computer Aided Design and Manufacture (CAD/CAM) progresses, the integration of activities such as design, analysis, process planning, assembly planning, production planning becomes ever more complex and important. It has been recognized that a feature based representation of parts is a key to solving this problem. Unfortunately, neither has a feature representation scheme (or standard) yet been generally accepted, nor has a CAD system successfully represented feature information. Ongoing research into process capability modelling is aimed at solving the above problems in the process planning domain. In this paper, a design by features system, which consists of a design by features user interface and an integrated Boundary Representation solid modeller, is introduced. A feature representation scheme that has been implemented in the system is also presented. Although the design by features approach still has limitations, it overcomes some severe problems with the alternative feature recognition approach, such as the complexity of the recognition process, the limited number of features that can be identified from the geometric representations of pans and the absence of the designer's intent

The implementation of a feature-based component representation for CAD/CAM integration

Recent research and development has the objective of increasing productivity and cost effectiveness by integrating many activities such as design, analysis, process planning, assembly planning and production planning which encompass the entire manufacturing planning and operational control aspects of a manufacturing enterprise. It has been recognized that a key to the integration lies in the determination of a representation scheme for products that can be interpreted for the various needs of these different applications. Geometric (solid) modellers were regarded by many researchers as the appropriate representation, but more recently a features approach has been proposed to enhance the capabilities of solid modellers. This paper introduces ongoing research which is aimed at the development of a feature-based design system for process planning. The system is fully integrated with a conventional boundary representation (Brep) modeller which enhances its modelling capabilities in representing, editing and validating features of components. The main aspects of the feature-based design system are described in detail, such as the feature library, feature taxonomy, feature operations, feature relationships and tolerances. The generation of a detailed data model for transmission to manufacturing planning activities is also described and demonstrated by reference to an example component. A brief indication is given of our parallel research work in using such models as the basis of process planning and process capability modelling

An experimental comparison of a feature based design system and a conventional solid modeller

Computer-Aided Design (CAD) systems are currently widely used in design and manufacturing industries. However, the integration of CAD systems with Computer- Aided Manufacturing (CAM) systems such as process planning, graphical numerical control (NC part programming), assembly and inspection planning requires a featurebased representation of components which is not found in conventional geometry-based CAD systems. To meet this requirement, feature-based CAD systems have been developed in research centres worldwide using feature-oriented user interfaces and feature-based representations of parts. The introduction of new technology (feature-based design in this instance) always raises important questions. For example, are feature-based systems easier to learn and more efficient than conventional geometric modellers?; and does the method generate more complete and accurate models? This paper reports an experiment which was carried out to compare a prototype feature-based design system with a conventional solid modeller, where both systems use an iconic interface. Eight engineering students were selected as subjects and each subject was required to generate six features using both systems. The time taken to generate each feature was recorded and the results were presented as a series of graphs and learning curves. The results of the experiment show that both systems are similar in terms of learning their operation and that the feature's approach has clear efficiency gains over the conventional geometric approach. The conclusions drawn from this experiment may be useful for both end users who are considering upgrading their existing systems and software vendors who are designing next generation of products

Process capability modelling for design and selection of processing equipment

Due to the increased complexity of modem manufacturing facilities and the increased demands for product variability and system flexibility there is a need for coherent formal representation of the basic knowledge domains supporting manufacturing applications such as equipment selection. The paper presents an integrated framework for equipment selection based upon describing process capability at generic, machine tool and manufacturing system levels. The decision making process is designed as a sequence of steps for transforming component design information into processing requirements which are mapped into specific physical machines organised as a processing system