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.
A Doctoral Thesis. Submitted in partial fulfillment of the requirements for the award of Doctor of Philosophy of Loughborough University.