The design activity is responsible not only for the performance and appearance of the product but also for the cost of the component. Design, therefore, cannot be an isolated activity but must address all available manufacturing routes, with a view to optimizing the quality and cost of the component. With reference to nett-forming, the design exercise is conducted not only to specify the component-form but also to address all manufacturing constraints—machine, material, tooling, and processing conditions.
Computer-aided “design for manufacture” is currently the main form of implementing of the “concurrent
engineering.” To enable this, CAD/CAM is popularly used as a design approach. Using CAD/CAM
approaches, simultaneous design would be effected efficiently by supporting the designer with information
on all possible resources required for the design and manufacture of components. Some CAD/CAM
systems [42] have demonstrated the potential for the development into decision-support systems for
component/tool design.
Computer-aided design and manufacture for nett-forming by injection forging is being developed as
an aspect of research associated with the development of a decision-support system [64].
Methodology
In order to develop a decision-support system for component/tool design using a CAD/CAM approach, several design/evaluation methods have been developed [58, 60, 64–68]. These are described briefly in the following texts.
Geometric Modeling
The popular strategy used for the development of the design-support systems for forging was to evolve
a 2D-CAD system for component and tool design. The system was linked to a knowledge-based system
to enable the evaluation of manufacturability. Subsequent to the evaluation of the geometry, the component
was transferred to a CAD software to enable detailed design. This approach required the design to operate in several software environments. An integrated system, supported by solid modeling, would enable design and assessment of a component more efficiently. A solid modeling-approach—principal feature modeling—was used to enable component-design for forging within a solid modeling environment [65, 66]; the approach enables integration of currently available 2D-based knowledge-based systems.
Design for manufacture requires that the component form is specified in a modular form in order to enable the evaluation of the design. The component may be defined as a combination of primitive forms as is the case in “design by features;” alternatively, the primitive forms which constitute the component may be extracted and identified automatically. Unfortunately, both these approaches are currently at a stage of refinement which only allows their applications to a limited range of component forms. Principal feature modeling [67] combines the strategies of both “design by feature” and “feature recognition” to enable efficient modeling and feature manipulation; the approach was proven to be particularly efficient for the modeling of forging/machining components [65]. Designing is attended to with reference to a prescribed set of performance requirements rather than to prescribed form features. The principal features, which represent the principal geometric profiles of a component, may be defined by the designer using arbitrary geometry—a group of curves on a plane or a curved surface. The principal features which have been generated are linked, exclusively, to a set of prescribed attributes which are catalogued in a database.
The solid model of the component may be created by geometric manipulation of a principal feature; several principal features may be defined for more complex components. Subsequent to the definition of the principal features for a particular component; local features may be added to produce the first iteration of the “performance” model of the component. The form of the additional features is generated
by the modification of the principal geometric entities; these additional features are extracted and
classified as individual manufacturing features. In circumstances where components cannot be modeled by
defining principal features, the model can be created by other approaches. This will enable the prescription
of the principal feature by the extraction of the curves on a feature plane, which is prescribed by the designer. In comparison with the “design by feature” approach, the proposed approach [67] does not require a pre-defined feature library that would constrain the flexibility of the system. Further, the difficulty and complexity of the routines for the recognition of form features are reduced since the principal features, which are recorded in the system, provide auxiliary geometric and topologic information of the component model; this simplifies the recognition of manufacturing features.
COMPUTER-AIDED DESIGN,
ENGINEERING, AND MANUFACTURING
Systems Techniques And Applications
VOLUME
V I
Editor
CORNELIUS LEONDES
Boca Raton London New York Washington, D.C.
CRC Press
MANUFACTURING
SYSTEMS PROCESSES
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