Using a design by features CAD system for process capability modelling

Process capability modelling offers a method of matching the shape, technological and cost capabilities of manufacturing equipment to the requirements of components, singly or as groups. This provides the basis of planning tools useful in the capital intensive business of the construction of new manufacturing facilities or the reconfiguration of existing ones. The success of this modelling approach is dependent upon having an appropriate representation of the design geometry. The representation must be such that all geometric inquiries raised by the process capability modelling are either explicitly held within some data representation or alternatively can be derived algorithmically by reference to a geometric model. The representation must also be capable of withstanding the rigours of use within the wider context of implementing an important part of the CAM interface within a CIM environment. This paper describes a feature-based representation based on a feature taxonomy which uses External Access Directions (EAD) as the characterizing aspect of geometry. These EADs become potential machining directions for a collection of features on a component, and are used as an essential link into generative process planning activities. The representation has been used in conjunction with process planning and process capability modelling applications. This paper concentrates on the latter, where the feature representation has been embedded within a proprietary geometric modeller which has been provided with a purpose-built user interface. A feature-based component model is created by the geometric modeller and accessed by functions which enable flexible component grouping and matching to process capability through the concept of a composite component. Subsequent process component grouping within the context of particular manufacturing systems strategies (cellular manufacture, flow-line, etc.) ultimately results in functional machine descriptions and variants.