Process capability modelling in an integrated concurrent engineering system — the feature-oriented capability module

Abstract

In this paper a system module which models cutting process capabilities is presented. A critical review of process capability modelling in Computer Automated Process Planning (CAPP) systems leads to an outline of current limitations. An approach to modelling of machining facilities which addresses these current limitations is then presented. The technologies of Expert Database Systems, Object Oriented and geometric reasoning techniques are used in the approach. The Feature Oriented Capability Module (FOCM) forms part of a Computer Automated Process Planning (CAPP) System within an integrated concurrent engineering system (Simultaneous Engineering Workstation). In the integrated Simultaneous Engineering Workstation (SEW), a Feature-Oriented Computer Aided Design (CAD) system is integrated with the CAPP system. The approach treats CAPP as an optimisation problem and it is the function of FOCM to provide a plan space of feasible manufacturing solutions on which the optimiser will work. There are several advantages to this approach. In particular it means that the global cost of a process plan is considered. This means that rather than just choosing the cheapest process feature-by-feature, the cheapest global plan is generated. In addition, the FOCM approach of finding sets of feasible plans enables related features to be planned easily and for geometric constraints of processes to be considered in planning. The FOCM takes as input a feature-oriented B-rep solid model description of the component to be planned. Various ‘knowledge sources’ contain sets of rules about manufacture of features and these can query a database and a solid modeller to retrieve data about process constraints. This data is used in the selection of feasible manufacturing processes for the CAPP optimiser plan space. The database provides sufficient detail for actual tool and machine facilities in a factory to be described. The solid modeller is used to provide information on the geometric constraints of operations selected from the database. The knowledge sources query the database to get information about the suitability of an operation in cases where potential tool obstruction, thin walls and intersecting features might make an otherwise suitable operation unsuitable. The queries use object-oriented tool models, machine models and error models which contain geometry descriptions as well as data from the detailed database.