A Formal Approach to Integrating Computer-Aided Process Planning and Shop Floor Control

Abstract

A formal approach for integrating Computer-Aided Design (CAD), Computer-Aided Process Planning (CAPP), and shop floor control for rotational components is presented in this paper. It is assumed that this approach will be implemented within the framework of a three level hierarchical CIM architecture that consists of the following levels in the hierarchy: shop floor, workstation and equipment (Joshi et al., 1991). Our approach to CAPP consists of machining feature identification, definition, classification, representation, and reasoning, provided through a CAD model of a product. Geometric entities are identified from a Drawing Exchange Format (DXF) file. The identified entities form the basis for the construction of primitive manufacturing features. The primitive features are assembled together based upon the precedence among features, into a graph, called a feature graph. However, the primitive features may or may not be manufacturable in terms of depth of cut, tool geometry, surface finish, and material handling required. Hence it is necessary to convert the feature graph into a manufacturing task graph, which consists of specifications of alternative functional tasks that are manufacturable. The task graph may be converted into a hierarchical set of process plans, based on the planning criteria at each level in the control hierachy, to reflect the processing requirements at each level. The shop planning function decomposes the task graph into a set of workstation level plans. Each workstation level plan is aggregated into a set of equipment level process plans by the workstation planning function. The equipment level plan is converted into a unique task sequence by the equipment planning function. This sequence is then executed according to specifications by the equipment level execution function. Provision of alternative routes in process plans provides for flexible means of on-line planning and control.

A closed-loop control architecture for CAM accounting for shop floor uncertainties

“…As an input to the closed-loop CAM system, alternative processing plans can be represented using process plan graphs as described in Derebail, Cho, and Wysk [7] and Cho et al [8]. A process plan graph is based on feature-based process planning and representation.…”

Iterative approach to operation selection and sequencing in process planning

“…In this paper, the tree-structured precedence graph is used since it can be used to generate operation sequences without considering alternative operations. For other representation methods for operation selection and sequencing in process planning, see Cho et al (1994), Lee and Jung (1995) and Kiritsis et al (1999). Figure 1(a) shows the tree-structured precedence graph for an example part with nine operations, in which there are four precedence paths and two sets of alternative operations {2, 8} and {5, 9}.…”

A feature modification framework for the generation of alternative process plans

“…There are many alternatives in the division of machining features in operation planning. In this paper, these alternatives are identi® ed using machining knowledge and then are represented using an AND/ OR graph (Cho 1994). A pro® le feature does need not to be decomposed if the appropriate tool (facing and turning tool) is used.…”

“…Cho (1994) introduced the polyshape concept for feature modi® cation. In that paper, the AND/OR representation method was used to represent alternative process plans.…”