یک روش برای طراحی درهم آمیختگی و برنامه ریزی عملیات

Interlinking design and process planning plays a key role in realizing Computer Integrated Manufacturing (CIM). Given a part geometry from a CAD system, CAPP generates a sequenced set of instructions to manufacture the specified part. In order to do that, CAPP has to recognize manufacturing features of the part and the relevant information about precision requirements such as surface roughness as well as dimensional and geometric tolerances. Since geometric models from most of the current CAD systems do not incorporate this manufacturing information, human intervention at the first stage of CAPP is inevitable. This has been a major hindrance to information flow between design and process planning. This paper proposes an approach for interlinking CAD and CAPP, and describes the relevant efforts towards it: recognition of machining features, handling of manufacturing information, and implementation of a neutral interface using ISO 10303-224.

Computer Integrated Manufacturing (CIM) is a conceptual basis for integrating the applications and information flow of product design, process planning, production planning, and manufacturing processes. The focus of CIM is on information as the crucial element linking all facets of the manufacturing enterprise. While the geometry information is created from the design activity, the manufacturing information is concerned with the process planning, production planning and plant operations. Given a part geometry, Computer Aided Process Planning (CAPP), the bridge between Computer Aided Design (CAD) and Computer Aided Manufacturing (CAM), generates a sequenced set of instructions to manufacture the specified part. To do that, CAPP has to extract manufacturing information such as machining features and precision specifications including surface roughness, and dimensional and geometric tolerances in order to select the necessary processes and determine the operation conditions. Despite a lot of effort done in the past to interlink design and process planning, sharing of manufacturing information still remains a bottleneck [1], [2] and [3]. One of the reasons is that tolerance and surface finish data are not embedded in the geometric model. At a glance, CAD models seem to incorporate these data as seen in the drawings. However, as a matter of fact, these data are not real attributes of CAD models but simply represented as text on the drawing the same as technical notes. This results from most of the current CAD systems not having the appropriate data structure to accommodate them. Therefore, when a CAD model is to be transferred to downstream users such as the process planner or the inspection planner, every user repeatedly needs to regenerate the necessary manufacturing information through human intervention. To avoid this inefficiency, an integrated product model should be achieved, in which manufacturing information and geometry data can be stored together. At the same time, a neutral format for the representation would be desirable for facilitating an interface between disparate computer systems. STandard for the Exchange of Product (STEP) model data, which is defined as the international standard ISO 10303 [4], [5] and [6], includes not only geometry but also technical and managerial information, and thus gives a clue to the solution. This paper proposes an approach to interlink design and process planning by representing manufacturing information together with part geometry in an integrated product model based on the STEP neutral format. Fig. 1 shows the problems to be considered for interlinking design and process planning, namely the recognition of machining features, the incorporation of manufacturing information such as surface roughness and tolerances, and the implementation of a neutral interface. Full-size image (11 K) Fig. 1. Elements needed to bridge design and process planning.

Three issues necessary to interlink design and manufacturing engineering have been addressed: recognition of machining features, handling of technical information, and implementation of a neutral interface. Emphasis has been put on the representation of tolerance information by using the neutral product data format STEP. A proper data structure to store various types of tolerance and surface finish data has been proposed and implemented. This can help a CAPP system extract manufacturing information contained in STEP AP224 file more easily, regardless of the CAD systems in use. The authors believe that this framework contributes towards removing the main barrier to computer-automated downstream systems such as process planning or inspection planning, i.e. difficulty in recognizing machining features and tolerance information. Despite the achievements in handling manufacturing information, recognition of relevant features of complex shapes still remains a bottleneck. Without a mature feature recognizing system, a seamless interface between design and manufacturing could not be automated. Therefore, more efforts is needed in the future in extending the capability of feature recognition.