represented in operation by options and the constraints expressed as relevant rules, functions or methods.

4.3 Process information model (PIM) for path planning

Now the PIM of process planning can be defined as the foundation to process planning. And the PCS of IMM is created to control and monitor the stamping feature and its operation features by the control variable or state variable.

The process planning of large complicated stampings is a dynamic process. The PIM must involve all data, such as process planning data, analysis data, die design data, and circumstance, etc. The basic knowledge expression of the model should have adaptability to the changes of geometry, attribute, features, constraints and the way of thinking.

Using the knowledge multi-expression format of KBE technology, the integrated information model of process planning for large complicated stampings is built based on the feature model. The process information model is shown in Fig. 7. The object-oriented method and feature technol- ogy are adopted mainly to form the model. There are three basic classes of features: stamping design features, oper- ation features, and sequence features, in which process knowledge, e.g. database, parameter, rules, and experience, acts as rules and attributes of the objects. Using feature technology and the geometry extraction method, the stamp- ing design features, such as the main forming feature (e.g. drawing, bend), flange, hole, emboss, notch, and so on, that are defined first as UG/UDO, can be extracted from a 3D solid model. Relevant appropriate operations can then be assigned from stamping design features of a product using a set of rules with a decision-making tree and model-based reasoning methods of feature-operation criteria. Hierarchy and framework of the product model and semantic net of feature-operation-tools are used to establish the relationship information for PIM. With PIM, where the knowledge is encapsulated in objects or decision-making knowledge pro- cedures, the process planning can be completed through corresponding sets of knowledge-reasoning.

This model is a dynamic expanded information model, in which the information can be added and updated along with the process of planning. Information management and control is a part of PCS in IMM of process planning, which can monitor the change or modification of process plan- ning, and timely update the information to insure the process information model and process planning synchro-

Fig. 4 Structure feature model for product data

Main feature layer

Second Feature layer

Third feature layer

Knowledge driving

No Flanging formable ?

Yes

Process analysis, Rule-based reasoning

No

Flanging High>H

Yes

No FlangingAngle>A

No FlangingRadius<R

Yes

Knowledge driving

Process analysis, Rule-based reasoning

Yes

H–minimum high for flanging; A–maximum angle for one time flanging; R–minimum flanging radius : € orders of operations

Fig. 5  Flanging operations reasoned from its stamping  feature

nization. In process planning, the information management and control begins its control and judgment from the time that the stamping design features have been created until the planning ends.

4.4 Process path planning and tools option

Generally, the forming of an automobile panel includes several operations, such as drawing, trimming, flanging, piercing, re-striking, hemming, etc. Among the operations, drawing, trimming and flanging are the main operations to form the main shape of the product, and other operations are auxiliary operations, which work together with the main operations to form complex shapes of the product. To get precedence relations among operations based on the PIM, the main operations must first be determined, and then the decisions are made about how to arrange the initial main operations, how to combine the auxiliary operations with the main operation, and how to insert auxiliary operations to the operation sequence. For the integration of planning, it should consider the stamping dies’ capability, cost and capacity of machinery or workshop as critical issues at the sequencing level.