Theoretically, case-based reasoning (CBR), rule-based reasoning (RBR), and model-based reasoning (MBR) are all applied for process planning. In this paper, CBR, RBR and artificial neural network are joined up as the decision- making methods after model-based reasoning during process planning, which is shown in Fig. 8. Firstly, the model-based reasoning is used to form a code of the product and operation for CBR based on feature entities and their interrelationships, and relevant rules or knowl- edge for others reasoning. Then the CBR is selected to get similar plans for the case base; if CBR is not suited, the RBR and ANN are select to complete the task coopera- tively. During sequencing of forming operations, the structure of the die for each operation can be performed from the operations and assigned stamping features. The system can plan the equipment and operators for each operation to meet design specifications, and to achieve minimum machining time and maximum efficiency based on the above activity and knowledge. Finally, the optimal process plans obtained can be added into the case base of plans for the planning of other similar products.

Customarily and practically, the relationships between operations consist of operations order constraint (do-after), which relates to the necessary order of operations to be

…

Draw

Bend

Simple Flange

Complex Flange

Round Hole

Rect. Hole

Abnormity Hole

Fig. 6  The semantic network for feature, operations and tools based on object-oriented   entities

Fig. 7 PIM for large compli- cated stampings

Operation knowledge

Planning knowledge

Process control knowledge

Resource information

used, and operations combination constraint, which relates to relevant operations that can be formed at one process and die together (mentioned in Sect. 4.1). For example, flanging is after trimming, while piercing and trimming are always formed in one process.

For the aims of economic efficiency and top-quality, it is always recommended to combine the potential operations together, while making the sequence operations practical. Therefore the initial main operation sequence is Blank- ing→ Drawing → Trimming → Flanging for a flange feature comprised part, and Blanking→ Drawing → Trimming for no flange feature part. With operations sequencing and combination rules, auxiliary operations are added to the initial main operation sequences to form final process routing. The following is the combination rules for hole1 and hole3 shown in Fig. 3:

(Logical) combination (for hole1 and hole3): IFdistance between hole1 and hole3 >DIS && the angle of the vectors of the two hole<15· THEN TRUE ELSE FALSE;

Thereafter, the structure of the die for each process can be performed from operations and the assigned features, while the process route is determined. Then the equipment such as a set of machinery or the product line can be selected to insure the stamping die meets design specifica- tions. For example, Fig. 9 shows generation routes of process planning for the automobile panel shown in Fig. 3. During process planning, different process routes can be found by different planners; therefore, the best process route should be selected according to the batch of production, design and manufacturing of stamping dies, cost, etc. while tool options, the equipment and dies for each process should be assigned to meet design specifica- tions, and to achieve minimum machining time and maximum efficiency. Finally, the optimization of process planning [20] is realized for multiple purposes (best- quality, maximizing efficiency, minimizing cost and time)