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The PIM must involve all data, such asprocess planning data, analysis data, die design data, andcircumstance, etc. The basic knowledge expression of themodel should have adaptability to the changes of geometry,attribute, features, constraints and the way of thinking.Using the knowledge multi-expression format of KBEtechnology, the integrated information model of processplanning for large complicated stampings is built based onthe feature model. The process information model is shownin Fig. 7. The object-oriented method and feature technol-ogy are adopted mainly to form the model. There are threebasic classes of features: stamping design features, oper-ation features, and sequence features, in which processknowledge, e.g. database, parameter, rules, and experience,acts as rules and attributes of the objects. Using featuretechnology 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 soon, that are defined first as UG/UDO, can be extracted froma 3D solid model. Relevant appropriate operations can thenbe assigned fromstamping design features of a product usinga set of rules with a decision-making tree and model-basedreasoning methods of feature-operation criteria. Hierarchyand framework of the product model and semantic net offeature-operation-tools are used to establish the relationshipinformation for PIM. With PIM, where the knowledge isencapsulated in objects or decision-making knowledge pro-cedures, the process planning can be completed throughcorresponding sets of knowledge-reasoning.This model is a dynamic expanded information model,in which the information can be added and updated alongwith the process of planning. Information management andcontrol is a part of PCS in IMM of process planning, whichcan monitor the change or modification of process plan-ning, and timely update the information to insure theprocess information model and process planning synchro- nization. In process planning, the information managementand control begins its control and judgment from the timethat the stamping design features have been created untilthe planning ends.4.4 Process path planning and tools optionGenerally, the forming of an automobile panel includesseveral operations, such as drawing, trimming, flanging,piercing, re-striking, hemming, etc. Among the operations,drawing, trimming and flanging are the main operations toform the main shape of the product, and other operationsare auxiliary operations, which work together with themain operations to form complex shapes of the product. Toget precedence relations among operations based on thePIM, the main operations must first be determined, andthen the decisions are made about how to arrange the initialmain operations, how to combine the auxiliary operationswith the main operation, and how to insert auxiliaryoperations to the operation sequence. For the integration ofplanning, it should consider the stamping dies’ capability,cost and capacity of machinery or workshop as criticalissues at the sequencing level.Theoretically, case-based reasoning (CBR), rule-basedreasoning (RBR), and model-based reasoning (MBR) areall applied for process planning. In this paper, CBR, RBRand artificial neural network are joined up as the decision-making methods after model-based reasoning duringprocess planning, which is shown in Fig. 8. Firstly, themodel-based reasoning is used to form a code of theproduct and operation for CBR based on feature entitiesand their interrelationships, and relevant rules or knowl-edge for others reasoning.
Then the CBR is selected to getsimilar plans for the case base; if CBR is not suited, theRBR and ANN are select to complete the task coopera-tively. During sequencing of forming operations, thestructure of the die for each operation can be performedfrom the operations and assigned stamping features. Thesystem can plan the equipment and operators for eachoperation to meet design specifications, and to achieveminimum machining time and maximum efficiency basedon the above activity and knowledge. Finally, the optimalprocess plans obtained can be added into the case base ofplans for the planning of other similar products.Customarily and practically, the relationships betweenoperations consist of operations order constraint (do-after),which relates to the necessary order of operations to be used, and operations combination constraint, which relatesto relevant operations that can be formed at one process anddie together (mentioned in Sect. 4.1). For example,flanging is after trimming, while piercing and trimmingare always formed in one process.For the aims of economic efficiency and top-quality, it isalways recommended to combine the potential operationstogether, while making the sequence operations practical.Therefore the initial main operation sequence is Blank-ing→ Drawing → Trimming → Flanging for a flangefeature comprised part, and Blanking→ Drawing →Trimming for no flange feature part. With operationssequencing and combination rules, auxiliary operations areadded to the initial main operation sequences to form finalprocess routing. The following is the combination rules forhole1 and hole3 shown in Fig. 3:(Logical) combination (for hole1 and hole3): IFdistancebetween hole1 and hole3 >DIS && the angle of the vectorsof the two hole<15· THEN TRUE ELSE FALSE;Thereafter, the structure of the die for each process canbe performed from operations and the assigned features,while the process route is determined. Then the equipmentsuch as a set of machinery or the product line can beselected to insure the stamping die meets design specifica-tions. For example, Fig. 9 shows generation routes ofprocess planning for the automobile panel shown in Fig. 3.During process planning, different process routes can befound by different planners; therefore, the best processroute should be selected according to the batch ofproduction, design and manufacturing of stamping dies,cost, etc. while tool options, the equipment and dies foreach process should be assigned to meet design specifica-tions, and to achieve minimum machining time andmaximum efficiency. Finally, the optimization of processplanning [20] is realized for multiple purposes (best-quality, maximizing efficiency, minimizing cost and time)by PPO based on KBE. 4.5 PCS in process path generationSince the process planning is a dynamic course with severalplans and design stages, PCS is a key point to ensureprocess planning is integrated and consistent. PCS man-ages the process information model, assists in generatingstamping process plans and detail design, and controlsthe changes during planning. There are several controlvariables for PCS including state variables for processplanning, control variables for IMM, and state variables forstamping features, etc. The process control structure isshown in Fig. 10.In this CAPP system, the process planning is defined as aproject. The project control can create a project, insert thepart or work-pieces to suitable positions of the project, anddecompose the process planning task into subtasks.In IMM and process planning, according to the knowl-edge expression and decision-making rules, the planningprocess control can set up the process information modelbased on features and their state variable, monitor planningprocess, feed the planning information and changes back toIMM, and control information transfer.The process planning is a dynamic process of informa-tion flow and transfer. The information link control ensuresprocess planning information is associative and consistent.The added, extended, and modified information and itseffects on the planning can be fed back to PIMand IMM sothat the information of process planning can be updatedtimely and shared by different parts of the system.For the complicated and mass geometry informationinvolved during the process planning, the links betweenfeatures and product geometric information have been dealtwith. The geometry link control can monitor and controlthe links and transfer the geometry information betweendifferent parts of the process planning.In IMM, the parts of PCS come into being dynamicallyalong with proceeding of the process planning. If one partof PCS is created, it will monitor and control relevantplanning and information subsequently.When some resultsof process planning are deleted, the corresponding PCSpart will fade away.5 ConclusionAs the automobile body panel is one kind of sheet metalpart with groups of free form surfaces and large size, theprocess planning is more complicated than common sheetmetal stamping. Yet the automobile panels can be con-sidered as a combination of some common stamping, suchProject control Planning process controlGeometry link control Detail design control Information link control Process control structure (PCS) Fig. 10 The process control structure as irregular drawing, flanging/bending, trimming, andpiercing, etc.