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#Abstract As automobile body panels are one kind of sheetmetal part with groups of free form surfaces, the processplanning is more complicated than common sheet metalstamping to implode effectively and practically. Based onKBE, new frameworks have been presented as intelligentmaster model at the system level and as procedure model atthe activity level. In accordance with these frameworks, anintelligent CAPP system has been specifically developed.Based on feature technology, features have been extractedand represented by the object-oriented method. Stampingfeatures and their parameters have been defined and ex-tracted based on feature technology and stamping processrules. The whole product knowledge has been representedby frames which directly map to objects (or features) in theobject-oriented sense. Relevant appropriate operations fea-tures have been assigned to stamping features of a productbased on feature-operation criteria, parameters of thestamping feature and their correlativity. 57948
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This assignment isa decision-making activity using a set of rules with adecision-making tree and model-based reasoning methods.With knowledge between operations, such as operationsorder constraint (do-after) and operations combination con-straint, process paths have been improved based on relevantintelligent reasoning methods. Based on the relationships(preferred-to) between processes and machines/dies, thestructure of die and machine for each process can be iden-tified, since the process route has been determined. In thisstamping process planning, the procedure and informationhave been controlled by a process control structure that isassociative and integrated.Keywords Automobile panel . KBE .Process planning . Feature 1 IntroductionRecently, research on the computer-aided process planning(CAPP) system for sheet metal has been widely reported.Park et al. [1] constructed an automated process planningsystem for axisymmetric deep drawing products. Tisza [2]and Kang and Park [3] presented a group technology andmodularity to construct a CAPP system for process se-quence design in an expert system for non-axisymmetricdeep drawing products with elliptical shape. Gao et al. [4]developed an advanced software toolset used for theautomation of sheet metal fabrication planning for aircraftcomponents.
Zussman and Horsch [5] proposed a motionplanning approach for robot-assisted multiple-bent partsbased on C-space and a potential field. Wang and Bourne[6] proposed an automatic process planning system withthe features well investigated and the production plansresearched with near-minimum manufacturing costs. DeVin et al. [7, 8] developed a sheet-metal CAPP systemcalled PART-S, which integrates cutting, nesting, bendingand welding processes for bending sequences. Streppel etal. [9] showed the ambiguity of conventional tolerancesand presented a method which replaces conventionaltolerances with geometrical tolerances for process planningin small batch sheet metal part manufacturing. Aomura etal. [10] proposed a method which generated feasiblebending sequences of a sheet metal part handled by a robot,and discussed the determination of the best graspingpositions and repositions. Aomura and Koguchi [11] pro-posed a method to generate bending sequences of a sheetmetal part handled by a robot. Liao and Wang [12]proposed an evolutionary path-planning approach forrobot-assisted handling of sheet metal parts in bending.Lutters et al. [13] developed a generic architecture forcomputer aided process planning based on informationmanagement for sheet metal manufacturing in a small batchpart environment. Kumar and Rajotia [14] had proposed amethod of scheduling and its integration with CAPP, sothat on-line process plans can be generated taking intoaccount the availability of machines and alternative routes.The contents above are mainly for process parameter calculating, path-planning and some sketch map of work-pieces for specific types of sheet metal, such as axisym-metric and non-axisymmetric deep drawings, complexbendings and shearings, and so on.The automobile body panel is one kind of sheet metalpart, which is complicated in shape, with groups of freeform surfaces, a large figure in size and is always man-ufactured by stamping processes. Automobile panels canbe considered as a combination of some common stamping,such as irregular drawing, flanging/bending, trimming andpiercing, etc. The process planning of these panels is morecomplicated than common sheet metal stamping, which isgenerally dependent on engineers experience to complete.It is believed that the process path plan for automobilepanels is requisite and acquirable.In essence, the stamping process path for automobilepanels is to determine the necessary forming processes andtheir sequences in order to produce a particular part eco-nomically and competitively. Process paths generation is adecision-making process. Decisions on stamping opera-tions for a particular feature have to be formed on variousindependent conditions such as which operation should beperformed with which die and tools and under whatforming parameters. A CAPP system for these should be anintegrated environment to deal with knowledge to reducethe dependence on engineers or experts, and realize theprocess planning with scientism. Thus, knowledge basedengineering (KBE) is applied to advance the stampingCAPP system for automobile panels, and even to improvethe competitiveness for the automobile industry. This paperis particularly concerned with the construction involvedwith developing a CAPP system based on KBE.2 KBE in CAPP system for stamping2.1 KBEKnowledge based engineering (KBE) is one innovativemethod of artificial intelligence for engineering designdeveloped in the 1980s. So far, there is no generallyaccepted and mature definition for KBE. However, it isrecognized that KBE is an intelligent method to resolveengineering problems, which can realize inheritance, inte-gration, innovation and management of domain expertknowledge through the drive, multiplication and applica-tion of knowledge. A knowledge-based system (KBS) isone that captures the expertise of inpiduals within aparticular field (the “domain”), and incorporates it andmakes it available within a computerized application [15].The level of complexity of the tasks performed by such asystem can vary greatly. However, it can generally be saidthat while a domain expert would find them routine, theywould be outside the capabilities of a person unfamiliarwith the domain [16].KBE provides an open architecture and reuse ability ofexperience and knowledge, which can deal with multi-domain and multi-expression of knowledge, and can forman integrated environment. A KBE application is furtherspecialized, and typically has the following components ofgeometry, configuration, and engineering knowledge:– Geometry – there is very often a substantial element ofcomputer-aided design (CAD). Most of the softwareused to create KBE applications either has CADcapabilities built in, or is able to integrate closely with aCAD package.– Configuration – this refers to the matching of validcombinations of components.– Engineering knowledge – this enables manufacturingand other considerations to be built into the productdesign.When a candidate application area requires a high degreeof integration of the above elements, KBE is likely to be thebest method for its integration. KBE is sometimes termedrule-based engineering, as within the discipline, knowledgeis often represented by rules. These may be mathematicalformulae or conditional statements, and although simple inconcept, they may then be combined to form complex andpowerful expressions. KBE systems, on the other hand, areusually provided with specialized geometrical capabilities,with the ability to embed engineering knowledge within aproduct model.