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The LE provides severalmethods to deal with these links, e.g. parameters variablelink, data structures link, and geometrical link.The PPO is a methodology of design optimum forcomplex engineering, which can deal with the complicatedoptimization problem of process planning in an economicview.3.2 The framework of CAPP system based KBEThe stamping CAPP system for automobile panels basedon the intelligent master model above consists of severalstages such as stamping features extraction from productdata, operation features reasoning from stamping featuresto form a process information model, process planning toget the sequence of operations and relevant tools, detaildesign for workpieces, simulation for detail design, andfinally the process plans and 3D die-face model generationwhich is shown in Fig. 2. It is a tangible activity level tocontrol and frame a CAPP system for automobile panels.Interface of CAD system Knowledge baseKBE Link AssociationProcess Information Model Process Control Structure Process Planning OptimizationFig. 1 IMM of process planning665 In the CAPP system, stamping process planning ofautomobile panels needs to first establish a processinformation model based on a 3D model product andfeature technology. Stamping features are extracted, andoperation features are attained subsequently. The featuresall carry knowledge about themselves, the process andconstraints. Then the PIM and PCS are established. There-after, the sequence planning is setup based on PIM andknowledge such as operation sequence rules, operationcombination guides and reasoning methods, and then thedies and machinery are options.Along with the process of the planning, PCS, PPO andLE of IMM are built by knowledge driving. PCS consistsof an integrated collection of tasks that can initiate, control,manage, evaluate and update all the planning informationand results timely. PPO optimizes process paths and enter-prises resource environments, and PCS and PPO carry outthe optimization and find the optimal solution. PCS and LEmake process planning associated and linkable.4 Key points of process path generationUnigraphics has several features that provide a subset ofthe capabilities of a KBE language—UG/KFL, whichprovides a way to specify knowledge rules that can coverall Unigraphics applications.
The stamping CAPP systemfor automobile panels has been developed based on theframeworks advanced above, which choose C and UG/KFlanguage as the implementation language, and ACCESSas its database on the UG/CAD development environ-ment. UG/Open and UG/Open++ allow customization andextension of Unigraphics using a standard procedurallanguage (C and C++). UG/KFL provides a way to specifyknowledge rules that can cover all Unigraphics applica-tions. Rules of UG/KFL are easily written by the developer,easy to read, understandable, and reusable by the user.Furthermore, UG/Open can be integrated with KBE byaccessing C programs from the KBE language describedunder External Function. For access to named attributesfrom C, there will be a utility program that takes a designdefinition in the language and produces C bindings toaccess the attributes of an object instance of that design.The access consists of functions and methods for gettingand setting the value of the named attributes of objectinstances. Additionally, there are UDF and UDO in UG/CAD and UG/KF, which can be dealt with by UG/Openand UG/KF. What is more, Unigraphics is integrated withmany other knowledge tools and sources, such as spreadsheets, other ICAD KBE language systems, finite elementanalysis, CAM, etc.4.1 Stamping featureTo generate appropriate process plans, the product datarequires the original inputs, which includes the geometry,topology, tolerance, material and quantity of product.Based on the feature technology and stamping technology,a stamping feature is the portion of a part which can beformed by means of certain stamping operations. For ex-ample, a drawn feature or bend feature is defined as themain feature, which is to describe the near net shape of acomponent, while flange, hole, emboss, bead, notch andflange-hole are defined as the auxiliary ones, which arerequired to describe the local part of the final shape.Using feature technology and the geometry extractionmethod, the stamping design features, such as the mainforming feature (e.g. drawing, bend), flange, hole, emboss,bead, notch, and so on, can be extracted from a 3D solidmodel, which are first defined as UG/UDO. For example,Fig. 3 shows the stamping features of one automobile panel.The stamping feature model should then be defined torepresent product knowledge integrated and unambiguous.The stamping feature is represented as object-oriented classor object and instance using UG/KF language (UG/KFL); it not only represents feature parameters, tolerance, material,etc. as attributes of class or instance, but also representsgeometrical objects by importing UG/UDO and UG/UDFreferenced solid geometry as an instance attribute or child.And this realizes the connectivity and integration betweenthe symbol of a feature and its geometrical object. It canalso get an attribute value from a function, rule, expressionand database.