3。2 The framework of CAPP system based KBE

The stamping CAPP system for automobile panels based on the intelligent master model above consists of several stages such as stamping features extraction from product data, operation features reasoning from stamping features to form a process information model, process planning to get the sequence of operations and relevant tools, detail design for work pieces, simulation for detail design, and finally the process plans and 3D die-face model generation which is shown in Fig。2。 It is a tangible activity level to control and frame a CAPP system for automobile panels。

In the CAPP system, stamping process planning of automobile panels needs to first establish a process information model based on a 3D model product and feature technology。 Stamping features are extracted, and operation features are attained subsequently。 The features all carry knowledge about themselves, the process and constraints。 Then the PIM and PCS are established。 There-after, the sequence planning is setup based on PIM and knowledge such as operation sequence rules, operation combination guides and reasoning methods, and then the dies and machinery are options。 Along with the process of the planning, PCS, PPO and LE of IMM are built by knowledge driving。 PCS consists of an integrated collection of tasks that can initiate, control, manage, evaluate and update all the planning information and results timely。 PPO optimizes process paths and enterprises resource environments, and PCS and PPO carry out the optimization and find the optimal solution。 PCS and LE make process planning associated and linkable。

4 Key points of process path generation

Unigraphics has several features that provide a subset of the capabilities of a KBE    language

—UG/KFL, which provides a way to specify knowledge rules that can cover all Unigraphics applications。 The stamping CAPP system for automobile panels has been developed based on the frameworks advanced above, which choose C and UG/KF language as t he implementation language, a nd ACCESS as its database o n t he UG/CA D development environment。 UG/Open and UG/Open++ allow custom i zation and extension of Unigraphics using a standard procedural language (C and C++)。 UG/KFL provides a way to specify knowledge rules that can cover all Unigraphics applications。 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 by accessing C programs from the KBE language described under External Function。 For access to named attributes from C, there will be a utility program that takes a design definition in the language and produces C bindings to access the attributes of an object instance of that design。 The access consists of functions and methods for getting and setting the value of the named attributes of object instances。 Additionally, there are UDF and UDO in UG/ CAD and UG/KF, which can be dealt with by UG/Open and UG/KF。 What is more, Unigraphics is integrated with many other knowledge tools and sources, such as spread sheets, other ICAD KBE language systems, finite element analysis, CAM, etc。

4。1 Stamping feature

To generate appropriate process plans, the product data requires 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 be formed by means of certain stamping operations。 For ex- ample, a drawn feature or bend feature is defined as the main feature, which is to describe the near net shape of a component, while flange, hole, emboss, bead, notch and flange-hole are defined as the auxiliary ones, which are required to describe the local part of the final shape。 Using feature technology and the geometry extraction method, the stamping design features, such as the main forming feature (e。g。 drawing, bend), flange, hole, emboss, bead, notch, and so on, can be extracted from a 3D solid model, 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 to represent product knowledge integrated and unambiguous。 The stamping feature is represented as object-oriented class or object and instance using UG/KF language (UG/KFL);it