Abstract: As automobile body panels are one kind of sheet metal part with groups of free form surfaces, the process planning is more complicated than common  sheet  metal stamping to implode effectively and practically。 Based on KBE, new frameworks have been presented as intelligent master model at the system level and as procedure model at the activity level。 In accordance with these frameworks, an intelligent CAPP system has been specifically developed。 Based on feature technology, features have been extracted and represented by the object-oriented method。 Stamping features and their parameters have been defined and extracted based on feature technology and stamping process rules。 The  whole  product knowledge has been represented by frames which directly map to objects (or features) in the object-oriented sense。 Relevant appropriate operations features have been assigned to stamping features of a product based on feature-operation criteria, parameters of the stamping feature and their correlativity。 This assignment is a decision-making activity using a set of rules with a decision-making tree and model-based reasoning methods。 With knowledge between operations, such as operations order constraint (do-after) and operations combination constraint, process paths have been improved based on relevant intelligent reasoning methods。 Based on the relationships (preferred-to) between processes and machines/dies, the structure of die and machine for each process can be identified, since the process route has been determined。 In this stamping process planning, the procedure and information have been controlled by a process control structure that is associative and integrated。74973

1 Introduction

Recently, research on the computer-aided process planning (CAPP) system for sheet metal has been widely reported。 Park et al。 [1] constructed an automated process planning system for ax symmetric deep drawing products。 Tessa [2] and Kang and Park [3] presented a group technology and modularity to construct a CAPP system for process sequence design in an expert system for non-ax symmetric deep drawing products with elliptical shape。 Gao et al。  [4] developed an advanced software toolset used for the automation of sheet metal fabrication planning for aircraft components。 Zussman and Horsch [5] proposed a motion planning approach for robot-assisted multiple-bent parts based on C-space and a potential field。 Wang and Bourne [6] proposed an automatic process planning system with the features well investigated and the production plans researched with near-minimum manufacturing costs。 De Vin et al。 [7 , 8] developed a sheet-metal CAPP system called PART-S, which integrates cutting, nesting, bending and welding processes for bending sequences。 Streppel et al。 [9] showed the ambiguity of conventional tolerances and presented a method which replaces conventional tolerances with geometrical tolerances for process planning in small batch sheet metal part manufacturing。 Amoral et al。 [10] proposed a method which generated feasible bending sequences of a sheet metal part handled by a robot, and discussed the determination of the best grasping positions and repositions。 Aomura and Koguchi [11] pro- posed a method to generate bending sequences

of a sheet metal part handled by a robot。 Liao and Wang [12] proposed an evolutionary path-planning approach for robot-assisted handling of sheet metal parts in bending。 Lutters et al。 [13] developed a generic architecture for computer aided process planning based on information management for sheet metal manufacturing in a small batch part environment。 Kumar and Rajotia [14] had proposed a method of scheduling and its integration with CAPP, so that on-line process plans can be generated taking into account 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 axis-metric and non-ax symmetric deep drawings, complex bandings and sheerings, and so on。 The automobile body panel is one kind of sheet metal part, which is complicated in shape, with groups of free form surfaces, a large figure in size and is always manufactured by stamping processes。 Automobile panels can be considered as a combination of some common stamping, such as irregular drawing, flanging/bending, trimming and piercing, etc。 The process planning of these panels is more complicated than common sheet metal stamping, which is generally dependent on engineers experience to complete。 It is believed that the process path plan for automobile panels  is requisite and acquirable。 In essence, the stamping process path for automobile panels is to determine the necessary forming processes and their sequences in order to produce a particular part economically and competitively。 Process paths generation is a decision-making process。 Decisions on stamping operations for a particular feature have to be formed on various independent conditions such as which operation should be performed with which die and tools and under what forming parameters。 A CAPP system for these should be an integrated environment to deal with knowledge to reduce the dependence on engineers or experts, and realize the process planning with scientism。 Thus, knowledge based engineering (KBE) is applied to advance the stamping CAPP system for automobile panels, and even to improve the competitiveness for the automobile industry。 This paper is particularly concerned with the construction involved with developing a CAPP system based on KBE。