W. Liu 1,a, Y.Y. Yang 1,b and Z.W. Xing 2,c

Transcription

1 Materials Science Forum Vols (2004) pp online at Materials (2004) Trans Science Tech Forum Publications, Vols. *** Switzerland (2004) pp Online available since 2004/Dec/15 online at Trans Tech Publications, Switzerland Study on Process Decision Methodology for Sheet Metal Stamping by Case Based Technology W. Liu 1,a, Y.Y. Yang 1,b and Z.W. Xing 2,c 1 P.O.Box 435, Room 204, School of Material Science and Engineering, Harbin Institute of Technology, Harbin , China 2 P.O.Box 425 School of Mechanical and Electrical Engineering, Harbin Institute of Technology, Harbin , China a liuweihit@163.com, b yyyanghit@hit.edu.cn, c JGJYS@hit.edu.cn Keywords: Sheet metal, Auto body panels, Case based, Stamping process Abstract. More powerful process design methods and tools of sheet metal stamping are needed to help engineers design better products, to reduce lead times and costs, and to increase product performance and accuracy. A novel model for representation of object-oriented case information constitution relationship is presented, Class-Property structure is proposed in order to refine the case representation, multi-types properties are adopt to describe more detailed information, three hierarchies of index strategy are used to realize case extraction. Furthermore, experts knowledge and experience on previous design cases and forming problems are collected, which can provide designers useful practical experience and data to aid design procedure and to solve the potential problems of sheet metal stamping. In order to illustrate these applications, database technology is used to realize a prototype system of auto body panels, which can be used to integrate process design information and manufacture resources. Introduction Tool and process design of auto body panels stamping are very complex and creative tasks which deal with large amounts of information involving many process factors. Engineers accomplish process design based on the product model, and make analogies with previous similar design cases [1]. So engineers usually make their decisions according to past experience rather than theoretical knowledge, to some extent, the design process remains a process of trial and error which often delays completion of tool design and can not allow engineers new to the subject, and to practice it [2,3]. To overcome these problems, computer-aided tools are developed and the basis of a novel software tool for sheet stamping is presented in this paper. Case-based Technology In recent years, it has been recognized that case based technology will provide a possible solution for improving experience based design methods and gaining competitive advantage by the development of tool software systems [4]. But, few of them concern sheet metal stamping, and even fewer are for complicated auto body panels [5-7]. Case based systems can store many kinds of experience, knowledge, and data of previous designs as important design resources. For a designer facing a new task which is similar to previous tasks, these cases stored in such a system could suggest feasible solutions by avoiding potential problems, providing necessary data to aid the design process, and make it possible to support designers in making correct decisions. Such system enable information memorized in databases or knowledge bases to be available to a number of designers. All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of the publisher: Trans Tech Publications Ltd, Switzerland, (ID: /04/08,12:09:41)

2 896 Advances in Materials Manufacturing Science and Technology 896 Advances in Materials Manufacturing Science and Technology This paper describes case based process decision support software, developed by the authors, for the stamping of auto body panels. The prototype system of the Stamping Information Supporter (SIS) is founded on a relational database in the Windows environment. Case-based Stamping Process Design Methodology Case-based Process Design System and Procedure. Data and knowledge are bases of process design case which should be readily accessible to speed up the process. So, the case can be described as: CASE={ DATA, KNOWLEDGE } Where, DATA=( D1, D2, D3,, Dn ), such as technique data, material physical properties, forming press parameters, etc. KNOWLEDGE=( K1, K2, K3,, Kn ), such as design experience or design rules, design cases and forming defect information, etc. As shown in Fig. 1. On inputting the product model information, the case base will support designers to access the design information listed above, aid them to refer to previous similar cases, warn them for potential problems which may be encountered, explain why they are likely to occur, and provide solutions or advice to avoid forming failures. As a result, it will be more easy than before for designers, particularly designers with little experience, to make decisions and propose solutions. Product Description Control Flow User Interface/Management System Information Flow Technique Material Press Database Designer Knowledge base Experience Knowledge Defects Decisions/Solutions Fig.1 Case based process design system and procedure Database Founded System. To build the case based system described in this paper, database technology has been used to realize the structure of the prototype software system. This software is composed of three modules: data base, knowledge base and the management system, as shown in Fig.1. The management system can provide the ability to add, modify, delete, query, and print, etc. The case is retrieved from the system through graphics display, and query report generation. Classification and Representation of Panel Products Modeling for Process Design Case. In this paper, computer technologies have been used to help transform the case from the concept model to the data structure and program [8]. The stamping process was modeled by using Class-Property approach, each class corresponds to a type of case which has its own

3 Materials Science Forum Vols Materials Science Forum Vols. *** 897 constitutes and properties. Furthermore, the relationship between different kinds of classes is expressed by using mapping method, such as one to one or one to multi mapping methods. Classification. Auto body panels are generally associated with and identified by their function [9, 10]. For example, the outer panels can be fenders, hoods, doors and others. The case model is organized around the major concepts of the panels represented by classes, and the concepts of design requirements associated with these classes. This work classifies the product information progressively by defining the following building blocks: (a)the panel class structure, (b)the related properties, (c)the class-properties relationship. Class and Property. In this paper, the object-oriented method is used primarily to represent the design objects. Each panel class has a definition which encapsulates its properties and the intended uses of information. For example, the front fender panel include the properties that define its geometry, material, defects, and so forth. The properties can be represented by different types, such as character, string, number, date, general, logic, etc, and the store space of a property value can be adjust according to its need. As illustrated in Fig.2, the properties used to describe parts can be classified into three hierarchies of information: FrontFenderPanel Properties PanelName PanelID DesignDate General information ID:001 PanelLength HeadLampOpeningCurvature WheelOpeningRadius Defects Mechanics Solutions Geometry feature Process knowledge ID:002 Fig. 2 Class and properties Fig. 3 Forming problems of the front fender Relationship Between Class and Properties. Each panel class has its own special properties which can be used only on this panel, and some common properties which can be used to all panels. For instance, all panels have the first level and the third level properties, but only the front fender panel has the HeadLampOpeningCurvature property of the second level which is much different from other panels. Because process design is different from product design, designers pay more attention on some crucial process parameters of typical features, such as, the stamping depth, press direction, etc, but not the detail geometrical data of 3-D model. So, the present representation method is proven sufficient for current purpose. Retrievals of Experience and Knowledge In the development of a case based system, the capture of knowledge is recognized as the bottle neck problem [11, 12]. However, in the collection of stamping process knowledge, it has been proved to be a very useful exercise to investigate in factories, discuss with experts and study from the design cases. To support design decisions, several kinds of case information are available to users, they are: (a) Forming difficulty problems of different cases with similar-shaped regions that have issues, including the detailed region descriptions of these forming issues and the shape of potential defects. This information

4 898 Advances in Materials Manufacturing Science and Technology 898 Advances in Materials Manufacturing Science and Technology warns designers to pay attention to these potential defects. (b) The mechanism or reasons arise from these potential problems, according to plastic theory and stamping process knowledge. This kind of knowledge will give designers an essential understanding of these phenomena. (c) The case summaries of manufacture of similar panels previously and the solutions to forming problems that have been successfully applied, so as to suggest possible design changes. (d) The design cases without issues. Case Study A Front Fender Panel. Fig.3 shows a summaries of the issues arising in the stamping of front fender panel. The table 1 records some typical issues in different regions. To see additional information, designer can choose a particular record, and the system will show the detailed contents for this particular issue, including information of the region in which that issue occurs, the mechanism and the solutions previously applied. Table 1 Mechanism and solutions of forming problems of the front fender ID Problems Mechanics Solutions 001 Impact line Too much material flow in 002 Surface deflection Defects remained after bending 1) Add a draw bead, increase resistance of flow in. 1) Adjust the height of addendum. 2) Use low yield strength material. 3) Decrease the die profile radius. Output Interface. The output interface makes it easy for users to extract knowledge and design information from the system, three levels of selection method are provided: (a) Query of cases by using low-level management information such as panel names, material types, panel models, etc. (b) Query high-level geometry-feature information according to potential forming problems. (c) Query the types of defects that happened in past forming processes or manufacture, and retrieve other information of defects, such as the regions in which they often occur, mechanis of causation and solutions to the problem. Conclusions The stamping process design is a very complex procedure which has amounts of design information and factors need to be handled, and it is very hard for designers to retrieve the necessary experience and data which are very important to avoid the potential problems when facing a new task. On this background, the case based process design methodology was presented to integrate these design resources for users. Furthermore, In order to study its application and realize a prototype system, the key technologies of modeling and representation of case have been solved. In the paper, we used the Class-Property approach to define the case information and represent the relationship between the classes. The object-oriented model as a means was applied to organize and encapsulate the panel products, other information such as shapes, features, etc, were described as properties according to the design requirements. In this study, it was found that database technology is a feasible and fast method to represent cases.

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