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Trends and developments in the automation of design and manufacture of tools for metal stampings
Journal of Materials Processing Technology 75 (1998) 240 – 252
Trends and developments in the automation of design and manufacture of tools for metal stampings B.T. Cheok a,*, A.Y.C. Nee b a
CAE/CAD/CAM Centre, Faculty of Engineering, National Uni6ersity of Singapore, 10 Kent Ridge Crescent, Singapore 0511, Singapore b Department of Mechanical and Production Engineering, Faculty of Engineering, National Uni6ersity of Singapore, Singapore Received 20 January 1997
Abstract Metal stampings play an important part in modern-day life. Together with plastic molds, they form the most important structural components of all electrical and electronic equipment. Researchers all over the world have spent a tremendous amount of time and effort trying to develop better computer aids for the design of tools and dies required to manufacture metal stampings. This paper explains the motivation to develop an integrated planning-and-design aid for the die designer. From the literature, trends and developments in the design automation of toolings for the manufacture of metal stampings are discussed. The application of various artificial intelligence (AI) techniques to solve problems that were previously exclusive domains of human designers is highlighted. A knowledge-based framework for developing an integrated software for the planning and design of progressive dies is illustrated. © 1998 Elsevier Science S.A. Keywords: Metal-stampings; Tool and die; Progressive die; Artificial intelligence; Knowledge-based systems; Precision engineering
1. Introduction
2. Need for a better mouse-trap
At present, metal stampings are used in almost every mass-produced product. According to a survey in the US, some 100 000 metal stampings could be found in the average American home in the 1980s [1]. Metal stamping manufacturing processes are popular because they are an economical and quick means of producing intricate, accurate, strong and durable articles in huge quantities. Simple dies, compound dies and progressive dies are used for producing metal stampings. In a progressive die, the workpieces are advanced from one station to another. At each station, one or more die operations, such as piercing, notching, blanking, lancing, shaving, drawing, embossing, coining and forming are performed on the sheet metal strip. The result is a finished component at every stroke of the press. There are many good textbooks [2 – 7] written to explain these metal stamping operations and the associated tooling design and manufacturing considerations.
In developing and developed countries, the manufacturing sector is probably the most important pillar of the economy. In Singapore, the manufacturing sector contributes more than 25% to the GDP with a total Gross Value Adding of more than S$ 24 billion. It also accounts for more than 400 000 jobs.[8]. In the same context, the precision engineering industry is an important pillar in Singapore‘s manufacturing sector, providing the tooling required for the production of high value added mechanical and electrical components and products. Metal stamping is a major downstream supporting industry in Singapore. In 1992, it employed some 4600 workers with an annual output of S$ 600 million and an output growth rate in excess of 10% [9]. One of the most skill-intensive tasks in the mass production of metal stampings is the design of progressive dies. Modern CAD/CAM technology, together with new ideas in the design and construction of tools, coupled with increased speed and rigidity of presses, have contributed towards the continual use of metal stamping production processes to manufacture increas-
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ingly more sophisticated products. However, these developments have demanded greater skills from the designers. In Singapore, the problem is further compounded by two factors: 1. In a dynamic and fast-growing economy, young people do not have the patience to undergo long periods of apprenticeship training to acquire the skills to be a die designer, hence, there are less people joining the trade. 2. The precision engineering industry in Singapore supports mainly the computer, tele-communications and electronics/electrical appliances market. Owing to rapid changes in consumer taste, these products have very short life cycles. In other words, there is a rapid demand for more sophisticated metal stampings and plastic parts. Die designers are under constant pressure to exploit the latest design and manufacturing technology in order to meet the market demand. To overcome these problems and to sustain competitiveness, there is an urgent need to provide an intelligent aid to the die designer so that the overall die design and manufacturing lead time can be shortened and metal stampings of improved qualities can be produced at lower costs.
3. A review of research and design in the design automation of toolings for metal stampings Traditionally, research in material processing has been focused on using experimental and numerical techniques to solve problems related to the behaviour of materials under a wide variety of stresses and strains. The published findings can be used to help the die designer to predict the behaviour of the workpiece and the tools. However, dies are still designed manually. With the introduction of computer graphics and CAD/ CAM systems, some researchers have started to exploit the advances in interactive computer graphics and CNC technology for the design and manufacture of metalstamping tooling, especially progressive dies. The Japanese industries were probably among the first to develop in-house turnkey CAD/CAM systems for progressive dies for industrial use. From the mid 1970s, researchers from Hitachi [10 – 13], Nippon Electric [14], the Mechanical Engineering Laboratory [15], Fujitsu and Matsushita Electric Works [16] and others [17] have reported extensively their custom-made integrated computer-aided design and manufacturing systems for press tools. The Hitachi system consists of three processors. The designer uses an APT-like language to input the part drawing into the pre-processor. The pre-processor generates a nested arrangement in the form of a blank layout drawing. The designer has to manually plan the
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strip and die layout and use the APT-like language to input the information to the main processor. The latter processor then determines the construction and size of the die and generates the part list. Finally, the post-processor plots the assembly and dimensioned part drawings. The system can reduce the time taken to design a die from 20 to 5 days. Nippon Electric developed a computer-aided manufacturing system for small lot-size sheet metal parts. The system takes care of process planning, nesting and CNC punching operations. The CAD system developed at the Mechanical Engineering Laboratory adopts the conventional design approach of two-dimensional progressive die design using a set of standard design operations with punch shapes as the key development concept. These early die-design systems attempted to use basic computer graphics facilities and programmes written in FORTRAN to improve the productivity of the die designer. Geometrical information has to be entered laboriously via the keyboard using APT-like command language. Most design decisions were made by the designer, the computer being used to improve productivity in drawing and to perform particular design calculations and NC programming. Yet, they were able to achieve productivity gains of 30–400% over the manual approach. Attempts to improve their die design productivity in the late 1970s and early 1980s indicates the importance of the metal stamping industry to the electrical and electronic components and equipment manufacturers. At that time, Japan was amongst the world’s largest exporter of electrical and electronic home appliances and office equipment. The early CAD/CAM systems for progressive die design and manufacturing may appear to be rather primitive by today‘s standard. However, these efforts laid a solid foundation for future developments. Concepts such as using standard punch shapes as primitive shapes for punch selection and de-composition, the standardisation of die components, the computer modelling of die components and die layout area and the standardisation of design procedures were followed to advantage by later researchers. The wide acceptance of CAD/CAM equipment in the mid 1980s represented the second thrust in the design automation of progressive dies. Most CAD/CAM equipment provide programming languages for customisation and/or is able to interface directly with a high level programming language such as FORTRAN. Researchers began to exploit these features to develop dedicated CAD/CAM systems for progressive die design. In Finland, the Laboratory of Metal Working and Heat Treatment [18] integrated FORTRAN calculation routines with Auto-trol, a 3D CAD/CAM system. Auto-trol provided the drafting, 3D wire-frame modelling and CAM functions. In addition, a volume-based folding and unfolding CAD system was used. The
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FORTRAN routines were integrated with the CAD/ CAM system to calculate stripper and punch forces, bending forces, bend radii and material utilisation, and to automate the selection and parametric sizing of some die components, and the generation of part listing and tool dimensioning. In Japan, Fujitsu and Matsushita [16] jointly developed an integrated CAD/CAM system for automating and improving productivity in the manufacture of injection molds and progressive dies used in producing electronic parts and precision machinery parts. The system has strong links with CADAM, another CAD/CAM system. Second generation die design systems represent a vast improvement over the first generation in terms of interactive graphics and 3D modelling functionality. However, as they are still based on procedural programming languages such as FORTRAN, they are only able to automate relatively simple calculations and data extraction (for example, the generation of a part list and tool dimensions) tasks. Most of the important decisions such as the design of punch shapes, the assessment of formability and the development of the strip layout, are still made interactively by the user. The mid 1980s also saw the introduction of many commercial CAD/CAM systems for progressive die design. At present, systems such as the Fanuc Progressive Die CAD/CAM System, Auto-trol’s Progressive Die System, the ADMS Die Master System, the U-Graph Assisted Die Design System, Pro/SHEETMETAL, MetalCAD, and the EXCESS and Striker Systems can be purchased ‘off-the-rack’. A review of the first four systems can be found in [19]. Most of these commercial systems are the customisation of existing CAD/CAM systems such as Fanuc, Auto-trol, Pro/ENGINEER and AutoCAD to provide the added functionalities required specifically by die designers. They are basically interactive in nature and can only be viewed as productivity enhancement aids for the die designer. This is because considerable human expertise is still needed to use these systems to arrive at the final design. Research and development of progressive die design automation systems was given a new dimension in the late 1980s and early 1990s when the applications of artificial intelligence techniques in engineering design started to take off [20 – 23] etc. Now, AI techniques are used increasingly in pattern recognition, production rules and frame-based inferencing and reasoning, fuzzy reasoning, feature-based design, etc., to design systems for the production of metal stampings. However, because of the complexity of the die-design process, most of the ‘intelligent’ die design automation prototypes are rather restrictive in their applications. One area of research that has attracted a considerable amount of attention is knowledge- and featurebased sheet metal forming. Some examples are as follows:
1. The Sheet Metal Advisor and Rule Tutor (SMAART) [24] is a feature-based CAD system developed to provide sheet metal manufacturing information for die designers. It uses a hybrid ruleand object- based representation of knowledge to store ten features in three levels of abstraction and about 65 forming violation rules. SMAART is designed to render advice immediately to the product designer on any violation of a design rule. In this way, the metal stampings that are designed will not cause any tooling design problems as far as forming is concerned. 2. Lee et al. [25] developed an assessment system consisting of a knowledge-based geometric-analysis module, a finite-element method (FEM) module and a formability analysis module. The geometric-analysis module uses geometric reasoning and feature recognition with a syntactic approach to extract high level geometric entities information from vertices of 2D forming profiles. The empirical rules for stamping die design are represented as frames in the knowledge base. If the formability information cannot be decided by geometric analysis, then a detailed FE simulation is performed using PAM-STAMP (a CAE software) where the strain distribution is obtained. Thereafter, the formability-analysis module uses a fracture energy criterion to assess the formability of the design. This software is suitable for assessing the formability of deeply formed parts such as automobile panels. 3. METEX (Metal Forming Expert System) [26] applies the principles of group technology to the process planning of multi-stage forming processes. It uses AutoCAD and AutoLISP to provide an expert system to generate possible forming solutions for deeply formed or drawn shapes, and adopts a hybrid classification utilising both geometric features and manufacturing characteristics for the coding of components to form part families for automatic process planning. A semi-automatic approach is used where human input is required when it is deemed that the computer is not suited to make particular decisions. 4. ASFEX (Axisymmetric Sequence Forming Expert System) [27] is an expert system developed by the Engineering Research Center for Net Shape Manufacturing (ERC/NSM) that uses design rules to generate process sequences for multi-stage drawing of round cups and tool geometry for each station of the sequence. 5. The ERC/NSM also developed a computer-aided analysis system [28] that uses Pro/Engineer sheet metal features to analyze the formability of complex sheet parts formed in multiple operations. At the same time, several universities and research institutes have adopted a wide variety of AI and tradi-
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tional computer approaches to develop die design automation systems: 1. Researchers at the National Taiwan Institute of Technology [29– 31] have developed PC-based expert prototypes for the design of shearing cut (blanking and piercing) progressive dies. ESSCP [29] is a prototype developed using FORTRAN, Micro Expert (the inference engine) and AutoCAD to plan and develop the progressive dies for the blanking and piercing of 2D parts with very simple geometrical profiles. In separate developments, the researchers also studied how uncertainties in design parameters can be processed using fuzzy mathematics for the detailed design of particular components in the die structure [30], and developed a knowledge-based system that uses a pattern recognition method called the new combined structural approach to develop the blank so as to optimise material cost, and a matching combination learning method for press procedures to optimise the number of stations in the die [31]. It is unclear whether they have integrated these AI techniques into an integrated system for the design of blanking and piercing progressive dies. 2. Researchers at the Huazhong University of Science and Technology, China also developed knowledgebased CAD/CAM packages for progressive dies for small-sized metal stampings [32 – 34]. Using features, a user can design a product in 3D wire-frame, thereafter the system will unfold it. After manually developing the blank layout, the user can use interactive commands to develop the strip layout. The user can then proceed to design the die structure interactively. Another feature of their research is the use of the directed and weighted graph approach for the automatic splitting of complicated die cavities [32]. Originally the system was developed on a Micro VAX mini-computer, but the system is now available on PCs and runs under the AutoCAD environment. 3. Researchers from the Department of Industrial Studies, University of Liverpool have also worked on expert systems for progressive piercing and blanking die design [35,36]. Their research concentrated on shape-coding and recognition techniques for the decomposing of the bridge scrap into smaller shapes [36]. However, their techniques are limited to straight-edge workpieces only. They also developed a UNIX-based expert system for the planning and design of progressive piercing and blanking dies [35]. The system was developed by integrating AutoCAD with Kappa and some C programs. 4. Researchers at the Department of Mechanical and Production Engineering, National University of Singapore have been developing algorithms for die design automation [1,19,37]. Initially, the work con-
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centrated on developing heuristics for nesting, automating the staging and punch shape selection and de-composition process. Later, it was extended to the use of a variety of knowledge-based approaches to extend the capabilities to include bending and forming, automatic punch shape selection, strip layout and 3D die configuration [38,39]. Another related development work is the development of a feature-based sheet-metal unfolder [40]. Experience gained from this research work has been used to establish a knowledge-based framework for the development of an integrated progressive die design software that will be presented later. 5. Researchers at the Shanghai Research Institute of Tool and Die Technology [41,42] have also developed CAD/CAM systems for progressive dies. The systems they developed rely on special relational data structures to describe the workpiece and the die structure. The strip layout is generated interactively. 6. Researchers at the Department of Industrial and Manufacturing Systems Engineering, University of Hong Kong developed BECAM, a CAD/CAM package for sheet metal blanking dies [43]. The program can help to develop the blank strip layout, the punch and die selection, and the drafting and generation of NC part programs. 7. CADDS, an automated die design system for sheetmetal blanking, was developed at the Indian Institute of Technology [44] using AutoCAD, AutoLISP and FORTRAN. The software is able to generate the strip layout automatically, conduct design checks for various die components, and generate the assembly views and the bill of materials for the die. Finally, there are researchers who seek to reduce the size of the problem by developing systems that concentrate on specific product types or on specific tasks. For example, a knowledge-based system based on ICAD was developed for the design of progressive dies for special order door hinges [45]. Similarly, the factors affecting the design of the high-speed precision blanking of thin sheet metals using progressive dies in the production of IC lead-frames are explained in [46]. Lee et al. [47] developed IKOOPP, a knowledge-based process planning system for the manufacture of progressive die plates. IKOOPP is able to automatically recognise the machining features from a 3D die plate modelled in Auto-trol and proceed to automatically plan the set up sequences, select the required machine tools, cutting tools, heat treatment, fixturing elements and sequence of operations.
4. Some comments on the current status A summary of the salient features of research and design work reviewed in terms of process planning,
Table 1 Salient features of the reserach and development work reviewed
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design and manufacturing functions and computer techniques used is given in Table 1. With emphasis on work done after the late 1980s, the following observations can be made: 1. Many of the systems built have demonstrated the technical feasibility of employing knowledge-based methods to solve design and manufacturing problems related to the forming process. However, there are very few attempts to integrate successful work done in these areas with die design automation software. 2. There are a few systems that appear to provide an integrated design and manufacturing aid for the die designer, however, their use is limited. They can either handle only piercing and blanking operations, or parts with relatively simple geometry or used for specialised products only. 3. Some of the researchers had demonstrated that particular AI techniques are potentially useful in terms of assisting users in some of the cognitive tasks associated with die design. 4. The die design automation systems reviewed in this paper still require a high degree of input by experienced designers during the design process. Progress in computer-aided die design automation still falls behind advances in computer technology, in particular advances in computer graphics and modelling, and the applications of AI in design, analysis and manufacturing. The research activities reviewed have indicated the growing importance and relevancy of particular AI techniques for the automation of some of the die design activities.
5. Framework for an integrated design system for progressive dies Researchers at the National University of Singapore have developed a framework for an integrated design system for progressive dies, the framework being developed based on experience gained in developing the earlier prototypes. The framework is based on the principles outlined in the following section.
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2. The use of a knowledge-based shell to store and manipulate the objects and rules associated with the die design process. The knowledge-based shell can either be a commercial package or a custom-made shell especially developed to handle stamping features and die components. 3. The use of high level computer languages such as C and C+ + to code the procedural and mathematical routines required to support the numerically intensive tasks. These numeric routines are coupled with the knowledge-based system such that the results produced by the former are returned as propositional logical expressions so that they can be formalised as well-formed equations for logical interpretation by the latter. 4. The use of multi-processing features of modern operating systems (such as Dynamic Data Exchange (DDE) provided by Windows or Inter-Process Communications (IPC routines provided by UNIX) to integrate the above-mentioned tools into a single software for the user. These approaches have proven to be very efficient in terms of computer-designer interaction by Cheok et al. [38,39] and Ismail et al. [35]. The resources can be integrated under the Windows operating environment using the architecture shown in Fig. 1.
5.2. Identification and use of the most appropriate AI techniques to handle the 6arious cogniti6e tasks in6ol6ed in progressi6e die design The tasks involved in the planning, design and manufacture of progressive dies are shown in Fig. 2. The experience of the authors has shown that the following AI techniques can be used to handle some of the cognitive tasks associated with die design: 1. Unfolding of a 3D product model into a flat pattern using features. The approach has proved to be very efficient, Toh et al. [40] and Li et al. [33,48]. 2. Heuristic rule-based approach for the selection of pilot and carrier schemes.
5.1. Identification, use of and integration of the most appropriate computer tools to handle the 6arious computing tasks in6ol6ed in progressi6e die design It is clear that the computer-aided die design process involves the following computing resources: 1. The use of a CADCAM system to provide the interactive graphical and geometrical modelling tools for the user to generate, view and manipulate the various plans and product and tooling models associated with the design.
Fig. 1. Computer architecture for die design and manufacture system.
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Fig. 2. Tasks involved in the planning, design and manufacture of progressive dies.
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3. Decomposition of punch shapes based on heuristics. 4. Recognition of punch shapes based on skeletal features and knowledge-based search techniques. 5. Heuristic rule-based approach for the staging of the die operations. 6. Model-based reasoning approach for the configuration of die assembly [49]. 7. Feature- and rule- based approach for the generation of process plans for the manufacture of die plates [25].
5.3. Sharing of design tasks between user and computer It is obvious that it is impossible for the computer to automate each and every design task identified in Fig. 2. In fact, progressive die design exhibits all the characteristics of the procedural design process [21] where the designer’s role is to control the design process to achieve the final solution. Hence, the framework is developed based on the concept of task sharing between the user and the computer, each playing a different role. The computer will be used to perform all the routine calculation, measurement, modelling and drafting activities. The designer’s guidance will be required in the following cases: 1. In a situation where a higher level of creativity is required rather than one that can only be achieved by the set of rules programmed into the system. 2. In a situation where it is reasonable to expect that the computer will not be able to make a good decision. 3. In a situation where the decision-making process is so complicated that the computer would require an unreasonably long time to arrive at a solution. For example, when deciding on the piloting scheme and the selection of pilot holes to guide the strip as it progresses along the die, one cannot expect the computer to come to a reasonable solution just by analysing the available holes, punch shape and sizes and the excess material on the strip. This is because the computer will tend to generate many possible solutions using standard pilot selection rules. Secondly, it is very difficult to program a set of design criteria that can be used to identify which of these numerous solutions is most appropriate. Instead, measurement routines and rules related to the selection of suitable pilot holes are used to present the ‘better’ solutions to the user. The user will then examine these solutions and use his/her judgment to make the final choice. In other cases, a ‘first-guess’ approach is adopted. Here, the computer will attempt to generate an initial solution which in most cases will form a reasonable starting point for the user to complete the solution. The user requires adequate interactive tools to input his decisions to the computer. For example, there is a need
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to de-compose the scrap material between the external profiles of the workpiece and the strip edges into smaller pieces so that they can be easily disposed from the die. In essence, there are no actual guidelines as to how the de-composition is done, and it is noted that most systems reviewed have left this task to the designer. The authors have developed routines to de-compose the scrap material into smaller ‘well-behaved’ strips by projecting horizontal or vertical lines from each and every vertice of the external profile to the neighbouring shape or to the edge of the strip. The solution will be presented graphically to the user. Thereafter, he/she can use interactive graphical aids to modify these strips into practical solutions for blanking the external shapes.
5.4. Use of metal-stamping features and the product feature-relationship tree as knowledge-based representation of the product Many researchers have used features to model metal stampings and the related information to assess their formability. The framework that the present authors have developed will use metal-stamping features and the feature-relationship tree to formalise the description of the product. The features and the feature-relationship tree of a simple metal stamping are shown in Fig. 3. The use of a feature tree provides an ideal starting point for an integrated knowledge-base to support the entire die design process. This is because each feature is associated with a stamping operation such that the attributes of the stamping operations can be used to generate the knowledge-based representation of the strip layout, and then the knowledge-based representation of the die components required to stamp the part. The inter-relationship between the features tree, the plan model and the engineering model in the knowledge base and the product drawings, the strip layout and the 3D solid model of the die is illustrated in Fig. 4. In addition to the modelling efficiency provided by this approach, the linking of the feature trees with the plan model and the engineering model provides the framework for concurrent engineering in die design. In other words, it is possible to design a system such that when the user makes a decision to modify the design at the down-stream operations, it can check how these decisions will affect the up-stream operations. Finally, it is noted that the feature-relationship tree provides global information about the manufacturing processes required to produce a product. Also, it can be translated into textual form, hence it can be used as a criterion to index the metal stampings in a design database. The design database is a database of products and their associated tooling manufactured by a company. It is noted that a die designer usually builds a progressive die by adopting an old design to meet the
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Fig. 3. Features and feature-relationship tree of a metal stamping.
manufacturing requirements of a new product. Hence the features and the topology of the feature-relationship tree of a new product can be used to search through the design database and retrieve the past design of the
nearest product manufactured by the company. Most important of all, the use of features to index a metal stamping form the basis for the development of a case-based planning system for progressive dies [50,51].
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Fig. 4. Symbolic relationships between the feature tree, the plan model and the engineering model.
5.5. Pro6iding two le6els of knowledge to meet the specific needs of indi6idual companies One of the greatest challenges to implementing highly automated integrated-design systems that would eliminate many of the decision-making functions from a designer is to acquire acceptance by industrial users. This is because all companies treat design knowledge and experience built up over the years as intellectual property that they are reluctant to share with others. In addition, each company has different design methodologies and practices and they are unwilling to surrender control to highly automated design systems. The provision of two levels of knowledge in the framework is aimed at overcoming initial industrial resistance. The first level of knowledge contains ‘generic’ design rules provided by die design textbooks and course materials. The second level of knowledge contains in-house design rules of the respective companies. The rules are assigned a priority index to indicate to the inference engine their relative importance in the respective decision making processes. Second level rules have higher priority than first-level rules. During a decision-making process, if second level rules exist, they will be referred to first and when a goal has been achieved the lower-priority rules will be ignored. In this
way, the individual companies will retain control over their design methodology. In the same context, facilities are provided for the companies to change the various parameters controlling design decisions. 6. Intelligent progressive die design After careful assessment of the technical feasibility of the framework described earlier, the present authors decided to seek verification from the industry. A series of half-day seminars were conducted separately for some of the largest local metal-stamping companies and instructors from the Institute of Technical Education to seek their feedback. During the seminars, the framework was explained in lay language and using industrial parts, the prototype software developed to prove the concepts was demonstrated. In addition, the scope for developing a proposed industrial prototype, Intelligent Progressive Die, IPD (Fig. 5) was presented. The researchers received very encouraging support from the industrial practitioners. The main features of IPD are: 1. It will provide an integrated knowledge-based design environment for the design of progressive dies for the manufacture of small metal-stampings for electrical and electronic equipment.
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Fig. 5. Scope of the Intelligent Progressive Die (IPD).
2. In addition, it will provide the following functionalities: (i) the ability to retrieve past case-studies for reference; (ii) an intelligent tutoring module for trainees; and (iii) a cost estimation/optimisation module. 3. It will provide facilities for a company to index, store and re-call past designs for reference. 4. It will have two separate data- and knowledgebases. The first level contains generic information from text-books, component manufacturers’ catalogues, etc., whilst the second level contains a company’s specific design rules, parameters and tooling
components. 5. As a company invests more time and effort entering additional company-specific design knowledge, tooling components and design case history, it is expected that a company’s IPD system will eventually become very different from that of other companies. In this way, an established company can continue to maintain its competitive advantage. 6. Every time that a designer uses the system to design a die, the knowledge is encapsulated. In this way, his/her expertise is retained by the company even after he/she leaves the company.
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7. Conclusions Modern consumption habits demand shorter product life-cycle. It is imperative that the overall die design and manufacturing lead time be reduced further to cope with the demands of the market. Conventional die design and manufactuing approaches using traditional CADCAM tools will be hard pressed to cope with these demands. In addition, there is a need for a company to retain its design expertise for future reference and to train new designers, and to retain its comparative advantage in the market place. This is especially important in a rapidly growing economy where job-hopping is a serious problem confronted by every employer. With the support of the Singapore Precision Engineering Trade Association (SPETA), the present authors have sought and obtained funding from the National Science and Technology Board (NSTB) of Singapore to develop IPD for industrial use. The project is also supported by some of the largest local metal-stamping companies, which will provide manpower and technical resources to help develop the core and company-specific components of IPD. References [1] A.Y.C. Nee, PC-based computer aids in sheet-metal working, J. Mech. Work. Technol. 19 (1989) 11–21. [2] P.B. Schubert, Die methods: Design, fabrication, maintenance, and application. Book One, Industrial Press, New York, 1966. [3] P.B. Schubert, Die methods: Design, fabrication, maintenance, and application. Book Two, Industrial Press, New York, 1966. [4] D.E. Ostergaard, Basic Diemaking, McGraw-Hill, New York, 1963. [5] D.E. Ostergaard, Advanced Diemaking, McGraw-Hill, New York, 1967. [6] J.A. Waller, Press tools and Presswork, Portcullis Press, Bristol, 1978. [7] E.G. Hoffman, Fundamentals of Tool design, 3rd ed., Society of Manufacturing Engineers, USA. 1991 [8] C.N. Tan, Synopsis of keynote address by Tan Chin Nam, Managing Director, Economic Development Board, in Proceedings MANUTECH 1993, Singapore, 8th September, 1993. [9] EDB, Singapore’s precision engineering industry, Singapore Precision Engineering Directory 1993/94, Economic Development Board of Singapore, 1993, pp. 14–18. [10] H. Murakami, K. Shirai, O. Yamada, K. Isoda, A CAD system for progressive dies, Proceedings of 21st Machine Tool Design and Research Conference, McMillan, London, 1980, pp. 687 – 592. [11] H. Murakami, K. Shirai, CAD system for press tools, in Proceedings of International Symposium on Design and Synthesis, Tokyo, Japan, (11 – 13 July, 1984) 1984, pp. 86–91. [12] K. Shirai, H. Murakami, Development of a CAD/CAM system for progressive dies, Ann. CIRP 34 (1) (1985) 187–190. [13] K. Shirai, H. Murakami, A compact and practical CAD/CAM system for progressive die, Bull. Jpn. Soc. Prec. Eng. 23 (1) (1989) 25 – 30. [14] M. Okada, Computer aided manufacturing system for sheet metal parts, Proceedings of the 21st Machine Tool Design Research Conference, McMillan, London, 1980, pp. 603– 609.
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[15] S. Nakahara, K. Toshio, K. Tamura, F. Asuke, C. Soda, T. Nakamura, Computer aided progressive die design, Proceedings of the 19th Machine Tool Design Research Conference, McMillan, London, 1978, pp. 171 – 176. [16] K. Fukuoka, K. Horiuchi, Integrated mold and die design and manufacturing system, Fujitsu Sci. Technol. J. 22 (5) (1986) 438 – 450. [17] M. Adachi, K. Inoue, T. Funayama, Integrated CAD system for progressive dies, Fujitsu Sci. Technol. J. 19 (2) (1983) 133–148. [18] K. Bergstorm, S. Kivivuori, S. Osenius, A. Korhonen, Computer aided design of a progressive die, in J.L. Chersot, E. Ohate (Eds), Modelling of Metal Forming Processes, Kluwer, Dordrecht, 1988, pp. 155 – 162. [19] A.Y.C. Nee, K.Y. Foong, Some considerations in the design and automatic staging of progressive dies, J. Mater. Process. Technol. 29 (1992) 147 – 158. [20] G. Chryssolouris, K. Wright, Knowledge-based systems in manufacturing, Ann CIRP 35 (2) (1986) 437 – 439. [21] M.J. Boyle, Interactive engineering systems design: A study for artificial intelligence applications, Artif. Intell. Eng. 49 (2) (1989) 58 – 69. [22] D.T. Pham, E. Tacgin, Techniques for intelligent computer-aided design, in: D.T. Pham (Ed.) Artificial Intelligence in Design, Springer-Verlag, New York, 1991. [23] C. Tong, D. Siriam, Artificial Intelligence in Engineering Design, Academic Press, Boston, MA, 1992. [24] A.S. Lazaro, D.T. Engquist, D.B. Edwards, An intelligent design for manufacturability system for sheet-metal, Concurr. Eng.: Res. Appli. 1 (2) (1993) 117 – 123. [25] R.S. Lee, L.C. Chuang, T.T. Yu, M.T. Wu, Development of an assessment system for sheet metal forming, in Proceedings of the International Conference on Precision Engineering 1995 (2nd ICMT) ‘Trends and Innovations in Precision Manufacturing Technologies’, Singapore (22 – 24 November 1995), (1995) pp. 515 – 518. [26] M. Tisza, Expert systems for metal forming, J. Mater. Process. Technol. 53 (1995) 423 – 432. [27] S.K. Esche, S. Khamitkar, G. Kinzel, T. Altan, Process and die design for multi-step forming of round parts from sheet metal, J. Mater. Process. Technol. 59 (1996) 24 – 33. [28] M. Mantripragada, G. Kinzel, T. Altan, A computer-aided engineering system for feature-based design of box-type sheet metal parts, J. Mater. Process. Technol. 59 (1996) 241 –248. [29] Z.C. Lin, C.Y. Hsu, K.H. Yao, Planning and building an integrated design software of blanking and piercing dies (ESSCP) with a micro expert system as a main structure, J. Chin. Soc. Mech. Engrs. 10 (2) (1989) 101 – 120. [30] Z.C. Lin, H. Chang, An investigation of expert systems for die design, J. Intell. Manuf. 5 (1994) 177 – 192. [31] Z.C. Lin, C.Y. Hsu, An Investigation of an expert system for shearing cut progressive die design, Int. J. Adv. Manuf. Technol. 11 (1996) 1 – 11. [32] Z. Li, Z. Chen, Y. Hong, X. Xiao, J. Xiao, Computer aided design of progressive die construction, in Proceedings of the International Conference on Die and Mould Technology, Shanghai, China (May 18 – 21, 1990), 1990, pp. 357 – 363. [33] Z. Li, J. Li, Z. Li, G. Wang, X. Xiao, J. Xiao, CAD/CAM of progressive dies for household electronic appliances, in Proceedings of the International Conference on Advanced Technology and Machinery in Metal Forming, Wuhan (22 – 24 October 1992), China, 1992, pp. 71 – 77. [34] X. Xiao, Z. Li, J. Li, Z. Li, J. Ma, J. Xiao, An intelligent approach to the strip layout of progressive die design, in Proceedings of the Fourth International Conference on the Technology of Plasticity, 1993, pp. 1817 – 1821. [35] K. Huang, H.S. Ismail, K.K.B. Hon, Automated design of progressive dies, Proceedings, Institution of Mechanical Engineers Part B:, J. Eng. Manuf. 210 (1996) 367 – 376.
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[36] H.S. Ismail, S.T. Chen, K.K.B. Hon, Feature-based design of progressive press tools, Int. J. Mach. Tools Manuf. 36 (3) (1996) 367 – 378. [37] A.Y.C. Nee, A heuristic algorithm for optimum layout of metal stamping blanks, Ann CIRP 33 (1984) 317–320. [38] B.T. Cheok, K.Y. Foong, A.Y.C. Nee, C.H. Teng, Some aspects of a knowledge-based approach for automating progressive metal stamping die design, Comput. Ind. 24 (1994) 81–96. [39] B.T. Cheok, K.Y. Foong, A.Y.C. Nee, An intelligent planning aid for the design of progressive dies. Proceedings of the Institute of Mechanical Engineering, Part B:, J. Eng. Manuf. 210 (1996) 25 – 35. [40] K.H. Toh See, H.T. Loh, A.Y.C. Nee, A feature-based flat pattern development system for sheet metal parts, J. Mater. Process. Technol. 48 (1–4) 89–95. [41] X.Y. Ruan, X.Z. Zeng, L.L. Wang, Y.T. Li, A blanking die CAD system on microcomputer, Adv. Technol. Plast. 1 (1987) 139 – 143. [42] B.W. Yuan, L. Wang, W.D. Zhang, J. Zhu, Graph processing and strip layout in a CAD system on mirco-computer for the multistage progressive die with bending and forming, in Proceedings of the International Conference on Die and Mould Technology. Shanghai, China, 18-21 May, 1990, pp. 434–441. [43] S.H. Choi, K.W. Wong, A CAD/CAM package for sheet metal blanking dies, in the Proceedings of the International Conference
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Trends and developments in the automation of design and manufacture of tools for metal stampings B.T. Cheok a,*, A.Y.C. Nee b a
CAE/CAD/CAM Centre, Faculty of Engineering, National Uni6ersity of Singapore, 10 Kent Ridge Crescent, Singapore 0511, Singapore b Department of Mechanical and Production Engineering, Faculty of Engineering, National Uni6ersity of Singapore, Singapore Received 20 January 1997
Abstract Metal stampings play an important part in modern-day life. Together with plastic molds, they form the most important structural components of all electrical and electronic equipment. Researchers all over the world have spent a tremendous amount of time and effort trying to develop better computer aids for the design of tools and dies required to manufacture metal stampings. This paper explains the motivation to develop an integrated planning-and-design aid for the die designer. From the literature, trends and developments in the design automation of toolings for the manufacture of metal stampings are discussed. The application of various artificial intelligence (AI) techniques to solve problems that were previously exclusive domains of human designers is highlighted. A knowledge-based framework for developing an integrated software for the planning and design of progressive dies is illustrated. © 1998 Elsevier Science S.A. Keywords: Metal-stampings; Tool and die; Progressive die; Artificial intelligence; Knowledge-based systems; Precision engineering
1. Introduction
2. Need for a better mouse-trap
At present, metal stampings are used in almost every mass-produced product. According to a survey in the US, some 100 000 metal stampings could be found in the average American home in the 1980s [1]. Metal stamping manufacturing processes are popular because they are an economical and quick means of producing intricate, accurate, strong and durable articles in huge quantities. Simple dies, compound dies and progressive dies are used for producing metal stampings. In a progressive die, the workpieces are advanced from one station to another. At each station, one or more die operations, such as piercing, notching, blanking, lancing, shaving, drawing, embossing, coining and forming are performed on the sheet metal strip. The result is a finished component at every stroke of the press. There are many good textbooks [2 – 7] written to explain these metal stamping operations and the associated tooling design and manufacturing considerations.
In developing and developed countries, the manufacturing sector is probably the most important pillar of the economy. In Singapore, the manufacturing sector contributes more than 25% to the GDP with a total Gross Value Adding of more than S$ 24 billion. It also accounts for more than 400 000 jobs.[8]. In the same context, the precision engineering industry is an important pillar in Singapore‘s manufacturing sector, providing the tooling required for the production of high value added mechanical and electrical components and products. Metal stamping is a major downstream supporting industry in Singapore. In 1992, it employed some 4600 workers with an annual output of S$ 600 million and an output growth rate in excess of 10% [9]. One of the most skill-intensive tasks in the mass production of metal stampings is the design of progressive dies. Modern CAD/CAM technology, together with new ideas in the design and construction of tools, coupled with increased speed and rigidity of presses, have contributed towards the continual use of metal stamping production processes to manufacture increas-
* Corresponding author. Fax: [email protected]
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ingly more sophisticated products. However, these developments have demanded greater skills from the designers. In Singapore, the problem is further compounded by two factors: 1. In a dynamic and fast-growing economy, young people do not have the patience to undergo long periods of apprenticeship training to acquire the skills to be a die designer, hence, there are less people joining the trade. 2. The precision engineering industry in Singapore supports mainly the computer, tele-communications and electronics/electrical appliances market. Owing to rapid changes in consumer taste, these products have very short life cycles. In other words, there is a rapid demand for more sophisticated metal stampings and plastic parts. Die designers are under constant pressure to exploit the latest design and manufacturing technology in order to meet the market demand. To overcome these problems and to sustain competitiveness, there is an urgent need to provide an intelligent aid to the die designer so that the overall die design and manufacturing lead time can be shortened and metal stampings of improved qualities can be produced at lower costs.
3. A review of research and design in the design automation of toolings for metal stampings Traditionally, research in material processing has been focused on using experimental and numerical techniques to solve problems related to the behaviour of materials under a wide variety of stresses and strains. The published findings can be used to help the die designer to predict the behaviour of the workpiece and the tools. However, dies are still designed manually. With the introduction of computer graphics and CAD/ CAM systems, some researchers have started to exploit the advances in interactive computer graphics and CNC technology for the design and manufacture of metalstamping tooling, especially progressive dies. The Japanese industries were probably among the first to develop in-house turnkey CAD/CAM systems for progressive dies for industrial use. From the mid 1970s, researchers from Hitachi [10 – 13], Nippon Electric [14], the Mechanical Engineering Laboratory [15], Fujitsu and Matsushita Electric Works [16] and others [17] have reported extensively their custom-made integrated computer-aided design and manufacturing systems for press tools. The Hitachi system consists of three processors. The designer uses an APT-like language to input the part drawing into the pre-processor. The pre-processor generates a nested arrangement in the form of a blank layout drawing. The designer has to manually plan the
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strip and die layout and use the APT-like language to input the information to the main processor. The latter processor then determines the construction and size of the die and generates the part list. Finally, the post-processor plots the assembly and dimensioned part drawings. The system can reduce the time taken to design a die from 20 to 5 days. Nippon Electric developed a computer-aided manufacturing system for small lot-size sheet metal parts. The system takes care of process planning, nesting and CNC punching operations. The CAD system developed at the Mechanical Engineering Laboratory adopts the conventional design approach of two-dimensional progressive die design using a set of standard design operations with punch shapes as the key development concept. These early die-design systems attempted to use basic computer graphics facilities and programmes written in FORTRAN to improve the productivity of the die designer. Geometrical information has to be entered laboriously via the keyboard using APT-like command language. Most design decisions were made by the designer, the computer being used to improve productivity in drawing and to perform particular design calculations and NC programming. Yet, they were able to achieve productivity gains of 30–400% over the manual approach. Attempts to improve their die design productivity in the late 1970s and early 1980s indicates the importance of the metal stamping industry to the electrical and electronic components and equipment manufacturers. At that time, Japan was amongst the world’s largest exporter of electrical and electronic home appliances and office equipment. The early CAD/CAM systems for progressive die design and manufacturing may appear to be rather primitive by today‘s standard. However, these efforts laid a solid foundation for future developments. Concepts such as using standard punch shapes as primitive shapes for punch selection and de-composition, the standardisation of die components, the computer modelling of die components and die layout area and the standardisation of design procedures were followed to advantage by later researchers. The wide acceptance of CAD/CAM equipment in the mid 1980s represented the second thrust in the design automation of progressive dies. Most CAD/CAM equipment provide programming languages for customisation and/or is able to interface directly with a high level programming language such as FORTRAN. Researchers began to exploit these features to develop dedicated CAD/CAM systems for progressive die design. In Finland, the Laboratory of Metal Working and Heat Treatment [18] integrated FORTRAN calculation routines with Auto-trol, a 3D CAD/CAM system. Auto-trol provided the drafting, 3D wire-frame modelling and CAM functions. In addition, a volume-based folding and unfolding CAD system was used. The
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FORTRAN routines were integrated with the CAD/ CAM system to calculate stripper and punch forces, bending forces, bend radii and material utilisation, and to automate the selection and parametric sizing of some die components, and the generation of part listing and tool dimensioning. In Japan, Fujitsu and Matsushita [16] jointly developed an integrated CAD/CAM system for automating and improving productivity in the manufacture of injection molds and progressive dies used in producing electronic parts and precision machinery parts. The system has strong links with CADAM, another CAD/CAM system. Second generation die design systems represent a vast improvement over the first generation in terms of interactive graphics and 3D modelling functionality. However, as they are still based on procedural programming languages such as FORTRAN, they are only able to automate relatively simple calculations and data extraction (for example, the generation of a part list and tool dimensions) tasks. Most of the important decisions such as the design of punch shapes, the assessment of formability and the development of the strip layout, are still made interactively by the user. The mid 1980s also saw the introduction of many commercial CAD/CAM systems for progressive die design. At present, systems such as the Fanuc Progressive Die CAD/CAM System, Auto-trol’s Progressive Die System, the ADMS Die Master System, the U-Graph Assisted Die Design System, Pro/SHEETMETAL, MetalCAD, and the EXCESS and Striker Systems can be purchased ‘off-the-rack’. A review of the first four systems can be found in [19]. Most of these commercial systems are the customisation of existing CAD/CAM systems such as Fanuc, Auto-trol, Pro/ENGINEER and AutoCAD to provide the added functionalities required specifically by die designers. They are basically interactive in nature and can only be viewed as productivity enhancement aids for the die designer. This is because considerable human expertise is still needed to use these systems to arrive at the final design. Research and development of progressive die design automation systems was given a new dimension in the late 1980s and early 1990s when the applications of artificial intelligence techniques in engineering design started to take off [20 – 23] etc. Now, AI techniques are used increasingly in pattern recognition, production rules and frame-based inferencing and reasoning, fuzzy reasoning, feature-based design, etc., to design systems for the production of metal stampings. However, because of the complexity of the die-design process, most of the ‘intelligent’ die design automation prototypes are rather restrictive in their applications. One area of research that has attracted a considerable amount of attention is knowledge- and featurebased sheet metal forming. Some examples are as follows:
1. The Sheet Metal Advisor and Rule Tutor (SMAART) [24] is a feature-based CAD system developed to provide sheet metal manufacturing information for die designers. It uses a hybrid ruleand object- based representation of knowledge to store ten features in three levels of abstraction and about 65 forming violation rules. SMAART is designed to render advice immediately to the product designer on any violation of a design rule. In this way, the metal stampings that are designed will not cause any tooling design problems as far as forming is concerned. 2. Lee et al. [25] developed an assessment system consisting of a knowledge-based geometric-analysis module, a finite-element method (FEM) module and a formability analysis module. The geometric-analysis module uses geometric reasoning and feature recognition with a syntactic approach to extract high level geometric entities information from vertices of 2D forming profiles. The empirical rules for stamping die design are represented as frames in the knowledge base. If the formability information cannot be decided by geometric analysis, then a detailed FE simulation is performed using PAM-STAMP (a CAE software) where the strain distribution is obtained. Thereafter, the formability-analysis module uses a fracture energy criterion to assess the formability of the design. This software is suitable for assessing the formability of deeply formed parts such as automobile panels. 3. METEX (Metal Forming Expert System) [26] applies the principles of group technology to the process planning of multi-stage forming processes. It uses AutoCAD and AutoLISP to provide an expert system to generate possible forming solutions for deeply formed or drawn shapes, and adopts a hybrid classification utilising both geometric features and manufacturing characteristics for the coding of components to form part families for automatic process planning. A semi-automatic approach is used where human input is required when it is deemed that the computer is not suited to make particular decisions. 4. ASFEX (Axisymmetric Sequence Forming Expert System) [27] is an expert system developed by the Engineering Research Center for Net Shape Manufacturing (ERC/NSM) that uses design rules to generate process sequences for multi-stage drawing of round cups and tool geometry for each station of the sequence. 5. The ERC/NSM also developed a computer-aided analysis system [28] that uses Pro/Engineer sheet metal features to analyze the formability of complex sheet parts formed in multiple operations. At the same time, several universities and research institutes have adopted a wide variety of AI and tradi-
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tional computer approaches to develop die design automation systems: 1. Researchers at the National Taiwan Institute of Technology [29– 31] have developed PC-based expert prototypes for the design of shearing cut (blanking and piercing) progressive dies. ESSCP [29] is a prototype developed using FORTRAN, Micro Expert (the inference engine) and AutoCAD to plan and develop the progressive dies for the blanking and piercing of 2D parts with very simple geometrical profiles. In separate developments, the researchers also studied how uncertainties in design parameters can be processed using fuzzy mathematics for the detailed design of particular components in the die structure [30], and developed a knowledge-based system that uses a pattern recognition method called the new combined structural approach to develop the blank so as to optimise material cost, and a matching combination learning method for press procedures to optimise the number of stations in the die [31]. It is unclear whether they have integrated these AI techniques into an integrated system for the design of blanking and piercing progressive dies. 2. Researchers at the Huazhong University of Science and Technology, China also developed knowledgebased CAD/CAM packages for progressive dies for small-sized metal stampings [32 – 34]. Using features, a user can design a product in 3D wire-frame, thereafter the system will unfold it. After manually developing the blank layout, the user can use interactive commands to develop the strip layout. The user can then proceed to design the die structure interactively. Another feature of their research is the use of the directed and weighted graph approach for the automatic splitting of complicated die cavities [32]. Originally the system was developed on a Micro VAX mini-computer, but the system is now available on PCs and runs under the AutoCAD environment. 3. Researchers from the Department of Industrial Studies, University of Liverpool have also worked on expert systems for progressive piercing and blanking die design [35,36]. Their research concentrated on shape-coding and recognition techniques for the decomposing of the bridge scrap into smaller shapes [36]. However, their techniques are limited to straight-edge workpieces only. They also developed a UNIX-based expert system for the planning and design of progressive piercing and blanking dies [35]. The system was developed by integrating AutoCAD with Kappa and some C programs. 4. Researchers at the Department of Mechanical and Production Engineering, National University of Singapore have been developing algorithms for die design automation [1,19,37]. Initially, the work con-
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centrated on developing heuristics for nesting, automating the staging and punch shape selection and de-composition process. Later, it was extended to the use of a variety of knowledge-based approaches to extend the capabilities to include bending and forming, automatic punch shape selection, strip layout and 3D die configuration [38,39]. Another related development work is the development of a feature-based sheet-metal unfolder [40]. Experience gained from this research work has been used to establish a knowledge-based framework for the development of an integrated progressive die design software that will be presented later. 5. Researchers at the Shanghai Research Institute of Tool and Die Technology [41,42] have also developed CAD/CAM systems for progressive dies. The systems they developed rely on special relational data structures to describe the workpiece and the die structure. The strip layout is generated interactively. 6. Researchers at the Department of Industrial and Manufacturing Systems Engineering, University of Hong Kong developed BECAM, a CAD/CAM package for sheet metal blanking dies [43]. The program can help to develop the blank strip layout, the punch and die selection, and the drafting and generation of NC part programs. 7. CADDS, an automated die design system for sheetmetal blanking, was developed at the Indian Institute of Technology [44] using AutoCAD, AutoLISP and FORTRAN. The software is able to generate the strip layout automatically, conduct design checks for various die components, and generate the assembly views and the bill of materials for the die. Finally, there are researchers who seek to reduce the size of the problem by developing systems that concentrate on specific product types or on specific tasks. For example, a knowledge-based system based on ICAD was developed for the design of progressive dies for special order door hinges [45]. Similarly, the factors affecting the design of the high-speed precision blanking of thin sheet metals using progressive dies in the production of IC lead-frames are explained in [46]. Lee et al. [47] developed IKOOPP, a knowledge-based process planning system for the manufacture of progressive die plates. IKOOPP is able to automatically recognise the machining features from a 3D die plate modelled in Auto-trol and proceed to automatically plan the set up sequences, select the required machine tools, cutting tools, heat treatment, fixturing elements and sequence of operations.
4. Some comments on the current status A summary of the salient features of research and design work reviewed in terms of process planning,
Table 1 Salient features of the reserach and development work reviewed
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design and manufacturing functions and computer techniques used is given in Table 1. With emphasis on work done after the late 1980s, the following observations can be made: 1. Many of the systems built have demonstrated the technical feasibility of employing knowledge-based methods to solve design and manufacturing problems related to the forming process. However, there are very few attempts to integrate successful work done in these areas with die design automation software. 2. There are a few systems that appear to provide an integrated design and manufacturing aid for the die designer, however, their use is limited. They can either handle only piercing and blanking operations, or parts with relatively simple geometry or used for specialised products only. 3. Some of the researchers had demonstrated that particular AI techniques are potentially useful in terms of assisting users in some of the cognitive tasks associated with die design. 4. The die design automation systems reviewed in this paper still require a high degree of input by experienced designers during the design process. Progress in computer-aided die design automation still falls behind advances in computer technology, in particular advances in computer graphics and modelling, and the applications of AI in design, analysis and manufacturing. The research activities reviewed have indicated the growing importance and relevancy of particular AI techniques for the automation of some of the die design activities.
5. Framework for an integrated design system for progressive dies Researchers at the National University of Singapore have developed a framework for an integrated design system for progressive dies, the framework being developed based on experience gained in developing the earlier prototypes. The framework is based on the principles outlined in the following section.
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2. The use of a knowledge-based shell to store and manipulate the objects and rules associated with the die design process. The knowledge-based shell can either be a commercial package or a custom-made shell especially developed to handle stamping features and die components. 3. The use of high level computer languages such as C and C+ + to code the procedural and mathematical routines required to support the numerically intensive tasks. These numeric routines are coupled with the knowledge-based system such that the results produced by the former are returned as propositional logical expressions so that they can be formalised as well-formed equations for logical interpretation by the latter. 4. The use of multi-processing features of modern operating systems (such as Dynamic Data Exchange (DDE) provided by Windows or Inter-Process Communications (IPC routines provided by UNIX) to integrate the above-mentioned tools into a single software for the user. These approaches have proven to be very efficient in terms of computer-designer interaction by Cheok et al. [38,39] and Ismail et al. [35]. The resources can be integrated under the Windows operating environment using the architecture shown in Fig. 1.
5.2. Identification and use of the most appropriate AI techniques to handle the 6arious cogniti6e tasks in6ol6ed in progressi6e die design The tasks involved in the planning, design and manufacture of progressive dies are shown in Fig. 2. The experience of the authors has shown that the following AI techniques can be used to handle some of the cognitive tasks associated with die design: 1. Unfolding of a 3D product model into a flat pattern using features. The approach has proved to be very efficient, Toh et al. [40] and Li et al. [33,48]. 2. Heuristic rule-based approach for the selection of pilot and carrier schemes.
5.1. Identification, use of and integration of the most appropriate computer tools to handle the 6arious computing tasks in6ol6ed in progressi6e die design It is clear that the computer-aided die design process involves the following computing resources: 1. The use of a CADCAM system to provide the interactive graphical and geometrical modelling tools for the user to generate, view and manipulate the various plans and product and tooling models associated with the design.
Fig. 1. Computer architecture for die design and manufacture system.
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Fig. 2. Tasks involved in the planning, design and manufacture of progressive dies.
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3. Decomposition of punch shapes based on heuristics. 4. Recognition of punch shapes based on skeletal features and knowledge-based search techniques. 5. Heuristic rule-based approach for the staging of the die operations. 6. Model-based reasoning approach for the configuration of die assembly [49]. 7. Feature- and rule- based approach for the generation of process plans for the manufacture of die plates [25].
5.3. Sharing of design tasks between user and computer It is obvious that it is impossible for the computer to automate each and every design task identified in Fig. 2. In fact, progressive die design exhibits all the characteristics of the procedural design process [21] where the designer’s role is to control the design process to achieve the final solution. Hence, the framework is developed based on the concept of task sharing between the user and the computer, each playing a different role. The computer will be used to perform all the routine calculation, measurement, modelling and drafting activities. The designer’s guidance will be required in the following cases: 1. In a situation where a higher level of creativity is required rather than one that can only be achieved by the set of rules programmed into the system. 2. In a situation where it is reasonable to expect that the computer will not be able to make a good decision. 3. In a situation where the decision-making process is so complicated that the computer would require an unreasonably long time to arrive at a solution. For example, when deciding on the piloting scheme and the selection of pilot holes to guide the strip as it progresses along the die, one cannot expect the computer to come to a reasonable solution just by analysing the available holes, punch shape and sizes and the excess material on the strip. This is because the computer will tend to generate many possible solutions using standard pilot selection rules. Secondly, it is very difficult to program a set of design criteria that can be used to identify which of these numerous solutions is most appropriate. Instead, measurement routines and rules related to the selection of suitable pilot holes are used to present the ‘better’ solutions to the user. The user will then examine these solutions and use his/her judgment to make the final choice. In other cases, a ‘first-guess’ approach is adopted. Here, the computer will attempt to generate an initial solution which in most cases will form a reasonable starting point for the user to complete the solution. The user requires adequate interactive tools to input his decisions to the computer. For example, there is a need
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to de-compose the scrap material between the external profiles of the workpiece and the strip edges into smaller pieces so that they can be easily disposed from the die. In essence, there are no actual guidelines as to how the de-composition is done, and it is noted that most systems reviewed have left this task to the designer. The authors have developed routines to de-compose the scrap material into smaller ‘well-behaved’ strips by projecting horizontal or vertical lines from each and every vertice of the external profile to the neighbouring shape or to the edge of the strip. The solution will be presented graphically to the user. Thereafter, he/she can use interactive graphical aids to modify these strips into practical solutions for blanking the external shapes.
5.4. Use of metal-stamping features and the product feature-relationship tree as knowledge-based representation of the product Many researchers have used features to model metal stampings and the related information to assess their formability. The framework that the present authors have developed will use metal-stamping features and the feature-relationship tree to formalise the description of the product. The features and the feature-relationship tree of a simple metal stamping are shown in Fig. 3. The use of a feature tree provides an ideal starting point for an integrated knowledge-base to support the entire die design process. This is because each feature is associated with a stamping operation such that the attributes of the stamping operations can be used to generate the knowledge-based representation of the strip layout, and then the knowledge-based representation of the die components required to stamp the part. The inter-relationship between the features tree, the plan model and the engineering model in the knowledge base and the product drawings, the strip layout and the 3D solid model of the die is illustrated in Fig. 4. In addition to the modelling efficiency provided by this approach, the linking of the feature trees with the plan model and the engineering model provides the framework for concurrent engineering in die design. In other words, it is possible to design a system such that when the user makes a decision to modify the design at the down-stream operations, it can check how these decisions will affect the up-stream operations. Finally, it is noted that the feature-relationship tree provides global information about the manufacturing processes required to produce a product. Also, it can be translated into textual form, hence it can be used as a criterion to index the metal stampings in a design database. The design database is a database of products and their associated tooling manufactured by a company. It is noted that a die designer usually builds a progressive die by adopting an old design to meet the
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Fig. 3. Features and feature-relationship tree of a metal stamping.
manufacturing requirements of a new product. Hence the features and the topology of the feature-relationship tree of a new product can be used to search through the design database and retrieve the past design of the
nearest product manufactured by the company. Most important of all, the use of features to index a metal stamping form the basis for the development of a case-based planning system for progressive dies [50,51].
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Fig. 4. Symbolic relationships between the feature tree, the plan model and the engineering model.
5.5. Pro6iding two le6els of knowledge to meet the specific needs of indi6idual companies One of the greatest challenges to implementing highly automated integrated-design systems that would eliminate many of the decision-making functions from a designer is to acquire acceptance by industrial users. This is because all companies treat design knowledge and experience built up over the years as intellectual property that they are reluctant to share with others. In addition, each company has different design methodologies and practices and they are unwilling to surrender control to highly automated design systems. The provision of two levels of knowledge in the framework is aimed at overcoming initial industrial resistance. The first level of knowledge contains ‘generic’ design rules provided by die design textbooks and course materials. The second level of knowledge contains in-house design rules of the respective companies. The rules are assigned a priority index to indicate to the inference engine their relative importance in the respective decision making processes. Second level rules have higher priority than first-level rules. During a decision-making process, if second level rules exist, they will be referred to first and when a goal has been achieved the lower-priority rules will be ignored. In this
way, the individual companies will retain control over their design methodology. In the same context, facilities are provided for the companies to change the various parameters controlling design decisions. 6. Intelligent progressive die design After careful assessment of the technical feasibility of the framework described earlier, the present authors decided to seek verification from the industry. A series of half-day seminars were conducted separately for some of the largest local metal-stamping companies and instructors from the Institute of Technical Education to seek their feedback. During the seminars, the framework was explained in lay language and using industrial parts, the prototype software developed to prove the concepts was demonstrated. In addition, the scope for developing a proposed industrial prototype, Intelligent Progressive Die, IPD (Fig. 5) was presented. The researchers received very encouraging support from the industrial practitioners. The main features of IPD are: 1. It will provide an integrated knowledge-based design environment for the design of progressive dies for the manufacture of small metal-stampings for electrical and electronic equipment.
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Fig. 5. Scope of the Intelligent Progressive Die (IPD).
2. In addition, it will provide the following functionalities: (i) the ability to retrieve past case-studies for reference; (ii) an intelligent tutoring module for trainees; and (iii) a cost estimation/optimisation module. 3. It will provide facilities for a company to index, store and re-call past designs for reference. 4. It will have two separate data- and knowledgebases. The first level contains generic information from text-books, component manufacturers’ catalogues, etc., whilst the second level contains a company’s specific design rules, parameters and tooling
components. 5. As a company invests more time and effort entering additional company-specific design knowledge, tooling components and design case history, it is expected that a company’s IPD system will eventually become very different from that of other companies. In this way, an established company can continue to maintain its competitive advantage. 6. Every time that a designer uses the system to design a die, the knowledge is encapsulated. In this way, his/her expertise is retained by the company even after he/she leaves the company.
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