Chapter 1 Introduction Chapter 1 Introduction 1. 1 The topic selection is based on the important role of molds in the product manufacturing process. The level of mold design largely determines the productivity. Effective mold design can reduce the times and time of resource adjustment, provide more optimization space for production planning and scheduling, and achieve the purpose of improving production efficiency [1]. Mold design is an important part of assembly system, which affects the efficiency and quality of product production. It is of great significance to study the mold design deeply. Mold industry is the basic industry of industry, and molds are widely used in various fields of industry. In electronics, automobiles, motors, electrical appliances, instruments, meters, home appliances, communications and other products, 60%-8% of the parts must be molded by molds. The high precision, high complexity, high consistency, high productivity and low consumption of parts produced by molds are incomparable to other processing and manufacturing methods. Mold is also a "benefit amplifier", and the value of the final product produced by mold is often dozens or even hundreds of times that of the mold itself. The technical level of mold production largely determines the quality and benefit of products and the development ability of new products, and becomes an important symbol to measure the manufacturing level of a country's products [3]. As the basic technological equipment of industrial production, molds play an important role in the national economy. In recent 10 years, mold CAD technology has developed rapidly and its application scope has been expanding day by day. Mold CAD technology provides an efficient, economical and fast method for mold design and manufacturing, which greatly improves the quality of mold, shortens the design and manufacturing cycle of mold and reduces the cost of mold. At present, there are many mold CAD systems at home and abroad. Although these systems have strong analysis and calculation ability and graphic processing ability, they can provide interactive design. However, in these systems, the mold design process is mainly carried out through human-computer interaction, and most designs depend on the design experience of operators. The computer only does some rule matching and calculation work, but the mold successfully designed by predecessors can not be effectively used, resulting in long mold design cycle, high cost and low development efficiency. Mold design based on case-based reasoning can enable designers to make use of previous design experience and construct new design schemes by combining and modifying previous design schemes. At the same time, in actual production, there have been many mold families with exactly the same mold parts types and assembly relationships, which can be the basis of new design. CRB technology abandons the construction and calculation of abstract knowledge rules in the past, directly solves problems with the help of existing examples, and realizes the design of new molds through the confirmation and correction of old examples [7]. In case-based reasoning system, past experiences are stored in case base in the form of examples according to some organizational structure. When solving a new problem, search the case base with an appropriate algorithm through related attributes, find one or several examples that are most similar to the new problem, and then modify these examples to solve the new problem [9l. CRB method is applied in mold design, and the thinking activity of computer mold brain is used in the design to complete the tasks previously completed by designers, which not only makes full use of the design experience of mold experts, but also conforms to the actual situation in engineering and human thinking habits. At the same time, the mold obtained by this method is based on previous successful examples, thus reducing the possibility that the new mold can not work normally and shortening the development cycle. 1.2 development status and trend of mold CAD 1.2. 1 mold CA. Overview of system development at home and abroad The mold CAD system has developed with the development of D technology and modern design theory and method, from the initial system based on two-dimensional graphics technology to the 1 10 stage characterized by three-dimensional graphics technology and feature configuration. In the late 1960s, foreign countries began to use D to research molds, and put them into production in the early 1970s. For example, 1973, Diecomp Company of the United States successfully developed the PDDc system for computer-aided design of progressive dies ['2 1]. The system has included the input of product graphics and material characteristics: on the basis of the input, die structure selection, die layout, punch and other insert design are carried out; Finally, draw the mold assembly drawing and parts drawing for NC programming. 1978, Japan Mechanical Engineering Laboratory developed a CAD system for blanking progressive dies, which consists of 10 modules such as product drawing input, die selection, blank layout, layout, die layout, process calculation and drawing. In 1980s, with the development of computer technology, the number of manufacturers using mold CAD technology increased greatly. In the CAD system of bending progressive die and automobile panel die, the plastic forming simulation technology is applied. The representative is the D/ M system of bending progressive die developed by Hitachi, Japan in 1982, which adopts the batch mode combining manual and computer design. Many commercial CAD/CAM systems appeared in 1990s, such as Pro/E and SolidWorks. Due to the late development of computer technology in China, the research of mold CAD began in the 1980s. Huazhong University of Science and Technology, Mechanical and Electrical Research Institute, Shanghai Jiaotong University and other units have started the research of blanking die system. In the mid-1990s, the CAD system of progressive die based on feature design in Huazhong University of Science and Technology was the representative of this period. 1.2.2 mold development trend Cao In recent years, the global manufacturing industry is shifting to the Asia-Pacific region, and China is becoming an important base of the world manufacturing industry [3] L. The change of manufacturing methods will inevitably generate the demand for new technologies and promote the development of CAD technology; The popularization of network technology will change our way of life and production to a greater extent. With China's entry into WTO, our products are required to be innovative, with higher quality and lower cost, and to be provided to users in a shorter time [4l 1. As an important process equipment for product manufacturing and one of the basic industries of the national economy, the mold industry will face the first line of competition. In addition to "highly skilled" employees, the mold industry also needs "high technology". (1) Collaborative innovative design will become the main direction of mold design. The vertical integration mode of manufacturing industry makes the division of labor among product sales, product design, product production and mold manufacturing more clear around the world. In order to shorten the product listing cycle and make the mold design fully understand the product design, the mold design starts at the same time in the product design stage, and the product design engineer and the mold design engineer need to enter the collaborative design state as soon as possible. In addition, the mold standard parts needed by mold manufacturers are generally provided by the mold standard parts factory. It is best to refer to various standards in the mold design stage and make full use of the data provided by the mold standard parts factory for design. Because the CAD systems used in each link of the manufacturing process are not necessarily the same, it requires the D system to have the ability of collaboration, to exchange upstream and downstream data at any time, to process other data, and to standardize data generation and processing. At present, mold manufacturers have widely adopted CNC machining technology. In order to ensure the machining quality, improve the machining efficiency and improve the manufacturing technology, a considerable number of mold manufacturing enterprises began to adopt multi-coordinate CNC machining, high-speed milling machining and mold manufacturing based on rapid prototyping. Due to the abundance of manufacturing equipment and the increase of manufacturing information, the future manufacturing information will not only be the code of numerical control programming, but more importantly, the manufacturing process will be considered from the beginning of design, that is, the process flow of mold manufacturing will be provided, including not only the process table and processing parameters, but also the fixture design of mold processing, the clamping process of processing and the codes of each process. Every process is simulated, using the network to realize * * * enjoyment. (2) The mold CAD technology based on ASP mode will become the development direction. Today's mold industry has become a high-tech intensive industry. It will be very expensive for any enterprise to master all advanced technologies, and it will be very difficult to train and retain talents who master these technologies. As a result, APS mode of mold CAD came into being, that is, application service units with various specialized technologies provided technical services for mold enterprises. In this way, the whole society has formed a large mold manufacturing enterprise, which will make maximum use of manufacturing resources according to the division of labor between value chain and manufacturing process. Application services include rapid prototyping, CNC outsourcing, mold design, mold forming process analysis, etc. In the past 20 years, due to the continuous adoption of new technology, mold manufacturing has been far away from the "manual workshop" in people's memory. 2.3 Characteristics and Advantages of Mould The characteristics of mould design of CAO system (1) are different from the traditional design of single part. Mold is the assembly of multiple parts, and mold design is an extremely complicated process, including product modeling, process analysis, mold scheme formulation, mold base selection, mold assembly drawing design, working part design, auxiliary device design and detailed part design. It is required to be able to generate final assembly drawings, assembly drawings and molds. B, generally speaking, there are few processes for processing parts by mold, and most of them are formed at one time, so the shape of the mold must have all the details of the processed parts. C. The repetition probability of mold design is high, so the geometric model of mold CAD should be updated repeatedly and repaired in time. (2) Modeling characteristics of mold cAD [4] Mold CAD modeling technology is an accurate modeling technology, which can be divided into solid modeling and surface modeling: a. Solid modeling technology can meet the design requirements for molds with simple structure, but it is not enough for parts with complex structure and high detail description accuracy, such as drawing surfaces, surface fillet transition and cavity design. B surface modeling technology is to generate smooth surface models from different surface construction features. It mainly includes the core technologies such as multi-surface equal variable fillet transition processing technology, automatic surface trimming technology, surface editing technology, surface analysis technology, smoothing processing and so on, which can assist solid modeling technology to complete all the details in mold design. Surface modeling technology is suitable for product mold design with complex appearance and high detail description accuracy. (3) Advantages of Mold CAD [] The advantages of Mold CAD endow it with infinite vitality, which enables it to develop rapidly and be widely used. No matter in improving productivity and quality, or in reducing cost and labor intensity, the advantages of D technology are incomparable to traditional mold design methods. ACD can improve the quality of mold design. In the computer system, the comprehensive technical knowledge of various related majors is stored, which provides a scientific basis for the design and process formulation of molds. The interaction between computer and designer is conducive to giving full play to their respective specialties and making the mold design and manufacturing process more reasonable. CAD can save time and improve productivity. The automation of design calculation and drawing greatly shortens the design time. The quality is improved, the reliability is enhanced, the decoration time is obviously reduced, and the delivery time of the mold is greatly shortened. Computer aided design can greatly reduce the cost. The high-speed operation and automatic drawing of the computer greatly save manpower and electricity. The optimized design saves raw materials. D.CAD technology liberates technicians from tedious calculation and drawing and engages in other creative work. 1.3 The research content of this paper systematically puts forward the theory and method of mold design based on case-based reasoning, and deeply studies the application of CRB technology in mold design. On the basis of theoretical research, a mold design system based on case-based reasoning is developed, which strongly proves that the application of CRB technology can improve the efficiency of mold design. The research contents of this paper mainly include: Chapter 1: Introduction: This paper summarizes the research significance of this paper, introduces the source and background of the subject, briefly describes the application of CRB technology in mold design, and studies the general situation and development trend of mold CAD at home and abroad. The second chapter is the overall design of mold CAD system, which mainly includes the process analysis, system demand analysis, system structure customization and functional module division of mold CAD. The third chapter describes the key technologies of case-based reasoning, and introduces the key technologies such as case representation, case retrieval strategy and case storage in detail. Chapter four: Case-based die design: The content and method of die case representation are introduced, and the storage and retrieval scheme of die case is put forward. The fifth chapter is the development of the prototype system: the UG development platform and tools are introduced, and the business process of the system is described. Chapter VI Conclusion and prospect. Summarize and prospect the research content of this paper.