CAD/CAM (Computer Aided Design and Manufacturing) technology came into being in the aviation and military industries of developed countries in the late 1950s, and it grew rapidly with the development of computer software and hardware technology and computer graphics technology. 1989, the national academy of engineering named CAD/CAM technology as one of the top ten outstanding achievements of engineering technology (1964- 1989). In the past 30 years, CAD technology and system have developed rapidly, and the application of CAD/CAM has been popularized rapidly. In developed countries, the application of CAD/CAM technology has rapidly expanded from military industry to civil industry, from large enterprises to small and medium-sized enterprises, and from high-tech applications to the design and manufacture of household appliances and light industrial products. This technology is flowing from developed countries to developing countries.

CAD is a very broad concept. Generally speaking, there are two kinds of CAD design objects: one is mechanical, electrical, electronic, light industry and textile products; The other is engineering design products, that is, engineering buildings, which are referred to as AEC (architecture, engineering and construction) in foreign countries. Nowadays, the application scope of CAD technology has been extended to art, film, animation, advertising, entertainment and other fields, which has produced great economic and social benefits and broad application prospects.

CAD is the earliest and most widely used in machinery manufacturing. Using CAD technology to design products can not only make designers get rid of drawing boards, update traditional design ideas, realize design automation, reduce product costs and improve the competitiveness of enterprises and their products in the market; It can also change the original serial operation into parallel operation, establish a brand-new design and production technology management system, shorten the product development cycle and improve labor productivity. Nowadays, the world's major aviation, aerospace and automobile manufacturing giants not only widely use CAD/CAM technology for product design, but also invest a lot of manpower, material resources and funds to develop CAD/CAM software, so as to maintain their leading position in technology and advantages in the international market.

Computer Aided Architectural Design (CAAD) is the application of CAD in the field of architecture, which has brought a real revolution to architectural design. With the development of CAAD software from 2D general drawing software to 3D building model software, CAAD technology has been widely used, which can not only improve the design quality, shorten the project cycle, but also save 2% to 5% of the construction investment. In recent years, China's annual capital construction investment has reached hundreds of billions of yuan. If nearly ten thousand engineering design units in China adopt CAD technology, the investment benefit of capital construction can be greatly improved.

CAD technology is also used in textile and clothing industries. In the past, the pattern design, pattern coordination, color transformation, pattern color separation, sketch drawing and color matching of textiles and garments in China were all done by hand, which was slow and inefficient. At present, the requirements of the international market for textiles and garments are small batch, various colors, high quality and fast delivery, which makes China's textile products uncompetitive in the international market. The adoption of CAD technology has greatly accelerated the pace of China textile and garment enterprises entering the international market.

Nowadays, CAD technology has entered people's daily life and played a great role in the fields of movies, animation, advertising, entertainment and so on. CAD technology has been used in film shooting for more than ten years. Hollywood film companies in the United States mainly use CAD technology to construct scenes, and can use virtual reality to design scenes that cannot be completed manually. This can not only save a lot of manpower and material resources, reduce the shooting cost of the film, but also create a strange and unimaginable environment for the audience and get huge box office income. For example, American sci-fi movies such as Star Wars, Alien, Jurassic Park, and Toy Story, which is made entirely by three-dimensional computer animation, have all achieved great success. The blockbuster Titanic, which caused a sensation all over the world, used a large number of three-dimensional animations to simulate the whole process of Tektronix's voyage and shipwreck with computers. In addition, computer modeling technology is fully used in animation and advertising production, and it is also a virtual reality technology in essence. Virtual reality technology is also used for real-time roaming and entertainment games of various simulators and scenes.

In recent ten years, with the advancement of CIMS engineering and CAD application engineering, the application of computer-aided design technology has become more and more common in China, and more and more design units and enterprises have adopted this technology to improve design efficiency, product quality and working conditions. At present, there are dozens of CAD software imported from abroad in China, and some domestic scientific research institutions, universities and software companies have also developed their own CAD software and put it on the market. The application of CAD technology in China presents a thriving scene.

Second, the technical status in the field of CAD/CAM

1 CAD technology

CAD technology is a comprehensive high-tech in computer and other fields, which integrates computer graphics, database, network communication and other knowledge. It is an important part of advanced manufacturing technology; It is also a key technology to improve design level, shorten product development cycle and enhance industry competitiveness. The characteristics of CAD technology are extensive and complex, rapid technological change, fierce competition, large investment, high risk and high output. The well-known modern CAD/CAM software is huge in scale, multi-functional and complex in system, so it is difficult to keep up with the rapid development of hardware platform and development environment, as well as the ever-changing and growing requirements of users.

2.2 hardware environment. CAD system

At present, the hardware environment of CAD system is mainly engineering workstation and personal computer. Workstation is an interactive computer system with high-speed scientific calculation, rich graphic processing and flexible window and network management functions. Generally, the central processing unit (CPU) with 32-bit or 64-bit word length widely uses RISC, superscalar, super pipeline and super-long instruction technology, has Unix operating system and X-window management system, and runs in a distributed network environment. At present, the popular workstations mainly include: SPARCStation 10 workstation of Sun Company, HP-PA workstation of Hewlett-Packard Company of the United States, Alpha workstation of DEC Company, SGI workstation and RS/6000 workstation of IBM Company. Although the workstation has superior performance and fast graphics processing speed, it is very expensive, which limits the promotion of CAD/CAM technology to some extent at present.

In the past, personal computers were very different from workstations in calculation, graphics, network and parallel processing. The system software such as DOS and Windows running on personal computer is not as good as the system software on workstation in reliability, security and efficiency. However, with the rapid development of computer hardware technology, the continuous improvement of personal computer's computing ability and graphics processing ability and the gradual improvement of operating system, the performance gap between personal computers and professional RISC/Unix workstations has gradually narrowed. In particular, the release of Intel's PentiumPro and Pentium II chips and Microsoft's WindowsNT make personal computers fully compete with low-end workstations in performance, and the low price of personal computers makes them play an irreplaceable role in popularizing CAD applications.

3. The mainstream technology in the field of CAD/CAM.

(1) Basic modeling technology (parametric design, variable design and feature modeling technology)

In the early days of the development of CAD technology, CAD was limited to computer-aided drawing. With the rapid development of computer software and hardware technology, CAD technology has developed from two-dimensional plane drawing to three-dimensional product modeling, and then three-dimensional wireframe modeling, surface modeling and solid modeling technologies have emerged. Nowadays, parametric and variable design ideas and feature modeling represent the development direction of CAD technology.

Traditional CAD drawing software always defines geometric elements with fixed size values. To modify the drawing, the original lines must be deleted and redrawn. The proofing design of new products is bound to be revised many times, and the shape and size of parts will be comprehensively coordinated and optimized. Most of the design work is carried out on the basis of the original design. Therefore, parametric and variable design modules are added to the new CAD system, so that the design drawings of products can be automatically modified with the modification of some structural dimensions and the change of the use environment, which can reduce a lot of repetitive work and reduce the design workload.

Parametric design generally means that the structural shape of the design object is relatively fixed, and a set of parameters can be used to stipulate the dimensional relationship. The solution of the parameters is relatively simple, and there is a clear correspondence between the parameters and the control size of the design object, and the modification of the design result is driven by the size. The most commonly used serialized standard parts in production belong to this type. Variationaldesign means that the modification of design objects requires more freedom, and the size and shape of products are determined by solving a set of constraint equations. Constraint equations can be geometric relations or engineering calculation conditions, and the modification of design results is driven by constraint equations. Variable design allows the existence of size constraints, so that designers can adopt the design method of shape before size, put the geometric shapes that meet the design requirements first, and temporarily ignore the size details, so the design process is relatively loose. Variable design can be used for tolerance analysis, coordination of motion mechanism, design optimization, selection of preliminary scheme design, etc. , especially in conceptual design.

When it comes to variable design, we can't help but mention VGX technology of SDRC company in the United States. VgX (short for Variation Algeometric Extended) is a milestone in the development of variable technology. Its idea is first embodied in the variable composition of the first edition of SDRC's software product I-Deamaster series. VGX technology has brought unprecedented ease of use to CAD software. Designers can operate and modify the three-dimensional geometric model of products intuitively and in real time, and they can dynamically capture the design, analysis and manufacturing intentions in one master model at one go. VGX technology greatly improves the intuition and reliability of interactive operation, thus making CAD software easier to use and more efficient.

Feature modeling is a new milestone of CAD modeling method, which was conceived and grown up in the historical process that the development and application of CAD/CAM technology reached a certain level and further improved the integration and automation of production organization. In the past, CAD technology began with two-dimensional drawing and experienced three-dimensional wireframe, surface and solid modeling, all of which focused on improving the geometric description ability of products, that is, only describing the geometric information of products; Feature modeling focuses on better expressing the complete function and production management information of products, and serves for establishing the integrated information model of products. As a technical term, feature has both shape and function attributes, including the specific geometric shape, topological relationship, typical function, drawing representation method, manufacturing process and tolerance requirements of products. Feature modeling technology makes product design work at a higher level, and the designer's operation object is no longer the original lines and voxels, but the functional elements of the product. The reference of features directly reflects the design intention, makes the established product model easier for people to understand and organize production, and creates a premise for developing a new generation of CAD/CAPP/CAM integrated system based on unified product information model.

(2) data exchange format and standardization; 2)CAD (DXF format, IGES format and STEP standard)

With the continuous development and maturity of CAD technology, as well as the deepening application of CAD in various industries, CAD standardization has shown its importance more and more. As a part of high-tech standardization, CAD standardization plays an important role in CAD technical work. During the Eighth Five-Year Plan period, the Industry Department of the State Science and Technology Commission and the Standards Department of the State Bureau of Technical Supervision jointly issued the General Technical Specification for CAD, which stipulated the standards of various aspects of CAD technology in China. CAD data exchange is an important issue faced by various industries after CAD is widely used. Due to the rapid expansion of CAD data, data files generated by different CAD systems adopt different data formats, and even the types of data elements in each CAD system are different, which potentially hinders the further application and development of CAD technology. Therefore, how to maximize the enjoyment and effective management of enterprise's CAD technical information is a very important topic facing standardization.

At present, the graphic file standards used for data exchange on microcomputers and workstations mainly include DXF(DataExchangeFile) file of AutoCAD system, IGES (initial graphics exchange specification) of the United States and step (standard for the exchange of product model data) of the international standard. Other important standards include: CAD-I standard (limited to finite element and shape data information) funded by ESPRIT (European information technology research and development strategic planning); German VDA-FS standard (mainly used in automobile industry); French SET standard (mainly used in aerospace industry) and so on.

AutoCAD DXF file is a special format ASCII text file, which is easy to read and be processed by other programs. It is mainly used to realize the connection between programs written in high-level languages and AutoCAD systems, or the exchange of graphic files between other CAD systems and AutoCAD. Because AutoCAD is widely used in the world, it has penetrated into all walks of life, and its data file format has become a de facto industrial standard. DXF graphic data exchange file provides great convenience for the popularization and application of CAD/CAM technology. However, due to the early development of DXF file, from the current point of view, it must have many shortcomings: it can not describe the complete geometric model of the product, and it is difficult to develop it further; Its information definition is incomplete, only the geometry and some attribute information in the original system data structure are retained, and a lot of topological information no longer exists; There are also many defects in its information description, which makes some information too lengthy; The file format is complicated and unreasonable. Therefore, Autodesk recently emphasized the use of binary DWG and DWF formats as its data transmission standards on the network, but these two formats are not public, so it is difficult to use them as industrial standards for other CAD systems.

IGES standard was first formulated by ANSI in the early 1980s. It is based on Boeing's CAD/CAM integrated information network, General Electric's central database and other data exchange formats. Its original version is limited to describing the geometry and annotations of engineering drawings, and then it includes electrical, finite element, factory design and architectural design. 1IGES4.0 released in June, 1988 absorbed CSG (construction methodology) and assembly model in ESP, and then extended it, adding new graphic representation, 3D pipeline model and FEM (finite element model) function improvement. The B-rep model is defined in IGES5.0. However, IGES unreasonably defines the direct access pointer system in the file structure. The main problems exposed in its application are:

The data file is too large and the data conversion processing time is too long;

Some geometric types are unstable;

Only pay attention to the transformation of graphic data and ignore the transformation of other information.

Nevertheless, IGES is still the de facto international standard data exchange format widely used in various countries, and China has adopted IGES3.0 as the national recommended standard since September 2003 1993.

The product model data exchange standard STEP is an internationally unified CAD data exchange standard formulated by SC4 Sub-committee of product model data external representation under Technical Committee TC 184 of International Organization for Standardization (ISO). The so-called product model data refers to all data elements of a product that are fully defined for application in the whole life cycle of the product. It includes data such as geometry, topology, tolerance, relationship, attributes and performance of parts or components that are fully defined for design, analysis, manufacturing, testing, inspection and product support, and may also include some data related to processing. Product model can provide comprehensive information for production tasks, direct quality control, testing and product support.

STEP provides a unique description and information expression form that can be processed by computer for products in their life cycle. This form is independent of any specific computer system and can ensure consistency in various applications and different systems. The standard also allows different implementation technologies to facilitate the access, transmission and archiving of product data. STEP standard is a public resource and application model developed to provide neutral product data for CAD/CAM system, which involves all product fields such as architecture, engineering, structure, machinery, electricity, electronic engineering and hull structure. In the aspect of product data sharing, STEP standard provides four levels of implementation methods: neutral files in ASCII code; An application program interface for accessing memory structure data; * * * Enjoy the database, * * * Enjoy the knowledge base. Undoubtedly, this will bring great changes to commerce and manufacturing, and the STEP standard has obvious advantages in the following aspects: First, it has remarkable economic benefits; Second, the data range is wide and the accuracy is high, and the application protocol eliminates the ambiguity of product data; Third, it is easy to integrate and expand; Fourthly, the technology is advanced and the level is clear, which is divided into three parts: general resources (sub-standard 40 series), application resources (sub-standard 100 series) and application protocols (sub-standard 200 series). Nowadays, STEP standard has become an internationally recognized global unified standard for CAD data file exchange, and many countries have formulated corresponding national standards according to STEP standard. The formulation of STEP standard in China was completed by CSBTSTC 159/SC4, and the corresponding standard number of STEP standard in China was GB 16656. The problem of STEP standard is that the whole system is extremely huge, the standard formulation process is slow, and the data file is larger than IGES. At present, the only STEP application protocol provided by commercial CAD system is AP203 Configuration Control Design, which includes product configuration management, surface and wireframe models, facet boundary representation and surface boundary representation of solid models, and AP2 14 Core Data of Automobile Mechanical Design Process.

Third, the current situation of domestic CAD market and mainstream CAD/CAM software products

1. Overview

Since China began to develop CAD software in the 1960s, after the achievements accumulated in the Sixth Five-Year Plan, the Seventh Five-Year Plan and the Eighth Five-Year Plan, the CAD software industry has begun to take shape in the fields of architecture, petrochemical, light industry, shipbuilding, machinery and electronics, as well as two-dimensional parametric drawing, finite element analysis, surface modeling, NC machining programming and so on, and achieved remarkable results, among which the architectural CAD software has occupied a dominant position in China. Well-known ones are: ABD series software of architecture, structure and equipment of China Research Institute of Building Science, BICAD integrated civil building structure system of Beijing Huaxia Zhengbang Technology Co., Ltd., PKPM series software of building engineering, Desai series software of building decoration ... At present, China independent copyright CAD software is basically a microcomputer version, and the price is appropriate, which conforms to the design habits of China designers. Although there is a certain gap compared with foreign similar CAD software in capital investment, commercial packaging, enterprise collectivization and scale, it still has broad market prospects and development potential. The following introduces the main CAD/CAM products in the domestic market at present.

2. Import major foreign software

(1)AutoCAD and MDT

AutoCAD system is an interactive drawing software developed by Autodesk Company of the United States for microcomputers. It is basically a two-dimensional engineering drawing software, with strong drawing, editing, drawing section lines and patterns, dimensioning and user-friendly secondary development functions, as well as some three-dimensional drawing and modeling functions. At present, it is the most widely used CAD software in the world, accounting for about 37% of the global PC CAD/CAE/CAM software market, and it is the leader of many microcomputer CAD software, leaving other microcomputer CAD software such as Cadkey, EagleCAD and CAD-Plan far behind. Now AutoCAD has released the R 14 version, and the latest version of China culture is on the market.

MDT(MechanicalDesktop) is a microcomputer CAD/CAM software based on parametric feature solid modeling and surface modeling introduced by Autodesk Company in the mechanical industry. It is said that more than 20,000 MDT units have been installed at present, and the users of MDT mainly include: China FAW Group, Philips of the Netherlands, Siemens of Germany, Toshiba of Japan and Hughes of the United States.

(2) Specialty/Engineer

Pro/Engineer system is a product of American Parametric Technology Company (PTC for short). As soon as it came out (1988), it was welcomed by users for its advanced parametric design and entity modeling based on feature design. Subsequently, major CAD/CAM companies have also introduced parametric modeling modules based on constraints. In addition, Pro/Engineer is built on the workstation from the beginning, which makes the system independent of hardware and easy to transplant. The user interface of the system is concise and the concept is clear, which conforms to the design ideas and habits of engineers. The whole system of Pro/Engineer is based on a unified database and has a complete and unified model, which can integrate the whole design and production process. It has more than 20 modules for users to choose from. Based on the above reasons, Pro/Engineer has become the most attractive system in the field of three-dimensional mechanical design in recent years, and its sales volume and user base are still developing at the fastest speed. Moreover, PTC recently acquired Computervision (CV for short), which further strengthened the strength of PTC.

(3)I-DEASMasterSeries5

I-Deamaster series is a new generation of mechanical design automation software launched by American SDRC (Structural Dynamics Research Company), from 1993. It is also the flagship product of SDRC in the field of CAD/CAE/CAM, which is famous for its high integration, powerful functions, easy learning and easy use. I-Deamaster Series 5 was first exhibited in the United States on June 20th this year. Its biggest breakthrough is the introduction of VGX technology, which greatly improves the intuition and reliability of interactive operation. In addition, this version also enhances the functions of complex part design, advanced surface modeling, finite element modeling and durability analysis. In China, there are more than 400 users who officially use the I-Deamaster series software, which occupies a leading position in the automation software of three-dimensional solid mechanical design. Because SDRC company developed gradually in the early stage based on engineering and structural analysis, and engineering analysis is the company's specialty. Recently, SDRC has also concentrated its superior strength and strengthened the development of CNC machining functions.

(4)CATIA

CATIA system is a product developed by the engineering department of DassaultSystems, a French aircraft company. The system was developed on the basis of CADAM system (originally developed by Lockheed Company of the United States and later merged into IBM Company of the United States). The source program of the original CADAM system is purchased in CAD, and the source program of the famous APT system is processed and purchased. After several years of efforts, a commercial system has been formed. CATIA system has developed into an integrated CAD/CAE/CAM system, which has a unified user interface, data management and compatible database and application interface, and has more than 20 independent pricing modules. The working environment of the system is IBM mainframe and RISC/6000 workstation. Nowadays, CATIA system has nearly 2000 users in more than 30 countries around the world, and Boeing 777 of Boeing Aircraft Company of the United States is one of its representative works.

(5) Euclid

Euclid software is a product of the information department of MATRA company in France. It was developed by the French National Scientific Research Center for the supersonic passenger plane Concorde jointly developed by Britain and France. The software has a unified object-oriented distributed database, and there is no need to convert any data between 3D solid, complex surface, 2D graphics and finite element analysis model. Because the data are mutually referenced, rather than simply copied, when users modify a part of the design, other related data will be updated by themselves. The software mainly runs on SGI, DEC, Sun and HP workstations. It is said that there are more than 65,438+0,200 users in nearly 40 countries. The main users are MATRA, Renault, Maya, Mercedes-Benz, Volkswagen/Audi, General Dynamics, Nissan, NEC and Omega watches.

(6) Unigraphics

UG originated from the products of McDonnell Douglas (MD) Company in the United States, and was merged into the EDS branch of General Motors Company in June of 199 1. Today, EDS is the largest information technology (IT) service company in the world, and UG is developed by its independent subsidiary UnigraphicsSolutions. UG is a mechanical engineering auxiliary system integrating CAD, CAE and CAM, which is suitable for the design, analysis and manufacture of aerospace vehicles, automobiles, general machinery and molds. The software can run on HP, Sun, SGI and other workstations, claiming that the total number of installations is nearly 30 thousand. UG adopts feature-based entity modeling, has size-driven editing function and unified database, and realizes free switching among CAD, CAE and CAM without data exchange. UG has strong NC machining ability, and can process and bore and mill complex curved surfaces with 2-2.5 axis and 3-5 axis linkage. UG also provides secondary development tools such as GRIP, UFUNG and ITK, allowing users to expand the functions of UG. UG entered the China market in the early 1990s and has installed about 2,000 units.

(7)SolidWorks

SolidWorks is a Windows-based CAD/CAE/CAM/PDM desktop integrated system, which was developed by SolidWorks Company of the United States on June 1995 1 1, and the price is only a quarter of that of workstation CAD system. The software adopts the top-down design method and can dynamically simulate the assembly process. It adopts feature-based entity modeling, which is called 100% parametric design and 100% modifiability. At the same time, it has both Chinese and English interfaces to select its advanced feature tree structure, which makes the operation simpler and more intuitive. The software was officially introduced to China by Shengxin International Co., Ltd. from June 65438 to August 0996. Because it is based on Windows platform and has a reasonable price, it has a broad market prospect in China.

3. Main software developed in China

( 1)PICAD

PICAD system and series software are CAD software with independent copyright jointly developed by Case Software Group of China Academy of Sciences and Beijing Case Bohong Application Engineering Company. The software is intelligent, parameterized and open, and can automatically capture and dynamically navigate feature points and coordinates. The system provides local graphics parameterization, parameterized pixel assembly and extensible parameter symbol library; Provide an open secondary development tool in an interactive environment, and users can add functions or develop professional application software at will. PICAD is the earliest commercial CAD support platform and the largest interactive engineering drawing system in China. Since 199 1 launched the first commercial 2D CAD system in China, after several years of development, PICAD users have spread all over various industries and provinces and cities, and nearly 8,000 sets have been installed by the end of 1997.

(2) Gao Hua CAD

Beijing Gaohua Computer Co., Ltd. is a high-tech enterprise jointly funded by Tsinghua University and Guangdong Kelon (Rong Sheng) Group, headquartered in Tsinghua University. Gaohua CAD series products include computer aided drawing support system GHDrafting, mechanical design and drawing system GHMDS, process design system GHCAPP, three-dimensional geometric modeling system GHGEMS, product data management system GHPDMS and automatic numerical control programming system GHCAM. Gaohua CAD is also an integrated CAD/CAE/CAM system based on parametric design, and it is one of the main products of national CAD application engineering, among which GHGEMS5.0 won the first place in the second national independent copyright CAD supporting software evaluation. Today, Gaohua CAD software has been adopted by more than 300 large and medium-sized enterprises and scientific research institutes, and the installed capacity is said to have exceeded 1 10,000 units.

(3) XTMCAD in Tsinghua

Tsinghua XTMCAD is a CAD software jointly developed by Tsinghua University Mechanical CAD Center and Beijing Tsinghua Exeter CIMS Technology Company, based on Win95, AutoCADR 12 and R 13. It has the functions of dynamic navigation, parametric design, establishment and management of graphic library, and also has modules of common parts optimization design, process module and engineering drawing management. As a software value-added developer registered and recognized by Autodesk, you can directly get technical support from Autodesk, and its advantage lies in the exchange and enjoyment of CIMS engineering support data.

(4) Mu Kai CAD

Mu Kai CAD is a computer-based CAD and drawing management software with independent copyright developed by the School of Mechanical Engineering, Huazhong University of Science and Technology. It faces engineering practice, simulates people's design and drawing ideas, is simple to operate, and the efficiency of mechanical drawing is much higher than AutoCAD. Mu Kai CAD supports multiple geometric constraints and multi-view driving at the same time, and has the function of local parameterization, which can deal with over-constraint and under-constraint in design. Mu Kai CAD has realized the integration of CAD, CAPP and CAM, which is suitable for the habits of China designers and is one of the main products of national CAD application engineering.