Since the birth of the world's first CNC machine tool in 1952, the development of CNC technology has been very rapid, and the CNC system has also evolved from the original hard-joined CNC to today's computer numerical control (CNC). However, the modern production has higher and higher requirements for the CNC. The incompatibility between the systems, the difficulty of programming, and the low degree of intelligence have greatly limited the development of modern production and numerical control technology itself. At the same time, people gradually realized that the G and M codes (ISO 6983) that CNC systems have been using have not been able to meet the needs of modern production and technological development. This NC program for motion and switch control limits the openness and intelligent development of the CNC system, and also creates a bottleneck between the CNC and CAX technology, which seriously hinders the development of the machinery manufacturing industry. In 1997, the European Community developed an object-oriented data model that complies with the STEP standard through the OPTIMAL program, redefines the object-oriented data model, redefines the programming interface for milling, and proposes the concept of STEP-NC. STEP-NC extended the product data conversion standard STEP to the CNC field, redefining the interface between CAD/CAM and CNC. It requires the CNC system to directly use the CAD 3D product data model (including geometric data, design and manufacturing features) in accordance with the STEP standard (ISO 10303), plus process information and tool information, directly generate machining programs to control the machine. Subsequently, STEP-NC became a hotspot in the research of industrialized countries in the world. Among the more representative research projects are the STEP-NC project in Europe, the Super Modal project in the United States, and the Digital Master project in Japan. Substantial progress has been made in the current research of the STEP-NC project. According to the US STEP Tools company's prediction, the STEP-NC controller will appear in the first decade of this century, when people will see a new vision of automated manufacturing.
STEP-NC data model
STEP-NC is a data standard redefined for the CNC system. It links the design information of the product with the manufacturing information based on the object-oriented form of STEP. STEP-NC defines a new STEP application protocol (AP-238, still under development) as a data exchange specification between CAM and CNC. AP-238 covers all the information needed from the concept to the finished product (parts), including 3D geometry information (AP-214), process information (such as milling, car, electrical discharge machining, etc.), inspection information (AP- 219) Wait. The current draft STEP-NC standard (ISO-DIS-14694) has been formed. The basic rules and milling standards (draft) have been completed, including basic concepts and rules (Part 1), general standards (Part 10), CNC milling processes (Part 11), milling tools (Part 111) and so on. The STEP-NC standards being developed include: CNC turning (Part 12), electrical discharge machining (Part 13), wood and glass processing (Part 14), testing (Part 15), etc. A simplified model such as generic data, including artifacts and work plans. The workpiece refers to the final product, and the area on the workpiece where material needs to be removed is defined by a series of processing features. The work plan includes several work steps (such as planes, complex surfaces, holes, etc.) that are linked to specific operations. The operation itself is also the concept defined in ISO-14649, designing machining methods, tools, guides, process strategies, etc.
Data program structure based on STEP-NC
The NC program based on STEP-NC discards the practice of directly programming the axes and tool actions in the traditional NC program, using the ISO-10303 data format and feature-oriented programming principles. It uses work steps as the basic unit of the process, linking features and technical information. Each work step defines only one type of operation ("what to do", "how to do", etc., but only one tool and one strategy).
The program itself also adopts the file format specified by ISO-10303, which can be divided into two parts: the file header and the data segment. The header is marked with "HEADER", which mainly describes the file name, programmer, date, and comment. The data segment begins with "DATA" and contains all the information and operational tasks required to machine the part. According to the regulations, it first needs a PROJECT statement, and the subsequent content can be divided into three parts: work plan and executable statement (Executable, including work steps, general NC functions such as information display, and control of the process), technical description ( Tool, machine function, machining strategy, etc.), geometric description (geometry data, machining features, etc.).
STEP-NC provides space for development of CNC
The development of STEP-NC has enabled the STEP standard to be extended to the underlying equipment for automated processing, creating a highway for the entire manufacturing network. It is foreseeable that in the future, the CNC system will undergo fundamental changes in terms of structure, function, and position in the manufacturing system, and this change will inevitably affect related CAX technologies (such as CAD, CAPP, CAM, CAE, PED, ERP, etc.), the development of tools, machine bodies and fixtures, and the facts of advanced production models. As far as the current research results are concerned, the more direct effects that can be foreseen are mainly due to the following aspects:
1) CNC programming interface: replacing ISO-6983 with ISO-14649 makes the programming interface greatly improved. On-site programming is convenient and replaces it for easy reuse. When certain features of the workpiece being machined are slightly changed, it is only necessary to change the geometric description of the feature, and other elements need not be changed. In addition, the unified program can be run directly on different models of machine tools.
2) Openness of CNC system: At present, due to the narrow coverage of ISO-6983, CNC manufacturers have to develop their own expansion instructions. Therefore, CAM and CNC must use the same set of code, otherwise a specific post-processing must be selected. For the STEP-NC controller, the data format (AP-238) is exactly the same. He tells the CNC what to process instead of the specific action, so no post-processing is needed. The specific action is determined by the CNC. The program has Good interoperability and portability.
3) Intelligentization of CNC system: As the interface between CAM and CNC, the formation process of G and M codes causes a lot of useful information loss, which is also a major reason for the low degree of CNC intelligence. In contrast, STEP-NC contains all the information needed to process a product, providing the basic conditions for the CNC system to perform autonomous processing based on a comprehensive understanding of the product.
4) Re-division of functions between CMA/CNC: CNC knows more about the operation of the machine than the CAM or CAPP system, and the specific process processing (such as tool selection, compensation, and determination of the route) in the CNC is more It is possible to get the best processing results. Therefore, the future CNC will complete some of the functions of the CAM system, and on this basis, it will be possible to install the embedded CAM system and directly process it according to the CAD data model.
5) Processing quality and efficiency: The proposed STEP-NC changed the status of the current CNC system as a passive performer of processing tasks. The enhancement of CNC functions also increases the efficiency of its upstream links. According to STEP Tools, the application of STEP and STEP-NC can reduce the production data preparation in the CAD stage by 75%, the machining process planning (CAM) time by 35%, and the machining time (CNC 5-axis high-speed milling) by 50%.
6) Data sharing and network manufacturing: The development of STEP-NC enables a two-way seamless connection between the STEP-NC based CNC system and all STEP-based CAX systems (for example, the CAD system can read STEP-NC directly from the CNC system). The geometric information in the data) creates conditions for network-based manufacturing models and technologies.
Conclusion: STEP-NC is both a CNC interface standard that is being improved and an implementation technology that enhances modern CNC. It provides a broad space for the openness and intelligence of the CNC, and it also solves the core problem of the two-way seamless connection between CNC and CAX, and has unpredictable and far-reaching impact on the future of automated manufacturing. Compared to the open CNC proposed by this premise, the STEP-NC controller (STEP-based CNC) is more meaningful (it looks at the seamless link of the product life cycle), and the implementation technology is more practical (from the data model) Start). At present, the research of STEP-NC controller is still in its infancy, but it is developing very fast (Siemens has successfully developed a prototype), and the prospects are very bright. This is also a good opportunity for China to narrow the gap, develop domestic CNC and even improve China's automated manufacturing level.
Metal Wood Burning Fireplace,Wood Burning Fireplace,Wood Burning Fireplace
Boge Technology (Shanghai) Co., Ltd. , http://www.shportablefireplace.com