I. Introduction In the manufacturing and processing industry, the direction of the new technology is to establish a transparent and open commercial operation based on the Internet/Intranet to replace the traditional seller-driven system. This requires the establishment of a networked manufacturing model that responds quickly to market forces and has a rapid response mechanism to make full use of corporate manufacturing resources and social manufacturing resources. CNC equipment is an important manufacturing resource. In order to adapt to networked manufacturing, the processing information related to CNC equipment needs to be integrated under a unified Web platform to realize the networked integration of CNC machining information.
Second, CAD/CAM system integration 1. Structure type of CAD/CAM integrated system
Traditional systems: Such systems were developed earlier, such as I-DEAS, UG-II, CADAM, CATIA, CADDS, and other well-known software. This kind of software professional features strong, due to the limitations of the hardware environment, design concepts and design methods at the beginning of development, these systems are not easy to adapt to the highly integrated requirements.
Improved systems: These systems were developed in the 1980s, such as CIMPLEX, Pro/ENGINEER, and others. Some of these systems are highly automated, such as parameterized feature design, system data and file management, and automatic generation of NC machining programs, but they still lack support for data exchange and shared information integration requirements.
Data-Driven Systems: This is a new generation of CAD/CAM integration systems that are evolving. Its basic starting point is to look at the entire life cycle of the product and seek ways to completely realize exchange and sharing of product data, with a view to achieving integration at a higher level and wider range. The main approach is to use STEP product data exchange standards, and gradually realize a unified system information structure design and system function design.
2. CAD/CAM integration method
Several integrated methods of CAD/CAM:
(1) CAD/CAM integration based on dedicated interface
Among all CAD/CAM integration methods, integration based on dedicated interfaces is the most primitive. For a dedicated interface, it can be understood from two aspects. First, there is no connection between the systems that are integrated. It is necessary to develop interfaces specifically to enable two different systems to communicate indirectly. The second is the dedicated interface developed by the system developer. In order to solve the exchange of information between their own family products.
(2) STEP-based CAD/CAM integration
The Standard for the Exchange of Product data (STEP) standard, which provides a neutral mechanism that does not depend on a specific system. It specifies product design, development, manufacturing, and even the product's overall product life cycle. , analytical models, materials, processing methods, assembly and decomposition sequence, inspection and testing, and other necessary information definition and data exchange external description. Thus STEP is based on an integrated product information model.
(3) Database-based CAD/CAM integration
CAD/CAM integrated systems often use engineering databases. In fact, due to the uniqueness of the engineering database in the storage and management of large amounts of complex data, the CAD/CAM integrated system built with the core of the engineering database has been widely used. The schematic diagram of the system structure is shown in the figure. There are data exchanges between the product design and manufacturing and the engineering database, and the whole system of data is shared.
Third, San\PDM and CAD/CAM integration PDM, with its ability to comprehensively manage information in the product life cycle, not only becomes an important part of the CAD/CAM integration system, but also offers the possibility of integration of CAD/CAM with the PDM system as a platform. From a development point of view, this system has a good application prospect.
(1) Integration of CAM and PDM
Because there is only the exchange of document information such as knife position file, NC code, product model,etc. between CAM and PDM system, so employ the encapsulation between CAM and PDM to meet the information integration requirement between them.
(2) Integration of CAPP and PDM
In addition to document exchanges between CAPP and PDM, the operation of the CAPP system also requires the acquisition of equipment resource information, raw material information, etc. from the PDM system. The process information generated by CAPP, in order to support information integration with the MRP-II or workshop control unit, also needs to be decomposed into basic information units (such as processes, steps, etc.) stored in the process information database for PDM and MRP-II integration Use it. Therefore, the integration between CAPP and PDM requires interface switching, and on the basis of implementing application encapsulation, the information exchange interface is further developed so that the CAPP system can directly obtain the support of equipment resources and raw material information from the PDM through the interface and generate The process information is stored directly in the PDM process information database via the interface. Since the PDM system does not directly provide the equipment resource library, raw material library, and process information library, users need to use the PDM development tools to develop the aforementioned library management modules.
(3) Integration of CAD and PDM
The integration of CAD and PDM is the most demanding and most difficult aspect of PDM implementation. The key is to ensure that the data changes in CAD are consistent with the data changes in PDM. From the perspective of user needs, the integration of CAD and PDM should achieve a true sense of tight integration. The application packaging of CAD and PDM only solves the problem of document management in CAD production. Component description attributes and product schedules need to import PDM through the interface. At the same time, bidirectional asynchronous exchange of data between PDM and CAD systems is realized through interface exchange. However, this exchange still cannot fully guarantee the consistency of product structure data in CAD and PDM. Therefore, to truly solve this problem, we must achieve a tight integration between CAD and PDM, that is, establish a shared product data model between CAD and PDM, achieve interoperability, and ensure the interaction between the modification in CAD and the modification in PDM. Consistency, true two-way synchronization consistency. At present, there is still a certain degree of difficulty in this kind of tight integration. A PDM system can only be closely integrated with one or two CAD products.
Fourth, based on Ethernet DNC ​​system 1 Ethernet-based DNC communication technology
Ethernet has become the mainstream technology of office automation because of its advantages of low cost, high stability, and high reliability. However, because its MAC layer protocol uses CSMA/CD, it has the defect of uncertain queuing delay, making it unable to be effective in industrial control. use. With the development of IT technology, the 802.3 standard has increased the Ethernet speed from the original 10 Mbps to 1 000 Mbps. Sufficient bandwidth and switching hub applications solve the uncertain problem of Ethernet, enabling Ethernet to meet the needs of real-time systems. Claim. For example, using switched Ethernet allows each node in the access network to occupy a single line of the network to avoid collisions. If high-speed backplane switching or microprocessor switching is used, the response time is determined. According to ARC's analysis, the 126-node 100M switch is used. The response time of Ethernet is 2-3 ms, which can meet the requirements of various control systems. Because of the advantages that Ethernet has already had, the extension of Ethernet as the mainstream technology of office automation to field devices has become the current development direction. The communication interface of the CNC machine tool determines the communication technology used in the DNC system. Although with the development of network technology, the new CNC machine tool provides Ethernet interface, but in the DNC system, the serial communication is mainly realized by the point-to-point or star structure. Or use fieldbus as communication network and serial converter to access CNC machine tools to realize fieldbus communication. These communication methods have the disadvantages of inability to achieve information network release, slow transmission speed, and low cost performance. This article proposes an Ethernet-based DNC communication technology, the network topology as shown below. The DNC controller is a programmable logic controller with network interface, serial port, and digital and analog input and output interfaces. It has an embedded Web service function and can implement HTTP access.
Network CNC processing system composition diagram
2 Ethernet-based information integration model
CNC machine tools are the ultimate implementers of products. Increasing the productivity of machine tools is an important way to shorten the product manufacturing cycle. Therefore, improving the productivity of machine tools has become the goal of information integration. On the one hand, the processing information such as numerical control programs and job plans are transferred via Ethernet to reduce the non-machining time of the machine tool; on the other hand, the machine tool operation information is properly arranged through the analysis of the machine tool operation information in the DNC system.
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