1 CNC system development trend
The first experimental CNC system was developed from the Massachusetts Institute of Technology in 1952 and has now gone through 53 years. The CNC system started from the original electronic tube and experienced the following stages of development:
Discrete transistor type - small-scale integrated circuit type - large-scale integrated circuit type - small computer type - very large scale integrated circuit - microcomputer type numerical control system. In the 1980s, the overall development trend was: CNC devices were developed from NC to CNC; 32-bit CPUs were widely used to form multi-microprocessor systems; system integration was improved, volume was reduced, and modular structure was adopted to facilitate cutting, expansion, and function upgrades. To meet the needs of different types of CNC machine tools; drive devices to the direction of communication and digitization; CNC devices to the direction of artificial intelligence; the use of new automatic programming systems; enhanced communication functions; CNC system reliability continues to improve. In short, the numerical control machine tool technology is constantly developing, the function is more and more perfect, the use is more and more convenient, the reliability is getting higher and higher, and the performance price ratio is getting higher and higher. By 1990, the world's professional CNC system manufacturers had an annual output of about 130,000 sets of CNC systems. The overall development trend of foreign CNC system technology development is:
●New generation CNC system adopts open architecture
Since the 1990s, due to the rapid development of computer technology, the CNC machine tool technology has been promoted to be updated faster. Many CNC system manufacturers in the world use PC's rich software and hardware resources to develop a new generation of CNC systems with open architecture. The open architecture makes the CNC system more versatile, flexible, adaptable and expandable, and has been greatly developed in the direction of intelligence and networking. In recent years, many countries have researched and developed such systems, such as the "Next Generation Workstation/Machine Controller Architecture" NGC jointly led by the American Center for Scientific Manufacturing (NCMS) and the Air Force, and the European Union's "Open Architecture in Automation Systems". "OSACA, Japan's OSEC program, etc. The development research results have been applied. For example, Cincinnati-Milacron has adopted the open architecture A2100 system in its production center, CNC milling machine and CNC lathe since 1995. The open architecture can use a large number of advanced technologies of general-purpose microcomputers, such as multimedia technology, to realize automatic voice-activated programming and automatic scanning of graphics scanning. The numerical control system continues to develop toward high integration, and more transistors can be integrated on each chip, making the system smaller, more compact and miniaturized. Reliability is greatly improved. Utilize the advantages of multiple CPUs to achieve automatic troubleshooting; enhance communication functions and improve incoming and networking capabilities. The new generation of CNC system with open architecture, its hardware, software and bus specifications are open to the outside world. Because there are sufficient software and hardware resources available, it not only makes the system integration of CNC system manufacturers and users powerful. Support, but also bring great convenience to the user's secondary development, promote the development and wide application of multi-grade and multi-variety of CNC system, which can be upgraded or tailored to form various grades of CNC system, and can be extended The numerical control system that constitutes different types of CNC machine tools greatly shortens the development and production cycle. This CNC system can be upgraded with the CPU upgrade, and the structure does not have to be changed.
●The control performance of the new generation CNC system is greatly improved
The numerical control system is developing intelligently in control performance. With the penetration and development of artificial intelligence in the computer field, the numerical control system introduces the control mechanism of adaptive control, fuzzy system and neural network, which not only has automatic programming, feedforward control, fuzzy control, learning control, adaptive control, process parameters. Automatic generation, 3D tool compensation, motion parameter dynamic compensation and other functions, and the human-machine interface is extremely friendly, and has a fault diagnosis expert system to make the self-diagnosis and fault monitoring functions more perfect. The servo system's intelligent spindle AC drive and intelligent feed servos automatically recognize the load and automatically optimize the adjustment parameters. The linear motor drive system has been put into practical use.
In short, the technical level of the new generation of numerical control system has been greatly improved, which has promoted the development of high-precision, high-speed and high-flexibility of CNC machine tools, and the level of flexible automatic machining technology has been continuously improved.
2 CNC machine tool development trend
In order to meet the needs of market and scientific and technological development, in order to meet the higher requirements of modern manufacturing technology for numerical control technology, the current development trend of CNC technology and its equipment is mainly reflected in the following aspects:
(1) High speed, high efficiency, high precision, high reliability
In order to improve the processing efficiency, it is necessary to first increase the cutting and feeding speed, and at the same time, shorten the processing time; to ensure the processing quality, the accuracy of the movement of the machine components must be improved, and the reliability is the basic guarantee of the above objectives. To this end, high-performance numerical control devices must be guaranteed.
●High speed and high efficiency
The development of machine tools in the direction of high speed can give full play to the performance of modern tool materials, which not only can greatly improve the processing efficiency, reduce the processing cost, but also improve the surface processing quality and precision of the parts. Ultra-high-speed machining technology has broad applicability to high-performance, high-quality, low-cost production in the manufacturing industry.
A new generation of CNC machine tools (including machining centers) can only increase their productivity by significantly reducing the cutting time by speeding up. Ultra-high-speed machining, especially ultra-high-speed milling, is closely related to the development and application of a new generation of high-speed CNC machine tools, especially high-speed machining centers. Since the 1990s, countries in Europe, the United States, and Japan have been competing to develop and apply a new generation of high-speed CNC machine tools, accelerating the pace of high-speed development of machine tools. High-speed spindle unit (electric spindle, speed 15000-100000r/min), high-speed and high acceleration/deceleration feed moving parts (fast-moving speed 60~120m/min, cutting feed rate up to 60m/min), high-performance CNC New breakthroughs have been made with servo systems and CNC tool systems, reaching new levels of technology. With ultra-high-speed cutting mechanism, super-hard wear-resistant long-life tool materials and abrasive tools, high-power high-speed electric spindles, high acceleration/deceleration linear motor drive feed components and high-performance control systems (including monitoring systems) and guards Such as the solution of key technologies in a series of technical fields, we should not miss the opportunity to develop and apply a new generation of high-speed CNC machine tools.
High-precision, high-response speed real-time processing of high-performance machine tool components thanks to fast and accurate digital transfer technology. Due to the new tool, the cutting speed of turning and milling has reached 5,000 meters to 8000 meters per minute. The spindle rotation speed is above 30,000 rpm (some up to 100,000 rpm); the movement speed of the table: (feed rate), at a resolution of 1 micron, at 100 m/min (some to Above 200 m / min), at a resolution of 0.1 μm, at 24 m / min; automatic tool change speed within 1 second; small line interpolation feed rate of 12 m / min. According to the high efficiency, high-volume production demand and the rapid development of electronic drive technology, the promotion and application of high-speed linear motors, developed a number of high-speed, high-efficiency high-speed response CNC machine tools to meet the needs of the automotive, agricultural machinery and other industries. Also, due to the accelerated cycle of new product replacement, the processing parts of the mold, aviation, military and other industries are not only complicated but also have increased varieties.
From precision machining to ultra-precision machining (special high-precision machining), it is the direction of development of various industrial powers in the world. Its accuracy ranges from micron to sub-micron, and even nano-scale (<10nm), and its application range is increasingly widespread. Ultra-precision machining mainly includes ultra-precision cutting (car, milling), ultra-precision grinding, ultra-precision grinding and polishing, and ultra-precision special processing (three-beam machining and micro-EDM machining, micro-electrolysis machining and various composite machining). With the development of modern science and technology, new requirements have been put forward for ultra-precision machining technology. The emergence of new materials and new parts, the introduction of higher precision requirements, etc. require ultra-precision machining processes, the development of new ultra-precision machining tools, and the improvement of modern ultra-precision machining technology to adapt to the development of modern technology.
At present, the requirements for high precision machining are as follows: ordinary machining accuracy is doubled to 5 microns; precision machining accuracy is increased by two orders of magnitude, ultra-precision machining accuracy is nanometer (0.001 micron), and spindle rotation accuracy is required to reach 0.01. ~0.05 micron, processing roundness is 0.1 micron, processing surface roughness Ra=0.003 micron and the like.
Precision is to meet the needs of high-tech development, but also to improve the performance, quality and reliability of ordinary mechanical and electrical products, reduce the workload of its assembly and improve the assembly efficiency. With the development of high technology and the improvement of the performance and quality requirements of electromechanical products, machine tool users have higher and higher requirements for machine tool processing accuracy. In order to meet the needs of users, the machining accuracy of general-grade CNC machine tools has been improved from ±10μm to ±5μm in the past 10 years, and the machining accuracy of precision machining centers has increased from ±3~5μm to ±1~1.5μm.
The reliability of the index control system is higher than the reliability of the controlled equipment by more than an order of magnitude, but it is not the higher the reliability, the better, and it is still moderately reliable, because it is a commodity, subject to the performance price ratio. For an unmanned factory that works two shifts a day, if the continuous operation is required within 16 hours, and the failure-free rate P(t)=99% or more, the MTBF of the CNC machine tool must be greater than 3000 hours. . The MTBF is more than 3000 hours. For the unmanned factory consisting of different numbers of CNC machine tools, the difference is mostly. For a CNC machine tool, if the ratio of the failure rate between the main machine and the CNC system is 10:1 (CNC Reliable is an order of magnitude higher than the host). At this time, the MTBF of the numerical control system is greater than 33333.3 hours, and the MTBF of the numerical control device, the main shaft and the drive must be greater than 100,000 hours.
At present, the MTBF value of foreign numerical control devices has reached more than 6,000 hours, and the driving device has reached more than 30,000 hours.
(2) Modular, intelligent, flexible and integrated
● modular, specialized and personalized
The machine tool structure is modular, the numerical control function is specialized, and the machine tool performance price ratio is significantly improved and the optimization is accelerated. In order to adapt to the characteristics of multi-variety and small batch of CNC machine tools, the machine tool structure is modularized, the numerical control function is specialized, and the machine tool performance price ratio is significantly improved and optimized. Personalization is a particularly obvious development trend in recent years.
Intelligent content includes all aspects of the CNC system:
——In order to pursue the intelligentization of processing efficiency and processing quality, such as adaptive control, process parameters are automatically generated;
——Intelligent for improving drive performance and convenient connection, such as feedforward control, adaptive calculation of motor parameters, automatic identification of load automatic selection model, self-tuning, etc.;
——Simplify programming and simplify the operation of intelligent, such as intelligent automatic programming, intelligent human-machine interface, etc.;
——Intelligent diagnosis, intelligent monitoring, and convenient system diagnosis and maintenance.
●Flexibility and integration
The trend of CNC machine tools to flexible automation systems is: from point (CNC stand-alone, machining center and CNC multi-tasking machine), line (FMC, FMS, FTL, FML) to the surface (in the workshop, independent manufacturing island, FA), body ( The development of CIMS and distributed network integrated manufacturing systems, on the other hand, focuses on application and economy. Flexible automation technology is the main means for the manufacturing industry to adapt to dynamic market demand and rapid product renewal. It is the mainstream trend of manufacturing development in various countries and the basic technology in the field of advanced manufacturing. The focus is on improving the reliability and practicality of the system, aiming at easy networking and integration; focusing on strengthening the development and improvement of unit technology; CNC single machine development towards high precision, high speed and high flexibility; The flexible manufacturing system can be easily connected with CAD, CAM, CAPP, MTS, and the direction of information integration; the network system is developing towards openness, integration and intelligence.
In order to meet the requirements of CNC incoming line, networking, popularized individualization, multi-variety, small batch, flexible and rapid development of CNC, the most important development trend is the openness of the architecture, design and production of open CNC systems, such as the United States. , the European Community and Japan's plans to develop open CNC.
(4) A new generation of CNC machining technology and equipment
——In order to adapt to the development of manufacturing automation, the basic equipment is provided to FMC, FMS and CIMS. The digital control manufacturing system is required to not only complete the usual processing functions, but also have automatic measurement, automatic loading and unloading, automatic tool change, and automatic spindle replacement. Robots and logistics systems are widely used in functions such as head (sometimes with coordinate transformation), automatic error compensation, automatic diagnosis, incoming line and networking;
- FMC, FMS Web-based manufacturing and no-drawing manufacturing technology;
——There have been breakthroughs in numerical control technology, manufacturing process technology in rapid prototyping, parallel mechanism machine tools, robotized machine tools, multi-function machine tools and other high-speed electric spindles, linear motors, software compensation accuracy and other unit technologies. The new CNC machine tool with parallel pole structure is practical. This kind of virtual axis CNC machine tool replaces the complexity of traditional machine tool mechanism with the complexity of software, and opens up a new field of CNC machine tool development;
—— Manufacturing information support technology and intelligent decision-making system based on computer-aided management and engineering database, Internet. Massive information storage and real-time processing in machining. The application of digital network technology makes the whole system of mechanical processing tend to be properly resourced and efficiently applied.
——Because of the use of neural network control technology, fuzzy control technology, digital network technology, mechanical processing is developing in the direction of virtual manufacturing.