[align=center]Current Status of CNC Machine Tool Technology Development Yang Honghua (Sino-German College, Tongji University, Shanghai 20000)[/align] Abstract: This paper briefly analyzes the development trends and current status of CNC machine tools, including high speed, high precision, high reliability, composite technology, intelligentization, networking, and greening. Keywords: CNC machine tool development trend, current status CLC number: TH132.41 Document code: A Article number: 1007-8320 (2008) 05-0188-02 Present Status of Computer Numerical Control Machine Yang Honghua Abstract: Computer numerical control has been increasingly widely used in most areas of manufacturing since its inception. The development tendencies of CNC, such as high speed, high accuracy, compound, intelligence, and so on, are analyzed, and the current status of CNC in our country is also pointed out. Key words: computer numerical control, development tendency, present status CNC machine tools have attracted worldwide attention with their excellent flexible automation performance, superior and stable precision, and agile and diversified functions. They have pioneered the development of mechanical products towards mechatronics and become a core technology in advanced manufacturing technology. The rapid advancement of CNC system technology has provided conditions for the technological progress of CNC machine tools. Currently, the development of CNC machine tools is mainly reflected in the following aspects: 1. High-speed and high-efficiency machine tools are developing towards higher speeds, which can not only significantly improve processing efficiency and reduce processing costs, but also improve the surface finish and precision of parts. Ultra-high-speed machining technology has wide applicability to achieving efficient, high-quality, and low-cost production in the manufacturing industry. Since the 1990s, European, American, and Japanese countries have been vying to develop and apply a new generation of high-speed CNC machine tools, accelerating the pace of high-speed machine tool development. High-speed spindle units (electric spindles, speeds of 15,000-100,000 r/min), high-speed and high acceleration/deceleration feed motion components (rapid traverse speeds of 60-120 m/min, cutting feed rates up to 60 m/min), high-performance CNC and servo systems, and CNC tool systems have all made new breakthroughs, reaching new technical levels. With the resolution of key technologies in a series of technical fields, such as ultra-high-speed cutting mechanisms, ultra-hard, wear-resistant, and long-life tool materials and abrasives, high-power high-speed electric spindles, high-acceleration/deceleration linear motor-driven feed components, and high-performance control systems (including monitoring systems) and protective devices, a technological foundation has been laid for the development and application of a new generation of high-speed CNC machine tools. Currently, in ultra-high-speed machining, turning and milling cutting speeds have reached over 5000–8000 m/min; spindle speeds are over 30,000 rpm (some reaching 100,000 rpm); table movement speeds (feed speeds) are over 100 m/min (some reaching 200 m/min) at a resolution of 1 micrometer, and over 24 m/min at a resolution of 0.1 m; automatic tool change speeds are within 1 second; and small-segment interpolation feed speeds reach 12 m/min. 2. High precision: The development from precision machining to ultra-precision machining is a direction that major industrial powers worldwide are striving to pursue. Its precision ranges from micrometers to submicrometers, and even nanometers (<10nm), and its application range is becoming increasingly wide. Currently, under the requirement of high precision in machining, the machining accuracy of ordinary CNC machine tools has improved from ±10 m to ±5 m; the machining accuracy of precision machining centers has improved from ±3~5 m to ±1~1.5 m, or even higher; ultra-precision machining accuracy has entered the nanometer level (0.001 m), with spindle rotation accuracy required to reach 0.01~0.05 m, machining roundness of 0.1 m, and machining surface roughness Ra=0.003 micrometers, etc. These machine tools generally adopt vector-controlled variable frequency drive electric spindles (motor and spindle integrated), with spindle radial runout less than 2 m, axial runout less than 1 m, and shaft imbalance reaching G0.4 level. The feed drive of high-speed and high-precision machining tools mainly includes two types: "rotary servo motor plus precision high-speed ball screw" and "linear motor direct drive". Furthermore, emerging parallel machine tools also easily achieve high-speed feed. Due to its mature technology and wide application, ball screws not only achieve high precision (ISO 34081 grade) but also have relatively low costs for high-speed implementation, thus remaining the preferred choice for many high-speed machining tools. Currently, the maximum traverse speed of high-speed machining tools driven by ball screws is 90 m/min, with an acceleration of 1.5g. Ball screws are mechanical transmissions, and elastic deformation, friction, and backlash are unavoidable during transmission, resulting in motion lag and other nonlinear errors. To eliminate the impact of these errors on machining accuracy, direct linear motor drive was first applied to machine tools in 1993. Because it is a "zero-transmission" system without intermediate links, it not only has low inertia, high system rigidity, and fast response, but also achieves very high speeds and accelerations. Theoretically, its stroke length is unlimited, and positioning accuracy can easily reach a high level with the help of a high-precision position feedback system. It is an ideal drive method for high-speed, high-precision machining tools, especially medium and large-sized machine tools. Currently, the maximum rapid traverse speed of high-speed, high-precision machine tools using linear motors has reached 208 m/min, with an acceleration of 2g, and there is still room for development. 3. High Reliability: With the development of networked applications for CNC machine tools, high reliability has become a goal pursued by both CNC system manufacturers and CNC machine tool manufacturers. For an unmanned factory operating in two shifts per day, if continuous normal operation is required for 16 hours with a failure-free rate of P(t) = 99% or higher, then the mean time between failures (MTBF) of the CNC machine tool must be greater than 3000 hours. Considering only a single CNC machine tool, if the failure rate ratio between the main machine and the CNC system is 10:1 (the reliability of the CNC is an order of magnitude higher than that of the main machine), then the MTBF of the CNC system must be greater than 33333.3 hours, and the MTBF of the CNC device, spindle, and drive, etc., must be greater than 100,000 hours. Currently, the MTBF (Mean Time Between Failures) of foreign CNC devices has reached over 6000 hours, and that of drive devices has reached over 30000 hours. However, it is clear that there is still a gap from the ideal target. 4. In the machining process, a significant amount of time is wasted on workpiece handling, loading and unloading, installation and adjustment, tool changing, and spindle speed adjustment. To minimize this wasted time, the goal is to integrate different machining functions onto a single machine tool. Therefore, multi-functional machine tools have become a rapidly developing type of machine in recent years. The concept of multi-functional machining in the flexible manufacturing field refers to a machine tool that, after a workpiece is clamped once, can automatically perform multiple machining operations using the same or different CNC machining methods according to the CNC machining program. This allows for the completion of major or even all machining operations such as turning, milling, drilling, boring, grinding, tapping, reaming, and hole enlargement for a complex-shaped part. For prismatic parts, machining centers are the most typical example of machine tools performing multi-operation multi-process machining using the same method. It has been proven that multi-functional machining can improve machining accuracy and efficiency, save floor space, and especially shorten the machining cycle of parts. 5. Multi-axis control: With the widespread adoption of 5-axis CNC systems and programming software, 5-axis CNC machining centers and CNC milling machines have become a hot development area. When machining free-form surfaces, 5-axis CNC programming for ball end mills is relatively simple, and it allows the ball end mill to maintain a reasonable cutting speed throughout the milling of 3D surfaces, significantly improving surface roughness and machining efficiency. In contrast, 3-axis CNC machines cannot avoid the ball end mill tip, with its near-zero cutting speed, participating in the cutting. Therefore, 5-axis CNC machine tools, with their irreplaceable performance advantages, have become a focus of development and competition among major machine tool manufacturers. Recently, foreign research has also focused on 6-axis CNC machining centers using non-rotary tools. Although they offer unrestricted machining shapes and very thin cutting depths, their low machining efficiency makes practical application difficult in the short term. 6. Intelligentization: Intelligentization is a major direction for manufacturing technology development in the 21st century. Intelligent machining is a type of machining based on neural network control, fuzzy control, and digital network technology and theory. It aims to simulate the intelligent activities of human experts during the machining process to solve many uncertainties that previously required manual intervention. The intelligent aspects include various aspects of the CNC system: intelligentization for pursuing machining efficiency and quality, such as adaptive control and automatic generation of process parameters; intelligentization for improving drive performance and ease of use and connection, such as feedforward control, adaptive calculation of motor parameters, automatic load identification and model selection, and self-tuning; intelligentization for simplifying programming and operation, such as intelligent automatic programming and intelligent human-machine interfaces; and intelligent diagnosis and monitoring for convenient system diagnosis and maintenance. Many intelligent cutting systems are currently under research worldwide, among which the intelligent machining solution for drilling developed by the Japan Intelligent CNC Device Research Association is representative. 7. Networked CNC machine tools: Networking mainly refers to the machine tool's connection and control with other external control systems or host computers through its equipped CNC system. CNC machine tools typically first connect to the production site and the company's internal local area network (LAN), and then connect to the outside world via the Internet—this is the so-called Internet/Intranet technology. With the maturity and development of network technology, the concept of digital manufacturing has recently been proposed in the industry. Digital manufacturing, also known as "e-manufacturing," is one of the hallmarks of modernization in machinery manufacturing enterprises and is currently the standard supply method for advanced international machine tool manufacturers. With the widespread adoption of information technology, more and more domestic users are demanding remote communication services and other functions from imported CNC machine tools. Machinery manufacturing enterprises are increasingly using CNC machining equipment, building upon the widespread adoption of CAD/CAM. CNC application software is becoming increasingly rich and "human-centered." High-end technologies such as virtual design and virtual manufacturing are also increasingly sought after by engineering and technical personnel. Replacing complex hardware with intelligent software is becoming an important trend in the development of modern machine tools. Under the goal of digital manufacturing, through process reengineering and information technology transformation, a number of advanced enterprise management software programs, such as ERP, have emerged, creating higher economic benefits for enterprises. 8. The trend of flexible CNC machine tools developing towards flexible automation systems is: from points (CNC single machines, machining centers, and CNC composite machining tools) and lines (FMC, FMS, FTL, FML) to surfaces (independent manufacturing islands in workshops, FA) and volumes (CIMS, distributed network integrated manufacturing systems), and on the other hand, towards emphasizing applicability and economy. Flexible automation technology is the main means for the manufacturing industry to adapt to dynamic market demands and rapid product updates. It is the mainstream trend of manufacturing development in various countries and a fundamental technology in the field of advanced manufacturing. Its focus is on improving the reliability and practicality of the system, with the goal of easy networking and integration; emphasizing the development and improvement of unit technologies; CNC single machines are developing towards high precision, high speed, and high flexibility; CNC machine tools and their constituent flexible manufacturing systems can be easily connected with CAD, CAM, CAPP, and MTS, developing towards information integration; network systems are developing towards openness, integration, and intelligence. 9. Greening: Metal cutting machine tools in the 21st century must place environmental protection and energy conservation in an important position, that is, to achieve greening of cutting processes. Currently, this green machining technology mainly focuses on eliminating the use of cutting fluid, primarily because cutting fluid pollutes the environment, harms worker health, and increases resource and energy consumption. Dry cutting is generally performed in an atmospheric environment, but it also includes cutting without cutting fluid in special gas atmospheres (nitrogen, cold air, or dry electrostatic cooling technology). However, for certain machining methods and workpiece combinations, completely fluid-free dry cutting is still difficult to apply in practice, hence the emergence of near-dry cutting using very small amount lubrication (MQL). Currently, in mass production in Europe, 10-15% of machining uses dry and near-dry cutting. For machine tools such as machining centers that handle multiple machining methods/workpiece combinations, near-dry cutting is mainly used, typically by spraying a very small amount of cutting oil mixed with compressed air through hollow channels within the machine tool spindle and tool into the cutting area. Among various metal cutting machine tools, gear hobbing machines use dry cutting the most. In conclusion, the advancement and development of CNC machine tool technology has provided favorable conditions for the development of modern manufacturing, prompting the manufacturing industry to develop towards high efficiency, high quality, and humanization. It is foreseeable that with the development of CNC machine tool technology and the widespread application of CNC machine tools, the manufacturing industry will usher in a profound revolution that will shake the traditional manufacturing model. References: [1] Lü Hongxia. The development trend and path of CNC technology [J]. Mechanical Manufacturing and Automation. 2005 [2] Yi Hong (ed.). CNC Technology [M]. Beijing: Machinery Industry Press. 2005 Related articles: "Analysis of the market development trend of China's machine tool industry through global analysis"