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The rapid advancement of CNC system technology has provided conditions for the technological advancement of CNC machine tools. In order to meet the needs of the market and meet the higher requirements of modern manufacturing technology for numerical control technology, the development of the world's numerical control technology and its equipment is mainly reflected in the following technical features:
First, high speed and high efficiency
The development of machine tools in the direction of high speed can not only 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.
Since the 1990s, countries in Europe, the United States, and Japan have rushed 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 The solution of key technologies in a series of technical fields provides a technical basis for the development and application of a new generation of high-speed CNC machine tools.
At present, in ultra-high-speed machining, the cutting speed of turning and milling has reached 5000~8000m/min; the number of spindle revolutions is above 30,000 rpm (some up to 100,000 r/min); the moving speed of the table (in Speed): at a resolution of 1 micron, above 100m/min (some to 200m/min), at a resolution of 0.1 microns, above 24m/min; automatic tool change speed within 1 second; small The line interpolation feed rate reaches 12m/min.
Second, high precision
From precision machining to ultra-precision machining, it is the direction of the world's industrial powers. Its accuracy ranges from micron to sub-micron, and even nano-scale (<10nm), and its application range is becoming more widespread. At present, under the requirements of high precision machining, the machining accuracy of ordinary CNC machine tools has been increased from ±10μm to ±5μm; the precision of precision machining centers is from ±3~5μm, Increase to ± 1~1.5μm, or even higher; ultra-precision machining accuracy into nanoscale (0.001 micron), spindle rotation accuracy of 0.01 to 0.05 micron, processing roundness of 0.1 micron, processing surface roughness Ra = 0.003 micron and so on. These machine tools generally use vector-controlled variable frequency drive electric spindle (motor and spindle integration), the spindle radial runout is less than 2 & mu; m, axial turbulence is less than 1 & mu; m, shaft unbalance degree reaches G0.4. The feed drive of high-speed and high-precision machine tools mainly includes “slewing servo motor plus precision high-speed ball screw” and “straight-line motor direct drive”. In addition, the emerging parallel machine tools are also easy to achieve high-speed feed.
Due to its mature technology and wide application, the ball screw not only has high precision (ISO3408 Class 1), but also has a relatively low cost for high-speed machining. So it has been used in many high-speed machining machines. At present, the high-speed machining machine using ball screw drive has a maximum moving speed of 90m/min and an acceleration of 1.5g.
The ball screw is a mechanical transmission. In the transmission process, there are inevitably elastic deformation, friction and backlash, which in turn cause motion lag and other nonlinear errors. In order to eliminate the influence of these errors on the machining accuracy, it started on the machine tool in 1993. Direct drive with linear motor, because there is no intermediate link "zero transmission", not only the small moment of inertia, the system stiffness, fast response, can achieve high speed and acceleration, and its stroke length is theoretically unlimited, The positioning accuracy is also easy to reach a high level under the action of the high-precision position feedback system. It is an ideal driving method for high-speed and high-precision machine tools, especially for medium and large machine tools. At present, the high-speed and high-precision machine tools using linear motors have a maximum rapid traverse speed of 208 m/min and an acceleration of 2 g, and there is still room for development.
Third, high reliability
With the development of networked application of CNC machine tools, the high reliability of CNC machine tools has become the goal pursued by CNC system manufacturers and CNC machine tool manufacturers. For unmanned factories that work two shifts a day, if the continuous operation is required within 16 hours, and the failure-free rate is above P(t)=99%, the MTBF of the CNC machine tool must be greater than 3000 hours. . For a CNC machine, we only have a 10:1 failure rate ratio between the main unit and the CNC system (the reliability of the CNC is an order of magnitude higher than the main unit). 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. However, it can be seen that there is still a gap from the ideal target.
There is a lot of useless time in the part processing process. In the workpiece handling, loading and unloading, installation adjustment, tool change and spindle up and down speed, in order to reduce these useless time as much as possible, people hope to integrate different processing functions in the same On the machine tool, therefore, the composite function machine tool has become a very fast-developing model in recent years.
The concept of machine tool composite machining in the flexible manufacturing category means that after the workpiece is clamped once, the machine tool can automatically perform the same type of process or multi-process processing of different types of processes according to the NC machining program to complete the main part of a complex shape part. All kinds of machining processes such as turning, milling, drilling, boring, grinding, tapping, reaming and reaming. In the case of prismatic parts, the machining center is the most typical machine tool that performs the same type of process and multi-process composite machining. It turns out that machine tool composite machining can improve machining accuracy and machining efficiency, saving floor space, especially shortening the machining cycle of parts.
With the popularization of 5-axis linkage CNC system and programming software, the 5-axis linkage control machining center and CNC milling machine have become a hot development point. Because of the 5-axis linkage control, NC programming of ball-end milling cutter when machining free-form surfaces It is relatively simple, and can make the ball end mill maintain a reasonable cutting speed in the process of milling 3D curved surface, which can significantly improve the roughness of the machined surface and greatly improve the machining efficiency, but the machine can not be controlled in 3-axis linkage control. Avoiding the end of the ball end mill with a cutting speed close to zero, the 5-axis linkage machine has become the focus of active development and competition among major machine tool manufacturers with its irreplaceable performance advantages.
Recently, foreign countries are still studying the machining center using non-rotating tools for 6-axis linkage control. Although the machining shape is not limited and the depth of cut can be very thin, the machining efficiency is too low and the fashion is difficult to put into practical use.
Intelligentization is a major direction in the development of manufacturing technology in the 21st century. Intelligent processing is a kind of processing based on neural network control, fuzzy control, digital network technology and theory. It is to simulate the intelligent activities of human experts in the process of processing to solve many uncertainties in the process, and to be manually interfered. solved problem. The intelligent content includes all aspects in the CNC system: for the pursuit of processing efficiency and processing quality intelligent, such as adaptive control, automatic generation of process parameters; intelligent to improve drive performance and easy to use connections, such as feedforward control , adaptive calculation of motor parameters, automatic identification of load automatic selection model, self-tuning, etc.; simplify programming, simplify the operation of intelligent, such as intelligent automatic programming, intelligent human-machine interface, etc.; intelligent diagnosis, intelligent monitoring, Convenient system diagnosis and maintenance. There are many intelligent cutting systems in the world that are being researched in the world. Among them, the Japanese intelligent numerical control device research representative is representative of the intelligent processing scheme for drilling.
The network of CNC machine tools mainly refers to the network connection and network control of the machine tool through the installed CNC system and other external control systems or host computers. CNC machine tools are generally oriented to the production site and the internal LAN of the enterprise, and then to the outside of the enterprise via the Internet. This is called Internet/Intranet technology.
With the maturity and development of network technology, the industry has recently proposed the concept of digital manufacturing. Digital manufacturing, also known as “e-manufacturing”, is one of the hallmarks of the modernization of machinery manufacturing companies and is the standard delivery method of today's advanced machine tool manufacturers. With the large-scale adoption of information technology, more and more domestic users are required to have remote communication services and other functions when importing CNC machine tools. Mechanical manufacturing companies are increasingly using CNC machining equipment on the basis of CAD/CAM. CNC application software is becoming more and more abundant and has “humanized”. High-end technologies such as virtual design and virtual manufacturing are increasingly being pursued by engineers and technicians. Replacing complex hardware with software intelligence is becoming an important trend in the development of modern machine tools. Under the goal of digital manufacturing, through process reengineering and information transformation, a number of advanced enterprise management software such as ERP have emerged to create higher economic benefits for enterprises.
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 (segment shop independently 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 the 21st century, the gold cutting machine tool must put environmental protection and energy saving at an important position, that is, to realize the greening of the cutting process. At present, this green processing technology is mainly focused on not using cutting fluid, which is mainly because the cutting fluid pollutes the environment and endangers the health of workers, and increases the consumption of resources and energy. Dry cutting is generally carried out in an atmospheric atmosphere, but it also includes cutting in a special gas atmosphere (nitrogen, cold air or dry electrostatic cooling) without cutting fluid. However, for some machining methods and workpiece combinations, dry cutting without cutting fluid at present is still difficult and practical, so there is a quasi-dry cutting using very small amount of lubrication (MQL). At present, 10 to 15% of the large-scale machining in Europe uses dry and quasi-dry cutting. For machine tools such as machining centers with multiple machining methods/workpiece combinations, quasi-dry cutting is mainly used, usually a mixture of a very small amount of cutting oil and compressed air is sprayed through the hollow shaft of the machine tool spindle and the tool. Cutting area. Among the various types of gold cutting machines, the most frequently used dry cutting is the hobbing machine.
In short, the advancement and development of CNC machine tool technology has provided good conditions for the development of modern manufacturing industry, and promoted the development of manufacturing in the direction of high efficiency, high quality and humanization. It can be foreseen that with the development of CNC machine tool technology and the wide application of CNC machine tools, the manufacturing industry will usher in a profound revolution that can incite the traditional manufacturing model.
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