The rapid advancement of numerical control system technology provides conditions for the technological progress of numerical control 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 current development of world numerical control technology and its equipment is mainly reflected in the following technical characteristics: 1. High speed, machine tools are developing towards high
, Not only can the processing efficiency be greatly improved, the processing cost can be reduced, but also the surface processing quality and precision of parts can be improved. Ultra-high-speed processing technology has wide applicability to high-quality and low-cost production in the manufacturing industry.
Since the 1990s, countries in Europe, the United States and Japan have been scrambling to develop and apply a new generation of high-speed CNC machine tools to accelerate the pace of high-speed development of machine tools. High-speed spindle unit (motorized spindle, speed 15000-100000r/min), high-speed and high acceleration/deceleration feed moving parts (rapid movement speed 60~120m/min, cutting feed rate up to 60m/min), high-performance CNC There have been new breakthroughs in servo systems and CNC tool systems, reaching a new level of technology. With the ultra-high-speed cutting mechanism, super-hard wear-resistant long-life tool materials and abrasive abrasives, high-power high-speed electric spindle, high acceleration/deceleration linear motor-driven feed components, high-performance control system (including monitoring system) and protection devices 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 above 5000~8000m/min; Giving speed): when the resolution is 1 micron, it is above 100m/min (some to 200m/min), when the resolution is 0.1 micron, it is above 24m/min; the automatic tool change speed is within 1 second; small The line segment interpolation feed speed reaches 12m/min.
2. High precision
The development from precision machining to ultra-precision machining is the direction that the world's industrial powers are committed to. Its precision ranges from micron level to submicron level, and even nanometer level (<10nm), and its application range is becoming wider and wider. 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 machining accuracy of precision-level machining centers has been increased from ±3~5μm to ±1~1.5μm, or even Higher; ultra-precision machining accuracy enters the nanometer level (0.001 micron), the spindle rotation accuracy is required to reach 0.01~0.05 micron, the machining roundness is 0.1 micron, and the machining surface roughness Ra=0.003 micron, etc. These machine tools generally use vector-controlled variable frequency drive electric spindles (motor and spindle are integrated), the radial runout of the spindle is less than 2 μm, the axial movement is less than 1 μm, and the unbalance of the shaft system reaches G0.4 level. The feed drive of high-speed and high-precision machining machine tools mainly includes two types: "rotary servo motor plus precision high-speed ball screw" and "linear motor direct drive". In addition, emerging parallel machine tools are also easy to achieve high-speed feed.
Due to the mature technology and wide application of ball screw, not only the precision can reach high (ISO3408 level 1), but also the cost of realizing high speed is relatively low, so it is still used by many high-speed processing machine tools so far. Currently, the maximum moving speed of the high-speed processing machine tool driven by the ball screw is 90m/min, and the acceleration is 1.5g.
The ball screw is a mechanical transmission, and there are inevitably elastic deformation, friction and backlash in the transmission process, correspondingly causing motion lag and other nonlinear errors. Directly driven by a linear motor, because it is a "zero transmission" without an intermediate link, not only the motion inertia is small, the system rigidity is large, and the response is fast, it can reach a high speed and acceleration, and its stroke length is theoretically unlimited. Positioning accuracy Under the action of the high-precision position feedback system, it is easy to reach a higher level, and it is an ideal driving method for high-speed and high-precision machine tools, especially medium and large machine tools. At present, the maximum fast-moving speed of high-speed and high-finishing machine tools using linear motors has reached 208 m/min, and the acceleration is 2g, and there is still room for development.
3. High reliability
With the development of the network 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 an unmanned factory that works two shifts a day, if it is required to work continuously within 16 hours, and the failure-free rate is above P(t)=99%, the average failure-free running time MTBF of the CNC machine tool must be greater than 3000 hours . We only consider one CNC machine tool, for example, the ratio of the failure rate of the main engine to the numerical control system is 10:1 (the reliability of the numerical control is an order of magnitude higher than that of the main engine). At this time, the MTBF of the CNC system must be greater than 33333.3 hours, and the MTBF of the CNC device, spindle and 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 goal.
In the process of parts processing, a lot of useless time is consumed in workpiece handling, loading and unloading, installation adjustment, tool change and spindle speed up and down. In order to reduce these useless times as much as possible, people hope to combine different processing The functions are integrated on the same machine tool, therefore, the machine tool with multiple functions has become a model that has developed rapidly in recent years.
The concept of machine tool compound processing in the field of flexible manufacturing means that after the workpiece is clamped once, the machine tool can automatically perform multi-process processing of the same process method or different process methods according to the CNC machining program, so as to complete the main and even processing of a complex shape part. All turning, milling, drilling, boring, grinding, tapping, reaming and reaming and other processing procedures. As far as prism parts are concerned, the machining center is the most typical machine tool for multi-process compound processing of the same process method. Facts have proved that compound machining of machine tools can improve machining accuracy and machining efficiency, save floor space and especially shorten the machining cycle of parts.
With the popularization of 5-axis linkage CNC systems and programming software, 5-axis linkage control machining centers and CNC milling machines have become a current development hotspot. Because 5-axis linkage control is used for CNC programming of ball-end milling cutters when processing free-form surfaces It is relatively simple, and can keep the ball end milling cutter at a reasonable cutting speed during the milling process of the 3D curved surface, thereby significantly improving the roughness of the machined surface and greatly improving the processing efficiency, while the machine tool with 3-axis linkage control cannot Avoid the cutting of the end of the ball-end milling cutter whose cutting speed is close to zero. Therefore, the 5-axis linkage machine tool has become the focus of active development and competition of major machine tool manufacturers with its irreplaceable performance advantages.
Recently, foreign countries are still studying 6-axis linkage control using non-rotating tool machining centers. Although the machining shape is not limited and the cutting depth can be very thin, the machining efficiency is too low and it is difficult to be practical.
Intelligentization is a general direction for the development of manufacturing technology in the 21st century. Intelligent processing is a 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 processing process to solve many uncertainties in the processing process. It can only be achieved by manual intervention. solved problem. The content of intelligence includes all aspects of the CNC system: in order to pursue the intelligence of processing efficiency and processing quality, such as adaptive control, automatic generation of process parameters; in order to improve the driving performance and use the intelligence of easy connection, such as feedforward control , Adaptive calculation of motor parameters, automatic identification of load, automatic selection of models, self-tuning, etc.; intelligentization of simplified programming and simplified operation, such as intelligent automatic programming, intelligent man-machine interface, etc.; intelligent diagnosis, intelligent monitoring, Facilitate system diagnosis and maintenance. There are many intelligent cutting processing systems being researched in the world, among which the intelligent processing scheme for drilling by the Japan Intelligent CNC Device Research Association is representative.
The networking of CNC machine tools mainly refers to the network connection and network control of the machine tool through the equipped CNC system and other external control systems or host computers. CNC machine tools generally first face the production site and the internal LAN of the enterprise, and then lead to the outside of the enterprise via the Internet. This is the so-called Internet/Intranet technology.
With the maturity and development of network technology, the industry has recently put forward the concept of digital manufacturing. Digital manufacturing, also known as "e-manufacturing", is one of the symbols of the modernization of machinery manufacturing enterprises, and it is also the supply method of the current standard configuration of international advanced machine tool manufacturers. With the extensive use of information technology, more and more domestic users require functions such as remote communication services when importing CNC machine tools. On the basis of the widespread adoption of CAD/CAM, machinery manufacturing enterprises are more and more widely using CNC processing equipment. Numerical control application software is increasingly rich and "humanized". High-end technologies such as virtual design and virtual manufacturing are increasingly pursued by engineers and technicians. Replacing complex hardware with software intelligence is becoming an important trend in the development of contemporary machine tools. Under the goal of digital manufacturing, through process reengineering and information transformation, a batch of advanced enterprise management software such as ERP has come to the fore, creating higher economic benefits for enterprises. 8. The development trend of flexible CNC machine tools to flexible automation systems is: from point (NC stand-alone machine, machining center and CNC composite processing machine tool), line (FMC, FMS, FTL, FML) to surface (independent manufacturing island of workshop,
), body (CIMS, distributed network integrated manufacturing system), and on the other hand, develop in the direction of 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 in the development of manufacturing industries in various countries and the basic technology in the field of advanced manufacturing. Its focus is on the premise of improving the reliability and practicality of the system, with the goal of easy networking and integration; focusing on strengthening the development and improvement of unit technology; CNC stand-alone machines are developing towards high precision, high speed and high flexibility; CNC machine tools and their The flexible manufacturing system can be easily connected with CAD, CAM, CAPP, MTS, and develops towards information integration; the network system develops towards openness, integration and intelligence.
Metal cutting machine tools in the 21st century must put environmental protection and energy saving in an important position, that is, to realize the green cutting process. At present, this green processing technology mainly focuses on not using cutting fluid, which is mainly because cutting fluid not only pollutes the environment and endangers the health of workers, but also 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 (in nitrogen, in cold wind, or using dry electrostatic cooling technology) without using cutting fluid. However, for certain processing methods and workpiece combinations, dry cutting without cutting fluid is still difficult to apply in practice, so quasi-dry cutting using minimal quantity lubrication (MQL) has appeared. At present, in the mass machining in Europe, 10-15% of the machining has used dry and quasi-dry cutting. For machine tools such as machining centers that face a variety of processing methods/workpiece combinations, quasi-dry cutting is mainly used, usually by allowing a very small amount of cutting oil and compressed air to be sprayed through the hollow passages in the machine tool spindle and tool. cutting zone. Among all kinds of metal cutting machine tools, gear hobbing machines are the most used in dry cutting.
In short, the progress and development of CNC machine tool technology provides good conditions for the development of modern manufacturing industry, and promotes the development of manufacturing industry in the direction of high quality and humanization. It can be predicted 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 shake the traditional manufacturing model.