The rapid development of CNC technology has provided conditions for the technological progress of CNC machine tools. In order to meet the needs of the market, to meet the higher requirements of modern manufacturing technology to numerical control technology, the development of the world numerical control technology and its equipment are mainly embodied in the following aspects:
1. High speed and high efficiency
The development of machine tools in the direction of high speed can not only greatly improve the processing efficiency and reduce the processing cost, but also improve the surface machining quality and accuracy of parts. Ultra high speed machining technology has wide applicability for manufacturing to achieve high efficiency, high quality and low cost production.
Since 1990s, Europe, the United States and Japan have been competing for the development of a new generation of high-speed CNC machine tools to speed up the development of high-speed machine tools. High speed spindle unit (spindle, speed 15000 - 100000r/min), high speed and high / low speed feed moving parts (fast moving speed 60~120m/min, cutting feed speed up to 60m/min), high performance CNC and servo system and CNC tool system all have new breakthroughs, reaching new technical level. With the mechanism of ultra high speed cutting, super hard wear-resisting and long life tool materials and abrasive tools, high power high-speed electric spindle, high addition / speed linear motor drive feed parts, high performance control system (including monitoring system) and protection device, a series of key techniques are solved in a series of technical fields, for the development and application of a new generation of high speed numbers. Control machine tools provide a technical basis.
At present, in ultra high speed machining, the cutting speed of turning and milling has reached more than 5000~8000m/min; the spindle number is more than 30000 RPM (up to 100 thousand r/min); the moving speed (feed speed) of the worktable: at the resolution of 1 microns, above the 100m/min (some to 200m/min) and at the resolution of 0.1 microns, in 24m /min above; automatic tool changing speed within one second; small line interpolation speed of 12m/min.
Two. High precision
From precision machining to ultra precision machining, it is the direction that all industrial powers in the world are committed to. Its accuracy ranges from micron to sub micron, and even nanometer (<10nm), and its application scope is more and more extensive. At present, under the requirement of high precision machining, the machining precision of the ordinary numerical control machine has been increased from 10 to 5 m to + 5 mu, and the precision of the precision machining center is increased from + 3~5 mu m to + 1~1.5 mu m, even higher; the precision of ultra precision machining enters nanoscale (0.001 microns), and the spindle rotary precision needs to be 0.01~0.05 micro M, processing roundness is 0.1 microns, machined surface roughness Ra=0.003 micron and so on. These machines generally use VVVF driven spindle (motor and spindle integration), the radial runout of the spindle is less than 2 mu m, the axial movement is less than 1 mu m, and the axis imbalance reaches G0.4 level. The feed drive of high speed and high precision machine tool mainly includes two types: rotary servo motor, precision high-speed ball screw and direct drive of linear motor. In addition, the new parallel machine tool is also easy to achieve high speed feed.
Ball screw is widely used because of its mature technology and high precision (ISO3408 1), and the cost of realizing high speed is relatively low. So far, it is still used by many high speed machine tools. At present, the maximum speed of the high speed machine tool driven by ball screws is 90m/min, and the acceleration is 1.5g.
The ball screw is a mechanical transmission, which inevitably exists elastic deformation, friction and reverse clearance in the transmission process, which causes the motion lag and other nonlinear errors. In order to eliminate the effect of these errors on the machining accuracy, the direct drive of linear motor is applied to the machine tool in 1993, because there is no intermediate link. "Zero transmission", not only has small motion inertia, large system stiffness, fast response, and can achieve very high speed and acceleration, but its travel length is not limited in theory. The positioning precision is also easy to reach high level under the action of high precision position feedback system. It is a high speed and high precision machine tool, especially medium and large machine tool. Ideal driving mode. At present, the maximum speed of high speed and high precision machine tool using linear motor has reached 208 m/min, the acceleration is 2G, and there is room for development.
Three. High reliability
With the development of networked application of CNC machine tools, the high reliability of CNC machine tools has become the goal of CNC system manufacturers and CNC machine manufacturers. For unmanned factories working two shifts per day, if the failure rate is more than P (T) = 99% or more in 16 hours, the average fault free time of the NC machine tool must be more than 3000 hours, MTBF. We only treat a CNC machine tool, for example, the ratio of failure rate of the host computer to the CNC system is 10:1 (the reliability of CNC is one order of magnitude higher than that of the host computer). At this point, the MTBF of the numerical control system will be larger than 33333.3 hours, and the MTBF of the numerical control device, spindle and drive must be more than 100 thousand hours.
At present, the MTBF value of the foreign numerical control device has reached more than 6000 hours, and the driving device has been more than 30000 hours. However, we can see that there is still a gap between the target and the ideal target.
In the process of parts processing, there is a lot of useless time consumed in the work, the up and down material, the installation and adjustment, the lifting and reducing of the spindle. In order to reduce the useless time as much as possible, people hope to integrate the different processing functions on the same machine tool. Therefore, the machine tool of complex function has developed very well in recent years. Fast machine.
The concept of machine tool compound machining in the flexible manufacturing category refers to the multi process processing of the machine tool, which is automatically carried out by the same kind of process methods or different kinds of process methods according to the NC machining program, to complete the main or even all the car, milling, boring, boring, tapping, hinges and hinges of a complex shape part. Reaming and other processing procedures. In terms of prismatic parts, the machining center is the most typical machine tool for multi process compound machining of the same process. Facts have proved that machine tool compound machining can improve machining accuracy and processing efficiency, save floor space, especially shorten the processing cycle of parts.
Five, multi axis
With the popularization of 5 axis CNC system and programming software, the machining center and CNC milling machine with 5 axis linkage control have become a hot spot of development at present. Because of the machining free surface, the NC programming of the ball head milling cutter is relatively simple with the 5 axis linkage control, and it can make the ball end milling cutter always in the process of milling 3 dimensional surface. With a reasonable cutting speed, the roughness of the machined surface is improved and the machining efficiency is greatly improved. The 3 axis machine tool can not avoid cutting the end of the ball end cutter with the cutting speed close to zero. Therefore, the 5 axis machine tool has been actively developed by the large machine tool manufacturers with its irreplaceable performance advantages. The focus of competition.
Recently, foreign countries are still studying the processing center using non rotating cutting tools with 6 axis linkage control. Although the machining shape is not restricted and the cutting depth can be thin, it is difficult to use the machining efficiency too low.
Intellectualization is a major direction in the development of manufacturing technology in the twenty-first 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 process of processing in order to solve many uncertainties in the processing process and to solve the problem by manual intervention. The intelligentized content includes all aspects of the CNC system: for the pursuit of processing efficiency and the intelligentization of processing quality, such as adaptive control, automatic process parameters generation, to improve the driving performance and the use of easy to connect intelligent, such as feedforward control, motor parameters self-adaptive operation, automatic identification of automatic identification load selection. Model, self-tuning, simplifying the programming, simplifying the operation of intelligent, such as intelligent automatic programming, intelligent human-machine interface, intelligent diagnosis, intelligent monitoring, convenient system diagnosis and maintenance. Many intelligent cutting systems are being studied in the world, and the research of Japanese intelligent numerical control device will be representative for the intelligent machining program of drilling.
The network of CNC machine tools mainly refers to the network connection and network control between the machine tools and the other control systems or the upper computer. CNC machine tools are generally first oriented to the production site and the internal LAN in the enterprise, and then through the Internet to the outside of the enterprise, this is the so-called Internet/Intranet technology.
With the maturity and development of network technology, the concept of digital manufacturing has been put forward recently. Digital manufacturing, also known as "e- manufacturing", is one of the symbols of the modernization of the machinery manufacturing enterprises. It is also the supply mode of the standard configuration of the international advanced machine tool manufacturers. With the adoption of information technology, more and more domestic users are required to have remote communication services when importing CNC machine tools. Machinery manufacturing enterprises widely use CNC machining equipment on the basis of CAD/CAM. NC application software is increasingly rich and "humanized". The high-end technologies such as virtual design and virtual manufacturing are increasingly being pursued by engineering and technical personnel. Replacing intelligent hardware with software intelligence is becoming an important trend in the development of modern machine tools. Under the target 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 the enterprise.
The trend of the development of CNC machine tools to flexible automation system is: from the point (NC single machine, machining center and CNC machine tool), line (FMC, FMS, FTL, FML) direction (independent manufacturing of island, FA), body (CIMS, distributed network integrated manufacturing system) in the workshop, and on the other hand to the application and economy. To develop. Flexible automation technology is the main means of manufacturing industry to adapt to dynamic market demand and the rapid renewal of products. It is the mainstream trend of the development of manufacturing industry in various countries, and it is the basic technology in the advanced manufacturing field. The key point is to improve the reliability and practicability of the system as the premise, to be easy to connect and integrate, and to strengthen the development and perfection of the unit technology; the CNC single machine develops to the high precision, high speed and high flexible direction, and the CNC machine tool and its flexible manufacturing system can be connected with CAD, CAM, CAPP and MTS conveniently. Interest integration is developing; network system is developing towards openness, integration and intellectualization.
In twenty-first Century, the gold cutting machine tool must put environmental protection and energy saving in an important position, that is, to realize the greening of the cutting process. At present, the green processing technology is mainly concentrated on the non use of cutting fluid, which is mainly because the cutting fluid not only pollutes the environment and endangering the health of the workers, but also increases the consumption of resources and energy. Dry cutting is usually carried out in the atmosphere, but it also includes cutting in a special gas atmosphere (nitrogen, cold air or dry electrostatic cooling) without the use of a cutting fluid. However, for the combination of some processing methods and workpieces, dry cutting without using the cutting fluid is difficult and practical, so a quasi dry cutting with very micro lubrication (MQL) has appeared. At present, 10~15% has been used for dry and quasi dry cutting in large scale machining in Europe. For machine tools such as machining centers for a variety of machining methods / workpieces, quasi dry cutting is mainly used, usually the mixture of very micro cutting oil and compressed air is sprayed to the cutting area via the hollow channel of the machine tool spindle and the tool. In all kinds of gold cutting machine tools, the most important part of dry cutting is hobbing machine.
In a word, the progress and development of CNC machine tool technology provide good conditions for the development of modern manufacturing industry, and promote the development of manufacturing industry in the direction of high efficiency, high quality and humanization. It is foreseeable 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 mode.