At present, the development of CNC machine tools is changing rapidly, high-speed, high-precision, composite, intelligent, open, parallel drive, network, extreme, green has become the trend and direction of the development of CNC machine tools. China, as a manufacturing country, is still mainly relying on the comparative advantages of labour, price, resources, etc., while the gap between the technological innovation and independent development of products and foreign counterparts is still very large.
China’s CNC industry can not rest on its laurels, should seize the opportunity to continue to develop, and strive to develop their own advanced technology, increase technological innovation and training of personnel, improve the comprehensive service capacity of enterprises, and strive to shorten the gap between the developed countries. Strive to achieve the early realization of CNC machine tools from low-end to high-end products, from the processing of primary products to high-precision product manufacturing transformation, to achieve from Made in China to China to create, from the manufacturing power to the transformation of manufacturing power.
1.Speed Up
With the high-speed development of automotive, defence, aviation, aerospace and other industries and the application of new materials such as aluminium alloys, the high speed of CNC machine tool machining is increasingly demanding.
(1) Spindle speed: The machine adopts an electric spindle (built-in spindle motor) with a maximum spindle speed of 200,000r/min;
(2) Feed rate: When the resolution is 0.01μm, the maximum feed rate reaches 240m/min and accurate machining of complex surfaces can be obtained;
(3) Computing speed: the rapid development of microprocessors for the CNC system to high-speed, high-precision direction provides a guarantee, the development of the CPU has been developed to 32-bit and 64-bit CNC system, the frequency increased to hundreds of megahertz, thousands of megahertz. Due to the great improvement in computing speed, so that when the resolution of 0.1μm, 0.01μm can still get up to 24 ~ 240m/min feed speed;
(4) Tool change speed: at present, the tool exchange time of advanced foreign machining centers is generally about 1s, and the high has reached 0.5s. German Chiron company will design the tool magazine into a basket style, with the spindle as the axis, the tool is arranged in the circumference of the knife, its knife to knife tool change time is only 0.9s.
2.High Precision
CNC machine tool accuracy requirements are now not limited to static geometric accuracy, machine tool motion accuracy, thermal deformation, as well as vibration monitoring and compensation is gaining more and more attention.
(1) Improve the control precision of CNC system: adopt high-speed interpolation technology to realize continuous feeding with tiny program segments, so as to refine the CNC control unit, and adopt high-resolution position detecting device to improve the position detecting precision (Japan has developed AC servo motors equipped with 106 pulses/revolution with built-in position detectors, whose position detecting precision can reach 0.01 μm/pulse), and the position servo system The position servo system adopts feed-forward control and nonlinear control and other methods;
(2) Adoption of error compensation technology: Adoption of reverse clearance compensation, screw pitch error compensation and tooling error compensation and other technologies to comprehensively compensate for the thermal deformation error and spatial error of the equipment. The research results show that the application of comprehensive error compensation technology can reduce the machining error by 60% to 80%;
(3) Grids are used to check and improve the accuracy of the motion trajectory of the machining centre and to predict the machining accuracy of the machine tool through simulation, so as to ensure the positioning accuracy and repetitive positioning accuracy of the machine tool, so that its performance is stable in the long term, and it is able to complete a variety of machining tasks under different operating conditions and to ensure the machining quality of the parts.
3.Functional Composite
The meaning of composite machine tool is to achieve or as far as possible in a machine tool to complete a variety of elements from the blank to the finished product processing. Its structural characteristics can be divided into two categories of process composite and process composite. Process composite machine tools such as boring, milling and drilling composite – machining centers, milling and turning composite – turning centers, milling, boring, drilling and turning composite machining centers, etc.; process composite machine tools, such as multi-faceted Multi-axis linkage machining composite machine tools and dual-spindle turning center, etc. The use of composite machine tools for processing, reducing the work-piece loading and unloading, replacement and adjustment of tools and auxiliary time as well as the intermediate process of the error generated by the process, improve the accuracy of parts processing, shorten the product manufacturing cycle, improve the production efficiency and the manufacturer’s ability to respond to the market, as opposed to the traditional process of dispersed production methods have obvious advantages.
The compounding of the machining process has also led to the development of machine tools towards modularity and multi-axis. Germany Index’s latest turning machining center is a modular structure, the machining center is able to complete turning, milling, drilling, grinding, laser heat treatment and other processes, can complete all the processing of complex parts. With the continuous improvement of modern machining requirements, a large number of multi-axis linkage CNC machine tools are increasingly welcomed by major enterprises. In the 2005 China International Machine Tool Show (CIMT2005), domestic and foreign manufacturers displayed a variety of forms of multi-axis processing machine tools (including dual spindle, dual tool holder, 9-axis control, etc.) as well as 4 to 5-axis linkage can be achieved five-axis high-speed gantry machining centers, five-axis linkage high-speed milling centers and so on.
4.Control Intelligence
With the development of artificial intelligence technology, in order to meet the development needs of manufacturing flexible production and manufacturing automation, the degree of intelligence of CNC machine tools is constantly improving. Specifically embodied in the following aspects:
(1)Adaptive control technology for machining process: by monitoring the cutting force, power, current and voltage of spindle and feed motor during machining process, and using traditional or modern algorithms to identify the force, wear and breakage status of cutting tools and the stability status of machine tool machining, and adjusting the machining parameters (spindle rotation speed, feed speed) and machining instructions in real time according to these status, so as to keep the equipment in the optimal operating state. According to these states, it adjusts the machining parameters (spindle speed, feed speed, and machining instructions) in real time, so that the equipment is in the best operating state, in order to improve machining accuracy, reduce the roughness of the machined surface, and improve the safety of equipment operation;
(2) Intelligent optimization and selection of machining parameters: the experience of process experts or technicians, the general and special rules of parts machining are combined with modern intelligent methods to construct the “intelligent optimization and selector of machining parameters” based on an expert system or a model, and the optimized machining parameters are obtained by using it to improve the efficiency of programming and the level of machining process and shorten the production preparation time. The purpose is to improve the programming efficiency and machining process level and shorten the production preparation time;
(3) Intelligent fault self-diagnosis and self-repair technology: according to the existing fault information, apply modern intelligent methods to achieve rapid and accurate fault location;
(4) Intelligent fault playback and fault simulation technology: it can record all kinds of information of the system completely, playback and simulate all kinds of errors and accidents occurred in CNC machine tools, so as to determine the causes of errors, find out the solutions to problems and accumulate production experience;
(5) Intelligent AC servo drives: intelligent servo systems that can automatically identify the load and automatically adjust the parameters, including intelligent spindle AC drives and intelligent feed servo devices. This kind of drive device can automatically identify the rotational inertia of the motor and the load, and automatically optimize and adjust the control system parameters, so that the drive system can obtain the best operation;
(6) Intelligent 4M CNC system: In the manufacturing process, the integration of processing and testing is an effective way to achieve rapid manufacturing, rapid testing and rapid response, and the four (i.e., 4M) of measurement (Measurement), modelling (Modelling), machining (Manufacturing), and machine operation (Manipulator) are fused together in one system. The 4M’s are integrated into one system, which enables information sharing and promotes the integration of measurement, modelling, machining, clamping and operation.
5.Openness of the System
(1) Openness to future technologies: As the hardware and software interfaces follow the recognized standard protocols, only a small amount of redesign and adjustment is required, and a new generation of general-purpose hardware and software resources may be adopted, assimilated and made compatible with the existing system, which means that the system’s development costs will be greatly reduced and the system’s performance and reliability will be continuously improved and be in a long life cycle;
(2) Openness to special user requirements: updating products, expanding functions, and providing various combinations of hardware and software products to meet special application requirements;
(3) Establishment of CNC standards: A new CNC system standard, ISO 14649 (STEP-NC), is being studied and developed internationally to provide a neutral mechanism, independent of specific systems, capable of describing a uniform data model throughout the life cycle of a product, so as to standardize the entire manufacturing process and even product information across all industrial sectors. A standardized programming language is both user-friendly and reduces labour consumption directly related to operational efficiency.
6.Parallelization of Drives
Parallel motion machine tools to overcome the traditional machine tool tandem mechanism of moving parts of large mass, low system rigidity, the tool can only feed along the fixed guideway, low degree of freedom of operation, equipment processing flexibility and mobility is not enough and other inherent defects, the main axis of the machine tool (generally for the dynamic platform) and the machine base (generally for the static platform) between the use of multiple rods in parallel with the coupling mechanism to drive the control of rod length in the rod system so that the rod system supported platform to obtain the corresponding degree of freedom of motion, can achieve multi-coordinate linkage CNC machining, assembly and measuring a variety of functions. By controlling the length of the rods in the rod system, the platform supported by the rod system can obtain the corresponding degree of freedom of movement, which can achieve multi-coordinate linkage CNC machining, assembly and measurement of a variety of functions, and better meet the processing of complex special parts, with a high degree of modularity of modern robots, lightweight and fast speed and other advantages. Parallel machine tool as a new type of processing equipment, has become an important research direction of the current machine tool technology, by the international machine tool industry attaches great importance to the machine tool industry, is considered to be “since the invention of CNC technology in the machine tool industry the most meaningful progress” and “21st century, a new generation of CNC processing equipment “.
7.Polarization (Up-scaling and Miniaturization)
The development of national defence, aviation, aerospace and energy and other basic industries, large-scale equipment needs to be large and good performance of the support of CNC machine tools. Ultra-precision machining technology and micro-nanotechnology is a strategic technology of the 21st century, the need to develop new manufacturing processes and equipment to adapt to the micro-small size and Micro-nano machining accuracy, so micro-machine tools, including micro-cutting (turning, milling, grinding) machine tools, micro-electrical machine tools, micro-laser machine tools and micro-presses, etc., the demand is gradually increasing.
8.Information Interaction Networking
For enterprises facing fierce competition, so that CNC machine tools with two-way, high-speed networking communication functions to ensure that the flow of information between the various departments of the workshop unimpeded is very important. Both can achieve network resource sharing, but also can achieve the remote monitoring, control, training, teaching, management of CNC machine tools, but also can achieve the digital service of CNC equipment (remote diagnosis of CNC machine tool failure, maintenance, etc.). For example, Japan’s Mazak launched a new generation of machining centers equipped with an external device called information tower (e-Tower), including computers, mobile phones, off-machine and on-machine cameras, etc., able to achieve voice, graphics, video and text communication fault alarm display, online help troubleshooting and other functions, is independent, autonomous management of the manufacturing unit.
9.New Functional Components
In order to improve the performance of all aspects of CNC machine tools, the application of new functional components with high precision and high reliability has become inevitable. Representative new functional components include:
(1)High-frequency electric spindle: high-frequency electric spindle is the integration of high-frequency motor and spindle components, with small size, high speed, stepless speed regulation and a series of advantages, in a variety of new CNC machine tools have been widely used;
(2) Linear motor: In recent years, the application of linear motor is becoming more and more widespread, although its price is higher than the traditional servo system, but due to the load change perturbation, thermal deformation compensation, magnetic isolation and protection of the application of key technologies, the mechanical transmission structure has been simplified, and the dynamic performance of the machine tool has been improved. For example: Siemens produced 1FN1 series of three-phase AC permanent magnet synchronous linear motors have begun to be widely used in high-speed milling machines, machining centers, grinding machines, parallel machine tools, and machine tools with high requirements for dynamic performance and motion accuracy; Germany’s XHC horizontal machining centre XHC three-way drive are used in two linear motors;
(3) Electric ball screw: electric ball screw is a servo motor and ball screw integration, can greatly simplify the structure of the CNC machine tool, with less transmission links, compact structure and a series of advantages.
10.High Reliability
CNC machine tools and traditional machine tools, compared with the increase in the number of CNC systems and the corresponding monitoring devices, such as the application of a large number of electrical, hydraulic and electromechanical devices, easy to lead to an increased probability of failure; industrial grid voltage fluctuations and interference in the reliability of CNC machine tools is extremely unfavourable, and CNC machine tools processing parts more complex surface, long processing cycle, the requirements of the average failure-free time of more than 20,000 hours. In order to ensure the high reliability of CNC machine tools, we must carefully design the system, strict manufacturing and clear reliability goals and through maintenance to analyse the failure mode and find out the weak links. Foreign CNC system average trouble-free time in 7 ~ 100,000 hours or more, the domestic CNC system average trouble-free time is only 10,000 hours or so, the average trouble-free working time of the whole machine abroad up to 800 hours or more, while the highest domestic only 300 hours.
11.Greening the Process
With increasingly stringent environmental and resource constraints, the greening of manufacturing and processing is becoming more and more important, and China’s resource and environmental problems are particularly prominent. Therefore, in recent years, no or less coolant, dry cutting, semi-dry cutting energy-saving and environmentally friendly machine tools continue to appear, and in constant development. In the 21st century, the general trend of green manufacturing will make all kinds of energy-saving and environmentally friendly machine tools to accelerate the development and occupy more of the world market.
12.Application of Multimedia Technology
Multimedia technology integrates computer, audio-visual and communication technologies, so that computers have the ability to comprehensively process sound, text, image and video information, and therefore also put forward graphical requirements for the user interface. Reasonable humane user interface greatly facilitates the use of non-professional users, people can operate through windows and menus to facilitate the blueprint programming and rapid programming, three-dimensional colour stereo dynamic graphics display, graphics simulation, graphics dynamic tracking and simulation, different directions of view and local display scale scaling functions. In addition to this, the application of multimedia technology in the field of numerical control technology can do information processing integrated, intelligent, applied to real-time monitoring system and production site equipment fault diagnosis, production process parameter monitoring, etc., and therefore has significant application value.
Domestic CNC machine tools lack of core technology, from high-performance CNC systems to key functional components are basically dependent on imports, even though in recent years some domestic manufacturers have struggled to create their own brands, but the function of their products, the reliability of the performance is still a gap with foreign products. In recent years, domestic manufacturers of CNC machine tools through the introduction of technology, mergers and acquisitions at home and abroad, as well as foreign procurement and other advanced CNC technology, but the lack of machine tool structure and precision, reliability, humane design and other basic technology research, ignoring the cultivation of independent development capabilities, the technical level of domestic CNC machine tools, performance and quality with foreign countries there is still a large gap between the same difficult to get the majority of the user’s recognition. The technical level, performance and quality of domestic CNC machine tools are still far from that of foreign countries.
Some domestic manufacturers of CNC machine tools do not pay enough attention to the overall process and manufacturing level of improvement, processing means are basically ordinary machine tools and inefficient tools, assembly and commissioning completely by hand, processing quality in the production schedule under the pressure can not be stable and improve. In addition, many domestic manufacturers of CNC machine tools production management is still used in the original manual ledger management, process level and management of inefficiency makes the enterprise can not form enough production scale. Such as foreign machine tool manufacturers can do weekly assembly and adjustment of products, while the domestic production cycle is too long and difficult to control. Therefore, we should pay attention to the introduction of technology at the same time to strengthen their technological transformation and management level.
Due to the rapid development of the CNC machine tool industry, a part of the enterprise does not care about long-term interests, to improve their comprehensive service level is not enough attention, and even the lack of a true understanding of the service, focusing only on sales without focusing on pre-sales and after-sales service. Some companies send personnel to the production of CNC machine tools lack of sufficient understanding, will not use or use bad CNC machine tools, not to mention the user can not guide the use of good machine tools; some of the advanced and efficient tool lack of basic understanding, can not provide a better process solution, the user naturally lacks confidence in the manufacturer. Manufacturers of services should start from the study of the user’s processing products, processes, types of production, quality requirements, to help users select equipment, recommended advanced technology and tools, equipped with professional training staff and a good training environment, to help users to play the maximum benefits of the machine tool, processing of high-quality end-products, so that we can gradually get the user’s recognition and improve the market share of domestic CNC machine tools.
Source: CNC Programming Network, World Advanced Manufacturing Technology Forum
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