In 1948, Parsons of the United States was commissioned by the US Air Force to develop processing equipment for helicopter propeller blade profile inspection.
Due to the complex and diverse shape of the sample, the high precision requirements, and the general processing equipment are difficult to adapt, so the idea of using a digital pulse to control the machine tool is proposed.
In 1949, the company began research together with the Massachusetts Institute of Technology (MIT), and in 1952 successfully produced the first three-axis CNC milling machine. At that time, the numerical control device used tube components.
In 1959, the numerical control device used transistor components and printed circuit boards, and a CNC machine tool with an automatic tool changer was called a machining center (MC Machining Center), which made the numerical control device enter the second generation.
In 1965, the third-generation integrated circuit numerical control device appeared, which not only had small volume, low power consumption, but also improved reliability and further reduced price, which promoted the development of CNC machine tools and output.
In the late 1960s, a direct numerical control system (referred to as DNC), which is also called a group control system, was directly controlled by one computer. The computer numerical control system (CNC) controlled by a small computer made the numerical control device enter the fourth generation which characterized by small computer.
In 1974, a microcomputer numerical control device (MNC) using a microprocessor and a semiconductor memory was successfully developed, which is a fifth-generation numerical control system.
In the early 1980s, with the development of computer software and hardware technology, there appeared a numerical control device capable of automatic programming of human-machine dialogue. The numerical control device became smaller and smaller, and could be directly installed on the machine tool; the automation degree of the numerical control machine tool further improved, and it has the functions of automatically monitoring tool breakage and automatically detecting workpieces.
In the late 1990s, the PC+CNC intelligent numerical control system appeared, that is, the PC was used as the hardware part of the control system, and the NC software system was installed on the PC. This method is easy to maintain and easy to implement networked manufacturing.
CNC technology is also called Computerized Numerical Control (CNC), which is a computer-based digital program control technology.
This technique uses a computer to perform control functions on the device in accordance with a previously stored control program.
Since the computer is used to replace the numerical control device which is originally composed of hardware logic circuits, the realization of various control functions such as storage, processing, calculation, logic judgment of input data can be completed by computer software.
CNC technology is an important part of manufacturing information technology.
The application of numerical control technology not only brought revolutionary changes to traditional manufacturing, but also made manufacturing a symbol of industrialization.
Moreover, with the continuous development of numerical control technology and the expansion of application fields, he plays an increasingly important role in the development of some important industries (IT, automobile, light industry, medical care, etc.) cause the digitization of the equipment needed in these industries is a major trend in modern development.
From the trend of the development of CNC technology and its equipment in the world, its main research hotspots are as follows:
- New trends in high-speed, high-precision machining technology and equipment
Efficiency and quality are the mainstays of advanced manufacturing technology.
High-speed, high-precision machining technology can greatly improve efficiency, improve product quality and grade, shorten production cycle and improve market competitiveness.
To this end, the Japan Advanced Technology Research Association listed it as one of the five modern manufacturing technologies, and the International Society of Production Engineering (CIRP) identified it as one of the central research directions of the 21st century.
In the car industry, the annual production cycle of 300,000 units is 40 seconds per vehicle, and multi-variety processing is one of the key issues that must be solved in car equipment.
In the aerospace and aerospace industries, the parts processed are mostly thin-walled and thin-ribbed, and the rigidity is very poor. The material is aluminum or aluminum alloy. Only when the cutting speed and cutting force are small, can these ribs, the wall be processed.
Large-scale aluminum alloy billet “hollowing” method is used to manufacture large parts such as wings and body to replace multiple parts. It is assembled by numerous rivets, screws and other joints to improve the strength, rigidity and reliability of the components. .
These all require high speed, high precision and high flexibility for processing equipment.
From the situation of EMO2001 exhibition, the feed speed of high-speed machining center can reach 80m/min or even higher, and the idle speed can reach about 100m/min.
Many automakers around the world, including Shanghai General Motors Corporation of China, have replaced production machines with production lines consisting of high-speed machining centers.
The CINCINNATI HyperMach machine has a feed rate of up to 60m/min, a fast speed of 100m/min, an acceleration of 2g and a spindle speed of 60,000r/min.
It takes only 30 minutes to process a thin-walled aircraft part, and the same part takes 3 hours for general high-speed milling machine and 8 hours for ordinary milling machine. The spindle speed and acceleration of German DMG double-spindle lathe are 12*1000r/mm and 1g.
In terms of machining accuracy, the machining accuracy of general-grade CNC machine tools has been increased from 10μm to 5μm, and the precision machining center has been improved from 3 to 5μm to 1 to 1.5μm, and ultra-precision machining accuracy has begun to enter the nano-scale (0.01μm). .
In terms of reliability, the MTBF value of foreign numerical control devices has reached more than 6,000h, and the MTBF value of the servo system has reached more than 30,000h, showing very high reliability.
In order to achieve high-speed, high-precision machining, the functional components such as electric spindles and linear motors have been rapidly developed, and the application fields have been further expanded.
- Five-axis linkage processing and compound machining machine tools develop rapidly
5-axis joint machining of 3D curved parts can be performed with the best geometry of the tool. Not only is the finishing good, but the efficiency is also greatly improved.
It is generally believed that the efficiency of a 5-axis linkage machine can be equal to two 3-axis linkage machines, especially when high-speed milling of hardened steel parts using ultra-hard material milling cutters such as cubic boron nitride, 5-axis simultaneous machining can achieve higher efficiency than 3-axis simultaneous machining.
However, in the past, due to the 5-axis linkage numerical control system and the complicated structure of the main engine, the price was several times higher than that of the 3-axis linkage CNC machine tool. In addition, the programming technique is difficult, which restricts the development of the 5-axis linkage machine tool.
At present, due to the emergence of the electric spindle, the structure of the composite spindle head for 5-axis simultaneous machining is greatly simplified, the manufacturing difficulty and cost are greatly reduced, and the price gap of the numerical control system is narrowed.
Therefore, the development of the composite spindle head type 5-axis linkage machine tool and the composite machining machine tool (including the 5-face machining machine tool) has been promoted.
At EMO2001, the 5-sided machining machine of Nippon Machine Co., Ltd. uses a composite spindle head to realize four vertical plane machining and machining at any angle, so that 5-sided machining and 5-axis machining can be realized on the same machine. Machining of inclined faces and inverted tapered holes is possible.
DMG of Germany exhibited the DMUVoution series of machining centers, which can be processed in 5 sides and 5 axes in one setup, and can be controlled directly or indirectly by CNC system control or CAD/CAM.
- Intelligent, open and networked become the main trend of the development of contemporary CNC systems
The 21st century CNC equipment will be a certain intelligent system.
Intelligent content includes all aspects of the CNC system:
In order to pursue the intelligentization of processing efficiency and processing quality, such as adaptive control of the processing process, process parameters are automatically generated;
In order to improve the driving performance and the convenience of using the connection, such as feedforward control, adaptive calculation of motor parameters, automatic identification of load automatic selection model, self-tuning, etc.;
Simplify programming and simplify the operation of intelligent, such as intelligent automatic programming, intelligent human-machine interface, etc.
There are also intelligent diagnostics, intelligent monitoring content, convenient system diagnosis and maintenance.
In order to solve the problems of the traditional CNC system closure and the industrial production of CNC application software.
Many countries have researched open CNC systems, such as The Next Generation Work-Station/Machine Control (NGC), OSACA (Open System Architecture for Control within Automation Systems), and Japan’s OSEC (Open System Environment for Controller), China’s ONC (Open Numerical Control System) and so on.
The openness of CNC systems has become the future of CNC systems.
The so-called open CNC system is the development of the CNC system can be on a unified operating platform.
For machine tool manufacturers and end users, by changing, adding or cutting structural objects (numerical control functions), serialization is formed, and users’ special applications and know-how can be easily integrated into the control system to quickly realize different varieties and grades. The open CNC system forms a brand-name product with distinctive personality.
The architecture specification, communication specification, configuration specification, operation platform, numerical control system function library and numerical control system function software development tools of the open CNC system are the core of the current research.
Networked CNC equipment is a new highlight of the internationally renowned machine tool fair in the past two years.
The network of CNC equipment will greatly meet the demand for information integration in production lines, manufacturing systems, and manufacturing enterprises. It is also the basic unit for implementing new manufacturing models such as agile manufacturing, virtual enterprise, and global manufacturing.
Some famous CNC machine tools and CNC system manufacturing companies at home and abroad have launched related new concepts and prototypes in the past two years.
For example, at the EMO 2001 exhibition, the “CyberProduction Center” (CPC) exhibited by Mazak Corporation of Japan;
Okuma Machine Tool Company of Japan exhibited “IT plaza” (Information Technology Plaza, IT Plaza for short);
The Open Manufacturing Environment (OME), exhibited by Siemens, Germany, etc.
It reflects the trend of CNC machine tool processing in the direction of networking.
- Emphasis on the establishment of new technical standards and norms
(1) About the design and development specifications of numerical control systems
As mentioned earlier, open CNC systems have better versatility, flexibility, adaptability and scalability.
The United States, the European Community and Japan have implemented strategic development plans and conducted research and development of open architecture numerical control system specifications (OMAC, OSACA, OSEC).
The world’s three largest economies have carried out almost the same scientific plans and norms in the short term, indicating the advent of a new era of revolution in CNC technology.
In 2000, China began to study and formulate the normative framework of China’s ONC numerical control system.
(2) About CNC standards
Numerical control standards are a trend in the development of manufacturing information technology.
The information exchange in the 50 years after the birth of CNC technology is based on the ISO6983 standard, that is, using G, M code to describe how to processing.
Its essential feature is oriented to the processing process.
Obviously, it has become increasingly unable to meet the needs of the rapid development of modern CNC technology.
To this end, a new CNC system standard ISO14649 (STEP-NC) is being researched and developed internationally.
Its purpose is to provide a neutral mechanism that does not depend on a specific system, and can describe a unified data model throughout the life cycle of a product, thereby realizing the standardization of product information throughout the manufacturing process and even in various industrial fields.
The emergence of STEP-NC may be a revolution in the field of numerical control technology, which will have a profound impact on the development of numerical control technology and the entire manufacturing industry.
First, STEP-NC proposes a new manufacturing concept.
In the traditional manufacturing concept, NC machining programs are concentrated on a single computer.
Under the new standard, NC programs can be scattered on the Internet. This is the direction of open and networked development of CNC technology.
Secondly, the STEP-NC CNC system can also greatly reduce the processing drawings (about 75%), machining programming time (about 35%) and processing time (about 50%).
European and American countries attach great importance to the research of STEP-NC, and Europe initiated the IMS plan of STEP-NC (1999.1.1~2001.12.31).
The program is attended by 20 CAD/CAM/CAPP/CNC users, vendors and academic institutions from Europe and Japan.
STEP Tools in the United States is the developer of manufacturing data exchange software worldwide.
He has developed a Super Model for the exchange of information for CNC machine tools, with the goal of describing all machining processes with a uniform specification.
This new data exchange format has been validated on prototypes equipped with SIEMENS, FIDIA and the European OSACA-NC control system.