Numerical Control Technology

Numerical Control Technology

Development History

In 1948, the United States Air Force commissioned Parsons in the US to develop processing equipment for inspecting helicopter propeller blade profiles. The complex and diverse shape of the samples, combined with the high precision requirements, made it difficult to adapt general processing equipment, leading to the proposal of using a digital pulse to control the machine tool.

In collaboration with the Massachusetts Institute of Technology (MIT), Parsons began research in 1949 and successfully produced the first three-axis CNC milling machine in 1952. At that time, the numerical control device was made up of tube components.

By 1959, the numerical control device had transitioned to using transistor components and printed circuit boards, and a CNC machine tool with an automatic tool changer was referred to as a machining center (MC Machining Center), marking the second generation of numerical control devices.

In 1965, the third-generation integrated circuit numerical control device was introduced, featuring a smaller size, lower power consumption, improved reliability, and a reduced price, thereby driving the development and output of CNC machine tools.

The late 1960s saw the development of a direct numerical control system, also known as a group control system, which was directly controlled by a computer. The advent of a computer numerical control system (CNC) controlled by a small computer marked the fourth generation of numerical control devices, characterized by the use of a small computer.

In 1974, a microcomputer numerical control device (MNC) using a microprocessor and a semiconductor memory was developed, marking the fifth generation of numerical control systems.

The early 1980s saw the development of numerical control devices capable of automatic programming through human-machine dialogue, thanks to advancements in computer software and hardware technology. These devices became smaller and could be directly installed on the machine tool, leading to further improvements in automation and the addition of features such as automatic tool breakage monitoring and workpiece detection.

In the late 1990s, the PC+CNC intelligent numerical control system was introduced, in which a PC served as the hardware component of the control system and the NC software system was installed on the PC. This approach was easier to maintain and allowed for the implementation of networked manufacturing.

CNC technology, also known as Computerized Numerical Control (CNC), is a computer-based, digital program control technology. It uses a computer to perform control functions on a device based on a previously stored control program. This allows various control functions, such as data storage, processing, calculation, and logic judgment, to be completed by computer software, replacing the hardware logic circuits used in traditional numerical control devices. CNC technology is an essential component of manufacturing information technology.

Development trend

The application of numerical control technology brought about a revolution in traditional manufacturing and has become a symbol of industrialization. With the ongoing development of numerical control technology and the increasing number of fields in which it is applied, it plays an increasingly critical role in the development of key industries such as IT, automobile, light industry, and healthcare. The digitization of equipment in these industries is a major trend in modern development.

The trend of CNC technology and equipment development around the world has several research hotspots, including:

  1. New trends in high-speed, high-precision machining technology and equipment
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Efficiency and quality are the cornerstones of advanced manufacturing technology. The use of high-speed and high-precision machining technology can significantly enhance efficiency, enhance product quality and grade, reduce production time, and increase market competitiveness.

As a result, the Japan Advanced Technology Research Association has listed it as one of the five modern manufacturing technologies, and the International Society of Production Engineering (CIRP) has identified it as a central research direction for the 21st century.

In the automotive industry, the production cycle for 300,000 units per year is just 40 seconds per vehicle, and multi-variety processing is a key challenge for automotive equipment.

In the aerospace and aeronautical industries, the parts processed are mostly thin-walled and thin-ribbed with low rigidity, typically made of aluminum or aluminum alloys. Only by reducing cutting speed and force can these parts be processed effectively.

A large-scale aluminum alloy billet “hollowing” method is used to manufacture large components such as wings and bodies, replacing multiple parts and improving strength, rigidity, and reliability through numerous rivets, screws, and other joints.

This requires processing equipment with high speed, high precision, and high flexibility. The feed speed of high-speed machining centers displayed at the EMO2001 exhibition can reach 80m/min or even higher, with idle speeds reaching about 100m/min.

Many automakers worldwide, including Shanghai General Motors Corporation in China, have replaced their 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 rapid speed of 100m/min, an acceleration of 2g, and a spindle speed of 60,000r/min.

With this machine, processing a thin-walled aircraft part takes only 30 minutes, compared to 3 hours with a general high-speed milling machine and 8 hours with an ordinary milling machine. The spindle speed and acceleration of the 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 improved from 10μm to 5μm, and that of precision machining centers has improved from 3 to 5μm to 1 to 1.5μm. Ultra-precision machining accuracy has even entered the nanoscale range (0.01μm).

Reliability has also improved, with the MTBF value of foreign numerical control devices reaching over 6,000h and the MTBF value of the servo system reaching over 30,000h, demonstrating exceptional reliability.

To achieve high-speed and high-precision machining, functional components such as electric spindles and linear motors have been rapidly developed and their application fields have been expanded.

  1. Five-axis linkage processing and compound machining machine tools develop rapidly

The 5-axis joint machining of 3D curved parts can be performed with optimal tool geometry, resulting in not only good finishing but also improved efficiency. It is commonly believed that the efficiency of a 5-axis linkage machine can be comparable to two 3-axis linkage machines, especially when high-speed milling of hardened steel parts is carried out using ultra-hard material milling cutters such as cubic boron nitride. In such cases, 5-axis simultaneous machining can deliver higher efficiency than 3-axis simultaneous machining.

In the past, the high cost of 5-axis linkage numerical control systems and the complex structure of the main engine made them several times more expensive than 3-axis linkage CNC machine tools. Additionally, the challenging programming techniques restricted the development of 5-axis linkage machine tools.

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However, the advent of electric spindles has greatly simplified the structure of the composite spindle head for 5-axis simultaneous machining, reducing both manufacturing difficulty and cost, and narrowing the price gap between the numerical control systems. This has led to the advancement of composite spindle head type 5-axis linkage machine tools and composite machining machine tools, including 5-face machining machine tools.

At EMO2001, Nippon Machine Co., Ltd. showcased a 5-sided machining machine that utilized a composite spindle head to achieve four vertical plane machining and machining at any angle, enabling both 5-sided and 5-axis machining on a single machine. The machine was capable of machining inclined faces and inverted tapered holes.

DMG of Germany displayed the DMUVolution series of machining centers, which can be processed on 5 sides and 5 axes in one setup, and can be controlled directly or indirectly by the CNC system or CAD/CAM.

  1. Intelligent, open and networked become the main trend of the development of contemporary CNC systems

The 21st century CNC equipment will be an intelligent system that encompasses all aspects of the CNC system. To enhance processing efficiency and quality, the system will feature adaptive control of the processing process and automatic generation of process parameters. The driving performance and ease of use will be improved through feedforward control, adaptive calculation of motor parameters, automatic identification of load, automatic selection of models, and self-tuning. Programming will be made simpler and more intuitive with intelligent automatic programming and an intelligent human-machine interface. The system will also include intelligent diagnostics and monitoring for convenient system diagnosis and maintenance.

To address the limitations of traditional CNC systems and the closure of industrial production 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), among others. The openness of CNC systems has become the future of the industry.

The open CNC system is developed on a unified operating platform, allowing for customization by machine tool manufacturers and end-users. By changing, adding, or removing structural objects (numerical control functions), serialization is achieved, 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 a unique personality. The architecture specification, communication specification, configuration specification, operating platform, numerical control system function library, and numerical control system function software development tools are the core of current research in this field.

Networked CNC equipment has been a highlight of international machine tool fairs over the past two years. The network of CNC equipment will greatly meet the demand for information integration in production lines, manufacturing systems, and enterprises, and it is the basic unit for implementing new manufacturing models such as agile manufacturing, virtual enterprise, and global manufacturing.

Famous CNC machine tool and system manufacturing companies have launched new concepts and prototypes in the past two years, such as the “CyberProduction Center” (CPC) exhibited by Mazak Corporation of Japan at the EMO 2001 exhibition, the “IT plaza” exhibited by Okuma Machine Tool Company of Japan, and the Open Manufacturing Environment (OME) exhibited by Siemens, Germany. These developments reflect the trend of CNC machine tool processing towards networking.

  1. Emphasis on the establishment of new technical standards and norms
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(1) About the Design and Development Specifications of Numerical Control Systems

As previously mentioned, open CNC systems offer better versatility, flexibility, adaptability, and scalability. The United States, the European Community, and Japan have all implemented strategic development plans and conducted research and development of open architecture numerical control system specifications (OMAC, OSACA, OSEC). These three largest economies have carried out similar scientific plans and norms in the short term, signaling the arrival of a new era in CNC technology. In 2000, China began studying and formulating the normative framework of its ONC numerical control system.

(2) About CNC Standards

Numerical control standards are a trend in the development of manufacturing information technology. For the first 50 years of CNC technology, information exchange was based on the ISO6983 standard, which used G and M codes to describe processing. This standard was focused on the processing process but is becoming increasingly inadequate for the rapid development of modern CNC technology. To address this issue, a new CNC system standard ISO14648 (STEP-NC) is being researched and developed globally. Its purpose is to provide a neutral mechanism that is not dependent on a specific system and can describe a unified data model throughout a product’s life cycle, leading to the standardization of product information throughout the manufacturing process and even across different industrial fields.

The introduction of STEP-NC may revolutionize the field of numerical control technology, with a profound impact on the development of numerical control technology and the entire manufacturing industry. Firstly, STEP-NC introduces a new manufacturing concept. In traditional manufacturing, NC machining programs were centralized on a single computer, but under the new standard, NC programs can be distributed across the internet, reflecting the open and networked development of CNC technology. Secondly, the STEP-NC CNC system can also significantly reduce the number of processing drawings (by approximately 75%), machining programming time (by approximately 35%), and processing time (by approximately 50%).

European and American countries attach great importance to the research of STEP-NC, with Europe initiating the IMS plan of STEP-NC from 1999 to 2001. The program was attended by 20 CAD/CAM/CAPP/CNC users, vendors, and academic institutions from Europe and Japan. STEP Tools in the United States is a global developer of manufacturing data exchange software and has developed a Super Model for exchanging information for CNC machine tools. This new data exchange format has been validated on prototypes equipped with SIEMENS, FIDIA, and the European OSACA-NC control system.

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