Numerical control machine tool, short for computer control machine tools, is an automatic machine tool equipped with a program control system and has been widely in modern CNC machining services. The control system can logically process the program with control code or other symbolic instructions, decode it, express it in coded Numbers, and input it into the numerical control device through the information carrier. The numerical control device sends out all kinds of control signals and controls the movement of the machine tool. According to the shape and size required by the drawing, the parts are processed automatically.
1. The Development of Numerical Control Machine Tooling
With the continuous progress of social production and science and technology, various kinds of new industrial products emerge in an endless stream. As the foundation of national industry, the mechanical manufacturing industry is becoming more and more sophisticated and complex. Ordinary machine tools or highly specialized automated machine tools are obviously unable to meet these requirements. CNC to better solve the complex, precise, small batch, multi varieties of parts processing problems, is a flexible, efficient automatic machine tools, represents the development direction of modern machine control technology.
Figure 1: Early Numerical control system
1.1. The Generation of Numerical Control Machine Tools.
The development of numerical control machine tools began in the United States. In 1948, when Parsons Co. finished the task of developing and processing the inspection template for helicopter impeller profile, it put forward the preliminary idea of developing the NC machine tool. In 1949, with the support of the U.S. Air Force Logistics Department, Parsons formally accepted the Commission to start the development of numerical control machine tools in collaboration with the Servo Mechanism Laboratory of the Massachusetts Institute of Technology MIT Servo Mechanism Laboratory of Technology. After three years of research, the world’s first numerical control machine tool test prototype was successfully manufactured in 1952.
1.2. The Classification of Manufacturing System
1.2.1. Computer direct CNC system
The so-called direct numerical control (DNC) system uses a computer to program automatically for several numerical control machine tools, and the programming results are transmitted directly to the control boxes of each numerical control machine tool through data lines. The central computer has enough memory capacity, so it can store, manage and control a large number of parts and programs in a unified way. With time-sharing operation system, the central computer can manage and control a group of NC machine tools at the same time, so it is also called computer group control system.
Figure2: Numerical control system
- Flexible manufacture system
Flexible Manufacturing System (FMS), also known as Computer Group Control Automation Line, connects a group of numerical control machine tools with automatic transmission system and places them under the unified control of a computer. To form a whole for manufacturing, Its characteristic is that a master computer manages the hardware and software of the whole system, controls two or more Numerical control machine tools by DNC mode, schedules and automatically transmits the workpiece between each machine tool, and realizes automatic feeding and unloading of parts by means of switching workbench or industrial robot. Machine tools can be manufactured 24 hours a day under the supervision of no one or very few people.
1. 2.2. Computer integrated manufacturing system
It refers to the flexible integrated manufacturing system which uses the most advanced computer technology to control the whole process from ordering, design, process, manufacturing to sales, so as to achieve the integration of information systems and high efficiency. It is based on the automation of production process (such as computer aided design, computer aided process planning, computer aided manufacturing, flexible manufacturing system, etc.), and combined with the development of other management information systems, it has the ability of analysis and control of various types of computers and their software systems. The production activities of the factory are linked together to realize the comprehensive automation of the whole factory.
1.3. The Component of CNC Machine Tools
There are many kinds of numerical control machine tools, but any Numerical control machine tool is composed of control medium, CNC system, servo system, auxiliary control system and machine body.
Figure3: The component of CNC
1.3.1. Control medium
When CNC system works, it does not need the operator to manipulate the machine tool directly, but the machine tool must carry out the intention of the human, which requires the establishment of a certain relationship between the human and the machine tool. The intermediary of this connection is called the control medium.
1.3.2. Numerical control system
CNC device is a kind of control system and the central link of numerical control machine tool. It can automatically read and decode the given number on the input carrier, so that the machine tool can feed and process parts. CNC system usually consists of four parts: input device, controller, calculator and output device.
1.3.3. Servo system
Servo system consists of servo drive motor and servo drive device, which is the executive part of CNC system. Servo system receives instruction information of NC system, and drives the moving parts of the machine body to move or make the executing parts act according to the requirement of instruction information, so as to process the workpiece that meets the requirement.
1.3.4. Auxiliary control system
Auxiliary control system is a powerful electric control device between numerical control device and machine tool machinery and hydraulic components. It receives command signals such as main motion speed change, tool selection exchange, assistant device action and so on, which are output by NC device. After necessary compilation, logical judgment and power amplification, it directly drives corresponding electrical, hydraulic, pneumatic and mechanical components to complete various specified actions.
1.3.5. Machine body
Machine tool body is the main body of numerical control machine tool, which consists of basic large parts (such as bed, base) and various moving parts (such as worktable, saddle, spindle, etc.). It is a mechanical part to complete various cutting processes, and is improved on the basis of ordinary machine tools.
Figure4: Modern machine tool
It has the following characteristics:
- numerical control machine tools use high-performance spindle and servo drive system, mechanical transmission device.
- The mechanical structure of NC machine tools has high stiffness, damping accuracy and wear resistance.
- More efficient transmission components are used, such as ball screw pairs and linear rolling guides.
CNC machine tool set of modern machinery manufacturing technology, computer technology, network technology, communication technology, control technology, hydraulic pneumatic technology, photoelectric technology in one, with high efficiency, high precision, high automation and high flexibility. So CNC machine tools are of great importance in the development of modern economy.