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1、Chapter1 Introduction,1 Background 2 Construction and working principles 3 Types and characteristics 4 Future development,1 Background,1.1 The development of NC machine tool After World War II, With the increasing complexity of aircraft components, in 1949, US air force asked Parsons company to deve
2、lop a special equipment to automatically machine those components.,With the concept of numerically controlled machine tool by Parsons company, in 1952, a control device that based on vacuum tube and relay has been developed for milling machine control. Vacuum tube, known as applied on first generati
3、on of NC machine tool.,Vacuum tube,By the end of 1950s, the second generation NC machine tool whose control circuits are consisted exclusively by transistors were successfully developed. After that, those expensive and fragile vacuum tube NC machine tools were gradually replaced. With the developmen
4、t of NC machine tools, practicability, flexibility, convenient maintenance and adaptability were required by users.,transistor,However, transistor circuits cannot meet all these requirements due to economy. In 1965, with the development of integrated circuits, the third generation of NC machines pro
5、vide solutions for those requirements.,Stage1 -1970s Numerical control (NC) Stage2 1970s Computer numerical control (CNC) Stage3 1970s-1980s Microprocessor control. It had significantly improved characteristics and reliability of machine tools. From then on, NC technology were rapidly developed and
6、widely applied all over the world. Stage4 1990s- PC platform.,1.2 Definition of NC machine tool NC technology- controlling mechanical movement and working process by numerical signals； NC machine tool- machine tools controlled by program system that can logically execute special codes.,Compared with
7、 conventional machine tools, a NC machine tool is a kind of automatic machining facility. When machining with a conventional machine tool, operators manipulate hand wheels to move the cutting tool along the desired contour of work piece. While using a NC machine tool, its NC system can complete the
8、machining process guided by program.,2. Construction and working principle of NC machine tools,2.1 Construction of NC machine tools NC machine tools have different purposes in various fields, however, each type of NC machine tool has similar constructions.,1) Control medium NC machine tool requires
9、no direct manual operation during working, but must perform as operator required. Therefore, a bridge between human being and machine tool must be established. The bridge is known as control medium, carrying all required machining information for NC device.,The exact type of control medium has punch
10、ed tape, punched card, magnetic tape, magnetic disk and USB hubs, depends on the NC device. Machining information must be transferred to NC device through readers, such as photoelectrical tape readers, tape machines, disk drivers and USB ports.,Punched tape,Punched card,Magnetic disk,Tape reader,2)
11、NC control equipment NC device is the brain of a NC machine tool. Today, most NC machining tools are controlled by microprocessors. NC device requires software to read and decode information, and requires hardware to run the software.,Construction of NC device,3) Servo system As the executor of a NC
12、 system, servo system consists of servo motor and servo drive system. Servo system drive cutting tools or worktable, and/or actuates accessories to machine workpieces that required. The operating information is in the form of pulses. Each pulse produces a displacement of a movable part, which is kno
13、wn as pulse equivalent, usually equals to 0.001mm.,4) Assistant control system Assistant control system is a sort of electric control equipment connecting NC device and mechanical components. It receives instruction signals (e.g. spindle speed, tool changing, coolant supply) from NC device. After de
14、coding, logic judgment and power amplification for the signals, the machine tool will be acting as desired driven by its electric, hydraulic, pneumatic or mechanical appliances. Moreover, assistant control systems feedback some switching signals to CNC.,Oil pump,5) Machine tool reality Machine tool
15、reality is the main body of a NC machine tool, consisting of basis (e.g. base and bed) and movable components (e.g. worktable, carriage （床鞍）, spindle). It is the mechanical components to perform machining processes, similar to conventional machine tools. It features of: Driven by high performance sp
16、indle and servo transmissions； Better rigidity and anti-vibration of structure； Efficient transmission components, e.g. lead screw pairs, rolling ways, etc.,CJK6136 NC lathe,Programming according to drawings Input program into NC device Decoding Servo mechanisms control machining process (spindle, feeding, tool changing, clamping, cooling, lubricating, etc.),2.2 Working principle of NC machine tools,3 Classifications and features of NC machine tools,3.1 Types 1. By functions 1) Ge
