西北工业大学明德学院本科毕业设计论文Characteristics of CNC machine toolsCNC machine operation and monitoring of all completed in the numerical control unit, which is the brains of CNC machine tools. Compared with the general machine tools, CNC machine tools has the following characteristics:（1） high precision, stable processing quality; （2） can be multi-axis linkage, can process complex shape parts; （3） processing part changes, generally only need to change the NC program, saving the production time to prepare; （4） high precision machine tool itself, rigidity, can choose the amount of benefit processing, production rate (usually as an ordinary machine 3 to 5 times); （5） high degree of automation tools, can reduce labor intensity; （6） the quality of the operators require a higher technical requirements on higher maintenance staff. CNC machine tools generally consists of the following components:（1） host, he is the subject of CNC machine tools, including machine tools, column, spindle, feed mechanism and other mechanical parts. He is used to complete a variety of machining mechanical parts. （2） CNC equipment, CNC machine tools is the core, including the hardware (printed circuit boards, CRT monitors, key boxes, paper tape reader, etc.) and the corresponding software for digital input part program, and complete the input information storage, data transformation, interpolation operations and achieve a variety of control functions. （3） drive, he was the implementing agencies CNC drive components, including the spindle drive unit, feed unit, spindle motor and feed motor. He was under the control of the NC device electrical or electro-hydraulic servo system to achieve through the spindle and feed drive. When several feed linkage, you can complete the position, line, plane curves and space curves processing. （4） assist device, the index control machine tools necessary supporting components to ensure the operation of CNC machine tools, such as cooling, chip removal, lubrication, lighting, monitoring. It consists of hydraulic and pneumatic devices, chip equipment, pallet, NC rotary table and CNC dividing head, including tools and monitoring detection devices. （5） Programming and other ancillary equipment, can be used to machine the part outside the programming and storage. Since 1952, Massachusetts Institute of Technology developed the world since the first CNC machine tools, CNC machine tools in manufacturing industry, especially in the automotive, aerospace, and military industries has been widely used, digital technology both in hardware and software have rapid development. Classification and application of CNC machine tools（1） use classification by technology Metal cutting type machine tools, including CNC lathes, CNC drilling, CNC milling, CNC grinding machines, CNC boring hair and processing center. These machines are suitable for single pieces, small batch and multiple varieties and parts processing, has good processing size consistency, high productivity and automation, and high equipment flexibility. CNC machine metal forming type; such machines, including CNC bending machines, CNC combined punch, CNC bending machine, CNC turret press and so on. CNC machine tools; such machines, including CNC wire (electrode) cutting machine, CNC EDM, CNC flame cutting machines, CNC laser cutting machine, special machine tool and so on. Other types of numerical control equipment; non-processing equipment using digital technology, such as automatic assembly machine, multi-coordinate measuring machines, automatic drawing machines and industrial robots. （2）classified according to movement pattern Position control; point control of CNC machine tools is characterized by moving parts of the machine can be achieved only from one location to another precise movement and positioning of the process in motion without any processing operations. Such as CNC drilling machines, a few at coordinate boring machine, CNC welding and tube bending machines. Linear control; point linear control characteristic is not only moving parts of the machine coordinates to achieve a precise location to another movement and positioning, but also to achieve a straight line parallel to the axis feed movement or control of the two oblique axes to achieve line feed movement. Contour control; contour control the characteristics of CNC machine tools is the machine moving parts to achieve two axes simultaneously control linkage. It requires not only control the moving parts of machine starting and ending coordinates of the location, but also for control of the process the speed of each point and the displacement, which called for control of the trajectories of the part processed into the plane straight line, curve or surface in space . （3） Classification by control Open-loop control; that position feedback devices without control. Semi-closed loop control; refers to the open-loop control with serv