Unit 1 The Applications of NC/CNC Machining Technology,1.1 Lesson 1 The Applications of C/CNC,NC technology has been used in industry for over 40 years. Simply speaking, numerical control is a method of automatically operating a manufacturing machine based on a code of letters, numbers, and special characters. A complete set of coded instructions for executing an operation is called a program. 1The program is translated into corresponding electrical signals for inputting to motors which run the machine. Numerical control machines can be programmed manually. If a computer is used to create a program, the process is known as computer-aided programming.,NC technology has found many applications, including lathes, and turning centers, milling machines and machining centers, punches, electrical discharge machines (EDM), flame cutters, grinders, and testing and inspection equipments. The most complex CNC machine tools are the turning center with a ten-station turret that accepts quick-change tools, the vertical machining center that the tool magazine is on the left of the machine and horizontal machining center equipped with an automatic tool changer, shown in Figure 1-1 and Figure 1-2 respectively. Generally speaking, tool magazines can store 200 cutting tools.,1.2 Lesson 2 Definition of CNC Machines,A computer numerical control(CNC)machine is an NC machine with the added feature of an on-board computer. The on-board computer is often referred to as the machine contro1unit or MCU. Control units for NC machines are usually hard wired. This means that the machine functions are controlled by the physical electronic elements that are built into the controller1.,The on-board computer, on the other hand, is “soft” wired. Thus, the machine functions are encoded into the computer at the time of manufacture. They will not be erased when the CNC machine is turned offComputer memory that holds such information is known as ROM or read-only memory. The MCU usually has an alphanumeric keyboard for direct or manual data input (MDI) of part programs. Such programs are stored in RAM or the random-access memory portion of the computer,They can be played back，edited，and processed by the controllerAll programs resided in RAM，however，are lost when the CNC machine is turned offThese programs can be saved on auxiliary storage devices such as punched tape，magnetic tape，or magnetic disk. The MCU units have graphics screens that can display not only the CNC program but also the cutter paths generated and any errors in the program.,1.3 Reading Materials 1 CNC Machining Centers,There are two main types of machining centers: the horizontal-spindle and the vertical-spindle machine. 1Horizontal-spindle type The traveling-column type is equipped with one or usually two tables on which the work can be mounted. With these types of machining center, the workpiece can be machined while the operator is loading a new workpiece on the other table. A CNC lathe is a typical one., The fixed-column type is equipped with a pallet shuttle. The pallet is a removable table on which the workpiece is mounted. After the wokpiece has been machined, the workpiece and pallet are moved to a shuttle which then rotates, bringing a new pallet and workpiece into position for machining. 2Vertical-spindle type The vertical spindle machining center is a saddle-type construction with sliding bedways which utilize a sliding vertical head instead of a quill movement. The CNC milling machine and CNC high-speed punch press are the typical ones.,1.4 Reading Materials 2 Classification of CNC Machines,Numerical control machines can be generally classified using the following categories: 1For power drives: (1) hydraulic drive, (2) pneumatic drive , (3) electric drive. 2For drives motors: (1) stepper motor, (2) DC servomotor, (3) AC servomotor, (4) fluid servomotor. 3For machine tool control: (1) point-to-point tool movements, (2) continuous-path (or contouring) tool movements.,4For tool positioning modes/programming: (1) incremental positioning mode, (2) absolute positioning mode, (3) diameter programming, (4) radius programming. 5For servo control systems: (1) open-loop control system, (2) closed-loop control system. 6For coordinate definition: (1) right-hand coordinate system, (2) left-hand coordinate system. 7For machine spindle: (1) vertical spindle machine, (2) horizontal spindle machine. 8For automatic tool changers: (1) magazines on NC/CNC machining centers, (2) turrets on NC/CNC turning center.,