Numerical control program is the work instruction of CNC lathe automatic machining parts. Based on the process analysis of the machined parts, the relative position of the part coordinate system on the machine coordinate system is determined. The size parameter of the relative movement of the tool and the part; The process route or processing sequence of parts processing, the process parameters of cutting processing and the action of auxiliary devices, etc. In this way, all the motion, size, process parameters and other processing information of the parts are obtained, and then the numerical control code composed of standard words, numbers and symbols is entered into the format according to the specified method to prepare the numerical control program list of the parts processing. Programming work can be carried out manually, or in the CNC lathes outside the automatic programming computer system to complete, more advanced CNC lathes, can be directly programmed on the CNC device.

The program must be stored in some kind of storage medium, such as paper tape, tape or disk, which storage carrier is used, depending on the design type of CNC device. The processing information recorded on the storage medium needs to be transmitted to the machine tool numerical control system by the input device, and the parts processing program in the machine tool memory can be transmitted to the storage medium by the output device. The input and output devices are the interfaces between the machine tool and the external devices. At present, the input devices are mainly paper tape readers, floppy disk drives, RS232C serial communication ports, MDI modes, etc.