When machining parts on ordinary machine tools, the process personnel usually formulate the machining process specifications for the parts in advance according to the design drawings. Formulate the machining process, cutting parameters, machine tool specifications, cutting tools, fixtures, and other contents of the parts in the process specification. The operator operates the machine tool according to the various steps of the process specification, and processes the parts given in the drawing. That is to say, the machining process of the parts is completed by people. For example, driving, parking, changing spindle speed, changing feed rate and direction, cutting fluid on/off, etc. are all manually operated by workers.

When machining parts on automatic machine tools controlled by cams or on copying machine tools, although it is not necessary for humans to operate it, the motion curve or profile of the cam must be designed according to the characteristics and process requirements of the part. The machine tool motion is controlled by the cam and profile, and finally the parts are machined. In this machining process, although it avoids the operator directly operating the machine tool, each cam mechanism or mold can only process one type of part. When changing the processed parts, it is necessary to replace the cam and mold. Therefore, it can only be used in large-scale, specialized production.

Numerical control machine tools are different from the two types of machine tools mentioned above. It automatically processes the workpiece according to a pre programmed machining program. We write the machining process route, process parameters, tool motion trajectory, displacement, cutting parameters (spindle speed, feed rate, back cutting amount, etc.) and auxiliary tools (tool change, spindle forward rotation, reverse rotation, cutting fluid on/off, etc.) of the parts into a machining program sheet according to the instruction code and program format specified by the CNC machine tool, and then record the contents of this program sheet on the control medium (such as perforated paper tape, magnetic tape, magnetic disk, magnetic bubble memory), and input them into the CNC device of the CNC machine tool to command the machine tool to process the parts.

The entire process from analyzing part drawings to producing control media is called the programming of numerical control programs. From the above analysis, it can be seen that the difference between CNC machine tools and ordinary machine tools for machining parts is that the control machine tool automatically processes parts according to a program, while ordinary machine tools need to be operated by humans. We only need to change the program that controls the machine tool action to achieve the purpose of machining different parts. Therefore, CNC machine tools are particularly suitable for processing small batches and parts with complex shapes that require high precision.

From the outside, CNC machine tools all have CRT screens, where we can see various processing parameters and other content on the screen. From an internal structure perspective, CNC machine tools do not have gearboxes, and the main and feed movements are completed by DC or AC continuously variable servo motors. In addition, CNC machine tools generally have a workpiece measurement system, which can reduce the number of manual measurements of the workpiece during the machining process. So the use of CNC machine tools in various industries will become increasingly popular in the future.

Due to the fact that CNC machine tools need to process parts according to the program, after the program designer compiles the program, they enter the CNC device to command the work of the machine tool. The input of the program is obtained through the control medium. There are various specific methods, such as punched paper tape, data tape, floppy disk, and manual input (MDI).