The basic components of CNC machine tools include machining program carrier, CNC device, servo drive device, machine tool main body and other auxiliary devices.

Main functions of each part:

1, processing program carrier

When CNC machine tools are working, it is not necessary for workers to directly operate the machine tools. To control CNC machine tools, machining programs must be compiled. The machining program of parts includes the relative motion trajectory of cutter and workpiece on the machine tool, process parameters (feed speed, spindle speed, etc.). ) and auxiliary exercise. Parts processing program is stored in a program carrier with a certain format and code, such as punched paper tape, cassette tape, floppy disk, etc. And the program information is input to the CNC unit through the input device of the CNC machine tool.

2, numerical control device

Numerical control device is the core of numerical control machine tool. Modern numerical control devices all adopt the form of CNC (computer numerical control), and generally use multiple microprocessors to realize numerical control functions in the form of programming software, so it is also called software NC. Numerical control system is a position control system, which interpolates the ideal motion trajectory according to the input data, and then outputs it to the executive parts to process the required parts. Therefore, the numerical control device is mainly composed of three basic parts: input, processing and output. All these tasks are reasonably organized by computer system programs, so that the whole system can work harmoniously.

1) input device: input NC instructions to NC devices, and there are different input devices according to different program carriers. There are mainly keyboard input, disk input, direct communication input of CAD/CAM system and DNC (direct numerical control) input connected to the upper computer. At present, many systems still keep the paper tape input form of photoelectric readers.

(1) paper tape input mode. The paper tape photoelectric reader can be used to read the part program and directly control the movement of the machine tool. It can also read the paper tape content into the memory and control the movement of the machine tool with the part program stored in the memory.

(2)MDI manual data input mode. The operator can use the keyboard on the operation panel to input the instructions of the machining program, which is suitable for shorter programs.

In the editing state of the control device, the machining program is input by software and stored in the memory of the control device. This input method can reuse the program. This method is generally used for manual programming.

On the NC equipment with session programming function, different menus can be selected according to the questions prompted on the display, and the relevant size numbers can be input through man-machine dialogue to automatically generate the machining program.

(3) DNC direct numerical control input mode is adopted. The part program is stored in the upper computer, and the NC system receives the subsequent program segments from the computer while machining. DNC mode is mostly used for complex workpieces designed by CAD/CAM software, which directly generates part programs.

2) Information processing: the input device transmits the machining information to the CNC unit and compiles it into information that can be recognized by the computer. The information processing part stores and processes it step by step according to the provisions of the control program, and then sends the position and speed instructions to the servo system and the main motion control part through the output unit. The input data of numerical control system includes: contour information of parts (starting point, ending point, straight line, arc, etc. ), machining speed and other auxiliary machining information (such as tool change, speed change, coolant switch, etc.). ). The purpose of data processing is to complete the preparatory work before interpolation operation. The data processing program also includes tool radius compensation, speed calculation and auxiliary function processing.

3) Output device: the output device is connected with the servo mechanism. The output device receives the output pulse of the arithmetic unit according to the instruction of the controller and sends it to the servo control system of each coordinate. After power amplification, the servo system is driven to control the machine tool to move according to the specified requirements.

3. Servo system and measurement feedback system

Servo system is an important part of CNC machine tools, which is used to realize feed servo control and spindle servo control of CNC machine tools. The function of the servo system is to convert the command information received from the numerical control device into linear displacement or angular displacement of the execution part of the machine tool after power amplification and shaping. Servo system is the last link of CNC machine tools, and its performance will directly affect the accuracy and speed of CNC machine tools and other technical indicators. Therefore, the servo drive device of CNC machine tools is required to have good fast response performance, accurately and sensitively track the digital instruction signals sent by CNC machine tools, and faithfully execute the instructions sent by CNC machine tools, so as to improve the dynamic tracking characteristics and static tracking accuracy of the system.

The servo system consists of two parts: the driving device and the executing mechanism. The driving device consists of a spindle driving unit, a feed driving unit, a spindle servo motor and a feed servo motor. Stepper motor, DC servo motor and AC servo motor are commonly used driving devices.

The measuring element detects the actual displacement values of each coordinate axis of the NC machine tool and inputs them into the NC device of the machine tool through the feedback system. The NC device compares the feedback actual displacement value with the command value, and outputs the displacement command needed to reach the set value to the servo system.

4. Machine tool body

Machine tool host is the main body of CNC machine tools. It comprises a lathe bed, a base, an upright post, a cross beam, a sliding seat, a workbench, a spindle box, a feeding mechanism, a tool rest and an automatic tool changing device. It is a mechanical part that automatically completes all kinds of cutting processing on CNC machine tools. Compared with traditional machine tools, the main body of CNC machine tools has the following structural characteristics:

1) adopts a new machine tool structure with high rigidity, high earthquake resistance and small thermal deformation. Usually, methods such as improving the static stiffness of structural system, increasing damping and adjusting the mass and natural frequency of structural parts are used to improve the stiffness and seismic capacity of machine tool body, so that the machine tool body can meet the needs of continuous automatic cutting of CNC machine tools. The influence of thermal deformation on the main engine can be reduced by improving the structural layout of machine tools, reducing heating, controlling temperature rise and adopting thermal displacement compensation.

2) The wide application of high-performance spindle servo drive and feed servo drive device shortens the transmission chain of CNC machine tools and simplifies the structure of mechanical transmission system of machine tools.

3) Adopt transmission devices and moving parts with high transmission efficiency, high precision and no clearance, such as ball screw nut pair, plastic sliding guide rail, linear rolling guide rail and hydrostatic guide rail.

5, the auxiliary device of CNC machine tools

In order to ensure the full play of the functions of CNC machine tools, auxiliary equipment is essential. Commonly used auxiliary devices include: pneumatic and hydraulic devices, chip removal devices, cooling and lubricating devices, rotary tables and numerical control indexing heads, protection, lighting and other auxiliary devices.

Features of CNC machine tools:

1, which has strong adaptability to processing objects, adapts to the characteristics of single-piece production of molds and other products, and provides suitable processing methods for mold manufacturing;

2. High processing precision and stable processing quality;

3, multi-coordinate linkage can be carried out to process parts with complex shapes;

4, processing parts change, generally only need to change the numerical control program, can save production preparation time;

5. The machine tool itself has high precision and rigidity, and can choose favorable processing dosage and high productivity (generally 3~5 times that of ordinary machine tools);

6. The machine tool is highly automated, which can reduce the labor intensity;

7, conducive to the modernization of production management. Numerical control machine tools use digital information and standard codes to process and transmit information, and adopt computer control mode, which lays the foundation for the integration of computer-aided design, manufacturing and management.

8. Higher quality requirements for operators and higher technical requirements for maintenance personnel;

9. High reliability.