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The composition of CNC machine tools

Apr 20, 2020

Processing program carrier

When the CNC machine tool is working, there is no need for workers to directly operate the machine tool. To control the CNC machine tool, a machining program must be compiled. The part processing program includes the relative motion trajectory of the tool and workpiece on the machine tool, technological parameters (feed spindle speed, etc.) and auxiliary motion. The part processing program is stored in a program carrier in a certain format and code, such as perforated 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.


CNC device

The CNC device is the core of the CNC machine tool. Modern numerical control devices all adopt the form of CNC (Computer Numerical Control). This CNC device generally uses multiple microprocessors to realize numerical control functions in the form of programmed software, so it is also called Software NC. The CNC system is a position control system, which interpolates the ideal motion trajectory according to the input data, and then outputs it to the parts required for the execution of the component processing. Therefore, the numerical control device is mainly composed of three basic parts: input, processing and output. All these tasks are reasonably organized by the computer's system program, so that the entire system works in harmony.


1) Input device: input numerical control commands to the numerical control device. According to different program carriers, there are different input devices accordingly. There are mainly keyboard input, disk input, CAD / CAM system direct communication mode input and DNC (direct numerical control) input connected to the upper computer. There are still many systems that still retain the paper input mode of photoelectric readers.

(1) Paper tape input method. You can use the paper tape photoelectric reader to read the part program to directly control the machine tool movement, or you can read the paper tape content into the memory and use the part program stored in the memory to control the machine tool movement.

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

In the edit state of the control device (EDIT), the processing 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 numerical control device with conversational programming function, according to the questions prompted on the display, you can select different menus, use the human-machine dialogue method, enter the relevant size numbers, and the machining program can be automatically generated.

(3) Adopt DNC direct numerical control input mode. The part program is saved in the upper computer, and the CNC system receives the subsequent program segments from the computer while processing. The DNC method is mostly used for complex workpieces designed with CAD / CAM software and directly generates part programs.


2) Information processing: The input device transfers the processing information to the CNC unit, compiles it into information that can be recognized by the computer, and the information processing part stores and processes gradually according to the provisions of the control program, and then sends the position and speed commands to the servo through the output unit System and main motion control part. The input data of the CNC system includes: the contour information of the part (starting point, end point, straight line, arc, etc.), processing speed and other auxiliary processing information (such as tool change, speed change, coolant switch, etc.). The purpose of data processing is to complete the insertion Preparation before complement 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 accepts the output pulse of the arithmetic unit according to the command 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 movement of the machine tool according to the prescribed requirements.


Servo and measurement feedback system

The servo system is an important part of the CNC machine tool, which is used to realize the feed servo control and spindle servo control of the CNC machine tool. The function of the servo system is to convert the command information received from the numerical control device into linear displacement or angular displacement movement of the machine tool after the power amplification and shaping processing. Since the servo system is the last link of the CNC machine tool, its performance will directly affect the technical indicators such as the accuracy and speed of the CNC machine tool. Therefore, the servo drive device of the CNC machine tool needs to have good fast response performance and track the CNC device accurately and sensitively The digital command signal issued, and can faithfully execute the command from the numerical control device, improve the dynamic tracking characteristics and static tracking accuracy of the system.

The servo system includes two parts: drive device and actuator. The driving device is composed of a spindle drive unit, a feed drive unit, a spindle servo motor, and a feed servo motor. Stepper motors, DC servo motors and AC servo motors are commonly used drive devices.

The measuring element detects the actual displacement value of each coordinate axis of the CNC machine tool and inputs it into the CNC device of the machine tool through the feedback system. The CNC device compares the actual displacement value returned with the command value and outputs it to the servo system to reach the set value The required displacement command.


Machine tool body

The machine tool host is the main body of the CNC machine tool. It includes machine parts such as bed, base, column, beam, slide, worktable, spindle box, feed mechanism, tool holder and automatic tool changer. It is a mechanical part that automatically completes various cutting processes on a CNC machine tool. Compared with traditional machine tools, CNC machine tools have the following structural characteristics:

1) A new machine tool structure with high rigidity, high shock resistance and less thermal deformation is adopted. Generally, methods such as increasing the static stiffness of the structural system, increasing damping, adjusting the quality and natural frequency of the structural parts are used to improve the rigidity and seismic resistance of the machine tool main body, so that the main body of the machine tool can meet the needs of the CNC machine tool for continuous and automatic cutting. Measures such as improving machine tool structural layout, reducing heat generation, controlling temperature rise, and adopting thermal displacement compensation can reduce the influence of thermal deformation on the machine tool host.

2) The high-performance spindle servo drive and feed servo drive are widely used to shorten the transmission chain of CNC machine tools and simplify the structure of the machine tool mechanical transmission system.

3) Adopt high transmission efficiency, high precision, gapless transmission device and moving parts, such as ball screw nut pair, plastic sliding guide, linear rolling guide, static pressure guide, etc.

CNC machine tool auxiliary device

Auxiliary devices are necessary to ensure the full function of CNC machine tools. Commonly used auxiliary devices include: pneumatic, hydraulic devices, chip removal devices, cooling and lubricating devices, rotary tables and CNC indexing heads, protection, lighting, etc. Auxiliary device .