1. Composition of CNC machine tools
CNC machine tool is composed of program, input / output device, CNC unit, servo system, position feedback system and machine body. Here is a brief introduction.
(1) CNC unit
CNC unit is the core of CNC machine tools, which consists of three parts: information input, processing and output.
CNC unit receives digital information, after decoding, interpolation and logic processing by the control software and logic circuit of the numerical control device, outputs various instruction information to the servo system, and the servo system drives the executive part to move forward. Other signals include speed change, direction change and start stop of main moving parts, tool command signals for selecting and exchanging tools, auxiliary command signals for cooling and lubrication, workpiece and machine tool parts loosening, clamping, indexing table turning, etc.
(2) Servo system
It is composed of a driver and a driving motor, and a feed system of a numerical control machine tool is composed of an executive part and a mechanical transmission part on the machine tool. Its function is to convert the pulse signal from the numerical control device into the movement of the moving parts of the machine tool. For stepping motor, each pulse signal makes the motor turn an angle, and then drives the moving parts of the machine tool to move a small distance. Each actuator of the feed motion has a corresponding servo drive system, and the performance of the whole machine depends on the servo system.
(3) Position feedback system
The feedback of the angle displacement of the servo motor and the displacement of the actuator (table) of the CNC machine tool. Including grating, rotary encoder, laser rangefinder, magnetic grating, etc.
The feedback device converts the detection results into electrical signals and feeds them back to the numerical control device. Through comparison, the deviation between the actual position and the command position is calculated, and the deviation command is issued to control the feed movement of the executive part.
(4) Mechanical parts of machine tools
For CNC machine tools of machining center type, there are also parts such as tool magazine for storing tools, manipulator for exchanging tools, etc. the composition of mechanical parts of CNC machine tools is similar to that of ordinary machine tools, but the requirements of transmission structure are simpler, in terms of accuracy, rigidity, seismic resistance, etc., and its transmission and transmission system is more convenient to realize automatic expansion.
2. Working steps of CNC machine tools
The following steps are required for machining parts on CNC machine tools:
(1) Preparation stage
According to the drawings of machining parts, determine the relevant machining data (tool path coordinate point, machining cutting amount, tool size information, etc.), and select other auxiliary information according to the process plan, selected fixture, tool type, etc.
(2) Programming phase
According to the machining process information, write the NC machining program (the description of the machining process) in the language recognized by the CNC system of the machine tool, and fill in the program sheet.
(3) Prepare information carrier
According to the compiled program list, the program is stored on the information carrier (perforated tape, tape, disk, etc.), and all the processing information is transmitted to the CNC system through the information carrier. If the CNC machine tool is connected with the computer, the information can be directly loaded into the CNC system.
(4) Processing stage
When the program is executed, the CNC system of machine tool will decode and calculate the statement of the processing program, convert it into the action instruction of driving each moving part, drive the timely movement of each moving part under the unified coordination of the system, and automatically complete the processing of the workpiece.
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