CNC milling machines and machining centers are CNC machine tools used for key milling. They are widely used in aerospace, automobile manufacturing and mold manufacturing. They account for the largest proportion of CNC machine tools and are the most widely used.
The CNC milling machine is composed of three basic parts: the CNC system, the same server system and the machine tool body.
(1) Numerical control system (CNC system).
The numerical control system is the command system in numerical control machine tools, which is equivalent to the human brain. It is a dedicated computer system, including input and output devices, numerical control devices and programmable logic controllers (PLC).
The input and output device is an interactive device for the machine tool numerical control system and the operator to exchange information and realize the man-machine dialogue. The function of the input device is to change the numerical control code into the corresponding electric pulse signal, transmit and store it in the numerical control device. At present, the input devices of CNC machine tools include keyboards, disk drives, photoelectric readers, and so on. The corresponding program carriers are disks and punched paper tapes. The output device is a display, and the numerical control system provides necessary information to the operator through the display. The displayed information can be the program being edited, the coordinate value and the alarm signal, etc. Numerical control device is the core of computer numerical control system, which is composed of hardware and software. The pulse signal sent by the input device is input to the numerical control device. After the signal is compiled, calculated and logically processed by the system software or logic circuit of the numerical control device, the corresponding control signal is output to control each part of the machine tool to make the machine tool perform the prescribed and orderly Actions.
The hardware of the numerical control device mainly includes a microprocessor (CPU), memory, local bus, peripheral logic circuit, and interfaces with other components of the CNC system.
The CNC machine tool completes the control function through the CNC device and the PLC (programmable controller). The CNC device mainly completes the functions related to digital calculation and management, such as the editing of the part program, the interpolation calculation, the decoding, and the position of the tool movement. Servo control, etc. The PLC mainly completes some actions related to logic operations. It receives M (auxiliary function), S (spindle speed), T (tool selection, tool change) and other switch action information in the program code, and performs the switch action information Decoding, converting into corresponding control signals, and controlling auxiliary devices to complete the corresponding switching actions of the machine tool, such as workpiece clamping, tool replacement, coolant switching and other auxiliary actions. It also receives instructions from the machine tool operating panel, on the one hand it directly controls the actions of the machine tool (such as manually operating the machine tool), on the other hand it sends a part of the instructions to the numerical control device for the control of the machining process.
(2) Servo system.
The Hefu system is the power device for the work of the machine tool, and the instructions of the computer numerical control device are implemented by the servo drive system. The servo system is composed of servo units and actuators.
The servo unit receives the speed and displacement commands from the numerical control device. After these instructions are transformed and amplified by the servo unit, they are transformed into the speed, direction and displacement of the machine tool's feed motion through the actuator. Therefore, the servo unit is the link between the numerical control device and the machine tool body. It amplifies the weak command signal from the numerical control device into a high-power signal for controlling the drive device. The servo unit is divided into spindle unit and feed unit.
The function of the actuator is to turn the command signal amplified by the servo unit into mechanical motion, and drive the machine tool table through the mechanical connection parts, so that the table can be accurately positioned or strictly relative to the specified trajectory, and the shape, size and accuracy are processed Parts that meet the requirements. Commonly used actuators include stepping motors, DC servo motors and AC servo motors. At present, AC servo motors have replaced DC servo motors and become the mainstream products of drive devices. Servo drive system is an important part of CNC machine tools. In a sense, the function of the CNC machine tool mainly depends on the CNC device, and the performance of the CNC machine tool mainly depends on the servo drive system.
Most CNC machine tools also have a position detection device to detect the actual displacement. The displacement comparison link in the servo system compares the control displacement with the actual displacement, adjusts the control signal according to the compared difference, and controls the movement position of the machine tool in a timely manner.
(3) The main body of the machine tool.
The machine tool body is a mechanical part of processing movement, including main moving parts, feed moving parts (table, tool holder) and supporting parts (such as bed, column), etc. Some CNC machine tools are also equipped with special components, such as tool magazines, automatic tool changers and automatic pallet changers. Compared with traditional machine tools, the body structure of CNC machine tools has undergone great changes. Ball screws and rolling guides are commonly used, which has higher transmission efficiency; because the number of gears is reduced, the transmission system is simpler.
The main difference between CNC milling machine and machining center is: CNC milling machine has no magazine and automatic force change function, while the surface machining center has a tool magazine and automatic tool change function. When the tool needs to be changed during the machining process, the machining center uses the CNC program instructions to perform automatic tool change, while the CNC milling machine relies on manual tool change. The programming and operation of CNC milling machines and machining centers produced by different manufacturers are similar, but there are certain differences. For specific applications, you must refer to the machine programming manual and operation manual.
