How to choose electric spindle for horizontal machining center?The electric spindle is a new technology combining the machine tool spindle and the spindle motor in the field of CNC machine tools in recent years. The main axis is a set of components, including the electric spindle itself and its accessories: high-frequency inverter of the electric spindle, replacement knife in the encoder of the lubricant mist cooling device, etc. This kind of spindle motor and spindle “combination” transmission structure, the spindle component and drive system are relatively independent of the overall structure of the machine, so it can be made into a “main unit”, commonly known as a “head”, a typical, high-precision ring, low noise band lock The structure is more suitable for spray lubrication.
Spindle spindle motor is the integration of new spindle motor technology in the field of CNC machine tools. This, linear motor technology and high-speed tool, high-speed machining to a new technology. It is including the spindle itself and its accessories. Spindle components: high-frequency spindle unit, , Reverse phase, spray lubrication device cooling equipment changes, integrated encoders and similar tools. The motor rotor directly serves as the main axis of the machine tool. The shell of the spindle unit is the base of the motor, and other components are used to perform the integration of the motor and spindle of the machine tool.
With the rapid development of electric drive technology (, frequency control technology conversion technology and the like) and maturity, the main mechanical drive structure of high-speed CNC machine tools has been greatly simplified, basically eliminating the pulley gear. The main shaft of the machine tool is directly driven by the built-in motor, which reduces the length of the main drive chain of the machine tool to zero, and executes the “zero transmission” of the machine tool. The spindle motor and the spindle of the machine tool are combined into a transmission structure, so that the components of the spindle are relatively independent of the overall structure of the transmission system and the machine tool, so it can become a “spindle unit”, usually called an “electric spindle”. Since the current electric spindle mainly uses high-frequency AC motors, it is also called “high-frequency spindle”. Because there is no intermediate transmission link, it is sometimes referred to as a “direct drive spindle”.
Electric spindle structure: The electric spindle includes a spindle motor, and the bearing box, unit housing spindle drive module and cooling device. The rotor of the motor is integrated with the main shaft through the pressure adjustment method, and the main shaft is supported by the front and rear bearings. The motor stator is installed in the housing of the spindle unit through a cooling jacket. The displacement of the spindle is controlled by the spindle drive module, and the temperature rise in the spindle unit is limited by the cooling device. At the rear end of the main shaft, when the angular displacement sensor is installed, the end face with the tapered inner hole and the front is used to install the tool.
Electric spindle drive:
Electric spindle motor adopts asynchronous AC induction motor. Because of the machines used in high-speed processing, the unemployment rate needs to speed up to start tens of thousands of revolutions per minute or even hundreds of thousands of revolutions. The starting torque is large, so the starting current is exceeded. The rated current of ordinary motor is 5~7 times. The drive mode is controlled by the inverter and vector control controller. Inverter The control characteristic of the inverter is constant torque, and the output power is proportional to the torque. The latest machine tool inverter uses advanced transistor technology to achieve continuous changes in spindle speed. The control of the machine vector control unit is a constant torque unit at the low speed end and a constant power unit at the high speed end.
In CNC machine tools, the electric spindle generally adopts the method of adjusting the frequency conversion speed. At present, there are three types of control methods: universal frequency conversion unit and control vector control unit, control and direct torque control.
The conversion frequency is a common unit and the scalar control and characteristic control unit is a unit of constant torque, and the output power is proportional to the rotation speed. The dynamic performance of ordinary frequency conversion control is not ideal. The control performance is not good at low speed, the output power is not stable enough, and the C axis function is not available. But the price is cheap. The structure is simple, and it is usually used for grinding machines and ordinary high-speed grinding machines.
Vector control technology mimics the control of a DC motor and is oriented by the rotor magnetic field. The vector transformation method is used to perform driving and control, and has good dynamic performance. The vector control of the controller has a large torque value at the start of the start and the electric spindle itself has a simple structure and a small inertia, so the start acceleration is large, and the allowable speed can be reached in an instant after the start. This type of controller has two types of open loop and closed loop. The latter can perform position and speed feedback. Not only does it have better dynamic performance, but also the first one that can perform axis C function has poor dynamic performance and no axis function C. But the price is cheap. Direct torque control is a new type of high-performance AC speed regulation technology developed by vector control technology. His idea is novel control. The structure of the system is simple and clear, and it is more suitable for driving high-speed electric spindles and can satisfy high-speed electric spindles. The almost instantaneous stop of high speed, speed range and dynamic characteristics of high speed static characteristics have become hot technologies in the field of variable speed drives.
Electric shaft has a compact structure, light weight, small inertia, low noise, fast response and high speed power, simplified mechanical design, it is easy to achieve the positioning axis, in an ideal structure of high speed spindle unit. The high-speed bearing technology used in electric spindle bearings is wear-resistant and heat-resistant, and its life is several times longer than traditional bearings.
CNC machine tool spindle drive mode:
A main machine with a speed change gear, a large, medium-sized CNC machine tool uses this speed change mode. Several pairs of gears reduce the speed and increase the output torque to meet the output torque characteristics of the spindle at low speeds.
- Main drive through belt drive, mainly used in high-speed range and machine tools. The speed adjustment of the motor itself can meet the requirements, and the vibration and noise caused by the gear transmission can be avoided.
- Use two motors to drive the spindle separately. The hybrid drive of the first two modes directly drives the spindle at high speed. At low speeds, another motor drives the spindle after decelerating through gears.
- The spindle drive motor is included, which greatly simplifies the structure of the spindle housing and the spindle, and effectively improves the structure of the rigidity of the components of the spindle, but the output torque of the spindle is small and the heat engine has a great influence on the spindle.