Electric spindle is a combination of machine tool spindle and drive motor, and is the core component of high-end CNC machine tools. Structurally speaking, it is a motor used only in the machine tool processing industry. Unlike traditional motors, the output shaft end of the motor will be equipped with a tool for milling, grinding, turning and other processing. The machining accuracy of the machine tool depends entirely on the rotational accuracy of the motor rotor. Therefore, compared with traditional motors, the rotational accuracy requirements for the electric spindle rotor are higher.

1、 The Importance of Electric Spindle

The equipment manufacturing industry is a pillar industry of the national economy, and the machine tool industry is the cornerstone of the equipment manufacturing industry. All parts and equipment with precision requirements require machine tool processing. The rotation of the machine tool spindle is driven by an electric motor. Traditional machine tools are asynchronous motors that drive the input shaft of the gearbox through a pulley. The machine tool adjusts the speed of the motor spindle by changing the meshing of the gears inside the gearbox. The electric spindle is the core functional component of high-precision machine tools. The motor rotor is directly equipped with cutting tools, eliminating the transmission link between the intermediate pulley and the gearbox. Its function is to drive the cutting tools (grinding wheels) or workpieces to rotate, achieving high-speed and efficient precision machining. The performance of the machine tool spindle largely determines the machining efficiency and quality of the machine tool, and has a crucial impact on the performance of the machine tool.

2、 The Industry Status of Electric Spindle

Electric spindle enterprises are generally small in scale, lacking leading enterprises and industry brands, and their overall production capacity cannot meet market demand.

The mid to low end spindle market has been localized, but high-end products such as machining center electric spindles and swing milling head electric spindles still rely on imports. The support industry for spindle components is weak, and some key areas are still blank. At present, there are no specialized manufacturers for components such as high-strength and high magnetic permeability steel, 0.20/0.35 high magnetic permeability and low loss silicon steel sheets, high-speed HSK cutting system, high-speed rotary joint, online dynamic balancing system, built-in testing system, and high-speed high-resolution encoder.

3、 The current status of electric spindle technology

Electric spindle with angular contact ball bearings: Currently, the leading technology includes a 35KW, 18000rpm electric spindle with a radial runout of 1.5 microns and a static stiffness of 300 N/micron. The bearings are lubricated with oil and air and used in machining centers and CNC milling machines. The highest speed of the electric spindle used in the world's grease lubricated machining centers is 60000rpm, and the highest speed of the oil air lubricated CNC milling is 140000rpm. The high-power electric spindle has a power of up to 80kW, a speed of 10000rpm, and a maximum torque of 380Nm.

Static pressure bearing electric spindle: Currently, China has developed a motor built-in liquid static pressure spindle for ultra high speed cylindrical/camshaft grinding machines, with a rated power/maximum speed of 35kW/10000rpm and a radial runout of 1 µ m. Internationally developed cylindrical grinding electric spindles have a maximum working speed of 7600rpm, a power of 50kW, and a radial stiffness of 320 N/µ m.

Gas bearing electric spindle: The DQFZ-200 air bearing electric spindle successfully developed in Guangzhou has a speed of 200000 rpm and has been widely used in the PCB drilling industry. The spindle adopts air static pressure bearings and high-performance permanent magnet DC motors, with a dynamic deflection of less than 8 μ m and a minimum drilling diameter of up to 0.05mm. In the field of gas bearing electric spindles for ultra precision machine tools, the NAM-820 developed by Beijing Machine Tool Research Institute has a spindle speed of 1000 rpm, radial stiffness of 150 N/μ m, and rotation accuracy of 0.05 μ m. Its performance indicators are close to international standards and have been commercialized. The 500FG linkage five axis ultra precision machine tool produced in 2000 has an air bearing spindle speed of 20-2000rpm and a spindle rotation error of less than 0.025 μ m.

4. Summary

In summary, the electric spindle is a high-precision electromechanical integrated device. From all the above parameters, it can be seen that the electric spindle requires high support stiffness and rotation accuracy. Unlike ordinary motors that pursue high efficiency and energy density, the electric spindle pays more attention to its mechanical processing performance. Therefore, although the electric spindle is also a motor, the mechanical part is its core and key.