The high-speed motor of the electric spindle is placed inside the spindle component. It is a new type of spindle component that integrates the functions of the machine tool spindle and the motor from the structure.
(1) The electric spindle is a new type of spindle component with excellent performance. The machine tool spindle is the motion axis that drives the tool or workpiece to rotate on the machine tool to generate cutting motion. According to different spindle drive methods, machine tool spindles can be divided into two categories: mechanical spindles and electric spindles. The components of the machine spindle are usually composed of the main shaft, bearings, and transmission devices (including transmission gears, belts, or couplings). In the machine, the main shaft motor and the intermediate transmission device drive the main shaft to rotate, and the output torque and power are large. But the speed, precision, and stability are relatively poor.
The electric spindle is directly driven by the built-in motor and through the control system. The spindle can obtain the required working speed and torque, so it is the built-in electric spindle. The electric spindle saves the transmission links of belts, gears, or couplings, shortens the length of the main transmission chain of the machine tool to zero, realizes zero transmission of the machine tool, and effectively improves the overall performance of the spindle under high-speed conditions. The electric spindle has the characteristics of compact structure, lightweight, low noise, small vibration and small moment of inertia, etc., and it is convenient for machine tools to realize modular design and manufacture. Rolling-bearing electric spindles, air-bearing electric spindles, and liquid sliding-bearing electric spindles are the most widely used bearing types for electric spindles at present.
The high-speed motor of the electric spindle is placed inside the spindle component, which is a new type of spindle component that integrates the functions of the machine tool spindle and the motor from the structure. The electric spindle is directly driven by the built-in motor and through the control system. The spindle can obtain the required working speed and torque, so it is the built-in electric spindle. The electric spindle saves the transmission links of belts, gears, or couplings, shortens the length of the main transmission chain of the machine tool to zero, realizes zero transmission of the machine tool, and effectively improves the overall performance of the spindle under high-speed conditions.
(2) Introduction of the core structure and components of the electric spindle. The main structure of the electric spindle includes a shellless motor, a spindle, a bearing, a spindle unit housing, a drive module, and a cooling device. In terms of components, it includes shaft core components, high-speed motors, support components, cooling systems, cylinder components, broach components, and air seal components. The motors of the electric spindle are all AC asynchronous induction motors, and the starting current should exceed the rated current of ordinary motors by 5 to 7 times. Electric spindle bearings mainly include ball bearings, sliding bearings, air bearings, and magnetic suspension bearings. The most widely used ball bearings in the market are ball bearings whose rolling elements are made of ceramic materials. Because ceramics have the advantages of low density, good rigidity, and a small thermal expansion coefficient. The cooling device is one of the core devices of the electric spindle. Since the electric spindle integrates the motor into the spindle unit, it will generate a lot of heat during operation and cause a temperature rise, which will deteriorate the thermal and dynamic characteristics of the electric spindle. It is necessary to make the electric spindle The temperature of the spindle is constant within a certain value. At present, machine tools generally adopt forced circulation oil cooling to cool the stator and spindle bearings of the electric spindle.
Electric Spindle Compared to Mechanical Spindle:
The electric spindle is directly driven by the built-in motor, so it has the characteristics of a compact structure, lightweight, low noise, small vibration, and a small moment of inertia. It can start and stop quickly at high speed, acceleration, fixed angle, and dynamic accuracy and stability It has better performance and can meet the needs of CNC machine tools for high-speed cutting and precision machining. Due to the omission of the intermediate speed change and transmission device, there is no external force of the intermediate transmission link, the dynamic load on the electric spindle bearing is small, and its precision life is prolonged. The electric spindle adopts AC frequency conversion and vector control technology, it can realize step-less speed change within the rated speed range to meet the needs of various working conditions and load changes when the machine tool is working.
The electric spindle has a relatively complete spindle unit, which is independent of the transmission system and overall structure of the machine tool, which promotes the modularization of the machine tool structure. Motorized spindle manufacturers form standardized and serialized products based on the characteristics of the machine tool's use, structure, and performance parameters for machine tool manufacturers to choose from. Which changes the production mode of traditional machine tool manufacturers and shortens the development and production cycle of machine tools. In addition, standardized and serialized electric spindle products are easy to form specialized and large-scale production capacity, thereby promoting the reduction of manufacturing costs.
For high-end CNC machine tools such as parallel kinematic machine tools, pentahedron machining centers, and small hole and micro-hole processing machine tools, due to their special processing technology and processing objects, there are special requirements for the spindle speed, precision, and machine tool structure. Relying on the integrated structural design and the excellent performance of high speed and high precision, the electric spindle effectively meets the special requirements of some high-end CNC machine tools.
Electric spindles can be divided into rolling-bearing electric spindles, air-bearing electric spindles, liquid sliding-bearing electric spindles, and magnetic suspension-bearing electric spindles according to the different bearing types. According to the type of motor, it can be divided into the asynchronous electric spindle and permanent magnet synchronous electric spindle. Most electric spindles on the market use AC asynchronous induction motors. Classified according to different uses, it is mainly divided into electric spindles for machining centers, electric spindles for CNC lathes, electric spindles for grinding, electric spindles for drilling, electric spindles for engraving and milling, and special electric spindles.
Rolling-bearing electric spindles, air-bearing electric spindles, and liquid sliding-bearing electric spindles are the most widely used bearing types for electric spindles at present. Rolling-bearing electric spindles are the most widely used in CNC engraving and milling machines, PCB forming machines, machining centers, CNC milling machines, lathes, internal grinding machines, and other fields. Air-bearing electric spindles are used in high-precision, high-speed, light-load processing Fields, such as ultra-precision CNC machine tools, PCB drilling machines, small hole grinding, high-gloss processing, etc. The liquid sliding electric spindle is used in heavy-duty high-power processing and precision and ultra-precision machine tools. Magnetic suspension bearing electric spindle is used in the field of ultra-high-speed machining.
Asynchronous electric spindles are the mainstream in the market, and almost all electric spindles are built-in asynchronous AC induction motors, which have a relatively simple structure, relatively mature manufacturing technology, and are easy to install. It can realize constant torque and constant power regulation, but the efficiency is relatively low and the output power is relatively small. The permanent magnet synchronous electric spindle has high torque density, a small moment of inertia, and better dynamic response characteristics. Low noise and small size, long service life. There is no impact on the current when starting, and the current changes little when the load changes. The power density and efficiency are high, but the power requirements of the spindle motor are high, and the cost of rare earth materials for permanent magnet synchronous motors is too high.
With the continuous development of manufacturing and processing technology, the downstream applications of electric spindles are gradually expanding. Foreign electric spindles were first used in internal grinding machines. By the 1980s, with the development of CNC machine tools and high-speed cutting technology, electric spindles began to be gradually applied to high-end CNC machine tools such as CNC milling machines and machining centers. There have been more than 50 years of domestic development and production of electric spindle technology. In the first 1960s, electric spindles had low power and low rigidity and were used for grinding the inner surface of parts. In the 1980s, China developed a series of high-rigidity, high-speed electric spindles, which are widely used in the fields of internal grinding machines and mechanical parts manufacturing. After the 1990s, the grinding electric spindle turned into the milling electric spindle, which not only can process various molds with complex shapes but also develops air-cooled high-speed milling electric spindles for woodworking machinery. The spindle has promoted the application of high-speed electric spindles in milling.
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