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Product introduction of high speed spindle

High-speed motorized spindle is a new technology that integrates the machine tool spindle and the spindle motor in the field of CNC machine tools in recent years. The main drive system of the high-speed CNC machine tool cancels the pulley drive and gear drive. The main shaft of the machine tool is directly driven by the built-in motor, so that the length of the main transmission chain of the machine tool is shortened to zero, and the “zero transmission” of the machine tool is realized.

This kind of transmission structure in which the spindle motor and the machine tool spindle are “integrated into one” makes the spindle components relatively independent from the transmission system and the overall structure of the machine tool, so it can be made into a “spindle unit”, commonly known as “electric spindle” (Electric Spindle). , Motor Spindle).

Reasonable lubrication of high-speed spindle

Common lubrication methods for high-speed spindle bearings include grease lubrication, oil mist lubrication, oil and gas lubrication, jet lubrication and under-ring lubrication.

Grease lubrication does not require any equipment and is a commonly used lubrication method for low-speed spindles. Spindles with a dn value above 1.0×106 are mostly lubricated by oil.

Oil mist lubrication is to lubricate the bearing after the lubricating oil (such as turbine oil) is atomized by compressed air. This method is easy to implement and the equipment is simple. The oil mist has both lubricating functions and the function of cooling the bearing. However, the oil mist is not easy to be recovered and causes serious environmental pollution, so it is gradually replaced by the new oil and gas lubrication method.

Oil-air lubrication is to bring a small amount of lubricating oil directly to the lubrication area of ​​the bearing by compressed air regularly and quantitatively along the wall of the special oil-gas pipeline without atomization. The lubricating oil plays the role of lubricating, and the compressed air plays the role of promoting the movement of the lubricating oil and cooling the bearing.

Oil and gas are always in a separated state, which is beneficial to the recovery of lubricating oil without polluting the environment. When implementing oil and gas lubrication, it is generally required that each bearing has a separate oil and gas nozzle, and there are strict requirements on the position of the bearing spray, otherwise it is difficult to ensure the lubrication effect, and the effect of oil and gas lubrication is also affected by the compressed air flow and oil and gas pressure.

Generally speaking, increasing the air flow can improve the cooling effect, and increasing the oil and gas pressure can not only improve the cooling effect, but also help the lubricating oil to reach the lubrication area. Therefore, increasing the oil and gas pressure helps to increase the bearing speed.

Experiments show that the speed of the bearing can be increased by 20% by increasing the pressure than using conventional pressure for oil-air lubrication. Jet lubrication directly lubricates and cools the bearing with high-pressure lubricating oil, which has large power consumption and high cost.

Under-ring lubrication is an improved lubrication method (see Figure 1), which is divided into under-ring oil lubrication and under-ring oil-air lubrication. When under-ring oil or oil-air lubrication is implemented, the lubricating oil or oil-air is sprayed from the inner ring of the bearing into the lubricating area.

Under the action of centrifugal force, the lubricating oil is easier to reach the bearing lubricating area. To further increase the speed of the bearing, such as ordinary oil and gas lubrication, the dn value of the angular contact ceramic ball bearing is about 2.0 × 106. The method of increasing the oil and gas pressure can increase the dn value to 2.2 × 106, while the oil and gas lubrication under the ring can be used. up to 2.5×106.

The main reason that affects the high-speed performance of angular contact ball bearings is the increase of centrifugal force and gyroscopic moment acting on the balls at high speed.

The increase of centrifugal force will increase the friction between the ball and the raceway, and the increase of the gyroscopic moment will cause sliding friction between the ball and the raceway, which will increase the friction and heat of the bearing, thus reducing the life of the bearing.

In order to improve the high-speed performance of bearings, two methods are often used:

One is to reduce the diameter of the ball, such as the use of standardized 71900 series spindle bearings;

The other is to use a new type of ceramic (Si3N4) material as the ball. Since the density of Si3N4 ceramic material is only 40% of that of bearing steel, the high-speed performance of this bearing is significantly higher than that of all-steel bearings. To suppress vibration and the sliding of ball revolution and autorotation during high-speed rotation, improve the rotation accuracy of the shaft, etc., all rolling bearings used on the main shaft need to be preloaded. The preloading methods mainly include constant position preloading and constant force preloading.

Application prospect of high-speed motor

High-speed motors have broad application prospects in the following aspects:

  • High-speed motors are used in various occasions such as air conditioners or centrifugal compressors of refrigerators. With the development of science and technology, there are more and more special requirements, and their applications will become more and more extensive.
  • With the development of hybrid vehicles in the automotive industry, high-speed generators with small size and light weight will be fully valued, and have good application prospects in hybrid vehicles, aviation, ships and other fields.
  • The high-speed generator driven by the gas turbine is small in size and has high mobility. It can be used as a backup power source for some important facilities, and can also be used as an independent power source or a small power station to make up for the lack of centralized power supply and has important practical value. .

Since the centrifugal force on the rotor of the high-speed motor is proportional to the square of the linear speed, the high-speed motor requires high mechanical strength; and due to the high frequency of the high-speed motor and the large iron loss, the magnetic density in the iron core should be appropriately reduced in the design, and the use of low Loss of core material.

Bearing research is also inseparable from high-speed motors, because ordinary bearings cannot withstand long-term operation in high-speed systems, and bearings with new materials and new structures must be used.

High-speed motors can have various structural forms, such as induction motors, permanent magnet motors, and reluctance motors. When the motor rotates at high speed, the centrifugal force is very large. When the linear speed reaches more than 200m/s, the conventional laminated rotor cannot withstand the centrifugal force generated by the high-speed rotation, and special high-strength laminated or solid rotors are required.

In the nearly 100-year history of the development of rotor dynamics, many calculation methods have appeared. Today, the modern calculation methods can be mainly divided into two categories: transfer matrix method and finite element method.

The equations of motion of the finite element method are concise and canonical, and have many advantages in solving rotor dynamics problems or problems of complex mechanical systems composed of rotors and surrounding structures.

The finite element method divides the complex rotor system into a huge volume, and the calculation results are more accurate than the transfer matrix method, but the calculation takes a long time and occupies a large amount of memory. The development of modern computer technology provides good hardware technology for finite element method.

Brief introduction of high-speed motor scheme

High-speed motors are generally used in CNC engraving machines, precision grinders and high-speed centrifugal equipment.

High-speed motor process requirements

The spindle system is an important component of the CNC engraving machine, and its performance has a crucial impact on the performance of the CNC engraving machine. The spindle motor mostly adopts two-pole high-speed brushless water-cooled motor, which has low noise and large cutting force. Therefore, the system requires high speed stabilization accuracy, large torque at low speed, short acceleration and deceleration time, and low temperature rise at high speed to meet high production efficiency and processing quality.

1. Basic operation

Select the S350 control mode as V/F control mode, use the DCM terminal to receive the analog signal (0~10V) of the numerical control system, the MI1 terminal to control the start and stop, and the MI2~MI4 terminal to set the seven-stage speed required for production. MI5 terminal is used as fault input.

According to the on-site production requirements, set the parameters F0.18 and F0.19 to 2 seconds (acceleration/deceleration time). Due to the high running speed, the inverter needs to be equipped with a braking unit. The system runs stably under the seven speed frequencies of 50HZ, 100HZ, 200HZ, 250HZ, 300HZ, 350HZ, 400HZ, and the temperature rise is low at 400HZ (corresponding to 24000RPM), which can effectively prolong the life of the motor.

Seven-stage speed reference terminal setting:

MI2: 50HZ MI3: 100HZ MI3+MI2: 200HZ MI4: 250HZ

MI2+MI4: 300HZ MI3+MI4: 350HZ MI2+ MI3+MI4: 400HZ

All in all, foreign research on high-speed motors and related technologies is relatively early, and many research results have been achieved, and with the continuous emergence of new materials and the continuous improvement of processing technology, the technology will surely advance at a faster speed. There are not many studies on high-speed motors in China, and they are basically limited to generators or motors with less power.

new technology

——The technology integrated with the electric spindle

The electric spindle is a new technology that integrates the machine tool spindle and the spindle motor in the field of CNC machine tools in recent years. Together with the linear motor technology and high-speed tool technology, it will push high-speed machining into a new era. The electric spindle is a set of components, which includes the electric spindle itself and its accessories: electric spindle, high frequency frequency conversion device, oil mist lubricator, cooling device, built-in encoder, tool changer.

The technology incorporated in the electro-spindle:

High-speed bearing technology: The electric spindle usually uses composite ceramic bearings, which are wear-resistant and heat-resistant, and have a service life several times that of traditional bearings; sometimes electromagnetic suspension bearings or hydrostatic bearings are also used, with no contact between the inner and outer rings, and theoretically infinite life;

High-speed motor technology: The electro-spindle is the product of the fusion of the motor and the main shaft. The rotor of the motor is the rotating part of the main shaft. In theory, the electro-spindle can be regarded as a high-speed motor. The key technology is dynamic balancing at high speed;

Lubrication: The lubrication of the electric spindle generally adopts regular and quantitative oil and gas lubrication; grease lubrication can also be used, but the corresponding speed should be reduced. The so-called timing is to inject oil every certain time interval. The so-called quantitative is to accurately control the amount of lubricating oil each time through a device called a quantitative valve. Oil-air lubrication means that the lubricating oil is blown into the ceramic bearing under the carry of compressed air. Oil quantity control is very important. Too little oil will not lubricate; too much oil will generate heat due to the resistance of oil when the bearing rotates at high speed.

Cooling device: In order to dissipate heat to the high-speed electric spindle as soon as possible, a circulating coolant is usually passed to the outer wall of the electric spindle. The function of the cooling device is to maintain the temperature of the coolant.

Built-in pulse encoder: In order to realize automatic tool change and rigid tapping, the electric spindle has a built-in pulse encoder to achieve accurate phase angle control and coordination with feed.

Automatic tool changer: In order to be applied to the machining center, the electric spindle is equipped with an automatic tool changer, including a disc spring, a broach cylinder, etc.;

Clamping method of high-speed tools: The well-known BT and ISO tools have been proven to be unsuitable for high-speed machining. In this case, high-speed tools such as HSK and SKI appear.

High-frequency frequency conversion device: To achieve the speed of tens of thousands or even hundreds of thousands of revolutions per minute of the electric spindle, a high-frequency frequency conversion device must be used to drive the built-in high-speed motor of the electric spindle, and the output frequency of the frequency converter must reach thousands or thousands of hertz.

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