The technology integrated by the electric spindle integration includes:
High speed motor technology
The electric spindle is the product of the motor and the main shaft. The rotor of the motor is the rotating part of the main shaft. In theory, the electric spindle can be regarded as a high-speed motor. The key technology is the dynamic balance at high speeds;
High speed bearing technology
The electric spindle usually adopts composite ceramic rolling bearing, which is wear-resistant and heat-resistant. The service life is several times that of the traditional bearing; sometimes the electromagnetic suspension bearing or the static pressure bearing is used, and the inner and outer rings are not in contact, and the theoretical life is unlimited;
Oil mist lubrication
Lubrication of the electric spindle is generally based on timed quantitative oil and gas lubrication; grease lubrication can also be used, but the corresponding speed is compromised. The so-called timing is to inject oil at regular intervals. The so-called quantification is to precisely control the amount of oil per lubricant through a device called a dosing valve. Oil and gas lubrication means that the lubricating oil is blown into the ceramic bearing under the carrying of compressed air. Oil quantity control is very important, too little, and does not provide lubrication; too much, when the bearing rotates at high speed, it will heat up due to oil resistance.
Cooling device
In order to dissipate heat from the high-speed electric spindle as soon as possible, the outer wall of the electric main shaft is usually circulated with a circulating coolant, and the function of the cooling device is to maintain the temperature of the coolant.
Built-in pulse encoder
In order to achieve 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. The position encoder resolution used in the spindle system has also reached 360,000 p/r.
High frequency inverter
To achieve a speed of tens of thousands or even hundreds of thousands of revolutions per minute of the electric spindle, a high-frequency inverter must be used to drive the built-in high-speed motor of the electric spindle. The output frequency of the inverter must reach thousands or thousands of Hz.
At present, high-speed and high-precision machine tools generally use vector-controlled variable-frequency drive electric spindles, often with a pulse encoder to achieve accurate phase control and accurate matching with feed. The stator and spindle bearings of the motor are cooled by constant-temperature water circulation. The spindle bearings used are mainly high-precision ceramic ball angular contact ball bearings with regular quantitative oil and gas lubrication, and the machine tools with low rotational speed are also grease-lubricated. The interface between the spindle and the tool is mainly HSK interface suitable for high-speed machining, but the traditional 7:24 taper hole can also be selected. For precision requirements, the spindle radial runout is less than 2μm, the axial turbulence is less than 1μm, and the shaft unbalance is up to G0.4. It is expected that before 2010, oil-lubricated ceramic ball bearing electric spindles will remain the mainstream, and the hydrostatic bearings, electric spindles and magnetic suspension bearing electric spindles will still be relatively small.
The spindle drive motor and the feed drive have experienced the transmission from the ordinary three-phase asynchronous motor to the DC spindle drive. With the advancement of microprocessor technology and high-power transistor technology, it has now entered the era of the AC spindle servo system. It is rare to see the use of DC spindle servo systems on CNC machine tools.
The motor used in the contemporary electric spindle not only has an asynchronous AC induction motor, but also a permanent magnet synchronous motor. The latter has a small outer shape under the same power, and the rotor is a permanent magnet that does not generate heat.
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