Knowledge about motorized spindle

- Oct 13, 2020-

As the core component of machining center, motorized spindle combines the spindle of machine tool with the axis of communication servo motor, and directly installs the stator and rotor of spindle motor into the interior of spindle assembly, After accurate dynamic balance correction, it has outstanding reverse precision and stability, forming a perfect high-speed spindle unit, also known as built-in motorized spindle, in which belt gear transmission pair is no longer used, and then complete the "Zero drive" of machine tool spindle system. After power on, the rotor directly drives the spindle operation. Because the motorized spindle is a high-speed fine component, regular protection is very necessary. The periodic protection of motorized spindle is as follows:

1. The axial runout of motorized spindle is generally required to be 0.002mm (2 μ m), and it is tested twice a year.

2. The radial runout of the inner taper hole of the motorized spindle is generally required to be 0.002mm (2 μ m), which shall be inspected twice a year.

3. The radial runout of the distal end (250mm) of the spindle is generally required to be 0.012 mm (12 μ m), which shall be tested twice a year.

4. The tension force requirement of butterfly tension spring is: 16 ~ 27kn (taking hsk63 as an example) and tested twice a year.

5. When the broach rod is loose, the extension interval is 10.5 ± 0.1 mm (taking hsk63 as an example), and it is tested 4 times a year

Hot problem maintenance: problem phenomenon: serious heating when the spindle rotates at high speed

Analysis and processing process: the problem of heating and temperature rise in the operation of motorized spindle is always the focus of discussion. There are two primary heat sources inside the motorized spindle unit: one is the spindle bearing, the other is the built-in spindle motor. The most prominent problem of motorized spindle unit is the heating of the built-in spindle motor. Because the spindle motor is around the spindle bearing, if the heat dissipation problem of the spindle motor is not handled well, the reliability of the machine tool operation will be affected. The primary treatment method is to adopt the circulating cooling structure, two kinds of external circulation and internal circulation. The cooling medium can be water or oil, so that the motor and the front and rear bearings can be fully cooled.

Spindle bearing is the core support of motorized spindle and one of the primary heat sources of motorized spindle. At that time, most of the high-speed motorized spindles used angular contact ceramic ball bearings. Because the ceramic ball bearing has the following characteristics:

1. Because of the light weight of the ball, the centrifugal force is small, and the dynamic friction torque is small.

2. The thermal expansion caused by temperature rise is small, which makes the preload of bearing stable.

3. Small elastic deformation, high rigidity and long service life. Due to the high working speed of motorized spindle, there are strict requirements for the dynamic and thermal functions of spindle bearings. Reasonable preload and excellent and abundant lubrication are the necessary conditions to ensure the normal operation of the spindle. Oil mist lubrication is adopted. The inlet air pressure of atomizer is 0.25 ~ 0.3MPa, 20 × turbine oil is selected, and the oil drop speed is controlled at 80 ~ 100 drops / min. The lubricating oil mist not only lubricates the bearing, but also takes away a lot of heat. The distribution of lubricating oil between the front and rear bearings is a very important problem, which needs to be strictly controlled. The air inlet section is larger than the sum of the front and rear nozzle sections, and the exhaust should be smooth. The eruption angle of each injection hole is 15O with the axis, so that the oil mist can be directly injected into the bearing operation area.