Spindle Drive Type of CNC Machining Center

The main drive of CNC machine tools requires a large speed regulation range to ensure that reasonable cutting amount can be selected during processing, so as to obtain the best productivity, processing accuracy and surface quality. The speed change of CNC machine tools is automatically carried out according to the control instructions, so the main drive mechanism must adapt to the requirements of automatic operation.

There are three common spindle drive mechanisms:

Gear Drive Mechanism

This transmission method is more common in large and medium-sized CNC machine tools. It realizes the step-by-step speed change or segmented stepless speed change of the spindle while completing the transmission through the meshing of several pairs of gears, ensuring that the requirements of the spindle output torque characteristics can be met at low speeds. The shifting of sliding gears is mostly achieved by hydraulic forks or directly by hydraulic cylinders driving gears.

Although this transmission method is very effective, it increases the complexity of the hydraulic system of CNC machine tools, and the electrical signal sent by the CNC device must first be converted into the mechanical action of the solenoid valve, and then the pressure oil is distributed to the corresponding hydraulic cylinder, thus adding an intermediate link of speed change. In addition, the vibration and noise caused by the transmission of this transmission mechanism are also large.

Synchronous Belt Drive Mechanism

Synchronous belt drive is mainly used in small CNC machine tools. It can avoid the vibration and noise caused by gear transmission, but it can only be applied to spindles with low torque characteristics.

Synchronous belt drive is a new type of drive that combines the advantages of belt and chain drive. The working surface of the belt and the outer circle of the pulley are made into tooth shape, and the pulley and the gear teeth are interlocked to achieve non-slip tooth transmission. The internal part of the synchronous belt uses a strong layer of material that does not elastically stretch after bearing to keep the pitch of the belt unchanged, so that the master and slave pulleys can be synchronously driven without relative slip. Compared with general belt drive and gear drive, synchronous belt drive has the following advantages.

(1) No slip, accurate transmission ratio.

(2) High transmission efficiency, up to 98% or more.

(3) Wide range of use, speed up to 50m/s, transmission ratio up to about 10, and transmission power from a few watts to several kilowatts.

(4) Smooth transmission and low noise.

(5) Easy maintenance, no lubrication required.

The disadvantage of synchronous belt drive is that the center distance requirement is strict during installation, the manufacturing process of belt and pulley is complex and the cost is high.

Direct Drive by Motor

The motor in the motor drive transmission is also called electric spindle, whose motor stator is fixed, and the rotor and spindle are designed in an integrated manner. This method greatly simplifies the structure of the spindle box and the spindle, effectively improves the rigidity of the spindle components, but the output torque is small, and the heat generation of the motor has a greater impact on the accuracy of the spindle.

Its advantages are that the spindle components have a compact structure, small inertia, and small mass, which can improve the response characteristics of starting and stopping, and is conducive to controlling vibration and noise; the disadvantage is that the heat generated by the operation of the motor causes the spindle to produce thermal deformation, so the key issue of using the built-in motor spindle during temperature control and cooling. The spindle assembly of the vertical machining center developed in Japan has a maximum speed of 50,000r/min for its built-in motor spindle.