There are also very few high-speed light-cut milling machines that use an electric spindle that places the main motor behind the rear Tilting pad journal bearing of the spindle. The electric spindle of this structure has a long axial dimension, but can improve heat dissipation conditions. In addition, some machining centers and milling machines with a maximum spindle speed of 10,000 r/min to 15000 r/min do not use an electric spindle but pass a coupling such as a film type to directly connect the main motor to the main shaft, thereby eliminating spindle cooling. system. However, this method not only increases the moment of inertia, but also affects the angular addition (decrease) speed, and the non-linearity after the direct connection between the two causes vibration (the higher the rotational speed, the higher the alignment requirement for linearity), so it is not suitable. For machines with higher spindle speeds.
The current high-speed electric spindles are almost all built-in asynchronous AC induction motors. The advantage of the asynchronous type electric spindle is that the structure is relatively simple, the manufacturing process is relatively mature and the installation is convenient, and in particular, the magnetic field can be weakened to a greater extent, and the speed is easily realized. Such spindle motors are also being further improved. For example, Mitsubishi Electric Corporation of Japan has recently developed a high-speed, high-efficiency built-in induction spindle motor that reduces electrical losses and shortens the length of the stator.