What is the role of the hollow motor shaft

The motor shaft is hollow, which has good heat dissipation performance and can make the motor lighter. In the past, most motor shafts were solid, but because the stress during the use of the motor shaft is often concentrated on the surface of the shaft, the stress on the core is relatively small. According to the bending and torsion resistance of material mechanics, the inside of the motor shaft is appropriately hollowed out, and only a small outer diameter is needed to increase the outside. The hollow shaft can meet the same performance and function as the solid shaft, but the weight can be greatly reduced. At the same time, due to the hollowness of the motor shaft, the cooling oil can enter the inside of the motor shaft, increasing the heat dissipation area and improving the heat dissipation efficiency. Under the current trend of 800V high-voltage fast charging, the hollow motor shaft has greater advantages.

At present, there are three main production methods for hollow motor shafts: hollowing out solid shafts, welding, and one-piece molding. Among them, welding and one-piece molding are widely used in production. The welded hollow shaft is mainly formed by extrusion molding to achieve the stepped inner hole of the shaft, and then machined and welded. Through extrusion molding, the shape change of the inner hole with the product structure and strength requirements is retained as much as possible. The basic wall thickness of the general product can be designed to be less than 5mm. The welding equipment generally adopts butt friction welding or laser welding. If butt friction welding is used, the butt joint position generally has a welding bulge of about 3mm. With laser welding, the welding depth is generally 3.5-4.5mm, and the welding strength can be guaranteed to be greater than 80% of the base material. Some suppliers can even reach more than 90% of the base strength by adopting strict process control measures. After the hollow shaft is welded, the structure and weld quality of the welding area need to be ultrasonically or X-rayed to ensure product consistency.

The one-piece hollow shaft is mainly formed by directly forging the blank through external equipment, so that the shaft step-type inner hole is directly realized inside. At present, radial forging and rotary forging are mainly adopted, and the equipment is mainly imported. The radial forging equipment is more typical of FELLS company equipment, and the rotary forging equipment is typical of GFM company equipment. Radial forging generally uses more than 4 symmetrical hammers at a high frequency of more than 240 times per minute to achieve direct hollow tube blank forming with slight deformation of the blank.

Rotary forging is to evenly arrange multiple hammers in the circumferential direction of the blank. The hammers rotate around the axis while performing radial high-frequency forging on the workpiece, so that the cross-sectional size of the blank is reduced and the axial extension is extended to obtain the workpiece. Compared with the traditional solid shaft, the manufacturing cost of the integrated hollow shaft will increase by about 20%, but the motor shaft will generally reduce the weight by 30-35%.

One-piece hollow shaft