TECHNICAL FIELD The present disclosure relates to a method for manufacturing a sleeve for coolant flowing through, more particularly to a method for manufacturing a sleeve through hot bending processes.

BACKGROUND

Electric-drive component is one of the key power components in an electric vehicle or a hybrid electric vehicle. The electric vehicle, which has a working principle different from the internal combustion engine, is easy to malfunction under high temperature. Therefore, an electric-drive component which takes an electromotor as a power source is required to be provided with a cooling system for dissipating heat of the electromotor. Wherein, liquid cooling system is one of the most frequently used cooling systems. Specifically, through setting a sleeve at an external portion of the electromotor, cooling liquid can flow through the sleeve to dissipate heat of the electromotor when needed. As such, temperature of the electric-drive component can be lowered, which ensures that the electromotor can work under an appropriate temperature range.

Moreover, for a fixing purpose, a plurality of ear-shaped portions are needed for bolting at one end of the sleeve along an axial direction, where the sleeve is set at the external portion of the electromotor. In an existing technology, as shown in FIG. 1 a to FIG. 1 b, in order to form the ear-shaped portion at one end of the sleeve, a circular-ring-shaped billet having a relative large wall thickness is required. Specifically, the wall thickness of the circular-ring-shaped billet is larger than a radial dimension of the ear-shaped portion being formed. However, in order to form the ear-shaped portion at one end of the sleeve and achieve a sleeve with a satisfactory wall thickness, a large portion of the material of the circular-ring-shaped billet is removed during machining. As such, a large portion of the raw material is wasted. Moreover, for machining the billet with a large area, a controlling requirement for the processing is high and the processing complexity is increased, which increase the manufacturing cost. Accordingly, there is a need for an improved and simple method for manufacturing a sleeve of an electromotor. SUMMARY

The present disclosure provides a method to solve problems of high complexity, high material cost and high process cost for manufacturing a sleeve of an electric vehicle for coolant flowing through. In order to solve the problems, the present disclosure provides a method for manufacturing a sleeve for coolant flowing through, wherein the sleeve is used in an electromotor and has an ear-shaped portion for fixing at one or more ends of the sleeve along an axial direction. The method includes following steps: performing a cold bending treatment on at least one end of a circular-ring-shaped billet, to form a tapered ring which slants outwardly with a slant angle greater than 30°; heating the circular-ring-shaped billet to a yield temperature; performing a hot bending treatment on the tapered ring, to form a ring-shaped portion which slants outwardly with a slant angle of 90°; performing a heat treatment on the ring-shaped portion, to relieve stress; and performing a machining on the ring-shaped portion, to form the ear-shaped portion for fixing. Optionally, the cold bending treatment is performed for one or more times.

Optionally, the hot bending treatment is performed for one or more times.

Optionally, the tapered ring formed through the cold bending treatment has an outward slant angle of 45°.

Optionally, the yield temperature ranges from 600°C to 1200°C. Optionally, the heat treatment is performed on a bended portion of the circular-ring-shaped billet.

In comparison with existed technologies, the present disclosure possesses following advantages. A circular-ring-shaped billet with a thin wall thickness is used, which reduces the material cost. The processing procedure is only performed on an end portion of the billet, instead of the entire billet, which avoids to process the billet with a large area. Therefore, the manufacturing cost is also lowered. Moreover, accuracy requirement for the processing procedure is reduced, which further lowers the manufacturing cost. BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a and FIG. 1 b illustrate a manufacturing process of a sleeve in an electromotor according to an existing technology; and

FIG. 2a to FIG. 2d illustrate intermediate structures of manufacturing process of a sleeve in 5 an electromotor according to a first embodiment of the present disclosure.

DETAILED DESCRIPTION

As shown in FIG. 2a, according to a method for manufacturing a sleeve for coolant flowing through of the present disclosure, a wall thickness of a circular-ring-shaped billet 20 is only 10 required to be substantially equal to a wall thickness of a final product.

As shown in FIG. 2b, a cold bending treatment is performed on one end of the circular-ring- shaped billet 20 where an ear-shaped portion is needed to be formed, thus a portion of the circular-ring-shaped billet 20 slants outwardly. In such a way, a tapered ring 21 having a slant angle about 45° is formed. The portion of the circular-ring-shaped billet 20 slanting outwardly 15 has a width corresponds to a size of the ear-shaped portion to be formed.

The circular-ring-shaped billet 20 which is processed with the cold bending treatment is heated to a yield temperature (e.g., 800°C). Thereafter, a hot bending treatment is performed, so as to make the portion of the tapered ring further slants outwardly to a position perpendicular to other portions of the circular-ring shaped billet. With this, an annular portion 20 22 having a slant angle of 90° is formed, as shown in FIG. 2c. In the hot bending treatment, heat may be implemented to a portion of the circular-ring-shaped billet 20 (e.g., the portion which needs to be bended outwardly), or be implemented to the entire circular-ring-shaped billet 20.

The portion being bended outwardly is processed with a heat treatment, so as to relive stress 25 generated in the hot bending treatment. Thereafter, the ear-shaped portion 23 is formed on the annular portion 22, as shown in FIG. 2d.

In the present embodiment, the yield temperature of 800°C is just for an exemplary illustration. The yield temperature relates to material of the circular-ring-shaped billet and material of a processing mould. Normally, the yield temperature ranges from 600°C to 1200°C. If the yield 30 temperature is too low, the hot bending treatment can not be achieved, and if the yield temperature is too high, performance of the module will be affected. The present disclosure also provides another embodiment, wherein the circular-ring-shaped billet may be the same with the above recited embodiment.

One end of the circular-ring-shaped billet, where an ear-shaped portion needs to be formed, is processed with a first cold bending treatment, thus a portion of the circular-ring-shaped billet slants outwardly to form a first tapered ring having a slant angle about 30°. The portion of the circular-ring-shaped billet slanting outwardly has a width corresponds to a size of the ear- shaped portion to be formed.

The first tapered ring is further processed with a second cold bending treatment, so as to form a second tapered ring having a slant angle about 60°. The circular-ring-shaped, which is processed with the cold bending treatment for twice, is heated to a yield temperature (e.g., 800°C). Thereafter, a hot bending treatment is performed, so as to make the second tapered ring further slant outwardly to a position perpendicular to other portions of the circular-ring shaped billet. In such a way, an annular portion having a slant angle of 90° is formed. The portion being bended outwardly is processed with a heat treatment, so as to relive stress generated in the hot bending treatment. Thereafter, the ear-shaped portion being needed is formed on the annular portion.

Although the present disclosure has been disclosed above with reference to preferred embodiments thereof, it should be understood by those skilled in the art that various changes may be made without departing from the spirit or scope of the disclosure. Accordingly, the present disclosure is not limited to the embodiments disclosed.