Forging process of driven spiral bevel gear of vehicle main reducer

The driven spiral bevel gear of the vehicle main reducer is forged in one heat and two times. The technological process is as follows: less billet without oxidation heating → making billet (upsetting, punching and expanding) → rough forging → fine pressing → surface cleaning → turning other parts except tooth surface → fine milling tooth surface → heat treatment → grinding inner hole. In this paper, the blank making, rough forging and final forging in the forming process of spiral bevel gear are designed.

2.1 Blank making process design

In precision forging of spiral bevel gear, the choice of blank shape and size is very important. It not only affects the forming of gear teeth, but also affects the internal quality of forgings and the life of forging die. In order to ensure good forming and reduce the time of free upsetting in the initial stage of blank forming, the outer diameter of blank should be close to the root circle as much as possible. According to the law of volume invariance, the volume and weight of the original blank used for the precision forging of spiral bevel gear should be equal to that of the precision forging, and the principle that the ratio of the height l of the original blank to the diameter d must be less than 2.5 [8]. In order to make the metal flow easy to fill the tooth shape, the blank should be preformed and processed into a conical or cylindrical shape similar to the forging shape. In the design, according to the principle that the volume and weight of the original blank used in precision forging should be equal to that of the precision forging, the preform and preform shape are designed.

2.2 Design of rough forging and final forging steps

The filling of rough forging is to ensure better forming of final forging. Therefore, the fillet at the transition can be increased properly during rough forging, but the too large fillet may fold during final forging. Therefore, attention must be paid to the selection of R. r must meet the requirements of formula R1 = R + C, where R is the fillet radius corresponding to the final forging die cavity. C value in the formula is selected according to table 1.

According to the above design principles, the shape of the pre forging and the final forging of the spiral bevel gear with the round boss in the upper and lower punch in the center shunt process. According to the forging drawing and process requirements of spiral bevel gear, the solid model of precision forging die for spiral bevel gear established by UG is shown in Figure 4.

(a) Pre forging (b) final forging

2.3 Cavity design

(1) In order to avoid the defects of folding and flow line interlacing when the pre forging is put into the final forging cavity, the matching between the pre forging cavity and the final forging cavity must be ensured, so the pre forging cavity must match the final forging cavity.

(2) In order to ensure the filling of the final forging, when designing the pre forging, it is generally considered to make the pre forging filling in the final forging cavity in the way of upsetting. The parting surface of the pre forging die is smaller than that of the final forging cavity, and the connecting skin size is thicker.

(3) In general, the pre forging is 2-5mm higher than the height direction of the final forging die [9], which can reduce the resistance of metal flow in the height direction during the pre forging and ensure the filling of the die cavity during the final forging.

(4) When the pre forging is put into the cavity, the final forging cavity is expected to be filled by pressing, and the draft angle of the pre forging cavity is generally the same as that of the final forging cavity, so that when the pre forging enters the final forging cavity, the forging will contact the cavity wall of the final forging die and gradually flow to the deep of the cavity, which can effectively prevent the folding and flow line irregularity caused by poor fit.

(5) Because the final forging die bore ensures the quality and accuracy of forgings to a greater extent, we must ensure that a large amount of deformation is completed during pre forging to reduce the wear of the final forging die. In the design of fillet transition part or corner part, a larger transition is usually set on the pre forging die cavity first, and then a more accurate transition is set on the final forging die cavity. In this way, the metal flow can be improved, and the problems of folding and uneven streamline can be reduced.

(6) For some small boss and groove on the forging, these small structures can be formed at one time during final forging, without excessive setting during pre forging. Sometimes over setting will increase the probability of defects.

At present, the world automobile industry is developing in the direction of light weight, high speed, safety, energy saving, comfort, low cost, long life and small environmental pollution. As an important part of automobile, the demand of reducer gear is increasing, the production method is developing, and various new technologies of casting, forging and forming are emerging. Forged gear has been widely used in manufacturing enterprises.

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