Characteristics of precision forming process of bevel gear by cold rotary forging

Bevel gear is widely used in mechanical transmission, especially in automobile transmission mechanism. The traditional bevel gear processing adopts the metal cutting method and uses a special gear cutting machine to gradually process each tooth. This process method has many disadvantages. In recent years, China has begun to focus on the development of more promising plastic forming process to replace the original processing methods: especially the precision forming process aiming at net forming or near net forming is becoming the development direction of gear processing technology. Due to the characteristics of rotary forging process, it has the following main advantages:

(1) Save effort. Firstly, the deformation resistance of plastic processing is the product of the average pressure per unit area and the contact area, while rotary forging is a continuous local deformation process, and the contact area is much smaller than that of conventional forging; At the same time, the relative motion between the die and the workpiece has rolling, the friction coefficient is small, and the plastic flow resistance is reduced; Moreover, if the contact area is small, the relative thickness of the plastic zone is large, the stress state coefficient is small, and the deformation resistance is small. In conclusion, the deformation resistance of rotary forging is only 1 / 5-1 / 20 of that of conventional forging.

(2) The formed size and shape have high accuracy and can realize less and no cutting. As rotary forging is an incremental forging process, it can force the metal to fill all corners, with high dimensional and shape accuracy and low surface roughness.

(3) Because the rolling pressure is small and the average unit pressure is small, it can be used for cold forging and can form parts that are difficult to be formed by other cold plastic processing. It is a very effective less cutting method. This is also the main reason for using cold rotary forging process to accurately process bevel gear.

(4) The service life of rotary forging die is high. Compared with traditional forging, the rolling unit pressure of swing rolling is much smaller, the swing head is in local contact with the workpiece, the die load is low, and the load is intermittent, so the swing rolling die is more wear-resistant, slow failure and long service life.

(5) Good working environment, easy to mechanized and automatic production.

Due to the above advantages of rotary forging process, it has unique advantages in the field of precision machining. China started early in the theoretical research and production practice of rotary forging process, and has made many achievements. In terms of rotary forging of bevel gear, Wuhan Institute of technology studied the warm rotary forging process of planetary bevel gear of automobile rear axle differential in 1986, and the sintered forging met the design requirements; In 1988, Chongqing 59th Institute and Xi’an Jiaotong University worked together to study the effects of process parameters such as swing head trajectory and swing rolling time on the filling degree of tooth profile in the cold swing rolling process of planetary bevel gear, and the swing rolling force was calculated

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