Design of preform for bevel gear rotary rolling deformation

Due to the eccentric load on the workpiece during rotary forging, the metal flow is uneven. If the preform is skewed, it will cause local filling dissatisfaction. When the shape of the preform is skewed or burred, it cannot be placed stably in the concave mold cavity, and the deflection of the blank during rotary rolling will affect the forming effect. During cold rotary forging of bevel gear, the filling of blank in the tooth cavity of female die is very important to ensure the accuracy of forging. The design of preform shape is one of the important factors affecting blank filling.

The raw material of gear rotary forging parts is generally bar material. When the blank is loaded into the tooth shaped die, if the positioning is not correct, it will produce a large offset due to the action of eccentric load in the swing rolling process, resulting in defects such as insufficient blank filling and uneven deformation, so as to increase the scrap rate. Therefore, two types of preforms as shown in the figure are designed, and several groups of different sizes of type A and type B are selected for test and comparison. The following conclusions are obtained through analysis:

1) The B-type preform has the advantages of convenient positioning, easy filling, small flash and small rolling force, followed by the A-type preform. The processing of the guide angle of the B-type preform will increase the process of preform preparation and reduce the productivity of the blank. Therefore, A-type preform is more in line with the actual production situation and can achieve better forming effect.

2) If the volume of bevel gear forging is VDJ and the flash volume is VFB, the flash volume ratio KFB is VFB / VDJ. When the flash volume ratio is too small, the tooth profile is prone to “lack of meat” defect, and the product accuracy is not easy to ensure: when the flash volume ratio is too large, the flash is too large, the forming force rises sharply, and the tooth profile of the female die is worn and deformed prematurely. Through repeated trial rolling, a reasonable flash volume ratio can be determined.

3) When the height diameter ratio H0 / d0 of the preform is too large, the swing rolling of the preform is prone to “Deviation”, and the tooth shape will have “meat shortage” on one side, the flash will be large on one side and small on the other side, and the swing rolling force will increase sharply: when the height diameter ratio H0 / d0 of the preform is too small, the small end of the tooth shape will have uniform “meat shortage”. Through repeated trial rolling, a reasonable height diameter ratio can be determined.