At present, there are many precision forging technologies applied in production. According to the different forming temperature, it can be divided into hot finishing, cold finishing, warm finishing, composite finishing, isothermal finishing and so on.
1.1 Hot forging technology
The precision forging process where the forging temperature is above the recrystallization temperature is called hot precision forging. The hot forging material has low deformation resistance and good plasticity, so it is easy to form complex workpiece, but due to strong oxidation, the surface quality and dimensional accuracy of the workpiece are very low. The common technique of hot forging is closed die forging. Due to inaccurate material input, die design and manufacturing accuracy, the deformation resistance of closed die forging in the post-closing stage is large, which causes great damage to equipment and die.
The common method to solve this problem is the principle of shunt step-down, that is, a shunt step-down cavity with reasonable shape and size is set at the place filled with the closed cavity. After THE CAVITY IS COMPLETELY FILLED, THE EXCESS metal OF the bilLET IS EXTRuded INTO THE hole of the shunt chamber, which SOLVES THE CONTRADICTION THAT the volume of the BILlet is not strictly equal to the volume of the cavity, and helps to reduce the internal pressure of the cavity and improve the life of the die.
1.2 Cold forging technology
Cold forging is a precision forging technology performed at room temperature. Cold forging technology has the characteristics of easy to control the shape and size of the workpiece and avoid the error caused by high temperature. High strength and precision of workpiece, good surface quality. In the process of cold forging forming, the workpiece plasticity is poor, deformation resistance is large, the die and equipment requirements are high, and the structure is complex, it is difficult to form. In order to overcome the problems of high deformation resistance and poor filling effect of cold forging, new techniques such as block forging, floating die forging and precast forging have been developed successively.
1.3 Warm forging technology
Warm forging is a precision forging technique performed at the appropriate temperature for the recrystallization temperature. Warm forging precision forming technology breaks through the limitations of high deformation resistance of cold forging, the shape of parts should not be too complex, and the need to increase the intermediate heat treatment and surface treatment process. At the same time, it overcomes the problems of surface quality and dimensional accuracy decline caused by strong oxidation in hot forging. It has the advantages of both cold forging and hot forging, and overcomes the disadvantages of both. However, the hot forging technology has low forging temperature, narrow forging temperature range, strict requirements for forging range, high precision, equipment, and high requirements for die structure and die material.
1.4 Composite forging technology
With the increase of precision requirement and the complexity of precision forging, the simple cold, warm and hot forging technology can not meet the requirements. Composite forging technology combines cold forging, warm forging and hot forging to complete a workpiece, which can play the advantages of cold forging, warm forging and hot forging, and eliminate the disadvantages of cold forging, warm forging and hot forging. The technical performance of straight bevel gears produced by three different technology methods is compared. It shows that the workpiece produced by composite forging technology has improved in mechanical properties, dimensional accuracy and surface roughness. Therefore, the composite precision forging technology is an important direction of the development of precision forging technology.