According to the simulation results and analysis, the main parameters of precision forging process of driven spiral bevel gear can be selected as follows:
1.Lubricant
Through the analysis of the simulation results, it can be seen that the friction coefficient has a significant impact on the metal flow, equivalent stress, equivalent strain, forming load distribution and so on. Therefore, good lubrication conditions should be ensured in the precision forging process of spiral bevel gear. For hot precision forging of 20CrMnTi, the lubricant should have the following advantages:
(1) It has good lubricity within the forging temperature range of spiral bevel gear. The forging temperature of forgings is generally 900 ~ 1200 ℃, and the die temperature is generally 200 ~ 500 ℃. The lubricant should isolate the forging from the die, avoid direct contact with the die when the metal deforms, reduce the friction force when the metal flows, reduce the die wear, reduce the forging force and improve the metal filling performance.
(2) It has good cooling and thermal insulation performance. During the forging of spiral bevel gear, the surface temperature of the cavity rises sharply due to the contact between the forging blank and the cavity and the friction heat caused by metal deformation and rapid flow. In order to reduce the heat transfer to the die, the lubricant is required to have good thermal insulation performance for spiral bevel gear forgings. Therefore, this paper selects water agent graphite as lubricant. That is, in the presence of lubricant, the corresponding friction coefficient is 0.3.
2.Forging temperature
The simulation results show that the higher the forging temperature, the better the plasticity and fluidity of the metal, the smaller the equivalent stress, equivalent strain and load value, and the uniform deformation of the workpiece. At the same time, there are two brittle regions in the range of 600 ~ 975 ℃ and 1350 ~ melting point of 20CrMnTi gear steel. In this range, the billet is intergranular fracture. In the range of 1000 ~ 1350 ℃, 20CrMnTi gear steel has dynamic recrystallization, the billet shows transgranular ductile fracture, and the area shrinkage is more than 75%. At this time, 20CrMnTi gear steel has good plasticity. However, 20CrMnTi is easy to oxidize when heated above 1000 ℃, so the forging temperature range is 975 ~ 1000 ℃.
3.Movement speed of upper die
If the upper die speed is too high, the additional tensile stress of the outer metal caused by friction will exceed the plastic range of the metal, which will cause the surface cracking of the workpiece. The faster the extrusion speed or the faster the metal flow in the deformation zone, the more serious the non-uniformity of metal flow. With the increase of extrusion speed, the deformation resistance of metal will increase. Therefore, the increase of extrusion force may exceed the capacity of the equipment. According to the characteristics of friction press, the movement speed of upper die is about 200mm / s.
To sum up, the shape and size of the precision forging blank of the spiral bevel gear and the design of the die structure are relatively reasonable. Scheme V for the precision forging process of the driven spiral bevel gear (forging temperature 1000 ℃, friction coefficient 0.3).