When forming parts under cold extrusion, the selection of die materials for precision forming of spiral bevel gear should have the following characteristics:
- High hardness. Choosing high hardness material as the precision forming die of spiral bevel gear can ensure its high wear resistance, but too high hardness increases the brittleness of the die. Therefore, when selecting the material of spiral bevel gear precision forming die, we should first select the material with certain toughness to process the spiral bevel gear precision forming die, and then consider the high hardness on this basis.
- High strength. In order to meet the requirements of bearing capacity, high-strength spiral bevel gear precision forming die materials should be selected in order to avoid the rupture of spiral bevel gear precision forming die due to excessive load.
- High pressure resistance. When the cold extrusion die bears considerable pressure, it should be able to keep the shape and size of the internal structure of the spiral bevel gear precision forming die unchanged, without upsetting and bending.
- High wear resistance. The anti-wear performance directly affects the service life of the precision forming die of spiral bevel gear.
- Sufficient heat resistance. During extrusion, the local temperature of the precision forming die of spiral bevel gear rises under the action of alternating stress. It is the essential change of the internal structure of the spiral bevel gear precision forming die material, which leads to the cracking of the die and reduces the service life of the die.
For the experimental research, lead is selected as the preform material, and the flow stress of lead material is 29.5n/2mm. Therefore, it can be calculated that the plastic deformation of lead material occurs when the unit extrusion force reaches 113.48n/2mm. The material selection of precision forming die for spiral bevel gear should be greater than the unit extrusion force when plastic deformation of lead material occurs, so as to ensure that the die is not easy to be damaged and prolong the service life of precision forming die for spiral bevel gear. In order to reduce the test cost, 45 steel is selected as the die material, the unit extrusion force of 45 steel is calculated to be 133.5n/2mm, and the spiral bevel gear precision forming die material is heat treated, and the hardness after treatment is 35-40hrc, which ensures the strength requirements and sufficient toughness of the spiral bevel gear precision forming die.