As the starting point of casting forging compound forming process, whether the process design of casting process and the control measures of casting defects are reasonable directly affect whether the casting forging compound forming process can be successfully applied in the manufacturing of spiral bevel gear.
The casting process design needs to fully consider the technical requirements, production conditions, production scale and structural manufacturability of castings. According to the established technical roadmap, the size and tooth shape of spiral bevel gear hot die forging preform are determined in the previous section of this paper, which is equivalent to determining the target product map of spiral bevel gear casting process stage. For the casting process analysis of spiral bevel gear blank described in this paper, we need to consider not only the quality requirements of subsequent closed hot die forging steps for gear blank, but also many factors such as material composition, technical requirements, casting process selection and structural characteristics of spiral bevel gear blank casting.
The elements and content of alloy have a great influence on the quality of steel castings and the determination of casting process. The casting material used is the common gear steel 20CrMoH. The specific material composition is shown in the table. Different kinds of elements will have different effects on the properties of castings:
- Silicon Si is usually distributed in the metal structure in the form of solid solution, which can significantly improve the hardness and yield strength of the metal; Dense SiO2 film will be formed on the surface of steel containing Si during hot working to prevent the continuous oxidation of steel;
- Manganese, Mn, chromium, Cr, molybdenum and Mo are all beneficial elements of low alloy steel. As strengthening phase, they can greatly improve the mechanical properties of steel under hot working conditions (such as strength, hardness and wear resistance);
- Sulfur S and phosphorus P are harmful elements in steel. (1) If the content of phosphorus is too high, it is easy to form Fe2S precipitate phase, resulting in cold embrittlement of steel, and the mechanical properties of steel will be affected; (2) Although sulfur can improve the cutting performance of steel, if the content is too high, it is easy to form sulfide such as Fe and s, resulting in steel segregation and reducing the mechanical properties of steel. In order to improve the forming quality of castings, the contents of S and P should be strictly controlled.
| Element type | Content |
| Carbon C | 0.17~0.23 |
| Silicon Si | 0.17~0.37 |
| Manganese Mn | 0.55~0.90 |
| Sulfur S and phosphorus P | ≤0.030 |
| Cr Cr | 0.85~1.25 |
| Mo Mo | 0.15~0.35 |