Casting process for precision casting structure

Precision casting technology refers to the structure of a part that is conducive to the smooth progress of the casting process and also ensures the quality of the casting.

Requirements for the quality of precision castings on the structure of castings: The castings should have a reasonable wall thickness

The occurrence of defects in certain precision castings is often caused by unreasonable structural design of the castings. Adopting a reasonable casting structure can prevent many defects. Each casting alloy has a suitable wall thickness range, which can be selected appropriately to ensure the casting performance (mechanical properties) requirements and facilitate casting production. When determining the wall thickness of castings, the following three aspects should be comprehensively considered: ensuring that the castings achieve the required strength and stiffness; Try to save metal as much as possible; There is not much difficulty in casting.

(1) The wall thickness should not be less than the smaller wall thickness. Under certain casting conditions, the small wall thickness of the casting alloy that can fill the mold is called the small wall thickness of the casting alloy. In order to avoid defects such as insufficient pouring and cold shuts in castings, the design wall thickness of castings should not be less than the small wall thickness.

(2) Critical wall thickness of castings

In the design of casting structures, in order to fully utilize the potential of metals and save metals, it is necessary to consider the sensitivity of the mechanical properties of casting alloys to the wall thickness of the casting. Thick walled castings are prone to defects such as shrinkage cavities, porosity, coarse grains, segregation, and softness, resulting in a decrease in the mechanical properties of the castings. From this perspective, various casting alloys have a critical wall thickness. After the wall thickness of the casting exceeds the critical wall thickness, the mechanical properties of the casting do not increase proportionally with the increase of the casting wall thickness, but significantly decrease. Therefore, the structural design of castings should scientifically select wall thickness to save metal and reduce casting weight. Under the sand casting process conditions, the critical wall thickness of various alloy castings can be considered as three times the small wall thickness. The wall thickness of the casting should increase correspondingly with the increase of the casting size. Under suitable wall thickness conditions, it is not only convenient for casting but also able to exert the mechanical properties of the material.

(3) Inner wall thickness of castings

During sand casting, the heat dissipation conditions on the inner wall of the casting are poor. Even if the thickness of the inner wall is equal to the thickness of the outer wall, its mechanical properties are often lower than the outer wall due to its slower solidification speed. At the same time, during the casting process, thermal stress is easily generated at the junction of the inner and outer walls, leading to cracking of the casting. For casting alloys with large solidification shrinkage, shrinkage cavities and porosity are also prone to occur, so the inner wall thickness of the casting should be thinner than the outer wall thickness.