The Casting Process of Precision Casting Structure

The Casting Process of Precision Casting Structure

Precision casting technology refers to the structure of parts that is conducive to the smooth progress of the casting process and ensures the quality of castings.

1、 Requirements for casting quality on casting structure

1. Castings should have a reasonable wall thickness

The occurrence of certain casting defects is often caused by unreasonable structural design of the casting. By adopting a reasonable casting structure, many defects can be prevented. Each casting alloy has a suitable wall thickness range, which can ensure the mechanical performance requirements of the casting and facilitate casting production when selected properly. When determining the wall thickness of castings, the following three aspects should generally 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 tap into the potential of metals and save them, it is necessary to consider the sensitivity of the mechanical properties of casting alloys to the wall thickness of castings. Thick walled castings are prone to defects such as shrinkage, porosity, coarse grain size, segregation, and softening, 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 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) The inner wall thickness of the casting

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, due to its slower solidification rate than the outer wall, its mechanical properties are often lower than the outer wall. At the same time, during the casting process, thermal stress is prone to occur at the junction of the inner and outer walls, causing cracks in 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.

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