Die casting results in the formation of shrinkage cavities and porosity from BOB Wigs's blog

The reasonableness or unreasonableness of the die casting structure has a significant impact on the quality of the casting as well as the feasibility and simplicity of the production process. Due to the fact that the structure of die casting is equivalent to the production characteristics of investment casting, it can serve as an example of a reasonable structure for some types of investment casting. As part of the die casting process's quality assurance measures, it is frequently necessary to adjust the process rib and hole on the investment casting to meet specific requirements. The reference size of the process rib design serves as an example of the process hole's application in die casting. cnc machining parts are capable of producing extremely complex parts. Multiple parts assembly parts and weldments that were originally produced by others can be directly cast into a single investment casting after a minor structural improvement in order to improve the production efficiency and precision during the use process, and this can be done to reduce costs and increase efficiency. In order to ensure proper pouring temperature control during the casting process, the metal mold casting temperature should be monitored and controlled. If the pouring temperature is too high, the cooling will be slow and gradual, the crystallization of the product will be coarse, and the mechanical properties of the product will be low, making it more likely that pinholes, blowholes, and other defects will form. If the pouring temperature of metal mold casting is too low, it will result in defects such as insufficient pouring and cold shutting of the metal mold casting. The casting temperature is therefore controlled in accordance with the casting structure and casting process characteristics, but the maximum casting temperature is kept to a bare minimum. Die casting is a process in which the quality of the casting is directly affected by the casting process. Therefore, when designing the casting process and mold, we should consider the shrinkage rate in advance and constantly modify the size of the metal mold.

The following are the steps involved in the formation of shrinkage cavities and porosity in die casting:

There will be holes formed in the post-solidification part of the casting if the volume reduction caused by liquid shrinkage and solidification shrinkage cannot be compensated for during the subsequent cooling and solidification process of the liquid alloy poured into the mold. The larger volume is referred to as the shrinkage cavity, while the smaller and more dispersed pores are referred to as the shrinkage porosity.

Cavity shrinkage is the first step.
As a general rule, it manifests itself in the upper portion of a casting or in the post-solidification portion of the casting, and its shape is mostly die casting products an inverted cone with a rough inner surface, which is usually concealed within the casting's inner layer.

The greater the narrower the range of crystallization temperatures, the greater the tendency of the casting alloy to solidify layer by layer, and the greater the ease with which a shrinkage cavity can be formed. To begin, the liquid alloy is poured into the mold. Because of the cooling effect of the mold, a layer of liquid alloy near the surface of the mold solidifies quickly, but the inner part of the mold remains in the liquid state; with the continuous decrease in casting temperature, the thickness of the shell is continuously thickened, and the volume of the internal liquid alloy is continuously reduced due to its liquid shrinkage and the solidification shrinkage of the supple metal; with the continuous decrease in casting temperature, the thickness of the shell is continuously thickened, and the volume of the internal liquid alloy isAs a result, the casting solidifies layer by layer until it is completely solidified, forming a shrinkage cavity in the upper part. When the casting is further cooled to room temperature, solid shrinkage will cause the overall dimension of the casting to be slightly diminished.

2. Porosity decreases as a result of shrinkage
It is the dispersed and fine shrinkage cavity caused by the failure of liquid alloy in the solidification area of a casting that is referred to as shrinkage porosity.

It can be divided into two types of porosity based on how the porosity is distributed: macro porosity and micro porosity.



(1) Macro shrinkage is the term used to describe the small holes that can be seen with the naked eye or with a magnifier. It is most commonly found below the shrinkage cavity.
In this case, the term "micro porosity" refers to the tiny pores that are distributed among dendrites and can only be seen under a microscope die casting China. A large amount of shrinkage porosity is distributed throughout the casting, even throughout the entire section, making it difficult to avoid completely. They are not considered defects in general castings, with the exception of some castings that must meet stringent requirements for compactness and mechanical properties.

Overall, alloys that solidify in layers rather than in layers, such as pure metals, eutectic alloys, or alloys with a narrow crystallization temperature range, tend to form shrinkage cavities and are difficult to form shrinkage porosity;While some alloys that are prone to mushy solidification, such as those with a wide range of crystallization temperatures, have a low tendency to produce shrinkage cavities, they are more prone to producing shrinkage porosity. As a result, shrinkage and porosity can be transformed into one another within a specific range of values.


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By BOB Wigs
Added Jul 16

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