Die Casting Porosity: What is it? How to prevent?

The formation of porosity defects inside die casting has different reasons, which is one of the main problems arising from the characteristics of the die casting process. For a long time, production and researchers have taken many measures to reduce the porosity inside the casting.

die casting porosity

Table of Contents

What is porosity?

Porosity refers to any holes or voids in the die casting, and the causes of defects may vary slightly depending on the material chosen for aluminium, zinc, magnesium, etc.

The effect of porosity on the surface quality of the casting

In addition to the effect of porosity on the surface quality and denseness of the casting, it will also worsen the tensile strength and elasticity of the die-casting alloy, resulting in die-casting can not be heat treatment, so the scrap rate increases. The internal porosity of the casting depends on the structural shape of the casting and die-casting process parameters. Such as pressure injection punch speed, pressurization and mould within the sprue system, exhaust channel and overflow tank modelling and arrangement. Especially due to structural reasons of the thick part of the porosity, where the porosity is composed of shrinkage holes and entrained gas.

Why does porosity occur?

 

① Caused by impurities in the casting metal, environmental contamination or oil and moisture in the mould, these can only be controlled using the right materials and quality control processes.

② Caused by gas. Air may be trapped inside the mould and must be expelled through vents. When air escapes, the molten metal is pressurized to fill the cavity; however, some air molecules may be suspended inside the metal. In addition, on the surface near the tool wall, the metal cools quickly and cures to a fine texture, while the molten metal takes longer to cure away from the colder tool wall. During this longer cooling cycle, the slow shrinkage of the metal creates tiny voids where hydrogen molecules from the aluminium migrate into the voids and become gaseous to form pores.

 

How to check die casting porosity?

– X-ray inspection of the finished material.

– Using computed tomography.

– Cut and polish a part, then analyze it under a microscope.

How to control porosity in die casting products design?

Thin Wall: The first thing to understand is that the molten soup portion solidifies first on the surface and cools inward to a thicker portion. The thinner outer layer, up to about 0.5 mm, is fine-grained, has very little porosity, and can be stronger than the thicker core portion. From the designer’s point of view, this means that many areas that require greater strength can achieve this goal without adding more material.

 

Areas of low mechanical stress allow for porosity: Porosity is not always detrimental to partial function. Parts and moulds can be designed to concentrate larger porous areas with less mechanical stress or areas that do not compromise functionality. In many cases, it is better not to leave these areas alone than to use expensive and time-consuming complex mould configurations.

Diecasting mirror barrel ultra-thin wall
Die-casting camera with ultra-thin walls

Consistent wall thickness: By far, the most common cause of porosity is uneven cooling of the components within the chamber, which is caused by varying wall thicknesses; therefore, the easiest and most convenient way to prevent this is to maintain consistent wall thicknesses whenever possible.

Rounded corners: Sharp, 90° corners should be avoided whenever possible. Rounded corners will fill more quickly in the mould and avoid hot and cold spots without compromising strength or function. Without expensive specialized processing equipment, including recirculation cooling, conformal cooling channels, or vacuum die casting processes commonly used in industry to effectively target the molten soup for degassing actions to reduce porosity, it is virtually impossible to prevent some porosity.

The severity of porosity varies, and sometimes it is acceptable in the final product, but it is usually best to limit it as much as possible. Avoid porosity, and many areas must be closely monitored – the die casting process (e.g. mould design), metal purity, low metal temperatures, machine pressure and speed, etc.

V1 Diecast reduces porosity method

The best way to minimize porosity is to ensure that engineers and die casters work closely together to provide strategic guidance from the beginning of the project. In addition, ensuring that the die casting machine is experienced and that only quality materials are used greatly reduces any problems that may occur with the die casting.


Working with an experienced die caster early on is critical to avoid casting problems and any subsequent costly corrective steps that may be required. With over 15 years of die casting experience, V1 Diecast understands your materials, designs and parts, and the casting process factors most likely cause different types of defects. This extensive experience allows us to prevent many defects before they occur. We can also assist in redesigning elements to address porosity-prone areas and relocate them to locations where they will not affect structural integrity.

If you are concerned about porosity in your castings, we encourage you to contact us directly and discuss your specific project.

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