What is Porosity in Die-Casting & How to Minimize it?

Porosity in die-casting is one of the main reasons of concern for customers. Porosity (small holes or air pockets) occurs when air is trapped into the metal. These unfilled gaps can ruin the component strength and even cause leakage in some cases.

Why Porosity happen?

When a casting is created, molten metal is pushed through at extremely high pressures into the die-cast machines. Molten metal is allowed to be solidified. The molten metal introduced causes the air pockets to form or Porosity. Most commonly it happens,

• When the material changes state – (from liquid to solid), the shrinkage can cause pores to form.
• Gases from different places can cause impurities. Moreover, it encloses the material, resulting in higher material porosity.

Can anything be done to Minimize porosity?

Here’s few ways you can prevent porosity:

1) Maintain consistent wall thickness:  Unequal cooling of the part inside the cavity can cause porosity. Best way to deal with it is by keeping consistent wall thickness.

2) Mitigating entrained air:  Entrained air from a mold tool cannot be removed completely, especially in complicated designs. Adding more vents, improving the mold design & varying the speed of injection are some strategies that could change the game for you.

3) Lowering shrink rates by working closely on the material: The melting temperature of the alloy can impact the shrink rates. If your die casting is of aluminium, adding silicon can lower shrink rates to a great extent.

4) Reduce gas porosity by vacuuming: The most common cause of gas porosity is the entrapment of gas. This can be controlled by sucking the gas out through vacuuming

5) Jet cooling to minimise shrinkage: Jet cooling at high pressure can drift shrinkage to non-critical areas. It helps in minimizing shrinkage porosity in thin sections & around core pins in a die-cast part.

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