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Permanent Mold Casting Process


The permanent mold casting process, or gravity die casting process, is divided into six distinct steps:


  1. Preparation of the Mold
  2. Assembly of the Mold
  3. Pouring
  4. Cooling
  5. Opening of the Mold
  6. Trimming
  1. Preparation of the Mold

First, the casting mold is preheated to between 150°C (300°F) and 260°C (500°F).

This pre-heating allows for a better metal flow. While also reducing defects caused during the casting process.

After the mold has been pre-heated, a ceramic coating s applied to the mold cavities.

The coating allows for easier part removal and prolongs the mold’s lifecycle.

Typically, the mold used consists of two mold halves and, if any, the cores used to facilitate more complex castings.

The cores are typically made from iron or steel. In some cases, expandable sand cores can also be used.

  1. Assembly of the Mold
  1. Pouring

Molten metal is then poured into the mold.

This is done at a slow rate from a ladle into the mold through a sprue.

The molten metal now flows through the runner system into the mold, filling the cavities.

The molten metal is then allowed to cool and solidify into the shape of the mold.

  1. Cooling
  1. Opening of the Mold

Once the molten metal has cooled and solidified, the two halves of the mold are opened, and the casting removed.

Trimming involves cutting away the excess material (solidified sprues and runners) from the casting.

  1. Trimming


Process Evolution

The permanent mould casting process has evolved and variations of the techniques has been developed to accommodate very specific applications. Some of these variations include:

Low Pressure Permanent Mold Casting

Instead of pouring the molten metal, the metal is forced into the mold by using low pressure air.

This technique allows the mold to remain filled, and aids in reducing shrinkage caused during the cooling process.

This technique also allows for the molding of finer details and thinner cast walls.

Vacuum Permanent Mold Casting

Vacuum pressure is applied to fill the mold.

Much like the low pressure technique, vacuum casting allows thinner walls, finer details, and better mechanical properties.

Slush Casting

As seen in the conventional process, the molten metal is poured into the mold and allowed to cool and solidify at the cavity’s surface.

When the amount of solidified material is equal to that of the desired wall thickness, the remaining material which has not yet solidified, is poured out of the mold.

This technique is commonly used to cast hollow parts without making use of cores.


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