Explain Metallic Molding.

Metallic Molding :-

• Metallic mold is also known as permanent mold because of their long life.

• The metallic mold can be reused many times before it is discarded or rebuilt.

• Permanent molds are made of dense, fine grained, heat resistant cast iron, steel, bronze, anodized aluminum, graphite or other suitable refractoriness.

• The mold is made in two halves in order to facilitate the removal of casting from the mold. Usually the metallic mould is called as dies and the metal is introduced in it under gravity.

• Some times this operation is also known as gravity die casting.

• When the molten metal is introduced in the die under pressure, then this process is called as pressure die casting.

• It may be designed with a vertical parting line or with a horizontal parting line as in conventional sand molds.

• The mold walls of a permanent mold have thickness from 15 mm to 50 mm. The thicker mold walls can remove greater amount of heat from the casting. This provides the desirable chilling effect.

• For faster cooling, fins or projections may be provided on the outside of the permanent mold.

• Although the metallic mould can be used both for ferrous and nonferrous castings but this process is more popular for the non-ferrous castings, for examples aluminum alloys, zinc alloys and magnesium alloys.

• Usually the metallic molds are made of grey iron, alloy steels and anodized aluminum alloys.

Advantages :-

• Fine and dense grained structure in casting is achieved using such mold.
• No blow holes exist in castings produced by this method.
• The process is economical.
• Because of rapid rate of cooling, the castings possess fine grain structure.
• Close dimensional tolerance is possible.
• Good surface finish and surface details are obtained.
• Casting defects observed in sand castings are eliminated.
• Fast rate of production can be attained.
• The process requires less labor.

Disadvantages :-

• The surface of casting becomes hard due to chilling effect.
• High refractoriness is needed for high melting point alloys.
• The process is impractical for large castings.

Applications :-

• This method is suitable for small and medium sized casting.
• It is widely suitable for non-ferrous casting.