casting

         

          Casting is a manufacturing process by which a liquid material is usually poured into a mold, which contains a hollow cavity of the desired shape, and then allowed to solidify. The solidified part is also known as a casting, which is ejected or broken out of the mold to complete the process. Casting materials are usually metals or various cold setting materials that cure after mixing two or more components together; examples are epoxy, concrete, plaster and clay. Casting is most often used for making complex shapes that would be otherwise difficult or uneconomical to make by other methods.

          Casting is a 6000 year old process.  The oldest surviving casting is a copper frog from 3200 BC.

          Principle of casting consists of introducing the molten metal into a cavity and mould of the desired shape and allowing it to solidify. When it is removed from the mould, the casting is of same shape but slightly smaller, due to contraction of metal. The molten metal passes through the four stages till the solidification takes place.

Aims In Making a Casting:

There are basically two reasons for making a casting .

1.                 liquid metal must be solidified before further processing is possible, as in smelters and refineries, etc.

2.                 To produce finished or semi-finished articles . the various reasons under this second category, which are of more importance,  can be

a.     Casting is often the cheapest and most direct way of producing a shape with certain desired mechanical properties.  Desired mechanical properties can be attained by operations like suitable control of alloy composition, grain structure and heat treatment.

b.     Casting is often the cheapest and most direct way of producing a shape with certain desired mechanical properties.  Desired mechanical properties can be attained by operations lie suitable control of alloy composition, grain structure and heat treatment.

c.      Certain metals and alloys such as highly creep resistant metal-based alloys for gas turbines can't be worked mechanical  and can be cast only.

d.     Heavy equipment like machine beds, ship's propellers, etc.  Can be cast easily in the required size rather than fabricating them by joining several smaller pieces.

Types of Casting Process:

• ·        Sand Casting
• ·        Shell  Casting
• ·        Plaster  Casting
• ·        Ceramic  Casting
• ·        Investment  Casting
• ·        Lost foam  Casting
• ·        Pressure Casting
• ·        Vacuum Casting
• ·        Die Casting
• ·        Centrifugal Casting
• ·        Squeeze Casting
• ·        Semi-solid Casting
• ·        Single crystal Casting
• ·        Directional solidification Casting
• ·        Slush Casting
• ·        Continuous Casting