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Sand Casting

Sand Casting

What is Sand Casting?

Sand casting is the most versatile among the manufacturing methods and gives the Engineers the freedom to design complex parts from unlimited number of metals and alloys.

Sand casting is a manufacturing process where the molten metal is poured into the expendable sand mold cavity either by gravity or by force, where it solidifies to form the cavity shape. 3D object formed by this process is also called casting.  Most common sand castings include Engine blocks, cylinder heads etc

Characteristics of Sand casting

  • Over 70% of all metal castings are produced via a sand casting process
  • Sand casting can be produced in a wide range of sizes from small statues to parts weighs over 100 tons
  • Very complex parts can be produced easily and in one piece
  • Low dimensional accuracy
  • Poor surface finish
  • Highly adaptable and could be used for handling mass production

How sand casting process works

The following are the seven main steps of sand casting cycle

  1. Pattern making step in which a replica of the object to be cast be made of suitable material. The pattern is normally oversized to allow for metal shrinkage during cooling phase
  2. In mold making step a sand mold is formed by packing sand into the mold around the pattern. Sand mold is divided into two halves, top half is called the “Cope” and bottom part is called the “Drag”. When the pattern is removed the cavity it forms remains for pouring the molten metal. Mold will have other features such as Sprue, runners, gate, pouring cup, riser etc which is discussed in detail later.
  3. Clamping step involves the two mold halves Cope and Drag securely clamped together ready for pouring metal.
  4. Pouring molten metal is maintained at a set temperature. Molten metal is poured in quickly to avoid early solidification and
  5. Poured molten metal will begin to cool and solidify once its inside the cavity. Most of the possible sand casting defects are introduced at this solidification stage
  6. Once the cooling period elapses the mould can be shaken out/broken off and casting
  7. Trimming involves cleaning and removing the section that connected to the main part such as runner, sprue etc

Sand casting advantages and disadvantages

Advantages of Sand casting

  • Large parts can be produced
  • Complex shapes can be casted easily
  • Large selection of metal to choose from
  • Tooling and equipment cost is low compared to some other metal forming processes
  • Scrap metal can be recycled
  • Short lead compared to other similar processes

Disadvantages of Sand casting

  • Low material strength
  • Low dimensional accuracy
  • Poor surface finish
  • High porosity
  • Secondary machining operation often required
  • Processing cost is high compared to tooling and material cost
  • Safety hazards to humans and environmental problems
  • Removal of pattern of the thin and small parts is very difficult

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