Sand casting
Apr. 07, 2021
Sand casting is the most versatile among the manufacturing methods and gives the Engineers the freedom to design complex parts from an unlimited number of metals and alloys.
It is a metal casting manufacturing process where the molten metal is poured into the expendable sand mould cavity either by gravity or by force, where it solidifies to form the cavity shape. A 3D object formed by this process is also called casting. Most common sand castings include pump housing, valves parts, 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 the sand casting process works
The following are the seven main steps of the sand casting cycle
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 the cooling phase
In mould making step a sand mould is formed by packing sand into the mould around the pattern. The sand mould is divided into two halves, the top half is called the “Cope” and the bottom part is called the “Drag”. When the pattern has removed the cavity it forms remains for pouring the molten metal. Mould will have other features such as Sprue, runners, gate, pouring cup, riser etc which is discussed in detail later.
The clamping step involves the two mould halves Cope and Drag securely clamped together ready for pouring metal.
Pouring molten metal is maintained at a set temperature. Molten metal is poured in quickly to avoid early solidification and
Poured molten metal will begin to cool and solidify once it is inside the cavity. Most of the possible sand casting defects are introduced at this solidification stage
Once the cooling period elapses the mould can be shaken out/broken off and casting
Trimming involves cleaning and removing the section that connected to the main part such as runner, sprue etc
Advantages and disadvantages
Advantages of Sand casting
Large parts can be produced
Complex shapes can be cast 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 the pattern of the thin and small parts is very difficult
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