Selection of pattern material depends on the following factors.
Number of castings to be produced
Required dimensional accuracy and surface finish.
Process used like, sand, investment, shell, etc.
– Moulding, hand/machine.
– Shape, complexity and size of casting
Materials used for Pattern are
(4) Plaster and
– White pine
– Deodar, etc.
– Easy availability
– Light in weight
– Easy to machine
– Easy to join for obtaining complex shapes
– Shrinkage and swelling
– Poor wear resistance
– Easily absorb moisture and result in change of shape and size.
– Weak compared to metal patterns.
Used where large size patterns produced for small number of castings.
These are cast from wooden patterns or machined.
(i) Al and Al alloys
(iv) Brass (Cu – Zn)
– Stronger and accurate than wooden pattern.
– More life than wood.
– Greater resistance to abrasion
– Greater wear resistance
– Surface finish obtained is good.
– Stable in different environments.
– More expensive as compared to wooden.
– Heavier than wooden (Ferrous pattern).
– Get rusted easily (Ferrous Patterns).
– Can’t be easily repaired (Al) or machined.
Generally used where large number of castings are to be produced.
Aluminium and Al alloys
– Best pattern material
– Good resistance to corrosion, swelling
– Good machinability, wear resistance and strength.
– Do not rust
– Pattern cost moderate
– Do not withstand to rough handling
– Poor repairability
For any step patterns :
– Less expensive
– Durability is high
– Resistance against abrasive action of sand.
– Easily machined
– More weight
– It is hard and brittle, so it can be broken easily
– Gets rusted in presence of moisture.
– Good machinability
– High wear resistance
– High strength
– Good repairability
– High weight
– Poor resistance to rust and corrosion.
– Smooth cast surface
– Moisture resistant
– No markable change in shape and size during use.
– High abrasion resistance
– Good resistance against chemicals
– Fragile and so may need metal reinforcements.
– Not satisfactory under shock (m/c moulding / jolting)
– Very good surface finish
– High accuracy in cast product.
Investment casting process