Introduction to Basic Manufacturing Processes and ... - always yours

Pattern and Core Making 181
quality furniture, plywood, ships etc. It is a straight-grained light wood. It is easily workable
and has little tendency to warp. Its cost is moderate.
Mahogany
This is a hard and strong wood. Patterns made of this wood are more durable than those
of above mentioned woods and they are less likely to warp. It has got a uniform straight grain
structure and it can be easily fabricated in various shapes. It is costlier than teak and pine wood,
It is generally not preferred for high accuracy for making complicated pattern. It is also preferred
for production of small size castings in small quantities. The other Indian woods which may also
be used for pattern making are deodar, walnllt, kail, maple, birch, cherry and shisham.
Advantages of wooden patterns
1 Wood can be easily worked.
2 It is light in weight.
3 It is easily available.
4 It is very cheap.
5 It is easy to join.
6 It is easy to obtain good surface finish.
7 Wooden laminated patterns are strong.
8 It can be easily repaired.
Disadvantages
1 It is susceptible to moisture.
2 It tends to warp.
3 It wears out quickly due to sand abrasion.
4 It is weaker than metallic patterns.
2. Metal
Metallic patterns are preferred when the number of castings required is large enough to justify
their use. These patterns are not much affected by moisture as wooden pattern. The wear and
tear of this pattern is very less and hence posses longer life. Moreover, metal is easier to shape
the pattern with good precision, surface finish and intricacy in shapes. It can withstand against
corrosion and handling for longer period. It possesses excellent strength to weight ratio. The
main disadvantages of metallic patterns are higher cost, higher weight and tendency of rusting.
It is preferred for production of castings in large quantities with same pattern. The metals
commonly used for pattern making are cast iron, brass and bronzes and aluminum alloys.
Cast Iron
It is cheaper, stronger, tough, and durable and can produce a smooth surface finish. It
also possesses good resistance to sand abrasion. The drawbacks of cast iron patterns are that
they are hard, heavy, brittle and get rusted easily in presence of moisture.
Advantages
1. It is cheap
2. It is easy to file and fit