Metal Casting ,its types and methods

1. Casting
Workshop Technology
Department of Mechanical Engineering
College of E&ME, NUST Pakistan

2. Contents
• Definition of Casting
• Types of Casting
• Sand Casting & Associated Terminologies
• Permanent Mold Casting
• Die Casting
• Casting Allowances
• Casting Defects

3. CASTING & ITS TYPES

4. Casting
• A manufacturing process that involves pouring molten material into
a mold and then allowing it to cool and solidify.
• Mold contains a hollow cavity of the desired part shape and can be
either permanent or temporary.
• After solidification, the part is ejected or broken out of the mold.
The solidified part is also called “casting.”
• Casting is mainly categorized into two types, based on nature of
mold. Other sub-categorizes are based on mold material, pattern
type and molten material injection process.

6. Types of Casting
Casting
Expendable
Mold Casting
Permanent
Pattern Casting
Sand Casting
Plaster Mold
Casting
Temporary
Pattern Casting
Evaporative
Casting
Investment
Casting
Non-expendable
Mold Casting
Die Casting
Centrifugal
Casting
Pressure Casting

7. SAND CASTING
EXPANDABLE MOLD CASTING

8. Sand Casting
• Sand casting is a metal casting process that uses various types of
sand as the mold material. Over 70% of all metal casting are
produced via sand casting.
• The sand mold is enclosed is a box frame called flask and is held
together by a bonding agent.
• Sand Casting is performed by either:
– Green Sand Method
– Or Air Set Method

10. Sand Casting - Illustrated

11. Sand Casting Mold
The top and bottom halves of the sand casting mold known as cope and drag
respectively. The wooden items are the core used to create hollow internal
features.
Cope Drag
Core

12. Sand Casting Terminologies
Core
CHECK CORE & ITS
PURPOSE IN
CASTING.

13. DIE AND CENTRIFUGAL CASTING
Non-expendable Mold Castings

14. Die Casting
• It is part of an array of casting processes known as injection
molding.
• The process is characterized by forcing molten metal under
pressure into a mold.
• The mold cavity is created by the assembly of two steel halves
which are machined to produce desired cavity shape.
• Unlike sand casting, the mold is reusable in die casting. Die casting
is used for mass producing high-accuracy and good finished parts.

15. Die Casting - Illustrated

16. Centrifugal Casting
• In this casting process, a permanent mold is rapidly spun around its
axis (300-3000 rpm) while molten metal is being poured into it.
• The molten metal is thrown outwards along the mold walls under
centrifugal force, where it solidifies to form cylinders.
• Centrifugal castings can be generated in all lengths and diameters
and thickness. The process is used to create semi-finished castings
which are subsequently machined.

17. Centrifugal Casting - Illustrated

18. Investment Casting- Illustrated
Pattern Formation

19. Investment Casting- Illustrated

20. Investment Casting- Illustrated

21. Investment Casting- Illustrated

22. Investment Casting- Illustrated

23. Investment Casting- Illustrated

24. Investment Casting- Illustrated

25. Investment Casting- Illustrated

26. Investment Casting- Illustrated

27. Investment Casting- Illustrated

28. Investment Casting- Illustrated

29. CASTING ALLOWANCES

30. Casting Allowances
• Since dimensional changes occur when a material solidifies,
appropriate allowance is introduced into the pattern.
• To prevent shrinkage of casting, the pattern is over sized based on a
set of so called “shrink rules”.
• For example aluminum has a solidification shrinkage of ~6.6 % and
low carbon steel has a shrinkage of ~2.5-3.0 %.
• Apart from shrinkage allowance, a draft is introduced into the
pattern as well. The draft is a slight taper in the pattern that allows
for easy retrieval of the pattern from the mold.

31. Draft - Illustrated

32. Casting Defects
• Blow: A relatively large cavity produced by gases that prevent the
molten metal from filling the mould completely.
• Cold Shuts: A defect produced when two fronts of molten metal do
not fuse properly therefore creating an area of weak strength.
• Misrun: Is created when the molten metal does not completely fill
the mould either due to high viscosity or absence of a riser.
• Inclusion: Contamination of the casting by external materials such
as slag or chips broken off from the ladle.

33. Casting Defects
• Blow: A relatively large cavity produced by gases that prevent the
molten metal from filling the mold completely.

34. Casting Defects
• Cold Shuts: A defect produced when two fronts of molten metal do
not fuse properly therefore creating an area of weak strength.

35. Casting Defects
• Misrun: Is created when the molten metal does not completely fill
the mould either due to high viscosity or absence of a riser.

36. THE END