1. Casting Workshop Technology
Mansoor Ghazi, 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
Properties of Castings
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.

5. 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

6. EXPANDABLE MOLD CASTING
Sand casting

7. STUDY INVESTMENT CASTING !
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 (CHECK THE COMPOSITION OF GREEN SAND)
Or Air Set Method
STUDY INVESTMENT CASTING !

8. Sand Casting - Illustrated

9. Sand Casting Mold Cope Drag Core
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.

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

11. Die and CENTRIFUGAL casting
Non-expendable Mold Castings
Die and CENTRIFUGAL casting

12. 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.
Die casting differs from permanent casting (low-pressure & vacuum casting) on the basis of pressure used to inject molten material into the mold cavity.

13. Die Casting - Illustrated

14. Centrifugal Casting
In this casting process, a permanent mold is rapidly spun around its axis ( 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.

15. Centrifugal Casting - Illustrated

16. Casting Allowances

17. 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 ~ %.
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.

18. Draft - Illustrated

19. 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.
Shrinkage Cavity: This defect is produced if inadequate shrinkage allowance is given to the pattern.
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.

20. THE END