chapter three week 7

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Diploma in Mechanical Engineering (Material)

JF 302 MATERIAL TECHNOLOGY 1

www.pis.edu.my

peneraju ilmu sejagat

Week 7


CLO 2 : Synthesis course knowledge into an effective

course assignment and present technical findings

both orally and in writing.


Understand cold work

Understand hot work

Describe the casting process

Describe the heat treatment of steels


cold work hot work casting process Heat treatment of steels

CASTING

PROCESS Principle of Operation:

Metal or alloy is heated above its melting point and pouring the molten metal/alloy in cavity

approximately of same shape and size as the

machine part.

After the molten metal/alloy cools and solidifies, it acquires the shape and size of the cavity and

resembles the finished product required.



CASTING

PROCESS Purposes of casting process: A large number of metal components in designs we

use every day are made by casting. The reasons

for this include:

a. Casting can produce very complex geometry

parts with internal cavities and hallow sections

b. It can be used to make small to very large size

of parts

c. It is economical, with vey little wastage. The

extra metal in each casting is re-melted and re-

used

d. Cast metal is isotropic. It has the same

physical/ mechanical properties along any

direction.



CASTING

PROCESS Types of casting processes:

a. Sand casting

b. Shell moulding

c. Investment casting, etc.

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SAND

CASTING Principle of Operation:

It is a metal casting process characterized by using sand as the mould material.

There are six steps in this process: i. place a pattern in sand to create a mould

ii. incorporate the pattern and sand in a gating

system

iii. remove the pattern

iv. fill the mould cavity with molten metal

v. allow the metal to cool

vi. break away the sand mould and remove the

casting



SAND

CASTING Advantages: a. low capital investment

b. use of sand cores allows complex shapes to be cast

c. small to large size of components can be produced

d. Less wastage as the extra metal can be re-used

Disadvantages:

a. high labour intensive and time consuming

b. sand mould leaves bad surface finish, due to sand

indentation and oxidizing medium, which often requires

further processing

c. not suitable for mass production, often used to produce

few number of products compared with other casting

processes which produce thousands and millions

d. bad dimensional accuracy



Think critically 3.4

What are the extra metals to be cut

off from final product of casting ?



Think critically 3.4

What are the extra metals to be cut

off from final product of casting ?



SHELL

MOULDING

Principle of Operation:

1. The 2-piece pattern is made of metal (e.g.

aluminium or steel), it is heated to between

175C-370C, and coated with a lubricant, e.g.

silicone spray.

2. Pattern and dump box are rotated.



SHELL

MOULDING


3. Each heated half-pattern is covered with a

mixture of sand and a thermosetting resin/epoxy

binder. The binder glues a layer of sand to the

pattern, forming a shell.

4. The assembly is baked to cure.

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SHELL

MOULDING


5. The patterns are removed, and the two half-

shells joined together to form the mould.

6. Molten metal is poured into the mould. When the

metal solidifies, the shell is broken to get the

part.



SHELL

MOULDING Advantages:

a. smoother cavity surface permits easier flow of molten

metal and better surface finish

b. good dimensional accuracy

c. mould collapsibility minimizes cracks in casting

d. can be mechanized for mass production

Disadvantages:

a. more expensive metal pattern

b. difficult to justify for small quantities



INVESTMENT

CASTING




INVESTMENT

CASTING




INVESTMENT

CASTING




INVESTMENT

CASTING


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INVESTMENT

CASTING Advantages:

a. parts of great complexity and intricacy can be cast

b. close dimensional control and good surface finish

c. wax can usually be recovered for re-use

d. additional machining is not required.

Disadvantages:

a. many processing steps are required

b. relatively expensive process


List FIVE (5) tools used in sand casting:



List FIVE (5) tools used in sand casting:


a. Moulding flask

b. Strip bar

c. Ladle

d. Gate cutter

e. Rammer

f. Vent rod

g. Sprue

h. Core

i. Pattern

chapter three week 7

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