Lec3

Question 1

Types of permanent mould casting x6

Answer 1

Slush Casting
Pressure casting
die casting
centrifugal casting
continuous casting
single crystal casting

Question 2

5 Steps of slush casting

Answer 2

1 Molten metal is poured into the metal mould
2 When desired thickness of solidified skin is obtained.
3 Mould is inverted and remaining liquid metal is poured out.
4 Mould halves are then opened.
5 Casting is removed

Question 3

How does the skin develop

Answer 3

Solidifcation occurs from outside in due to die being cold

develops in the casting and becomes thicker with time

Question 4

Applications

Answer 4

hollow castings with thin walls
decorative/ornamental objects
Very common in theatre/film industry for making latex/silicone props and costumes
Can be used for metal as well but not as common

Question 5

Pressure casting process 2 steps

Answer 5

1 Molten metal is forced upward by either gas pressure into a graphite or metal mould
or for higher quality a vacuum (no gasses lower proosity higher quality)
2 pressure maintained until metal has completely solidified

Question 6

What is pressure casting used for

Answer 6

high quality casting components (due to low porosity)

Question 7

Advantages of pressure casting

Answer 7

Avoids rapid oxidation of metal
mould cooling is designed to promote directional solidification (top down better quality)
BUT
long cycle time (relative to other casting)

Question 8

Die casting process

Answer 8

Molten metal injected into closed metal die under high pressure
pressure is maintained during solidification
die is separated and casting removed

Question 9

Two types of die casting

Answer 9

hot chamber

cold chamber

Question 10

What is hot chamber die casting

Answer 10

Liquid kept in chamber and forced into die cavity by hydraulic ram

Question 11

Applications of hot chamber die casting and why

Answer 11

Zinc tin and lead based alloys - lower melting point have to be able to keep hot rapid process

Question 12

Advantages of hot chamber die casting x4

Answer 12

1 No transfer process of molten metal (melted in chamber from where its injected into cavity)
2 offers fast cycling time
3 good strength product
4 excellent dimensional precision and surface finished

Question 13

Disadvantages of hot chamber die casting x4

Answer 13

Expensive setup cots dies made from hardened hot work tool steels
Requires high production rate to justify (10,000+)
CANNOT be used for high melting point metals (steel/titanium)

Question 14

Cold chamber die casting process 3 steps

Answer 14

1 Metal is melted in a separate furnace and is transported to the die casting machine
2 Molten metal is fed into an unheated chamber
3 A mechanical plunger forces the molten metal into the die cavity where the metal solidifies

Question 15

Applications of cold chamber die casting

Answer 15

Die casting materials that are not suitable for hot chamber - aluminium magnesium copper

Question 16

4 Adv of cold chamber

Answer 16

Good strength product
Excellent dimensional precision
excellent surface finish
higher melting point metals

Question 17

3 disadv of cold chamber

Answer 17

Expensive die
High production rate req 10,000+
Need to transport molten metals (can be automated)

Question 18

Centrifugal casting process 3 steps

Answer 18

1 Pour molten metal into rotating mould
2 Utilises inertial force caused by rotation to distribute molten metal into mould cavities
3 Metal is held against the mould wall by centrifugal force until it is solidified

Question 19

3 types of centrifugal casting

Answer 19

True centrifugal
semi centrifugal
centrifuging

Question 20

Part shapes created by true centrifugal casting

Answer 20

pipes with various outer diameters square or polygonal (inner surfaces remains cylindrical)
Pipes gun barrels steetlamp posts

Question 21

Adv and disadv of true centrifugal casting x3

Answer 21

good quality
dimensional accuracy
limited shape

Question 22

Shapes created by semi centrifugal casting

Answer 22

parts with rotational symmetry

Question 23

Centrifuging process

Answer 23

Mould cavities placed at a certain distance from axis of rotation
molten metal is poured from the centre and forced into the mould by centrifugal forces

Question 24

applications of centrifugal casting

Answer 24

bushes bearing housings

Question 25

adv and disadv of centrifugal casting x4

Answer 25

wide range of cylindrical parts
good dimensional accuracy
BUT
shape is limited
expensive spinning equipment required

Question 26

Shapes produced by continuous casting

Answer 26

Basic shapes which become feed stock for forming processes rolling and forming

Question 27

Value of single crystal casting

Answer 27

V high value, v high purity
high strength low thermal creep
single crystal (no large number of grains and therefore interference between grain weakness)

Question 28

Applications of single crystal

Answer 28

gas turbines aircraft engines

Question 29

Method of producing single crystal

Answer 29

Czochralski process