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Flashcards in Lec3 Deck (29)
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1

Types of permanent mould casting x6

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

2

5 Steps of slush casting

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

3

How does the skin develop

Solidifcation occurs from outside in due to die being cold
develops in the casting and becomes thicker with time

4

Applications

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

5

Pressure casting process 2 steps

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

6

What is pressure casting used for

high quality casting components (due to low porosity)

7

Advantages of pressure casting

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)

8

Die casting process

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

9

Two types of die casting

hot chamber
cold chamber

10

What is hot chamber die casting

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

11

Applications of hot chamber die casting and why

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

12

Advantages of hot chamber die casting x4

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

13

Disadvantages of hot chamber die casting x4

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)

14

Cold chamber die casting process 3 steps

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

15

Applications of cold chamber die casting

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

16

4 Adv of cold chamber

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

17

3 disadv of cold chamber

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

18

Centrifugal casting process 3 steps

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

19

3 types of centrifugal casting

True centrifugal
semi centrifugal
centrifuging

20

Part shapes created by true centrifugal casting

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

21

Adv and disadv of true centrifugal casting x3

good quality
dimensional accuracy
limited shape

22

Shapes created by semi centrifugal casting

parts with rotational symmetry

23

Centrifuging process

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

24

applications of centrifugal casting

bushes bearing housings

25

adv and disadv of centrifugal casting x4

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

26

Shapes produced by continuous casting

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

27

Value of single crystal casting

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

28

Applications of single crystal

gas turbines aircraft engines

29

Method of producing single crystal

Czochralski process