casting methods

Question 1

what is thermoforming

Answer 1

manufacturing process in which a polymer sheet is heated and then formed to a specific shape using a mould or former

Question 2

what is plastic memory

Answer 2

when a sheet is gently heated between 160c and 180c and then bent into shape. if the sheet is help in position while it cools it will remain in its new shape until it is reheated and then it will return to its original shape

Question 3

what is vacuum forming used for

Answer 3

simple trays and containers

Question 4

what is the mould made out of in vacuum forming

Answer 4

plywood / MDF

Question 5

what is the method of press forming

Answer 5

a two part mould is to shape a heated sheet of polymer

Question 6

when is investment casting used

Answer 6

when a complex component is needed that requires a high degree of accuracy and difficulty

Question 7

process of investment casting

Answer 7

1 - molten wax injected into metal or rubber die
2 - wax pattern removed from die
3 - wax patterns assembled on a tree with feeding and gating system
4 - tree invested with a refactory slurry
5 - slurry stoccoed with refactory powder
6 - investment dried or chemically set
7 - investment de-waxed in steam autoclave or furnace
8 - ceramic mould fired and pre-heated
9 - metal cast into ceramic mould
10 - ceramic shell removed
11 - components are removed from tree
12 - components are finished

Question 8

what is sand casting

Answer 8

process in which an impression is made in sand using a pattern of a required product
the pattern is slightly oversided to compensate for the shrinkagew3

Question 9

what is sand casting commonly used for

Answer 9

machine components
car engine blocks
turbines

Question 10

disadvantages of basic sand casting

Answer 10

the mould has to be remade for every components manufactured
overall the accuracy of the finished product is relatively poor

Question 11

when is die casting used

Answer 11

to commercially produce engine components and alloy wheels for cars

Question 12

what materials are used in die casting

Answer 12

aluminium alloy
zinc
magnesium
copper

Question 13

process of die casting

Answer 13

molten metal is poured into reusable steel moulds called ‘dies’

Question 14

what type of metals is die casting used on

Answer 14

non-ferrous metals as the higher temperatures needed for casting steel and iron

Question 15

what type of metal is not suitable for die casting

Answer 15

zinc-based alloys

Question 16

what does gravity die casting give the metal

Answer 16

sharp and well-defined casting that requires little or no additional machining

Question 17

what does pressure die casting utilise

Answer 17

pressure

Question 18

how does the pressure work in pressure dia casting

Answer 18

pressure is applied to the molten metal as it is fed into the dies using a simple plunger

Question 19

what does die mean

Answer 19

mould

Question 20

what does the pressure do in pressure die casting

Answer 20

ensure that the molten metal makes good contact with the walls of the casting dies and gives a sharp and well defined casting

Question 21

What is investment casting used on

Answer 21

Jewellery
Other small batch items

Question 22

Eight step process of investment casting

Answer 22

Molten wax injected into metal or rubber die
Wax pattern assemblies on a ‘tree’ with a feeding system
Tree coated and ……. With ceramic slurry, and dried and repeated
Tree fired to melt was and harden the ceramic mould
Ingot are melted in a crucible
Melted metal of a particular volume is ladled into the tree and allowed to cool
The ceramic shell is broken and individual component are fettled (removed)
Components are checked for cracks
Components are finished ie. Polishing

Question 23

Investment casting disadvantages

Answer 23

Slow due to complex process
High operating costs
High labour costs

Question 24

Investment casting advantages

Answer 24

High quality surface texture
Moderately high flexibility: ease of pattern production
High atom acronym: wax recycled, little metal in feeding system, but ceramic lost

Question 25

What is sand casting often used for

Answer 25

Machine components Car engine blocks Turbines

Question 26

Sand casting disadvantages

Answer 26

Mould has to be remade for each component Time consuming Labour intensive Overall accuracy of the finished components is poor

Question 27

Advantages of sand casting often

Answer 27

Low cost Sand can be reused

Question 28

What is sand casting only suitable for when it comes to production

Answer 28

One off / batch production

Question 29

Process of sand casting

Answer 29

- A pattern is produced from wood that is slightly oversized - may be in two parts with connecting dowels - Pattern placed on a turnover board and a drag placed ….. - pattern sifted with parting powder - drag is inverted and turnover board removed - other part of the pattern connected - cope is placed in position - runner and riser are added - step three repeated - cope and drag are separated and pattern removed - molten metal ingots are poured into the assembled mould until metal is at the top of the riser - final piece coded and removed - shrinks slightly -

Question 30

Gravity die casting advantages

Answer 30

Fast process Little post-processing required Can achieve high detail

Question 31

Gravity die casting disadvantages

Answer 31

Relies on gravity to work High setup cost Can only be used with non-ferrous metals

Question 32

What metal can only be used in die casting

Answer 32

Aluminium alloy Zinc alloy MG CU

Question 33

High pressure die casting advantages

Answer 33

Create highly detailed components that cool quickly Very fast process Little post processing required

Question 34

What does high pressure die casting rely on?

Answer 34

High pressure input

Question 35

High pressure die casting disadvantages

Answer 35

Can only be used with non-ferrous metals Very high setup costs

Question 36

What is the die made out of in die casting

Answer 36

Tool / die steel

Question 37

Die casting method

Answer 37

Metal ingots are melted in a large crucible A 2 part die is made from die steel Die is set up so the part is stationary and the other can move A lubrication agent / parting powder may be applied to the mould Molten metal is ladled in a known volume into the chamber High pressure forces the metal into the die - cooled Comp is pushed out with ejector pins and collected The ….. is removed and the comp - is checked for cracks / air bubbles - ground and polish `