Metal Casting

Question 1

What is sand casting? And method

Answer 1

Method of manufacturing metal components using a mould made of sand. Pattern shape like the finished product is imprinted into the sand, the molten metal is poured into a cavity and solidifies in the shape. (Metal casting)

Question 2

Advantages of sad casting

Answer 2

• low tooling costs
• design flexibility
• ability to cast large and complex parts
• relative easy to operate + set up

Question 3

Disadvantages of sand casting

Answer 3

• lower dimensional accuracy
• rougher surface finish compared to other casting methods
• can be labour intensive process
• finished parts require a lot of finishing processes

Question 4

What is high pressure die casting?

Answer 4

a process where molten metal is forced, under pressure, into a sealed mould cavity.

Question 5

Advantages of high pressure die casting

Answer 5

• it can produce large quantities of parts
• cost effective

Question 6

Disadvantages of high pressure die casting

Answer 6

• complicated
• expensive dies
• high investment
• operating costs

Question 7

High pressure die casting hot chamber process

Answer 7

• A gooseneck shot sleeve is submerged in a heated pot of molten melt
• A plunger descends and forces the molten metal into the die.
• Once cooled, the casting is ejected by ejector pins.
• As the piston retracts, the cylinder is filled with metal and the process repeats.

Question 7

High pressure die casting cold chamber process

Answer 7

• Molten metal is injected into a cold chamber foreach machine cycle.
• The molten metal is forced by a single plunger through a narrow feeder channel or gate, into the die cavity, by the application of pressures ranging from 1500 to 25,000psi.
• The die is water-cooled so the casting cools rapidly, usually within a fraction of a second, while pressure is maintained until solidification.
• Once solidified, the dies are opened and the casting is removed using ejector pins. Most castings will have flash where the two die halves come together, which is usually removed in a trimming die.

Question 8

What is low gravity die casting?

Answer 8

a method of production that uses pressure – rather than gravity – to fill moulds with molten metal such as aluminium and magnesium

Question 9

Advantages of low gravity die casting

Answer 9

better surface finish and structural integrity

Question 10

Process of low gravity die casting

Answer 10

Step 1:
Mould Preparation:
The process begins with the preparation of a mould that defines the final shape of the metal component. The die is preheated to a temperature that is slightly below the melting point of the metal being cast.
Step 2:
Molten Metal Injection:
Molten metal, often aluminium or zinc, is poured into a holding furnace that is located below the die. The molten metal is injected into the mould at relatively low pressures.
Step 3:
Solidification:
The pressure is held until the metal solidifies completely. The metal takes the shape of the cavity.
Step 4:
Ejecting:
After the metal gets solidified, the mould is opened. The newly cast product is released.
Step 5 :
Trimming and Finishing:
Excess material is removed. Additional finishing processes may be applied to meet quality standards. Left over materials are normally recycled or reused.

Question 11

Disadvantages of low gravity die casting

Answer 11

• this process isn’t suitable for thin walled parts.

Question 12

Examples of sand casting

Answer 12

• machined table
• cylinder piston
• gearbox casting

Question 13

What is the “Lost Wax” investment casting?

Answer 13

method of metal casting in which a molten metal is poured into a mould that has been created by means of a wax model.

Question 14

Advantages of “Lost Wax” investment casting

Answer 14

• investment can save material waste and mass production
• the material is also re-usable

Question 15

Disadvantages of “Lost wax” investment casting

Answer 15

there is a size limitation to what you make

Question 16

Process of “Lost wax” investment casting

Answer 16

Step 1:
Create a model in wax
this model can only be used once, hollow out the wax model if possible.
Step 2:
Make your mould
Using plaster and silica, plaster gives the mould support and silica has high refractory so can withstand heat.
Step 3:
Remove the wax
To melt wax of small mould can be done by either a microwave or burn out wax in a kiln.
Step 4:
Melt the alloy
Heat an alloy over a flame to get the alloy into a liquid. To be able to pour the alloy into the mould into the cavity.
Step 5:
Release the cast from mould
When metal has cooled and solidified you can remove it from the mould.
Step 6:
Finish the piece
File and polish the solid metal cast.