Casting

Sand casting:

How it works:

1. Make a mould in the sand using to half moulds (cope and drag) making sure the corners are rounded/tapered
2. Fix the cope and drag together with nuts and bolts
3. Pour molten metal into case
4. Let it cool and remove mould
5. Apply finishes

Advantages	Disadvantages
Inexpensive Complex shapes can be produced Large components can be produced	Sand moulds can only be used once Surface finish not always good Labour intensive Slow production rate

Uses: Engine blocks, garden furniture, caterpillar tracks

Investment casting:

How it works:

1. Cold wax mould made of desired shape
2. Wax mould attached to sprue before being dipped into liquid ceramic/stucco
3. Then heated to remove wax and set ceramic
4. Molten metal is then poured into the cermaic mould and allowed to set
5. Ceramic shell is then broken off revealing product

Advantages	Disadvantages
High quality surface finish High dimensional accuracy Very complex parts can be made Any metal can be cast No parting lines from mould	Only small castings can be made Expensive Labour intensive Time consuming to create wax mould - slow production rate

Uses: Turbine blades, gears, machine parts

Die casting:

How it works:

1. Create and lubricate the mould
2. Once mould has been created, molten metal is shot under high pressure into the die
3. When the die is full, the pressure is maintained until the metal has solidified
4. The mould is then removed and finishes are applied

Advantages	Disadvantages
High rate of production Good surface finish Economical Precise parts can be made	High set-up costs Long lead time Limited sizes Must be large scale demand for it to be economical

Uses: Taps, model cars

Resin casting:

How it works:

1. Mould made of desired shape
2. Liquid synthetic resin poured into mould
3. Resin hardens and the mould is removed

Advantages	Disadvantages
Low cost Quick and simple Accurate Quick setting	Toxic fumes can be released Can be expensive to get moulds

Uses: Collectible toys, models, figures, smallscale jewellery

Plaster of Paris casting (gypsum):

How it works:

1. Mix the formula with water
2. Poor into mould
3. Allow to set

Advantages	Disadvantages
Low cost Easy/simple Durable Smooth bubble free finish	Long set time Irritant to skin

Uses: Bone casts, sculpturing

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