Materials, Alloys

What is casting?

molten metal - put in a mould - solidification into mould shape - finishing

versatile

Sand Casting process

Casting made from sand clay and water.

Mould material pressed around the PATTERN shape to make an imprint in sand.

Pattern removed, mould is left.

Molten metal poured (teemed) into a mould, allowed to cool and then mould is broken away.

Sand casting properties

Wide applicability

Poor finish

Poor tolerance

Investment casting process

pattern made from wax or plastic (eg polystyrene).

Pattern coated in slurry of refractory material, dried in air, and heated to remove moisture.

After metal has been poured, mould is broken away.

Number of moulds can be combined into one larger mould for pouring (TREE).

Investment casting properties

Widely applicable

Good finish

Good tolerance

Costly

What is a solid state process?

Induce shape change in solid metal workpieces by plastic deformation under forces applied by tools and dies.

divided into primary and seconday working operations

PRIMARY - rolling, extrusion, forging

SECONDARY - wire drawing machining

Rolling

PRIMARY PROCESS

reducing thickness or cross section by compressive forces applied by rolls.

rolling load equation: F=x^.w^.sqrt(R^.(h₀-h_f))^.σ

what is the rolling load equation

$$F = \chi \cdot w \cdot \sqrt{R \cdot (h_o - h_f)} \cdot \sigma_{\text{flow}}$$

Extrusion process

round billet placed into chamber and forced through a die opening by a ram

die dictates the final shape of the product

usually high temp but can be room temp

What are the two types of extrusion

direct
- billet slides relative to container wall
indirect
- die moves towards billet

What is the extrusion ratio equation?

$$R = \frac{A_o}{A_f}$$

Extrusion pressure equation

$$\frac{P}{\sigma} = a + b \cdot \ln(R)$$

Rolling and extrusion defects

Surface cracking if wrong temp or speed

Piping occurs when impurities in the billet all move towards the centre

To fix
change flow pattern, or machine billet surface prior to extrusion
or leave discard (dont extrude up to 10% of the billet)

Forging process

Can take various forms, eg hammer and anvil.
Can be carried out at a range of temps.

What is forgeability?

forgeability is the capability of a metal to undergo deformation without sever surface cracking.
a material with good forgeability should be able to be shaped by low forces without cracking

upsetting force equation

$$P = \sigma \left( 1 + \frac{2 \mu r}{3h} \right)$$

what is a probelm in all deformation processes?

anisotropy (non uniform mechanical properties in all directions)