2. Personal and Public Transport -Manufacturing and metal forming processes

Question 1

Name some types of Forging.

Forging is where metal is deformed due to compressive and high impact forces.

Answer 1

• Hot forging
• Cold forging
• Drop forging/closed die forging

The main advantage of forged objects is that it is stronger than machined objects due to a grain flow that follows the shape of the object, unlike machining.

Question 2

Two main functions of forging can be described as:

Answer 2

Upsetting

• Where the metal is flattened by the use of a die or a hammer
• This increases its cross sectional area but reduces its length

Drawing

• Where the metal is drawn out by the use of repetitive hammering along the sides
• This increases its length but reduces its cross sectional area.

Question 3

Describe hot Forging

Answer 3

• Heating to above the recrystallisation temperature
• Working it while it is at the temperature
• Leaving it to cool
• It requires a lot less energy to hot forge due to the metal’s more malleable state
• Yet its dimensional accuracy and surface finish are poor, so it needs machining

Question 4

Describe cold forging

Answer 4

• Applying large amounts of force to an object at room temperature
• Usually has a good surface finish and dimensional accuracy

Question 5

What is drop forging/closed die forging

Answer 5

• Heating metal to above the recrystalisation temperature
• Placed in a series of dies
• Struck at high speed and force, usually with aid of gravity
• This is then repeated in different dies in the series to achieve the desired shape
• Leaving it to cool
• Usually produces an excess flash, which is trimmed or machined off.

Question 6

What is Rolling?

Answer 6

Rolling is when metal is shaped by being squeezed from some sides on a roller.

Question 7

Describe Hot rolling

Answer 7

• Increases ductility and toughness
• Is done above the austenitic range/ recrystalisation temperature
• Produces fine but equiaxed and unstressed grains
• Causes less stress on machinery
• Final products not that dimensionally accurate
• A black oxide layer (firescale) could form over the finished product

Question 8

Describe Cold Rolling

Answer 8

• Increases UTS and hardness
• Less malleability/ductility + workability
• Done below the recrystallisation temperature
• Produces elongated and stressed grains
• Harder and stronger final product (increases strength ans hardness)
• increases strength, hardness, resilience and toughness OTEN
• Better surface finish due to lack of oxides
• Requires heavier machinery

 Has only two directional strength due to elongated grains
 Dimensional accuracy and surface finish

Question 9

Describe Casting

(Pic: Different grain structures)

Answer 9

• Casting mainly involves pouring molten metal into a mould and taking it out after it’s cooled
• There are many types of casting, and the biggest difference is how they make the mould
• Most of the time, casting is used where fabricating or machining from a solid is too hard
• Low waste (excess can be melted and reused)
• Cools from outside in (just have to know the grain structure)
• Often heat treated (normalised) after to:
• Remove the difference in stresses
• Refine the difference in grain sizes caused by dirrering cooling rates