Manufacturing Processes for Ferrous Metals

Question 1

Describe the Forging process

Answer 1

• Metals are shaped through force
• The cross-sectional area will be changed in the process.

DRAWING - reduce area, UPSETTING - increasing

Question 2

Describe the process of forging

Answer 2

Shaping metal through the use of force. It could be done above or below recrystallisation temperature. The grainflow resulting in the forged item is stronger than machined as it removed plains of weakness.

Question 3

Rolling

Answer 3

Rolling could be done above or below the recrystallisation temperature. When above, it creates unstressed grains whilst cold rolling will result in stressed grains which is harder to dislocated.

Question 4

Dis/Advantage of hot rolling

Answer 4

Ad: less stress on machinery, unstressed finished product
Dis: might not be dimensionally accurate. will have black oxide layer over finished product

Question 5

Dis/Advantage of cold rollign

Answer 5

Ad: harder final product that is more dimensionally accurate.
Dis: very expensive to make as the machinery has to be very strong

Question 6

Describe Extrusion

Answer 6

• A hot working process where metal is forced through a die to create desired shape
• A ram is used to push the metal through the die for DIRECT extrusion, requires low effort but only for ductile metals
• The ram and the die are together for INDIRECT extrusion, more expensive but can extrude metals with lower ductility

Question 7

What is impact extrusion

Answer 7

• A cold forming extrusion process
• Uses a hammer to extrude a shape
• The hammer hits a material blank that sits within a die. When impact is made, the material blank will be forced from the die around the hammer.

Question 8

Describe Powder Forming

Answer 8

• Metal powder mixed with stearate based dry lubricants are pressed into a mould to form desired shape
• The item is then sintered in a furnace at a temperature that allows atoms to diffuse between grains.
• This will create a homogenous grain structure that gives the product strength

Question 9

Name products of powder forming

Answer 9

• Porous metals
• Complex articles
• Products difficult to machine
• Composites

Question 10

What are the advantages and disadvantages of powder forming

Answer 10

• Allows complicated shapes to be made
• Not as strong as a conventionally produced item
• Expensive

Question 11

What happens in the heat-affected zone

Answer 11

• the cells that were stressed are now unstressed as they were heated up

Question 12

Describe how casting works.

Answer 12

A molten metal is poured into a mould and left to cool, resulting in a solid metal object in the shape of the mould.

Question 13

Des the process of continuous casting.

Answer 13

A molten metal is poured into a water cooled mould with a open bottom. When the molten metal hits the cooler mould, it solidifies into the shape of the mould. The open bottom allows the shape to be continuously made by extracting each new section.

Question 14

Des sand casting

Answer 14

Sand is packed around a finished product, then removed to result in a mould.
Cope is top side, drag is bottom side of the moulds.
Molten metal is poured through a hole in the cope and allowed to cool. Then the final product is machined.
Cheap, fast, common asf.
Surface finish is poor and inaccurate
Poor dimensional stability

Question 15

Des centrifugal casting

Answer 15

This method uses centrifugal forces to make the metal spin to the outside of the mould thus creating a hollow cylinder. Usually used for making metal pipes.

Question 16

Describe Die casting

Answer 16

This method utilises a permanent mould that can be reused. This method is much cheaper but must only product objects that are able to break away from the mould.
Cost effective, good for mass production.
Good surface finish but is quite expensive on smaller scales.

Question 17

Investment casting/Lost wax casting

Answer 17

The final product is made from wax in which ceramic is poured over the wax to form a brittle shell over the wax. Then molten metal is poured over the wax which evaporates and lets the metal take shape of the wax. Then the mould is destroyed to obtain the final product.
Expensive but very good surface finish and dimensionally accurate.

Question 18

Investment casting/Lost wax casting

Answer 18

The final product is made from wax in which ceramic is poured over the wax to form a brittle shell over the wax. Then molten metal is poured over the wax which evaporates and lets the metal take shape of the wax. Then the mould is destroyed to obtain the final product.
Expensive but very good surface finish and dimensionally accurate.

Question 19

Full Mould process

Answer 19

Similar to lost wax casting. The final product is made of polystyrene then packed into sand. Then molten metal is poured over the foam in which it evaporates and results in the final product.
Usually used for prototypes as good surface finishes arent required