Manufacturing Processes - Week 3

Question 1

What 4 groups makeup processes?

Answer 1

-Casting
-Cutting
-Forming
-Joining

Question 2

What does forging do to a metal?

Answer 2

It makes it harder

Question 3

What does annealing do to a metal?

Answer 3

It makes it softer as it heats up the metal

Question 4

What is the process of vulcanizing?

Answer 4

A chemical process in which rubber is heated to make it more stretchy and elastic

Question 5

What is casting?

Answer 5

Filling a mould with a fluid metal, polymer, glass or ceramic, which then solidifies in the shape of the mould cavity

Question 6

How do you distinguish between various casting processes?

Answer 6

-Using the precise nature of the material flow, heat transfer and subsequent solidification
-Casting is distinguished from moulding by the low viscosity of the liquid: It fills the mould by flow under its own weight or under a modest pressure (more suitable for metals).

Question 7

What is casting used to make?

Answer 7

Casting is used to make an enormous range of products from pump housings to cheap plastic toys.

Question 8

What is the process of moulding?

Answer 8

Moulding (more suitable for thermoplastics and glasses ) involves the hot viscous fluid being pressed or injected into a die under considerable pressure, where it cools and solidifies.

Question 9

The type of mould required depends upon?

Answer 9

-The material to be cast
-The shape (complex shapes require multi-piece moulds)

Question 10

Metal are cast when…

Answer 10

They are molten

Question 11

How are polymers moulded?

Answer 11

Polymers are forced into moulds (i.e. injection moulding) when their viscosity is sufficiently low for them to be able to flow (~200C); most polymers start to degrade before they reach a sufficiently high temperature to fill a mould adequately under gravity alone

Question 12

How does shape influence choice of process?

Answer 12

Shape influences the choice of process:

• Complex shapes can be made by casting, for example, can produce more complex shapes than forging, because liquids can fill intricate cavities.
• Slender shapes can be made easily by rolling or drawing but not by casting.
• Hollow shapes cannot be made by forging, but they can by casting or moulding. However, forgings can often be made into complex shapes by secondary machining and assembly processes.

Question 13

What is sand casting?

Answer 13

• Molten metal is poured into an expendable sand mould cavity by gravity or force, where it solidifies to form the cavity shape part
• Common process for making complex metal shapes such as car engine air inlet manifolds.

Question 14

What is permanent pattern casting?

Answer 14

• This type of casting uses a model, or pattern, of the final product to make an impression, which forms the mould cavity. Each mould is destroyed after use but the same pattern is used over and over again.
• The moulds are usually made from ceramic materials which are recycled.

Question 15

What is the permanent mould process?

Answer 15

This process uses the same mould for producing a large number of castings. Each casting is released by opening the mould rather than destroying it.

Question 16

What materials are used for this process and how costly is it?

Answer 16

Mould materials are usually metal and therefore the processes are generally associated with low melting temperature metal alloys and polymers. The moulds are expensive, necessitating long production runs.

Question 17

What casting is used for metal alloys?

Answer 17

Gravity die-casting is common for simple shapes whilst pressure die-casting is used for more complex shapes and thin sections as it is forced in, and held together

Question 18

What moulding is used for thermoplastic polymers?

Answer 18

Extrusion moulding and injection moulding are used for producing simple and complex shapes

Question 19

What is contact moulding used for?

Answer 19

Contact moulding is generally used for large simple shapes involving thermosetting polymers, such as GRP polyester boat hulls

Question 20

What is investment casting?

Answer 20

Using a ceramic shell (investment), represents a common process for producing relatively small but complex components

Question 21

Summary points

Answer 21

• Shape influences the choice of process
• Material selection important for properties/cost
• Processing can also change the properties of the material
• Distinct differences between metal and polymer moulding but also some similarities
• The mould and its design tend to be the highest cost
• Variety of methods resulting in a wide range of lead times from days to seconds to form components