Metal Casting Part 1

Question 1

Advantages of Casting

Answer 1

• Large components can be made
• Components can be mass produced
• can create complex part geometries

Question 2

Disadvantages of Casting

Answer 2

• Limitations on mechanical properties
• Poor dimensional accuracy
• Dangerous to works due to hot molten metals
• Environmental Problems

Question 3

Why must the size and shape of the cavity be slightly larger for the component?

Answer 3

To allow for Shrinkage during solidification and cooling

Question 4

What materials are moulds made out of?

Answer 4

• Sand
• Plaster
• Ceramic
• Metal

Question 5

What are the two types of moulds

Answer 5

Expendable Mould and Permeant Mould

Question 6

What is an Expendable Mould and what can it be made out of

Answer 6

A mould which must be destroyed in order to retrieve the component. Normally made from sand, plaster, and similar materials plus a binder material

Question 7

What is a permanent mould and what are they normally made out of

Answer 7

A closed mould which can be reused again to produce many castings and is normally made out of metal or ceramic

Question 8

Advantage of expendable mould

Answer 8

It can create more complex shape

Question 9

disadvantage of an expendable mould

Answer 9

Takes a long time to make the mould which will decrease the output of component and decrease productivity

Question 10

advantages of a permanent mould

Answer 10

High Production Rates

Question 11

disadvantage of Permanent mould

Answer 11

changing the geometries will be hard as the mould needs to be open up

Question 12

what are most commercial castings made out of and why?

Answer 12

Alloys as they are easier to cast and the properties of the finished product will be better

Question 13

what can casting alloys be classified as

Answer 13

• Ferrous

- Non-Ferrous

Question 14

disadvantage of sand casting

Answer 14

Moulds must be destroyed and reconstructed for each part

Question 15

advantage of sand casting

Answer 15

Parts can be really big or small

Question 16

what’s the top and bottom of a sand casting called

Answer 16

Top is called the Cope

Bottom is Called the Drag

Question 17

what must a sand casting contain

Answer 17

A Gating and Riser System

Question 18

What are the mould requirements

Answer 18

Strength - to maintain shape and resist erosion
Permeability - to allow hot air and gases to pass through voids in sand
Thermal stability - to resist cracking on contact with molten metal
Collapsibility - ability to give way and allow casting to shrink without cracking the casting
Reusability - can sand from broken mould be reused to make other
moulds?

Question 19

Primary material for sand casting?

Answer 19

Silica as it has good refractory properties for high temperatures, it will leave a better surface finish on components.

Question 20

what’s the core part for and what is it made out of

Answer 20

It is placed inside of the mould to help shape the interior part of the component and is normally made from the same material as the casting but lubrication is applied so it won’t fuse together

Question 21

what is required for the core in the mould

Answer 21

it requires some form of support in order to keep the core in position

Question 22

what’s the name of the support of the core called

Answer 22

Chaplet

Question 23

what is the gating system and what does it consist of

Answer 23

The channel which molten metal flows into the cavity of the mould. It consists of the pouring cup, then the downsprue, and then the runner

Question 24

why is a pouring cup used at the beginning of the mould

Answer 24

This allows minimal splashes and pouring the molten metal as it flows into the downsprue

Question 25

Why must the downsprue be carefully designed

Answer 25

It must maintain a constant volume of flow rate to prevent air pockets becoming trapped and affecting the finished component

Question 26

what are the 2 equations to design the downsprue?

Answer 26

Velocity = (2 x g x Height)^1/2

Volume Flow Rate = Velocity x Area

Question 27

what’s the point of the riser into the mould

Answer 27

a spare source of liquid metal for any shrinkage of the component. This is also usually used as waste material and cut off from the component

Question 28

What is the Chvorinov’s Rule

Answer 28

The Total Solidification Time Formula

TTS = (The mould constant) x (Volume/Area)^2

Question 29

what does the Chvorinov’s Rule tell us

Answer 29

TTS for the molten liquid to pour into the riser must be greater than the TTS for the main casting

Question 30

which direction do you want the solidification to start

Answer 30

Ideally, the most distant part of the component from the riser as this allows molten metal to continue to flow from the riser.