Metal Casting Part 1 Flashcards
Advantages of Casting
- Large components can be made
- Components can be mass produced
- can create complex part geometries
Disadvantages of Casting
- Limitations on mechanical properties
- Poor dimensional accuracy
- Dangerous to works due to hot molten metals
- Environmental Problems
Why must the size and shape of the cavity be slightly larger for the component?
To allow for Shrinkage during solidification and cooling
What materials are moulds made out of?
- Sand
- Plaster
- Ceramic
- Metal
What are the two types of moulds
Expendable Mould and Permeant Mould
What is an Expendable Mould and what can it be made out of
A mould which must be destroyed in order to retrieve the component. Normally made from sand, plaster, and similar materials plus a binder material
What is a permanent mould and what are they normally made out of
A closed mould which can be reused again to produce many castings and is normally made out of metal or ceramic
Advantage of expendable mould
It can create more complex shape
disadvantage of an expendable mould
Takes a long time to make the mould which will decrease the output of component and decrease productivity
advantages of a permanent mould
High Production Rates
disadvantage of Permanent mould
changing the geometries will be hard as the mould needs to be open up
what are most commercial castings made out of and why?
Alloys as they are easier to cast and the properties of the finished product will be better
what can casting alloys be classified as
- Ferrous
- Non-Ferrous
disadvantage of sand casting
Moulds must be destroyed and reconstructed for each part
advantage of sand casting
Parts can be really big or small
what’s the top and bottom of a sand casting called
Top is called the Cope
Bottom is Called the Drag
what must a sand casting contain
A Gating and Riser System
What are the mould requirements
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?
Primary material for sand casting?
Silica as it has good refractory properties for high temperatures, it will leave a better surface finish on components.
what’s the core part for and what is it made out of
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
what is required for the core in the mould
it requires some form of support in order to keep the core in position
what’s the name of the support of the core called
Chaplet
what is the gating system and what does it consist of
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
why is a pouring cup used at the beginning of the mould
This allows minimal splashes and pouring the molten metal as it flows into the downsprue
Why must the downsprue be carefully designed
It must maintain a constant volume of flow rate to prevent air pockets becoming trapped and affecting the finished component
what are the 2 equations to design the downsprue?
Velocity = (2 x g x Height)^1/2
Volume Flow Rate = Velocity x Area
what’s the point of the riser into the mould
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
What is the Chvorinov’s Rule
The Total Solidification Time Formula
TTS = (The mould constant) x (Volume/Area)^2
what does the Chvorinov’s Rule tell us
TTS for the molten liquid to pour into the riser must be greater than the TTS for the main casting
which direction do you want the solidification to start
Ideally, the most distant part of the component from the riser as this allows molten metal to continue to flow from the riser.
