Metal Casting Part 2 Flashcards
Advantage of shell casting
- Component will have a smooth finish
- Allows excellent metal flow into the mould
- Lower plant capital costs compared to sand casting
- lightweight
- good dimensional accuracy can be achieved
- components with a thin wall can be casted
Disadvantage of shell casting
- limited size and weight of casting
- generates bad fumes
- a new mould must be created for each cast
How to Shell Mould
1 - A Metal Pattern is heated up and placed over a box containing sand mixed with thermosetting resin
2- The sand falls onto the hot pattern, then flipped to get rid of excess
3 - the sand shell is heated in an oven for several minutes to complete the curing
3 - mould is then removed from the pattern which is assisted by the ejector pins
5 - Two halves of the shell is used to make one big mould for the component and is clamped
6- metal is then poured into the shell mould leaving with the finished component
Applications for polystyrene casting
Mass production for casting car engines
what is investment casting
A Pattern is made of wax with refractory material to make the mould which then is coated with a ceramic slurry, after which the wax is melted away when pouring in the molten metal and leaves a ceramic mould by itself
Steps for investment casting
1 - wax subpatterns are produced
2 - patterns then form one wax pattern tree
3 - the pattern is then coated with a thin layer of ceramic slurry
4 -The mould is then heated and allows the wax to drip out, leaving the ceramic mould by itself
5 - Mould is then broken away leaving the pattern tree and the subparts are then separated from the tree
what is permanent mould casting
A Reusable Mould where there a two separate parts. The insides are lubricated and a core is placed inside (Lubrication needed to stop the molten metal fusing with the mould and the core).
Permanent casting steps
1 - The mould is preheated and is lubricated to prevent the component from fusing with the mould
2 - cores are inserted (If any) and a piston helps close the mould
3 - molten metal is poured in and then the mould opens to acquire the finished component
What is Die casting and what’s special about it
a process where the molten metal is injected with high pressure into the mould. Because of the use of high pressure, there is no shrinkage for the final component and can be achieved by using hot and cold chambers. This is mostly used for low melting point metals as they don’t damage the plunger and other mechanical components in the mould
What is Centrifugal Casting
A process where the mould is rotated at a high speed so the centrifugal force distributes the molten metal to the outer region of the Cavity
What are the three groups for centrifugal castign
- True centrifugal casting
- semi centrifugal casting
- centrifuge casting
What is the difference between Centrifugal, semi, and centrifuge casting
- centrifugal is where the mould spins 360 degrees
- semi is where it spins horizontally
- centrifuge is where there are parts of cavities located around the edge of the horizontally spinning mould
What are the steps after solidification
- Trimming
- Removing the core
- Surface Cleaning
- Inspection
- Repairment if required
- Heat treatment
Advantage of polystyrene casting
- pattern doesn’t need to be removed from mould
- Fewer defects
Disadvantage of polystyrene casting
- A new pattern is needed for each new casting
- the quality of the cast is determined by the quality of the pattern
- complex shapes may require multipiece patterns
- limitation of minimum section thickness
Advantage of investment casting
- good surface finish
- wax can be reused
- complex part can be casted
disadvantage of investment casting
- many steps are required
- expensive process
- limit to the size of the casting
Advantage of permanent casting
-Good dimensional control
-good surface finish
-rapid solidification allows the finished component to be much stronger
(Also applies to die casting)
disadvantages of permanent casting
-can only be done with low melting point metals
-high cost of mould
(Also applies to die casting)
What are the general defects
- misruns
- cold shuts
- cold shots
- shrinkage
- hot cracking
Advantage of a permenant mould
- Good dimensional control
- Good surface finish
- can create a high volume of production
Disadvantages of permanent and die mould casting
- only limited to metals with a low melting point
- high cost of mould
what is semi centrifugal casting
Where the mould spins on the horizontal axis
what is centrifuge casting *(Not Centrifugal)
This is where the mould spins horizontally and fill cavities that are located on the outside of the mould
