Metal Casting Flashcards
What parts are made by casting?
- Large parts, e.g. pipes, ship propellers
- Small parts, e.g. toy cars, jewelry
Definition of Casting?
Casting is the process whereby a part is produced by solidification to take the shape of a mould
What is the process of Casting? (HINT:5)
- Pattern/mould making
- Melt preparation
- Pour molten metal into a mould
- Allow it to solidify
- Remove part from mould
Why is Casting useful and important? (6)
- versatile to any metal that can be heated to liquid state
- wide range of parts from mm to m in one piece
- capable of complex shapes with internal cavities
- capable of processing materials not possible by other means
- competitive with other manufacturing processes
- can produce parts to both net and near net shape
What are the two main categories of Casting processes?
Expendable and Permanent mould processes
What is expendable process casting? (2)
- uses a non-permanent mould, which must be destroyed to remove the casting
- More intricate geometries are possible
What is Permanent process casting? (2)
- uses a permanent mold, can be used to produce many castings
- parts shapes are limited by the need to open the mold to remove casting
What are the main features of a Sand Mould? (9)
- Consists of two halves: cope=upper and drag= bottom
- Flask = box that mold halves are contained in
- two halves separated at the parting line
- Cores = allow defining the interior geometry, broken for removal from casting
- Pouring cup = used to minimize splash and turbulence as metal flows into downsprue
- Runner = metal enters from downsprue and leads to main cavity
- Riser = Acts as a reservoir to compensate for shrinkage during solidification
- Mould Cavity = made in sand in the shape of the desired casting by using a pattern
- sand for moulds made from silica and grains
Advantages and disadvantages of Sand Casting? (3/5)
- Low surface detail (post processing required)
- Difficulties in meeting exact engineering and metallurgical requirements
- Attention must be paid to flow and shrinkage as its a gravity driven process
- Labour intensive with a long cycle time
-Safety hazards and environmental problems - Wide variety of metal and shapes
- Suited to lower production volumes
- Relatively cheap molds
What are the Key features of Die Casting? (5)
- Moulds are called dies
- use of high pressure to inject metal into the die cavity
- cycle time - 10’s of seconds for avg. component
- greater capital expenditure
- Tool grade steel
What are 2 mains type of pressure die casting?
hot chamber and cold chamber
What is the process steps of die casting? (6)
- Lubrication of dies
- Closing and locking of dies
- Molten metal is forced into the die cavity
- Held under pressure until it solidifies
- Die opens
- Casting ejected
What is the process of Hot chamber die casting?
Metal is melted in a container and a piston injects liquid metal under high pressure into the die cavity
Advs and Disadvs of hot chamber?
- High production rates
- Applications limited to low melting points that do not chemically attack plunger
What metals can be used in Hot chamber casting? (4)
Zinc, Tin, Lead, and Magnesium
What is the process of Cold chamber die Casting?
Molten metal is poured into an UNHEATED chamber from external melting container and a piston injects metal under a higher pressure into a die cavity
What is the production rate of Cold chamber Casting?
High production but less than hot chamber due to pouring step
What metals can be used in Cold chamber casting? (3)
Aluminium, brass and magnesium alloys
What are the advantages of Die Casting? (4)
- Economical for large production quantities
- Good accuracy and surface finish
- Thin sections possible
- Rapid cooling means small grain size and good strength in casting
