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
