Lecture 2 Flashcards
(25 cards)
Examples of expendable mould casting
- sand
- investment (lost wax)
- evaporative pattern (lost foam)
Examples of permanent mould casting
- gravity die
- pressure die
- centrifugal
sand casting
- make cavity in sand of desired casting using pattern
- permeable: still lets gases through
- allows metal to shrink avoiding heat tears
what are cores
in sand casting: core prints used to hold and align the core in the cavity
what are chaplets
in sand casting: metal supports to provide extra stability to the core
sand casting advantages:
- no size limit, variety of metals and shapes
- cheap moulds
sand casting disadvantages
- dificult to meet exact engineering requirements e.g. tolerances
- suited to low production volumes
sand - what type of casting?
permanent pattern
investment/lost wax casting
- no split mould
- pattern surrounded by ceramic coating that becomes mould
lost wax process
- produce master pattern, die and wax patterns
- assemble on tree and coat
- allow to harden and melt out wax pattern
- pour molten metal into mould and let it solidify
lost wax casting advantages
- only method for producing precision casting of high melting point materials
- requires minimal finishing
lost wax - what type of casting
expendable mould and pattren
evaporative pattern/lost foam casting
- pattern made from expanded polystyrene
what are permanent mould
- not broken up - designed to be removed from mould
permanent mould advantages
- reusable
- good accuracy and surface finish
permanent mould disadvantages
- suited to lower melting point materials
- wear of mould
gravity die casting
- no external force applied other than atmospheric pressure
- involves feeder
gravity die advantages
long die life, minimal machining
gravity die disavantages
slow production rates and limited complexity
gravity die - what type of casting
permanent mould
pressure die casting
forces molten metal into mould under high pressure
pressure die casting process
- lube and lock dies
- molten metal forced into cavity
- held under pressure until solidification
hot chamber process
in pressure die casting:
- metal maintained molten
- some metal forced through shaped channel
cold chamber process
in pressure die casting:
- molten metal poured into injection cylinder
- cylinder not heated