Material Processing And Forming Techniques Flashcards
What is casting?
The pouring or forcing of molten metal into a cavity and then allowing metal to cool
What are the basic steps of sand casting?
- Produce a mould out of wood
- Pack drag (bottom) with sand
- Pack cope (top) with sand
- Mould removed and cope and drag screwed in place
- Molten metal poured into cavity via runner
- Excess metal will rise up riser
- Metal is left to cool and is split apart
Give 3 advantages of sand casting
Inexpensive
Complex shapes can be produced
Large components can be produced
Give 4 disadvantages of sand casting
Moulds can only be used once
Surface finish not always good
Labour intensive
Slow production rate
Give 3 applications of sand cast products
Engine blocks
Garden furniture
Caterpillar tracks
What are the basic steps of die casting?
- Mould sprayed with lubricant
- Molten metal shot into die at high pressure
- Pressure maintained till metal is solidified
- Die opened and removed with ejector pins
Give 3 advantages of die casting
High production rate
Good surface finish
Elements e.g. screw thread can be included in the mould
Give 3 disadvantages of die casting
High set up costs
Long lead time
Large volume required to be economical
Give 2 applications of die cast products
Taps
Model cars
What are the basic steps of injection moulding?
- Plastic granules in hopper are forced into heat chamber using a Archimedean screw
- Plastic is forced into two-part mould under pressure
- Component is rapidly cooled and ejected
Give 3 advantages of injection moulding
Low unit costs; ideal for mass production
Precision moulding
High quality finish
Give a disadvantage of injection moulding
High initial set up costs due to expensive mould
Which polymers are used in injection moulding?
ABS
HDPE
Nylon
PP
Give 2 applications of injection moulded products
Castings for electronic products
Containers
What is extrusion?
Used to create long products with a particular cross section
What are the basic steps of blow moulding?
- Plastic granules are fed into hopper
- Archimedean screw feeds granules through heated chamber
- Softened plastic is extruded into parison
- Parison clamped into mould and air pumped into it
- Parison inflates to shape of mould
- Once cooled mould is opened and bottle ejected
Give 3 advantages of blow moulding
Intricate shapes can be formed
Low unit costs; ideal for mass production
Can produce hollow shapes with thin walls
Give a disadvantage of blow moulding
High initial set-up costs due to expensive mould
Which polymers are used in blow moulding?
HPDE
LDPE
PP
PVC
Give an application of a blow moulded product
Plastic bottle
Containers
What are the basic steps of vacuum forming?
- Produce high quality former, with 1° taper and no undercuts
- Former place into machine and plastic clamped over
- Heat applied, plastic softens
- Former raised into plastic, air removed
- Pressure forces plastic around former, taking shape
- Once cooled, remove from machine
Give 2 advantages of vacuum forming
Inexpensive; ideal for batch production
Easy to make moulds that can be modified
Give 2 disadvantages of vacuum forming
Mould needs to be accurate to prevent webbing
Large amounts of waste
Which polymers are used in vacuum forming?
Acrylic
PVC
HIPS
Give 2 applications of vacuum formed products
Yoghurt pots
Insides of fridges
What are the basic steps of rotational moulding?
- Powdered polymer is loaded into mould
- Heat is applied and mould is rotated in tumbling action
- Polymer is melted and sticks to mould wall
- Cooled by water or air, component removed
Give 4 advantages of rotational moulding
Easy to produce large products
End product has no seams
Wall of product is uniform thickness
Rarely need finishing
Give 3 disadvantages of rotational moulding
Lower volume production
Long cycle times
Labour intensive
Give 3 applications of rotational moulded products
Plastic footballs
Buckets
Traffic cones
