Moulding

Question 1

Plastic

Answer 1

-

Question 2

Rotational moulding

Answer 2

• mould opened filled with plastic powder
• moulds machined
• the mould is heated to 300 degrees
• mould rotates to maintain an even coating of plastic
• cooled whilst rotating
• mould opened and the product is removed

Question 3

Blow moulding (preform)

Answer 3

• a preform is mould (injection moulded)
• clamped inside a mould that is larger than it
• heated air is blown in the preform
• expands to fill the mould and leaves a hollow interior
• plastic is cooled and removed

Question 4

Blow moulding (parison)

Answer 4

• plastic grains fed into a hopper
• large thread moves it into a heater and liquifies
• extruded through a hole to make a tube
• clamped at the bottom to seal
• air is forced in to expand to the shape of the mould
• product is cooled and removed

Question 5

Injection moulding

Answer 5

• Plastic granules fed from a hopper liquify and enter the screw which moves it towards the mould
• forced into the mould with a hydraulic ram
• plastic cools and the two part mould opens
• removed with ejector pins

( extrusion moulding is the same it just forces the plastic out a nozzle to form a rod rather than into a mould)

Question 6

Vacuum moulding

Answer 6

• sheet of hips is heated until soft
• mould is raised up and forms a seal with the sheet
• a vacuum is created and the sheet is sucked around the mould
• sheet cools and the mould is removed

Is used for batch production, inexpensive and easy to use but produces lots of waste material and an accurate mould is required

Question 7

Metal

Answer 7

-

Question 8

Die casting

Answer 8

• aluminium melted in an argon atmosphere
• transferred to a furnace to keep it molten
• hydraulic ram forces the aluminium through to the mould via a pipe
• the mould opens and ejector pins remove the metal
• inspected and then shot blasted to clean the part

Pros - high accuracy, fast, thinner walls, good finish

Cons - can only be small parts, high cost

Question 9

Sand casting

Answer 9

• make a two part pattern, top is the cope and the bottom is the drag
• place the drag in a frame and compact sand to create a mould
• repeat for the cope
• create a runner and riser and vents to ensure it fully fills
• pour in the runner until it comes out the riser
• allow to cool
• remove extras and shot blast to finish

Pros - inexpensive, complex shapes can be made, can make large parts

Cons - can only be used once, surface finish can be poor, labour intensive, slow

Question 10

Investment casting

Answer 10

• create a wax form using another process eg. Sculpted or injection moulded
• dip in ceramic slurry and sand around 10 times to produce a hard shell
• bake in a kiln to remove all the wax
• preheat the mould and pour in the metal
• destroy the shell to get the part
• clean the part

Pros - excellent finish, high accuracy, any metal can be cast, no flash or parting lines

Cons - cost is relatively high, specialised equipment required, limited to small quantities