Moulding

Blow moulding:

How it works:

1. Plastic granules fed through hopper
2. Heated/melted along the Archimedes screw
3. Extruded into hollow tube (parison)
4. Tube is then clamped into metal mould
5. Air is pumped in to inflate mould
6. Mould/bottle is cooled to solidify plastic
7. Product is ejected and trimmed

Advantages	Disadvantages
Intricate shapes can be formed Can produce hollow shapes Ideal for mass production	High initial set up costs Moulds are expensive to create

Uses: Plastic bottles, containers

Injection moulding:

How it works:

1. Plastic granules fed through hopper
2. Heated/melted along the Archimedes screw
3. Plastic injected into the mould
4. Two-part mould "negative" of the product
5. Product rapidly cooled and ejected from mould

Advantages	Disadvantages
Ideal for mass production Low unit cost Precise moulding High quality finish	High initial set up costs Moulds are expensice to create Can create large mouldings

Uses: Casings for electric products, containers for storage/packaging

Vacuum forming:

How it works:

1. Create mould (air gaps, tapers, angles, rounded egdges)
2. Place the mould on the platen and lower
3. Clamps HIPS and heat until 'bouncy'
4. Raise platen into plastic
5. Vacuum pump air out
6. Blowback a little bit of air to help release mould

Advantages	Disadvantages
Ideal for batch production Inexpensive Easy to make mould/can be modified Low temperatures which reduce energy use Flexible manufacturing process	Moulds need to be accurate to avoid webbing Large amounts of waste materials produced - bad for environment Can only mould thin products which are weak/prone to cracking

Uses: Yoghurt pots, blister packaging, inside of fridges

Extrusion:

How it works:

1. Plastic granules fed through hopper
2. Heated/melted along the Archimedes screw
3. Plastic forced into the die
4. The plastic is extruded 'pulled' throug the die and cooled
5. Rollers pull plastic continuously
6. The extruded product is cut to the desired lengths

Advantages	Disadvantages
Low cost relative to other moulding processes Uses thermoplastics which can be remoulded Waste material can be reused Plastic can be manipulated after extrusion before fully cooled (e.g. bends/curves)	Hard to predict die swell (expansion) Can only manufacture certain products

Uses: Collapsible tubes, guttering, straws, gear blanks

Rotational moulding:

How it works:

1. Powdered polymer loaded into mould
2. Heat is applied to the mould
3. At the same time the mould is rotated on all 3 axis (x, y, z)
4. After some time, the mould is cooled and the component is removed

Advantages	Disadvantages
Easy to produce large products Uniform thickness Corners of products are stress free Colour is easy to integrate into products	Lower volume production (slow process) Materials available are limited Labour intensive

Uses: Buckets, plastic footballs, dustbins, oil drums

Topic test: