Plastic Processes Flashcards
Step by step of plastic extrusion
Granules of plastic or plastic powder are fed into a hopper
A motor turns the archimedes screw
This screw turns, melting the plastic granules
This moltenplastic moves towards the end of the screw where it is forced through a die
As plastic leaves the die it is cooled.
The extruded product is then cut to the required length
advantages of plastic extrusion
Not suitable for one-off production
Fast simplistic process
Only requires simple dies, 2D
Little waste, closed loop system
The best way to make products with the same profile.
disadvantages of plastic extrusion
Products require further processes such as trimming or drilling.
Cant make complex shapes
Succeptible to die swell
The fast heating and coolong causes expansion
step by step of injection moulding
Plastic granules are fed into a hopper
The granules fall into the flutes of an Archimedes screw
This screw turns, melting the plastic granules
This moltenplastic moves towards the end of the screw
The plastic is forced into a mould at high pressure.
It cools and the mould is opened
advantages of injection moulding
Extremely complex 3D shapes can be produced
High volumes can be produced at high speed with good quality
There is an opportunity for double injection and over moulding of products
Little waste, closed loop system
No further finish needs to be applied to the products.
Disadvantages of injection moulding
The products made often have a poor quality surface finish and require further sanding.
Only work for high volumes of products.
The moulds are extremely expensive.
High initial tooling cost.
Step by step of rotational moulding
oulds are loaded with a precise amout of plastic granules
The mould is heated
The mould is then rotated.
Ensuring plastic coats the whole of the mould
The mould is cooled and opened
The product is extracted
advantages of rotational moulding
Surface finishes can be applied inside the mould
Different types of material can be moulded together.
There is no material wastage
Ideal for tough rigid 3D shapes
A hollow part can be made with no seam or join lines
disadvantages of rotational moulding
The process is slow and can be succeptible to swell
The plastic must be ground into a powder
Manufacturing cost is high
The process is not as fast as blow or injection moulding.
Step by step of thermoforming?
Sheet plastic is held securely between the two moulds
The plastic is heated just above its softening point
The mould halves close and the vacuum is applied
The upper mould ensures the product is the right shape
The product is extracted
Advantages of thermoforming?
Better quality than vacuum forming
High quality products can be produced
Works well creating smooth shapes
Fast process and highly detailed
Disadvantages of thermoforming?
Limited to simple designs
Parts of the plastic can be thin and stretched
Undercuts cannot be achieved
High part cost.
step by step of vacuum forming?
A sheet of plastic is heated to a temperature suitable for moulding
This is when the plastic is nearly molten
A mould is then pushed up into the plastic
A vacuum is turned on which conforms the plastic to the shape of the mould
The plastic cools in the shape of the mould andair is blasted to take it off.
advantages of vacuum forming?
Less safety risk than other plastic processes
Suitable for one-off and large scale production
The moulds can be made from a range of materials that are inexpensive
Simple process, easy to use
Available to schools colleges and industries
disadvantages of vacuum forming?
