Flashcards in Plastic Manufacturing Processes Deck (55)
What is injection moulding?
A method of forming thermoplastics into complex 3D shapes.
What is the first stage of injection moulding?
-Plastic granules are placed in the hopper.
-The granules fall through the hopper into the Archimedean screw.
What is the second stage of injection moulding?
-The screw is rotated via the motor and gearbox.
-The polymer is forced forwards towards the heaters.
-The polymer becomes softened and is injected into the mould.
What is the third stage of injection moulding?
-The hydraulic ram forces the softened polymer through the feedhole into the mould.
-Pressure from the ram fills the cavity.
What is the fourth stage of injection moulding?
-Once the polymer has solidified, the mould halves are opened.
-Ejector pins release the product from the mould.
What is the fifth stage of injection moulding?
-The mould is resealed for another cycle.
Give three advantages of injection moulding.
-Complex 3D shapes can be produced.
-High volumes of consistent quality can be produced.
-Metal inserts can be included in the product.
Give two disadvantages of injection moulding.
-Initial setup costs are high.
-Moulds are expensive.
What is blow moulding?
A method of forming thermoplastics into shapes with a single opening.
Give an example of a product produced using blow moulding.
What is the first stage of blow moulding?
A tube of softened polymer is extruded vertically. (parison)
What is a parison?
The extruded thermoplastic used in blow moulding.
What is the second stage of blow moulding?
The mould halves close trapping and sealing the top of the parison.
What is the third stage of blow moulding?
Hot air is blown into the parison forcing it into the shape of the mould.
What is the fourth stage of blow moulding?
The polymer is cooled by the mould and released.
What is the fifth stage of blow moulding?
The mould halves are opened and the product is extracted.
Give two advantages of blow moulding.
-It is a quick method of producing hollow products.
-Non-circular shapes can be produced.
Give three disadvantages of blow moulding.
-Moulds are expensive.
-Complex shapes are hard to make.
-Triangles are hard to produce.
What is rotational moulding?
A method of forming thermoplastics by rotating a mould about a fixed central point.
What is the first stage of rotational moulding?
-The moulds are loaded with a precise weight of thermoplastic.
-The mould halves are then clamped together.
What is the second stage of rotational moulding?
-The moulds are rotated about two arms though a heated chamber.
-The continuous rotation ensures the plastic covers the whole mould.
What is the third stage of rotational moulding?
The mould is then moved to a cooling chamber.
What is the fourth stage of rotational moulding?
The mould is returned to the start where the moulds are separated.
Give six advantages of rotational moulding.
-One piece mouldings can be produced.
-Both rigid and flexible shapes can be produced.
-A large range of sizes can be produced.
-Surface textures can be applied.
-Moulds are cheaper since high pressures aren't required.
-Lower production runs are possible.
Give a disadvantage of rotational moulding.
Only hollow shapes can be produced.
What is thermoforming?
A form of vacuum forming that uses air pressure and a female mould.
What is vacuum forming?
A process where thermoplastic is heated and pulled onto a simple mould.
Give two advantages of thermoforming.
-Low cost process
-Good for smooth shapes with additional detail
Give three disadvantages of thermoforming.
-Walls can become thinned where the material has been stretched.
-Limited to simple designs.
-Trimming is usually needed.