Plastic Manufacturing Processes

Question 1

What is injection moulding?

Answer 1

A method of forming thermoplastics into complex 3D shapes.

Question 2

What is the first stage of injection moulding?

Answer 2

• Plastic granules are placed in the hopper.

- The granules fall through the hopper into the Archimedean screw.

Question 3

What is the second stage of injection moulding?

Answer 3

• 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.

Question 4

What is the third stage of injection moulding?

Answer 4

• The hydraulic ram forces the softened polymer through the feedhole into the mould.
• Pressure from the ram fills the cavity.

Question 5

What is the fourth stage of injection moulding?

Answer 5

• Once the polymer has solidified, the mould halves are opened.
• Ejector pins release the product from the mould.

Question 6

What is the fifth stage of injection moulding?

Answer 6

-The mould is resealed for another cycle.

Question 7

Give three advantages of injection moulding.

Answer 7

• Complex 3D shapes can be produced.
• High volumes of consistent quality can be produced.
• Metal inserts can be included in the product.

Question 8

Give two disadvantages of injection moulding.

Answer 8

• Initial setup costs are high.

- Moulds are expensive.

Question 9

What is blow moulding?

Answer 9

A method of forming thermoplastics into shapes with a single opening.

Question 10

Give an example of a product produced using blow moulding.

Answer 10

Drinks bottles

Question 11

What is the first stage of blow moulding?

Answer 11

A tube of softened polymer is extruded vertically. (parison)

Question 12

What is a parison?

Answer 12

The extruded thermoplastic used in blow moulding.

Question 13

What is the second stage of blow moulding?

Answer 13

The mould halves close trapping and sealing the top of the parison.

Question 14

What is the third stage of blow moulding?

Answer 14

Hot air is blown into the parison forcing it into the shape of the mould.

Question 15

What is the fourth stage of blow moulding?

Answer 15

The polymer is cooled by the mould and released.

Question 16

What is the fifth stage of blow moulding?

Answer 16

The mould halves are opened and the product is extracted.

Question 17

Give two advantages of blow moulding.

Answer 17

• It is a quick method of producing hollow products.

- Non-circular shapes can be produced.

Question 18

Give three disadvantages of blow moulding.

Answer 18

• Moulds are expensive.
• Complex shapes are hard to make.
• Triangles are hard to produce.

Question 19

What is rotational moulding?

Answer 19

A method of forming thermoplastics by rotating a mould about a fixed central point.

Question 20

What is the first stage of rotational moulding?

Answer 20

• The moulds are loaded with a precise weight of thermoplastic.
• The mould halves are then clamped together.

Question 21

What is the second stage of rotational moulding?

Answer 21

• The moulds are rotated about two arms though a heated chamber.
• The continuous rotation ensures the plastic covers the whole mould.

Question 22

What is the third stage of rotational moulding?

Answer 22

The mould is then moved to a cooling chamber.

Question 23

What is the fourth stage of rotational moulding?

Answer 23

The mould is returned to the start where the moulds are separated.

Question 24

Give six advantages of rotational moulding.

Answer 24

• 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.

Question 25

Give a disadvantage of rotational moulding.

Answer 25

Only hollow shapes can be produced.

Question 26

What is thermoforming?

Answer 26

A form of vacuum forming that uses air pressure and a female mould.

Question 27

What is vacuum forming?

Answer 27

A process where thermoplastic is heated and pulled onto a simple mould.

Question 28

Give two advantages of thermoforming.

Answer 28

- Low cost process | - Good for smooth shapes with additional detail

Question 29

Give three disadvantages of thermoforming.

Answer 29

- Walls can become thinned where the material has been stretched. - Limited to simple designs. - Trimming is usually needed.

Question 30

What is extrusion?

Answer 30

A process used to produce plastic products with a uniform cross-section.

Question 31

What is the first stage of extrusion?

Answer 31

- Thermoplastic powder is placed in the hopper and falls into a rotating Archimedean screw. - This pushes the material towards the heated section of the extruder.

Question 32

What is the second stage of extrusion?

Answer 32

The heaters soften the plastic which is forced through the die by the rotating screw.

Question 33

What is the third stage of extrusion?

Answer 33

The plastic is cooled by a water jet.

Question 34

What is the fourth stage of extrusion?

Answer 34

The product is cut to the required length.

Question 35

What is calendaring?

Answer 35

A process used to manufacture thermoplastic sheets.

Question 36

What is the first stage of calendaring?

Answer 36

The rollers are heated to just above the softening point of the thermoplastic.

Question 37

What is the second stage of calendaring?

Answer 37

The plastic is forced through the rollers which determine the thickness of the sheet.

Question 38

What is the third stage of calendaring?

Answer 38

The final roller cools the material.

Question 39

What is line bending?

Answer 39

A method of processing thermoplastic sheets that involves using a single heating strip.

Question 40

How are accurate bends achieved when using a line bender?

Answer 40

A bending jig is used

Question 41

What is compression moulding?

Answer 41

The main manufacturing process for thermosetting plastics.

Question 42

What is the first stage of compression moulding?

Answer 42

A preformed slug is placed between the two halves of the mould.

Question 43

What is the second stage of compression moulding?

Answer 43

The mould is heated to a temperature that causes cross links to be formed.

Question 44

What is the third stage of compression moulding?

Answer 44

- The mould is closed onto the preform and the pressure forces out excess material. - The moulds are held closed under pressure giving the material time to cure.

Question 45

What is the fourth stage of compression moulding?

Answer 45

The product can ejected whilst it's still hot.

Question 46

Give two advantages of compression moulding.

Answer 46

- Startup costs are relatively low. | - There is little waste material.

Question 47

Give two disadvantages of compression moulding.

Answer 47

- A preform has to be manufactured. | - Products can't be overly complex.

Question 48

Give one way of identifying a product that has been injection moulded.

Answer 48

They often have ejector pin marks.

Question 49

Give one way of identifying a product that has been blow moulded.

Answer 49

There is often a sprue at the bottom of the product.

Question 50

Give one way of identifying a product that has been rotation moulded.

Answer 50

There will be seam lines where the mould halves have been joined.

Question 51

Which process would be used to manufacture a bottle?

Answer 51

Blow moulding

Question 52

Which process would be used to manufacture a bottle top?

Answer 52

Injection moulding

Question 53

Which process would be used to manufacture a bottle?

Answer 53

Calendaring with LDPE

Question 54

What is overmoulding?

Answer 54

Injecting a second polymer over specific areas of a component.

Question 55

What is twinshot injection moulding?

Answer 55

Injecting two polymers using two separate barrels but a single mould.