7 - Manufacturing Processes

Question 1

Outline the blow moulding process.

Answer 1

-Plastic powder is fed through a screw and heated.
-Molten plastic is shaped to the mould using compressed air.
-Plastic is left to cool.

Question 2

What are the advantages of blow moulding?

Answer 2

-Low costs.
-Fast production.
-Can make complex parts.
-External threads can be made.
-Large open-ended parts.

Question 3

What are the disadvantages of blow moulding?

Answer 3

-Limited to hollow parts.
-Low strength.
-Not always recyclable (may be laminated).
-Limited to thermoplastics.

Question 4

Give an example of a blow-moulded product.

Answer 4

Single-use plastic water bottles.

Question 5

Outline the rotation moulding process.

Answer 5

-A polymer ‘slug’ is placed in a mould.
-It is heated and rotated to cover the outside of the mould.
-Shape is left to cool.

Question 6

What are the advantages of rotation moulding?

Answer 6

-Low costs.
-Versatile.
-Uniform wall thickness (improves strength).
-Minimal waste.
-Closed-off hollow parts.

Question 7

What are the disadvantages of rotation moulding?

Answer 7

-Slow process time.
-Does not allow for specific tolerances.
-Difficult to maintain purity.
-Limited material options.

Question 8

Give an example of a rotation-moulded product.

Answer 8

Fuel tanks.

Question 9

Outline the extrusion process.

Answer 9

-Plastic powder is fed through a screw and heated.
-It is pushed through a steel die, making a long shape that can be cut into smaller bits.

Question 10

What are the advantages of extrusion?

Answer 10

-Fast production.
-Low material cost.
-Thermoplastic reuse.
-Flexible.
-Stock forms are made quickly.

Question 11

What are the disadvantages of extrusion?

Answer 11

-High setup costs.
-Simple shapes.
-Size variations.
-Die swell (expands after leaving the die).

Question 12

Give an example of an extruded product.

Answer 12

Pipes.

Question 13

Outline the injection moulding process.

Answer 13

-Plastic powder is fed through a screw and heated.
-Molten plastic is forced into a two part mould by a hydraulic system.

Question 14

What are the advantages of injection moulding?

Answer 14

-Low cost per part.
-High precision.
-Fast production.
-Low waste.
-Design flexibility.
-Consistency.

Question 15

What are the disadvantages of injection moulding?

Answer 15

-High initial cost.
-High lead time.
-Less suitable for low volume production.

Question 16

Give an example of an injection moulded product.

Answer 16

Children’s toys, including LEGO.

Question 17

What is the difference between compression & transfer moulding?

Answer 17

In compression moulding, a ‘charge’ is placed into an open mould and squished into shape. In transfer moulding, the charge is forced through a hole into a closed mould.