Moulding Processes

Question 1

Die-casting (Metal)

Answer 1

Molten metal is squeezed into a metal mould.

Used to Make: Large volumes of complex parts: Engineering components, toy cars, precision mechanisms.

Identifying Features: Superb surface finish, complex shapes, high accuracy. Ejector pin marks, mould split lines, sprue and gate marks, draft angles.

Used if: I needed a huge number of complex parts which had a brilliant finish to them. For die-casting I’d need a factory.

Question 2

Sand-Casting (Metal)

Answer 2

Molten metal is poured into a mould made of sand

Used to Make: Engine parts, tools, vices.

Identifying Features: Orange-peel like surface, large corners and fillets, large draft angles, mould split line.

Used if: I needed to make a small number of tough metal parts, and I wasn’t bothered about surface finish.

Question 3

Injection Moulding (Plastic)

Answer 3

Molten plastic is squeezed into a metal mould.

Used to Make: Toys, storage tubs, games controllers, Lego, chairs.

Identifying Features: Thin walls, superb surface finish, complex shapes, high accuracy. Ejector pin marks, mould split lines, sprue and gate marks, draft angles.

Used if: I needed a huge number of complex parts with an excellent finish. I’d need a factory to do injection moulding.

Question 4

Rotational Moulding (Plastic)

Answer 4

Molten plastic is tumbled inside a rotating mould.

Used to Make: Kayaks, suitcases, bins.

Identifying Features: Hollow object, no visible seams, uniform wall thickness

Used if: I needed products that were large, plastic and hollow. I could make small or large amounts of them in a factory.

Question 5

Drop-Forging (Metal)

Answer 5

Very high pressure hammers beat and squeeze metal into shape

Used to Make: Tools, golf clubs, gun parts.

Identifying Features: Simple forms, thick sections or walls, large radius corners and draft angles

Used if: I wanted to create a medium volume of very strong metal components with a decent surface finish.

Question 6

Compression Moulding (Thermoset Plastics)

Answer 6

Thermoset plastic is heated and squeezed between two moulds.

Used to Make: Wellies, safety hats, tyre treads, composite panels, shoe grips.

Identifying Features: Thin walls, good surface finish, complex shapes, high accuracy. Ejector pin marks, mould split lines, sprue and gate marks, draft angles. No undercuts or overhangs.

Used if: I wanted to create a low to medium volume of moulded rubber or resin parts.

Question 7

Blow Moulding (Plastic)

Answer 7

Softened plastic is inflated inside a round mould.

Used to Make: Bottles, containers, medical vessels.

Identifying Features: Hollow containers, simple forms, no interior detailing, constant wall thickness.

Used if: I wanted to make a large volume of bottles or hollow containers incredibly quickly and cheaply.

Question 8

Extrusion (Metals, Plastics)

Answer 8

Molten material is forced through a small opening like toothpaste.

Used to Make: Window frames, pipes, beams.

Identifying Features: Long, thin objects, continuous cross section, complex cross sections.

Used if: I wanted components that were long, thin and had a continuous cross-section. Easily automated for mass production.