Injection moulding works by...

• A. A screw thread turns forcing the plastic material through a heater melting it, then acts as a ram and forces the plastic into the mould where it cools and solidifies
• B. A mould is created from wood or epoxy resin
• C. A sheet of plastic is heated and placed over a mould
• D. A tube of molten plastic is extruded between two halves of a mould

Answer: (A)

Injection moulding works by heating plastic until it becomes molten, then forcing that molten material into a mould cavity where it takes the shape of the part as it cools and solidifies. In practice, a screw in a heated barrel melts the polymer and pushes it forward, injecting it through a nozzle into the closed mould. Once the cavity is filled and the material has cooled, the mould opens and the part is ejected. This approach allows high-volume production with accurate detail, good surface finish, and the ability to form complex geometries.

The other descriptions don’t fit: the mould is not typically made from wood or epoxy resin in industrial use; thermoforming involves heating a sheet of plastic and draping it over a mould; extrusion into a mould describes a different process where material is forced through a die rather than injected into a mould cavity.