Vacuum forming involves...

• A. A mould is created from wood or epoxy resin and placed in the machine, a sheet of plastic is heated until it becomes soft and placed over the mould
• B. A tube of molten plastic is extruded between two halves of a mould, air is blown into the molten plastic to make the shape of the product
• C. A sheet of plastic is heated until it becomes soft and placed over the mould
• D. A sheet of metal is pressed into a mould

Answer: (D)

Vacuum forming works by heating a plastic sheet until it becomes soft and placing it over a mould, with a vacuum then drawing the sheet tightly against the mould to form the shape. This combination of heating, positioning over the mould, and using air pressure (vacuum) to pull the material ensures a smooth, accurate contour and relatively uniform wall thickness.

The option that matches this process best states that a sheet of plastic is heated until soft and placed over the mould. That captures the essential initial steps of vacuum forming—the plastic is softened and set over the mould for shaping (with vacuum applied subsequently to seal to the mould). The other options describe different manufacturing processes: extrusion and blowing for blow moulding, pressing a sheet of metal for metal forming, or focusing on the mould material rather than the forming action itself.