The big idea: A forming technique reshapes the material without adding or removing any of it, so there is almost no waste.
The forming bargain: Every forming process is the same bargain: an expensive tool made once, then very cheap parts. Volume is what settles whether that bargain is worth taking.
Each process drawn as the tool that makes the shape — because the tool is the whole question.
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| Process | How it works | What it makes |
|---|---|---|
| Bending | Sheet or bar is bent over a former or in a press brake, past its elastic limit so the shape stays | Folded sheet parts — brackets, enclosures, chassis, handles |
| Press forming | A punch presses sheet metal into a die, drawing it into a three-dimensional shape in one stroke | Car body panels, sinks, saucepans, tin lids, washing-machine drums |
| Casting | Molten metal is poured into a mould cavity and solidifies in its shape | Engine blocks, machine bases, iron cookware — thick shapes that would be wasteful to machine |
| Injection moulding | Molten polymer is forced under high pressure into a closed steel mould, cooled and ejected | Almost every plastic product — housings, caps, crates, toys, connectors |
| Extrusion | Softened material is pushed continuously through a shaped die and cut to length | Anything with a constant cross-section — window frames, pipe, guttering, aluminium sections |
| Rotational moulding | Powder is placed in a hollow mould which is heated and rotated about two axes so the melt coats the inside | Large hollow seamless parts — water tanks, kayaks, road cones, play equipment |
| Blow moulding | A soft tube of polymer is clamped in a mould and air is blown into it, pressing it against the cavity | Bottles, containers, fuel tanks — thin-walled hollow parts with a narrow neck |
| Vacuum forming | A thermoplastic sheet is heated until soft and sucked onto a one-sided mould | Trays, packaging, signage, machine guards, bath tubs — open shapes with one good face |
Four more the papers ask about
Casting, step by step
Heat the metal above its melting point, pour it into a mould, let it solidify, then remove it. Cast-iron pans, bronze statues.
Compression moulding
A charge of thermoset (urea- or melamine-formaldehyde) goes into a heated open mould, which closes and presses; heat cures it. Socket covers, melamine plates.
Lay-up moulding (composites)
Glass-fibre mat is laid in a mould and resin brushed or sprayed on; it cures to the mould's shape. Boat hulls, fibreglass chairs.
Two stages: a PET bottle
A small preform is injection moulded, then reheated and blow moulded into the bottle. One product, two forming processes.
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| Process | Tooling | Volume it needs |
|---|---|---|
| Vacuum forming | A one-sided mould, often wood or resin | Dozens upwards — which is why schools own one |
| Rotational moulding | A cheap hollow mould, but a slow cycle | Low to medium; the opposite bargain to injection moulding |
| Bending | A simple former or a press brake with standard tools | One-off upwards |
| Extrusion | A die, which is only a profile and comparatively cheap | High, and continuous |
| Press forming | A hardened steel punch and die | High — the die is expensive and each stroke takes seconds |
| Injection moulding | A precision steel tool costing thousands | Very high — tens of thousands of parts to justify it |
Hollow shapes have their own three: Blow moulding for a thin-walled bottle with a narrow neck. Rotational moulding for a large seamless tank. Vacuum forming for an open shape with one good face.
All three make hollow parts, and the shape decides which — not the material.
How this is tested — explaining how components are produced by forming techniques. It comes up two ways:
Paper 1 — multiple choice
- Identify the forming process used for a named product.
- Choose the process suited to a stated shape and volume.
Paper 2 — analysing a product
- Explain how a named component is formed.
- Justify a forming process against the alternatives.
The trap: Recommending injection moulding for everything. It needs tens of thousands of parts to pay for the tool, and a 200-off run would be vacuum formed or machined instead.
A company makes 400 large polyethylene water tanks a year and 400,000 polyethylene bottle caps. Justify a different forming process for each.
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