Why does the way you make a product change completely as you go from one prototype to a million units?
The main shaping, forming, casting, moulding and joining processes for the material families, and how scale of production (one-off, batch, mass and continuous) drives the choice of process, tooling and cost.
A focused answer to AQA A-Level Design and Technology Product Design 3.1.3, covering the main manufacturing processes for each material family and how the scale of production drives the choice of process, tooling and cost.
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What this dot point is asking
AQA wants you to know the main shaping, forming, casting, moulding and joining processes for each material family, and to explain how the scale of production (one-off, batch, mass and continuous) determines which process is sensible, how much tooling costs and what the unit cost will be.
Processes by material family
- Polymers: injection moulding, blow moulding, vacuum forming, extrusion, rotational moulding, line bending of acrylic.
- Metals: sand and die casting, forging, turning and milling, press forming, deep drawing.
- Timbers: sawing, routing, laminating, steam bending, CNC machining.
- Composites: lay-up of glass or carbon fibre with resin into a mould.
It helps to group processes by what they do to the material. Wasting (subtractive) processes remove material to leave the shape, such as turning, milling, routing, drilling and laser cutting; they are accurate and flexible but waste the removed material and are limited to shapes a tool can reach. Forming and shaping processes deform material into a new shape without removing much, such as vacuum forming, line bending, deep drawing and press forming; they are fast and waste little. Casting and moulding processes pour or force liquid material into a mould cavity, such as injection moulding, die casting and sand casting; they make complex shapes in one operation but need a mould. Joining processes assemble parts permanently (welding, brazing, riveting, adhesives) or temporarily (screws, bolts, clips), and the choice between permanent and temporary joints links straight to design for disassembly and repair.
Scales of production
Scale drives the process
The reasoning is a break-even comparison. Each process has a fixed tooling cost paid once, plus a variable cost per part. A cheap-tooling, high-per-part process (vacuum forming, 3D printing) wins at low volume; an expensive-tooling, low-per-part process (injection moulding) wins above a break-even volume where its tiny per-part cost has paid back the die. You find the break-even by setting the two total-cost expressions equal and solving for the quantity, which is exactly the kind of calculation AQA sets. As volume rises, manufacturers also move from manual and flexible methods to automated, dedicated tooling, jigs and fixtures (which hold and guide work so every part is identical without skilled marking out), and just-in-time supply, all of which cut unit cost and keep quality consistent across very large runs. The same finished shape can be made by very different processes, so the examiner expects the choice to be justified by both the material and the production volume, never by the shape alone.
Exam-style practice questions
Practice questions written in the style of AQA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
AQA 20196 marksA company can make a plastic casing either by vacuum forming (tooling cost 400 pounds, 3 pounds per part) or by injection moulding (tooling cost 24,000 pounds, 0.50 pounds per part). Calculate the production volume at which injection moulding becomes cheaper, and discuss which process suits a one-off prototype and which suits mass production. [6 marks]Show worked answer →
A worked applied-calculation question linking process to scale. Markers reward a correct break-even plus the reasoning. Set total costs equal: . Rearranging gives , so parts. Award marks for the equation, the rearrangement, and the break-even of about 9440 units, above which injection moulding is cheaper. Award discussion marks: for a one-off prototype, vacuum forming (or 3D printing) is right because the tooling is cheap and the high per-part cost is irrelevant at low volume; for mass production of tens or hundreds of thousands, injection moulding's expensive steel die is spread thin to give a very low unit cost. A top answer states the general rule that tooling cost is justified only when divided across a high enough volume.
AQA 20214 marksExplain the difference between batch and mass production, and give one product suited to each. [4 marks]Show worked answer →
A short-answer item. Award marks for: batch production makes a set quantity of identical products together, then the line is changed over to make a different product, suiting moderate volumes and variety (a run of a particular loaf at a bakery, or a seasonal product); mass production makes very high volumes of the same product continuously on a dedicated line with specialised tooling, suiting high-demand standard goods (drinks bottles, fasteners, standard electronics). Full marks need the set-quantity-with-changeover versus continuous-dedicated-line distinction plus a valid example each. Treating batch and mass as the same scale is the common error.
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