The big idea: The scale of production decides which manufacturing techniques a product can afford, because tooling is a fixed cost divided by the number of parts.
Five scales
- One-off
- Batch
- Mass
- Mass customisation
- Continuous
Why it matters: Where a product sits on that curve decides the process, the system and often the design itself.
Cost per part against quantity, with the five scales marked on the curve.
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| Scale | Quantity | Techniques it can afford |
|---|---|---|
| One-off | A single unique item | Hand tools, machining, bending, 3D printing, welding — anything with no tooling to make first |
| Batch | A set number, then the line changes to something else | Vacuum forming, sand casting, rotational moulding, CNC machining, laser cutting — cheap tooling that pays off in dozens |
| Mass | Very large numbers of an identical product | Injection moulding, press forming, die casting, extrusion — expensive precision tooling spread over a huge run |
| Mass customisation | Large numbers, with each unit different | Additive manufacturing, CNC from a file, or modular assembly of standard parts in different combinations |
| Continuous | Running twenty-four hours a day, indefinitely | Extrusion, rolling, float glass, chemical and food processing — output measured in metres or tonnes |
Why continuous production never stops: Starting and stopping a float glass line or a chemical plant costs more than running it, because the process has to be brought back to temperature and the first output is scrap.
So it runs continuously and the product is stockpiled — which is a manufacturing decision that shapes a whole industry.
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Choosing a technique from the quantity
One-off to a handful
No tooling at all. Machine it, print it, bend it or build it by hand — a designer's time is the dominant cost.
Dozens to a few hundred
Cheap tooling that pays off quickly: a vacuum-forming mould in MDF, a sand casting pattern, a printing run.
Thousands
The crossover region, where the answer genuinely depends on the shape and on how long the product will be made.
Tens of thousands upwards
Expensive precision tooling: injection moulding, press forming, die casting. Seconds per part, pennies per part.
Batch production has a hidden cost: Every change of batch means a set-up: tools changed, machines reset, the first few parts scrapped while it is dialled in.
Same total, different cost: A batch of 50 made ten times a year costs far more per unit than a batch of 500 made once, even though the annual total is the same. That is why batch sizes are a real design and planning decision.
One product, three scales over its life
One-off
A single prototype at the end of development: tested, shown to investors and buyers, used to check it can be made.
Batch
A set number, e.g. 300 for a launch: the line is set up for that quantity, and sales show whether larger runs are worth it.
Mass customization
Standard parts made in volume, then finished to each order: customers choose colours or upload graphics online, gaining choice with economies of scale.
Mass or continuous
Huge numbers of identical units on a line for a proven product; continuous when the line never stops (glass, chemicals, cans).
How this is tested — determining appropriate manufacturing techniques for each scale of production. It comes up two ways:
Paper 1 — multiple choice
- Match a technique to a stated scale of production.
- Identify the scale a described product is made at.
Paper 2 — analysing a product
- Determine techniques for a product at a stated volume.
- Explain how the scale of production changes the design.
The trap: Recommending injection moulding at every scale. Below a few thousand parts the tooling dominates, and vacuum forming or machining is cheaper per unit.
A plastic enclosure is needed first as one prototype, then as 300 for a trial, then as 150,000 a year. Explain the technique you would use at each scale.
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