OCR A-Level Product Design manufacturing processes and scales of production: a complete overview

What this topic demands

The manufacturing topic tests whether you can describe a process, choose the right one for a product, work with the economics of scale, evaluate digital manufacture and control quality. Marks are lost when a process is described without the scale logic, or when a unit-cost calculation ignores the fixed cost, and gained by tying every process to a named product and volume. This overview ties the four dot-point pages together.

Shaping and forming processes

Metals are shaped by casting (molten metal into a mould, for complex shapes; sand for one-offs, die for mass), forging (deforming hot metal, which aligns the grain for strength) and machining (turning for cylinders, milling for profiles). Polymers are shaped by injection moulding (solid complex parts, high tooling, mass production), extrusion (constant cross-section), blow moulding (thin-walled hollow bottles), vacuum forming (open shallow shells) and rotational moulding (large hollow seamless shells). Timber is sawn, turned and laminated into curves. The choice follows the material, the shape and the scale. See shaping and forming processes.

Scales of production

There are four scales: one-off (unique, skilled, high unit cost), batch (a set quantity, jigs and fixtures, medium cost), mass (large numbers of a discrete product, automated, low unit cost) and continuous (non-stop bulk commodity). The economics are that unit cost is the fixed (tooling) cost shared per unit plus the variable cost, $\text{unit cost} = \frac{\text{fixed cost}}{\text{number made}} + \text{variable cost}$, so high-tooling processes only beat low-tooling ones above a break-even volume. Just in Time stock control delivers parts when needed, cutting storage cost but relying on dependable suppliers. See scales of production.

Digital manufacture

CAD models and simulates designs on screen for fast iteration; CAM drives machines from the CAD file; CNC machines cut precisely and repeatably; 3D printing (additive manufacture) builds parts layer by layer with no tooling, ideal for prototypes, one-offs and mass customisation; laser cutting cuts flat sheet quickly. The benefits are speed, accuracy, repeatability and customisation; the drawbacks are high equipment cost, the need for skilled operators, job displacement, and the slow speed of 3D printing for mass production. See digital manufacture, CAD and CAM.

Quality control and tolerances

Quality control is reactive checking to remove faults; quality assurance is proactive process management to prevent them. A tolerance is the permitted variation in a dimension ($25 \pm 0.1$ mm gives limits of $25.1$ and $24.9$ mm, a band of $0.2$ mm); tighter tolerances cost more, so they are set as wide as the function allows. Jigs and fixtures keep parts within tolerance, and ISO 9000, the BSI Kitemark and CE marking certify quality and conformity. See quality control and tolerances.

How to revise this topic

1. Match process to shape and scale. For each process, learn the material, the shape it makes and the volume it suits.
2. Drill the cost calculations. Practise unit cost and break-even volume until the method is automatic.
3. Learn the digital pros and cons. Be ready to evaluate CAD, CAM and 3D printing for a named product.
4. Get QC versus QA exact. Reactive checking versus proactive prevention.
5. Work the tolerance maths. Find limits and the band, and link a tighter tolerance to higher cost, then attempt the quiz.