B2.2 — Modelling and prototyping

Key concepts

The terms "model" and "prototype" are often used interchangeably, but they serve different purposes. A model communicates aspects of a design — appearance, scale, spatial relationships — but may not function. A prototype tests functional behaviour — does it work, does it fit, does it hold up?

Every model or prototype should answer a specific question. Vague prototypes that "look a bit like the final product" waste time. Focused prototypes that answer "does this grip comfortable after 15 minutes?" produce knowledge.

Physical modelling

Physical models are built from cardboard, foam, MDF, clay, or other quick materials. Their strength is tactile reality — you can hold them, feel weight and balance, interact as a user would.

• Scale models — shrunk or enlarged representations (architectural models, exhibition mock-ups).
• Mock-ups — full-scale non-functional representations used for form and proportion.
• Appearance models — carefully finished models conveying the look and feel of the final product without the internals.
• Functional models — built to demonstrate specific mechanisms or operations.

Physical models force commitment — you cannot hide behind renders. If the form is awkward in foam, it will be awkward in the final product.

Digital modelling and CAD

Computer-Aided Design (CAD) tools (Fusion 360, SolidWorks, Onshape, Rhino, Blender) let designers model in three dimensions with precise geometry. CAD enables:

• Precise dimensions — parts fit together exactly
• Rapid modification — change a dimension, update the whole model
• Multiple variants — explore options without building each physically
• Simulation — stress analysis, motion studies, fluid flow
• Direct manufacturing — STL files to 3D printers, DXF files to laser cutters, G-code to CNC machines

CAD is efficient but seductive. A beautiful render implies finished thinking. Many designers use CAD too early, locking in forms before user testing. The best practice is low-fidelity physical exploration first, CAD once direction is stable.

CAM (Computer-Aided Manufacturing)

CAM converts CAD models into instructions that drive manufacturing machines. A student designing a phone stand might produce a CAD model, export DXF profiles for laser-cut parts, and STL files for 3D-printed connectors — all from the same source file.

Scale and purpose

A single project may involve several models, each answering a different question.

Communication through models

Models communicate design intent to people who cannot read CAD files — users, clients, manufacturing partners, examiners. A good model makes the invisible visible: stresses, user interactions, spatial relationships.

For IA submissions, models photographed with context (a user holding it, a ruler for scale, text callouts explaining features) communicate far more than renders alone.

Choosing physical or digital

Strong designers switch fluidly between both.

Case studies

Apple product development — legendary for both digital and physical modelling. Jony Ive's team produced dozens of CNC-milled aluminium mock-ups at every size and curvature variant, picked favourites by holding them, then returned to CAD for final specification. Physical and digital reinforce each other.

Architectural firms (Zaha Hadid, Foster + Partners) — build both 3D-printed scale models and full-scale mock-ups of details (window frames, cladding attachments). The scale model communicates the project; the detail mock-up verifies manufacturability.

Ford Gran Torino clay modelling — traditional automotive design uses full-scale clay models sculpted by hand, then 3D-scanned into CAD. The clay phase allows designers to evaluate surfaces in real light, which monitors cannot replicate.

Lego brick design — each new brick is modelled in CAD, tested in simulation for stress and clutch power, then injection-moulded as a prototype and physically tested. The cycle repeats until tolerances meet Lego's ±2 micron standard.

Glossary

• Model — a representation that communicates aspects of a design.
• Prototype — a testable version of a design that evaluates function.
• Mock-up — a full-scale non-functional representation of a design.
• CAD — Computer-Aided Design software for digital modelling.
• CAM — Computer-Aided Manufacturing software that converts CAD to machine instructions.
• STL — file format used to send 3D geometry to 3D printers.
• Appearance model — a model finished to show the look of the final product without functioning internals.
• Working prototype — a prototype that demonstrates or tests functional behaviour.

Check your understanding

1. Distinguish between a model and a prototype.

A model communicates aspects of a design — appearance, scale, spatial arrangement — but may not function. A prototype is built to test function — does the mechanism work, does the grip stay comfortable, does the circuit perform as expected. Both are valuable, but for different stages and purposes. A painted foam car body is a model; an engine bench-tested for 100 hours is a prototype.

2. Compare physical and digital prototyping for evaluating the ergonomics of a hand tool.

Physical prototyping gives authentic tactile feedback — real weight, texture, balance, temperature — and surfaces interaction problems the designer cannot anticipate (grip slipping when hands are damp, sharp edges felt only under load). Digital prototyping using CAD with digital human models provides precise dimensions, rapid variant exploration, and reach/clearance analysis, but cannot replicate felt experience. The strongest workflow uses CAD to explore many options quickly, then physical prototypes for final user testing.

3. Explain what CAD/CAM means and why the pairing accelerates modern design work.

CAD (Computer-Aided Design) creates precise 3D models of products. CAM (Computer-Aided Manufacturing) converts those models into machine instructions (G-code, DXF, STL) that drive CNC mills, laser cutters, and 3D printers. The pairing means a designer's CAD file can go directly to manufacture without re-drawing — reducing errors and lead time. A student can model a bracket, export STL, and 3D print it in an hour.

4. A student submits an IA with only a single final 3D-printed model and polished CAD renders. Why does this risk scoring poorly?

The IA is assessed on process evidence. A single end-model shows no iteration, no testing, no refinement. Renders show the student's CAD skills but not their design thinking. Examiners cannot award marks for criteria C and E (developing ideas, evaluating) without seeing intermediate prototypes, test results, and reflection. A process-rich portfolio with modest physical prototypes outscores a glossy product with no documentation.

Teacher's notes — additional examples and activities

Fidelity over time

A core principle: fidelity should increase across iterations. Early prototypes are low-fidelity (cardboard, sketches); later ones climb to high-fidelity (CAD, 3D prints, working electronics). Plot fidelity on Y, time on X — the line should rise through iterations.

SOAR framework for communicating ideas

• Sketch
• Outline
• Annotate
• Render

Every sketch in the IA should pass this four-stage test. Annotations ≤10 words each, in white boxes with black outlines, keeping ideas legible and compact.

CAD vs CAM — the distinction

• CAD (Computer Aided Design) — creating, modifying, and analysing designs digitally. Tools: Fusion 360, SolidWorks, Tinkercad, Onshape.
• CAM (Computer Aided Manufacturing) — converting CAD files to machine instructions (G-code, STL, DXF) that drive 3D printers, laser cutters, or CNC mills.

Students should be able to identify examples of each in their workflow.

Surface vs solid modelling

• Surface modelling — realistic exterior with no internal volume data; limited machining information. Good for visuals.
• Solid modelling — complete geometric representation of a part, including all internal details. Required for manufacturing, stress analysis, and simulations.

Manufacturers need solid models to mass-produce a product.

FEA (Finite Element Analysis)

Computerised simulation of how an object responds to physical forces. Predicts stress distribution, deflection, and failure points before physical prototypes are built. Saves time and money; reduces risk of late-stage redesign. Still, certain tests (drop tests, thermal cycling, regulatory compliance) must be physical.

Compare in a table: CAD testing vs physical testing — benefits, limitations, appropriate stages.

Virtual prototyping

Photorealistic CAD-based interactive models using surface + solid modelling. Enable: - Visual simulation - Reduced lead times - Reduced development costs - Fewer human errors

Digital humans and haptic technology

• Digital humans — motion capture, VR animation of bodies at different percentiles. Test ergonomics before building physical prototypes.
• Haptic technology — applies forces to the user via touch. Used in VR training, surgical simulators, remote operation.

Relates to biomechanics and anthropometrics (A1.1).

Rapid prototyping quick definition

Building physical prototypes quickly from digital designs, layer by layer. Materials include plastic (FDM, SLA), metal (SLS), and powder (binder jetting). Enables rapid user feedback cycles.

Iterative CAD workflow

1. Build a low-fidelity CAD model from the hand sketches
2. 3D print or laser cut
3. Evaluate against users
4. Re-design the CAD model
5. Print or cut again

Document each iteration — the evolution is what examiners reward.