Computer-aided design (CAD) uses digital geometry to construct, modify, visualize, and test models before physical production. Surface models define a product's exterior, solid models represent its complete volume, and virtual models allow designers to communicate or simulate its appearance and performance.
How each model is created and used
| CAD model | Creation and use |
|---|---|
| Surface model | The designer creates connected two-dimensional surfaces that form an object's outer skin. Curves, splines, and control points allow complex forms to be developed, making surface modelling useful for vehicle bodies, packaging, and other products where aesthetics and aerodynamics are important. |
| Solid model | CAD defines a fully enclosed three-dimensional volume using features such as extrusions, revolutions, sweeps, and Boolean operations. Because the model contains volumetric data, software can calculate mass, volume, centre of mass, and material requirements. It can also support interference checks and preparation for CNC manufacture or additive manufacturing. |
| Virtual model | A digital representation is given materials, colours, textures, lighting, and an operating environment. Designers use rendering, animation, virtual reality, or simulation to communicate proposals, evaluate user interaction, and predict behaviour without immediately producing a physical prototype. |
CAD supports iterative design because dimensions, geometry, materials, and components can be changed quickly. A parametric solid model, for example, may allow a designer to alter one dimension while dependent features update automatically. The revised model can then be tested through simulations such as stress analysis or motion analysis.
A common misconception is that surface models and solid models are equally suitable for engineering analysis. A surface model may appear complete but can lack thickness and internal volume; a solid model contains the closed geometry needed for many mass-property calculations and manufacturing operations.
Exam technique
For an IB Design Technology response on B2.2 Modelling and prototyping, identify the model type, explain how CAD constructs it, and link it to a specific design purpose. Do not merely state that CAD “makes a 3D model”; distinguish exterior geometry, enclosed volume, and virtual visualization or testing.