Parametric modeling

Parametric modeling is an approach to building 3D CAD models in which geometry is defined by parameters (dimensions, angles, radii) and by relationships, or constraints, between geometric elements. A change to one parameter automatically propagates to every dependent feature, and the model rebuilds.

Unlike direct modeling, where you edit geometry by pushing and pulling faces, a parametric model preserves design intent: for example, a hole diameter is always half the cylinder diameter, or a length is always three times the width. This enables fast iterations, because changing an input parameter updates the entire model.

Parametric modeling is the dominant approach in mechanical CAD systems such as SolidWorks, CATIA, Inventor and NX. The model is built as a sequence of features (sketch, extrude, fillet, hole and so on) recorded in a feature tree, which is why it is also called history-based or feature-based modeling. Each feature is defined parametrically and can be edited later.

Good parameterization is key to working efficiently: meaningful parameter names, equations for linked dimensions, and sketches that are neither over-defined nor under-defined. A well-parameterized model can be modified by another engineer without having to consult the original author.

A parametric approach pays off for parts and assemblies that will change or come in variants: product families in several sizes, configurable machines, parts whose dimensions depend on the surrounding installation space, or designs still in development where many iterations are expected.

It also suits reverse engineering, where a clean model with clearly defined dimensions is rebuilt from scan data, and any situation in which the model will be taken over and further edited by another engineer or another company.

A badly built parametric model can be worse than no model at all. A long feature tree with references to random edges and faces falls apart when something changes, and repairing it takes longer than modeling the part again from scratch. Reference features to the base planes and to driving (layout) sketches, not to edges created by fillets or chamfers.

When you take over a model from a supplier, check that you are getting native files with the full feature history (not just STEP), which software version they were saved in and whether the sketches are fully defined. If you expect variants, say so up front so the model can be built with configurations or a design table.