Parametric modelling basics
In parametric CAD, geometry is defined by parameters (dimensions and values) and relations (equations and constraints). Change a parameter and the model updates. This is the foundation of all design automation.
The parametric automation ladder
| Level | Tools | What it does |
|---|---|---|
| 1. Equations | Equations, relations, user parameters | Links dimensions within a part |
| 2. Tables | Design tables, family tables, iParts | Defines size families |
| 3. Rules in the model | iLogic, Creo relations and Pro/PROGRAM, CATIA Knowledgeware | Adds if/then logic, feature suppression, component swaps |
| 4. External automation | API add-ins in C#, C++, Python | Drives many models, drawings, data and integrations |
| 5. Knowledge-based engineering | Rules engines with CAD generation | Designs complete products from requirements |
Example: iLogic rule in Inventor
' Choose flange thickness and hole count by pipe diameter
If PipeDia <= 100 Then
FlangeThk = 12
HoleCount = 4
ElseIf PipeDia <= 250 Then
FlangeThk = 16
HoleCount = 8
Else
FlangeThk = 20
HoleCount = 12
End If
Feature.IsActive("Stiffener") = (PipeDia > 250)
iLogicVb.UpdateWhenDone = TrueBuilding robust parametric models
- Plan the design intent before modelling: what changes and what stays fixed.
- Reference stable geometry such as origin planes, not faces that may disappear.
- Name parameters clearly (Length, not d23).
- Test the extremes: smallest, largest and unusual combinations.
- Keep models simple; complexity makes rebuild failures more likely.
When to move beyond in-model rules
In-model rules are great for single parts and small assemblies. Move to external automation when you need to manage many files, create drawings and BOMs, connect to ERP or Excel, or share rules across CAD systems.
Parametric automation succeeds or fails on model quality. Good templates are the most valuable asset in the project.
Benefits
- New variants in minutes instead of hours.
- Engineering rules applied consistently.
- Easy maintenance: change a rule once, apply it everywhere.
Parametric automation with ENGIMANDI
We build parametric templates, iLogic rules and full design automation for Inventor, SolidWorks, Creo and CATIA.