CAD and Non-Product Geometry

Solid modeling software has the ability to create geometry that is not part of the product. Why is the creation of this type of geometry to ensure that requirements and constraints are being met not part of basic CAD software offerings?

Something I think CAD tools could do much better is to enable and help organize the creation of Non-Product Geometry. This is the geometry that some designers (too few in my opinion) create to represent geometric constraints; basically virtual GO/NO-GO gauges. The source of the constraints could be driven from many sources:

  • Functional Requirements (size and mass limits for example)
  • Manufacturing Process Limitations (draft angles, undercuts, tooling clearances)
  • Logistical or Service Implications (shipping tie-downs, fork pockets, tooling clearances – perhaps with different tools than what was used for initial manufacturing/assembly)
  • Industry Standards & Internal Best Practices (walkways, access panels, clearance/keep-out zones)
  • Standard Interfaces 
The geometry that is typically created to represent these constraints is usually quite simple (sketches, primitive 2D/3D shapes/volumes) but most CAD programs do not have standard ways of organizing this non-product geometry and applying standard rules (for example, keep-out geometry should always be red, translucent, and excluded from any size, surface-area, volume, and mass calculations). Designers and engineers that incorporate this type of geometry into their models to guide the design come up with their own standards that may or not be corporate standards. I’m not aware of any widely used, 3D solid modeling software that easily deals with the creation and management of this type of geometry. To be clear, creating the geometry in the CAD system is the trivial part; the unaddressed issue is treating these bits of geometry in special ways depending on what it is. The real trick is featureizing (I have been using that word for a long time, spell checkers always flag it!) the geometry with a task that allows for compliance to be checked; PTC’s Pro/Engineer, now PTC Creo, has had this capability since the early 2000’s and SolidWorks has a limited capability to create “sensors” for several releases now.
If being able to work easily with constraint geometry was standard functionality within CAD software, I’m pretty sure it would enable higher quality products to be developed faster and at lower costs. Finding out that a design was completed without having a way to get a wrench around a nut may not just be an inconvenience and not incorporating sufficient space around high-voltage electrical may prevent product certification (yes, I’ve seen this happen). What are other users doing when this type of functionality is not part of their CAD software?