When speaking about design processes using Computer-Aided Design (CAD) solutions, people often refer to “engineering intent.” Not being a CAD guy (and not playing one on TV either), I would ask colleagues about exactly what this meant. Most of the conversations left me confused, because they would talk about history trees, and the problems with one person having to make changes to another’s design and having to unravel the steps that were used to transform shapes into the desired part or assembly.

This left me believing that a lot of what people referred to as engineering intent was really “geometric intent,” the steps that a person executed using their CAD solution of choice to create the desired result. As a lapsed mathematician, I knew that there were many geometric ways to skin the cat, if you will. You can get to a desired geometric end result using different transformations. How you got there was a function of what ways your chosen CAD solution provided to you, and you knowledge of how best to use them. That is not to say that there is NO engineering intent in these steps, it was just that what I was hearing was more about geometry than engineering.

One explicit way that engineering intent does get into models is through parametrics. The requirements that engineers start with can often be expressed by mathematical relationships between faces or other features in the model. Another is what some term “design in context,” where there are contraints on your model that result from the other adjacent parts and assemblies into which your part must fit.

So why is this important, and why did I choose the title of a 90s “chick flick” for this post? Because in the last few years, several CAD suppliers have introduced solutions that make it easier to repurpose, modify, and otherwise change existing geometry. Siemens PLM Software talks about Synchronous Technology. SpaceClaim is making a business around helping people downstream from geometry creation to tweak things to make them easier to use (like CAE analysts or manufacturing people or people in supply chains).

It is this issue that raises serious questions for me. How can downstream users modify existing geometry and really KNOW they are not doing so in a way that affects the true engineering intent? You can’t really embed all of that intent in the model, and downstream people may not know about the real requirements. If your analysis reveals a weakness in the structure, and the analyst can change that structure, how can you be sure that the resulting part still meets the original spec? This example is not so bad, because if they are in the same organization you can have it kick off an engineering change process to make sure this happens.

But what about people outside your four walls and not so clearly under your control? Contract manufacturing organizations for instance. The results of such downstream changes could indeed be cruel to your organization. (Not sure that Reese, Ryan and Selma thought about this one.)

OK, if anybody is still listening, please explain to me the error of my ways. I look forward to the discussion. Follow Stan on Twitter @smprezbo.