Is Parametrics History?

New CAD tools lately have been SpaceClaim, Moment of Inspiration, and even CosmicBlobs Pro, along with tools like T-splines, Free Dimension, modo, maybe some others. What do all of these have in common? Well, nothing, really, but in general, they center around making changes easier and concepting. Oh, and one other thing. None of these are parametric history based modelers (MOI has some history based concepts, I think). Most of these are for shapely parts, but SpaceClaim and MOI are also adept at prismatic parts.

So what is the industry telling us? I don’t know that either. You’d have to find “the industry” and ask him. Or her. or whatever. But, here is what I’m hearing, regardless if its only the little voices in my head that are saying it: Concepting and ease of change. Here’s what I’m not hearing: design intent.

You see, parametric history based modeling is great for making parts with intelligence. But what kinds of parts can you design with intelligence? Well, a lot of stuff. Machine design parts are great for it. Plastic parts are mainly great for it as well. But what do you do when some of your parts look like this:

And the changes you want to make to them are more like silly putty than anything else.

This is a medical part, an interlaryngeal airway mask, which seals off against the back of your throat during anesthesiology procedures. It is blow molded or injection moded from soft silicone. Developing geometry to fit the shapes of internal organs can be a challenge. This part is hollow, the outer loop functions as a balloon, but also allows gas to travel through the big hole at the end. It is shown half cut away and transparent here to help you see the internal features.

I’ve been working on a set of products like this for the past couple of years, and the changes that need to be made sometimes require either drastic rebuilds because they don’t fit the original “design intent”, or they might require an ugly hack just to get the geometry without worrying about the parametrics.

I’m going to guess that I’m not the only person that has this kind of problem. With shapes like this you really don’t want to have to deal with the overhead of parametrics. SolidWorks is so sensitive sometimes that just moving a couple of spline points causes a whole set of what seem to be unnecessary repercussions down the tree, things like a trim reordering the resulting bodies, resulting in a different selection to keep than you intended, or losing track of the edges of a planar surface selection, the list is really endless, these are just the problems I had today with this model. Of course this is just reflecting problems with the implementation of the technology, not the technology itself, but when it comes down to it, is there another tool which handles the implemetation better? Would I stop having problems with parametrics if I were using say Pro/E? Probably not.

Still, I don’t think direct geometry editors can handle this type of work either. SpaceClaim certainly could not modify this model in the ways I need to model it, nor could SolidWorks make the changes if it were an imported model. You would need to work with Rhino, but there is no guarantee that it would be easier than working with native data in SolidWorks. Its an ugly problem. Parts that combine complex shapes with internal geometry and the need to morph organically are problematic no matter where you work on them.

So what do you do? What tools do you use to create and more importantly change geometry like this? Mesh and subdivision modelers are sophisticated, especially when it comes to morphing shapes, but not sophisticated enough in the ways needed for creating manufacturable geometry.

Have you ever seen the movie The Incredibles? 3D animated cg stuff. Its really a movie about what you can do with mesh modelers. The characters stretch and deform and flex in ways you can’t even imagine doing in an engineering CAD tool, but we still sometimes need to be able to do that kind of work with our parts. You can’t do that kind of stuff with parametric history based modelers. Not efficiently anyway. So what do we do? Use a mesh modeler like Maya or 3DS Max? No, they can’t hold the accuracy that NURBS modelers hold. So for the time being we are stuck. Changing shapes organically is too complex for parametrics, and too precise for mesh modelers.

I don’t think this is just a case of somehow making users smarter. Parametrics can be challenging even on far more easily defined prismatic parts. Certainly there are “best practice” rules you can follow to some extent to help make changes more likely to update properly, but the truth is that the SolidWorks execution of the technological concepts of parametrics for complex shapes is imperfect (uh, it doesn’t always act predictably).

How is this going to work out? Will parametrics ever make the technological leap needed to make NURBS modeling practical from an organic manufacturing model accuracy and flexibility standpoint? Will mesh modelers progress in accuracy? This no mans land of organic CAD models is a lonely place to live, really half way between two very different worlds, neither of which really satisfies all of its needs.