Last year, Autodesk added mesh modeling to AutoCAD; this year, they added surfaces. “How does Autodesk differentiate their surface modeler from others, such as Rhino, I wondered? AutoCAD 2011 is not just a NURBS modeler, but also allows: direct manipulation and associativity in surfaces.
When you design with surfaces, you usually begin with splines, which act as the framework onto which surfaces are applied. “How healthy are our splines?” asked the demo jock. He showed new ways to create splines with control vertices, knots, and freehand sketching. Freehand splines are based on the old Sketch command and are meant for use with a tablet and stylus, he demo’ed to us. Once you place the 2D and 3D splines, you can edit them directly, changing endpoints, moving control vertices, and so on — in the same way it is done in Inventor.
With the splines forming the outlines of the object being designed, the next step is to apply surfaces, of which AutoCAD has several types. There is one for “adding the skin to the splines” with a network surface, another for lofting, yet another for fixing holes with a cap surface.
More than a NURBS surface, however, surfaces in AutoCAD are explicit surfaces that remember all properties of their creation. (A standard NURBS surface would not remember.) When one surface is connected to another, you can define the continuity between them: G0 (square edge), G1 and G2 (varying roundness) — no need to apply the Fillet command. The continuity can be changed at any time.
Surface associativity connects the splines with the surfaces from which they were made. For example, when you trim a surface with a circle, the trim is associative. I asked if this was two-way associativity? No, because normally you do not adjust the surface; rather, you adjust the objects that define the surface. (You can, of course, edit surfaces directly, if you really need to, and AutoCAD 2011 comes with numerous surface editing commands, like FilletEdge and 3dEditTool.)
AutoCAD 2011 includes three lightweight analysis commands: zebra, curvature, and draft. I asked what the purpose of these were, relative to the heavyweight analysis provided by MoldFlow and ALGOR? These are meant to be early stage analysis tools that help the designer before the AutoCAD file is sent to Inventor (via DWG), where more extensive analysis is applied.
The basic design can now be done in AutoCAD; once in Inventor, it can be modeled more extensively, such as shelling and adding ribs.
