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Surfacing with Solid Works

SolidWorks has more surfacing capability than many users realize. This write-up is for the benefit of new users and comments from experts.



What is surface modeling ,Engineering surfacing, Graphics surfacing, Curvature Continuity, Splines ?

(A)  Surface modeling allows you to create faces of required shape, and then join them. Surface modeling requires a lot more work than solid modeling, because solid modeling is an automation of surface modeling.

(B)  Engineering surfaces can be of 2 types: algebraic (analytic) and NURBS surfaces. Algebraic surfaces are created using extrudes and revolves using lines and arcs.NURBS (Non-Uniform Rational B-Splines) work by interpolating a surface between curves in two roughly perpendicular directions. These curves are called U-V isoparameters, which are roughly similar to longitude and latitude lines on a globe. The term isoparameter means that the curves in U direction lie along a fixed parameter along the V direction. When all these curves are displayed, it looks like a grid.One implication of creating surfaces from grid is that resulting surfaces have a tendency of being four-sided. This is common limitation of NURBS. One way to address this is by trimming. The other way is degenerate surface, but it has problems.Trimmed Surfaces combine the underlying surface and definition of boundary. This combination is called b-rep. Because of b-rep, we can remove boundary from imported surface and just get the underlying surface.

(C)  There is also a non-engineering surface type, which is mesh or subDivision surface. It is used in 3D graphics art. It is not purely surfacing. It is collection of 2D points. Adjacent 3 or 4 points are joined to form triangular or quadrilateral flat faces.SubD surfaces work well in graphics and animation, but in CAD applications, the surfaces need to be mathematically correct, and so faceted approximations don’t work. SolidWorks has add-in of scan-to-3D to convert mesh data to NURBS data.

(D)  The surfacing capability of a CAD software is decided by its ability to create complex model without edges. In SolidWorks, in most situations, it’s not possible to avoid edges. Edges separate faces created by different math.Thus, curvature continuity is essential for better surfacing.

(E)   Splines are very important construction geometry in creating good surfaces.Splines are sketch entities that offer infinite possibilities to create shapes. Spline is a long flexible strip of wood, used in drawing curves. The strip is pinned down in various locations, and the shape occurring naturally due to bending of material would be traced by pencil.SolidWorks offers spline functionality in 2D or 3D space. There are tools like control points, control polygon. Evaluation tools like curvature comb, inflection point, and minimum radius are also available. Surface evaluation techniques like zebra stripes are also there.