Surface-Surface Blending with Variational Sweep

Posted by Wayne McClelland to the ICCON Bulletin Board, 9-Nov-1997

As users of I-DEAS, we look forward to the explicit ability to fillet between two non-intersecting surfaces.  But in the meantime, the Variational Sweep functionality in I-DEAS is an effective and (in most all cases) productive workaround.   Furthermore, as we master Variational Sweep we find that this very powerful tool can be of great benefit in a wide variety of advanced surfacing situations.  The example below is intended to motivate you (and colleagues and doomsayers) to use Variational Sweep for these and other interesting applications.

Surface-Surface Blend with Variational Sweep

I've created some parts in the "before", "during", and "after" stages for the classic "Sphere/Sculpted Surface Example" shown above.  To access these files, just do the following:

bulletDownload Library File (93kb)
bulletUnzip the file (this will extract a package file and four part files)
bulletIf you're on Unix, you'll also need to convert the library by using the new I-DEAS Heterogeneous Data Sharing.
bulletOpen a new model file, enter the Design application, Master Modeler task
bulletFile, Import, I-DEAS Library Data... enter the library file that you downloaded and unzipped
bulletGet-from-Library... the "surf-surf" library, the parts "ssblend1", "ssblend2", "ssblend3", and "ssblend4"

OK, first let's walk through reconstructing this example.  (After looking at the precreated parts, I'll give you some step-by-step instructions on how to do it yourself.)

bulletGet the "ssblend1" part to the workbench.  This of course shows the classic case of non-intersecting surfaces that we wish to fillet, but for which there is no intersection edge as needed by the I-DEAS Fillet command.  Note that the two bodies have been Added together into one part.

two non-connecting surfaces (ssblend1)

bullet

Put away all parts on the workbench and Get the "ssblend2" part to the workbench.  To arrive at this stage, I simply created a reference plane, sketched the circular path on the reference plane, and then sketched-on-path to create the desired arc fillet section tangent to the parent surfaces.

Path and Section for Variational Sweep (ssblend2)

bullet

Put away all parts on the workbench and Get the "ssblend3" part to the workbench. This is the desired final result of using Variational Sweep to create the blend surface, stitched into the parent surfaces.

Blend surface auto-stitched to parent surfaces

bullet

Put away all parts on the workbench and Get the "ssblend4" part to the workbench.  Just to confirm the quality of the surface tangencies, we can shell the part (first deleting the two trimmed surfaces enclosed by the blend surface) and then plane cut the part for visual verification.

Result shelled and plane cut

bullet

The resulting part is fully history supported, associative, and editable.

bullet

The simple example above assumes of course a constant radius arc fillet.   We could have just as easily blended a number of more complex situations, including:

bulletthe radius (or any other section dimension) could vary along the sweep path.
bulletsketching a conic section (e.g. parabola) for the fillet
bulletsketching a general spline section with tangency and also curvature continuity with the parent surfaces
bulletsketching a sweep section with more than one curve.  In the case below we see a circular "ring" inserted in the section and constrained to be a fixed chord distance from the top rail of the blend.  I suspect that this case would be very difficult if not impossible to model without the Variational Sweep capability.

Blend with multi-curve section

The more comprehensive step-by-step instructions below are provided so that you can conduct the Variational Sweep yourself live.

Step 1:  Access the desired geometry to be blended (or make your own sphere and sculpted surface, Add them into one part, and skip this step)
bulletNew model file
bulletApplication=Design, Task=Master Modeler
bullet(import the library as noted in the box above)
bulletGet "ssblend1"  (or make your own geometry)
Step 2:  Prepare the Path and Section for Variational Sweep (yes, I realize that you wouldn't have to do Step 2 at all if I-DEAS had an explicit surface/surface fillet --- for the case of the arc fillet.   But this step is very powerful for more complex situations.)
bulletCreate a Reference Plane, Axis, ZX, translated from the center of the sphere -30mm (location is not particularly critical)
bulletCircle by Center-Edge... MB3=Focus on the center of the sphere, and about 30mm in radius (again, not particularly critical)
bulletDelete... [circle diameter dimension], [coincident point constraint at the circle center] (constraints are not currently allowed in variational sweep paths)
bulletSketch-on-path... [pick the circular path], at say a [point] near the xy plane (not critical)
bulletArc-three-points...
bulletMB3=Intersect... [select the sphere] to create an intersection curve with the sketch plane
bulletMB3=Intersect... [select the sculpted surface] to create an intersection curve with the sketch plane
bulletusing screen picks, approximately sketch 3 points for the cross section of the arc fillet (unfortunately, the dynamic navigator will not snap to the surface intersection curves just created)
bulletConstraint, Coincident... (the following will take some time to compute -- approx. 15-20 seconds)
bullet[pick the upper arc end]... [pick the sphere intersection curve] (light blue)
bullet[pick the lower arc end]... [pick the sculpted surface intersection curve] (light blue)
bulletConstraint, Tangent...
bullet[pick the upper end of the arc]... [pick the sphere intersection curve]
bullet[pick the lower end of the arc]... [pick the sculpted surface intersection curve]
Step 3:  Variationally Sweep the Blend (remember that Step 3 applies even if the section created in Step 2 was much more complicated than just a simple arc)
bulletVariational Sweep (in the Extrude icon stack)
bullet[pick the circle as the path], then done
bullet[pick the section], then done
bullet(I-DEAS will take some time to compute the desired sweep sections -- approx. 1-2 minutes)
bullet(at this point you could do a bunch of optional advanced things, such as setting variable radii along the sweep path, matching dimensions, etc)
bulletStitch... OK
Step 4:  (optional) Shell and Plane Cut
bulletDelete... [pick the lower surface of the sphere], [pick the portion of the sculpted surface now surrounded by the blend surface]
bulletShell... [pick the part], 3mm
bulletPlane-Cut... [pick the part], Axis-plane, XY, pick point, [center of the sphere], Negative side

 

 
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