(continued from page 3)

Step Three: Integrate the Individual Parts

With geometry from your Master Model as a backbone for parametric control and creative flexibility, you are ready to build the individual parts.

We recommend working with surfaces for as long as possible before merging surface quilts and solidifying the part with the Protrusion, Use Quilt command. Modeling in surfaces makes it easier to visualize the part design, significantly speeds regeneration, and provides the greatest design versatility. For example, you can more readily and cleanly add or delete subquilts from the primary quilt using this approach than you can using solid Boolean operations.

It’s also important to consider your shell-building strategy before merging surface quilts and solidifying the part. Even if they offset individually, primary surfaces that are merged may create surface intersections that will not shell. To test for these occurrences, merge the surfaces in question and then offset the resulting quilt.

Another stumbling block you may encounter is the presence of singularities, which are points of convergence commonly created by three-sided surfaces. If you can’t avoid building a surface with a singularity, see if you can remove it, cut it away, or relocate it outside the boundaries of the merges.

Complex surface geometries, such as those mentioned above, tend to preclude use of the default Shell option. To sidestep these situations, we have established a few advanced “manual” shelling techniques (see sidebar).

Once shelling is complete, incorporate mechanical details such as bosses, ribs, and snaps. Then add draft to mechanical details, and always add rounds last. The exception to this rule is when a round drives some other feature or when the value of the radius is larger than the wall thickness. In this case, you would incorporate the round much earlier in the model, before creating the shell.

Favorite Advanced Surfacing Techniques

This list includes the surfacing techniques we use most frequently at Lunar Design and that provide the greatest control, versatility, and ability to maintain complex ID intent.

Variable Section Sweep. Represents the best method for building draft into a cosmetic surface or for controlling cross-sections through any given length of geometry. It’s simple and effective when you drive it with a two-point spline and reference a Pivot Dir plane to drive the draft.

Variable Section Sweeps enable tangents to neighboring surfaces and accommodate multiple trajectories. The Graph-Driven or Trajpar options expand functionality and let you tightly control surface quality. Variable Section Sweeps are more robust than boundary surfaces because they usually offset or shell, but you can’t control tangency at the ends of the sweep.

Swept Blend. Behaves similarly to a Variable Section Sweep, except that it enables multiple sections to drive a surface without using multiple trajectories or boundaries in the second direction. In other words, if you want the surface of a few known sections to follow a single spline, you can avoid using Graph-Driven or Trajpar relations. If you create sections on surfaces, you can drive tangency at both ends by projecting the end-section curves onto the surfaces to which you want to maintain tangency.

Boundary Surface. Provides control of all surface boundaries to maintain design intent at intersections between surfaces and at specific cross-sections. You can’t, however, control surfaces between curves. This technique lets you maintain tangency at all adjacent surfaces. (Variable Section Sweeps, in contrast, can only be tangent to trajectories, but not at start and finish.) You can preserve curvature continuity to create visually smoother transitions between adjacent surfaces, although C2 can only take place at boundaries in one direction. You can also generate three-sided surfaces, but we don’t recommend it because they rarely offset or shell.

Pro/DESIGNER®. Lets you create complex surfaces beyond the capabilities of the Pro/ENGINEER Advanced Surface Extension, with more free-forming, scaling, and other techniques. It removes parametric functionality without sacrificing Pro/ENGINEER compatibility. But you must modify surfaces in a separate environment, outside the main Pro/ENGINEER window, which makes iterations slightly more cumbersome. (For more information, please consult your local Pro/DESIGNER expert.)

Surfaces Imported from Other Platforms. Adds the surfacing versatility of third-party platforms that can complement the capabilities of Pro/ENGINEER. This technique is useful when the design contains geometry from other high-level visualization tools, such as Alias. Because data are primarily imported from IGES format, you will sacrifice the parametric functionality of the surfaces and have to make design changes in the other platform and re-import them. This makes revisions difficult to manage, because you can potentially lose edge and intersection references. One workaround is to import each surface as an individual feature instead of importing the entire quilt in one step. While more tedious, this procedure facilitates robust management of surface references.

Rigorous Process, Flexible Design

Managing high-profile industrial design requires discipline and a rigorous process to faithfully capture cosmetic design intent and build in the flexibility to make numerous changes. Following standard processes and construction techniques also enables a user who inherits a colleague’s model to get started quickly and accurately, and facilitates maintenance of the files. While we haven’t covered every detail of how we use Pro/ENGINEER software to achieve these goals at Lunar Design, we hope you can use the information presented here to develop your own strategies for success.

Andrew Zee is former director of ventures and Joel Jacobs is director of product design at Lunar Design, Inc., a full-service product development firm offering industrial design, mechanical engineering, graphic design, imaging, and branding. Please direct inquiries to joel@lunar.com.