Surface definition improves at the core

This cetrifugal blower is part of an air conditioner designed by Trane Corp. in Mechanical Desktop 2.- using the Acis 3.0- modeling kernel. Surface details for the molded housing (yellow) are accurately created using a new 3-D sweep feature, then translated into the moldmaker's CAM system using an SAT file format.

For mold designers and manufacturers, surfaces are everything. If cavity and core surfaces are not accurately defined, the resulting tool paths for CNC equipment will also contain errors. On the flip side of the spectrum, product designers often prefer to work in 3-D solids. When a solid CAD file is imported into the mold designer's system via IGES translation, surface definition can be lacking. As a result, surfaces either have to be created anew or tend to need a lot of repair.

While software vendors are waking up to this lapse, many rely on a "modeling kernel" or geometry core that supplies solid modeling and surface design engines. If the core lacks the necessary capabilities for creating or extracting surfaces, incorporating this function into a program becomes next to impossible.

Spatial Technologies, developers of the Acis modeling kernel, believes the answer lies in its newest release, dubbed Acis 3.0. You'll find it in the newest releases of Autodesk's Mechanical Desktop, Baystate Technologies' Cadkey, Delcam's PowerMill, and SmartCAM from SDRC/Camax. The new kernel enables these and other applications to add advanced surface modeling features. According to David Prawel, marketing director at Spatial, Acis 3.0 contains several functions aimed at easier, more accurate mold design. Users can now sweep a profile along an arbitrary 3-D path, use a rolling ball blend, and "sheet" blend between two surfaces rather than having to blend two faces that reside in a solid. Surfaces are also more easily extended and trimmed.

Prawel tells IMM that two years ago, Spatial brought two developers on board whose expertise in surfaces was put to use in creating new surface functions. One of the results is a new subsystem that uses mathematical functions, or laws, to define surfaces. Now, rather than using B-spline approximations for curves, users can input the exact equation to define the surface. "One benefit for mold design is that applying the draft angle becomes simple," says Prawel. "It's a straight-line linear sweep of a profile through a mathematical equation."

Another advantage to any Acis-enabled program is that it offers SAT interoperability. The SAT file format, created by Spatial, contains all the attributes and topology of a model created in any Acis application. Currently, there are 104 commercial applications available, the largest customer base of the three modeling core vendors by far. (In addition to Spatial, the group includes Parasolid by EDS and Designbase by Ricoh.)

An example of SAT file format benefits involves an IM tool for a logo badge. Several failed attempts at recreating the complex front surface of the badge put the project seriously behind schedule. Satellite Models (Mountain View, CA), a firm that specializes in prototypes and short production runs, got the S.O.S. call. "Our customer had created the badge in a solid modeling program, and sent the 5.7-Mb IGES file," says Kelly Hand, president, "which we translated into SmartCAM. Unfortunately, the surfaces everyone was concerned about were missing." Satellite contacted the designer, who sent an SAT file created in Mechanical Desktop 2.0. It transferred smoothly into SmartCAM, and supplied all of the surfaces. Tool paths were generated in less than 2 hours, and the tool was express shipped the same day.