Surfaces, solids, and wireframes for faster mold design

September 08, 1998

Nowhere in the molding industry are production time constraints more keenly felt than in moldmaking. Speeding up the concept, design, and analysis phases of product development is a relatively simple task compared to compressing the time it takes to make a mold. In the past, using 3-D CAD to create complex cores and cavities was one answer to the problem. Unfortunately, mold designers often had trouble when the time came to translate those solids into the surfaces needed for NC machining.

Baystate Technologies' president Robert Bean believes the company's newest version of Cadkey 97 (release 2) can smooth the process from solid to surface to wireframe. The new software incorporates Acis 3.0 modeling kernel ("Surface definition improves at the core," November 1997 IMM, p. 79), which brings significant improvements in robustness, speed, and shelling for plastic part design.

'One of the major obstacles for moldmaking has been the ability to accurately translate various parametric CAD files.'

During a recent interview, Bean explained why features of this newest version are attractive to moldmakers. "One of the major obstacles for moldmaking has been the ability to accurately translate various parametric CAD files. So we have improved IGES translations for surfaces and solids, conducting benchmarking tests with Catia files and others. Also, there are additional translators, such as the IGES translator available from FastSurf, so you're not stuck with one way to get geometry in and out."

Developing mold core and cavity blocks from the solid model for this housing normally requires IGES translations and surface geometry rework. But the process can be streamlined using several translation tools available in Cadkey 97. Advanced mold design and reverse engineering add-on modules are also available.

With the new release, users can work on the model without worrying about the parametrics. There are some limitations--while mold designers can delete features or holes, refillet, or delete fillets, they can't change shell thickness. In the future, an add-on module will allow users to work with parametrics if they choose.

Rather than one specific tool, Cadkey 97 provides 2-D, 3-D solids, wireframe, and surfaces with FastSurf or FastSolid, as well as NC programming with FastNurbs (see sidebar story). "Real designers are often working in all of these areas, so we've created an approach to everyday design that says you can use any method interchangeably," notes Bean. "In the future we will be adding a deformable surfacing capability, which allows you to select a surface and stretch it."

'We've created an approach to everyday design that says you can use any method interchangeably.'

Another benefit of the new version is that it includes Acis DLL, which allows users to keep one copy in memory and lets other programs share it. "You don't have to load another copy of Acis," Bean says. "Every time you load a solid-modelingbased product, you use up memory and slow down processing time. That doesn't happen with DLL."

Cadkey 97 offers the ability to develop and modify molded parts in wireframe to check for clearances, while also using solid modeling to construct more complex shell forms. Part walls for this electronic enclosure were designed with the solids modeler. Original 3-D profiles of the inner and outer rim were created in wireframe, and slots were calculated with the Boolean difference of the primitive block.

Because tooling applications are a target market for Cadkey, Baystate conducted some extensive feedback sessions with current users and potential ones. Moldmakers who participated in the research indicated they were generally looking for easier editing techniques.

So the software now contains an easy way to define hot keys specifically for tasks such as mold design, modeling, or drafting. Other, more esoteric modeling features include tweaking, which allows designers to take a face on a solid and project or extrude up to another surface. Finally, users can get detail drawings from the solid model. Cross sections and side views are created automatically.

Across the board, Cadkey 97 R2 contains large performance increases. According to Bean, loading part files is now twice as fast as the previous version, and rendering is up to three times as fast. A 2-D file for a catamaran car ferry, for example, used to load in 40 seconds, and now loads in 5 seconds.

Getting from design to NC toolpaths

Basilius Tool (Toledo, OH) is a third-generation business that is family owned and operated. Using the latest technology available to manufacture injection molds and injection molded parts, the company serves customers in automotive, medical, and electronics industries. "We are able to satisfy all of our design requirements now with Cadkey, Fastsurf, and Fastsolid," says Scott Basilius, owner and chief technology officer. However, Basilius and crew had less than ideal results with other CAM programming systems.

Several months ago, mold designers began using FastNurbs NC in combination with Cadkey, Fastsurf, and Fastsolid. Basilius explains, "Now we share surface data between Cadkey and FastNurbs, which is integrated under the Cadkey interface. No more writing out IGES files from Cadkey, then reading them back into our programming system. Our learning curve was greatly reduced because we were already familiar with operating Cadkey," he says.

Unlike systems that create a triangular mesh to approximate a surface, FastNurbs NC generates tool paths directly from the surface data. Basilius reports that the surface finish of machined electrodes has greatly improved as a result. To further reduce machining time without compromising surface quality, Basilius Tool also purchased a high-speed vertical machining center that uses Nurbs-based interpolation. "By creating a tool path as a series of weighted node points instead of a large number of short line segments, the processing time required in our machine tool control is reduced by about 30 percent," he adds. "Customer demands for fast deliveries have mandated us to find ways to improve our manufacturing ways, and our software investments have not been a disappointment."

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