Software predicts plastic part looks

New software from Dow looks at the three key components of a plastic part's appearance -- the color, gloss, and texture

Midland, MI—Appearances really can be deceiving, especially when it comes to molded plastic parts. It has become notoriously difficult to predict how a prospective part will look, due to the growing number of aesthetic possibilities and the complex interplay of material, pigment, light source, glosses, textures, and even molding condition. New software from Dow Plastics promises to take some of the guesswork out of appearance forecasting.

The company's Appearance Engineering software creates appearance models that simulate not only colors but also polymer gloss levels and textures. Working with commercial rendering software from Alias, the software then imparts these virtual "looks" to the surface of the part's CAD model. At first glance, this approach may not seem much different than what an ordinary rendering program does. Yet Dow software stands apart because it combines a detailed color-and-material database with proprietary gloss and texture models. "In the past, virtual appearance models haven't done a good job matching reality because they haven't adequately taken gloss and texture into account," says Scott Collick, global color manager for Dow Plastics.

Glossy predictions. To get a handle on gloss, for example, Dow scientists developed a mathematical model that goes beyond material type to incorporate molding conditions. "Mold temperature, hold times, and a variety of other molding parameters can affect gloss levels," Collick notes. Dow also used multi-angle spectrophotometry techniques to get a handle on the color characteristics of various pigment and plastic combinations at different viewing angles. This advanced technique yielded more than a conventional color database; it also provided information to feed into the gloss models, Collick explains: "The end result is that you see gloss on the screen as it would be seen on the final part."

And to incorporate textured surfaces into the appearance models, Dow has built a database of common tooling finishes. Coming up with realistic texture data required Dow scientists to perform a series of high-resolution(&1micron) surface scans of actual tooling finishes.

Skilled interpretation. Because it takes some skill to correctly interpret the appearance models, Collick says the software will remain in the hands of specially trained Dow "appearance engineers" for the time being. They will use the software for several kinds of customer projects. Quickly trying out different looks on a new design is one likely use. Another involves matching existing color standards—either from a prototype or an earlier product due for a materials change. Collick says the software will suggest a combination of colorants, materials, and processing conditions needed to match the existing color.

This color-matching capability opens up an important cost saving opportunity: Take away logistical and technical headaches of color matching, and engineers can mix high-performing and low-cost plastics based only on mechanical needs. "Sometimes components are over-engineered just to avoid color matching," Collick says.

As a brand new tool, the Appearance Engineering software does have a couple of limitations. For one, it can't yet include special effects, such as a translucent look. For another, the software focuses only on Dow's thermoplastics. Yet Collick expects both these limitations to disappear as the software matures.

For more information about appearance engineering from Dow Plastics: Enter 537