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Polystyrene Molds

3D Printing for Low-Volume Tooling

With the right material, 3D printed molds can withstand the steam and chemical exposure required for polystyrene molds. As an alternative to traditional machining, 3D printing molds directly from CAD data saves time and cost while maintaining accuracy.

EPS Polystyrene Molds

PPSF withstands high temperatures to manufacture helmet liners.

Real Challenge

Gentex requires EPS (expanded polystyrene) parts in different shapes, sizes and densities to manufacture helmets. The EPS parts are typically manufactured in low–volume production runs, making traditional aluminum molds costly and inefficient. The molding process employs pentene gas and steam, so a durable material was required. Also, the PPSF parts had to be accurate to minimize post process machining, to fi t into the molding press precisely, and to produce accurate EPS parts that would fit the final helmet product.

Real Solution

Three separate builds were required – a cavity, core and frontal insert. Sizes were 14.8 x 13.4 x 7.8 inches for the cavity and core, and 10 x 4.1 x 3.2 inches for the insert. Fortus PPSF material was selected because of the application temperature (250°F), chemical resistance and abrasion resistance.

A high–temperature primer paint was used to fill in “stepped” spots on the parts. This allowed sanding and kept the PPSF part dimensions intact, preserving the overall accuracy of the part.

When Gentex received the mold pieces, they drilled and press–fit approximately 20 stainless steel vents into each mold half. The average out–of–tolerance measurement was 0.006 inches, which exceeded the demands of this application.

The mold pieces were also cycled through an autoclave system to test the PPSF material for future tooling processes. Again, the PPSF withstood the temperature and pressure without distortion.

Real Results

Gentex saved $3,360 to $6,360 per mold assembly and shaved four weeks off the manufacturing process, compared to traditional CNC aluminum molds. Material selection, build envelope size, part accuracy and durability were key factors in choosing FDM. The ease of design iterations and flexibility for tooling design allowed for future projects.