EPS Polystyrene Molds
PPSF withstands high temperatures to manufacture helmet liners.
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.
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
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
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.