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Recent trends in automotive interior trim include part consolidation, elimination of painting and lower gloss, all of which require better molding materials, be it general purpose or high heat grades. These requirements, larger and more complex parts and uniform surface appearance, have led the plastics industry to respond with softer flowing grades. These grades provide longer flow length, and better pick up of the mold surface details for the final appearance. To produce a softer flowing polymer, the polymer viscosity is reduced through material structure engineering. At the same time that these soft flow polymers provided the needed moldability it was found that molding could be accomplished at lower melt and mold temperatures while still achieving the desired surface appearance. Lower molding temperatures make it possible to shorten the cooling cycle and possibly the total cycle time.

The design and material selection for interior trim parts must take into account the expected service life and environment of the part. This environment is largely the high temperatures encountered in the automobile interior and occasional contact with various interior cleaning agents. Material selection is customarily based on information found in material data sheets. This data is generated by using standard ASTM test specimens and test methods. While those results are useful, the data is generated under molding conditions which may be far from the ones under which actual parts are produced. Molding conditions, material characteristics, part design, and gating play a major role in the real performance of the molded parts. This paper will demonstrate the effect of some of those parameters on the actual performance of interior parts.