Fastening Characteristics of Fiberglass Reinforced S/MA Copolymers in Instrument Panel Substrates

A large percentage of the total number of instrument panel substrates in North American vehicles are injection molded from a fiberglass reinforced and rubber modified thermoplastic copolymer comprised of styrene and maleic anhydride (S/MA). Most of these instrument panels contain a number of molded-in attachment bosses, which are used in conjunction with a variety of metal screws. Previous SAE Technical Papers* have defined processing and design parameters for these thermoplastic materials and have suggested improved designs to optimize these structural attachment bosses.

The purpose of this paper is to further describe the fastening characteristics of these molded S/MA bosses with a laboratory evaluation which includes standard torque measurements, evaluation of various bearing surfaces, and evaluation of insertional speed. Improvement of torque retention over time is of great interest in this automotive application and suggestions for its optimization will be made.