Joint performance of injection-molded thermoplastic bosses containing post-consumer recyclate: possible squeak and rattle implications

摘要

Post-Consumer Recyclate (PCR) or Post-Industrial Regrind (PIR) used to manufacture thermoplastic (or thermoset) automotive parts and components, has increased over the last 20 years. Therefore, automotive designers are challenged with the question of how recycled material differs in performance from virgin? In addition, automotive OEMs are requiring increased durability of thermoplastic parts and their attachments (joints), so that warranty costs, associated with interior squeaks and rattles are minimized. From this durability need there have grown several techniques for determining an attachment's performance capabilities, they are: strip-to-drive torque ratios, screw pull-out force, and clamp load fall-off. For example, if a boss has a low strip-to-drive torque ration (<3) there exists the potential for assembly and/or field failures. Also, a thermoplastic attachment (i.e., boss) which experiences clamp load fall-off (stress relaxation) will result in a loose fitting joint and would subsequently lead to interior squeaks and rattles. Attachments/Joints, such as injection-molded thermoplastic bosses, are on a variety of interior automotive components such as: instrument panel substrates, interior trim, consoles, package trays, cowl vents, side seat shields, and knee bolsters. To prevent squeaks and rattles, these components must be robustly designed to survive extreme environmental conditions. Ford Motor Company evaluation vehicles, in Arizona, have experienced interior temperature variations between 66°C (for below the beltline interior trim) to as high as 114°C (for package trays). Instrument panels can experience surface temperatures anywhere from 60°C to 105°C. These large variations in temperature will cause physical property changes in thermoplastics. Temperature changes will lead to expansions and contractions, due to the materials coefficient of thermal expansion (CTE), and reduction in the storage modulus (E), resulting in loose fitting joints. The purpose of this paper is to evaluate the joint durability of virgin and PCR containing thermoplastic bosses, using the following metrics: 1.) pull-out forces, 2.) strip-to-drive ratios, and 3.) changes in the clamp load, with respect to environmental effects (i.e., thermal exposure). Our paper will emphasize the differences between virgin and PCR containing bosses and how this possibly relates to their squeak and rattle performance.