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Technical Paper

Effect of Regrind on SMA Copolymer Boss/Joint Performance

To minimize warranty costs, due to squeak and rattle from ill fitting joints, automotive OEMs are requiring increased durability of thermoplastic attachments. There are several evaluation techniques for determining thermoplastic joint durability performance such as: strip-to-drive torque, screw pull-out force, and clamp load fall-off. A thermoplastic attachment (i.e. boss) which experiences clamp load fall-off will result in a loose fitting joint and subsequently lead to squeaks and rattles. In conjunction with the boss's performance the type of captured material between the screw and the joint can also contribute significantly to the overall retention qualities of the attachment. The purpose of this paper is to evaluate: 1.) strip-to-drive ratios for thermoplastic bosses, and 2.) changes in clamp load with respect to environmental effects (i.e. thermal exposure) on thermoplastic bosses.
Technical Paper

Understanding the Mechanical Behavior of Threaded Fasteners in Thermoplastic Bosses Under Load

Because it is common to attach plastic parts to other plastic, metal, or ceramic assemblies with mechanical fasteners that are often stronger and stiffer than the plastic with which they are mated, it is important to be able to predict the retention of the fastener in the polymeric component. The ability to predict this information allows engineers to more accurately estimate length of part service life. A study was initiated to understand the behavior of threaded fasteners in bosses molded from engineering thermoplastic resins. The study examined fastening dynamics during and after insertion of the fastener and the effects of friction on the subsequent performance of the resin. Tests were conducted at ambient temperatures over a range of torques and loads using several fixtures that were specially designed for the study. Materials evaluated include modified-polyphenylene ether (M-PPE), polyetherimide (PEI), polybutylene terephthalate (PBT), and polycarbonate (PC).