Investigation of the fastening behavior of self-tapping plastic joints with various supporting ribs

Abstract

This work aimed at investigating the fastening behavior of self-tapping screw joints installed on a tubular-shaped plastic boss with supporting ribs using finite element analysis (FEA) and experiments. For joining the commercial vehicle interior components, most plastic plates are mounted on the ribs of the boss for easier assembly unlike conventional plastic joints, so the ribs endure the preload of the screw rather than the boss itself. Because of this distinctive structural characteristic, different fastening behaviors were observed for the shape of the rib. For a boss with relatively weak ribs, the clamping force did not increase above a specific value, even when the tightening torque gradually increased during the fastening process. The relationships among the tightening torque, clamping force, and rotating angle of the screw were investigated using FEA, for nine different bosses with ribs of various shapes. Tightening experiments on the two types of bosses were also conducted to validate the FEA results. Finally, the joint performance, the maximum clamping force, of the nine bosses was compared on a basis of the normalized stiffness of the rib.