Mechanical properties of 3D-printed staking polypropylene posts for repairing automotive headlights

Additive manufacturing (AM) processes present unique opportunities for the repair of high-value-added industrial and consumer plastic products, which otherwise are destined for the landfill at the end of their life and contribute to the growing environmental and health issues. In this work, we propose a novel method of integrating fused filament-based additive fabrication with the hot staking method to repair a complex automotive component, namely headlight. Newly formulated polypropylene-based composite filaments were used to 3D print a set of staking posts and the missing brackets in the damaged headlight to enable their effective reuse of the repaired assembly. Three staking designs were tested in the first phase of the experiments with the respective geometrical configurations, viz. knurled, domed, and hollow. Strength tests were conducted to rank the performance of the joints against the highest ultimate shear strength values, toughness, and repeatability. The joint design with a domed-shaped profile ranked the best across these criteria. In the second phase of the study, the main printing parameters, including printing temperature, nozzle head penetration in the substrate, printing speed, and layer height, were optimised to increase the joint strength. Based on the design of experiment, the dome-shaped stakes, which were printed using a nozzle temperature of 240 ∘C\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$^\circ{\rm C}$$\end{document}, tip penetration of 0.3 mm, 3D printing speed of 12 mm/s, and a layer height of 0.15 mm demonstrated the highest mechanical performance with the bond strength of 7.27 MPa. The repaired headlight was tested under cycling loading showing excellent durability without noticeable degradation of the staked joints upon 10,000 cycles.