The emerging Additive manufacturing technologies are being adopted by different industries, which require developing new materials and procedures. Here we report the development of polypropylene (PP) based composite materials for fused filament fabrication (FFF) process with the aim of enabling fully automatic robotic repair application of plastic components in automotive industry. A key challenge in repair and joining of polyolefins, which are widely used in such applications, is understanding the interplay of microstructural features and the joining mechanisms employed to achieve a uniform and fully functional repaired components. Specifically, for components manufactured from polypropylene based material, we show that the addition of ethylene propylene diene monomer (EPDM), polyisobutylene (PIB) and carbon black (CB) successfully modifies its matrix and produces a composite material ideal for additively repairing of complex geometries found in the automotive applications.This was brought about by effective reduction of the crystallinity of the composite PP matrix from 46.2% to 34.4% and resulting in a net reduction in warpage of the FFF 3D printed samples. Further, the thermal stability of the developed composite was improved with the addition of a moderate amount of carbon filler, enabling an FFF process with higher hot-end temperatures, which subsequently allowed for tuning of the raw material's viscosity, and hence ensuring consistent deposition of molten filaments for building successive layers. Mechanical properties' analysis revealed that the addition of 10 wt.% CB increased the true stiffness (storage modulus) by 20%, the impact strength by 62%, with the drop in ultimate tensile strength of 11%.The optimal elongation at break and toughness were achieved for the samples containing 2 wt.% CB increasing these key properties by 62% and 58%, respectively. In terms of the melt flow index (MFI), as a key rheological indicator, the measured value ranged between 12.5 and 19.0 g=10 min for all compositions suitable for the FFF process. Morphological analysis of the extruded filaments and fracture surface of impact test samples showed a mesoscale interspersion of polymer phases and a
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 $$^\circ{\rm C}$$ ∘ C , 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.
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