Effects of Process Parameters on the Interlayer Bond Quality of Multi-material Thermoplastic Polyurethane Parts Built by Extrusion-Based 3D Printing

Extrusion-based 3D printing, such as Fused Filament Fabrication (FFF), has become one of the most used Additive Manufacturing techniques due to its low cost, design flexibility, materials diversity, customization power, and user-friendly interface. The capability of FFF to produce multi-material components with localized functional properties has attracted the attention of people from different areas, such as health care, electronics, robotics, and consumer products. However, the interfacial interlayer bond between different materials could have a great influence on the mechanical properties and operation performance of 3D-printed multi-material parts. In this context, this study aims to investigate the impact of seven 3D printing parameters (filament retraction length, extrusion and bed temperature, infill and perimeter speed, cooling fan activation, and extrusion multiplier) on the mechanical strength of the bond between layers in multi-material FFF-printed parts. For this purpose, an open-source 3D printer and commercially available filaments of insulating thermoplastic polyurethane (i-TPU) and TPU filled with conductive carbon black (c-TPU) were used. A parametric study, based on an orthogonal Taguchi array, was performed to determine the influence of printing parameters on the general print quality and interface strength of TPU/TPU-CB parts using a pull-out test. The results show that the extrusion temperature and infill speed are critical factors to improving printing quality and mechanical properties. On the other hand, bed temperature and filament retraction do not influence the bond of multi-material connection. In conclusion, the multi-material TPU-CB/TPU parts produced have demonstrated promising mechanical integrity, suggesting their potential use for different technological applications.