EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

The advantages provided by Additive Manufacturing (AM) techniques are well known for both metals and polymers with respect to possible part geometries and reduction of manufacturing steps. However, coupling different AM techniques to produce polymer-metal hybrid parts is yet to be thoroughly explored. While conventional joining technologies such as fastening and adhesive bonding would be capable of joining polymer and metal AM parts, this work aims towards using AM itself as a joining technology for such a scenario. Known as AddJoining, this approach resorts to Fused-Filament Fabrication principles to manufacture parts directly onto metallic substrates, dispensing any kind of joining step, fasteners or bolts. Since the AddJoining relies on the softened extruded polymer flowing through surface irregularities, using a substrate with an appropriate roughness is important. In a scenario where the substrate has been produced by powder-based AM techniques, its raw surface, which normally would need to be milled out for most applications, can be utilized to provide anchoring spots for the semi-liquid extruded polymer. The objective of this work is to quantify the influence of the surface roughness of Ti-64 parts produced by Laser Powder Bed Fusion on the strength of metal-polymer joints produced by AddJoining. In order to test the joints, a 3-point bending method based on ISO 14679:1997 standard was deployed. The roughness was varied by 3D-printing the substrate with different leaning angles (from 40 to 90 degrees). As for the polymer part, layer height and printing speed of the coating layer (the polymer layer immediately in contact with the metal) were varied. Results were interpreted by ANOVA. It was concluded that the joint strength is strongly dependent on the substrate roughness. Moreover, AddJoining parameters were only statistically significant insofar as the surface roughness was high enough.