Application of additive manufacturing to improve the joinability of 316L stainless steel – PEEK-20CF hybrid joints produced by Ultrasonic Joining

Additive manufacturing (AM) is a growing key technology with potential to make a longstanding impact on the development world since, due to its layer-by-layer manufacturing nature, it allows the production of complex and highly customized components. Currently, different AM techniques are applied for several materials mostly for the rapid prototyping, thereby supporting the development process of new products or technologies and drastically shortening their commercialization time. As an emerging production technology, AM has plenty of room to grow in unexplored directions. Joining of metal-composite and metal-polymer hybrid AM structures is still an unexplored field. The present study aims to investigate the joinability of laser powder bed fusion (LPBF) and fused filament fabrication (FFF) AM parts by ultrasonic energy. The case study combination LPBF 316L stainless steel and FFF PEEK-20CF and the ultrasonic joining (U-Joining) technique were selected for this purpose. The U-Joining is a novel friction-based joining technology capable of producing through-the-thickness reinforced (TTR) hybrid joints between surface-structured metals and unreinforced or fiber-reinforced thermoplastics. Finite element analysis and design of experiments were used to optimize the metallic part geometry and joint mechanical performance, respectively. The obtained results show that the achieved mechanical performance strongly depends on the reinforcement geometry and features, as well as the joining energy and pressure. Microstructural analyses were carried out at the metal-composite interface of the optimized condition, as well as quasi-static lap shear test. Strong joints were achieved, whereby the micromechanical interlocking of TTR and the adhesion forces between consolidated polymer and metal contributed to increase joint damage tolerance.