Joining Feasibility Between Metallic- and Polymeric-Based Materials by Friction Stir Forming

Nowadays, the research efforts must result in a reduction of environmental pollution emissions. Consequently, the products have to be designed in such a way that the performance criteria are achieved at the minimum weight. Taking the lightweighting to its extreme and aiming at satisfying the product requirements, a revolutionary body concept should result in an optimal material selection and distribution. The joining methods, among many manufacturing technologies, have been considered as key enabling solutions in making innovative and sustainable products. The joint between dissimilar materials is a current challenge and different solutions have been proposed in each of the joining categories, i.e. adhesive bonding, welding and mechanical fastening. In the proposed research, the fastenerless-riveting by friction stir extrusion has been analyzed to connect metallic- and polymeric-based materials in a single shot process sequence. Specifically, the process consists of a rotating non-consumable tool, which is first vertically dipped inside the metal sheet (according to a specific penetration depth p), and after a heating up idle time, the tool moves (according to a rotational speed (S) and to a forming velocity (v)) through the sheet, stirring and extruding the material into a further blank, placed below the metal one and previously holed. The analyzed materials, an aluminum alloy (AA1050) and a high-performance plastic (PEEK), were chosen because they are characterized by extremely different thermal properties, starting from their working and melting temperatures. In this regard, friction stir forming leads to a temperature variation around the working area, which could result in a not joining phase feasibility owing to the material dissimilarities. Herein, AA1050 and PEEK parts were connected by extruding the pins from the metal sheet. Different process configurations were investigated to test the joint feasibility in a one-shot sequence and the results discussed.