Force-Controlled Friction Riveting - A Hybrid Joining Process

Friction Surfacing (FS) is a solid-state welding technique. It harnesses the frictional heat generated from the contact between a rotating consumable rod and a fixed substrate to drastically soften the former, enabling its mechanical conformation by means of severe plastic deformation. Currently, the process is most known for its ability to produce metallic coatings below melting temperature. This particular feature is responsible for suppressing common problems usually present on fusion-based processes, such as pores, inclusions, high residual stresses induced by solidification and coring effects, which are also present to a certain extent on many additive manufacturing (AM) processes. Moreover, the layer-by-layer approach utilized by the FS technique, as well as its relatively high deposition rates and the enhancement in mechanical properties promoted by the thermo-mechanical processing indicate that additive manufacturing parts by FS may be a viable alternative to fusion-based AM techniques. However, at the current stage, multi-layer FS depositions have not been extensively explored for several alloys; the printing resolution is still considerably lower than on other techniques and the scrap produced during both the process and the posterior milling steps has not been properly addressed. Therefore, future work shall be concentrated on the aforementioned challenges, as well as on alternatives to optimize the rod feed to improve deposition rates.