Development and Implementation of Temperature Control for Additive Friction Stir Deposition

Additive Friction Stir Deposition (AFSD), commercialized by MELD Manufacturing Corporation as the MELD® process, is a bulk-near net shape, solid state, additive manufacturing process where the principals of friction stir welding and severe plastic deformation are leveraged to produce uniform microstructures and isotropic properties on a large scale. Unlike many forms of additive manufacturing which require powder, thin films, or wires for the feed material, AFSD uses commercially produced bar stock. Compared to other solid state metal forming processes like rolling, extrusion, and forging, AFSD is unique in that the volume being deformed at any given time is small compared to both the whole part and any given cross section. This allows for much higher levels of deformation to be put into each voxel of material and with more uniformity than if deformation was applied on a larger scale. Just like any other thermomechanical processing method, for the appropriate materials, a heat treatment may be applied post processing to achieve desired tempered properties. Rather than precipitation hardened materials which require heat treatments post deposition, AFSD is particularly well suited for materials with strong Hall-Petch relationships, meaning their yield strength increases significantly with decreasing grain size. Farbi et al. have demonstrated the excellent tensile performance of AFSD Ti-6Al-4V against both other additive methods and traditional processing e.g. wrought, forged, cast, etc. For this presentation, an overview of the development of a temperature based closed-loop feedback control system for the MELD process will be reviewed. Specific examples related to both Al7075 and Ti64 will be used as case studies, including a discussion on key processing parameters, microstructure, chemical analysis, and mechanical properties.