Thermal Stir Welding (TSW) provides advancement over the more conventional Friction Stir Welding (C-FSW) process because it separates the primary processes variables thereby allowing independent control of metal stirring and forging from the stir zone temperature. However, the feedback for precise control of the stir zone temperature, and hence the process parameters to sustain that temperature within a narrow range, does not currently exist on the TSW machine at the NASA Marshall Space Flight Center (MSFC). At present, the current state of the art for the selection of process parameters for both TSWing and C-FSWing parameters is highly empirical and by nature is based on phenomenological knowledge. In response to this need, Keystone is proposing this Phase II STTR project to demonstrate the feasibility of closed-loop control of the TSW process and to enable the establishment of a analytically derived processing map to accelerate process understanding and selection of parameters for a given material and pin tool design. The close-loop control system will enable sustainment of a steady-state temperature at the stir rod as a function of spindle RPM and the travel velocity for a given z-axis loading and stir rod design. Use of this theoretically derived processing map will provide guidance in the optimization of the process parameter domain for solid-state welding of a given material. This capability will in turn enable rapid process qualification of the TSW process and components produced by the process.