Friction Stir based welding and processing (FSW/P) technologies are solid-state processing technologies that employ non-consumable tools to promote the heating and the plastic deformation of the materials to be worked. The quality of the processed materials is intrinsically dependent on the thermomechanical conditions developed during FSW/P, which are governed by the interaction between the tool and the base material [1], [2]. Depending on the equipment used, the process may be operated under force control, which defines the axial load applied by the tool, or under position control, which defines the tool penetration depth. Despite previous experimental studies indicate that the process control mode may significantly influence the temperature evolution and the material flow during processing [3], the available literature does not provide any comparative analysis of the data obtained under the two different conditions. This work presents a coupled experimental-numerical analysis, developed with the objective of providing a deeper understanding of the differences in thermomechanical conditions imposed under force and position control FSW/P. The study is focused on a comparative analysis of processing conditions for four aluminium alloys with distinct constitutive behaviour: heat-treatable alloys (2xxx, 6xxx, and 7xxx series) and non-heat-treatable alloys (5xxx series). To enable an easier assessment of the differences in processing conditions, the experiments and the simulations were performed assuming spot processing of thick plates of each alloy. Numerical simulations were calibrated using the experimental data of temperature, force, and torque. The numerical results allowed correlating the influence of each alloy constitutive properties, with the machine control system response and the processed materials properties. REFERENCES [1] D. G. Andrade, C. Leitão, N. Dialami, M. Chiumenti, and D. M. Rodrigues, “Modelling torque and temperature in Friction Stir Welding of Aluminium Alloys,” Int. J. Mech. Sci., p. 105725, 2020, doi: https://doi.org/10.1016/j.ijmecsci.2020.105725. [2] D. G. Andrade, C. Leitão, N. Dialami, M. Chiumenti, and D. M. Rodrigues, “Analysis of contact conditions and its influence on strain rate and temperature in friction stir welding,” Int. J. Mech. Sci., vol. 191, 2021, doi: 10.1016/j.ijmecsci.2020.106095. [3] C. Leitão, R. Louro, and D. M. Rodrigues, “Analysis of high temperature plastic behaviour and its relation with weldability in