This paper presents a systematic approach for estimating the forces applied to tools during friction stir welding (FSW), which can be implemented by the following two steps: (1) computing the temperature field of metal sheets through numerical simulation and (2) substituting the obtained thermal cycles of several points on the metal sheets into an analytical model of tool forces. The novelty of this approach lies in that it ingeniously combines the numerical simulation model of the temperature field and the analytical model of tool forces. In this case, the axial force, traverse force, and torque can be easily determined by only measuring temperature at a specific location underneath the sheets, thus avoiding time-consuming numerical simulations of large plastic deformations of the metal sheet material and expensive force sensors. After a brief description of the tool forces modelling strategy, the numerical simulation modelling of the temperature field and the analytical modelling of tool forces are introduced in detail. Then, an illustrative example comprising the simulation and corresponding experiment is carried out to demonstrate the effectiveness of the proposed approach. The consistency between the simulation and experimental values of the tool forces demonstrates the great potential of the proposed method in tool force prediction and other FSW applications. [ABSTRACT FROM AUTHOR]