The paper presents results of the FEM simulation of FSW process. The object of the research was a heat exchanger used for cooling of electrical components of propulsion systems. The tests enabled the obtainment of the field of temperature, stresses and displacements during the process and residual stresses and displacements of welded elements after cooling. Knowledge of the thermal conditions of the process, the stress and strain fields were used while designing clamps and pads of a welding stand for the welding of the heat exchanger components.