With regard to the rotary friction welding process as used for joining of large rotationally symmetric structures in the aerospace industry, the finite element software "MSC. Marc" coupled with the optimisation code INVSYS was used to simulate the friction welding of two cylindrical titanium alloy Ti 6246 specimens while optimising parameters in the friction model. The friction model took into account the friction coefficient variation as a function of normal pressure in the contact, temperature and relative sliding velocity. The unconstrained subspace searching simplex method was employed for optimisation. An objective function was formulated to minimise the error between calculated and measured torques, and a parameter set was identified that produced better flash geometry agreement with experiment.