Abstract: The 2D coupled thermo-mechanical model was established to numerically simulate the effects of temperature and material flow on the flash formation of ring parts during continuous driven friction welding.The calculated results show that the material in friction stage mainly flew axially,while the radial velocity was nearly zero.During the forging stage,the material in or near the edge of friction surface mainly flew along the radial direction under large axial forging pressure,which resulted in the formation of flash.And the dimensions and bending degree of the flash increased with increasing of welding time,rotating speed and axial forging pressure.Based on the shape of flashes,suitable welding parameters were determined for continuous driven friction welding of 45 steel ring structures.