Abstract: Because of the requirement on the high precision of the thin-wall tube, and it is hard to meet the quality requirement by sinking without mandrel, so the the thin-wall tube of high precision must be manufactured by sinking with a mandrel. The process of sinking tube is forming by extruding. In the process, the main default is instability on the tube wall, and the extrusion force is limited. It is important to calculate the extrusion force accurately and to find a way to decrease the force in the scheme design. Firstly, the new kinematically admissible velocity fields is designed. An upper bound analytical method is proposed on the tube sinking with a stationary mandrel or with a moving one. At last, with the drive shaft tube of the car as the example, the parameters of the process are analyzed .

Key words: Lighten the wall thickness of the tube, Mandrel, Sinking, Upper bound method