Abstract: The forming of open-die extrusion with mandrel for the thick walled tube is of low material consumption and high efficiency compared with the traditional cutting. An analysis on the forming characteristics of the mandrel open-die cold extrusion is performed and the main influence parameters of the forming limit are defined. Continuous velocity field of the deformation zone is established by using stream function method, the theoretical model of forming limit is obtained by using upper bound theory. By programming calculation and analysis, the effect of various parameters (the original blank thickness to diameter ratio, friction coefficient, die cone angle) on the forming limit is put forward. With the increase of die angle, the limit reduction (forming limit) first increases and then decreases, i.e. the limit reduction has a maximum and obtains the optimal die angle in the range of 15°～20°. With the increase of friction coefficient, the limit reduction decreases. Comparing the theoretical calculation result with the experimental result shows that the error is less than 8%, which meets the engineering requirement. The research contents and results have important guiding function in mapping out the process of thick-walled tube open-die cold extrusion forming with mandrel.

Key words: Forming limit, Open-die cold extrusion with mandrel, Optimal die cone angle, Stream function, Upper bound theory