In the present paper, we describe a tube drawing method with diameter expansion for the effectively formation of thin-walled tubes. The proposed method makes the tube thickness easier to reduce than the conventional method, because the tube wall stretches biaxially in the axial and hoop directions. The effects of the plug half-angle on the forming limit, drawing load, thickness reduction, the precision of the inner diameter, and the strength of the formed tube were investigated by a series of experiments and finite element method (FEM) analysis. As a result, the forming limit was the highest at a plug half-angle α of 36˚, and then the maximum thickness reduction ratio γ max of 32 % was obtained by increasing the expansion ratio. In addition, the thickness reduction ratio increased with the plug half-angle owing to the increase in drawing load. On the other hand, the dimensional precision of the tube inner diameter deteriorated with the increase in plug half-angle because of an overshoot of the tube wall, indicating a gap between the tube wall and the plug. The effect of the plug half-angle on the strength was small, while elongation changed with the plug half-angle. The above results suggest that the plug half-angle should be selected appropriately to obtain the target dimension and mechanical properties.
