Based on studies, an optimum die design was created that decreases axial tensile residual stress. The axial residual stress after drawing was investigated by experimental method and calculated by the elastic-plastic FEM. The results were obtained as follows. If the corner radius and bearing length nearly equal zero, the maximum axial tensile residual stress is generated on the surface of the bar. When the radius and length become larger, the residual stress decreases on the surfaces as compared with the interior. An optimum die shape was designed for the purpose of decreasing the axial tensile residual stress after drawing. The optimum die shape is as follows:The die semi-angle a is the range of the contact length ratio l/d_0<0.5.The transient radius between approach and bearing length is the range of R/d_1<0.5.The bearing length is within the range of 0.4 <=L/d_2<=0.6.A die with a protrusion in the bearing was suggested to decrease residual stress. This die led to a dramatic generation of compressive residual stress on the surface of the bar.
展开▼
