【文章內(nèi)容簡(jiǎn)介】 deformation cannot occur due to the friction. For the convenience, the vonMises yield criterion can be described by [15] where J2 is the second invariant of the deviator stress, and σS is the flow stress of the work piece, which is a constant value. Using invariant J2, the division of stress field without or with the guiding angle can be shown in . The regions marked with shadow represent the areas where the plastic deformation occurs. Division of rigid and plastic regions under conditions of without (a) and with (b) guiding angle (a) shows that without the guiding angle, the region of the workpiece in the upper part of the container and in the lower corner of the container does not deform plastically. In the extrusion with the guiding angle, as shown in (b), the plastic region is larger, and there is no dead zone. So it can be assumed that the guiding angle increases the area of plastic deformation of the metal at the bottom corner of the container. Types of deformation Lode’s parameter 181。 is used to represent the stress situation regularly since it can reflect the relative magnitude of the second principal stress, and it is also relative with the type of strain state. ?1≤ 181。＜ 0 represents tensile strain state, 181。=0 represents plane strain state and 0≤ 181。＜ 1 represents pressive strain state. That is, the type of strain state and the degree of plicacy can be determined by Lode’s coefficient. Through the analysis of Lode’s coefficient, some measures can be taken to change the stress situation, and then change the plastic deformation condition to improve the forming property of the billet. Based on the rigidplastic division, the strain of the material in the plastic area during extrusion process can be classified into different types using the visual display of Lode’s coefficient, as shown in . Division of Lode’s coefficient under conditions of without (a) and with (b) guiding angle It can be seen from (a) that without the guiding angle, Lode’s coefficient in most of the region near the die is negative, . the strain in the material is tensile. The region where Lode’s coefficient equals zero belongs to plane strain。 while at the corner of the container, Lode’s coefficient is positive, . the strain is pressive. In the extrusion with active friction, the strain in the plastic region is everywhere tensile, as shown in (b). So, pared with the extrusion without the guiding angle, the metal flow in the container is more homogeneous. 5 Experimental Comparison of the metal flow line at the final stage of extrusion is shown in . Flow line in the container is inhomogeneous at the last stage of conventional extrusion. It bends more seriously at bottom die corner in the extrusion process, which indicates that the hard deforming area increases. Flow velocity near the container and axis is greatly different, and the metal at axis flows faster, which tends to cause the shrinkage cavity, as shown in (a). 6 Conclusions (1) When the guiding angle is used, axial stress state of the metal near the axis changes from tensile stress to pressive stress, and the shrinkage cavity caused by the higher flow velocity of the axial metal is reduced. (2) The axial stress at the die exit is decreased by using the guiding angle, the inhomogeneity of flow velocity is reduced remarkably, and the twisting caused by the inhomogeneous metal flow is decreased. Therefore, the surface cracks caused by additional stress are avoided. (3) The results indicate that when the metal extruded with the guiding angle by deformation division, the dead zone of metal pletely disappears, the deformation type of the metal in the plastic deformation area changes from three types to a type of tension, and the homogeneity of the deformation as well as metal flow are greatly improved, which is helpful for extruding and promoting the quality of extrudates. References [1] PONALAGUSAMY R, NARAYANASAMY R, SRINIVASAN P. Design and development of streamlined extrusion dies: A Bezier curve approach [J]. Journal of Materials Processing Technology, 2021, 161(3): 375?380. [2] DAMODARAN D, SHIVPURI R. Prediction and control of part distortion during the hot extrusion of titanium alloys [J]. Journal of Materials Processing Technology, 2021, 150(1/2): 70?75. [3] DENG Xiaomin, SUN Hongjian, LI Shengzhi, FANG Muyun, CAO Jie. Friction and friction coefficient for aluminium alloyextrusion [J]. The Chinese Journal of Nonferrous Metals, 2021, 13(3): 599?605. (in Chinese) [4] HAMBLI R, BADIE L D. Damage