An investigation of the forming mechanisms of curved bars and twisted bars by extrusion through a die aperture with asymmetric cross section

采用数值模拟的方法，研究了矩形棒材和梯形棒材在模具孔内以固定角度挤压成形的机理。模具倾角越大或孔径出口角越大，出口杆的曲率半径越小。计算得到的曲率半径与实验观测到的曲率半径吻合较好。在此基础上，以模拟结果之一的颗粒流型为基础，研究了曲率产生的机理。在挤压长条形棒材的情况下，当模具倾角增大时，死金属体积增大，导致物料在垂直于挤压方向的平面内流动。这在挤压棒中产生了曲率。还发现，当截面为梯形时，容器孔径的不对称造成了顶部和底部物料流速的差异；这些差异影响了曲率。

The mechanisms responsible for the forming of rectangular bars and trapezoidal bars by extrusion at a fixed angle through a die aperture were investigated using numerical simulations. The greater the die inclination angle or the greater the aperture exit angle, the smaller the radius of curvature of the exiting bar. The calculated radius of curvature agreed well with the radius observed in experiments. The particle flow pattern, one of the outputs of the simulation, was used as a basis to investigate the mechanisms of curvature generation. When the die inclination angle was increased in the case of extrusion of rectangular bars, the volume of dead metal increased, causing material flow in the plane perpendicular to the extrusion direction. This gave rise to curvature in the extruded bar. It was also found that when the cross section was trapezoidal, the asymmetry of the container aperture caused differences in material flow velocity between the top and bottom portions; those differences affected curvature.