An investigation of the variable cross-section extrusion process

In this work, a flexible extrusion process which involves extruding the materials via one fixed and one movable die was studied. The novel extrusion process is termed as variable cross-section extrusion which can produce near net shape bars or tubes with variable cross sections along the length. During the extrusion process, the key is accurately and dynamically adjusting the geometry and size of die hole. Based on the “equivalent volume theory,” a novel motion control model was proposed for the movable dies. Besides, a numerical calculation method and a program for the model were also presented. By using the program, the motion parameters of movable dies were calculated for extruding a typical variable cross section. Finite element method (FEM) simulation and experimental work were carried out to analyze the precision and accuracy of the control model. According to the simulation results, the shapes of extrusion parts agree well with the designed shape. However, the measured dimensions of the FEM extrusion part are always smaller than the designed curves with absolute deviation of 0.81 mm. According to the experimental results, the dimensional tolerances are 0.35 and −0.22 mm when the movable die is moving upward and downward, respectively. These-dimensional tolerances are associated with the instant transformation of moving direction of the movable die, which were driven and controlled by an electrohydraulic servo system. All results have shown the motion control model has enough precision and accuracy and can be used in the processes of design and parameter calculation.