This paper is concerned with forward rod extrusion combined simultaneously with
backward tube extrusion process in both steady and transient states. The analysis has been conducted
in numerical manner by employing a rigid-plastic finite element method. AA 2024 aluminum alloy
was selected as a model material for analysis. Among many process parameters, major design factors
chosen for analysis include frictional condition, thickness of tube in backward direction, punch
corner radius, and die corner radius. The main goal of this study is to investigate the material flow
characteristics in combined extrusion process, i.e. forward rod extrusion combined simultaneously
with backward tube extrusion process. Simulation results have been summarized in term of
relationships between process parameters and extruded length and volume ratios, and between
process parameters and force requirements, respectively. The extruded length ratio is defined as the
ratio of tube length extruded in backward direction to rod length extruded in forward direction, and
the volume ratio as that of extruded volume in backward direction to that in forward direction,
respectively. It has been revealed from the simulation results that material flow into both backward
and forward directions are mostly influenced by the backward tube thickness, and other process
parameters such as die corner radius etc. have little influence on the volume ratio particularly in
steady state of combined extrusion process. The pressure distributions along the tool-workpiece
interface have been also analyzed such that the pressure exerted on die is not so significant in this
particular process such as combined operation process. Comparisons between multi-stage forming
process in sequence operation and one stage combined operation have been also made in terms of
forming load and pressure exerted on die. The simulation results shows that the combined extrusion
process has the greatest advantage of lower forming load comparing to that in sequence operation.
