A non-steady state FE analysis of Al tubes hot extrusion by a porthole die

Porthole die extrusion has a great advantage in the forming of hollow sections of Al alloy tubes that are difficult to produce by conventional extrusion with a mandrel fixed at the stem. In general, the porthole die extrusion process consists of three stages (dividing, welding, and forming stage) through the complex die structure composed of container, porthole, mandrel, welding chamber and bearing part. Thus, in order to obtain the detailed mechanics, to assist in the design of proper die shapes and sizes, and to improve the quality of products with high welding strength, porthole die extrusion should be analyzed in as non-steady state as possible. This paper analyzed porthole die extrusion processes through 3D FE simulation in the non-steady state during the entire process for following process variables: initial billet temperature, bearing length, tube thickness, and extrusion ratio. The extrusion load for each stage, the welding pressure, and the dead metal zone in the welding chamber were examined through a numerical analysis. Extrusion loads found by FE simulation were compared with experimental results. The surface state of extruded products was also examined. Whole investigations were made for Al7003.