Deformation conditions in the extrusion weld zone when using pointed and square ended bridge

Abstract

In porthole extrusion of hollow aluminium profiles metal streams flow around the die bridges and re-join in the welding chamber behind the bridges through the process of solid state bonding creating an extrusion weld. The welding process is of complex nature and it is required to understand the deformation phenomena present in the region where the seam weld is created. New knowledge of metal deformations when the metal joins behind a die bridge is obtained in our study performed in a simple 2D die arrangement. When two metal streams joins behind the bridge the material flow here is influenced by the design of the die bridge. In the current study the extrusion welding process have been compared when using butt or pointed rear end shape of the bridge. The main focus has been on the region behind the bridges where the metal streams join and welding takes place. The location of the dead zones and their effect on the characteristics of material flow are investigated. A quantitative analysis of the pressure build-up along the weld is performed. The extensions of the interfacial layer which makes up the seam weld are quantified. The conditions of strain rate in the welding zone are compared for bridges with square and pointed rear end. A “stretching zone” has been identified behind the two types of bridges. In this zone there is high strain rate and the deformations here are quantitatively compared in the study. The work contributes to better understanding of the mechanisms by which extrusion welding takes place. Finite element modeling has extensively been used while an experimental grid pattern technique has been used to secure good agreement between simulation and experiments. In simulation the grid pattern technique has also been used to investigate the deformation of the metal as it flows through the stretching zone.