Joining of metal streams in extrusion welding

The extrusion weld seam is commonly considered to be formed between two metal streams which flow past a tool element in an extrusion die, commonly called the bridge and then encounter at the rear end of it. Here the streams are pressed together firmly and joining occurs across the interface by pressure welding. Experiments were performed in an ideal 2D-die where two metal streams were created by splitting the forward flowing material by means of a die bridge and joining them again behind the bridge. Metal flow through the die was mapped by an advanced grid pattern technique. The experiments were later reproduced in a 2D FEM model and the model parameters were set so that there was excellent agreement between simulated and experimental metal flow. The FEM model was utilised to gain knowledge of the flow of encountering interfaces of each stream, when starting with an initially empty die. This is what occurs when a new die is taken into use in an extrusion plant the first time. Correspondingly the mechanism of welding of streams when extruding into a die filled with rest metal from the previous extrusion cycle was also studied. The later process, when additional billets are extruded through already filled die, is a normal industrial production case of extrusion welding with exception of the very first billet in a new die. This way the authors have been able to present improved understanding of the fundamental mechanisms active in aluminium extrusion processes where joining takes place by extrusion welding.