Effect of Die Design on Charge Welds in Aluminium Extrusion

Aluminium extrusions are used in more and more applications in different industrial fields, due to their properties and productivity. However, in-process scrap produced in aluminium extrusions needs to be reduced to increase material yield, process efficiency and sustainability. An important source of in-process scrap is the charge weld created in billet-to-billet extrusion, which is an inevitable transition zone occurring in the extruded product due to the transition between successive aluminium billets. Therefore, understanding how to reduce and control the charge weld in extrusion is crucial to the carbon footprint of the extrusion process while reducing the risk of failures of the extruded product in service and use. This paper aims to provide preliminary insights into the formation of charge welds and how to minimize their impact on in-process scrap in extrusion, with a primary focus on the role of die design and process parameters. First, four typical types of extrusion die structures were designed: spreader, feeder, flat and pyramid die. Second, a finite element (FE) model of aluminium extrusion was developed based on QForm. The simulations were validated by representative industrial extrusion experiments. Based on the FE model, the processing formation history of charge welds with different die types was investigated, with a particular focus on the effect of material flow behaviour and dead-metal zones on the charge weld. Finally, a sensitivity study on the effect of ram speed and billet temperature was performed.