Extrusion of aluminium hollow pipes:seam weld quality assessment via numerical simulation

The continuous extrusion of an aluminium alloy for hollow tubes production was investigated by numerical simulations. A variety of model runs were carried out exploring different combinations of die geometries and extrusion speeds. The primary objective of this work was to compare different criteria for evaluating the quality of longitudinal seam welds. The results of the numerical experiments show that the currently used quality indices, based on the integration of some characteristic variables across the welding surface are significantly affected by the extension of the dead flow zones. As a result, they do not behave coherently with respect to changes in shapes of the mandrel legs. The use of a novel Lagrangian approach in the estimation of the quality indices - based on the integration of the variables along the actual welding paths - leads to a more consistent behavior of the parameters with respect to both the extrusion velocity and the front leg shape. In this study we also show that the Lagrangian parameters can be applied to get a deeper insight into the quality of the extruded products, like the seam weld quality along the tube thickness. Further research is needed to investigate the relation between the Lagrangian quality indices and the microstructure of the material