Extrusion of sections with varying thickness through pocket dies

The quality of extruded product depends on many technological factors and the proper die design. This study investigates the influence of pocket die geometry on the flow behaviour during extrusion of profiles with varying thickness and, in consequence on its geometrical stability and surface quality. Material microstructure and the mechanical properties on the extrudates cross-section were also explored. The extrusion force was measured for all the dies tested. Based on physical modelling and extrusion trials on AlMgSi (6060) alloy, it was found that pocket dies considerably change the way of the metal flow in comparison to conventional flat dies. Properly designed pocket die allowed obtaining more uniform metal flow through the die, resulting in improved geometrical stability of the profile extruded. The use of pocket dies is also associated with more advantageous state of stresses in the die orifice, which in consequence enhances both material deformability and surface quality of extrudates. The higher values of micro-hardness were obtained while using the pocket dies. Moreover, the pocket dies contribute to the small increase in extrusion force, compared to the flat dies, whereas a considerable decrease in the extrusion force can be expected while extruding hard deformable materials. The criterion for pocket design was proposed and evaluated.