Controlling heat balance in hot aluminum extrusion by additive manufactured extrusion dies with conformal cooling channels

To prevent overheating of the workpiece material, an extrusion die with integrated local cooling was designed and manufactured by selective laser melting (SLM) as an additive manufacturing technology. The major advantage of SLM is the geometric freedom of the components that can be manufactured, which has been used to produce a die with integrated multidirectional channels for a cooling medium and the integration of thermocouples for temperature measurement. To analyze the influence of the die cooling on the heat balance in hot extrusion, extrusion trials at different ram speeds and billet preheating temperatures with and without applying die cooling were performed. Compressed air was used as coolant. At lower ram speeds, a significant reduction of the profile's exit temperature in hot aluminum extrusion was achieved without causing an excessive rising of the extrusion force. At higher production speeds, surface defects in the shape of stripes of rough surfaces occurred but could be prevented by applying internal die cooling. Due to focusing of the heat exchange on the area of the die bearings, only a little influence of the cooling on the microstructure can be observed.