Application of DLC Coating Dies to Variable Shape Extrusion of Aluminum Square Pipes

Abstract

Aluminum space frame is one of the candidate to be applied to a structure of car bodies in future because of its light weight as well as high strength. To omit the secondary forming process in the production of aluminum space frame, variable shape extrusion apparatus which has a taper mandrel and four movable dies was developed and the characteristics of hot extrusion were investigated. As a result, it was found that the step mandrel provides good dimensional accuracy due to its bearings which is parallel to the extruding direction. But on the other hand, it was also found that pick-up was easy to occur on the surface of extrusions, by using the step-mandrel. Dies were coated with DLC around its bearings to prevent the dies from sticking of aluminum, and it was confirmed that the DLC coating has a significant effect to improve the conditions of the surface of extruded pipes.