Blank hydroforming using granular material as medium - investigations on leakage

For high and ultra-high strength steel grades a forming at elevated temperatures is advantageous due to higher forming limits and reduced flow stresses resulting in low process forces. For highly complex parts out of these materials hydroforming is an appropriate production method allowing undercuts and homogeneous stretching of the material. In case of forming temperatures above 350 degrees C typical liquid forming media no longer can be used and gases are in the focus of interest. The big disadvantage of blank hydroforming at elevated temperatures results from the increase of friction coefficient by temperature and the need of sealing the cavity by high contact pressures in the flange area of the part. To overcome this challenge a third class of media, granular material like sand or small ceramic spheres can be used as forming media. For investigations of the process limits, especially the sealing limit of granular material, an experimental tool was built up. (C) 2014 Published by Elsevier Ltd.