Enhanced granular medium-based tube press hardening
  Active and passive control strategies of internal pressure for hot forming of tubes and profiles with granular media are described. Force transmission and plastic deformation of granular medium is experimentally investigated. Friction between tube, granular medium and die as also the external stress field are shown to be essential for the process understanding. Wrinkling, thinning and insufficient forming of the tube establishes the process window for the active pressure process. By improving the punch geometry and controlling tribological conditions, the process limits are extended. Examples for the passive pressure process reveal new opportunities for hot forming of tubes and profiles. 
Hui Chen, Sigrid Hess, Jan Haeberle, Sebastian Pitikaris, Philip Born,   Alper G\"uner, Matthias Sperl, and A. Erman Tekkaya
cond-mat.soft