  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.
