Thixoforming : Semi-solid Metal Processing

402j 10 Thixoforging and Rheoforging of Steel and Aluminium Alloys
Figure 10.32 Simulated results of temperature distribution during forming operation (LARSTRAN).
the forming step coincide approximately if a few adjustments regarding the heat
transfer coefficient are considered.
As shown in Figure 10.32, the temperature increases very rapidly in contact areas
of the billet and the die. Initially the material flows into the bush until a narrow
channel of semi-solid material occurs due to the fast solidification at the contact
zones. The required flow stress increases for this area so that the material flow
reverses to the flange. When the flange is completely filled, the existing force of the
plunger subsequently suffices to fill the bush with semi-solid material. As shown for
the experimental part, existing failures in the area of the bush such as pores and
separation of solid and liquid phases can be caused by the sequence of filling and the
accompanying cooling of the material near the solidus temperature.
The main heat transfer occurs after completing the forming operation. For these
calculations, the geometry of the component and its resulting temperature distribution
are imported to ABAQUS. The thermal interactions during the cooling procedure,
which was varied in its process duration analogous to the experiment, were
calculated with the algorithm heat transfer and following boundary conditions