Thixoforming : Semi-solid Metal Processing

Figure 10.31 Scheme of the heat transfer experiment and typical
temperature development of the sample.
Regarding the specific heat conductivity, in the case of the steel tool there will be
less heat transfer. This advantage for the cooling behaviour of the sample causes on
the other hand high temperatures in the surface of the tool because of retaining heat
in the contact area of tool and semi-solid material. In the case of the TZM tool,
transferred heat can be transmitted faster and critical temperature peaks can be
avoided at and below the surface.
10.4.2
Simulation of a Thixoforged Component
10.4 Simulation of the Thixoforming Processj401
The axisymmetric component in the form of a wheel hub is chosen for numerical
analyses of the thixoforging process. Thermomechanical, coupled simulations are
used in the case of the forming operation and thermal simulations for the cooling
operation. In both simulations, thermophysical and thermodynamic data are
implemented that are investigated in several experimental and numerical analyses
of the utilized materials within the SFB289. Additionally, flow curve data are provided
for a temperature range of 965–1280 C, a strain of 0–0.7 and a strain rate of
0.1–10 s 1 . The viscoplastic approach in LARSTRAN/SHAPE allows the description
of nonlinear functions of flow stress as a function of temperature, strain and strain
rate. Especially for the temperature range above the solidus temperature and the
resulting low flow stress, the consideration of the temperature dependence is of
particular importance.
The initial temperature of the billet is 1300 C and that of the dies is 300 C. Due to
the short process duration of about 0.5 s, LARSTRAN/SHAPE is applied for the
forming operation even though the definition of rigid dies has an influence on the
heat flow compared with the experimental values. It is assumed that the results after