Thixoforming : Semi-solid Metal Processing

438j 11 Thixoextrusion
Figure 11.30 Velocity and forming of dead zone of the simulation shown in Figure 11.29.
billet cooled significantly during upsetting and extrusion due to the forming die
temperature of 25 C. The formed shell was massive enough to be extruded through
the extrusion channel.
Due to the required extrusion time, the temperature of the forming die increased
and reached temperatures which made an active cooling of the forming die essential.
With such a cooling system, the press velocity could eventually be increased while
realizing complete solidification the die. Figure 11.32 shows an extrusion simulation
with integrated active cooling in the forming die. The press velocity was set to
3mms 1 and the forming die height was 65 mm. The forming die temperature was
set to 25 C and the water temperature was 20 C. Figure 11.32 shows that the core of
the bar is still semi-solid on exiting the extrusion channel.
The simulation of the experiments showed, as estimated, the incomplete solidification
of the billet material in the extrusion channel. Furthermore, the phenomenon
of shell formation which was observed in the experiments could be simulated. With
the chosen reduced press velocities, complete solidification in the extrusion channel
could be realized in the simulations. Using an active cooling system, complete
Figure 11.31 Realized complete solidification in the extrusion channel.