Thixoforming : Semi-solid Metal Processing

Figure 9.12 Components of cartridge system, cartridge in shot chamber.
The isolated billet has a protection tube that ensures sure handling from the
reheating device to the shot chamber and an exact positioning in the shot chamber
axially. A crack-resistant ceramic pipe made of aluminium titanate was used which
results in an almost ideal quality profile. The measurements confirmed the excellent
isolation effect of the concept with a temperature loss of less than 8 K in 60 s.
For the cartridges, a new charging zone for the shot chamber has to be designed.
For precise threading into the pressure part of the shot chamber, first a piston of
length 320 mm was used. Because of increased wear, the length of the high-strength
CuCoNiBe piston was increased to 580 mm from an alloying last. This piston
generates a sharp edge to separate the isolation material. This isolation material
protects the piston from excessive heat entry and reliably prevents excessive wear.
9.3.2
Casting Technology and Systems
9.3 Thixocasting of Steel Alloysj323
9.3.2.1 Systems Engineering for Thixo- and Rheoprocesses
To be able to characterize semi-solid materials during and after thixoforming,
a locking force of 725 tons in a machine from B€uhler AG is used (Figure 9.13).
The real-time shot control permits exact programming of the piston velocity
(0.02–8ms 1 ), movement and pressure during the fractions of a second that are
needed to fill a mould cavity. Depending on thickness or geometry, the metal velocity
can be increased or reduced at predetermined points and after complete filling a postpressure
can be applied to compact the material. The dies can be tempered with
thermal oil, using three independent heater cooler units from Thermobiel with two
circuits each up to a temperature of 350 C. A Fondarex system to reduce the presence
of air in the mould cavity completes the peripheries of the HPDC machine.
9.3.2.2 Process-adapted Shot Chamber System
A process-adapted shot chamber has been designed and constructed in close
cooperation with Ortmann Druckgiesstechnik GmbH. In the preparation for
the construction, an approximate simulation of the thermal loads occurring during
the thixocasting process of semi-solid steels was performed with the numerical