Thixoforming : Semi-solid Metal Processing

Figure 9.15 Process adapted multipart shot chamber system (a)
with separate pressure and charging sleeves, complete shot
chamber including the piston rod, wiring and an argon supply for
the charging area (b), and coated chamber prepared for a
thixocasting cycle (c).
9.3 Thixocasting of Steel Alloysj325
The newly designed process-adapted shot sleeve system shows very promising
results in terms of high temperature stability and wear resistance and also the
influences on the properties of semi-solid steels castings. A detailed analysis of the
performance is currently under investigation.
9.3.2.3 Technological Design Layout
For the form, layouts were supported by the use of MAGMAsoft. For the simulation of
the thixocasting process, a specific thixo-module that permits the calculation of the
behaviour of semi-solid metals was used. In addition, the database had to be enlarged
with sheer rate-dependent viscosity values which serve for the description of the
thixotropic material behaviour according to the Ostwald–de Waele potential law
of [35]. These simulations need to be validated by using step-shooting experiments.
These partial fillings of the form cavity represent a basic aid for the determination
of the form filling characteristics of semi-solid thixomaterials. The shot piston is
stopped at a time at which the metal has reached an interesting change in flow
direction or metal velocity because of the mould geometry. In the context of several
tests, the dynamics of the filling stage can be shown by freezing the different filling
stages. In this way it is possible to distinguish between laminar and turbulent form
filling. Furthermore, important knowledge is gained for the optimization of the form
construction.
The gating system and the ingate exert a decisive influence on the form filling
behaviour of the slurry and at least on the mechanical quality of the parts in the
thixocasting process. In principle, the ingate system must be designed in such a way
that no inclusions, such as oxides, reach the component which would degrade the
mechanical qualities. It is a further requirement that an even and laminar form filling