Thixoforming : Semi-solid Metal Processing

Figure 8.48 Self-heating ceramic thixoextrusion die.
(a) Schematic cross section; (b) view into recipient.
impacts. Thus, the inner forming die has to be supported by the isolation shell made
of a low-porosity refractory castable. A tool prototype for self-heating ceramic
thixoforging dies is presented in Figure 8.49. The inner alumina die is surrounded
by a Kanthal A1 heating core and heated to 1000 C prior to forming. Temperatures of
the steel forging table were less than 100 C.
Similarly to thixoforging tools, self-heating ceramic thixocasting moulds have to
withstand cyclic mechanical loads, although the process forces are applied indirectly
on the tool surface. However, special attention has to be paid to the construction of the
gate system in order to obtain a smooth material flow into the cavity. Figure 8.50
shows a self-heating thixocasting mould consisting of alumina plates containing a
geometrically complex freeform-shaped cavity. The insulation body surrounding the
alumina moulds is made of lightweight insulating firebricks.
These prototypes reveal the variety of possible tool setups and prove the principle
applicability of the underlying tool concept for semi-solid metal forming.
Figure 8.49 Self-heating ceramic thixoforging die. (a) Heated tool;
(b) IR image showing temperatures of 1000 C in the centre
(yellow) and