Thixoforming : Semi-solid Metal Processing

340j 9 Rheocasting of Aluminium Alloys and Thixocasting of Steels
Figure 9.30 Validation of the MAGMAsoft simulation by
step-shots; comparison of Figures 9.30 and 9.31 shows almost
identical results in flow fronts.
One lets the metal flow in at the back end of the handle and directs it along the knife
longitudinal axis. This simplifies the design of the gating and the tool construction
because it does not require any strong redirection in the cavity. The other variant lets
the material flow through a fan-shaped ingate with much larger crosscut, which
makes the form filling faster but more complex.
The MAGMAsoft simulation program predicted for the first variant a filling with
the metal speed accelerated at the first core and subsequently with a nearly constant
velocity up to the end of the form filling (Figures 9.30 and 9.32). The flowing fronts
split in front of the first core and unite almost without a time lag before pouring into
the blade. The small cross-section of the runner has a negative effect since presolidification
cannot be definitely prevented and because feeding problems with the
risk of shrink marks have to be assumed.
This is considerably less the case with the second variant. The great ingate length
generates a broad metal front contemporaneously flowing through the cores, which
makes it possible to reduce the air inclusions in the region of the handle. For the
experiments this variant was chosen (Figure 9.30).
At a piston speed of 1 m s 1 , the initial ingate velocity of metal is approximately
16 m s 1 , which increases up to almost 30 m s 1 when the front passes the last core.