Manufacturing – Casting methods - European Aluminium Association

1.10.4 Main process parameters of semi-solid forming and their
influence on quality
Casting speed
It is important that the metal front stays together during mould filling. A too high speed can
lead to turbulences and air entrapment. At too low speed mould filling could be incomplete.
Geometry of the runner system
Due to the fact that metal is already partly solid, thicker cross sections and short runners are
necessary in comparison to die casting. Numerical simulation is a very valuable tool for
designing runner systems.
Die temperature
To avoid cold shots, die temperature has to be high enough. Very often, die temperatures of
200 - 250°C lead to good results.
Die parting agent
Main requirements on mould release agent are:
Good separation between mould and metal;
Good wetting and adhesion on the mould;
Low gas production in contact with metal;
Low build up on mould.
Die venting
The air in the mould cavity has to be evacuated during mould filling. This is achieved by
venting slots positioned at places which are filled last. These slots should not be thicker than
0.2 mm.
Final metal pressure
Due to the partly solid metal, the risk of shrinkage porosity or hot tears is limited. To avoid it
completely, a high final pressure of 500 to 1500 bars is often necessary.
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