In squeeze casting, an accurately dosed quantity of molten metal is cast into the lower half of a mould. By applying a large pressure, the upper half of the mould is then used to close the mould and the molten metal solidifies in the mould. The mould clamping force is maintained during the solidification phase. This prevents the formation of shrinkage porosity and cavities as well as the occurrence of hot shortness.
The prevention of hot shortness also enables medium and high strength wrought alloys such as 6082 or 7075, to be used; they are subsequently heat treated. This process is usually used to produce castings with relatively thick wall cross-sections that solidify uniformly.
The machines used are similar to forging presses. The high pressures applied necessitate robust, hydraulically operated units.
Indirect squeeze casting:
In this process the metal to be cast is forced into the mould slowly and in a laminar manner in accurately dosed quantities via large gates. Whereas during pressure die-casting the mould filling takes place at a flow rate of about 30 m/s, in this process the rate is reduced to about 0.5 m/s. Solidification of the metal takes place at a high pressure in excess of 1000 bar; at the same time, thanks to the large cross-sections of the gates, metal can be topped up during the solidification phase.
The process enables castings to be made that have few pores and are pressure-tight, can be welded and heat treated and which are partly decoratively anodisable. In principle, wrought alloys can be processed and can result in elongations to fracture of up to 10%. Furthermore, with this process it is possible to strengthen the aluminium with fibrous material (fibre preforms). In this way, one can increase in particular the tensile strength, the 0.2% proof stress, the elastic modulus, as well as the high-temperature strength.