Professor Schwam and Zhu explained that the earliest reports on squeeze casting originated in 1878
Russian literature, the reports suggested pressure should be applied to molten metal while it solidifies
in a mould. The commercial development of squeeze casting began to take place in Europe, North
America and Japan only after 1960. Two types of squeeze casting technology have evolved based on
different approaches to metal metering and metal movement during die filling. These have been named
direct and indirect squeeze casting.In the case of direct squeeze casting, the melt is
poured directly into an open die, and a hydraulic
ram is moved down into the melt to apply the
pressure. The biggest advantage of the direct
squeeze casting process is that the pressure is
applied to the entire surface of the liquid metal
during freezing, producing a casting of full density.
This technique, inevitably, gives the most rapid
heat transfer, yielding the finest grain structure,
but it does not control the die filling stage.
This leads to turbulent flow and the entrapment of
brittle surface oxide films. The inherent time delay
occurring after the metal is poured and prior to
pressurisation with the ram leads to premature
solidification. A highly accurate metering system is
needed to control the dimensions of the casting.
In comparison, when using the indirect squeeze
casting process the pressure is more difficult to
apply. The melt is injected into the bottom of the
cavity with a hydraulic ram. The metal flow can be
controlled via the injection speed, and pressure
application begins as soon as the die is filled. The
casting forms inside a closed die cavity, and the
dimensions of the casting are easier to control.