Pressure die casting is the injection of melted metal or plastic under high pressure into a mould cavity.
Before injecting the melted metal into the cavity, the mould is "closed" i.e. the two halves of the mould, called dies are brought together, after which dies are held together while the melted metal is forced into the cavity they form. The metal is allowed to solidify in the shape of mould cavity and then the dies are pulled apart so that solidified object may be ejected and the cycle repeated.
To manufacture die castings free of pores and shrink holes it is normal practice to fill the mould at high pressure and to let the metal solidify while under high pressure so as to effect compression of die casted metal. The apparatus which closes the dies and holds them together needs to have capacity to withstand this high pressure and it is required to work for long hours.
To simplify the clamping procedure for holding the dies together the apparatus uses a die casting machine which has one die fixed on the machine base and second die half is removable into and out of apparatus. Thus movement and control apparatus might be given for one half of die. This has an additional advantage that the hot melted metal can be fed into the mould cavity or chamber between the dies through a sprue in the fixed die.