Die casting dies are made of alloy tool steels in at least two sections called fixed die half and ejector die half. The fixed die half is mounted on the side toward the molten metal injection system. The ejector die half, to which the die casting adheres, and from which it is ejected when the die is opened, is mounted on the moveable platen of the machine.
The fixed die half of the die is designed to contain the sprue hole through which molten metal enters the die. The ejector half usually contains the runners (passage ways) and gates (inlets) which route molten metal to the cavity (or cavities) of the die. The ejector half is also connected to an ejector box which houses the mechanism for ejecting the casting from the die. Ejection occurs when pins connected to the ejector plate move forward to force the casting from the cavity. This usually occurs as part of the opening stroke of the machine. Placement of ejector pins must be carefully arranged so force placed upon the casting during ejection will not cause deformation. Return pins attached to the ejector plate return this plate to its casting position as the die closes.
Fixed and moveable cores are often used in dies. If fixed, the core axis must be parallel to the direction of die opening. If moveable, they are often attached to core slides. Should the side of a die casting design require a depression, the die can be made with one or more slides to obtain the desired result without affecting ejection of the casting from the die cavity. All moveable slides and cores must be carefully fitted, and have the ability to be securely locked into position during the casting cycle. Otherwise, molten metal could be forced into their slideways causing a disruption of operations. Although slides and cores add to the complexity and cost of die construction, they make it possible to produce die castings in a wide variety of configurations, and usually more economically than any other metalworking process.