Die castings or dies are made in a minimum of two sections, but can be more depending on how complex the design is. How this works is the castings are done in a fixed or ejector die half. The fixed half, also known as the cover half, is used for castings that do not require anything special done to them. How the fixed half works is the molten metal is injected into the casting through sprue holes. The molten metal is injected into the casting until the entire cavity is filled with the molten metal. The ejector half is used to make castings that require special accommodations, such as holes and threads. To make these holes, threads and other special accommodations castings have cores, moveable slides, and other sections built into the casting. The molten metal is injected into the ejector side where passageways and inlets control where the metal is able to move.
One mistake that many people make when they are first learning about die casting construction is that the fixed and cover die halves are the only types of dies used. The truth is the fixed and ejector die halves are not the same thing as the dies used to make the products. There are currently four types of dies being used for castings. Here is a closer look at the four dies in use:
Single Cavity – The single cavity die is used by manufacturers who are looking to produce one component. This type of die is more popular for manufacturers who are producing a larger part or even medium sized parts.
Multiple Cavity Die – This is one of the more popular dies used with castings because it enables the manufacturing process to go faster. With a multiple cavity die manufacturers can produce identical parts in larger numbers.
Unit Die – A unit die is used by manufacturers to produce several different parts at the same time. A great example of a unit die would be a single die and multiple cavity die being combined together to produce two separate parts all at once.
Combination Die – The combination die is quite similar to the unit die because both dies are used to make different parts at the same time. The biggest difference between these two dies is the combination die is used to produce several different parts that are designed to be assembly to make one part.
Once the right die is chosen the manufacturer will place the die into the die casting machine. Once the machine closes the two halves of the die are locked together, which where they lock together is referred to as the die parting line. The mold cannot open during the die casting process because they are held in place by the machine hydraulic pressure. How much pressure is used is determined by the pressure that is needed to inject the molten metal into the die and the how much surface area is being cast, which is measured at the die parting line.