The Mechanism of Die Casting Process

Update:Nov 04 2016

Have you ever wondered how some of the most common elem […]

Have you ever wondered how some of the most common elements of your favorite everyday items (like cars) are made? In fact, they are usually created in a process called "die casting." It is a process where metal is molded into a required shape. It's a rather simple (but intense) procedure that is often taken for granted in our use of the products made through die casting.

This process is also described as "metal casting." It is completed by forcing liquid metal (metals heated to a point where they become a molten/fluid) into a mold under extremely high pressures. The molds are usually made of steel and come in two pieces. They are shaped and work comparable to injection molds. Most of these die casts are made of metals like aluminum and zinc.

Because the process is so intense and costly, it is usually limited to high volumes of production. The entire process consists of only four main steps. This keeps incremental costs down and makes die casting best suited towards large amounts of small to medium sized castings.

Die casting was first invented in the early 1800s. It was first used for the printing industry but soon helped in the growth of consumer products. It basically made the production of intricate parts affordable in high volumes. There are basically two different types of die cast machines, namely, hot chamber and cold chamber. And whether the chamber used in the process of die casting is hot or cold depends largely on the type of metal used.

Hot chamber machines use a pool of molten/liquid metal to feed the die. The liquid metal essentially fills a "gooseneck," after which a piston forces the metal out and into the die itself. It is characterized by fast cycle times (15 per minute) and convenience. Unfortunately, metals that have very high melting points cannot be used. So these chambers are used with metals like zinc, tin, and lead based metals.

Cold chamber machines are utilized when hot chamber machines are not possible to use. Aluminum is a typical metal that uses cold chamber machines to cast. Other metals used with this type of machine are magnesium and copper. With cold chamber die casting machines, however, the metal needs to be melted in a separate furnace. The pre-melted metal is then fed into an unheated chamber and is driven into the die via hydraulics/mechanics. Cold chambers have considerably slower cycle times, plus the inconvenience of pre-melting the metal.

Normally, two dies are used in the entire process. Both parts work together, known individually as the "cover die" and "ejector die." The cover die contains the hole where the metal flows through while the ejector die contains pins to allow the casting to be removed from the die. The castings slide off the cover die half and stay in the ejector half to ensure that the casting is ejected every cycle (via the ejector pins). Other components include cores and slides which can produce holes, other details and undercut surfaces. These other components tend to increase the cost of the dies.