How Does Die Casting in an Aluminum Foundry

Update:Nov 29 2016
Summary:

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? 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. You can tell something has been die cast by its clean and good quality surface finish. The measurements of the casting are also very consistent.

Die casting was first invented in the early 1800s. It was first used for the printing industry but soon after 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 - hot chamber and cold chamber. 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. These chambers are used with metals like zinc, tin and lead based metals.

Cold chamber machines when hot chamber machines are not possible to use. Aluminum is die cast using cold chamber machines. 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.

In sand casting, re-usable, permanent patterns are used to make the sand moulds. The preparation and the bonding of this sand mould are the critical step and very often are the rate-controlling step of this process.