The die casting process is the method of producing precision castings by pouring molten (liquid) metal into metal dies with pressure, letting the poured metal solidify and then removing the metal dies so that the cast component may be retrieved. The process is widely used to manufacture castings for various types of applications such as: the automobile industry, housings, blades, and pump bodies, etc.
Dies are made in two or more sections with: holes, bosses, lugs, cavities and contours corresponding to the component, machined in the inside face. When the two or more sections are mated, or bolted together, the inside cavity will be the component form.
The pressure that is used in die casting can range from about 1,400 (PSI) up to 30,000 (PSI). Pressure is used in the molding process to make sure that the cast object will be more uniform and will have an attractive finish. In most instances there is very little or no post-casting machining required to finish the item. Intricate die-casting, if done with expertise, can give a near net shape of +/-0.003 inches. This is essential for parts that are used in products with interchangeable components. The die must be very accurately designed and precisely made to get the desired results.
Dies are usually made of low carbon, heat-treated steel, chromium-vanadium or tungsten steel. While designing dies, suitable care must be taken to place proper vents which allow the hot air and gases to be released and subsequently burnt. Various alloys such as aluminum, bronze, brass, copper, etc. can be die cast. However, die casting isn’t suitable for all types of metal. Iron and steel cannot be die cast because they would bond with the casting equipment while they are in a molten state.
There are two basic forms of die casting processes, which are cold chamber and hot chamber, and the method that you use will depend on the type of metal that is being cast.
In the cold chamber process, metals such as aluminum and copper are generally used as they usually alloy with the iron in the casting equipment at higher temperatures. In this procedure the chamber is filled with hot metal and is injected into the mold.
In the hot chamber process of die casting, the injecting and molding equipment is immersed in the liquid metal that is going to be cast. This allows the chamber to automatically load each time the plunger is pulled back. This also allows the process to be done at a faster speed. The metal that is used in this method of casting needs to be a type that doesn’t easily alloy with the iron in the equipment such as lead, metal and tin, as the molten metal is constantly in contact with it.