Introduction to the Die-Casting Process

Die-casting, by definition, is a process in which molten metal is injected into metallic molds under pressure to form objects. The molds, which are generally made of steel and referred to as "dies", can be designed to create very detailed parts with little or no post-machining required after production. Die-casting is similar in many ways to plastic injection molding. Dies can be reused multiple times because the temperatures of the molten metal are not high enough to affect the steel die. Die-cast parts are generally lightweight, and for this reason are often used in aircraft and automobile applications.

History of the Die-Casting Process

Die-casting by pouring molten metal into a die, also known as the gravity pressure method, is a manufacturing method that has been used for hundreds of years. The more modern method of pressure injection die-casting was patented in the mid-1800's to create lead printer's type. The use of die-casting as a manufacturing technique exploded in the early 1900's, particularly when zinc and aluminum alloys became more readily available. Today, die-casting is a process used for a wide range of products and applications.

Materials Used in Die-Casting

In order to preserve the integrity of the die and allow it to be used for many castings, only alloys with relatively low melting temperatures can be used in the die casting process. Historically, lead and tin were the primary materials for die-cast parts, since they could easily be melted using conventional processes. Today, the majority of die-cast parts are created from aluminum or zinc alloys, but other metals such as magnesium or copper can be used. Each alloy delivers its own benefits, and therefore the product requirements drive the material choice. Aluminum can be found in aircraft and automobile parts, while copper may be used for parts that must conduct electricity.

Description of the Die-Casting Process

Before casting is performed, the mold is assembled. A mold can consist of two or more parts, depending on the complexity of the part being fabricated. Die-casting machines are categorized as either cold chamber machines or hot chamber machines. In a cold chamber machine, the molten metal is poured into a "cold" cylinder that is attached to the die. A hydraulic piston seals the cylinder and forces the metal into the die. In a hot chamber machine, the injection system sits in a bath of molten metal. A plunger is raised to pull molten metal into the injection chamber, and then pushed to inject the molten metal into the die. The mechanism of a hot chamber machine is much like a pneumatic bicycle pump, which pulls air in from around the pump and injects it into a tire through the tube and fitting.

After the casting process, the part may have flash or thin metal around the part where the two halves of the die come together around it. The flash is removed during post-machining processes. Some die-cast parts are plated or painted after manufacture for appearance, but the surface of die-cast parts are generally very smooth and hold fine detail.

Examples of Die-Cast Components

Many plumbing fixtures, such as bathtub spouts are manufactured from zinc alloys using a die-casting process and then plated with a chrome coating. Lightweight aircraft components can be die-cast from aluminum alloys. Other examples include heat sinks with complex shapes and large surface areas for electronic components, lightweight aluminum automobile parts, and lighting fixtures. Die-cast parts require very little post-manufacturing machining, saving time and labor costs in the manufacturing process.

Die-casting is a manufacturing process used for a variety of applications, including toys. In the Napoleonic era, gravity pressure methods were used to cast lead military figures. Die-cast vehicles have been available nearly as long as the vehicles themselves have existed. Early die cast manufacturers existing at the turn of the 20th century include Meccano in the United Kingdom and Dowst Brothers in the United States. Companies such as Ertl have been producing die-cast farm vehicles since 1945.