Die-Casting Terminology

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Die-Casting Terminology

As with any manufacturing technique, the die-casting process has unique names and terminology. The following definitions clarify some of the terms that the hobbyist may encounter when researching die-cast parts.

Alloy – An alloy is a particular mix of metals used for a manufacturing process, such as die casting. Different alloys can provide different benefits, and a specific alloy for a part is chosen based on the required characteristics of the final part. These characteristics can include strength, hardness, shear strength, or electrical conductivity.

Blister – A blister is caused by a pocket of gas that is trapped in the mold near the surface of the casting during the casting process. A blister can look like a bubble in the surface of the die-cast part.

Blowhole – A blowhole is a void that occurs in heavy cast sections due to trapped gas during the casting process or shrinkage of the metal during cooling.

Cavity – A cavity is a concave surface within the interior of a die that will be filled with metal during the casting process.

Cold Chamber Casting - 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 is used to force the metal into the die. The mechanism of a cold chamber machine is much like a caulking gun.

Die – A die, also referred to as a mold, serves as the pattern for the part to be created. The die contains the molten metal during injection, and holds the metal until it has cooled and hardened. Dies are generally manufactured from steel to withstand the temperatures of the molten metal alloys used in the die-casting process.

Draft – Draft is a slight angle designed into the vertical surfaces of the die to allow easier ejection of the part from the die after the die-casting process. Draft angles between 1º and 3º are common.

Flash – Flash is thin metal that surrounds the die-cast part where the two halves of the die were mated. Flash results from the molten metal seeping between the two halves of the die during injection and then hardening. Flash is generally removed post-casting using a trim die, or by using abrasives such as a grinding wheel. In many cases, particularly in aluminum castings, the flash can be recovered and recycled.

Hot Chamber Casting - 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.

Injection – Injection is the step in the die-casting process when the metal is forced under pressure into the prepared die.

Trim Die – A trim die is often used in post-casting processes to remove the flash from the edges of the die-cast component.

Void – A void is caused by a pocket of gas that is trapped in a thin section of a mold, resulting in a hole in the surface of the cast part.

Sources

North American Die Casting Association web site - http://www.diecasting.org/
Kinetic Die Casting web site - http://www.kineticdiecasting.com/