FAQ About Die Casting

Automation – Industry term commonly used to describe the mechanization of various aspects of the die casting process.

Biscuit – Excess of ladled metal remaining in the shot sleeve of a cold chamber die casting machine. It is part of the cast shot and is removed from the die with the casting.

Blister – A surface bubble caused by gas expansion (usually from heating) which was trapped within the die casting or beneath the plating.

Blow holes – Voids or pores which may occur due to entrapped gas or shrinkage during solidification, usually evident in heavy sections (see porosity).

Cavity – The recess or impressions in a die in which the casting is formed.

Cold chamber machine – A type of casting machine in which the metal injection mechanism is not submerged in molten metal.

Checking – Fine cracks on the surface of a die which produce corresponding raised veins on die castings. Caused by repeated heating of the die surface by injected molten alloys.

Creep – Plastic deformation of metals held for long periods at stresses lower than yield strength.

Die lubricant – Liquid formulations applied to the die to facilitate casting release and prevent soldering.

Dimensional stability – Ability of a component to retain its shape and size over a long period in service.

Dowel pin – A guide pin which assures registry between cavities in two die halves.

Draft – The taper given to walls, cores and other parts of the die cavity to permit easy ejection of the casting.

Ejector marks – Marks left on castings by ejector pins.

Ejector plate – A plate to which ejector pins are attached and which actuates them.

Fillet – Curved junction of two surfaces, e.g., walls which would meet at a sharp angle.

Flash – A thin web or fin of metal on a casting which occurs at die partings, vents and around moveable cores. This excess metal is due to working and operating clearances in a die.

Gate – Passage for molten metal which connects runner with die cavity. Also, the entire ejected content of a die, including castings, gates, runners, sprue (or biscuit) and flash.

Gooseneck – Spout connecting a metal pot or chamber with a nozzle or sprue hole in the die and containing a passage through which molten metal is forced on its way to the die. It is the metal injection mechanism in a hot chamber type of die casting machine.

Growth – Expansion of a casting as a result of aging or of intergranular corrosion, or both.

Heat checking – (See checking)

Hot chamber machines – Die casting machines which have the plunger, gooseneck (metal pressure chamber) immersed in molten metal in the holding furnace.

Hot short – Term used to describe an alloy which is brittle or lacks strength at elevated temperatures.

Impact strength – Ability to resist shock, as measured by a suitable testing machine.

Impression – Cavity in a die. Also, the mark or recess left by a ball, or penetrator of a hardness tester.

Ingot – Metal or alloy cast in a convenient shape for storage, shipping and remelting.

Injection – The process of forcing molten metal into a die.

Insert – A piece of material, usually metal, which is placed in a die before each shot. When molten metal is cast around it, it becomes an integral part of the die casting.

Intergranular corrosion – A type of corrosion which preferentially attacks grain boundaries of metals or alloys, resulting in deep penetration.

Loose piece, knockout – A type of core (which forms undercuts) which is positioned in, but not fastened to a die. It is so arranged as to be ejected with the casting and from which it is removed. It is used repeatedly for the same purpose.

Metal saver – Core used primarily to reduce amount of metal in a casting and to avoid sections of excessive thickness.

Multiple cavity die – A die having more than one duplicate impression.

Nozzle – Outlet end of a gooseneck or the tubular fitting which joins the gooseneck to the sprue hole.

Overflow-well – A recess in a die connected to a die cavity by a gate to assist in proper venting.

Parting line – A mark left on a die casting where the die halves meet; also, the mating surface of the cover and ejector portions of the die.

Plunger – Ram or piston which forces molten metal into a die.

Port – Opening through which molten metal enters the injection cylinder.

Porosity – Voids or pores resulting from trapped gas, or shrinkage during solidification.

Process control – Where parameters of a process are studied and correctly applied in the manufacturing process to produce high quality parts.

Runner – Die passage connecting sprue or plunger holes of a die to the gate where molten metal enters the cavity or cavities.

Shot – That segment of the casting cycle in which molten metal is forced into the die.

Shrinkage, solidification – Dimensional reduction that accompanies the freezing (solidification) of metal passing from the molten to the solid state.

Shrink mark – A surface depression which sometimes occurs next to a heavy section that cools more slowly than adjacent areas.

Slide – The portion of the die arranged to move parallel to die parting. The inner end forms a part of the die cavity wall that involves one or more undercuts and sometimes includes a core or cores.

Soldering – Adherence of molten metal to portions of the die.

Split gate – A gate of castings having the sprue or plunger axis in the die parting.

Sprue – Metal that fills the conical passage (sprue hole) which connects the nozzle with runners.

Sprue pin – A tapered pin with rounded end projecting into a sprue hole and acting as a core which deflects metal and aids in the removal of the sprue.

Toggle – Linkage employed to mechanically multiply pressure when locking the dies of a casting machine.

Trim die – A die for shearing or shaving flash from a die casting.

Unit die – A die interchangeable with others in a common holder.

Undercut – Recess in the side wall or cored hole of a casting disposed so that a slide or special form of core (such as a knockout) is required to permit ejection of the casting from the die.

Vent – Narrow passage at the die parting which permits air to escape from the die cavity as it is filled with molten metal.

Void – A large pore or hole within the wall of a casting usually caused by entrapped gas. A blow hole.

Waterline – A tube or passage through which water is circulated to cool a casting die.

Additional Resources

One of the principal resources for additional information about die casting is the North American Die Casting Association. NADCA is the only trade association in the United States that represents all major segments of the die casting industry. Its goals include advancing the technology of the die casting process and providing information to its members and the general public. For more information, visit www.diecasting.org.

In addition, "Design for Die Casting" is available online. It provides technical information, video clips, computer graphic simulations and audio explaining die casting.

Publications

NADCA has a number of books available that provide more detailed information about die casting.

Introduction to Die Casting: A detailed overview of the industry, including the die casting process, machinery, quality, safety and costs. 2000©.

Die Casting Handbook: General technical information about die casting, as well as markets served and environmental issues. 2001©.

Product Design for Die Casting: A comprehensive review of strategic design considerations, as well as the selection of alloys and the appropriate die casting process. 1998©.

NADCA Product Specification Standards for Die Castings: A complete collection of guidelines to aid product designers and specifiers. 2003©.

The Zinc Die Casting Process: Basic information on die casting this specific alloy.

Designing Die Casting Dies: Information concerning the design of die casting tooling.