Core

Where it comes up

• Plastic injection moldingMolten thermoplastic injected into a steel or aluminum mold. Lowest piece price for plastic parts at 5,000+ a year.
• Zinc and aluminum die castingMolten zinc or aluminum injected into steel dies at high pressure. Thin walls and net shape at 2,500+ parts a year.

Related terms

Cavity

A cavity is the hollow in a mold that forms the part's shape, typically the outside or cosmetic side. A mold may have one cavity or many; a 4-cavity mold makes four parts per cycle. More cavities raise tooling cost and lower piece price.

Ejector pin

An ejector pin is a hardened steel pin in a mold that pushes the finished part off the core when the mold opens. Ejector pins leave small round witness marks, so designers place them on noncosmetic surfaces. Too few pins, or too little draft, can distort or crack parts.

Draft angle

Draft angle is the taper applied to part walls parallel to the direction of mold opening so the part releases without dragging. Injection molded parts typically need 1–2° of draft, plus about 1–1.5° more per 0.001 in (0.025 mm) of texture depth. Die castings typically need 0.5–2°.