Parting line

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.
• ForgingClosed-die and open-die forgings in carbon, alloy, and stainless steel and aluminum, with grain flow for strength.
• Rubber extrusion and moldingSeals, gaskets, grommets, and profiles extruded or molded in EPDM, silicone, nitrile, neoprene, FKM, and TPE.

Related terms

Flash

Flash is excess material that escapes past the parting line or between die halves and hardens as a thin fin on the part. In molding and die casting it signals worn tooling, low clamp force, or excess pressure. In forging, flash is designed in on purpose, then trimmed off.

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°.

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.

Core

A core is the half or insert of a mold that forms a part's inside features, such as the interior of a housing or a hole. In injection molding the core usually sits on the moving half, and the part shrinks onto it, so ejection happens from the core side.