Cavity

In practice

Cavity count is chosen from annual volume, press size, and cycle time. Multi-cavity molds need balanced runners so every cavity fills the same.

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

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.

Family mold

A family mold is an injection mold that makes two or more different parts in the same shot, such as a housing top and bottom. It saves tooling cost at low to medium volumes, but the parts must share a material and color, and balancing fill across different cavities is harder.

Parting line

A parting line is the line on a molded or cast part where the two mold halves meet. It usually leaves a slight witness line and is where flash forms as the tool wears. Designers place it on an edge or noncosmetic surface and set draft away from it.

Cycle time

Cycle time is the time needed to complete one full production cycle, such as one mold shot, one press stroke, or one machined part. It sets machine hours per part, so it is a primary input to piece price. In injection molding, cooling usually takes most of the cycle.