Shenzhen Alu Rapid Prototype Precision Co., Ltd.

In injection molding, an undercut refers to a geometric feature in a part design—such as an indentation, recess, protrusion, or overhang—that prevents the molded part from being easily ejected from a straight-pull mold (where the mold halves separate linearly along the parting line). These features "lock" the part into the mold cavity, potentially causing damage or requiring additional tooling.

Why Undercuts Matter

Design Impact: They add complexity and cost to the molding process, as standard molds can't release the part without mechanisms like side actions, slides, lifters, or unscrewing devices.

Common Examples:Internal threads or snap-fit tabs.

Holes or bosses perpendicular to the mold's pull direction.

Concave curves or ribs that face inward.

Handling Undercuts

To incorporate undercuts successfully:Redesign the part to minimize them (e.g., by angling features at 1–5° draft for easier release).

Use specialized mold actions for unavoidable cases, which can increase tooling costs by 10–30%.