overmolded

Overmolded refers to a part produced by molding a second material over a pre-formed substrate to form a single integrated part. The second material adheres to the substrate to produce a user-facing feature (grip, seal, or housing) and can encapsulate parts for insulation and protection.

The process involves insert overmolding or two-shot injection molding. In insert overmolding, a pre-existing component (often metal, ceramic, or molded plastic) is placed in a mold and a second material is injected to form the overmold around it. In two-shot molding, both materials are injected sequentially in a single machine into a single part cavity.

Common materials for the overmold layer include thermoplastic elastomers (TPEs), silicone, and polyurethane; the substrate is often rigid plastics (ABS, polycarbonate, PBT) or metals. Material compatibility and surface preparation are critical for adhesion and long-term performance.

Applications include electrical connectors with a flexible grip, medical devices requiring biocompatible elastomer skins, consumer electronics housings, automotive sensors and switches, and tool grips with improved ergonomics and vibration damping.

Benefits include improved grip, impact resistance, sealing against moisture or dust, electrical insulation at interfaces, and the ability to customize color and tactile feel. Challenges include bonding between dissimilar materials, mold design complexity, potential differential thermal expansion or shrinkage, and higher tooling costs and cycle times.

Design considerations include material compatibility, surface treatment, mold gating and venting, and post-molding inspection. Quality often relies on pull tests for bond strength, and environmental aging tests for adhesion.