overmoldings

Overmolding is a plastic manufacturing process in which one material is molded over another to create a single, integrated component. The overmold typically provides a different material property than the base substrate, such as a soft, compliant elastomer over a rigid plastic, enabling features like improved grip, insulation, or sealing.

The process can be performed in several ways. In two-shot molding, both materials are injected sequentially within the same mold cavity. In insert molding, a preformed substrate is placed in the mold and then overmolded with another material. Sequential overmolding uses separate molds and tooling, aligning parts between operations. These methods allow multiple materials with distinct properties to form a single part.

Common base substrates are rigid thermoplastics such as ABS, PC, or PBT. Overmold materials are typically elastomers or flexible plastics, including TPEs, TPUs, silicones, or polyurethanes. Material compatibility, adhesion, and surface energy are important considerations, often requiring surface treatments or tethering agents to ensure strong bonding.

Design considerations include adequate surface preparation, proper wall thickness, and mechanical interlock features to promote adhesion. Draft angles, part geometry, and mold register accuracy affect tool wear and part quality. Designers also account for thermal contraction and potential delamination under vibration or impact.

Overmolding provides ergonomic grips, tactile feedback, electrical insulation, and seam sealing, while reducing assembly steps and part count. It is widely used in consumer electronics, medical devices, automotive controls, power tools, and sporting goods, where combined material properties add value.

Challenges include higher tooling and mold complexity, longer cycle times, and cost. Delamination, moisture absorption, and process control issues may arise if materials are not well matched or if mold conditions drift.