What is Overmolding?

Overmolding is an advanced injection molding process that allows combining two or more materials into a single part by molding one material over another previously molded substrate. This technique has gained popularity in the plastics industry due to its ability to enhance functionality, aesthetics, and ergonomics without requiring additional assembly. The result is multi-component plastic parts with high added value, both technically and visually.

Plastic overmolding is based on multiple-material injection, where the first material (typically more rigid) is molded to form the base component. Then, a second material (usually softer or with different properties) is injected over selected areas of the initial part. This combination creates a physical or chemical bond between the materials, eliminating the need for adhesives or mechanical fasteners.

Overmolding is used in a wide range of applications. It is common in products with non-slip grips, integrated seals, soft-touch surfaces, or decorative color and texture contrasts. Typical examples include tool handles, electronic device housings, control buttons, automotive components, and medical parts with flexible zones.

Success in plastic overmolding depends largely on material compatibility. Not all polymers bond well, so it’s critical to choose the right material combinations and define precise process parameters. Common pairings include polypropylene (PP) with TPE (thermoplastic elastomer), polycarbonate with TPU, or ABS with liquid silicone.

Another advantage of overmolding is enhanced product performance. It can provide localized thermal or electrical insulation, impact cushioning, chemical resistance, or watertight sealing zones—all without increasing assembly steps or costs, improving overall production efficiency.

Technically, plastic overmolding can be carried out using different machine and mold configurations. Popular systems include rotary platen molds, movable core molds, or dual-shot injection machines. The choice depends on part geometry, materials involved, and production volume.

At companies like Plásticos Lezo, where multiple-material injection is part of their expertise, overmolding is used to deliver customized solutions that integrate aesthetics, ergonomics, and performance. This approach reduces the number of parts, lowers assembly errors, and enhances product perception—especially in automotive, consumer electronics, or medical device industries.

Mold design is another critical aspect of overmolding. It requires careful planning of runner systems, injection points, and parting lines to avoid flash, misalignment, or bonding issues. Precise control of temperature and pressure during both injection phases is also essential to ensure a strong material bond.

In summary, overmolding, or plastic overmolding, is a key technology for producing multi-component plastic parts that combine enhanced functionality, optimized design, and added value. Thanks to multiple-material injection, it is possible to integrate different properties into a single part, simplifying processes and unlocking new possibilities in plastic product design and manufacturing.