overmolds

Overmolds refer to a manufacturing process in which a material is molded over a pre-formed substrate to produce a single, integrated component. The substrate is typically rigid or flexible and can be a plastic, metal, or composite. The overmold material is usually different in properties, often softer for grip or sealing, such as a thermoplastic elastomer, rubber, or silicone.

Two-shot injection molding is a common method, where a substrate is molded first, then moved to a second shot where the overmold material is injected around or onto it. In-mold assembly and insert molding are related approaches. Substrate pretreatment (e.g., plasma, corona, flame) and surface roughening improve adhesion. Mold design must accommodate mechanical interlocks, undercuts, shrinkage, and venting.

Common substrate materials include ABS, PC, PC/ABS, or metals; overmolds include TPEs, TPUs, silicones, elastomeric polymers. Applications span consumer electronics grips, tool handles, automotive interior trim, medical devices, and sporting goods, where combined stiffness and tactile or sealing properties are beneficial.

Benefits include enhanced ergonomics, grip, vibration damping, weather sealing, and aesthetics. Challenges comprise potential delamination between materials, differing thermal expansion and shrinkage, and higher tooling costs. Quality control often involves adhesion testing (peel or pull-off), inspection for delamination, and functional tests for sealing and grip.