Overmolding and insert molding are specialized injection molding processes that combine multiple materials or embed functional components into a single molded part. These processes add functionality, improve aesthetics, and reduce assembly costs.
Overmolding involves molding a second material over a previously molded substrate. Common applications: soft-touch grips (TPE over ABS or PC), two-color cosmetic parts, dual-durometer seals, and encapsulated electronics. Material compatibility is critical — the substrate and overmold material must bond chemically or mechanically.
Insert molding places pre-formed components (metal inserts, threaded inserts, electronic components, magnets) into the mold cavity before injection. The plastic flows around and encapsulates the insert during injection. Applications: threaded inserts for assembly, encapsulated electronic connectors, metal reinforcement in structural parts, and magnetic encoder components.
Minimum wall thickness over inserts: 1.5mm. Insert should be knurled, undercut, or through-hole for mechanical retention. Keep inserts at least 3mm from part edges. Avoid sharp corners on inserts to reduce stress concentration. Pre-heat inserts for thick metal sections to prevent plastic freezing before the cavity fills.