About Overmolding & Insert Molding

About Overmolding & Insert Molding

Aug. 24, 2021

Our rapid overmolding and insert molding processes produce custom prototypes and on-demand production parts in as fast as 15 days. We use aluminum molds that offer cost-efficient tooling, producing parts from a range of thermoplastic and liquid silicone rubber materials.

What is Overmolding?

With overmolding, the production of the substrate parts is a standard injection molding process involving an aluminum mold with no heating or cooling lines running through it. Cycle times are a bit longer, which allows our molders to monitor fill pressure, cosmetic concerns, and the basic quality of the parts. When the total run of substrate parts are molded, overmold tooling is then assembled to the press. The substrate parts are placed by hand into mold where each part is overmolded with either a thermoplastic or liquid silicone rubber material.

What is Insert Molding?

Insert molding is a similar process but instead uses a preformed part—often metal—that is loaded into a mold where it is then overmolded with a thermoplastic resin to create a final component. When the run is complete, parts are boxed and shipped shortly thereafter.

About Overmolding

Insert Molding Capabilities

Instead of a mold that produces a final part using two separate shots like overmolding, insert molding generally consists of a preformed part—often metal—that is loaded into a mold, where it is then overmolded with plastic to create a part with improved functional or mechanical properties. We currently accept inserts from PEM, Dodge, Tri-Star, Spirol, and Tappex. A complete chart of stocked inserts at Protolabs is available here.


One way insert molding is used is with threaded inserts, which reinforce the mechanical properties of plastic parts’ ability to be fastened together, especially over repeated assembly. Bushings and sleeves are another great way to increase part durability for mating components that need more abrasion resistance due to moving parts.

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