Overmolding & Insert Molding

Our Shunjing 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.

  • 25 to 10,000+ parts
  • Shipped in 15 days or less
  • Molds starting at $1,995
Common Applications
  • low-volume production
  • bridge tooling
  • pilot runs
  • functional prototyping


Watch: Designing Overmolded Parts

See how to important design consideration for overmolded parts can improve functionality and moldability.

on demand manufacturing injection molded machine

Molding Options: Prototyping or On-demand Manufacturing?

Consider part quantities, lifetime maintenance, level of inspection, and cost when determining which option is right for injection molding.

Design Guidelines

Our basic guidelines for overmolding and insert molding include important design considerations to help improve part manufacturability, enhance cosmetic appearance, and reduce overall production time.

Overmolding Materials and Inserts

We stock a range of thermoplastic and LSR materials for overmolding that are suitable for various part applications and industries. Customer-supplied metal inserts are also accepted.
Comparison Guide


press operator examines liquid silicone rubber part

Free moldability analysis within hours