Overmolding Material Bonding

Chemical bonding between overmolded materials is possible, but material compatibility should be considered in order to achieve desired bond strength. Incorporation of an adequate mechanical bond is strongly recommended if bonding is critical to your application. An undercut is a good example of a mechanical bond

( M = mechanical bond (recommended)      C = chemical bond )

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  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.
  
  

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  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.