Insert Molding & Overmolding

Both insert molding and overmolding are kinds of injection molding and are generally used to produce products that combine two materials, such as knobs with metal screws , or rubber bonded rollers. Insert molding or overmolding can bond the two materials together. Two-shot injection requires more complex design, processing, and material selection than single-shot injection, but it offers significant advantages:

- Allows material combinations, provide properties that cannot be provided by a single material
- Assembly steps can be eliminated, saving time and money
- Materials can be fused in a way that the assembly process cannot match
- Inserts increase the strength and durability of the part

What is insert molding?

Insert molding refers to pre-installing the insert in the mold and injecting resin. The molten resin is combined with the insert to melt. The insert is usually metal, and the injected plastic material is usually rigid plastic. During the molding process, the insert usually needs to be preheated so that its surface temperature is close to the melting point of the cover material for optimal bonding.

What is over molding?

Overmolding is a process of taking a substrate parts and then using injection molding to add additional layers over it, like thermoplastic or silicone rubber material. Traditionally, the substrate parts are plastic or metal with higher melting point, once that parts is cooled, the layer is injection molded over it. So the cycle time is a bit longer. Usually overmolding is used to create a grip or roller.