Have a look at toothbrushes, do you find that most of stiff frame is combined with rubberized grips on the handle? This is a widely- used process as what we called overmolding.

Wintech Rapid Tooling provides and commits to a series of specialized plastic injection molding service, including overmolding that is one of our main technologies for aesthetic and functional purpose in kinds of industries, such as Automotive, Home Appliances, Medical Devices, Electronics, etc.

In brief, overmolding is a plastic injection molding process in which one thermoplastics material or metals is molded over another plastic, and finally to form a strong bonding part.


  • Molded as one assembly. Fast production speed with low materials and labor cost.
  • Unique visual appeal with multiple designs.
  • Improve the strength and structure of parts, and realize multifunction for end product.
  • Provide strong and stable adhesion bond. Prevent from loosening and improve resistance to shock and vibration.


Different from single- part molded, we should first think about the classification of overmolding and material selection before running an overmolding project. We will work together with our customers to study the feasibility and provide our engineering suggestions.

Generally speaking, overmolding is classified into three types, insert- molding, two-shot molding and co- injection molding. Only after getting knowledge of their difference can we properly build a mold tool.

Insert molding, which is to mold thermoplastics over metal parts, including any kinds of pins, nuts and thread inserts. One mold tool is enough, the overall structure must be well considerate, and our engineers will build a precise tool cavity according to assembly drawing. When the metal part is ready and it will be placed into the tool in advance, and then inject plastic resin in to form a final part.

Two-shot molding, which is to mold thermoplastics over another hard/soft plastic.  In rapid tooling industry, we normally build two sets of tools. One of mold tools is for the base layer part, and another one is for final assembly shape. In other words, two-shot molding requires two injection machines to do secondary injection.

Co- injection molding, this is a very expensive and complex process compared with the other two. Even though the substrate material and molded material can be injected into the same mold on one machine, it is used less because of long lead- time, high cost and difficult operation. Also, it is essential to analysis compatibility between materials.

A wide range of thermoplastic materials can be used for overmolding, typically, soft plastics as urethanes and elastomers, and hard plastics as polycarbonate and nylon.

The most common case is molding elastomers or urethanes over hard plastic or metal parts. It could help improve the hand touch feeling, skid resistance, heat insulation, shock resistance or work as other function. What if using hard plastic to mold over hard segment? That is attainable as well but please feel free to contact us to have a preliminary check for you.

Last but not least, other factors like melting temperature, shrinkage, deformation and injection gate is also indispensable for our considerations. Wintech will be always on your side to give full support.