3 Things To Consider For Plastic Overmolding

3 Things To Consider For Plastic Overmolding

By Blog-manager

What are the things to consider for plastic overmolding?

  1. Material selection
  2. Design principles 
  3. Applications


Plastic injection molding in China has made it possible to produce some of today’s most intricately-designed plastic parts. It is a process ideal for producing large quantities of plastic parts, including medical devices, bottle caps, containers, automobile parts, and even children’s toys. Sometimes, however, plastic parts require additional features such as a soft grip, handle, sleeve, or cover. This is where plastic overmolding comes into the picture. 

The ability to overmold any other material over plastic can enhance the properties of a part. However, there are various things to consider for plastic overmolding. There is a need to select the right materials, follow certain design principles, etc.  

But first, let’s begin with answering the question: what is plastic overmolding? How can this injection molding process help produce the plastic part your enterprise needs?   

What Is Plastic Overmolding?

In simple terms, plastic overmolding is a process that refers to layering multiple materials on the same plastic component. Typically, this entails a plastic complement being partially or fully covered by other materials during the injection molding process.

To perform this operation, plastic injection molders need specific equipment. They require special injection molding equipment with two or more barrels in particular. This is necessary to enable the injection molder to place two (or more) materials at once throughout the molding cycle. 

Some of the common products that require overmolding include power tools that need ergonomic grips or a surgical instrument that needs a non-slip grip. Different materials and textures are used for added enhanced grip and comfort.   

Things To Consider for Plastic Overmolding

Plastic overmolding accommodates both functional and aesthetic requirements, which is why diverse industries rely on this process. Before delving into any overmolding project, here are a few things to consider:

Material selection

Material selection

Proper material selection is important for any manufacturing process as it is the foundation for achieving operational needs. However, proper material selection is especially crucial for plastic overmolding. 

Through plastic overmolding, you can combine various materials. This can include polybutylene terephthalate (PBT) and glass-filled nylon, or liquid silicone rubber and plastic — the possibilities are endless. But, the substrate material and overmolding material must be compatible — forming chemical and mechanical bonds during the plastic injection process. This is what ensures the part is durable. 

Here is a list of some of the materials that are commonly used as the substrate in overmolding projects:

  • Polycarbonate (PC)
  • ABS
  • Polystyrene
  • Acetal
  • PPO
  • Polypropylene

Incompatible materials can result in part deformations or failure. It would be wise to consult an expert plastic mold maker starting from the design phase. 

As the leading plastic injection molding company in China, Richfields follow a strict compatibility chart when helping clients select their overmolding materials. This is done to ensure the additional materials and resins selected are both chemically and mechanically compatible to meet the toughest operation conditions while ensuring product repeatability.

Design principles 

When it comes to plastic overmolding, there are various design principles to keep in mind. These include the following: 

  • Uniform wall thickness, proper draft angles, and smooth transition lines should be observed for both the plastic part and the overmold material 
  • The overmold’s material thickness should be equal to or than that of the substrate 
  • The overmold material’s melting temperature should be less than that of the substrate
  • The overmolded part’s surface should be slightly below or even with any adjacent substrate
  • Add a radius to sharp corners to minimize stress in the part 

At Richfields, we ensure each plastic overmolding project follows the necessary design principles to ensure durability. 



Finally, overmolded plastics have a wide range of applications in multiple industries. Some of the most common applications of the plastic overmolding process include:

  • Metal or plastic parts with a soft grip handle
  • Knobs for appliances
  • Medical devices
  • Electrical components
  • Encapsulated electronic devices
  • Controls
  • Automotive parts

When delving into an overmolding project, it’s important to consider the application at hand to ensure the production of durable parts. 

Key Takeaway

As discussed above, there are several things to consider for plastic overmolding techniques such as material selection, design principles, knowing the application in hand, etc. Observing these help to keep the quality, tolerances, and reliability of your plastic-molded products. 

If you’re in search of a reputable plastic mold maker in China that offers overmolding services, you may contact Richfields today! Our expert team has years of experience across multiple industries, and we highly prioritize careful planning to give you the best results you need with your plastic-molded projects. 

From waterproof seals, to rubber grips, we can help clients produce plastic products through overmolding. This is one of our cost cost-effective and quick injection molding processes that can create various types of plastic products with quality in mind.