There are various types of plastic injection molding methods and OEMs may wonder which technique is best for a given molding project. The answer is that it depends on the components being produced. This is why it is important for OEMs to have a good understanding of the different molding methods in order to select the best technique for a particular application. Additionally, it is advantageous for OEMs to leverage the expertise of an injection molding partner, such as Crescent, that has experience in a myriad of injection molding techniques including overmolding and insert molding – two common molding processes that are often confused.

Each process has its benefits and applications that it is best suited for. While there are some similarities in these two techniques, such as the fact that they are both multi-material molding processes, there are also some key differentiators. Below is an overview of overmolding and insert molding that will shed light on the similarities and differences between these two methods. 

What is Overmolding? 

Simply put, overmolding is when one material is molded over another material. With this technique, a base layer is molded first and then an additional plastic layer is molded over and around the base layer – resulting in a single, finished product. Oftentimes, the exterior layer is an elastomer that gives the desired surface texture or physical property such as pliability. 

Since two or more plastic materials are being used to create the final part, material selection is critical to the success of an overmolding project. The materials do not have to be the same but they must be compatible and bond together chemically and/or mechanically in order to avoid mold defects such as distortion or warping. 

Overmolding is a very common and versatile injection molding option. This technique is employed across a variety of industries including medical, pharmaceutical, dental, military applications, electrical/electronics, and safety. Examples of medical devices manufactured using the overmolding technique are surgical instruments. The instruments are injection molded first then the soft grip plastic layer is molded over the instrument to achieve the desired grip and aesthetic. 

There are many benefits to overmolding and below are the biggest advantages:

  • Increase Cost-Efficiency: overmolding is often a cost-effective option as it reduces the number of production steps! This process allows the second layer to be molded directly onto the base layer, avoiding the separate molding of two parts that need to be assembled post-production – reducing production times and saving OEMs money.
  • Extend Product Life: the addition of a second layer that is typically an elastomer offers many benefits such as sealing, sound absorption, and vibration dampening. These benefits result in a more durable product with an extended life time.
  • Improve safety and ergonomics: the use of a soft elastomer on top of a harder base layer provides a non-slip grip on many different products, providing a safer interaction with the product.
  • Improve Aesthetics: overmolding opens up endless possibilities for OEMs to create more attractive products via the use of multiple colors and/or patterns. 

What is Insert Molding? 

Insert molding is a process in which an insert is placed in the tool for molten plastic to flow around. With this process, the plastic encapsulates or surrounds the insert in order to integrate it into a larger injection molded part.

Inserts are often metal and, therefore, must be placed in the mold either robotically or manually prior to the injection of the plastic. The insert and the plastic, often a rigid plastic, must mechanically bond together in order for the insert to remain embedded in the plastic. Generally, insert molding results in better and more reproduceable encapsulation than other techniques such as heat staking or ultrasonic welding where the plastic part is melted post-molding in order to add the insert. 

Similar to overmolding, insert molding is found in a variety of products across a wide range of industries including medical, pharmaceutical, dental, military applications, electrical/electronics, and safety. Insert molding was developed to place threaded inserts in molded components, and to encapsulate the wire-plug connection on electrical cords; however, this technique has evolved to include inserts as intricate as motors and batteries. Some examples of products manufactured by insert molding include metal knives with plastic handles, and plastic parts with protruding metal screws that allow for repeated fastening and unfastening. 

Like overmolding, insert molding offers many advantages such as:

  • Increase Cost-Efficiency: molding an insert directly into the product avoids post-production operations – reducing production time and saving money!
  • Enhance Strength: this method creates a single molded plastic piece that is typically more durable and robust than if the product were created via secondary assembly.
  • Improves Cost-Effectiveness Over Metal: the use of plastic in insert molding decreases the part weight and reduces the amount of metal or other more costly materials needed - decreasing the overall product cost. 
  • Increase Design Options: insert molding allows the combination of plastic with metal or other insert materials, increasing the product design options available to OEMs.

Many of the similarities and differences between overmolding and insert molding have already been noted; however, there is one other distinction and that is production time. Generally speaking, insert molding is slightly faster than overmolding because the two materials are molded at the same time in a single molding step; whereas, overmolding is a two-step process where the base layer is molded first and allowed to cool; then, the second layer is poured over the base layer and allowed to cool. 

Crescent Injection Molding Capabilities 

For 70+ years, Crescent has been providing an integrated single source solution for customer’s plastic injection molded components utilizing our advanced engineering capabilities, in-houses tooling, and production facilities. Our capabilities allow us to mold a comprehensive range of engineered and commodity grade resins. We currently serve the medical, pharmaceutical, dental, defense, safety, electrical/electronic, aerospace and OEM/Industrial markets. 

Contact us today to learn more about our in-house tooling and complete manufacturing solutions.

Topics: plastic injection molding, injection molded tooling, insert molding