The Ultimate FAQ- Overmolding

Every day we use household products made of different materials like plastic and metal. Manufacturers mold and bond these materials to create a new product. With overmolding, insert molding, and several other processes, they design a range of products. Let us learn more about overmolding.

Table of Contents

What is Overmolding?

Overmolding refers to the injection molding process that may involve more than 2 materials to combine the connector and wire. The goal is to make a single part. The bonding of these materials is normally chemical bonding. However, some professionals also use both mechanical and chemical bonding. Primary materials are known as Substrates, while the secondary ones are called Subsequent.


The substrate can be molded plastic, machined metal components, electric connectors, screws, and threaded inserts. Thus, it is the major piece that helps create a single consistent part with mechanically interlocked and chemically bonded materials.


Injection overmolding :It can be the best method for adding different materials on top of brittle objects. Thus, it can make the product impact-resistant and more durable. Overmolding also increases the aesthetic value of the product. You can choose overmolding services to add different materials and colors to the main material.


Some manufacturers prefer overmolding due to the reduced manufacturing cost to create a part. For instance, the injection-molded dashboard can be molded with rubbing linings by applying overmolding techniques. There is no need to assemble the rubber and injection-molded parts. So, the overall production cost becomes low. Moreover, you can incorporate a complicated design assembly in the over-molding process.

What is Overmolding Used For?-Overmolding Application

The low pressure overmolding process involves materials of different types based on the product to be designed. There are several uses of overmolding.


  • Overmolding rubber on metal-In this case, a metal substrate undergoes machining and casting processes. Then, you can insert the substrate into the injection overmold tooling system. It also involves TPU overmolding, as rubber is molded onto the metal. This process presents you with a soft grip surface.
  • Overmolding rubber on plastic-Manufacturers mold a plastic substrate for this purpose. Soft rubber is molded around this substrate. The part acquires a soft grip.
  • Overmolding with TPU-In the case of thermoplastic overmolding, there is a combination of the injection molding process and a fiber-reinforced plastic laminate. Using the polyurethane overmolding technique, you can mold TPU into shapes like caps, gaskets, and grips.
  • Plastic on metal-The metal substrate undergoes a machining and casting process to get into the injection molding tool. The plastic part is also molded onto the metal. It helps in retaining metal parts in the plastic component.

Some Other Applications of Overmolds

Although TPE overmolding is common, professionals use other materials to create a bold and make different products

Hardware tools

Overmolding is the most commonly chosen process for manufacturing hardware tools like wrenches, screwdrivers, hammers, knives, and blades. Some household items ensure a better grip due to silicone overmolding.

Surgical Devices

Medical overmolding is good for product safety and precision. Doctors, nurses, and surgeons need safer plastic materials while using surgical tools. More importantly, these tools have to be sterile and easily cleanable to prevent contamination.

Car trims

Car moldings refer to the parts like bumper, side body, door edge, wheels, and fender. Although they have a decorative value, they provide some functional benefits. An insert overmolding process is used for these car trims.


You can find overmolded parts in food containers, cookware, and kitchen utensils. Moreover, knives, pot covers, and cutting boards use high-quality plastics that never affect the quality and taste of food.

How is Overmolding done?- Overmolding Process

Overmolding is such a process that involves the creation of a single object by blending different/same materials. There are several ways of blending these materials. To know how the overmolding process works, you have to learn about the major components. While dealing with an overmolding project, you will find 2 parts that we have already mentioned. The secondary material is the overmold, while the base material acts as the substrate.

To say in other words, overmolding is a 2-step procedure where individually molded parts get bonded to refine a product’s features. In most cases, a plastic part is created with the plastic injection molding process. Then, you have to cool it down and place it over your overmolding tool. Apply a coat with rubber and molten thermoplastic materials. The insert molding process is different as it involves the encapsulation of an object in molded plastic.

You can choose a 2-shot molding process while using the injection molding systems. You have to insert the hard part first and then get the elastomeric mold into your molding machine. Choose the mold’s design based on the project. However, the substrate must be in a gel state.

What is Insert Molding?

Insert molding refers to the industrial-grade process that relies on innovative injection molding technology. It has revolutionized the modern manufacturing sector. Moreover, the insert molding process combines metal, plastics, and other materials and components to make a single unit.

Furthermore, the process involves engineering plastics to ensure wear resistance, weight reduction, and tensile strength. You can choose metallic materials for strength and conductivity.

During your insert molding project, you can make almost any configuration. For instance, in the 3D circuit board manufacturing process, overmolding enables it to move freely from the inner to the outer side. The plastic helps in tying the parts together.

The insert molding process can blend thermoplastic with several components, reducing labor costs. After overmolding a stamp, you can create different circuit paths.

The best fact is that the insert-molded parts do not become loose. There are no concerns for misalignments, improper terminations, and other issues. The thermoplastic resin used in the process ensures resistance to shock and vibration.

You need to go through some steps for the plastic insert molding process

  • Load a customized mold with inserts.
  • Add molten plastic into the mold.
  • Cool it down and open the mold to remove components.
  • Separate the components and analyze them.
  • Post-molding assembly involves other activities like circuit testing, micro-soldering, and bonding.

What is the Difference Between Insert Molding and Overmolding?

Insert molding and overmolding both involve the process of joining plastics, metals, and other materials. Liquid plastic is useful for creating products of different materials. But, in the case of insert molding, you need to pre-manufactured inserts. Elastomers in the insert molding process are the adhesion bond. However, the elastomer is heated for your chemical adhesion.

Insert molding refers to a subset of different injection molding processes. So, it has some similarities with overmolding, which involves the placement of metal components into the mold cavity. You can do the precise positioning of the insert robotically and manually. It is better to choose metal inserts to ensure stiffness and strength. You can choose plastic for other parts to minimize weight.

However, one disadvantage is that when you need a custom-designed insert, you have to use a CNC machining system.

On the contrary, overmolding is advantageous in several ways. It enables you to use materials of different types to create complicated parts of varying properties. There is no need to use adhesives. That is why the product gains a high level of durability. You can mold soft seals into the desired parts.

For instance, an electronics enclosure should have IP ratings. The part may need a groove where you will install an o-ring. But, it is more robust and cost-efficient to mold the seal permanently as one of the integral parts.

Let us now clarify more differences between overmolding and insert molding. Almost any overmolding project involves insert molding. However, an insert molding process does not always include overmolding.

Insert molding is useful for manufacturing electronic sockets, connectors, and other parts assembled properly with fasteners. It is also effective in providing protective surfaces on medical and aerospace devices.

On the other hand, overmolding is a more complicated plastic injection process for creating parts from multiple materials. You can use the insert molding technique to facilitate overmolding.

The substrate for the insert molding process is non-plastic. But, it is plastic for the overmold. That is why you can choose to insert molding for molding plastics on the non-plastic substance.

What are the Molding Types?

What are the Molding Types?

Plastic injection molding is a process for creating end-use production parts and prototypes within the shortest period. Aluminum molds provide you with the most cost-effective tooling and faster manufacturing cycles. Designers need to know the guidelines for plastic injection molding.

Best professionals use a technology-driven injection molding process that takes advantage of automation. They send CAD models to the production department to start the mold milling process. However, they can fabricate molds from aluminum for faster tooling.

There are some reasons for choosing aluminum for your thermoplastic injection molding projects. This metal is ideal for efficient heat transfer, and so it is better than steel. There is no need to have cooling channels for this purpose, and thus, you will save time. You can concentrate more on cosmetic issues and the quality of the parts.

Load the resin pellets into the barrel to melt and compress them. Put the hot resin into the mold cavity, and it helps in molding the part.

Silicone overmolding

It is the injection molding procedure to silicone over and under the substrate to design the desired component. Product designers can combine different materials to ensure rigidity. For instance, you can mold a silicone rubber over a handle made of plastic that adds strength.

Silicone overmolding helps designers to ensure color variations, ergonomics, and unique brand details. Used as the overmolding material, silicone provides vibration damping, impact resistance, and weather resistance. Silicone overmolding makes a product design more valuable.

It is something more than a layering process. The substrate material is useful for assembling purposes. The strength of the mechanical and chemical bond is important.

You need to choose between insert molding and a multi-shot molding process for liquid silicone overmolding. In the case of the double-shot molding process, you can pick the substrate as the primary material. The overmold is the secondary material.

LSR Molding (Liquid Silicone Molding)

The method applied for manufacturing liquid silicone rubber components is known as liquid injection molding. LSR is pure platinum cured silicone with thermal, physical, and chemical properties. Moreover, LSR is useful for the transparency and coloring of the product. The materials act as insulators based on the chemical compositions. Molded components designed with LSR are elastic, tasteless, and odorless.

To deal with LSR molding, the liquid material is combined from separate components. The ratio maintained in this respect is 1:1. The curing process does not take much time, and it is highly advantageous for the faster cycling process.

As LSR is flexible, parts are detached from the mold. There is no need to integrate ejector pins into your mold design. You have to use CNC machining for creating an LSR molding tool.

Materials for Overmolding

You have to choose thermally and chemically compatible materials for your overmolding process. Choose metal substrates for your plastic overmold. However, while dealing with plastic and plastic injection overmolding, you can find compatibility issues. When the overmolding materials and substrate are not compatible, there will be a deformed product. The most common materials for overmolding are

  • Polymethyl Methacrylate Acrylic– Highly economical and useful for applications that need light.
  • High-density polyethylene– Highly versatile plastic to manufacture corrosion-resistant piping and other products
  • TPU & TPE -Excellent at the flowing, which can be shaped and wrapped very well.

Polyetheretherketone, Polymethyl methacrylate, and Polyetherimide are other materials for overmolding. There are several material combinations, but compatibility is the most important factor.

Materials have to bond together to accomplish the process of the overmolding procedure. Although bonding is not compulsory, it is significant. Materials not bonded properly need indents and undercuts.

Friction is another vital factor in your plastic injection overmolding. This term indicates the potential of moving one surface against the other.

You must also focus on the material thickness to identify the effectiveness of performance. Thicker materials feel soft and absorb vibration, whereas the thinner ones do not have vibration absorption capacity.