What You Need to Know About the Overmolding Process

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What You Need to Know About the Overmolding Process

Overmolding is an injection molding process employed in many industrial capabilities. It is an important part of rapid prototyping and custom production, where it is important in the overlay of plastics (plastic overmolding) and metals.

In this article, you will get to know about the overmolding process. This will include how the process works, the materials, its applications, and its advantages. When you finish the article, you will know a lot about the process. Let’s get right on it.

What is Overmolding Process?

Overmolding injection molding process involves creating a single material from the combination of two or more materials through molding. The materials can be the same or different.

Understanding the overmolding injection molding process comes with understanding the two categories of materials used in the process. These materials are the overmold and the substrate.

substrate and overmold

What is an overmold and substrate? The overmold is the materials molded on the substrate, while the substrate is the base material. There can be two or more overmold depending on the end-product and the manufacturer’s creativity.

How Overmolding Process Works?

Understanding the plastic overmolding process comes with knowing the three categories under the process. Below are the three types of overmolding.

Insert Molding

In molding soft elastomers or rigid plastic, insert molding is the best type of overmolding. It is the best type because it is economical and less difficult than the other. In insert molding, the hard segments are first separated into tools before the soft materials’ ejection.

It also involves the use of elastomers as an adhesion bond. This can be in the form of mechanical locks, chemicals, etc. For chemical adhesion to take place, you must heat the elastomer to the right temperature. This is needed to heat the hard segment’s surface.

Two-Shot Molding

Unlike the insert molding, the two-shot molding requires you to use two injection molding machines. You will inject the hard segment first, which follows the elastomeric mold into the injection molding machine.

The heated substrate used is always in a semi-solid or gel state. The mold’s design can be modeled to project the lateral part of the hard segment on the substrate. The two-shot overmolding injection molding process is the right one for those who value stable mechanical bond.

Co-Injection Molding

Of the three types of overmolding, co-injection molding is the most expensive and difficult to control. Its process is also different since it requires the injection of the substrate and the elastomer into the same mold. This also requires that the materials are compatible.

In terms of the quality overmolding, co-injection is the best. This is because all the materials are in the same molten state.

Evaluations of Materials Used in Overmolding Process

To people new to overmolding, choosing the right material can be a messy decision. This is because there are many materials, and many are being developed every week. Therefore, instead of only knowing the materials used for the process, the right thing is to know the evaluation process. In terms of selecting the materials, you should consider both the substrate and overmold. Below are what you should look at when choosing a material.

evaluations of materials used in overmolding process


In every overmolding injection molding process, the materials used should bond together. While it is unnecessary for them to bond, the ideal situation necessitates the materials’ complete bonding. If the materials do not include bond completely, there is a need for undercuts and indents to better connect the substrate and overmold.


Depending on the type of overmolding injection molding process, you might need to ensure the retainment of the substrate and overmold’s features. Therefore, there must not be a deformation of materials due to temperature change.

Friction Coefficient

Friction is an important factor in the plastic overmolding injection molding process because it varies with plastics. It is the term used for how easy a surface moves against the other. It is measured by the coefficient of friction, and together with surface texture, are very important factors in overmolding.


Hardness in overmolding is how great overmolding materials can resist indentation. It is measured in scales in which different materials used in a particular process must be on the scale.

Flexural Modulus
Flexural modulus is the resistance of a material to bending. It is an important property to consider because it affects the grip effect of the end product.

Material Thickness

Material thickness is another property that determines how effective the materials are in terms of performance. Thick materials will absorb vibration and feel soft while thin wall does not absorb vibration.

Choosing the right material is an important part of the overmolding process. This is because it will determine the success of the process. Below are common materials ideal for the process.

  • HDPE.
  • ABS.
  • PMMA (Acrylic).
  • Acetal Copolymer (POM).
  • PEEK.
  • PEI.
  • PBTR.

Difference Between Overmolding Process and Insert Molding

Insert molding and overmolding might involve the same molding process. However, both are different. In insert molding, the substrate is a non-plastic material, while the overmold is a plastic material. Therefore, we can say that insert molding is molding a plastic material on a non-plastic material. However, in overmolding, both the substrate and overmold are plastic materials.

Applications of Overmolding

applications of overmolding

Overmolding is a popular injection molding process of which TPE is a commonly used overmold. The substrate used in the process can be any materials ranging from plastic to metals. This makes the overmolding injection molding process an important industrial process with a lot of applications highlighted below.

Vibration Dampening in Automobile

Overmolding process is ideal for making products that are isolated from vibrations. A rubber-like connection between one component and the other can remove vibrations. This makes the process a necessary one in making motors and pumps.

Overmolding Process in Making Comfortable Tools

Overmolded materials provide comfort due to the better grip they have. This makes the process great for making products that provide better ergonomics. The molding process can take many shapes and can fit anything. This is the ideal reason while overmolding is applicable in making bicycle grips or kitchen utensils.

Overmolding Process in Water Resistant Products

Depending on the type of plastic used, overmolding is a great process for making water-resistant products. This makes it applicable in the electronic world. This makes plastic overmolding an ideal water-tight substitution material for traditional seals like O-rings. Not only are they water-resistant, but they can also be made to be flexible.

Making Sound Absorption Products

Overmolding is an ideal process to use for making products that need to absorb sound waves. It is the right process to make cases that can absorb the motor’s sound—thereby making the device quieter.

Generally, overmolding is an important process with applications in the following industries:

  • Automotive.
  • Appliance.
  • Controls.
  • Medical devices.
  • Electronic devices.

Advantages of Using Overmolding Process

advantages of using plastic overmolding process

Manufacturers with a need for design, grip, and stylish appearance all love what the overmolding process gives its product. Overmolding process is also not that costly, yet it has improved over the years leading to top-notch customer satisfaction. Below are the advantages of using overmolding.

Better Product Performance

When you use an overmolding process with a material, it will improve the product performance. This includes product performance in reducing shock and vibration, electrical insulation, and resistance to chemicals. A good example of such material is TPE, which creates a non-grip property when used in making some products. It can also act as an environmental barrier in terms of the properties mentioned above.

Increased Shelf Appeal

Overmolding process is ideal for making visually attractive surfaces. It is the ideal method since it comes in a variety of colors. It can also be further optimized for different finishes in clear or patterned form.

Lower Production Costs

Even though overmolding is a very useful process due to its many advantages, it has a very low production cost. This makes it an ideal manufacturing process in rapid production.

Rapid Direct Overmolding Process

The best overmolded products come from the total understanding of the process. We are talking about having the right team in charge of making your product, answering questions, and giving suggestions.

Maybe that is why you are having a problem with getting the best. It is because you have not been exposed to us at Rapid Direct. By choosing us, you have placed your assignments in reliable hands and experienced minds.

In Rapid Direct, we have perfect our overmolding injection molding process such that it is easy for you to request our services. Therefore, even if you are on a tight schedule, you can use our online quotation and have your quotes in minutes.

At Rapid Direct, you are assured of quality, reasonable price, and faster lead time


Overmolding injection molding process is a popular, useful process yet. It is not costly. To use the process, you have to understand the way it works. Therefore, to understand it, this article the manufacturing process, how it works, its applications, and its advantages. We believe that you’ve learned something about overmolding and would trust us at Rapid Direct for the best overmolding services


What does overmolding mean?

Overmolding is an injection molding process that involves creating a single material from the combination of two or more materials. The two materials used, which are the substrate and the overmold, can be the same or different. The substrate is the base material, while the overmold is the materials molded on the substrate. There can be two or more overmold depending on the substrate and the creativity of your mind. You can go through the article to know what overmolding entails.

What is the difference between insert molding and overmolding?

Insert molding and overmolding undergo the same molding process in general. However, they are different. In insert molding, the substrate is a non-plastic material, while the overmold is a plastic material. Therefore, we can say that insert molding is molding a plastic material on a non-plastic material. However, in overmolding, both the substrate and overmold are plastic materials.

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