Insert Molding vs. Overmolding: Key Differences and How to Choose the Right Process

Overmolding and insert molding are two injection molding processes used in making commercial and industrial products. Both use the same concept, i.e., they involve molding a plastic part over another part. However, both differ regarding the properties and functions of the “other part.” As a result, they have different applications.

Using the two processes without proper understanding can lead to several adverse effects. Common ones are product failure, wastage of time materials, and increased production costs. As a result, this article does an insert molding vs overmolding comparison to help you choose the right process for your project.

Overview of Insert Molding

What is Insert Molding?

Insert molding is a part manufacturing process applicable in molding plastic over a non-plastic part (usually metal, also known as inserts). The process follows the normal injection molding procedure with the addition of an insert. It involves placing an insert in a mold and injecting molten plastic into the mold. As a result, the insert becomes encapsulated with plastic material. Afterward, ejection occurs.

Insert molding can occur in two ways: manual and automated. On the one hand, a manual process is less costly and gives the operator easier control. On the other hand, the automatic process ensures repeatability, reduction of error, and overall production efficiency.

Applications of Insert Molding

Insert molding is common in aerospace, medical, electronic, and defense industries. Common insert molding examples are products such as screwdrivers, spring contacts, clips, and pins.

Advantages of Insert Molding

Insert molding has wide applications due to its advantages. Below are a few reasons you should consider the process for your project.

• Insert molding is suitable for creating strong and reusable connections.
• It is cost-effective.
• Applicable in making thin-walled cases that are untappable
• There is a reduction in the need for part assembly.
• Enhances the combination of plastic and metal parts which improves part performance.
• Suitable for making products resistant to pull-out, vibration, moisture, and dust.

Disadvantages of Insert Molding

• Insert molding is suitable for several products. However, it is not suitable for others. Use the following. Below are a few disadvantages of the process.
• Resin can shrink around or enter the insert leading to a functional problem.
• It requires a high level of technical expertise for complex parts.
• It requires multiple manufacturing technologies, i.e., metal and plastic.

Overveiw of Overmolding

What is Overmolding?

Overmolding is another common injection molding process that involves molding a plastic material over another plastic material. It is a double injection molding process. As a result, it is called two-shot molding.

Overmolding involves injecting the plastic into a mold to form the first plastic part (also known as the substrate). Then, on solidification, the substrate is placed in another mold and injected with the second plastic material (overmold). Finally, the substrate becomes encapsulated with the overmold. Afterwards, ejection then occurs.

Keynote: Both processes take place simultaneously, i.e., the formation of the substrate and overmold is not separate. This ensures that both plastic materials fuses.

Applications of Overmolding

The overmolding injection molding process has a wide application (even synonymous to insert molding) in many industrial and commercial industries. Overmolded parts are applicable in the following ways:

• Products that need a comfortable grip, e.g., plastic handles.
• Parts used in an environment susceptible to vibration, heat, and electric shock.
• For making products with better aesthetic appeal due to the molding of complementary or contrasting color.
• Products with embossed or debossed areas featuring a business name or logo.

Advantages of Overmolding

Overmolding has wide applications due to its advantages. Below are a few reasons you should consider the process for your project.

• Increase in material flexibility due to the use of different plastic parts.
• There is no need for plastic welding or other joining mechanisms such as adhesives.
• Improvement of product performance by increasing the product durability.
• It creates a strong connection between the two plastic materials.

Disadvantages of Overmolding

Overmolding is suitable for several products. However, it is not suitable for others. Below are a few disadvantages of the process.

• It requires multiple injection molding processes, which increase the cycle time and the cost of production.
• It requires more tools than a single injection molding due to the two-step process, which will increase the development cost.
• Delamination can occur due to fluctuation in the optimal temperature range.
• It can also require special tools, which also increases the development cost as suppliers might not have them and will charge more to make them.
• Not all plastic materials are compatible with each other. As a result, you should work well with your injection molding service provider for the best material.

Differences Between Insert Molding and Overmolding

Both processes are similar. However, there are many differences that you have to take note of before choosing the right one for your project. The overmolding vs insert molding difference entails the following:

Insert Molding vs Overmolding: Process

The major insert molding vs overmolding difference is the molding process. On the one hand, overmolding is a two-step manufacturing process (hence the name two-shot molding) that involves molding a plastic (overmold) on another plastic (substrate). On the other hand, insert molding involves molding plastic on a non-plastic material. Unlike the overmolding process, it is a one-step manufacturing process (the insert is manufactured separately)

Insert Molding vs Overmolding: Production Speed

Both processes take time. However, insert molding is relatively more time-consuming due to the molding of another layer on the product, i.e., the total product encapsulation of the insert. In contrast, the overmolding injection molding process entails partial encapsulation. Aside from that, insert molding does not require separate production of the two plastic parts, unlike overmolding, which has the substrate and overmold.

Insert Molding vs Overmolding: Material Selection

On the one hand, overmolded parts come from plastic parts that can form chemical bonds with each other. However, not all plastic materials are compatible with each other. For example, ABS is compatible with ABS, Polycarbonate, and Polyethylene but not with POM. On the other hand, most plastic materials are compatible with non-plastic parts. As a result, insert molding has broader material compatibility.

Keynote: Ensure you are familiar with many injection molding materials before selecting any process. Better, you should seek the advice of an injection molding service provider on the right material to choose.

Insert Molding vs Overmolding: Cost

Overmolding is a more expensive project due to the two injection processes. Aside from that, insert molding reduces assemblage cost and improves project productivity, especially in high-volume production. They are, however, costlier than injection molding.

Should I Choose Insert Molding or Overmolding?

The right process between insert molding and overmolding depends on the application. However, it is impossible to choose any for your project. Nevertheless, you can judge from the plethora of insert molded and overmolded parts to determine the right process. Consider the factors below:

When to Use Insert Molding

Consider insert molding when making products that have the following attributes or applications:

• When working with a prefabricated substrate.
• If the substrate contains computerized parts, metals, or wires.
• The final piece needs to be a solid piece.
• Cover metal or other non-plastic parts with a plastic polymer or resin, e.g., a screwdriver.

When to Use Overmolding

Consider overmolding when making products that have the following attributes or applications:

• Rubber or thermoplastics can be part of the finished product.
• There are multiple layers of colors on the finished products.
• When production of a second layer and the substrate will take place simultaneously.
• There is no need for dissembling the final piece
• If you intend to improve the grip and texture of a part
• When you want to add cushioning and shock absorption to household items.

Conclusion

Overmolding and insert molding are injection processes that use the same concept, i.e., molding a plastic part over another. However, they differed based on processes, cost, speed, and material selection. Before you choose any of them, you need a proper understanding of the process. As a result, this article did an insert molding vs overmolding comparison to help you choose.

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FAQs

What is two-shot injection molding?

Two-shot molding is another name for overmolding. Also known as dual-shot, multi-shot, or double-shot molding, it simply involves simultaneously molding a plastic part (overmold) on another plastic part (substrate). The process takes place simultaneously and allows engineers to create multi-material or multi-colored parts without assembly.

What are inserts in injection molding?

Inserts are non-plastic parts that are important in insert molding. They are placed in the mold and injected with plastic material. Most commonly, they are simple objects, e.g., thread or rod. However, they can also be complex, e.g., battery.