Overmolding and Insert Molding: From Prototyping to Fabrication

Overmolding and Insert Molding- From Prototyping to Fabrication

Overmolding and insert molding are both advantages for parts manufacturing and product designing. While comparing over-molding vs. insert molding, you can see great differences and similarities as both techniques can increase functionality, durability, and appearance of parts in a CNC machining process.

This comprehension guide offers a deep understanding of these two techniques and can be helpful for designers, manufacturers, and engineers and describes processes from prototyping to parts fabrication.

What is Over Molding?

Overmolding and Insert Molding- From Prototyping to Fabrication

Overmolding is a manufacturing procedure also known as two-shot molding. It includes forming a single functional product after various materials are joined. Commonly a material such as metal or plastic is molded over a plastic material.

The combined material may exhibit various characteristics, such as different colors or physical or chemical properties. The end product formed after the over-molding process offers a specific desired function.

This versatile technique is gaining popularity on a larger scale because of being used for different beneficial purposes.

Overmolding Process:

As we know, it is a process that involves different materials contributing to fabricating a product. Usually, it contains a substrate layer containing another layer of over-molded material around it. There are no limitations for using any material as a substrate, such as plastic or metal.

The over-molding material is also usually plastic. If you use a metallic material as a substrate and plastic as an over-molding material, you may face no compatibility problems because of entirely different materials.

In contrast, if you use plastic as a substrate and over-molding material, you can avoid such problems.

The process consists of two main steps, which are as under.

Step 1: Molding and Curing of Substrate:

The first step of the over-molding process involves molding and curing the substrate material into a mold. Initially, the substrate is allowed to be molded. After molding, its curing is done to prepare it to receive another layer of over-molded material.

Step 2: Adding Over-molding Material Over Substrate:

Step 2- Adding Over-molding Material Over Substrate

After the substrate is molded and cured, you can place it in another mold. The over-molded material is then put over the substrate and is allowed to cure.

After solidification, both folded materials are firmly combined and act as a single functional product. After both materials are fused properly, they are ejected out.

Materials Commonly Used in Over Molding:


Some materials for this purpose are as follows.

  • TPR (Thermoplastic rubber)
  • TPE (Thermoplastic elastomers)
  • Polyacetals (polyoxometalate, POM)
  • PP (Polypropylene)
  • PMMA (Acrylic)
  • Polyamides (standard or GF-filled Nylon 6, 66, and 12)
  • PEI (Polyetherimide)
  • PC (Polycarbonate)
  • Copolyester (TritanTM)
  • PEEK (Polyether Ether Ketone)
  • ABS (Acrylonitrile Butadiene Styrene)
  • Polystyrene
  • TPU (Thermoplastic polyurethane)
  • SI (Silicone)
  • POM (Polyoxymethylene)
  • PBTR (Polybutylene Terephthalate)
  • PE (Polyethylene)
  • Nylon (Polyamide)
  • Acetal copolymer
  • HDPE (High-density Polyethylene)
  • ASA (acrylonitrile styrene acrylate copolymers)

Benefits and Limitations of Overmolding:

The over-molding process is advantageous in the following ways.

  • Various materials can form a single product. The process usually has less cost of labor.
  • You don’t need to use any adhesive to combine the materials. The substrate and over-molding material itself fuse to form the final product.
  • The product formed by this process exhibits greater flexibility due to multiple materials having varying properties.
  • The process takes less time to accomplish because of eliminating the need for special molding machines.
  • It helps in the production of more compact product designs.
  • These products offer greater productivity and performance.

Limitations of the Over-Molding Process:

Delamination is the main limitation of the over-molding process. If the required temperature is not provided to the substrate and over-molded material during bonding, the product may disassemble after formation.

Therefore, it is required to provide an adequate amount of temperature during bonding. This process also shows an enhanced part-cycle time due to the two-step process.

How to Define Insert Molding Process?

How to Define Insert Molding Process

It is a procedure in which a plastic part is molded on a non-plastic material so you can get the desired functional product. The non-plastic material used is referred to as insert. Adding the insert is the only thing differentiating it from the injection molding process.

This process is used on a large scale to produce different useful products. The products produced by this process offer greater durability because of their higher strength.

Insert Molding Method:

The process has the following steps.

1- Placement of Insert Into Mold:

Insert Molding Method

In the first step, an insert is carefully loaded into a mold. The loading of the insert in the mold is completed in two methods.

You can place it through automated insertion or load it through your hands. In automated insertion, you can use various automated methods or robots; in the latter, you load the insert yourself.

2- Molten Plastic Injection Over Insert in a Mold

Once the insert is loaded in the mold, you can inject molten plastic over the insert in the same mold under high pressure.

The high pressure automatically facilitates the fusing of the molten plastic with the insert. As a result, both are fused, forming a surprising product offering special functions. Later, the product is ejected.

Materials Commonly Used in Insert Molding:


The insert molding process includes plastic materials and inserts. In the case of inserts, you can use different types of materials. Some of these materials are as follows.

  • Nickel
  • Copper
  • Aluminum
  • Stainless steel
  • Monel
  • Bronze Brass etc.

Benefits and Limitations of Insert Molding:

Some Advantages of Insert Molding

Some Advantages of Insert Molding:

  • You can manufacture products with high strength and quality. These products do not demand assembly.
  • This method allows you to manufacture various parts with definite designs and shapes.
  • The products manufactured with insert molding show high resistance to moisture content.
  • The parts produced by insert molding are budget-friendly.
  • It effectively allows the production of small-sized and thin parts exhibiting greater accuracy.
  • The insert molding components do not produce vibrations as they are vibration-resistant.
  • Fusing injected plastic material and insert requires no adhesive for proper fusion.
  • The insert molded parts remain unaffected by the dust particle because of possessing greater dust-resistant properties.

Limitations of Insert Molding:

The procedure has several restrictions. It is recommended to use a 3D printer during the production of prototypes. If you don’t use such printers, you can face various complications and even a production of a defaulted prototype.

In addition, you must carefully select the insert you will use during the process. The insert must have high pressure bearing capacity. You may have the desired product if it can tolerate the pressure.

The shape of the tooling must be according to the shape of your desired final product. If you don’t use the correct shape of tooling, then the final part will not meet demanded requirements.

Where Can We Implement Over-molding and Insert Molding?

Their most notable applications are discussed below.

Automobile Industry:

Automobile Industry

Over-molding is used to manufacture machinery that requires combining various materials. Such components may include vehicle structural reinforcement frames, door and dash panels, headrest parts, knobs, etc.

You can manufacture lightweight automotive parts having high quality and durability. These components are usually made up of plastic material. Some of these components may include knobs, door panels, etc.

Medical Device Industry:

Medical Device Industry

In the Medical industry, over-moulding is used to manufacture highly precise handles for surgical devices for strong gripping. It is also used to manufacture several other components for medical devices.

It is used for encasing those medical components that are weak interiorly, such as medical cables. The encasing is done with plastic to protect them and make cleaning easier.

Consumer Electronic Industry:

Consumer Electronic Industry

In the consumer electronic industry, over-molding is used for manufacturing many products with varying colors. These products include shampoo bottles, bowling pins, portable electric fans, mirrors, kitchen utensils, games for children, etc.

You can manufacture useful consumer electronics products, such as threaded fasteners, plugs, etc.

Aerospace and Defense Industry:

Aerospace and Defense Industry

In the aerospace industry, over-moulding is used to manufacture lightweight parts that need high resistance against high temperatures and radiation. Similarly, in the defense sector, it is used to manufacture strong and precise components.

The aerospace industry utilized over-molding to manufacture lightweight components. These components must also show high strength and durability, which is the main requirement of this sector.

It is also used in the defense industry to manufacture accurate and economic components such as munitions.

How Do You Compare Overmolding VS. Insert-molding to Find Which is Better for Your Business?

If you need clarification about choosing any of these processes for your project, this guideline will help you select a suitable one for manufacturing an appropriate product.

You must go for over-molding if you want a product made of various materials, thermoplastics, rubber, or vary in color. You should also choose it when you want to enhance the gripping property of your product.

The over-molding process is perfect if you need a product with enhanced shock absorption capacity and improved texture.

In contrast, over-molding does not work with prefabricated substrates or substrates containing wires and computerized or metallic components. Thus, insert molding is best for projects involving such types of substrates. In addition, if you want an end product in a solid form, then you must also prioritize insert molding.

Considerations for Over-molding and Insert Molding:

1- Material Selection:

Material Selection

The substrate can differ in material. It can be metal or plastic. The product formed by over-molding can combine two plastic materials and plastic-metal materials.

In comparison, the over-molding material is usually plastic. It means the products formed by inserting molding combine metal and plastic.

2- Design Modification:

Here are common design modifications of over-molding.

  • The wall thicknesses of the molded components must be uniform and even. The uneven thickness can result in voids and marks in the end product.
  • The design considerations of insert molding are as follows.
  • During insert molding, the corners of the material should be smooth. Otherwise, the sharp corners can be unsuccessful due to increased parts stress.
  • In-molded components, keeping the boss’s diameter greater than the insert’s diameter, i.e., 1.5 times greater, is recommended to enhance its stress-bearing capacity.
  • The bonding between metal and plastic material should be mechanical to prevent disassembling of the end product.

Tool and Equipment Limitations:

Over-molding and insert molding do not require any use of adhesive for combining multiple materials. The toolings in both processes should be accurate.

If the tooling is different from the shape of the mold you want, then you will end up with an undesired product. Therefore you must check the tooling before forming a mold of a specific size and shape.

Common Challenges in Over-molding and Insert Molding Production:

Here are the common challenges of both processes.

Material Compatibility:


In over-molding, plastic parts are combined with either plastic or metal parts. The combinations of the two plastic materials may need to be more compatible, which can be challenging.

In contrast, plastic materials fused with non-plastic materials show high compatibility in the insert molding. Thus, the material compatibility of insert molding is higher than over-molding.

Design Modifications:

Design modification is a critical factor to consider, and it covers many sub-areas, such as mold design, material selection, wall thickness, undercuts, and draft angles.

Consider all these factors while designing the modification process. Compatible material and mold design should be accommodated to subtract and insert to ensure evenly material distribution.

Quality Control:

Quality Control

You may need help with the poor quality of over-molding products. It can be due to the inappropriate fusing of the substrate and over-molding material, over-mold flashing, wrapped components, bad knit lines, and non-uniform coloration of materials.

Proper precautions must be taken to prevent these problems for producing high-quality products.

The quality can be affected if you choose the wrong insert type. You must select a definite type of insert having high pressure bearing ability.

The Profit Impact of Over-molding and Insert Molding Production:

The Profit Impact of Over-molding and Insert Molding Production

1- To Reduce Production Costs:

Overmolding and insert molding play a significant role in reducing the overall production cost. You can manufacture numerous components using these processes with less assemblage cost, making it profitable.

But overall, over-molding is more expensive than insert molding. The reason behind this is the accomplishment of over-molding in dual steps.

2-Improve Product Quality and Performance:

Different materials combine to form a specific product in over-molding and insert molding. The combination of different materials enhances the end product’s quality and performance. Thus, the end product exhibits improved quality and better performance.

3-Increase Consumer Appeal:

The products formed are either a combination of plastic metal or plastic. These products possess distinct features and functions that are enough to increase the customers’ appeal. Thus, more customers invest in these products, enhancing the overall profit.

How to Choose the Right Manufacturing Supplier?

Choosing the right manufacturing supplier is important to get products with unmatched quality. Always choose a reliable and confident manufacturer to quickly provide you with many high-quality parts.

The verified and authentic company must not charge you extra money for the products, but the prices will be according to the quality and performance of the product. The supplier must also have strong communication skills and must respond to you as early as possible.

Prototyping Using Over-molding and Insert Molding From Kemal:

Prototyping Using Over-molding and Insert Molding From Kemal

Kemal is a renowned manufacturer known for its excellent manufacturing capabilities worldwide. We have been working for 30 years and providing exceptional services in CNC machining, injection molding, mold making, and several other manufacturing services.

We are adopting over-molding and insert molding processes to manufacture high-quality prototyping exhibiting efficient performance.

Our prototypes are durable and exactly match the end products. You must invest in our prototypes to enjoy an unbeatable experience and to make your business successful.

Put your parts into production today

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