May 27, 2024

Insert Molding Explained: Materials, Process, and Applications

insert molding

Insert molding is an advanced manufacturing process that has transformed complex and durable part production in different sectors. The integration of metal and plastic components into a single part in insert molding eliminates the possibility of breaking off or separating during use while also providing superior strength, precision, and design flexibility. It is important to note that this is absolutely necessary for industries like automotive as well as medical devices where every component’s dependability and performance is crucial. In this article, we will delve into the materials, processes and wide range of applications of insert molding providing a comprehensive guide for anyone who wants to understand this innovative technology.

What is Insert Molding?

It involves introducing pre-formed inserts, usually made of metal, into a mold cavity; then liquid plastic is injected around these inserts which enclose them forming one piece. This method differs from conventional injection molding where the entire part consists of only plastic. Due to the combination of dissimilar materials by insert molding desirable properties are produced in products.

The first step in the insert injection molding process entails placing the insert within the mold with accuracy. After that, molten plastic typically thermoplastic resin) is injected under high pressure into the mold cavity before it later cools and solidifies thus holding tightly against the insert. This method finds its best application when there is need for an object having both metal strength qualities with versatility associated with plastics such as automotive parts or medical devices.

Common Materials Used in Insert Molding


Among wide range of materials in insert injection molding are thermoplastics, which are highly versatile and easy to process. These can be melted, reshaped and solidified several times over making them suitable for different applications. An extensive array of common thermoplastic materials used in insert molding includes polycarbonate, polyethylene, and polyamide.

The impact resistance and clarity associated with polycarbonates makes them ideal for protective gear and optical lenses.

On the other hand, polyethylene is highly valued for its flexibility as well as chemical resistance making it suitable for packaging and tubing.

Polyamide is a strong nylon that has high thermal stability hence common in automotive or industrial components.

They opt for these materials because they produce durable flexible sections able to withstand extreme temperatures as well as environmental conditions without wearing thus achieving long life span coupled with reliability of their uses.


Insert molding is also applicable to demanding environments through the utilization of thermoset materials such as epoxy resins and phenolic resins; this provides unique benefits to this molding method. Thermosets do not melt when heated unlike thermoplastics do. When they cure, they become rigid structures that resist heat permanently; therefore good for applications that need high temperature tolerance and structural integrity like electrical insulators or automobile parts production.

Epoxy resins are preferred because of their excellent adhesive strength combined with resistance against chemicals used in coatings and composites production.

Phenolic resins have got good mechanical properties under load plus flame retardance which make it ideal material for circuit boards or brake pads.


Elastomers, including silicone and rubber, are essential for insert molding when flexibility and resilience are required. These materials can stretch and return to their original shape, which is crucial for applications that need to absorb shocks, resist moisture, and maintain structural integrity under stress.

Silicone elastomers are prized for their excellent thermal stability and biocompatibility, making them ideal for medical devices, such as prosthetics and surgical instruments.

Rubber elastomers, such as natural rubber and synthetic variations like EPDM, are used in automotive seals, gaskets, and vibration dampening components.

The ability of elastomers to withstand harsh conditions while providing flexibility and resilience makes them a vital choice for many engineering applications.

insert molding

Advantages of Insert Molding

Strength and Durability

Insert molding makes the final product much stronger and more durable. It does this by combining the strong features of metal insert molding with the flexible nature of plastic. This mix is very important for parts that need to handle a lot of stress and wear.

For example, in cars, parts like engine mounts and transmission components need to be very tough. Insert molding helps these parts handle the high pressures they face. Research shows that insert molding can make parts 30% stronger than regular plastic molding.

This extra strength means products last longer and work better in tough conditions. As a result, there’s less need for frequent replacements and repairs.

Design Flexibility

Insert molding offers unmatched design flexibility. Engineers can create complex shapes and combine multiple functions into one part. This is very useful for making detailed medical devices and advanced consumer electronics.

For example, insert molding allows electrical connectors to be built into plastic casings. This simplifies the manufacturing process and makes the final product more reliable. In the medical field, parts like catheter tips and surgical instrument handles are often made with insert molding. This allows for precise customization to fit patients’ needs.

Moreover, this flexibility improves product performance. It also opens up new possibilities for innovation and design.

Cost Efficiency

One of the best things about insert molding is that it saves money. This method combines many parts into one single piece, which cuts down on the time and effort needed to put things together. This helps lower the cost of making products and gets them to market faster. This is very helpful for making large numbers of products. A report by Grand View Research says that the global market for insert molding will grow by 12.1% each year from 2020 to 2027 because it saves money. Companies can save a lot on materials and labor since there is less work to do after molding. This smoother production process not only makes more money but also makes manufacturing more efficient, helping businesses stay competitive.

Limitations and Challenges of Insert Molding

Design Complexity

Even though insert molding gives it so much design freedom it is also accompanied by mold design complexity. The precise engineering and advanced mold-making techniques are required to ensure proper placement and alignment of inserts making the process challenging.

Material Compatibility Issues

The most important thing in the process of insert molding is compatibility between the molten plastic and material of the insert. When materials do not match, they result in poor adhesion, internal strain, and ultimately, component failures. Material compatibility is a major factor to consider during the insert molding process. So as to avert these pitfalls however considerate selection and testing of supplies must be done.

Detailed Process of Insert Molding

Preparation of Inserts

The first and most important step in insert molding is getting the inserts ready. This means cleaning and treating them very carefully so they have no dirt, oil, or other stuff that can mess up the molding. Usually, inserts are cleaned with special machines like ultrasonic cleaners or chemical baths to get rid of anything on the surface. Sometimes, they are also coated with special materials to help them stick better to the plastic. It is really important to prepare the inserts well because it makes sure they bond strongly with the plastic. If the inserts are not cleaned properly, they might not stick well, which can make the final product weak and more likely to break. So, paying close attention to this step is key to making a strong and durable product.

Injection of Molten Plastic

After the inserts are cleaned and put in the mold, the next step is to inject the molten material, typically plastic, into the mold. The plastic starts as small pellets that are heated in a machine until they melt and can flow. Controlling the temperature and pressure is very important. The molten plastic is then pushed into the mold at high pressure. This helps the plastic move around the inserts and fill the mold completely. It’s important to watch this process closely to make sure the plastic fills all parts of the mold without any empty spaces or air bubbles, which can make the part weak. Modern machines use digital screens to keep track of and change settings as needed, making sure everything stays just right. This careful control helps make sure the final part has the right shape and strength.

Read More: Plastic Melting Point Guide: Understanding Temperature Ranges

Cooling and Ejection of the Molded Part

After the plastic is injected into the mold, it needs to cool down and harden to make the final part. Cooling is very important because it affects the shape and strength of the part. The mold has cooling systems, like water channels, to help remove heat. The cooling speed must be just right to avoid problems like warping or shrinking, and maintaining a holding pressure helps reduce these effects. If the part cools too fast, it can get internal stress; if it cools too slow, it can change shape. Once the part is cool and solid, it is pushed out of the mold with ejector pins or other tools. This step must be done gently to avoid breaking the part. After ejection, the part is checked to make sure it meets all size and quality standards. Good cooling and ejection make sure the part is high-quality and ready to use.

Insert Molding vs. Overmolding

Key Differences and Similarities

Insert molding and overmolding are both advanced manufacturing techniques used to enhance part functionality and durability, but they differ significantly in their processes and applications. Let’s delve into their key differences and similarities:


  • Both insert molding and overmolding involve the injection of plastic material into a mold.
  • Each process enhances the functionality of the final product by combining different materials to leverage their respective strengths.
  • Both techniques require precise control of molding parameters to ensure quality and performance.


  • Process: Insert molding places a preformed insert into the mold before injecting molten plastic, integrating the insert into the plastic part. Overmolding process involves molding additional material over an already existing part, creating a layered structure.
  • Applications: Insert molding is typically used for parts that require a combination of metal and plastic for enhanced mechanical strength and conductivity, such as automotive and electronic components. Overmolding is more suited for adding features like soft-touch surfaces or protective layers, commonly seen in consumer electronics and medical devices.
  • Complexity: Insert molding demands precise insert placement and adhesion, whereas overmolding involves additional steps to mold material over a preformed part.

Here’s a detailed comparison table to highlight these aspects:

FeatureInsert MoldingOvermolding
Primary PurposeIntegrate inserts into plastic partsAdd layers/features to existing parts
Process StepsInsert placed in mold, then plastic injectedInitial part molded, then overmolded with additional material
Materials UsedCombination of metal and plasticTypically plastic over plastic, or plastic over metal
Typical ApplicationsAutomotive components, electronic housingsGrips for tools, soft-touch handles, seals
BenefitsEnhanced strength, durability, and conductivityImproved ergonomics, added insulation, enhanced appearance
ComplexityHigh, due to precise insert placementHigh, due to multi-stage molding

When to Use Each Process

Choosing between insert molding and overmolding depends on the specific application and desired properties of the final product. Insert molding is ideal for parts requiring the integration of metal and plastic, providing enhanced strength and durability. For example, in the automotive industry, insert molding is used to create strong parts that must withstand mechanical stress and wear, such as engine mounts and transmission components. In electronics, insert molding can integrate metal connectors within plastic housings, ensuring structural integrity and conductivity.

Overmolding, on the other hand, is better suited for applications where adding a soft-touch surface or protective layers is beneficial. This process is frequently used in consumer electronics to provide better grip and aesthetic appeal, such as in smartphone cases and remote controls. In medical devices, overmolding improves the ergonomics and safety of tools by adding a soft, tactile surface. The decision between these processes hinges on the functional requirements, desired aesthetics, and specific use case of the final product.

Applications of Insert Molding

insert molding

Automotive Industry

Automotive industries widely employ insert molding to manufacture strong and durable parts that can perform optimally and be reliable as required in automobiles. This process is important in making parts such as dashboard assemblies, sensor housings, and structural parts. For example, it is common to use metal inserts in the plastic parts to enhance the strength of the product. In a report by MarketsandMarkets, the automotive injection molding market was estimated to be worth $42.5 billion in 2020 and is expected to grow up to $ 56.3 billion by 2025, with a Compound Annual Growth Rate (CAGR) of 5.7%. Insert molding plays a significant role in satisfying the automotive industry’s high standards by creating parts that can endure high temperatures, mechanical pressure, and chemical solutions, which in turn enhances vehicle safety and efficiency.

Consumer Electronics

The process of insert molding is a common technique used in the consumer electronic industry to produce components with metal parts inserted into them, making electronic gadgets more durable and serviceable. This manufacturing method is typically employed when making complex devices such as connectors, cases and other components that need both mechanical strength and electrical function. For instance, by putting in metallic connectors inside plastic enclosures it makes sure there is proper flow of electricity while preventing them from getting destroyed. As per Grand View Research report the global size of consumer electronics market stood at $1.1 trillion in 2020 and will grow at a CAGR of 8.0% between 2021 and 2028. In this area, insert molding enables the production of stronger and more dependable electronic devices that cater for present day’s consumers’ demands.

Medical Devices

Medical devices are one of the industries that can greatly benefit from insert molding because of the need for accuracy, durability, and compatibility with the human body. Some of the uses of insert molding in the medical industry are in the manufacture of surgical and dental instruments, and parts of medical devices. These devices have to adhere to very high regulatory requirements and have to function properly in high risk applications. For instance, insert molding is applied in the production of handles for surgical instruments where metal strength is blended with the ergonomic plastic to enhance the comfort and productivity of the surgeons. In a report by BCC Research, the global market for medical plastics, which encompasses insert molding materials, was estimated at $25.1 billion in 2020 and is projected to reach $38.3 billion by 2025, with the compound annual growth rate of 8%. The accuracy and consistency of insert molding make it a crucial technology in the manufacturing of medical devices that are safe for the patient and efficient in the treatment process.

Design Considerations for Insert Molding

Insert Material Properties

Choosing the right material for the insert is very important for making insert molding work well. You need to think about things like how stable the material is with heat, how strong it is, and if it works well with the plastic. For example, brass is often used for electrical connectors because it is easy to shape and doesn’t rust. Glass-filled nylon is strong and light, so it’s great for airplane parts. Making sure the insert and plastic work well together helps reduce heat stress and makes the part last longer and work better.

Insert Placement and Orientation

Where and how you place the inserts in the mold is very important. Correct placement spreads out stress evenly and makes the molded part stronger. For example, threaded inserts in plastic housings need to be lined up right to make sure the threads work. In parts like plastic gears with metal centers, the insert should be in the middle to spread out the load evenly. Engineers use pins or special tools to keep inserts in place during molding to make sure they are precise. Proper insert placement and orientation, also known as the location of the insert, stops defects and makes the final product more reliable and better performing.


Insert molding is a very effective and flexible process of manufacturing that is widely used in the production of high quality and intricate parts. Through this article, manufacturers will be able to gain insight on the materials, processes, and design factors that can be used to effectively employ insert molding in the production of quality components for various uses. From the automotive to the consumer electronics or medical fields, insert molding is a proven method for combining metal and plastic into a single, unified component.

Contact ACO Mold Today

If you’re interested in learning more about insert molding or exploring how this process can benefit your production needs, contact ACO Mold today. Our team of experts is ready to assist you with all your insert molding requirements, providing customized solutions to meet your specific needs.


What are the labor cost implications of insert molding?

Insert molding can significantly reduce labor costs by integrating multiple components into a single part, thus minimizing assembly time. This process is especially beneficial in large production runs where labor savings are more pronounced.

How does production volume affect the insert molding process?

Higher production volumes can justify the initial costs of designing and manufacturing complex molds, making insert molding more cost-effective. Large production runs benefit from economies of scale, reducing the overall cost per completed part.

What considerations are there for the surface finish of molded parts?

Achieving a high-quality surface finish in insert molding involves precise control of the mold design and processing conditions. Surface finish is crucial for aesthetic and functional purposes, particularly in consumer electronics and medical devices.

Why is the design of the mold critical in insert molding?

The design of the mold directly impacts the quality and functionality of the molded part. Factors such as the location of inserts, flow of molten plastic, and cooling rates must be meticulously planned to produce defect-free parts.

How does humidity control impact the insert molding process?

Controlling humidity is essential to prevent moisture absorption in both the plastic and the metal components, which can lead to defects. Proper humidity control ensures the stability and quality of the finished parts.

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