Insert Injection Molding

insert molding

Insert Injection Molding: Process, Applications & Design Considerations

Today, manufacturers are at the frontline of innovation, and they use plastic to make it compatible with metals or other materials to produce a wide range of products. Among the main technologies that are driving this progress is insert molding, a common technique in plastic injection molding. This way, manufacturers can combine engineering plastics with inserts made of different materials, which results in products that are wear-resistant, lightweight, and have high tensile strength. The article focuses on comprehensive details on insert molding and discusses its pros and cons. Furthermore, we will be looking into the applications of insert molding injection parts and giving you valuable tips and insights on how to achieve success in insert injection molding.

Insert Injection Molding: An Overview

Insert Injection molding or simple say insert molding, it is a specific type of plastic injection molding process where inserts, typically of metal, are either incorporated or combined with an injection-molded part. The process is about inserting the mold into the cavity and then injecting molten plastic under high pressure around it. Subsequently, when the insert is cooled, it melts with the plastic and forms a strong and unified part.

This method is used to manufacture plastic products that are strong, durable, and lightweight, by adding metal components. Metal insert molding is a multi-functional and efficient technique used widely across many industries due to its compatibility and effectiveness in producing high-quality parts.

insert injection molding

The Workflow of Insert Injection Molding

Insert molding injection is a conventional molding process for fabricating various end-use products, which involves melting and injecting molten plastic into a mold or die cavity under controlled conditions. The key feature is that injection mold threaded inserts are added to the mold, which makes it different from other traditional injection molding techniques. The below-mentioned steps are involved in the insert injection molding process.

Step 1: Insert Loading Into Mold

The design engineers meticulously design molds for insert molding by taking into account the exact placement of injection mold inserts within the mold cavity. Correct molding orientation and placement are of utmost importance during the molding phase. This technique guarantees that the inserts are firmly held in place, thus the orientation and position of the inserts are maintained as desired in the molded part.

There are two primary methods of inserting components into a mold:

  1. Automated Insertion:

Automated insertion uses robots and automated systems for the insertion of components into a mold. This method has the advantages of such as consistent insert placement, increased efficiency, and high precision. Automated machines can deal with high-temperature environments, which ensures a quick production turnaround with the ability to produce more parts per hour. Nevertheless, the initial investment for automated systems is more, which causes the production cost to be higher.

  1. Manual Insertion:

Manual insertion is the process of putting components into a mold with the hands. This is the method that is applicable in low-volume production situations. It is more suitable for jobs that require detailed part inspection and for operations that are not costly like packaging and assembly. Nevertheless, manual insertion does not have the precision and repeatability of automated systems. The operators can also have dexterity issues due to the high temperatures involved, which may require the use of gloves.

Step 2: Push the Molten Plastic into the Mold

The second step in the insert molding injection process is an injection of engineered-grade plastic resin into a die cavity through the injection unit. The injection takes place under high pressure, so the plastic is pushed to fill all the parts of the mold. This pressure leads to the ventilation of air through the molds, which in turn certifies that the plastic sticks to the inserts completely. By maintaining the optimal injection temperature, and pressure and temperature within the acceptable range is of paramount importance for uniform filling and defect-free end-use molded parts.

Step 3: Take off the Mold and Get the Molded Part

The molten plastic is then poured into an intended mold cavity and allowed to solidify for ejecting the final part. Finally, the mold is opened and the part is meticulously removed. Holding pressure during cooling will help to prevent the shrinking effects and to make sure that there is no backflow into the injection barrel. The cooling time and temperature are carefully overseen to make sure the solidification of the molded part is uniform and the part doesn’t warp or distort. The mold then cools down and opens up, which facilitates the effortless extraction of the molded part from the mold cavity. The cycles then repeat for continuous production.

Step 4: Take the Molded Part off the Sprue.

The bulk of molded parts are linked to sprues, which are the channels where the liquid plastic flows in and out of the mold cavity. The molded part must be parted from the sprue before it can be implemented. This separation is done manually mostly by simple tools such as scissors or knives. The molding step should be closely monitored to make sure that the part does not get damaged or lost.

Step 5: Post-Processing Treatments

The molding and ejection of the part from the sprue may be followed by other post-processing operations to complete the insert-molded part before final use.

Some common post-processing treatments include:

Deburring: removal of the surplus material or burrs that can impart the appearance or the performance of the molded part. Deburring is generally done by hand by using tools to eliminate burrs.

Heat Treatment: processes such as annealing or stress relieving, related to heat treatment might be used in the molded part to remove the internal stresses. Furthermore, it can provide the parts with enhanced strength and dimensional accuracy.

Surface Finish: The final stage could be carried out in various forms, including by printing, painting, or electroplating. The finishing processes are not only able to make parts beautiful, and durable, and even give them some special features such as corrosion resistance.

Humidity control: process of managing the moisture in the environment that will affect the shrinkage of objects, prevention of oxidation, and the rate of water absorption. This process is usually performed by objects being placed into a humid environment that is created by different methods including immersing the objects in hot water baths or exposing them to steam chambers.

Pre-Insert Molding Considerations 

There are many things to consider before the insert molding such that the production process proceeds smoothly and without any hitch. : As a reminder, this is what you need to focus on:

  1. Types of Inserts:

Inserts that are used in the insert molding process are one of the most important factors that can lead to the success of the process. Determine the inserts that can endure the temperature and pressure swings which are usually an inherent part of molding.

  1. Insert Location:

The positioning of inserts in the molds is one of the most important things to be considered when it comes to the durability and maintenance of the molds in the future. Imagine the forces that act on the insert and ensure that there is enough plastic material under and around it to guarantee that it remains in position.

  1. Gap Width for Metal Inserts:

It is important to maintain the gap between the metal inserts and the liquid material at a safe distance to avoid the negative impact of this on the final products. Closing the gap between the mold and the part ensures that the part bonds together to form a reliable finished molded component.

  1. Resin Selection and Molding Conditions:

The selection of the right resin type and molding conditions is crucial, since through this we can mold complex parts (electronic components, glass). The resin must be strong enough to seal the inserts well and fix them properly.

  1. Mold Design:

The mold not only shapes the material but also keeps the inserts immobile during the molding process. Use molds having inserts that are manufactured to keep them firm throughout the production stage.

  1. Cost Considerations:

The total price should cover the insert costs, the operator’s expenses (for manual insertion), and the price rise that may occur because of the inclusion of inserts. Add a cost-benefit analysis to your decision-making process and make it fact-based.

  1. Production Volume:

Pick between a manual or automatic loading option based on the production volume. Analyze the production requirements and evaluate the merits and demerits of all loading methods to achieve the highest possible levels of efficiency and cost-effectiveness.

Brass insert moulding

injection molding threaded inserts

Considerations During Insert Molding

Precision in the process of insert injection molding is the key point that ensures the highest quality performance. These are the essential points you should have in mind.

  1. Mold Design:

The design of the mold is the key factor in the process that is created to protect the insert from damage which is usually an outcome of high temperatures and pressure. The critical factor that will determine the mold design will be the degree of security and stability that the mold needs for it to be successfully done.

  1. Secure Insert Placement:

Insert placement and stability are the critical points, which are significant in successful operation of inserts in the molding process. The smallest shake or move will give us a flawed final product. Find out different ways to achieve the perfect hold of inserts during molding.

  1. Undercut Features:

The injection mold inserts not only bring aesthetic value to the parts but also improve the structural integrity, and strength of the parts. It binds which enables the components to remain cohesive.

  1. Partner Selection:

It would be wise to choose a reliable and experienced partner for insert molding. Collaboration with corporations provides you with a chance to benefit from the most recent inventions and skills in assembling components to manufacture integrated parts of premium quality.

Benefits & Limitations of Insert Injection Molding

Injection molding inserts offer numerous advantages that make them a popular choice in manufacturing processes:

Cost-Efficiency: The injection molding inserts are one of the techniques that are used in the reduction of the assembly and labor costs as it eliminates the post-molding assembly hence the overall cost savings.

Weight Reduction: Inserts are a way to reduce the mass and volume of molded products so they are more portable and easier to handle.

Design Flexibility: Inserts are a design device that designers use to make their products stand out from the crowd by making them more complex and unique.

Enhanced Parts’ Strength: The metal inserts that are integrated with the molding process give the molded parts mechanical properties that are stronger than the regular ones thus increasing their durability and performance.

Despite these advantages, there are also certain drawbacks associated with injection molding inserts.

Complexity and Cost: The design of insert molds is much more intricate and costly compared to the regular molding processes which require one to consider additional factors and allocate resources.

Material Compatibility: Some of the materials used for the inserts may not be suitable for molding due to the dissimilarity in the coefficient of thermal expansion, and this may cause problems during production.

Positioning Accuracy: Errors may be encountered in the molded parts if the injection molding inserts are not properly aligned in the mold, which may result to defects in the end product.

Increased Cycle Time: The inclusion of inserts may lead to an increase in cycle time as they have to be carefully positioned within the mold before the molding process starts and this may affect the efficiency of production.

Insert Molding and Overmolding are compared

The two different injection molding processes that are used to create a molded part with special features are insert molding and overmolding. Despite the same goals they all strive for, they are very different in the ways they reach their goal and the end result.



The insert molding process is a special way where the plastic material is shaped around the pre-formed insert which is put in the mold. This is achieved by the plastic material adhering tightly to the insert so that it becomes a single integral part. Insert molding is a one-shot injection molding technique that has the advantage of speed and cost-effectiveness, as well as the economical use of materials.

Primarily, overmolding is a two-shot molding process, which means molding of a rubber-like plastic over a plastic substrate. The complexity and cost of this dual injection molding process are higher as compared to the single injection molding process, which is because of the extra layer of material and the over mold that consists of additional mold cost.

The main objective of the insert molding process is to strengthen the molded parts by adding inserts in the initial design phase. The former, which is used to add comfort, beauty, and protective layers to a product, thus giving it better functionality and appearance, is different from the latter.

As a result, the main aim of insert molding is to enhance the strength and the material efficiency, whilst overmolding is more about functional versatility and aesthetics, so each technique is good for certain applications and design requirements.

Simple sumrize, insert injection molding only needs one mold cost (overmold), overmolding process that needs two molds investments , substrate mold (the first mold) and over mold (the second mold).

Insert Molding Applications in Many Different Industries

Molding nowadays is a widely demanded manufacturing process due to its diversity and efficiency. Let’s talk about the main industries that take advantage of insert molding and the particular applications in each of them.

Aerospace Industry:

Insert injection molding is the most popular technique used in the aerospace industry for the production of critical parts, such as aircraft seats, stowage bin latches, lavatories, handles, and user interface switches. These aspects should be a mixture of strong, durable, and lightweight designs. Injection molding can be the answer to all of these attributes. With the insert molding the space industry gets lightweight aircraft, high-strength components, shorter manufacturing and assembly times, and design improvement.

Automotive Sector:

In the auto industry, insert injection molding is the process that is used to replace metal parts with plastic parts which are more durable.

This transformation results in the manufacture of lightweight auto parts, which in turn, improves fuel economy and reduces assembly costs. Insert molding is one of the most common manufacturing processes in the automotive industry that are used to produce interior panels, knobs, handles, electronic connectors, and structural parts. Furthermore, the insert molding technique provides both flexibility and reliability, which allows automotive manufacturers to innovate and come up with new designs and functionalities.

Medical Device Manufacturing:

Molding inserts, which are widely used in the medical device manufacturing industry, require precision, biocompatibility, and reliability to be at the highest level. Medical devices from simple tools to sophisticated implants and surgical instruments are made using insert molding techniques. For example, tubes, medical equipment components, dental instruments, prosthetics, surgical blades, and enclosures for medical devices are some of the applications. The insert molding process guarantees the smooth transition of different materials and meets the high quality and safety standards of the medical industry.

Consumer Electronics Industry:

The insert molding technique has been a game changer in the consumer electronics industry as it allows for the simplification of assembly processes by doing away with fasteners and soldering. The industry of molding inserts is very broad and it is often used for encapsulating threaded inserts, wire plugs, and producing digital control panels, assemblies, and knobs for appliances. Besides, insert molding has a wide range of applications in military equipment, threaded fasteners, and various electronic components used in consumer electronics.

Defense Sector:

In the defense industry, insert molding is a key enabling technology for the manufacture of military-grade equipment that is cost-effective, efficient, and lightweight. This technology is used to make handheld communication devices, weaponry components, battery packs, munitions, and housing for optical instruments like binoculars and monoculars. Insert molding has the advantage of creating parts with robust and reliable structures, which have intricate designs and functionalities, and meet the high standards required for defense applications.

These industries take advantage of the fact that insert molding can unite different materials, increase product durability, reduce manufacturing costs, and improve overall product performance, which makes it the preferred manufacturing method for a wide range of applications.


Q1.Why do we need inserts in injection molding?

Inserts are the key elements of the molded plastic products that increase the strength and durability of the products and moreover, they are made of metal.

Q2.Is insert injection molding applicable for the manufacture of large parts?

Insert molding is the best choice for the production of small and medium-sized parts. Challenges like higher tooling costs and complexity in insert placement are the issues that are faced while dealing with the bigger parts.

Q3.What are the generally used inserts in insert injection molding?

The inserts are usually used by manufacturers to reinforce the strength and performance of molded parts. These inserts are made of metal parts such as studs and screws, electronic elements such as connectors, terminals, switches, and buttons, and plastic parts.

Summing Up:

Insert molding is a manufacturing process that combines plastic with non-plastic materials, which is popular with industries such as aerospace, defense, automotive, and medical equipment for several reasons. These include cost-saving, improved part reliability, and better design flexibility.

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