The Complete Guide to Overmolding

Table of Contents

I. Introduction

Several methods in the manufacturing industry to get devices and products as designed. However, very few are as innovative as overmolding methods. As you might probably have guessed from the name, this manufacturing technique requires molding a pliable material over a solid material shaped in the form of the final product. But that is just scratching the surface of information that overmolding is all about. This article will go into great detail on overmolding, covering the numerous overmolding kinds, design considerations, advantages, and materials used in overmolding production. More importantly, we will highlight what you need to consider when deciding the suitability of overmolding for your project. So, strap on tight and come along if you’re ready to know more about this brilliant manufacturing method.

II. Understanding Overmolding

In a world where intricate design details are becoming very important for functionality and improved user experience, overmolding has become the go-to manufacturing method to achieve these details. To understand overmolding, you’ll need to think of it as forming a shape with a fluid material over a solid mold to get a final product that is both precise in detail and high in quality and performance. This method has many unique features that give it many advantages over other manufacturing methods. Especially for industries like automotive and consumer goods industries where ergonomics is vital, employing overmolding for such production ensures that manufacturers get their ergonomics accurately.

Overmolding is a quick and easy method to produce complex shapes with hard-to-reach areas that would have been very difficult to achieve using other methods. This advantage is quite crucial for manufacturers that produce specialized products for the automotive, aerospace, and medical industries, where tools and devices come in different shapes and sizes. Other important advantages unique to overmolding include the ease of molding different materials over each other without worrying about compatibility issues that often bedevil other manufacturing procedures like coating and welding.

Overmolding, with all its merits, has been attractive to many manufacturers in many industries, including electronic manufacturing, where it is used for manufacturing ergonomic button designs. It is also extensively used in the automotive industries for manufacturing ergonomic seats and accessories, including door handles and headrests. But that’s not all. In the medical industry, it is used to manufacture special tools designed to reach hidden areas during medical procedures like surgeries. So many other industries, including oil and gas, energy, and defense, employ overmolding techniques to achieve complex designs that many manufacturing industries are not equipped to produce. Overall, overmolding has been quite beneficial and continues to enhance the efficiency of numerous manufacturing processes where precision and ergonomics are key.  

However, it has certain limitations which the right technical know-how and equipment can easily overcome. But more on that later. But for now, understand that overmolding is a viable alternative method for manufacturing intricate and complex shapes with high accuracy.


III. Types of Overmolding

An understanding of the different types of overmolding is critical not just for mold design but also for engineers, manufacturers, and machine operators involved in the manufacturing process. Understanding the various forms of overmolding frequently assists engineers and designers in specifying the best overmolding type for a certain project. We have highlighted the different overmolding types below for better understanding.

  1. Insert overmolding: By far the most popular type of overmolding, insert overmolding requires three parts to form the final product. The first is the mold made from any suitable material, and the second is a plastic or metal substrate placed inside the mold before the molding procedure. Finally, a third part is the mold material which can be plastic, fiber, or any other suitable material specified by the designer, which is then molded over the substrate. The automobile sector is a popular use for these overmolding kinds, with items such as door handles and gear knobs made utilizing the insert overmolding process.
  2. Two-shot (multi-shot) overmolding: This overmolding process is a monolithic approach in which two sections are joined to produce a block.  Here, the underlying material acts as both the substrate and the mold, with the second material serving as the molding material and molded over the substrate. The result is a single product where the substrate often acts as reinforcement to strengthen the overmolding material. An application of this overmolding method is usually found in the electronic industry, where keypads and buttons are designed to function ergonomically. It also enhances the aesthetics of these devices with the overmolding material having a pleasing but different color to the substrate.
  3. Film insert molding: In this method, there is a similarity with the insert method considering that this overmolding method also requires the insertion of a substrate. However, in this method, the substrate is a thin film, not plastic or metal, as is the case with the insert overmolding method. The film in this case tends to have a different function to enhance the overall effectiveness of the final product. This technology is used in the manufacture of medical equipment such as syringes and catheters, where the film forms the tube through which liquids travel.

The uniqueness of these different overmolding methods makes them suitable for specific production purposes. However, they may vary in merits which can influence manufacturers’ and designers’ decisions to apply them in projects. Nevertheless, the most versatile yet cost-effective of the three remains the insert overmolding method. Also, film insert molding is mainly used for thin tubing and bendable substrate. At the same time, complicated geometries are better achieved with the two-shot overmolding method, especially where color variation is required.


IV. Materials Used in Overmolding

Material evaluation is crucial in overmolding procedures since the end product is frequently made up of two materials. This realization often creates a compatibility issue around the materials intended for use. Also, the intended utility of the final product based on its designed properties is a huge determinant of the materials used as substrate and overmolding. The adhesion properties of the substrate with the overmolding materials are also essential to ensure the reliability and durability of the final product.

Nevertheless, materials used as substrates are usually made from sturdy materials that can act as a reinforcement for the overmolding materials. Some popular materials that fit these descriptions include metals, some of the most robust materials used in manufacturing, providing other valuable properties, including wear resistance and machinability. Examples of common metals used as substrates include steel, aluminum, and brass. Their significant resistance to stress and extreme temperature are favorable factors that attract manufacturers to use metals as substrates. Other materials employed as substrate include plastics like polypropylene, ABS, and polycarbonate, which are favored for their strength and affordability. Additionally, glass materials are also employed in some unique instances as substrates.

On the flip side, overmolding materials are often required to be pliable during the overmolding process but sturdy once the production process is complete. This reason explains why elastomeric materials are usually preferred for overmolding. Some common overmolding materials are thermoplastic urethane (TPU), known for durability, sturdiness, and high machinability using methods like CNC machining. Also, thermoplastic elastomers (TPE) have similar properties to TPU and are used extensively as overmolding materials. Silicone is another popular overmolding application in the medical sector, where biocompatible devices are delivered using overmolding production. The biocompatibility of silicon and its high resistance to extreme temperatures are a few reasons it is utilized as an overmolding material, especially in the medical industry. All the overmolding materials highlighted are also popular because of their compatibility with a wide variety of substrate materials, making them very versatile.

Aside from the compatibility and adhesion factors, you should also consider when selecting a suitable substrate and overmolding material, including the ease of surface preparation and chemical and mechanical properties of the materials. Also, the melting point of these materials is crucial, especially if they will be subjected to extreme heat during their operational lifespan, as it can affect their durability and functionality if ignored. Ultimately, the final product’s intended use and desired benefit, including enhanced performance and aesthetics, will significantly determine the choice of substrate and overmolding materials.

V. Design Guidelines for Overmolding

To achieve a quality product that meets the design’s specifications regarding purpose, aesthetics, and durability, certain considerations must be put in place. The shape of the planned product, material specifications, and bonding between the substrate and the overmolding materials are the major criteria for meeting the overmolding design. The details of these parameters are highlighted below.

  1. Part geometry and design considerations

The geometry of the designed product plays a vital role in achieving the desired outcome without losing the intended purpose and desired finish specified by the product designer. The complexity of the geometry determines the difficulty the manufacturer will encounter during the production process. Also, geometry is a significant determiner of the expertise, equipment, and technology required to achieve the desired result. Hence, product designers who want to use overmolding must consider the geometry of the material in selecting the type of overmolding, the material, and the material surface requirement to achieve the needed bonding between the substrate and the overmolding material. For instance, a rough-surfaced substrate makes for better bonding with the overmolding material. Furthermore, the product designer must anticipate the flow of overmolding material over with the substrate dimensioned to take care of heat-induced shrinkage as the overmolding material solidifies.

  1. Selecting appropriate materials for specific applications

An appropriate substrate and overmolding material must be chosen for a successful overmolding technique and a long-lasting end product. The most important material selection criteria remain the chemical, thermal, physical, and mechanical compatibility of the overmolding materials to achieve the desired product functionality.

  • Chemical compatibility – It means that the combination of the substrate and overmolding material should not cause any chemical reaction that can negatively impact the final product’s functionality, strength, and surface finish.
  • Thermal compatibility – The substrate material should accommodate the heat generated as the overmolding material is molded. Hence, a suitable substrate with a significantly higher melting point than the overmolding material is often better.
  • Physical compatibility – To achieve good bonding and a final quality result, physical features such as the substrate’s size, thickness, and weight, as well as the overmolding material, must match.
  • Mechanical compatibility – The stress created in the final product’s usage must be considered when selecting the materials for overmolding, as materials with less strength and rigidity can lead to the failure of the final product.
  1. Achieving optimal bonding and performance

The bonding between the substrate and the overmolding material directly impacts the final product’s performance. As a result, while performing the overmolding technique, establishing good bonding between these materials is crucial. Here are some tips for achieving good adhesion between the substrate and the overmolding material.  

  • Contaminants such as dirt, debris, and oil materials often inhibit adequate adhesion, and you should remove them during the surface preparation of the substrate.
  • Adding special additives and chemicals to the overmolding material can increase the adhesion rate.
  • Carefully select materials that are compatible and have high adhesion to each other.
  • Ensure overmolding process parameters including temperature and injection rate are accurate during the overmolding procedure.

VI. Overmolding Process and Equipment

In carrying out overmolding [procedures successfully, specific equipment and tools are necessary to support experienced hands that are saddled with the success of the operation. This equipment is sophisticated, which not only requires that the operator understands its workings but also comprehends perfectly the overmolding process. The procedure normally begins with mold manufacturing, depending on the sort of overmolding requested for your project.

The mold here is called the substrate, often made of a suitably stiff material. It is then inserted into another mold void with a pliable overmold material. The combination of the substrate and the overmolding materials becomes monolithic after it has solidified to give the final product. However, when it comes to the equipment used for achieving overmolding, you don’t need to look too far as the equipment is set up, and the process is a lot like the standard injection molding machine. They only come with unique features that are absent in a conventional injection molding machine. Among these characteristics are multiple injection modules, as well as controls that are especially tuned to the demands of overmolding operations.

They also ensure the possibility double-shot injection processes associated with overmolding procedures. Other equally important parts of the machine are the substrate’s core and the mold, which allows for adequate bonding between the substrate and the overmolding material.

Additionally, secondary tools and machine parts accompany the main equipment, such as the conveyors and automation systems that include robots and material sorting systems. These complimentary tools help to increase the efficiency of the main overmolding machine. But that’s not all. Specific controls are essential to regulate and optimize parameters like temperature, injection rate, pressure, and speed to ensure the achievement of the product to the desired quality.

In the end, understanding the equipment setup and the overmolding processes helps you accurately control the essential parameters, which helps to achieve the designed product without any defects.


VII. Quality Control and Inspection

Quality control is an essential part of any manufacturing process, including overmolding. Its benefits include cutting costs, considering that rework often comes at a high production cost and wastes a lot of time. Therefore, carrying out specific inspection procedures and tests pre-production, during production, and post-production of the overmolding is necessary to ascertain critical design parameters and to ensure a final quality product.

The binding specification of the materials is often a critical inspection parameter for quality inspectors. The reason is that the adhesion properties of the material used in the production are a significant indicator of the durability and quality of the product. Hence, quality personnel often check the integrity of the bonding between the substrate and the overmolding material to score its quality.

Frankly, careful consideration of the product design and dimension gives quality professionals an indication of the material bonding quality. If this is missing in quality inspection considerations, there is a tendency to end up with a defective product. Another important consideration in quality assessment is the material selection of the substrate and the overmolding material. Choosing incompatible materials can have an impact on bonding and, as a result, material quality.  

Inspection should not be left till the end of the overmolding process to start identifying defective products. Instead, continuous assessment during the production process is better and often more beneficial. Also, employing technology, including automated systems and robotic inspection, can enhance the accuracy of the examination, eliminating inspection errors attributed to inevitable and costly human mistakes. Furthermore, implementing an up-to-date quality system can standardize your quality assessment process, helping you achieve quality that complies with the highest industry standards.

VIII. Cost Factors and ROI

Calculating production cost is often essential for many manufacturers as this shows how financially feasible a production process can be. This is even more important when employing a sophisticated technique like overmolding, where special equipment and a highly skilled workforce are required. It can mean a substantial initial investment with a positive cost-to-benefit evaluation where the benefit far outweighs the initial purchase cost.

With benefits that include increased product performance, durability, and strength, overmolding is worth its cost. However, it is vital to consider the operational and maintenance cost, as the overall cost of regularly maintaining overmolding equipment can increase the overall cost significantly. Nevertheless, the lifetime return on investment (ROI) can be a huge determining factor in adopting overmolding methods for your production. Since the ROI will depend on several factors, including the project size, industry, and product type, it is crucial to carefully examine these factors to calculate your lifetime ROI and decide if overmolding suits your project. Yet, many facilities often adopt overmolding, seeing that the ROI is usually high and worthwhile over the years with benefits that include improved product performance, durability, high quality, and fast production time with little or no defective product. However, these returns, including reduced production cost and product quality, often take a while to start seeing, and manufacturers should see overmolding as a long-term investment. Moreover, the positive industry reputation that overmolding brings to the company in terms of quality production often attracts more clients, and you can make more profit using overmolding.

Ultimately, a careful cost-to-benefits analysis is vital for any company considering adopting overmolding for their projects, as this will give you the true picture of its financial practicality. Also, partnering with an experience overmolding facility is a fast way of achieving your goals as you are not burdened with the initial equipment and setup cost, including the regular maintenance cost.

IX. Environmental Impact and Sustainability

Environmental sustainability is at the forefront of most manufacturing companies, as the impact of manufacturing on the environment over the years has been catastrophic. Many companies are now seeking alternative manufacturing methods, equipment, and materials that help to reduce the negative impact on the environment. This paradigm has also been extended to the overmolding production process as its impact is significant on the environment, especially with waste generation. There can be so much waste generated in the course of carrying out overmolding procedures leading to massive environmental pollution. Nonetheless, manufacturers are now adopting several methods to reduce the waste generated during overmolding processes, including the reuse and recycle concepts. Reusable materials can be put back into the overmolding process as raw materials, reducing the waste usually generated by this manufacturing method. Also, energy consumption with overmolding production can significantly contribute to environmental pollution. One way manufacturers tackle this is by using alternative or green energy sources, including solar and wind power. Another way is by employing automation and assembly lines with more efficient power usage.

Again, manufacturing long-lasting products that reduce the need for frequent replacements also reduces waste generation and environmental pollution. Using biodegradable raw materials is another environmental-friendly and innovative option that reduces waste and pollution sources with a sustainable outlook for overmolding.

X. Choosing the Right Overmolding Partner

While setting up an overmolding equipment and facility comes with a high initial cost, many manufacturers find partnerships with already established overmolding companies a better option. That way, you are not bogged down with high maintenance costs while focusing on the primary production activities. However, getting a reliable overmolding partner can be daunting, especially if you’re starting it new. Still, carefully considering the factors highlighted below will significantly reduce your stress.

  • Experience and Expertise: The experience of the prospective overmolding partner, which includes the number of years in the industry, equipment sophistication, and complexity of their past jobs, will give you an indication of their ability.
  • Technical Knowledge and Capabilities: You should consider the skill level of a prospective partner’s technicians, including their ability to operate advanced overmolding machines and successfully carry out jobs with intricate details.
  • Customer Service and Communication: Communication is key to achieving success in any production process, including overmolding, and a prospective partner should be able to pass information in clear, simple, and easily understandable ways. Attending to inquiries and giving timely updates will make the job faster and hitch-free.
  • Quality Assurance and Certifications: Implementing a working quality management system with industry-accepted certification like ISO 9001 shows a prospective partner’s commitment to quality production processes. This will also ensure clients get quality products.
  • Cost and Lead Time: Competitive pricing and timely delivery of projects are essential considerations for choosing an overmolding partner. This can impact on your bottom line and your competitiveness in the industry.

XI. Future Trends and Developments in Overmolding

With the fast rise in technological advances, virtually all industries are beginning to turn to technology for faster, easier, and better production quality, for instance, rapid prototyping. Overmolding is not exempt from this trend as it experiences significant development and advancements in specific areas.

One area overmolding has started seeing advancements is in the materials employed in overmolding. New materials are constantly developed to care for issues like the performance and durability of products with the increased bonding ability of these materials. Also, these materials are beginning to increase the possibilities of overmolding as a production method.

The areas where overmolding is now applicable continue to grow with advancements in materials and equipment industries like aerospace, medical, and automotive and are beginning to find new and innovative applications for overmolding.

However, there are still challenges that potentially face overmolding despite its significant growth and available opportunities. High production cost is the top of the challenges manufacturers often encounter with overmolding. Also, the complexities involved in overmolding can be nerve-racking for many manufacturers. Nevertheless, getting the right skilled hands and tools can help solve these challenges.

XII. Conclusion

In a nutshell, the versatility of overmolding coupled with its numerous benefits, including durability, high performance, and extensive industry application, are some of the attractive factors for overmolding. Nevertheless, before adopting it, they need to consider factors like size, complexity, and the associated cost of using overmolding for their projects. Still, the benefits of overmolding often outweigh its cost, and manufacturers can expect a high return on investment (ROI) even though it may take some time. More importantly, the opportunities and growth potential for overmolding seem limitless as technological advancements continue to increase with more durable materials and sophisticated equipment coming up.


Gary Liao

Gary Liao

Gary Liao is the Engineering Manager of TDL Company and has more than 20 years of mold design experience.

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