This article will give a detailed discussion on overmolding.
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Many everyday products rely heavily on rubber and plastic, thanks to their durability, versatility, and ability to be molded into virtually any shape needed for industrial applications. Some types of these materials are engineered to endure extreme conditions, making them suitable for challenging tasks. Moreover, the process of overmolding enhances the functionality of rubber and plastic products. By applying multiple layers of these materials, manufacturers can create industrial products that are not only more robust and visually appealing but also serve additional functions.
Several different manufacturing and industrial sectors can use the overmolding technique. Overmolding is an injection molding technique that uses many materials to form a single object. Two or more layers of material can be molded together with this injection molding. Both rubber and plastic overmolding might benefit from the procedure. The first substance is typically referred to as the substrate substance, which may be partially or completely covered by subsequent substances (overmolded materials).
Originally used to improve the appearance of consumer goods, injection overmolding has now become quite prevalent. This technique serves a variety of purposes, including enhancing a product’s performance. It can increase chemical resistance, provide electrical insulation, create a more secure and durable grip, and more.
There are primarily two main types of overmolding processes used in product production.
Industries that require rapid prototyping of various industrial machine components can greatly benefit from overmolding. This technique is particularly valuable for producing custom parts that integrate rubber or plastic with other materials, such as metals.
Overmolding serves various purposes, with one of the most common being to enhance a product's grip while preserving its durability. For instance, it can improve the handle of a power tool or the non-slip grip of a surgical instrument. In these cases, thermoplastic polyurethane (TPU) often outperforms acrylonitrile butadiene styrene (ABS). Additionally, overmolding can be used to achieve aesthetic and branding goals. For example, a sports team might use two-tone overmolded mouthguards in their team colors, while a well-known tractor manufacturer might use green and yellow overmolded cowlings to decorate its riding lawn mowers.
Overmolding is a highly favored and innovative rapid tooling technique known for its significant potential to lower production costs, reduce cycle times, and offer new design possibilities. It has been widely adopted across various industries, including mobile phones, pen manufacturing, automotive, home appliances, hand tools, and consumer goods, thanks to its diverse design benefits.
The overmolding process involves creating a machine part or component by fusing two or more materials together. These materials can be identical or different, with no restrictions on the combinations used. To fully grasp how overmolding works, it's important to understand its two key stages. The first stage involves the substrate, and the second stage is the overmolding itself. Each overmolding project consists of these two components.
The substrate is the primary material used in overmolding and can be composed of a wide variety of materials. The secondary material, known as the overmold, is applied to "mold over" the substrate. In some cases, manufacturers may use multiple overmolds in their process. The number of overmolds used depends on the design of the final product and the manufacturer's innovation.
Overmolding is an excellent method for improving a product’s physical properties or aesthetic appeal. It operates on similar principles as traditional injection molding processes, though with some additional constraints.
To ensure the highest quality products, manufacturers must consider several factors during the overmolding process. End customers should also take these factors into account when selecting the ideal overmolded part for their application. Here are some key considerations for overmolding:
The overlay will break before separating from the substrate in a perfectly overmolded item and may even take some of the underlying material. The formation of a strong chemical link is only sometimes possible or even essential, though. For example, consider a molded electronics housing cover with a soft sealing gasket overmolded. The gasket has nowhere to go once the cover is fixed in place. All that is required is sufficient binding to secure the gasket to the substrate and prevent it from coming loose or disappearing during assembly. Since it eliminates the requirement for a stamped paper or rubber gasket that must be manually glued in place, this is a great application for overmolding.
The goal of any overmolding process is to ensure the materials fuse effectively. Some materials may struggle to bond naturally, and in such cases, they might need additional assistance to join properly. Techniques like creating indentations or undercuts in one of the materials can help facilitate this bonding process.
Engineers often recommend using a mechanical interlock alongside or instead of a chemical bond to ensure a strong connection. This can be achieved by incorporating an undercut into the substrate component or by drilling a series of reverse-tapered or counterbored holes into the part. These features allow the overmolded material to flow and secure a reliable bond, even in challenging conditions.
Techniques for Bonding Overmolded Parts:
Although some materials are ideal for flexible applications, they may not endure high temperatures effectively. As most overmolding techniques involve heat, especially in injection molding, manufacturers must select materials that retain their properties under elevated temperatures. This requirement applies to both the substrate material and the overmolded component.
Each material used in the overmolding process has a unique coefficient of friction, which dictates how easily it can slide against another material. The coefficient of friction measures the amount of resistance between surfaces. The effectiveness of bonding materials together largely depends on this coefficient and the surface texture. Generally, materials with higher surface texture and friction bond more readily.
Material thickness is another key performance factor in overmolding. In applications designed for sound or vibration damping, thicker materials are often required to ensure effectiveness. Thicker materials are better at absorbing vibrations and provide a softer feel. Conversely, thinner materials may feel stiffer and be less effective at dampening sound or vibrations.
The effectiveness of substances for overmolding depends on the specific end goal, as countless material combinations are possible. Each material offers distinct advantages and properties: some excel in harsh environments, while others provide superior strength and flexibility. Smart manufacturers employ a standardized evaluation process to assess and compare materials for overmolding, rather than evaluating each material individually. This approach helps in keeping up with the continuous development of new materials and ensures a consistent basis for selection.
Materials used in the overmolding process may be affected during manufacturing. Sometimes, a material strong enough to resist indentation is needed. Users must also evaluate whether the material will bend under pressure, as this can impact the final product's grip. If the material bends, it could compromise the effectiveness of the grip and, consequently, the bond between the two materials in the final product.
Manufacturers use various overmolding techniques based on the materials and the specific overmolding methods required. These categories encompass most overmolding practices in the manufacturing industry.
It's important to note that not all materials are suitable for overmolding. There are four main types of overmolding techniques:
In addition to the various types of overmolding, there are several manufacturing processes that can be used to achieve it.
Dual-injection molding is a commonly used overmolding technique, known for being both expensive and complex to manage. Unlike other methods, this technique does not involve injecting an overmold onto an existing substrate. Instead, both the substrate and the overmold are injected into the same mold. This requires that both materials be compatible, adding a layer of complexity to the process. One of the key advantages of dual-injection molding is that all materials are in liquid form during the injection process, which ensures optimal molding and adherence between the materials.
The 2K (two-color) overmolding process involves two main steps. First, a material is injected into a mold cavity using a 2K injection molding machine. After this initial injection, the machine switches to another material and molds it onto the first material in the same cavity. This technique creates products that incorporate two different materials. With a twin-cylinder (or double-mold) injection molding machine, it's possible to simultaneously produce items from two different materials. The components created are then used as inserts for other products, enhancing their functionality or appearance.
The first shot of hard plastic injection molding is still hot when it enters the second cavity of the 2K injection molding machine, which is one benefit of 2K overmolding. However, due to the lack of moisture absorption during the transfer process, the surface may easily be ablated by the high-temperature TPE melt to create an incredibly thin layer. There is also no effect of water vapor adsorption.
When working with plastic overmolding, insert molding is the most common technique. This technique includes both flexible elastomers and strong, rigid plastics. Because the insert molding technique is simpler to complete, it is the optimal type of overmolding for these materials. It follows that of the overmolding procedures, it is also the most cost-effective. The hard plastic components must first be divided into tools before performing an insert mold. The softer materials are then inserted after that. These flexible elastomers help the two materials adhere to one another. The adhesion bonding procedure might be challenging. The soft elastomers must achieve the correct temperature for the adhesion bond to function effectively. Heating the elastomer also heats the surface of the hard plastic, allowing the two components to connect.
Another process is two-shot overmolding, which involves two main stages. Initially, a material is injected into a mold using a molding machine. The partially formed part is then transferred to a second mold where a different material is injected. This process typically requires two injection molding machines operating simultaneously. The first material injected is usually a hard substance, which is often in a semi-solid or gel form. When injected, it conforms to the shape of the pre-set elastomeric mold, creating a two-material component.
In the insert molding process, a rigid component is first created and placed into a mold chamber. Subsequently, thermoplastic elastomer (TPE) is injected to create additional molding around this component. Standard injection molding machinery can be used for insert molding, with either manual or motorized arms employed to position the rigid components. This technique is often used for coated metal parts. In a two-shot overmolding process, one mold is used for the substrate, and another mold is used for the final over-molded product. Additionally, a person is needed to operate the machine, load the substrate components, and unload the finished products—a task referred to as "pick-and-place" rather than traditional molding.
The two-shot overmolding method provides manufacturers with a robust mechanical bond, resulting in enhanced strength and stability for the final products. This process offers significant advantages, making it a valuable technique for many manufacturing businesses.
Many plastic parts and products are manufactured using the industrial-strength resin known as urethane. It's a fantastic material since it can be tailored to fit hard or supple, flexible items. Urethane is poured into a mold during the procedure, and the mold is let to dry. The material cures while sitting, giving the producer its finished product. Many commercial producers favor urethane casting as an alternative to molding. The reason is that urethane casting is a terrific approach to creating models and parts that are both affordable and of good quality. It's also a fantastic technique for more intricate designs.
Manufacturers begin the overmolding process by creating a silicone mold, usually produced using a CNC machine or 3D printer. Once the mold is prepared, silicone is poured into it. As the silicone cools, it conforms to the shape of the mold. Next, urethane is introduced as two separate liquids that must be mixed in a 1:1 ratio. Combining these liquids triggers a chemical reaction, known as curing, which transforms the urethane from a liquid to a solid.
Urethane generally requires about an hour to cure, but it's important to consult the specific instructions for the urethane being used, as curing times can vary. Once the urethane has fully dried and hardened, the new part or model can be removed from the mold. A single silicone mold can typically be used for up to twenty castings using this technique.
Numerous overmolding machines are available, playing a crucial role in today's industry by enabling the efficient and cost-effective production of complex, multi-material products with enhanced functionality and improved design. These machines are essential for applications in automotive parts, cookware, hardware tools, and everyday household items. Below are several well-known brands that specialize in overmolding processes.
Arburg provides a variety of injection molding machines, including their Allrounder series, which is renowned for its versatility and precision in overmolding applications. These machines are equipped with advanced control systems and user-friendly interfaces, ensuring efficient and reliable production.
Engel's Victory series of injection molding machines is extensively utilized in overmolding applications. Renowned for their high precision and energy efficiency, these machines feature advanced technologies such as servo-electric drives and multi-component capabilities.
Sumitomo (SHI) Demag's IntElect Multi series is tailored for multi-component and overmolding processes. These machines provide high-speed, high-precision injection capabilities and feature advanced automation and control options.
Husky's HyPET Multi-Component systems are extensively used for overmolding. These machines integrate advanced injection molding expertise with hot runner technology to deliver precise and efficient multi-material overmolding.
Milacron's Elektron Multi-Shot series is designed for high-performance multi-shot and overmolding applications. These machines provide precision, flexibility, and energy efficiency, making them a popular choice for producing complex, multi-material parts.
Please be aware that specific models and features may vary. For the most up-to-date information on overmolding machines available in the United States and Canada, it's best to consult the respective manufacturers or industry resources.
Food safety is crucial when using plastic for items such as cookware, food containers, and kitchen utensils. Therefore, it’s not surprising that overmolding plays a vital role in the production of cookware parts and components.
Overmolding is employed in cookware for various components, including spatula handles, pot covers, stove trims, knives, and cutting boards. These products utilize high-grade polymers that ensure food flavor and freshness are not compromised, enhancing consumer safety.
As mentioned earlier, overmolding enhances the ease of handling, use, and cleaning of items. Additionally, it improves various product properties, including chemical resistance, vibration dampening, and sound insulation.
It's no surprise that many household items, such as toothbrushes, kitchen utensils, portable electric fans, mirrors, pens, multi-port chargers, shampoo bottles, and reusable food containers, are produced using overmolding. This process not only makes products easier to clean and use but also reduces wear and tear, extending their lifespan and improving overall quality for users.
Various hardware tools serve as excellent examples of overmolding in action. These tools include blades, pocket knives, pliers, wrenches, hammers, tape measures, and other similar items.
The primary machining components of these tools are usually made from steel, which is utilized for cutting, bending, drawing, punching, and various other fabrication processes. However, for the tools to be used safely and ergonomically by the end-user, overmolding plays a crucial role in enhancing their handleability and comfort.
Using common tools can be challenging without overmolded handles, whether you're working on automotive repairs or home improvement projects. The substrate for the overmolding process can be made from various polymers. In a two-step injection molding procedure, a rubberized plastic is then added to this substrate to create the handle, improving the user's grip and overall comfort.
Precision and product safety are crucial in the medical sector. For instance, surgical tools used by doctors, surgeons, and nurses must be made from reliable, safe plastic materials. Furthermore, these tools should be designed for easy cleaning and sterilization to prevent infections.
Overmolding is widely employed in the medical industry to enhance various products. It is used to manufacture components such as equipment housings and surgical instruments, creating finished parts that improve usability. Examples include syringes, patient monitors, needles, catheters, dilators, and soft-touch buttons.
Car trims or moldings are components found in various parts of an automobile, including the door edges, side body, fenders, bumpers, wheels, and interior areas. While car trims often serve a decorative purpose, they also offer practical benefits, such as reducing the vehicle's weight. Overmolding, as discussed earlier, provides several functional advantages and is a versatile plastic production technology with numerous creative applications. It allows for the creation of custom or pre-set automotive trims in a range of colors, tailored to customer preferences.
To be combined with additional materials like steel, chromium, or metal plating, overmolded trims can undergo a different process called insert molding.
The overmolding technique offers several advantages that can be observed across various applications, including electrical assemblies and household items.
The overmolding technique creates a protective bond around PCBs, wires, cables, and connectors, safeguarding electrical components from dirt, dust, and debris. An overmolded electrical assembly can achieve IP67, IP68, and IP69K ratings for protection.
Combining two materials to create a finished product enhances long-term performance. This approach can result in products that last longer compared to those made from a single material.
Moreover, overmolded products are better at absorbing shock and vibration. Additionally, overmolding can enhance a product's chemical resistance.
TPE is an example of such a material. After the overmolding process, TPE can provide a non-slip surface and, when needed, act as an environmental barrier.
Overmolding can significantly enhance the designs of various tools, parts, and models. By using materials in different colors, it is easy to create visually appealing overmolded products.
Overmolding is an ideal process for designers looking to create a single plastic item with multiple colors or surface treatments. For instance, different colored or textured components can be overmolded together to produce a part with seamlessly integrated colors and finishes. As an example, a clear resin part can be overmolded with a black resin part to create a single automotive lens. Additionally, metal inserts that are overmolded into plastic often have a more polished appearance compared to those manually placed within plastic parts.
Overmolding can significantly enhance the comfort and appearance of many products. For instance, it can be used to add comfortable rubber grips to tools such as hammers, saws, and other equipment, improving their usability and aesthetic appeal.
Electrical connections can experience stress from frequent plugging and unplugging or from movement in various applications. Overmolded connections are far more resilient compared to traditional shields like heat shrink, potting, and backshell connectors. Overmolding provides flexibility, which helps distribute stress more evenly across a broader area, reducing strain and enhancing durability.
Without adequate shielding, shock and vibration can lead to mechanical breakdowns in electrical components. To ensure the connection remains robust under significant vibration or shock, it's crucial to prevent components from moving within the assembly. Overmolding is an effective method for preventing fatigue and damage, as it fills gaps around internal components, eliminating air pockets that could cause movement and instability.
Shaping an aluminum piece to the exact specifications needed to protect an electrical connection or PCB can serve as the basis for creating a mold for an electrical assembly. An overmolding mold typically consists of a top and bottom piece that fit together around the intended component. Once created, the mold can be stored and reused for future production runs.
During the overmolding process, the plastic applied over the substrate is melted and then cured, resulting in a more robust assembly. This method ensures that the components molded together have a better fit compared to two components that are manufactured separately and then assembled.
Despite the perception that overmolding is expensive, it is actually quite cost-effective. One of the key advantages of overmolding is its ability to deliver significant benefits at a relatively low cost.
Overmolding allows manufacturers to create superior electrical assemblies while using less expensive components. For example, unsealed connectors are more affordable than sealed connectors. If overmolding is planned during the design phase, unsealed connectors can be used, as the overmolding process will provide a robust, weather-tight seal that often surpasses that of a sealed connector. This approach applies to terminals and PCBs as well. It is crucial to use durable materials and test them in their intended environment to ensure they perform effectively.
Overmolding allows for high-quality outcomes while keeping manufacturing costs low. Additionally, the relatively straightforward nature of this process makes it particularly valuable in industries that require rapid production.
Manufacturers delegate the construction of molds to machines, which then handle the overmolding process. These machines can complete the overmolding of two connections in just 30 seconds, significantly faster than other connection protection methods. This efficiency increases throughput and reduces labor costs.
End users find elastomers such as rubber or polyurethane more comfortable to use compared to hard plastic or metal items. By applying a soft coating to hard plastic and metal parts, their texture can be softened, making them more user-friendly. In contrast, hard plastic and metal pieces can be quite uncomfortable to the touch.
One of the less obvious benefits of overmolding cable assemblies is the degree of customization it allows. While it is possible to overmold existing assemblies, manufacturers can also create a custom product tailored precisely to the specific needs of a given application.
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