Two shot molding and overmolding are two of the most popular processes for designing plastic parts. While both involve the combination of multiple materials, they differ in their respective operation methods and final products. If you’re considering either process for a new project, it’s important to understand which method is best suited for achieving your desired results.
In this article, we'll take a closer look at overmolding and dual shot molding and help you determine which is the best choice for your application.
In order to accurately compare two-material injection molding and overmolding, it is necessary to give a brief overview of the concepts of the two processes.
Overmolding is an injection molding process that essentially combines a rigid substrate with a flexible plastic outer layer by injecting resin into one tool to form the substrate, which is moved to an overmold cavity in another tool after it has cooled and solidified. A second molten material - called the overmold - is then injected into the overmold cavity around the substrate. These two layers of material are mechanically or chemically bonded to form the final product.
Two-shot injection molding also known as bi-injection or twin-shot molding, is an advanced manufacturing process used to produce complex parts from two different types of plastic materials in a single automated cycle, creating multi-material or multi-color parts without adding additional assembly steps.
Both two-shot injection molding and overmolding (also known as laminating molding) are advanced manufacturing processes that allow the production of complex parts from multiple materials in a single cycle. However, they differ in their specific molding processes.
Two shot molding process
In the two molding processes, the work is divided into two main parts.
The first stage is similar to the traditional plastic injection molding technique. The first plastic resin is first injected into the mold to create a substrate for the other materials to be molded. Then as the base material solidifies and cools, it is transferred to another mold cavity.
The second stage of the process involves the transfer of the solidified substrate to another mold cavity. When the mold is opened, the portion of the mold that houses the substrate is rotated 180 degrees to accommodate the injection molding nozzle and other mold cavities. With the substrate in place, the engineer injects a second material. This material forms a molecular bond with the base material, creating a strong support. Once both materials have cured, the final part can be ejected from the mold.
It is important to note that the choice of transfer method affects the overall speed and efficiency of the two-color ball injection molding process. Manual transfers or the use of a robotic arm tend to take longer than transfers using a rotary plane. However, the use of rotary planes is more costly and may be more efficient for high volume production.
Overmolding is a manufacturing process that involves applying a secondary layer of material over a preformed part, resulting in a multi-material, integrated component. Here is an analysis of the working principle of overmolding.
The key principle behind overmolding is that the overmolded material bonds to the substrate, creating a strong mechanical bond between the two materials.
A pre-formed part is first prepared, usually a molded part made of a rigid material such as metal or plastic as a base or foundation material. Once the substrate is ready, it is placed on a mold specifically designed for overmolding and allowed to inject a second material, which is then injected into the mold through a runner or channel. The molten material flows around the base material, cools and then bonds to the base material. After the molten material is injected, it begins to cool and cure. Once the material has solidified, the mold is opened and the overmolded part is removed.
Dual injection molding and overmolding are versatile solutions. But what makes one approach more practical than another for a given application? Comparing the strengths and weaknesses of each technology provides insight into how they support project goals and outcomes.
Enhanced product durability and functionality:The durability, strength and functionality of the final part are enhanced by using two or more materials with complementary properties.
Reduced time and costs: Two-time molding can integrate multiple materials or components into one molded part without a secondary assembly process, reducing labor costs and production time, improving the quality and production efficiency of the overall part.
Increased design flexibility:From a design perspective, secondary molding provides designers with the flexibility to combine different materials into a single part with different properties, and to create complex lists of Unicode geometries to accommodate the production of multiple product colors.
Increased Aesthetic Appeal:Overmolding is able to combine different colors, textures in a single component to create a visually appealing and high quality product. This is often done in consumer products, automotive interiors and other applications where aesthetics play an important role.
Reduced Assembly and Labor Costs: Overmolding eliminates or reduces the need for secondary assembly processes, streamlines production, reduces labor costs, and minimizes the risk of assembly errors or misalignment of parts.
Better Product Performance:Overmolding adds an additional protective layer to the substrate, making it more resistant to shock, vibration and abrasion. The second material provides better resistance to chemicals, UV radiation, moisture and other environmental factors, thus increasing the overall durability and life of the product.
Limited Material Selection:The range of materials for which secondary injection molding is applicable is more limited than for single shot molding. Some material combinations cannot be effectively bonded together, limiting the choice of material options. This limitation may affect mechanical properties, chemical resistance or other properties.
Increased complexity and cost: Secondary molding is a more complex process than traditional injection molding. It requires specialized equipment and tooling, and involves a series of steps such as meticulous design, testing and mold making, which can lead to higher initial job costs, thus reducing the cost effectiveness of small-scale production.
Design Constraints: The overmolding process has certain design limitations due to the substrate and laminate involved. The substrate material must have the ability to withstand the heat and stress of the overmolding process without deformation or degradation. This can limit the choice of substrate materials and, in turn, the design possibilities of the final product.
Material adhesion issues: Achieving proper adhesion and bonding between the substrate and cladding material can be a challenge. Factors such as material compatibility, surface finish and processing conditions can affect the quality and durability of the bond. Without proper adhesion, delamination and weak spots can occur, resulting in premature damage to the overmolded part.
Both secondary molding and overmolding are widely used in the manufacturing industry to break away from traditional manufacturing methods and provide a more efficient production method.The following is a distinction between the different applications of overmolding and two-shot molding.
Consumer Products: In the manufacturing of consumer products, dual injection molding is commonly used to produce hand tools, personal care products and housewares, while lamination is mainly used to produce products such as toothbrushes, razors and kitchen appliances. Both primarily enhance the grip, ergonomics and durability of the product, providing a better user experience.
Medical Devices: Two-Shot molding and overmolding is an important part of medical device production. Using this method, ergonomic grips and buttons can be designed in a variety of materials and colors. Seals made through this injection molding process provide an additional layer of protection, providing users with a reliable and safe medical product. In turn, the overmolding process is used to create surgical instruments with comfortable and ergonomic grips, waterproof seals for wearable medical sensors, and soft-touch components for medical devices.
Automotive Components：Two-Shot molding is widely used in the automotive industry to produce a variety of components. This includes internal components such as instrument panels, door handles, buttons and switches. Overmolding is widely used in the automotive sector for interior components such as steering wheel handles, shifter knobs, and instrument panel elements. It enhances aesthetics, provides improved grip, and provides impact resistance.
Packaging：In the packaging industry, two-shot molding enables the production of containers, caps and closures with contrasting colors, soft-touch features or built-in sealing elements. Overmolding, on the other hand, is often used to create custom designed and branded packaging solutions. It allows for the integration of different materials and colors to enhance product visibility, branding and functionality.
Electronics: The use of two-injection molding in the manufacture of electronic devices allows the creation of keypads, buttons and housings in a wide range of materials and colors, providing tactile and visually appealing user interfaces. Overmolding is widely used to produce devices and components such as overmolded connectors, cable assemblies and circuit board enclosures.
Choosing between overmolding and two-shot molding depends on several factors and considerations. Here are some key points to help you make a decision:
Generally, a design evaluation of the manufactured product is performed first. Overmolding is typically appropriate for applications where a single substrate is covered or enhanced with additional materials. On the other hand, overmolding is the ideal solution for more complex designs that require multiple materials or colors to be integrated into a single part.
Cost and Efficiency
From a cost and efficiency perspective of the manufacturing process, overmolding may be more cost effective for simpler designs, while for complex parts, two-shot molding may be more efficient despite potentially higher tooling costs. Overmolding typically requires a single injection molding process, while secondary molding involves multiple shots and specialized equipment, increasing the upfront cost investment.
Consider the expected production volume of your product. Overmolding is ideal for small production runs, while twice-molding is usually more effective for large production runs due to its potential for faster production cycles.
Consider the compatibility of materials needed for your product. Overmolding requires the substrate and overmold materials to bond together effectively. If you need to combine materials that do not bond well through overmolding, two-shot molding may be a better choice as it allows for the use of different materials in separate shots.
Combining the considerations mentioned above with a detailed understanding of the contents of double injection and overmolding, to increase the success of your project, consult an experienced molding professional or manufacturer to assess your needs and determine the most appropriate molding technology for your application.When evaluating a professional injection molding supplier, consider the following aspects:
Start with a solid track record and extensive experience. Consider their expertise in the specific molding techniques you need, such as dual-material molding or overmolding. A supplier with a deep understanding of these processes can provide valuable insight and guidance throughout your project.
Secondly,Assess the supplier's technical capabilities, including their machinery, equipment, and tooling. Verify that they have the necessary resources and expertise to handle your project requirements, such as part complexity, material compatibility, and production volume. A well-equipped supplier with modern technology is more likely to deliver high-quality results.
Last but not least, timely delivery is critical. Evaluate the supplier's delivery record and their ability to meet deadlines. Ask about their production capabilities and delivery times to ensure they can meet your project schedule.
As mentioned above, overmolding and twice-molding are both excellent methods for manufacturing plastic parts, both with their unique properties, and understanding and selecting the right process is necessary to ensure the manufacture of a high quality product. The choice between overmolding and secondary molding depends on the specific product requirements of your project, cost considerations, and production volumes.
If you have a need, please consult Key-Plast, one of the leading injection molding manufacturers in Huangyan, with rich manufacturing experience and machinery, we will evaluate your needs professionally and provide you with the most suitable technical solution.