Injection molding has proven to be incredibly valuable for the fast and precise creation of high-quality plastic parts. It is a practical choice for a wide range of applications for various industries. However, different processes fall under the umbrella of injection molding. Two of the most popular techniques in this category are two-shot molding and overmolding.
When discussing two-shot molding vs. overmolding, it is pretty easy to confuse the two processes. They share several similar characteristics, and they offer similar benefits in manufacturing. However, there are major distinctions you must note to get the best results. The difference between two-shot molding and overmolding will help you choose the best option for your projects.
Therefore, this article aims to give a detailed overview of overmolding and two-shot molding, helping you understand their various differences. We will also discuss the benefits and drawbacks of these techniques. At the end of this article, you will be able to decide on the best molding services for your applications.
What Is Two-Shot Molding?
This process is also referred to as multi-shot, double-shot, or dual-shot molding. This injection molding process involves the molding together of two separate plastic resins in a single machining cycle. As a result, engineers can easily create multi-material and multi-colored parts without extra machining steps.
How Does Two-Shot Molding Work?
The two-shot injection molding process consists of two phases. The first phase is similar to the conventional plastic injection molding technique. It involves injecting a shot of the first plastic resin into the mold to create the substrate for the other material (s) to be molded around. The substrate is then allowed to solidify and cool before transferring to the other mold chamber.
It is important to note that the method of transferring the substrate can affect the speed of 2-shot injection molding. Manual transfers or the use of robotic arms often take longer than transferring with a rotary plane. However, using rotary planes is more expensive and may be more efficient for high-volume productions.
The second phase involves the introduction of the second material. Once the mold opens, the part of the mold holding the substrate will rotate 180 degrees to meet the injection molding nozzle and the other mold chamber. With the substrate in place, the engineer injects the second plastic resin. This resin forms a molecular bond with the substrate to create a firm hold. The second layer is also allowed to cool before ejecting the final component.
Mold design may affect the ease of bonding between the molding materials. Therefore, machinists and engineers must ensure the correct alignment of molds to ensure easy adhesion and prevent defects.
Double-shot molding is ideal for complex, multi-material, and multi-color products. It is a highly versatile method, useful for many applications in different industries, including:
- Movable parts or components
- Automotive interior parts
- Medical and surgical devices
- Kitchenware and bottle dispensers
- Panel buttons with soft grips
What Is Overmolding?
Overmolding is another multi-shot injection molding technique that creates an end product from two or more plastic materials. This process is applicable to various manufacturing and industrial uses. It is ideal for building high-quality functional and aesthetically pleasing components. Many manufacturers also use this method for plastic prototype development and to produce sub-sections of components.
How Does Overmolding Work?
Like the two-shot molding process, the overmolding process also starts with the molding of the substrate. Although the substrate can be any kind of material, it’s best to use the more rigid material as the base. The next step involves placing the substrate in an overmold cavity within the same molding tool.
Once the substrate is in the cavity, the molten secondary material (overmold) is molded onto or around the substrate. After cooling, the overmold and the substrate become mechanically or chemically bonded to give the end product.
Some products may require two or more overmolds. An important point to note is that the plastic resins used in overmolding must be thermally or chemically compatible with one another. Incompatibility between the substrate and overmold may give a poorly bonded or deformed product. Sometimes, plastic resins can also be molded over metal substrates. In this case, compatibility may not be a big issue.
Overmolding injection molding is a vital industrial process with many diverse applications. Some of the uses are highlighted below:
- Vibration dampening in automobiles
- Making comfortable, easy-grip tools
- Water-resistant electronic products
- Medical equipment
- Solar energy components
- Industrial/OEM applications
Two-Shot Molding vs. Overmolding: Pros and Cons
We can’t discuss overmolding vs. two-shot molding without mentioning their advantages and disadvantages. Although these processes are essentially similar, there are peculiarities you must look out for.
Let’s check them out.
Pros of Two-Shot Molding
Two-shot plastic injection molding offers the following benefits.
Enhanced Product Quality
There are several ways by which dual-shot molding enhances product quality, including the following:
- Improved ergonomics. The process is compatible with soft materials, helping to produce ergonomically designed parts. This is crucial for medical devices, appliances, and other hand-held products.
- Excellent combination of soft and hard plastic polymers to ensure functionality and outstanding comfort for every product.
- Improved aesthetics, with products looking more appealing to consumers when there’s a combination of two or more colors or materials.
- Creation of complex mold designs with multiple materials and adequate bonding, ensuring durability, reliability, and longer life.
- Reduction in the level of misalignments compared to traditional insert or overmolding processes, thereby preventing plastic injection molding defects.
Although it is a two-phase process, it uses only one machining cycle. Within the single cycle, the initial mold is rotated out of the way, giving room for the insertion of the second molding material. With just one cycle involved, two-shot molding involves fewer costs and labor requirements. It also creates more items within a short period.
2-shot molding allows the combination of different materials and colors for functional and attractive final products. There are many possibilities available with this process, including:
- Silicone and thermoplastics
- Thermoplastic elastomers and nylon
- Hard nylon and soft-touch materials
Such combination possibilities solve not only production difficulties but also the ability to produce components for applications in different industries.
With this technique, designers have more freedom for innovative designs. The process can accommodate complex mold designs, incorporating multiple materials and making parts with complex geometries.
Cons of Two-Shot Molding
The following are the drawbacks of the two-shot technique:
High Tooling Costs
Two-shot injection molding involves in-depth and careful designing, testing, and mold tooling. Initial designing and prototyping may be done via CNC machining or 3D printing. Then the development of mold tooling follows, helping to create replicas of the intended part. Extensive functional and market testing is done to ensure the efficiency of the process before final production begins. Therefore, the initial costs involved in this injection molding process are usually high.
May Not Be Cost-Effective for Small Production Runs
The tooling involved in this technique is complex. There is also a need to remove previous materials from the machine before the next production run. As a result, setup time may be quite long. Therefore, using the two-shot technique for small runs may be too expensive.
Part Design Restrictions
The two-shot process follows the traditional injection molding rules. Therefore, aluminum or steel injection molds are still used in this process, making design iterations quite difficult. Reducing tool cavity size may be difficult and sometimes result in scrapping the entire batch of product. As a result, you may be incurring cost overruns.
Pros of Overmolding
Manufacturers who require innovative product design, ergonomics, and a distinctive product appearance are all fans of plastic injection overmolding. The overmolding method has evolved over time, resulting in high customer satisfaction.
The following are the benefits of employing overmolding:
Better Product Performance
This process improves the product’s performance, including shock and vibration reduction, chemical resistance, and electrical insulation. TPE is one such material that, when employed to make various items, produces a non-grip feature. It can also operate as an environmental barrier due to the abovementioned qualities.
Generally, products made from overmolding have the qualities of two materials, thereby enhancing their performance.
Increased Aesthetic Appeal
Overmolding is excellent for creating aesthetically appealing structures. It is the best approach since it is available in a range of colors and materials. They may also be modified for other surface finishes to improve their cosmetic appearance further.
Increased Material Flexibility
Overmolding necessitates the assembly of several materials. This enhances the part’s flexibility by utilizing all of the capabilities of the materials involved. Furthermore, manufacturers can boost flexibility by using the overmolding design guide.
Eliminates the Need for Fasteners and Adhesives
Overmolding eliminates the need for adhesives and fasteners since separate pieces can merge. As a result, the products’ durability improves. There is also a reduction in total production costs.
Cons of Overmolding
Although the technique enhances product performance, there are some downsides involved in its use. They include the following:
Multiple Production Steps
Overmolding involves two processes in the production line, which increases the part’s cycle time. When you need to mold a single item in a single operation, the production cost tends to rise. Furthermore, because overmolding is a two-step procedure, it necessitates the use of additional equipment than single molding.
When two separate pieces are fused together in a mold, there is a danger of delamination. Delamination will occur when the ideal temperature range fluctuates. Mechanical interlocks are required when the available heat cannot properly fuse the materials.
How to Choose Between Two-Shot Molding and Overmolding
Two-shot molding and overmolding are simple but effective molding processes, helping to create durable, high-quality components. However, there are times when you may need to compare two-shot molding vs. overmolding to ensure you get the best result.
Two-shot molding is ideal for larger production runs, considering the difference between two-shot molding and overmolding. A significant drawback to the 2-shot injection molding process is the higher initial costs and expensive tooling. Therefore, it will be better to choose this process for larger productions. It is also great for flexibility, control, quality, and efficiency.
On the other hand, overmolding is best suitable for low-volume production. It is also ideal for rubber parts that do not have strict tolerance requirements. Overmolding services can be done on standard injection molding machines. Therefore, this technique is a great choice for manufacturers that do not want to invest in new machining tools.
However, design teams and engineers must evaluate critical considerations against their project requirements. This way, you can ensure the benefits outweigh the risks and make the best choices.
Get Your Plastic Molded Parts at RapidDirect
Knowing the comparison between overmolding vs. two-shot molding may not be enough. Working with a skilled and experienced manufacturing partner like RapidDirect will streamline your decision. We boast a team of designers, engineers, and machinists with many years of experience. Our expert teams are ready to see you through every part of the production process, from design to process selection and final manufacturing.
RapidDirect is ready to work with your team to choose the suitable technique for your project. Our injection molding services are ideal for prototyping and production for applications in various industries. We assure fast turnarounds of high-quality products are competitive prices. Upload your CAD files today to get an instant online quote.
This article covered two-shot molding vs. overmolding, detailing the steps involved in the two techniques. These injection molding techniques are ideal for creating functional and aesthetically pleasing components for various industries. The various benefits and downsides of the processes will help you make the right selection for your project.
Remember that 2-shot injection molding is best for high-volume production while overmolding is ideal for low-volume production runs. Contact us at RapidDirect today, and let’s discuss your injection molding project.