Injection molding is used in many industries. It helps create complex-shaped products while maintaining quality. Overmolding and two-shot molding are subcategories of injection molding. However, the workings of these two types vary. This distinction excites people to debate Overmolding vs Two-Shot molding.
Both are undoubtedly excellent manufacturing methods and are used worldwide. However, their differences make them suitable for making different types of products. In this article, I will help you understand their primary differences. After reading this, you can decide which is best for your needs. So, let’s get started!
Overview of Overmolding & Two-Shot Molding
In a previous article, I discussed over-molding and compared it with Insert Molding. However, this article will differ as we will differentiate over-molding from 2K molding.
Two-shot molding is a single-step, advanced, and cost-effective manufacturing process. It uses a single mold that rotates at 360. On the other hand, Overmolding is a slow process that uses two molding cycles and two molds. However, this method can create aesthetically pleasing products.
I don’t consider them a head-to-head match. The reason is that they vary in terms of their output. For example, the two-shot method gives multiple-layered products of two different materials. Moreover, you can use two different colors in a single molding cycle. As a result, you get colored products.
On the flip side, over-molding is different as it first creates the base (substrate). After that, this substrate goes into the second mold. The second material is then molded on the substrate for the final product. This method does not allow for efficient product-colored products. The reason is that we use two different molding cycles. The substrate is first made in a separate mold.
Once it is dried, it goes into a second mold. If you add colored material in the second mold, it won’t blend effectively with the substrate product. Game controllers are generally produced through two-shot molding. On the other hand, the toothbrush is an example of an over-molding process.
Key Highlight: Don’t you know anything about two-shot molding? Worry not! We have a detailed article on the topic of the two-shot molding process. You must read that for a better understanding. If you have information, you should be good enough to understand this comparison guide!
How Does Two-Shot Molding Work?
Dual-shot, multi-shot, or double-shot molding all refer to two-shot molding. Let’s discuss how this molding method works. First, this method uses a single molding cycle and mold. The first material is injected into the first mold.
The two-shot molding machine consists of two injection units. They help by putting two materials in the same mold. Interestingly, the machine comes with a robotic arm that rotates the mold 360 degrees. This means that once the first material is in the mold, it rotates to get the second material from the second injection unit or nozzle.
The first injection unit fills the mold. Once the material is filled in the mold, it can cool slightly and become a semi-solid structure. The mold then rotates at 360 degrees. As a result, the mold cavity goes just under the second injection unit (nozzle). The second injection unit injects the material into the mold after the first semi-solid material.
This way, the injected materials cool together and form a strong bond. As the first material is in semi-solid conditions, any color added to the second material blends effectively in the first material. Moreover, the bond between these two materials is very robust. So, we get a final product in a single molding cycle without using two different molds.
Advantages & Disadvantages of Dual-Shot Molding
This method is generally considered advanced and superior to over-molding. However, it also has some drawbacks that must be considered. Here is a table showing the pros and cons of this manufacturing process:
| Advantages | Disadvantages |
| Single-Step Production | Two-shot molding machine is costly |
| Strong Material Bonding | Limited Material Compatibility |
| Can create Precise & Complex Designs | Inefficient for low-volume production. |
| Faster Production Speed | Two-shot machines require more upkeep |
| Create high-quality & Durable products | Best for medium-sized parts |
| Cost-Effective for Large Production | Changes are costly once molds are created. |
How Does Overmolding Work?
The over-molding process is different and more time-consuming than two-shot. In this method, you’ll have to create two molds. First, the injection unit puts the molten material into the first mold. Remember, this mold shape and design match the shape of your desired base product.
Once the mold is filled, it undergoes a cooling process. In this stage, the molten material inside cools down and adopts the shape of the material. Unlike two-shot molding, this molten material dries entirely and makes a solid product. This first product is called a base product or substrate. Now, you will have to transfer the substrate into the second mold.
This mold design is made in such a way that substrate easily fis on it. It is then placed under the injection unit (nozzle). The injection unit injects the molten material in this second material. This material can be similar to what was injected on the first mold, or different.
This molten material will sit on or around the substrate per the mold design. As a result, you get the final product. For example, you can create a toothbrush with this method. The hard plastic (base) will be made using the first method. The rubber material will be molded on the base in the second molding cycle, creating a grip.
Quick Highlight: Remember, the over-molding method uses two molding cycles. Each cycle requires a separate mold. The creation and design of these two molds can be costly. Moreover, the two-step process makes this method very slow and time-consuming.
Advantages & Disadvantages of Overmolding
Have you understood how the overmolding process works? I don’t consider it very efficient, especially for bulk production. Why? Because it is relatively slower due to its multiple molding cycles. Here is a table showing the pros and cons of Overmolding:
| Advantages | Disadvantages |
| Offer products that are resistant to wear | Longer production time |
| It gives the product a smooth grip | Two steps make it inefficient for bulk |
| Help in retrofitting existing products | Material bonding is not very strong |
| Increases Waterproofing & Sealing | It requires two separate molds |
| Eliminates the need for separate adhesives | Not as Precise as Two-Shot Molding – |
| Create aesthetically pleasing products of unique shapes. | Requires additional handling between the two molding cycles. |
Differences Between Overmolding & Two-shot Molding
The above is dedicated to providing their overall understanding. However, their selection depends on their differences. Knowing them will help you make the right decisions. Let’s compare these two molding processes head-to-head.
1- Material Considerations
Both of these methods work with a variety of materials. You can use rubber and plastics, and you’ll be good to go. However, two-shot molding requires only those materials that bond with each other. As you know, two molten materials combine in two-shot molding and make chemical bonds.
The product’s durability will be compromised if these two materials don’t bond effectively. You can use any two materials, but ensure you make the chemical bonds with each. In the case of over-molding, there is no such restriction. Why? Because manufacturers add adhesion to materials to make mechanical bonds. You can use any two materials and use them to complete the over-molding.
2- Molding Cycles & Mold Creations
Two-shot molding is a straightforward process that is completed in single molding cycles. It does not use two different molds. On the other hand, over-molding is a very complex manufacturing process. It uses two separate molds and completes two molding cycles.
Base products are made in the first molding cycle, and the upper layer is made on the base product in the second cycle. These two steps make overmolding very slow. Moreover, it also requires more labor to handle two molding cycles. All these factors make overmolding inferior to dual-shot molding.
3- Complexity & Labor Cost
As said earlier, the two-shot molding method uses advanced molding machines. Unlike conventional machines, these machines consist of two injection units. Moreover, these machines can rotate the mold 360 degrees. As a result, the mold can easily reach the first and second injection nozzles. Operating this machine is very straightforward.
When switched on, the first nozzle injection material is in the mold. After filling, the mold rotates and goes just under the second injection unit nozzle. This section unit fills the mold. After the cooling process, we get the final product. There is no involvement in two separate molding cycles.
So, this two-shot molding is straightforward and also reduces labor costs. How? The mold rotates itself into the injection unit. There is no manual effort needed for rotation. The robotic arms of these machines do the rotation work. On the other hand, the over-molding uses two separate molds and completes two molding cycles.
Overmolding machines require more labor. First, the base product is made. After that, workers have to transfer this base product to the second mold. This requires more labor efforts, resulting in high labor costs. Moreover, the overmolding process is very complex and requires skillful operators.
4- Automation & Speed
As I said above, the two-molding machine is very advanced. It has a robotic arm that enhances automation. This arm rotates the mold 360 degrees, speeding up the manufacturing process. Moreover, it completes a single molding cycle, reducing its operation time.
On the flip side, the over-molding is very slow due to the involvement of two molding cycles. Moreover, the Overmolding machines don’t have any robotic arm or any other automation feature. Workers manually have to transfer base products from one mold to another. This increases the time and makes the Overmolding less efficient when you need products quickly.
5- Cost and Volume Efficiency
The two-shot molding machines are very costly. Due to this, many people consider 2k molding expensive, which is wrong. Although the two-shot machine has a higher initial cost, it makes this process cost-effective in the long run. Its automation feature increases productivity. As a business owner, you will be able to complete high-volume production with ease.
Moreover, wear and tear is also minimal. On the flip side, Overmolding machines are inexpensive. However, they are very slow. Due to their slow working, they are not suitable for high-volume production. However, this process may fit your small needs if you are a small-scale manufacturer.
Conclusion
Still confused about Overmolding vs. two-shot molding? I recommend using the two-shot molding method. It is cost-effective, advanced, and versatile. Its quick operational speed will help you complete high-volume products with ease. If you have limited money and want small-scale production, you can consider the overmolding process.
Despite its slow pace, it will still help create a small production volume. Remember, with over-molding, you will need more labor for product handling and transferring from one mold to another. Before making a final decision, you must understand each method’s pros and cons (listed above).