Injection molding is a very popular manufacturing process. It has transformed how different products are made. This method is very diverse and has many types. Insert and overmolding are two of its types that differ from each other. Their differences create debates on insert molding vs overmolding.
Many people confuse these two and consider them one. The reason is that the differences between these methods are smallish. However, those minor distinctions significantly impact their usability and applications. I will explore the key differences between insert and over-molding in this article. So, let’s get started!
Overview of Insert Molding & Overmolding
In the previous article, I discussed the working of insert molding. However, this article will focus more on its comparison with overmolding.
Insert molding is a single-step process that uses an insert. The molten material fills the mold in which the insert is present. After solidification, the material becomes part of the insert. Over-molding is a two-step process that does not use an insert. It also uses two product formations in a single manufacturing cycle.
Overmolding is a subtype of the insert molding method. We use an insert (a pre-made part or product) in insert molding. This product is placed in the mold. Then, an injection unit injects molten material into this mold containing an insert. The molten material, upon cooling, becomes part of the insert and makes a strong bond with it. The insert is generally made of metal.
Insert molding is a single-step process. However, over-molding consists of two injection molding cycles. Manufacturers design a mold and inject material into it. This results in the formation of the first product or substrate. Now, this substrate is placed in a second mold. The molten material is injected over this substrate.
Second injected material cools, and mechanically makes bonds with the first material (subrate). So manufacturers have to design and make two molds. The example of insert molding is manufacturing of screwdriver with rubber grip. On the other hand, the truth brush is the best example of overmolding. The base is plastic, and the grip consists of rubber material. Rubber material is injected on the plastic base.
Insert Molding vs Overmolding: Key Differences
Have you understood how these two methods differ in terms of their process? Let’s dive deeper and discuss the primary differences between them. This will help you know which molding method fulfills your needs and requirements.
1- Speed
For manufacturers, speed and production times matter the most. The insert molding method is rapid and efficient. It involves only a single molding cycle. Once you have an insert, you place it in the mold. The injection molding machine will inject the molten material into this mold.
The molten material, upon cooling, forms a strong bond with the insert. However, over-molding is a two-step process, making it more time-consuming. First, the manufacturer must make a substrate; for this, a mold of the desired shape must be made. The mold then undergoes an injection process, filling it with molten material.
Upon cooling, the first substrate is obtained. Then, this substrate is placed in the second mold, where the injection machine injects material. This process also requires the design and creation of two different molds. All these steps make over-molding very slow and complex.
2- Complexity
The insert molding method is relatively straightforward to follow. As I said earlier, it involves a single manufacturing cycle or step. You won’t have to create two molds. On the flip side, the over-molding method is very complex and tedious. Manufacturers have to create two molds. Moreover, this method also requires two separate molding steps.
In the first step, the substrate is made. In the second, molten material is poured on the substrate made in the first step. For example, you have completed the first step and made the substrate. But if the substrate does not perfectly fit on the second mold, your efforts in the first step will be wasted. A slight mistake can cause the whole molding method to fail. Therefore, I consider insert molding simple and user-friendly.
3- Strength & Durability
Regarding strength, you might hear different opinions. Some people consider insert molding to offer a stronger product. Other stands with overmolding. We have been using both of these methods for many years.
I consider inserting molding superior when it comes to product durability. Why? In this step, the molten material makes mechanical bonds with the insert. Moreover, manufacturers add some adhesion to the molten material. This adhesion helps the material stick to the insert more strongly. The result is a very robust, durable product.
On the flip side, the over-molding is also good but slightly lags. The second material is poured on top of the first material, making a layer on it. This layer is not very robust, making the product a bit weaker. However, this method is suitable when you need one material sitting over another, such as when creating a toothbrush.
Quick Highlight: The individual experience can vary from what I said about durability. The reason is that the strength of the final product depends on many factors. Those include curing time, material quality, and properties. That’s why you might hear different opinions from the manufacturers regarding durability.
4- Materials Used
Both of these methods use different materials. For example, the insert molding method uses metal, ceramic, and plastic materials. The insert can be ceramic or metal, but the injected material is plastic or rubber.
On the flip side, over-molding doesn’t use metal or ceramic materials. Instead, it only uses rubber or plastics. Most of the time, plastics are preferred over rubber materials. Some people confuse substrate with insert and believe both are made of metal. This is wrong; the insert is generally metal, but the substrate consists of plastic materials.
5- Number of Steps
The insert molding method consists of a single injection molding step. On the flip side, the overmolding involves two steps for the final product. But there is a twist—the insert molding method also uses additional manufacturing steps. How? This injection molding requires an insert. The manufacturer has to make the insert first.
However, this insert manufacturing is not done through molding methods. Instead, CNC machines cut, shape, and create an insert. Although the insert molding requires one molding step. But the whale process is also complete in two steps, i-e injection molding, and insert manufacturing.
6- Cost & Applications
The insert molding is inexpensive as compared to overmolding. The reason is that it is a less complex method with a single molding step. It requires single mold designing and creation. On the other hand, the overmolding is a complex process and complete in two molding cycles. It requires two separate molds, making the process very costly.
Therefore, I recommend choosing insert molding if you have a tight budget. However, in some applications, the overmolding performs better. You should analyze your product needs before selecting any of these two types. Here are some popular uses of these two methods:
| Insert Molding Uses | Overmolding Uses |
| Kitchen knives – Plastic handle around the metal blade. | Toothbrush handles – Soft grip over plastic. |
| Screwdrivers – Plastic molded over metal shaft. | Razors – Rubber grip on plastic handle. |
| Electrical plugs – Plastic encasing metal prongs. | Phone cases – Silicone over plastic for protection. |
| Car keys – Metal keys embedded in plastic. | Gaming controllers – Soft-touch rubber grip. |
| Scissors – Plastic grips over metal blades. | Power tools – Rubber grip for comfort. |
| Phone chargers – Metal pins molded into plastic. | Flashlights – Shock-resistant rubber coating. |
Pros & Cons of Insert Molding & Overmolding
Still confused about which of these molding methods is suitable for you? Worry not! I understand that they offer excellent perks, making their selection tedious. The section below will give you the pros and cons of these two molding types. Understanding them will help you make the right decision. Let’s start with insert molding:
| Advantages of Insert Molding | Disadvantages of Insert Molding |
| Secure connection between metal and plastic. | Higher Initial cost of tooling |
| Reduces assembly time | Risk of misalignment |
| Saves labor and material costs. | Limited material compatibility |
| Create lightweight products | Metal inserts can wear molds faster. |
| Improved strength and bonding | Warping or shrinkage risks |
The disadvantages mentioned happen in worst-case scenarios. For example, the risk of misalignment, wrapping, etc., is uncommon. Moreover, these issues can be avoided with the right skills and guidance. Here is a table showing the pros and cons of the over-molding method:
| Advantages of Overmolding | Disadvantages of Overmolding |
| Offer excellent Grip & Comfort. | Uses multiple steps and materials, increasing expenses. |
| Protects the core material from wear. | Requires multiple molding stages. |
| Enables multi-color, enhanced look | Material Compatibility Issues |
| Eliminates the Need for Adhesives | Higher levels of complexity |
| This method does not use a fastener to make a bond. | At times, this results in weaker attachment between two materials |
When Should You Choose Insert Molding & Overmolding?
Selection between insert and over-molding can be confusing, especially if you are a newbie. If you have a tight budget, I recommend insert molding. It will help you get your desired product at an affordable price. However, your choice also depends on what kind of product you need, for example, if you want a combination of two different materials.
You might need a plastic and metal product, such as a screwdriver, keys, or scissors. In such a case, you should also opt for insert molding. On the flip side, you might need a product of the same material, such as a toothbrush. In this case, you should choose over-molding methods. Moreover, over-molding is ideal for creating a smooth, soft cover or grip.
Remember, this method does not use metal. It makes the product using plastic material in the molding step. Last but not least, the overmolding will stand out if you prefer the aesthetics of the product. It can use material of different colors in two molding steps. It will result in a product with an eye-catching look. Before making a final decision, you must understand what these methods are capable of!
Conclusion
As I said earlier, the difference between insert and over-molding is minimal. However, those minor distinctions make a significant impact. In my opinion, insert molding is a superior option. However, different products have different requirements. In some cases, insert molding fits the requirement. In other cases, manufacturers have to opt for over-molding.
It all depends on what kind of product you want. In this article, I have explained the differences between insert molding and overmolding. Do you want your product made using any of these two methods? Worry not, as we offer these two manufacturing services. Contact us and get all the information you need to get started!