Insert molding and over molding are two types of injection molding commonly applied in producing everyday plastic items such as handles, bottles, toothbrushes, hardware, and food containers. However, it’s easy to confuse these two processes, especially because both molding processes involve injecting molten plastic into molds.
So, what is the difference between these two categories of injection molding? In this article, we discuss what insert molding and over molding entail, the application of the two processes and outline the differences and similarities between the two processes.
What Is Insert Molding?
Insert molding is a type of injection molding that involves forming a plastic layer over a pre-existing substrate, usually a metal. It is a typical manufacturing process where a plastic or rubber material is molded over, around, or on an existing metal. Adding a handle on a screwdriver is a perfect example that elaborates on this molding type.
This manufacturing process often involves single injection shots. Inserts are placed in molds, and a single shot of molten plastic is injected. Once the plastic solidifies, the inserts are removed and now enclosed with the plastic. The bond formed between the inserts and the plastic is usually strong; thus, this molding usually results in solid parts that do not require further assembly. Some standard inserts include screwdrivers, threaded nuts, knobs, blades, pins, and bushing.
The Applications of Insert Molding
Insert molding has wide application thanks to the broader selection of materials and the strong bonds that result from the process. It is commonly applied to create plastic housing over metal inserts and wires. Some of the applications of insert molding include:
Electrical wires
Typically, electrical wires are insulated with rubber or plastic to make them weather resistant and protect consumers from electric shocks. When it comes to housing wires and other electrical components in plastic, insert molding is the way to go.
Medical devices and implants
Another application of insert molding is creating plastic housing medical devices such as implants, medical cables, and defibrillators. The insert molding forms a surface that is easy to sterilize while protecting the fragile parts.
Some of the best scenarios to use insert molding include where:
- A final product comprises a metal or threaded insert
- Your internal component are wires, circuit boards, or other electronic parts
- A cheap single-shot mold is a goal
What Is Ovemolding?
Over molding is a two-shot stage process that allows you to combine multiple parts into a single item. In this process, a substrate, usually plastic, is poured and allowed to solidify. A second layer is injected directly onto the substrate to form a single product. As the second shot cools off, a strong bond is formed to create a durable product.
Ideally, over-molding is applied where you want to create multi-material parts without further assembly or using adhesives. This type of injection is also applied where you want to improve the look or the texture of your final product, adding decoration or enhancing the grip of your plastic product. An excellent example of over-molding is the different materials and textures used on the hand power tools to improve the user’s grip.
Application of Overmolding
Overmolding is an excellent process for improving the features of your semi-final product and is mainly applied to enhance ergonomics and ease of cleaning. Some of the everyday items whose manufacturing process involves overmolding include:
Hand power tools
This process is perfect for improving the grip and comfort of hardware tools such as wrenches, screwdrivers, angle grinder, hand saw, and hammers. When handles are molded, a second pliable layer is injected into them to enhance the texture and, thus, their grip and comfort.
Surgical devices
Like in power tools, double injection is applied in surgical instruments to improve the grip and, thus, the user’s precision. Moreover, the proper selection of materials allows you to manufacture easy medical tools to clean and sterilize. Some standard medical devices made from this process include dilators, syringes, and soft-touch buttons.
Cookware
Another common application of this double shot process is in cookware. When the handles have been injected with plastic, a second shot of molten plastic is done to make the handles ergonomic and safe.
The list is not exhaustive, as overmolding has wide applications—the list below guides you on when to consider using over molding.
- Where you want to create a surface with decorative features
- A plastic handle with good grip and comfort is desired
- You want to create a surface with different thermal properties
- To improve the anti-vibration properties of your hand tool
- Enhancing the softness of your surface
Similarity Between Insert Molding and Overmolding
The main similarity between these two processes is that they manufacture products that do not require further assembly or adhesive. The plastic bonds formed as the molten solidify strong and help to create a durable plastic compound.
The Differences Between Insert Molding and Overmolding
Insert molding and overmolding form common types of injection molding used in manufacturing various plastic compounds. However, for most people, differentiating the two is quite tricky as both processes result in products that do not require further assembly. And, thus most will ask, what is the difference between the two injection processes?
Shots
One notable difference between these processes is the shots involved. While insert molding only involves a single injection, over molding involves two shots; one to form the base and a second layer to form the over mold.
Cycle time
Generally, insert molding is faster compared to its counterpart. This is because you only need to wait for a substrate layer to solidify. Overmolding, on the other hand, involves two layers of molten plastic; once the substrate has hardened, you also have to wait for the over mold to set.
Application
While the application of the two might seem identical, there is a slight difference between the two. Insert molding is a common application for manufacturing processes that involves forming a plastic housing over or onto metal inserts. On the other hand, overmolding is an injection process that allows you to mold various thermoplastic materials into one component. It forms a secondary method to insert molding that helps enhance the usability of your product.
Cost
Another difference between the two processes is the cost. Generally, overmolding is expensive as it involves two injections requiring more time and materials. On the other hand, insert molding involves a single shot and thus is cheaper than the double shot injection.
Conclusion
Insert molding and overmolding form a typical injection molding used in manufacturing daily plastic items. Insert molds are mainly applied in components that involve metal inserts and only consist of single-shot injection. Over molds are done on the thermoplastic substrate and thus involve double shots injections; hence the difference between the two molding types.
