Manufacturing involves various processes that will create numerous items we use every day. Two of these processes, insert molding and overmolding, have differences that set them apart despite their common use in plastic manufacturing. Understanding these methods and their applications will make it easy to understand which works best for manufacturing. Read on to learn more about their differences.

What Is Molding in Plastic Manufacturing?

Plastic molding, or injection molding, is a method in manufacturing used to shape and create plastic. The plastic used to make plastic products will start as a hot liquid that injects into a pre-manufactured mold.

The mold will shape the fluid, which will then cool into the shape of that mold. This method creates the many plastic products we see in our world with such complex shapes.

How Does Injection Molding Differ From Other Molding?

Other types of molding that use plastic, such as blow molding, will create a thin plastic product with a hollowed-out inside. The walls of a plastic product used in blow molding have thinner walls than those manufactured using injection molding. Blow molding expands a hollow tube with air to create a specific shape that fits the mold, while injection molding injects the molten plastic into the mold and creates a large amount of pressure to create a more solid plastic barrier.

Other moldings, such as extrusion molding, will create cylindrical shapes like pipe or straw. This type of molding lacks the complex properties of injection molding but works well for simple-shaped objects. Injection molding stands out amongst older molding methods by having two methods: insert molding and overmolding.

Insert Molding

What is it?

In manufacturing, insert molding is a method of injection molding that pushes molten plastic into a mold to cool and harden. Still, a primary difference is a connector inside the mold.

A screw, nut, or bolt lies inside the molding, and when the plastic forms, it forms over the connector piece and molds around it, becoming a part of the final product. Most insert molding occurs in parts that require assembly or need some form of the metal piece to connect to another metal piece.

An example of an insert molded product would be the blades of a plastic fan. The blades will usually have a symmetrical shape as one piece made of plastic, but in the center of the blades, there is a metal cylinder that is a part of the blades and attaches to the motor of an electric fan. This item is only one example of an insert molded product among a large variety of different ones we see daily.

Applications

The applications of insert molding help manufacturers construct items more easily than simple injection molding. Combining plastic and metal to form a part that connects and seals is essential for many tools and devices that need a stable frame that won’t break easily.

In the medical industry, insert molding creates prosthetics that will bend, tubes that connect to sources, and components such as knobs on machines. Other industries that use pipes will have metal connectors with plastic surrounding them with either male or female leads. Thanks to the malleability of injection molding, insert molding gives people the option of custom plastic molding for various applications.

Pros

Insert molding works well in modern injection molding machines, so there isn’t a need to upgrade to begin the process. The metal components will seal permanently into place, preventing shaking, loosening, and moisture build-up.

Items with insert molding with plastic handles and a metal piece such as handlebars will have better grip and won’t come loose randomly. Insert molding is also a less expensive option since you won’t need to cover an entire product in plastic and will only need to focus on the parts you’ll contact

Cons

While insert molding is beneficial in most cases, there are some drawbacks. The tool that injects the plastic resin will need to have compatibility with the insert, and if they don’t fit together correctly, the mold may break from the pressure of the injection.

Insert molding machines will often have a human operation and requires constant attention. If you have a higher quota of products to make, the labor costs will increase.

Overmolding

What is it?

The primary difference between overmolding and insert molding is the effect each one creates to make a product. Overmolding will take a piece of hard plastic and mold another plastic over the surface to create a softer surface with a great grip. The plastic used for the injection will normally be a softer plastic such as silicone or TPU.

An example of an over-molded item would be a drill. Most drills will have plastic as their outer shell protecting the electronic and mechanical parts. On certain parts of the drill, especially the handle, a rubberized surface will have silicone molded over the hard plastic to create a better grip surface.

Applications

Overmolding enhances numerous items with two different plastics and makes it easier to use them. The second plastic injected into the rigid plastic will also create an interesting design pattern in some applications, but overmolding will normally help the product’s usability.

Overmolding will also have some function in insert molding. The metal connector will become over-molded by the molten plastic to make it easier to handle. This combination of molding is why we have some knobs with a silicone handle that connects via a metal tube or lead.

Pros

Sealing an item and preventing it from taking on water or dirt is a great benefit of overmolding. The plastic will seal an area of the item closed and make an excellent cover for certain parts. The electrical and thermal insulation makes over-molded items safer and prevents shock and burns from dangerous sources such as a hot skillet or circuit breaker.

Cons

Overmolding typically requires multiple molds to create a final product. The hard, rigid plastic product requires one mold, while the other needs a specially made mold for molding the softer plastic onto the plastic item. These molds will cost large amounts of money, especially in manufacturing scenarios when large quantities are necessary, such as an order from a large company.

Another difference between overmolding and insert molding is the time it takes to make an over-molded item. Both plastics from both modeling processes need to cool properly, or the plastic won’t take on the correct shape, causing the item to be scrapped. Time and money are essential in injection molding, and it’s especially important in overmolding.

Overmolding and insert molding are different methods of producing effective products. Knowing the differences will help you find the right method for your item and enable you to have the most efficient production line for your clients.