Guide to Insert Molding

If you’re looking to blend the strength of metal with the lightweight and flexibility of plastics, inserts molding might be the answer. Insert molding is a versatile, single-step process that accommodates a wide range of metals and plastics for products used in everything from household toothbrushes to military aircraft. Parts range from simple to complex, and this process can often help you achieve unique designs with fast turnarounds and valuable physical characteristics. 

We’ll take a closer look at plastic insert molding, including the materials used, the process and how it compares to other molding methods.

What Is Insert Molding?

Insert molding is a type of injection molding used to bond plastic and nonplastic materials. The nonplastic insert is encapsulated by plastic. The insert is usually made of brass, steel or stainless steel, but it can also be made of another plastic, ceramic or another suitable material. Molten plastic is injected into a mold, and the insert is placed inside it. Once the plastic cures, the completed part is released from the mold. The plastic and nonplastic parts now have an exceptionally strong bond, helping eliminate or minimize the need for soldering, adhesives or fasteners.

The design and process of insert-molded parts offer some unique benefits:

Minimal assembly costs: Since insert molding creates a single, bonded piece, you can reduce the labor costs and delays associated with additional assembly.
Reduced size and weight: Plastics are generally much lighter and smaller than fasteners and connectors, so using them to join various components helps reduce the size and weight of the final part while offering the necessary strength.
Better reliability: The molding process offers precise alignment capabilities and a tight bond. The resin helps the part withstand vibration and shock for a longer lifespan, making it a useful way to resist wear in heavy-duty situations.
Strength and structure: Insert molding can deliver exceptionally strong parts by combining the properties of the plastic resin with a sturdy insert. For instance, the metal piece might provide rigidity where it joins with another part, while the plastic minimizes vibration and friction between the metal piece and other components.
Design flexibility: With an endless array of ways to combine inserts and materials, insert molding can accommodate many different designs. Designers can avoid some of the restrictions of working with mechanical fasteners and connections.
Consolidation: By eliminating the need for fasteners, connectors or adhesives, you limit the number of parts you need to keep on hand and the inventory demands that come with them.

Insert-molded components are often made with thermoplastics, thermosets or elastomers. Thermoplastics and thermosets are similar, with a wide range of appearance options. Thermoplastics, including nylon, polystyrene and polyethylene, can be melted down and reused again after they’ve cured. Thermosets, like epoxy and phenolic, cannot be reused after curing. Elastomers, like natural rubber and polyurethane, can be natural or synthetic and may be recyclable.

Applications for Insert Molding

Insert molding can be used in a wide variety of settings, including automotive, medical, defense, industrial and consumer industries. It can create a strong seal and mechanical support for various applications. Insert molding is commonly used to surround a threaded insert or encapsulate electrical components.

Some other insert molding examples include:

Screws.
Studs.
Knobs.
Contacts.
Pins.
Surface mount pads.

These are just a few examples — plastic insert molding can be used for a wide range of parts, including extremely complex and precise pieces.

The Plastic Insert Molding Process

Insert molding uses the same process as general injection molding but with one additional step. Both start by pushing molten raw material into a mold with a sophisticated press. For insert molding, the nonplastic insert is added into the mold by hand or machine at this stage. Typically, insert molding machines use vertical presses that rely on gravity to hold the insert in place. Horizontal molds tend to be more difficult to work with and less accurate, especially for high-tolerance parts.

After the plastic cures, the press opens up and ejects the finished part. The result is a single piece combining metal and plastic into one tightly bonded part with several unique characteristics to support its application.

Overmolding vs. Insert Molding

Insert molding is often used interchangeably with overmolding since both methods refer to types of injection molding. The two are similar but with a distinct difference:

Overmolding: Overmolding is a two-step process. First, a plastic part is made through the injection molding process. Then, that mold becomes the insert for a new mold. The result is a product with a thin, rubber-like layer surrounding the initial mold. It might be used to add a new texture or grip to a product or protect it from shock, vibration and moisture. For example, you might see it used with power tools or vibrating toothbrushes to reduce damage to the electrical components and create a more enjoyable user experience.
Insert molding: The process for insert molding doesn’t require two runs through the press — it is a one-step operation, which helps speed things up. The liquid plastic is pushed into the mold, where the pre-made insert is added. After releasing the mold, the two items are bonded into one part without requiring additional steps.

Both methods are useful for different manufacturing needs. Overmolding is typically used to add texture or protection, while insert molding might be used to make parts faster or parts that are smaller and lighter in weight. Insert molding is a great way to combine the benefits of sturdy metal parts with the weight and design flexibility of plastic. Overmolding, on the other hand, generally relies on different types of plastic and focuses on creating an outer layer with specific properties.

Insert Molding With New Concept Technology

If insert molding sounds like the right option for your next project, or you’re not sure what you need, the experts at New Concept Technology can help. We offer a wide range of insert molding manufacturing services in our state-of-the-art facility, along with expert design and automation and assembly services. 

With several leading certifications and a team devoted to innovation, our insert molding services meet the needs of diverse businesses, including those in demanding industries like medical, aerospace and military production. We offer true precision tolerance of ±0.002″ and have experience with many different resin types.

Whether you know exactly what you need or still need some direction, our knowledgeable team can help you find the right molding solution for your application. Learn more about working with New Concept Technology and whether insert molding is right for your application by reaching out to us today!