The Insert Molding Process

Insert molding is an integral manufacturing process used in several industries. It combines plastic injection molding with precast plastic, metal or other materials to form a single mold. This insert molding design guide will explore the concept in depth to cover the process, its benefits and its applications.

New Concept Technology has comprehensive insert molding solutions for your custom project. Trust us to help you meet your project objectives from start to completion.

Understanding the Benefits and Applications of Insert Molding

If you’re looking to blend the strength of metal with the lightweight and flexibility of plastics, insert molding might be the answer. Insert molding is a versatile, single-step process that accommodates various metals and plastics for products, 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 examine plastic insert molding in more detail, including the materials used, the process and how it compares to other molding methods.

What Is Insert Molding?

Insert molding is 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 can also be made of plastic, ceramic, or another suitable material. 

Molten plastic is injected into a mold, and the insert is placed inside. 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.

Benefits of Insert Molding

Insert molding is used in simple and complex applications due to its versatility. Explore how insert molding can benefit your business:

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 final part’s size and weight 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 life span, making it useful for resisting wear in heavy-duty situations. It also performs significantly better under strain and can support heavier loads and stresses with its reinforced strength and solid bond.
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 when it joins with another part, while the plastic minimizes vibration and friction between the metal piece and other components. The enhanced structural integrity makes it ideal for strenuous applications.
Design flexibility: Insert molding offers endless ways to combine inserts and materials, accommodating many designs. Designers can avoid some restrictions when 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 after being 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.
Improved aesthetics: Parts and products created with insert molds usually lack visible flaws, appear smooth and are aesthetically appealing. Parts can be customized with rich colors in different textures, further elevating its appearance.

While traditional injection molding provides numerous benefits such as cost efficiency and versatility, exploring the advantages of insert molding can reveal additional opportunities for innovation in product design and manufacturing.

Applications for Insert Molding

IInsert molding can be used in various 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:

Automotive parts: Vehicle parts such as electrical components, dashboard parts and fasteners and clips. 
Medical devices: Surgical tools and other medical components used in the industry, with features designed to improve performance.
Telecommunications: Communication device housing, connectors and adapters.
Aerospace: Structural components for aircraft and spacecraft, aviation equipment housing and interior fixture molding.
Electronic components: Plugs and sockets that require metal inserts for increased conductivity and mobile device cases for enhanced protection.
Household appliances: Vacuum cleaner components, blender parts and other consumer products that require the insert molds to modify their structural integrity.
General applications: Screws, studs, knobs, contacts, pins and surface mount pads are all common objects in which insert molding is used.

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. To simplify this, we’ve presented the process in a few steps:

Insert preparation: Cleaned inserts are placed into the mold cavity manually or automatically before the plastic is injected.
Mold creation: A steel or aluminum mold is designed and manufactured to resemble the real product according to its specifications.
Mold injection: Once the thermoplastic material is selected, it is heated, melted and injected into the mold cavity.
Cooling and solidification: The cooled plastic solidifies around the inserts, where the molded part and insert bond.
Ejection: Ejector pins release the final product from the mold after cooling.

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 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 smaller and lighter in weight. Insert molding is a great way to combine the benefits of sturdy metal parts with plastic’s weight and design flexibility. Overmolding, on the other hand, generally relies on different types of plastic and focuses on creating an outer layer with specific properties.

Why New Concept Technology Is the Right Choice

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, 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.

Transform Your Project With Insert Molding Solutions

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. Contact us today for a free engineering evaluation or to learn more about working with New Concept Technology and whether insert molding suits your application.

To learn more about our diverse manufacturing capabilities, including advanced processes like injection molding and insert molding, visit our capabilities page.