3 Types of Insert Molding and Encapsulation

Insert Injection Molding

Insert molding is a specialized form of injection molding used to embed a plastic or metal component (the insert) into a final plastic product. Some inserts—such as wood and metal stiffening inserts—may be included solely for structural support, but others will add functionality to a product, such as threaded inserts. 

The exact technique used to embed a component varies based on the component’s size and shape, and it’s important to select the appropriate technique to ensure a stable, durable result. When done properly, insert molding can yield a stronger, longer-lasting component compared to an injection-molded part. It is also a highly cost-effective and efficient process, making it a viable option for customers with a range of budgets.

Whatever your motivation in choosing insert molding, our team at Darter Plastics will guide you toward the optimal choice of insert type, material, and manufacturing method to achieve the best possible result.

The Insert Molding (Encapsulation) Process

While the exact process varies with the type of insert molding, there is a series of general steps common to all encapsulation processes.

• The first step is to create the tooling that will be used to form the product. This typically requires engineers to design a custom mold that resembles the finished shape while allowing space for the insert. 
• The insert itself may then need preparation. Even if the insert is already sized and shaped appropriately, hollow ends still need to be sealed before insertion, and the whole insert must be cleaned and sometimes roughened to ensure that it stays in place. 
• Once all preparation is complete, the injection molding process can begin. This is the part of the process that might differ substantially, depending on the exact technique. 
• Finally, once the injected plastic has cooled and the insert been embedded, the component is removed from the mold and subjected to any number of secondary services, such as drilling or surface finishing.

Types of Molding

There are three main techniques for encapsulating an insert:

• Multi-component injection molding, also known as co-molding, involves injecting some combination of multiple plastics and metals into the mold at the same time. These materials then join together, resulting in a stiffer, stronger piece. 
• Multi-shot injection molding is similar to multi-component molding, but rather than inserting all of the materials at once, the operator layers them into the mold one at a time. As with multi-component molding, the different materials bond strongly to one another, although they do so in ordered layers. 
• Overmolding is a slightly different approach to encapsulation. Rather than starting with a mold and molten materials, it begins with a pre-molded part onto which the insert is placed. From there, injection molding layers plastic over the insert, sealing it in place.

Benefits of Insert Molding

Insert molding is one of the most cost-effective ways to stiffen a component, making it better able to resist strong forces. Since there are multiple ways to accomplish encapsulation, engineers have significant flexibility in the design process and their mock-ups can be completed with fewer assembly steps. 

Plastic Insert Molding Materials

Part of insert molding’s flexibility comes from its compatibility with a wide range of materials. Stiffening inserts are usually made from metal, but wood is a low-cost alternative that still provides some gains. The molding material is typically a thermoplastic or elastomer chosen for its physical characteristics. 

Materials compatible with injection molding include:

• ABS
• Acetal
• Acrylic
• Copolymer and homopolymer polypropylene
• Flexible PVC
• HTPE/LDPE
• Microcellular
• Nylon
• PEEK
• PET
• Polyaryletheretherketone
• Polycarbonate
• Polyester
• Polypropylene
• Polystyrene
• Polyurethane
• Thermoplastic
• Thermoset

Darter works with all of these materials and most other compatible plastics except rigid PVC.

Darter’s Insert Molding Expertise

At Darter, we’ve developed our insert molding and injection molding services over a period of several decades to ensure that our methods are as affordable and efficient as possible. We work with almost any plastic that is suitable for injection molding, and we craft components of any size and almost any production volume. With our 15 state-of-the-art presses, we can achieve tolerances down to 0.005 inches, and our attention to precision makes us an excellent choice for industries such as aerospace, military, optical, medical, electronics, and more.

To speak with our team about the best insert molding process for your component, contact us or request a quote today.