What Is Insert Molding?

Insert molding is a type of injection molding that allows metal inserts to be molded into plastic. The inserts can be loaded into the mold manually or by robotics systems and then molten plastic is injected around them.

This process reduces assembly costs and improves the reliability of the product. It averts loosening of parts, misalignment, and improper terminations by holding them firmly in the thermoplastic resin.


In the insert molding process, metal or plastic inserts are placed into an injection mold before molten plastic is injected around them. This creates a single molded part with a stronger bond than possible with secondary assembly processes.

This process reduces the cost of production by minimizing assembly and labor costs. It also increases product reliability by eliminating loosening, faulty terminations, and misalignment. It also improves resistance to vibration and shock.

Moreover, insert molding can produce parts that are up to 50% lighter than their metal counterparts. This makes it an ideal choice for industries that need to reduce the weight of their products, such as the automotive industry and healthcare.

Another advantage of insert molding is its design flexibility. It allows for nearly limitless permutations and can be used to produce complex geometries. This feature makes it an attractive tool for the manufacture of complex, high-quality parts that are difficult to make with other manufacturing methods.

Design flexibility

Insert molding allows you to use multiple materials in a single product, which gives designers more freedom and can result in improved product functionality. This process is ideal for incorporating metal or non-plastic components into plastic parts, and the bonding between the materials can be stronger than other assembly methods.

To create an insert-molded product, a custom-designed insert is placed inside the mold, and then molten plastic is injected into the mold to cover the insert. This creates a strong, bonded bond between the plastic and the insert, eliminating the need for soldering or adhesives.

This process can be performed manually or automatically, and it can reduce production costs by reducing assembling and labor costs. In addition, it can also reduce motion waste by eliminating the need for separating and installing separate metal or plastic parts. It is often used in manufacturing products like tube valves, needle hubs, knobs and electric components. It can also be used in the medical, automotive, aerospace and consumer goods industries.


Insert molding is an environmentally-friendly production process and allows for the incorporation of metal inserts into plastic products. This method eliminates secondary procedures like gluing and screw fasteners, which can increase production costs. It is also compatible with a wide range of materials and end-use applications.

Choosing the proper insert for a particular application is essential. Using an incorrect insert may result in a host of defects, including delayed cracking. This is caused by the differential stress of the molded plastic and metal components. To avoid this problem, designers should carefully consider the inserts’ hoop stresses and ensure that they are positioned properly within the mold.

Another important design consideration is wall thickness. Choosing an appropriate wall thickness is crucial for cost-efficiency and part consistency. Thin walls require excessive pressure and can cause air trapping. Conversely, thick walls are expensive because they require more materials and longer machine cycles. Moreover, thin walls are more prone to knit lines, small hair-like discolorations that occur when the molten plastic flows around an insert.


Because insert molding is a single-shot process that eliminates post-molding assembly and part installation, it cuts down on labor costs. It also reduces movement of parts and saves production time. Furthermore, insert injection molding allows for design flexibility, making it ideal for various industries. In the automotive industry, for example, this process can replace metal components with plastic ones, which reduces weight and improves fuel economy. It can also be used to produce medical devices that require durability and strength.

Insert molding involves loading a custom-designed hardware into a tool that is then overmolded with thermoplastic resin. This step can be automated or manual, depending on the volume of the job. For the best results, product teams should adhere to common design for manufacturability practices such as rounded knurling and avoiding sharp corners. Inserts can be made of a variety of materials, including engineering polymers and metallic materials that provide a wide range of performance properties.

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