What Is Overmolding?

In manufacturing, overmolding refers to the process of combining two different materials on one surface. The technique is a common practice for creating consumer electronics, automobiles, and many other products. However, it can be tricky to get right. In the wrong hands, overmolding can produce a substandard product that is either not functional or unsightly. To avoid these issues, manufacturers must pay close attention to their overmolding process and the materials they choose.

Overmolding can be achieved in a few different ways, including co-injection molding, two-shot injection molding, and insert molding. Co-injection molding involves injecting both the substrate and elastomer into the same mold, while two-shot injection molding uses separate injection molds for each material. The type of overmolding method chosen will have a significant impact on production costs, cycle times, and time-to-market.

The most important consideration when choosing overmolding materials is that they must be compatible with the substrate. To ensure that the two materials bond correctly, it is necessary to select a plastic with good adhesion properties. A variety of testing methods can be used to assess the bonding strength of overmolded plastics, such as pure shear, tensile, and peeling tests.

Besides adhesion, the overmolding process must take into account other properties such as flexural modulus, hardness, and friction. The latter varies with plastic, but it is typically measured by the coefficient of friction, which relates to how easily surfaces move against each other. The flexural modulus is a measure of how much the material can bend before breaking. Hardness is a property that refers to the material’s ability to resist indentation, and it also varies with plastic.

While overmolding is commonly used in the manufacture of electronics and automotive plastic parts, it can be found throughout our homes. For example, toothbrushes, cell phone cases, and patio chairs often undergo overmolding or insert molding processes to give them the appearance and functionality that they need. It is also common to see cosmetics packaging with overmolded surfaces that feature contrasting colors and textures.

Overmolding is a great choice for products that require a comfortable grip, or those that are exposed to harsh environments. The specialized plastics used in overmolding can withstand high-pressure wash downs, frequent strain or flex, and exposure to dust or debris. Moreover, this process is ideal for cable assemblies that must be as durable as they are aesthetically pleasing. For these reasons, overmolding is a popular option for products in solar energy, military equipment, consumer electronics, and industrial/OEM applications.