Overmolding is a manufacturing process that involves molding one material over another. It can be used to add texture, color, or function to a product, and it eliminates the need for bonding steps, improving component reliability. This type of plastic molding is a popular choice for creating medical equipment and automobile components. Overmolding is also commonly used to make household goods, such as toothbrushes and cell phone cases. Other common examples include two-tone plastic furniture, such as patio chairs and step stools, and plastic housing for GPS units and other navigational devices.
In the overmolding process, a rigid base is formed from thermoplastic injection. Once the base is made, a softer, more flexible layer—often made from silicone or other elastomer—is injected in, on, or around it. The molded materials then bond together to form a single, unified part. The process can be performed manually for small production runs or automatically for larger runs.
The materials chosen for overmolding are crucial to a successful result. The ideal scenario is for the overmolded and substrate materials to bond completely, but there are cases where this does not happen. In these situations, the substrate and overmold must be carefully evaluated to ensure that they connect correctly.
When selecting a hard plastic for overmolding, it is important to consider its chemical adhesion. Ideally, the overmolded and substrate materials will have similar chemical properties. If the two materials are not matched, they will not fuse well and may tear before breaking apart. Moreover, the substrate and overmold must be compatible in terms of temperature, mechanical properties, and other factors.
Elastomers can be a good choice for overmolding because they are highly resistant to chemicals, temperatures, and other environmental factors. They are also extremely flexible and can be molded into complex shapes. Thermoplastics, such as ABS, polycarbonate, and PBT Valox, are suitable for overmolding with elastomers. However, some engineered resins, such as PEEK and Ultem, are not well-suited to overmolding with elastomers.
Plastic overmolding is also an excellent choice for making products that require a comfortable grip. It provides a rubber-like connection that absorbs vibrations and reduces the likelihood of injury. It is particularly useful for producing automotive parts that must withstand high levels of vibration and shock, such as steering wheels and control panels.
In addition to overmolding, there are a variety of inspection techniques that can be used to assess the quality of finished products. These include visual inspection, dimensional measurement, and surface finish analysis. Visual inspection is performed using a variety of tools, including calipers and coordinate measuring machines. Dimensional measurement uses specialized tools to verify that parts meet specified dimensions. Finally, surface finish analysis involves the use of instruments to evaluate the smoothness or roughness of a plastic surface. By using these techniques, manufacturers can be confident that their products are up to standards. By utilizing these inspection methods, companies can improve their product quality and minimize costs. In the end, they can reduce the time to market and increase profitability.