Overmolding is a manufacturing technique that adds texture, color and functionality to products. It’s common for products that require durability and grip, as well as a sleek design. You’ll find it in toothbrushes, kitchen utensils, portable electric fans and mirrors, pens, multi-port chargers and shampoo bottles, to name just a few. Overmolding can also increase a product’s chemical resistance, vibration dampening and sound insulation properties.
Overmolds are formed when two different materials fuse together to create a single, unified component. The two materials could be the same or different, but they must have a compatible bond and meet certain specifications to ensure that the process is successful. For example, the substrate material must allow the overmold to flow in, around and on it without creating any gaps or discontinuities. In addition, the overmold material must have a melting point that is lower than or equal to the temperature of the substrate. This helps prevent the overmold from melting and separating from the substrate.
Depending on the type of project, there are several types of overmolding processes. Manufacturers can use a manual two-stage process for small production runs, or they can utilize an automated two-shot method that is ideal for larger scale projects. In either case, the two-shot process begins with a thermoplastic injection molding that forms the rigid substrate part. Then, a second shot of the overmolding material is injected in, on or around the substrate and bonded to it with a chemical or mechanical bond.
The most important factor in overmolding is selecting the right materials. In order for the overmold to work, it must be made of a compatible grade with the substrate that allows it to fuse with the plastic and form a strong bond. The thickness of the material is another factor that can impact performance. For instance, thicker walls tend to absorb vibration and feel softer, while thinner walls are more rigid.
Another critical factor is ensuring that the overmolding and substrate parts are properly designed. The overmolding material should be molded with proper draft angles, uniform wall thickness and clean transition lines. It’s also important to take into account the material flow when designing the parts. Overmolding experts recommend using centrally located gates and avoiding any features that inhibit the flow of the overmolding material.
Choosing the right material is also important because it will dictate the overall function of the overmolded product. For instance, if the overmolded product is intended to seal a container, engineers will make sure the overmolding is resistant to the chemicals and moisture that it’ll be exposed to in use. They will also ensure that the overmolding can withstand stress and strain, frequent wash-downs or any other harsh conditions it may encounter during use.
Overmolding is a popular production method because it eliminates the need for assembly line steps and saves time and money. It’s essential that manufacturers understand the unique requirements of overmolding and consult with overmolding professionals to ensure success.