Overmolding is a manufacturing process whereby a second layer of material, typically a thermoplastic such as polyurethane or rubber, is molded directly onto the top of another plastic component. In doing so, manufacturers can reduce assembly steps and overall part count. Overmolding can be used to create products like handheld electronics devices and household appliances, or even complex machinery components such as cockpit controls and electrical connectors.
Using a standard injection molding tool, workers first mold the base substrate, which can be made from either metal or plastic, into the required shape. Once cured, the molded substrate is placed into a special overmolding tool. This injects molten overmolding plastic into the cavity, which will encase the substrate and cool around it to form a strong chemical bond. Once cooled and solidified, the overmolding is removed from the tool, and the final product is produced.
This technique can also be used to add a soft coating or grip to rigid parts, making them more comfortable to hold and use. Common examples include the handles on hand tools such as knives, wrenches, pliers and hammers, which are often molded with a soft rubber to improve their user experience and safety. The overmolded handle of a tool is one of the most critical components to ensure its durability and longevity, as it’s often a primary contact point for end users.
The mechanical interlock Overmolding between the two layers can also help prevent delamination or other issues resulting from separation of the materials. To achieve this, engineers may employ techniques such as creating indents or undercuts in the substrate component to aid in the flow of overmolding material to secure a robust physical bond. Depending on the complexity of the overmolded part, other inspection methods may be employed to guarantee its quality, such as non-destructive testing (NDT) that uses X-rays, ultrasound or dye penetrants to uncover defects without harming the part.
Overmolding requires close attention to the design of both the substrate and overmolded layer, as well as to the selection of compatible resins. For example, the chemical compatibility of resins, their relative melting points and proximal shrinkage rates, and how they’re handled during manufacturing will all impact their ability to adhere to one another. This is why it’s important to work with an experienced and knowledgeable partner who understands the nuances of this specialized process. At Protolabs, we can help identify the right combination of overmolding resins for your project, and provide guidance through the overmolding process to ensure optimal results. Learn more about our wide range of precision prototyping services, including injection molding, insert overmolding and two-shot overmolding. Contact us today to request a quote or to discuss your next engineering project. We’re here to support you every step of the way.
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