Plastic overmolding can reduce production time because the second piece is molded directly onto the first part rather than manufacturing the two pieces separately and then assembling them. Overmolding is a complex process requiring adherence to tight tolerances both mechanically and chemically. The good news is that the toolers / molders have dialed in the process for use in many creative ways.
What is Overmolding?
At the most basic level, the process involves creating a single molded or cast part using a combination of two or more plastic and elastomer materials. The base part is molded first and then additional plastic layer(s) are molded over and around the original part (usually a rubber like material like TPE). One or more plastic resins may be used depending on material compatibility to achieve a specific texture or look. Overmolding is used for a range of applications including wearables, medical devices, automotive parts, and more.
A common example of injection overmolding is a toothbrush with a stiff frame and rubberized grips on the handle. Different overmolding material options are also used to add color contrast for aesthetics or to create flexible areas on rigid components.
Image source: https://www.123rf.com/profile_kenishirotie
Benefits of plastic overmolding include:
Reduced secondary operations, assembly and labor costs
Improved grip and ergonomics
Creating a waterproof seal
Providing electrical insulation
Dampening of vibrations or to absorb sound
Colorful aesthetics
Flexible mechanical features for fitment and / or function
Examples of Overmolding
The Fusion Design team takes a holistic approach to enclosure design that begins with an in-depth understanding of the client’s business/product objectives and the expected experience of the intended user. We leveraged the overmolding process for these tools by Snap-On with overmolded grips for comfortable handling and rugged operation.
For another design, we integrated an aesthetic accent and a grip feature to a studsensor for Zircon. It also helped ruggedize the part in the “tool box” marketplace it resides. Over the years we did over 30 versions of these and other hand tools. The customer success test was to throw the device across the parking lot and it must work after impact.
The Overmolding Process
Overmolding is a two-step process where separately molded parts are combined to enhance a product’s features. Typically a plastic component is produced using plastic injection molding and after it has cooled, it is placed into an overmolding tool where it is then coated with molten thermoplastic or rubber. The process for insert molding is different because it involves encapsulating a product in molded plastic.
A wide range of thermoplastic materials can be overmolded, including soft plastics such as urethanes and thermoplastic elastomers (TPE) and hard plastics such as nylon and polycarbonate. Some common forms of overmolding are:
Epoxy over metal
Silicone over metal
Plastic over plastic
Plastic over metal
Rubber over plastic
Rubber over metal
Benefits for our Clients
The overmolding process can be used to add texture, color, or functions to a product. Because the parts are permanently joined together, overmolding eliminates the bonding step for improved component reliability. Device design is more and more about the ergonomics and aesthetics as well as the function. Overmolding is a great way to address both areas in a very reliable way.
