More manufacturers are turning to over molding as they learn how it adds value to their product lines. Not only does it improve functionality, performance, and aesthetics, but it lowers total production costs—a rare combination these days.
Overmolding is a one-shot or two-shot process that bonds a thin layer of TPE (thermoplastic elastomer) to a product substrate. It is this outer layer that creates the soft-touch grip that is famous for a wide range of products, from personal care products such as toothbrushes to power tools. Overmolding also reduces shock and vibration, dampens sound, provides electrical insulation, enhances chemical/UV resistance, and can be a barrier to oxygen and moisture.
As a result, more consumers are demanding this feeling about the products they buy, so applications continue to expand. The availability of this technology also gives product engineers more options to create attractive and functional products and stay on the cutting edge of design leading in their markets.
However, not every injection mold can be oversaturated; It requires extensive training, specialized equipment, and precise control of multiple variables throughout the life of production. Even the slightest of differences can affect the quality, so skilled operators are a must. Much of this knowledge relates to the type of TPE and substrate used, so a deep understanding of materials science and chemical behavior is also required. New resin blends are constantly being engineered to provide expanded properties, including chemical and heat resistance, UV resistance, hardness, scratch resistance, clarity, and UL standards.
A key step in the overmolding process is to select the best TPE/substrate combination for optimal bonding, followed by mold design and appropriate tooling. Maintaining the TPE melt temperature (which determines how easily the TPE flows, as well as its bondability) is critical. The surface of the substrate must be extremely clean and free of contamination including dirt, dust, excess moisture or skin oil (gloves should be used at all times when handling) – if the substrate is even slightly contaminated, the bond between the TPE and the substrate may weaken or even break. Since the moisture level of both TPE and the substrate can adversely affect the chemical bond, both materials must be carefully dried prior to casting.
For tooling, the holes must be of appropriate size and placed in the mold to allow air to be released from the mold cavity during overmolding; Trapped air can weaken the bond between the TPE and the substrate. Closures must also be properly designed for the material involved to eliminate the risk of jamming or kinking. The gate size is determined according to the material type, viscosity, flow rate and amount of shear that may be required.
Rarely can advanced technology improve product feasibility and customer satisfaction, yet it can still reduce overall production costs. Overall costs are lower because overmolding can reduce the number of steps involved in making the product. For example, the TPE layer forms a strong bond with the substrate that eliminates the need for some secondary finishing processes such as priming, coating, or coating. By combining these steps into a single injection molding process, the overmolding process increases quality, reduces waste, enhances productivity, and reduces overall production cost.
