Two-Shot Molding Significantly Improves the Manufacturing Process
For product integrity, it is necessary when designing 2-shot components to take into account both mechanical and chemical bonding properties between the two resins used.
Medbio specializes in the two-shot molding process. Two-shot molding, also sometimes referred to as overmolding or multi-shot molding, is a process wherein plastic resin is molded around a part made of another resin without removing the part from the molding press. This may be accomplished either by use of a robot, or a rotary platen within the molding press.
Typically, 2 different resins with different physical or chemical properties are used to create an assembly complete form the molding press in a single process. Some common examples are:
- Finished plastic parts with multiple colors
- Instrument handles or controls with a soft-grip surface molded over a rigid base
- Mechatronic assemblies using resins with different shrink rates to create moveable multi-part assemblies without a secondary assembly process
- Valves and seals requiring a low durometer sealing surface on a rigid structural base
Produce products that provide dual functionality such as multi-colored, structural substrate with soft-touch features, components that require gasket or sealing type features, etc.
Using the ‘single tool concept’, part variation is greatly minimized and controlled, creating a high level of repeatability. This removes the potential risk of contamination that exists using a typical two-tool over-molding process.
The entire substrate and over-mold process is accomplished in a single and simultaneous injection molding cycle requiring only ‘one’ tool. A typical alternative to true two-shot molding is an over-mold process that requires additional tooling (one tool and molding process to create the substrate, and another tool and process to complete the over-mold), as well as additional handling and labor. Two-shot can also be used to achieve a high quality multi-color product in lieu of a painting process (which can rub off).
By joining two compatible materials in a single molding cycle, a very strong bond is created without the use of adhesives between the two parts. This process yields a far more robust bonding process then using a over-mold process involving two separate tools and molding operations.